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How to run SSH server Mac OS X and set it to auto boot on Mac Book system start

Monday, February 5th, 2024

How to run SSH Server on Mac OS X to administrate remotely your MAC OS to access remote MacBook Air or Mac OS

Linux / UNIX users know it is pretty easy to run OpenSSH server on old Linux SystemV releases

it is done with cmd:

# /etc/init.d/sshd start

On newer Linux distros where systemd is the standard it is done wtih:

# systemctl start ssh.service

To enable ssh service on boot on systemd distros

# systemctl enable ssh.service

To enable SSH access on Mac OS X this is done wtih a simple command

To check the status of SSH server being on or OFF, either connect with netcat to TCP port 22, which is usually installed by default on most MAC OS-es or run:

# systemsetup -getremotelogin

To start and enable SSH service on Mac OS X run:

# systemsetup -setremotelogin on

If you later need to turn off the SSH service

# systemsetup -setremotelogin off

Actually systemsetup command can do pretty much on MAC OS X and it is worthy to take a look at it, if you're running a MAC PC or Mac Book laptop.

systemsetup can set the current date, change time server host, set computer name (hostname) and much more.

sh-3.2# systemsetup -help

systemsetup Help Information
————————————-
Usage: systemsetup -getdate
Display current date.

Usage: systemsetup -setdate <mm:dd:yy>
Set current date to <mm:dd:yy>.

Usage: systemsetup -gettime
Display current time.

Usage: systemsetup -settime <hh:mm:ss>
Set current time to <hh:mm:ss>.

Usage: systemsetup -gettimezone
Display current time zone.

Usage: systemsetup -settimezone <timezone>
Set current time zone to <timezone>. Use "-listtimezones" to list time zones.

Usage: systemsetup -listtimezones
List time zones supported by this machine.

Usage: systemsetup -getusingnetworktime
Display whether network time is on or off.

Usage: systemsetup -setusingnetworktime <on off>
Set using network time to either <on> or <off>.

Usage: systemsetup -getnetworktimeserver
Display network time server.

Usage: systemsetup -setnetworktimeserver <timeserver>
Set network time server to <timeserver>.

Usage: systemsetup -getsleep
Display amount of idle time until computer, display and hard disk sleep.

Usage: systemsetup -setsleep <minutes>
Set amount of idle time until computer, display and hard disk sleep to <minutes>.
Specify "Never" or "Off" for never.

Usage: systemsetup -getcomputersleep
Display amount of idle time until computer sleeps.

Usage: systemsetup -setcomputersleep <minutes>
Set amount of idle time until compputer sleeps to <minutes>.
Specify "Never" or "Off" for never.

Usage: systemsetup -getdisplaysleep
Display amount of idle time until display sleeps.

Usage: systemsetup -setdisplaysleep <minutes>
Set amount of idle time until display sleeps to <minutes>.
Specify "Never" or "Off" for never.

Usage: systemsetup -getharddisksleep
Display amount of idle time until hard disk sleeps.

Usage: systemsetup -setharddisksleep <minutes>
Set amount of idle time until hard disk sleeps to <minutes>.
Specify "Never" or "Off" for never.

Usage: systemsetup -getwakeonmodem
Display whether wake on modem is on or off.

Usage: systemsetup -setwakeonmodem <on off>
Set wake on modem to either <on> or <off>.

Usage: systemsetup -getwakeonnetworkaccess
Display whether wake on network access is on or off.

Usage: systemsetup -setwakeonnetworkaccess <on off>
Set wake on network access to either <on> or <off>.

Usage: systemsetup -getrestartpowerfailure
Display whether restart on power failure is on or off.

Usage: systemsetup -setrestartpowerfailure <on off>
Set restart on power failure to either <on> or <off>.

Usage: systemsetup -getrestartfreeze
Display whether restart on freeze is on or off.

Usage: systemsetup -setrestartfreeze <on off>
Set restart on freeze to either <on> or <off>.

Usage: systemsetup -getallowpowerbuttontosleepcomputer
Display whether the power button is able to sleep the computer.

Usage: systemsetup -setallowpowerbuttontosleepcomputer <on off>
Enable or disable whether the power button can sleep the computer.

Usage: systemsetup -getremotelogin
Display whether remote login is on or off.

Usage: systemsetup -setremotelogin <on off>
Set remote login to either <on> or <off>. Use "systemsetup -f -setremotelogin off" to suppress prompting when turning remote login off.

Usage: systemsetup -getremoteappleevents
Display whether remote apple events are on or off.

Usage: systemsetup -setremoteappleevents <on off>
Set remote apple events to either <on> or <off>.

Usage: systemsetup -getcomputername
Display computer name.

Usage: systemsetup -setcomputername <computername>
Set computer name to <computername>.

Usage: systemsetup -getlocalsubnetname
Display local subnet name.

Usage: systemsetup -setlocalsubnetname <name>
Set local subnet name to <name>.

Usage: systemsetup -getstartupdisk
Display current startup disk.

Usage: systemsetup -setstartupdisk <disk>
Set current startup disk to <disk>.

Usage: systemsetup -liststartupdisks
List startup disks on this machine.

Usage: systemsetup -getwaitforstartupafterpowerfailure
Get the number of seconds after which the computer will start up after a power failure.

Usage: systemsetup -setwaitforstartupafterpowerfailure <seconds>
Set the number of seconds after which the computer will start up after a power failure. The <seconds> value must be a multiple of 30 seconds.

Usage: systemsetup -getdisablekeyboardwhenenclosurelockisengaged
Get whether or not the keyboard should be disabled when the X Serve enclosure lock is engaged.

Usage: systemsetup -setdisablekeyboardwhenenclosurelockisengaged <yes no>
Set whether or not the keyboard should be disabled when the X Serve enclosure lock is engaged.

Usage: systemsetup -version
Display version of systemsetup tool.

Usage: systemsetup -help
Display help.

Usage: systemsetup -printCommands
Display commands.

Enabling SSH in Mac OS X computers can be done also from Graphical interface for the lazy ones.

enable-ssh-mac-remote-login-from-mac-OS-X-gui

Tags: Display, either, hard disk, hostname, How to, network, power, Set, sleep, ssh, time server, Usage
Posted in Linux, Mac OS X, Networking, Various | No Comments »

Debugging routing and network issues on Linux common approaches. A step by step guide to find out why routing or network service fails

Thursday, November 30th, 2023

For system administrators having a Network issue is among the Hell-ish stuff that can happen every now and then. That is especially true in Heterogenous / Hybrid and complicated Network topologies (with missing well crafted documentation), that were build without an initial overview "on the fly".
Such a networking connectivity or routing issues are faced by every novice, mid or even expert system administrators as the Company's Network IT environments are becoming more and more complicated day by day.

When the "Disaster" of being unable to connect two servers or at times home laptops / PCs to see each other even though on the Physical layer / Transport Layer (Hardware such as external Switches / Routers / Repeaters / Cabling etc.) is Present machines are connected and everything on the 1 Physical Layer from OSI layears is present happens, then it is time to Debug it with some software tools and methods.

To each operating system the tools and methods to test networking connection and routings is a bit different but generally speaking most concepts are pretty much the same across different types of operating systems (Linux ditros / OpenBSD / FreeBSD / Mac OS / Android / iOS / HP-UX / IBM AIX / DOS / Windows etc.).

Debugging network issues across separate operating systems has its variations but in this specific (ideas) are much close to this article. As the goal at that guide will be to point out how to debug network issues on Linux, in future if I have the time or need to debug other OS-es from Linux, I'll try to put an article on how to debug Network issues on Windows when have some time to do it.

Consider to look for the issue following the basic TCP / IP OSI Level model, every system administrator should have idea about it already, it is part of most basic networking courses such as Cisco's CCNA

1. Check what is the Link status of the Interface with ethtool

root@freak:~# ethtool eno1
Settings for eno1:
   Supported ports: [ TP ]
   Supported link modes: 10baseT/Half 10baseT/Full
   100baseT/Half 100baseT/Full
   1000baseT/Full
   Supported pause frame use: Symmetric
   Supports auto-negotiation: Yes
   Supported FEC modes: Not reported
   Advertised link modes: 10baseT/Half 10baseT/Full
   100baseT/Half 100baseT/Full
   1000baseT/Full
   Advertised pause frame use: Symmetric
   Advertised auto-negotiation: Yes
   Advertised FEC modes: Not reported
   Speed: 100Mb/s
   Duplex: Full
   Auto-negotiation: on
   Port: Twisted Pair
   PHYAD: 1
   Transceiver: internal
   MDI-X: on (auto)
   Supports Wake-on: pumbg
   Wake-on: g
Current message level: 0x00000007 (7)
drv probe link
   Link detected: yes

root@freak:~# ethtool eno2
Settings for eno2:
   Supported ports: [ TP ]
   Supported link modes: 10baseT/Half 10baseT/Full
   100baseT/Half 100baseT/Full
   1000baseT/Full
   Supported pause frame use: Symmetric
   Supports auto-negotiation: Yes
   Supported FEC modes: Not reported
   Advertised link modes: 10baseT/Half 10baseT/Full
   100baseT/Half 100baseT/Full
   1000baseT/Full
   Advertised pause frame use: Symmetric
   Advertised auto-negotiation: Yes
   Advertised FEC modes: Not reported
   Speed: 1000Mb/s
   Duplex: Full
   Auto-negotiation: on
   Port: Twisted Pair
   PHYAD: 1
   Transceiver: internal
   MDI-X: on (auto)
   Supports Wake-on: pumbg
   Wake-on: g
Current message level: 0x00000007 (7)
drv probe link
   Link detected: yes

For example lets check only if Cable of Network card is plugged in and detected to have a network connection to remote node or switch and show the connection speed on which the 'autoneg on' (autonegiation option) of the LAN card has detected the network exat maximum speed:

root@pcfreak:~# ethtool eth0|grep -i 'link detected'; ethtool eth0 |grep 'Speed: '
Link detected: yes
Speed: 100Mb/s

1. Check ip command network configuration output

root@freak:~# ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 1000
link/ether 70:e2:84:13:44:15 brd ff:ff:ff:ff:ff:ff
altname enp7s0
3: eno2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 1000
link/ether 70:e2:84:13:44:17 brd ff:ff:ff:ff:ff:ff
altname enp8s0
4: xenbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 70:e2:84:13:44:13 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.7/24 brd 192.168.1.255 scope global dynamic xenbr0
valid_lft 7361188sec preferred_lft 7361188sec
5: xenbr1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 70:e2:84:13:44:15 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.5/24 brd 192.168.0.255 scope global dynamic xenbr1
valid_lft 536138sec preferred_lft 536138sec
10: vif2.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
11: vif2.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
12: vif3.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
13: vif3.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
14: vif4.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
15: vif4.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
16: vif5.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
17: vif5.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
18: vif6.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
19: vif6.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
30: vif17.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
31: vif17.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
34: vif21.0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr0 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
35: vif21.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master xenbr1 state UP group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
48: vif25.0-emu: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master xenbr0 state UNKNOWN group default qlen 1000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
49: vif25.1-emu: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master xenbr1 state UNKNOWN group default qlen 1000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
50: vif25.0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq master xenbr0 state DOWN group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
51: vif25.1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq master xenbr1 state DOWN group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
118: vif47.0-emu: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master xenbr0 state UNKNOWN group default qlen 1000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
119: vif47.1-emu: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master xenbr1 state UNKNOWN group default qlen 1000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
120: vif47.0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq master xenbr0 state DOWN group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
121: vif47.1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq master xenbr1 state DOWN group default qlen 2000
link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
root@freak:~#

ip a s (is a also a shortcut command alias) you can enjoy if you have to deal with ip command frequently.

2. Check the status of the interfaces

Old fashioned way is to just do:

/sbin/ifconfig

root@freak:~# ifconfig
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 70:e2:84:13:44:15 txqueuelen 1000 (Ethernet)
RX packets 52366502 bytes 10622469320 (9.8 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 242622195 bytes 274688121244 (255.8 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0xfb200000-fb27ffff

eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 70:e2:84:13:44:17 txqueuelen 1000 (Ethernet)
RX packets 220995454 bytes 269698276095 (251.1 GiB)
RX errors 0 dropped 7 overruns 0 frame 0
TX packets 192319925 bytes 166233773782 (154.8 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0xfb100000-fb17ffff

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
RX packets 2553 bytes 147410 (143.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2553 bytes 147410 (143.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif17.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 14517375 bytes 133226551792 (124.0 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 139688950 bytes 145111993017 (135.1 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif17.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 86113294 bytes 156944058681 (146.1 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 181513904 bytes 267892940821 (249.4 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif2.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 1521875 bytes 88282472 (84.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 152691174 bytes 278372314505 (259.2 GiB)
TX errors 0 dropped 3 overruns 0 carrier 0 collisions 0

vif2.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 454915 bytes 81069760 (77.3 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 266953989 bytes 425692364876 (396.4 GiB)
TX errors 0 dropped 26 overruns 0 carrier 0 collisions 0

vif21.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 20043711 bytes 1283926794 (1.1 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 141580485 bytes 277396881113 (258.3 GiB)
TX errors 0 dropped 3 overruns 0 carrier 0 collisions 0

vif21.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 73004 bytes 3802174 (3.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 267151006 bytes 425621892663 (396.3 GiB)
TX errors 0 dropped 14 overruns 0 carrier 0 collisions 0

vif25.0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif25.1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif25.0-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 2736348 bytes 295661367 (281.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 260385509 bytes 265751226663 (247.5 GiB)
TX errors 0 dropped 200 overruns 0 carrier 0 collisions 0

vif25.1-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 145387 bytes 36011655 (34.3 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 370314760 bytes 394725961081 (367.6 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif3.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 55382861 bytes 130042280927 (121.1 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 99040097 bytes 147929196318 (137.7 GiB)
TX errors 0 dropped 1 overruns 0 carrier 0 collisions 0

vif3.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 5132631 bytes 295493762 (281.8 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 262314199 bytes 425416945203 (396.2 GiB)
TX errors 0 dropped 16 overruns 0 carrier 0 collisions 0

vif4.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 4902015 bytes 615387539 (586.8 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 149342891 bytes 277802504143 (258.7 GiB)
TX errors 0 dropped 1 overruns 0 carrier 0 collisions 0

vif4.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 276927 bytes 30720101 (29.2 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 267132395 bytes 425745668273 (396.5 GiB)
TX errors 0 dropped 14 overruns 0 carrier 0 collisions 0

vif47.0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif47.1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif47.0-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 208745 bytes 20096596 (19.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 110905731 bytes 110723486135 (103.1 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif47.1-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 140517 bytes 14596061 (13.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 150831959 bytes 162931572456 (151.7 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif5.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 2030528 bytes 363988589 (347.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 152264264 bytes 278131541781 (259.0 GiB)
TX errors 0 dropped 1 overruns 0 carrier 0 collisions 0

vif5.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 4169244 bytes 1045889687 (997.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 263561100 bytes 424894400987 (395.7 GiB)
TX errors 0 dropped 7 overruns 0 carrier 0 collisions 0

vif6.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 300242 bytes 16210963 (15.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 153909576 bytes 278461295620 (259.3 GiB)
TX errors 0 dropped 2 overruns 0 carrier 0 collisions 0

vif6.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 43 bytes 1932 (1.8 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 154205631 bytes 278481298141 (259.3 GiB)
TX errors 0 dropped 2 overruns 0 carrier 0 collisions 0

xenbr0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.8 netmask 255.255.255.0 broadcast 192.168.1.255
ether 70:e2:84:13:44:11 txqueuelen 1000 (Ethernet)
RX packets 13689902 bytes 923464162 (880.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 12072932 bytes 1307055530 (1.2 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

xenbr1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.0.3 netmask 255.255.255.0 broadcast 192.168.0.255
ether 70:e2:84:13:44:12 txqueuelen 1000 (Ethernet)
RX packets 626995 bytes 180026901 (171.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 12815 bytes 942092 (920.0 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

root@freak:~# ifconfig
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 70:e2:84:13:44:11 txqueuelen 1000 (Ethernet)
RX packets 52373358 bytes 10623034427 (9.8 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 242660000 bytes 274734018669 (255.8 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0xfb200000-fb27ffff

eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 70:e2:84:13:44:12 txqueuelen 1000 (Ethernet)
RX packets 221197892 bytes 269978137472 (251.4 GiB)
RX errors 0 dropped 7 overruns 0 frame 0
TX packets 192573206 bytes 166491370299 (155.0 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0xfb100000-fb17ffff

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
RX packets 2553 bytes 147410 (143.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2553 bytes 147410 (143.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif17.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 14519247 bytes 133248290251 (124.0 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 139708738 bytes 145135168676 (135.1 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif17.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 86206104 bytes 157189755115 (146.3 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 181685983 bytes 268170806613 (249.7 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif2.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 1522072 bytes 88293701 (84.2 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 152712638 bytes 278417240910 (259.2 GiB)
TX errors 0 dropped 3 overruns 0 carrier 0 collisions 0

vif2.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 454933 bytes 81071616 (77.3 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 267218860 bytes 426217224334 (396.9 GiB)
TX errors 0 dropped 26 overruns 0 carrier 0 collisions 0

vif21.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 20045530 bytes 1284038375 (1.1 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 141601066 bytes 277441739746 (258.3 GiB)
TX errors 0 dropped 3 overruns 0 carrier 0 collisions 0

vif21.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 73010 bytes 3802474 (3.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 267415889 bytes 426146753845 (396.8 GiB)
TX errors 0 dropped 14 overruns 0 carrier 0 collisions 0

vif25.0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif25.1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif25.0-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 2736576 bytes 295678097 (281.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 260429831 bytes 265797660906 (247.5 GiB)
TX errors 0 dropped 200 overruns 0 carrier 0 collisions 0

vif25.1-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 145425 bytes 36018716 (34.3 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 370770440 bytes 395263409640 (368.1 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif3.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 55392503 bytes 130064444520 (121.1 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 99052116 bytes 147951838129 (137.7 GiB)
TX errors 0 dropped 1 overruns 0 carrier 0 collisions 0

vif3.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 5133054 bytes 295517366 (281.8 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 262578665 bytes 425941777243 (396.6 GiB)
TX errors 0 dropped 16 overruns 0 carrier 0 collisions 0

vif4.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 4902949 bytes 615496460 (586.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 149363618 bytes 277847322538 (258.7 GiB)
TX errors 0 dropped 1 overruns 0 carrier 0 collisions 0

vif4.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 276943 bytes 30721141 (29.2 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 267397268 bytes 426270528575 (396.9 GiB)
TX errors 0 dropped 14 overruns 0 carrier 0 collisions 0

vif47.0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif47.1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif47.0-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 208790 bytes 20100733 (19.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 110950236 bytes 110769932971 (103.1 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif47.1-emu: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 1000 (Ethernet)
RX packets 140551 bytes 14599509 (13.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 151287643 bytes 163469024604 (152.2 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

vif5.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 2030676 bytes 363997181 (347.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 152285777 bytes 278176471509 (259.0 GiB)
TX errors 0 dropped 1 overruns 0 carrier 0 collisions 0

vif5.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 4169387 bytes 1045898303 (997.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 263825846 bytes 425419251935 (396.2 GiB)
TX errors 0 dropped 7 overruns 0 carrier 0 collisions 0

vif6.0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 300266 bytes 16212271 (15.4 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 153931212 bytes 278506234302 (259.3 GiB)
TX errors 0 dropped 2 overruns 0 carrier 0 collisions 0

vif6.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether fe:ff:ff:ff:ff:ff txqueuelen 2000 (Ethernet)
RX packets 43 bytes 1932 (1.8 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 154227291 bytes 278526238467 (259.3 GiB)
TX errors 0 dropped 2 overruns 0 carrier 0 collisions 0

xenbr0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.8 netmask 255.255.255.0 broadcast 192.168.1.255
ether 70:e2:84:13:44:11 txqueuelen 1000 (Ethernet)
RX packets 13690768 bytes 923520126 (880.7 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 12073667 bytes 1307127765 (1.2 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

xenbr1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.0.3 netmask 255.255.255.0 broadcast 192.168.0.255
ether 70:e2:84:13:44:12 txqueuelen 1000 (Ethernet)
RX packets 627010 bytes 180028847 (171.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 12815 bytes 942092 (920.0 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

To see ethernet interfaces that seem up and then do a ifconfig -a to check whether some interfaces are down (e.g. not shown in the simple ifconfig list).
/sbin/ifconfig -a

! Please note that some virtual IP configurations might not appear and noly be visible in an (ip addr show) command.

3. Check iproute2 for special rt_tables (Routing Tables) rules

By default Linux distributions does not have any additional rules in /etc/iproute2/rt_tables however some Linux router machines, needs to have a multiple Gateways. Perhaps the most elegant way to do multiple routings with Linux is to use iproute2's routing tables rt_tables.

Here is example of an OpenXEN system that has 2 Internet providers attached and routes different traffic via

root@freak:~# cat /etc/iproute2/rt_tables
#
# reserved values
#
255   local
254   main
253   default

100   INET1
200 INET2
0   unspec
#
# local
#
#1   inr.ruhep

root@freak:~# ip rule list
0:   from all lookup local
32762:   from all to 192.168.1.8 lookup INET2
32763:   from 192.168.1.8 lookup INET2
32764:   from all to 192.168.0.3 lookup INET1
32765:   from 192.168.0.3 lookup INET1
32766:   from all lookup main
32767:   from all lookup default
root@freak:~#

4. Using ip route get to find out traffic route (path)

root@freak:~# ip route get 192.168.0.1
192.168.0.1 via 192.168.0.1 dev xenbr1 src 192.168.0.3 uid 0
cache

root@freak:~# /sbin/route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 xenbr0
192.168.0.0 192.168.0.1 255.255.255.0 UG 0 0 0 xenbr1
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 xenbr1
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 xenbr0
root@freak:~#

root@freak:~# ip route show
default via 192.168.1.1 dev xenbr0
192.168.0.0/24 via 192.168.0.1 dev xenbr1
192.168.0.0/24 dev xenbr1 proto kernel scope link src 192.168.0.3
192.168.1.0/24 dev xenbr0 proto kernel scope link src 192.168.1.8

If you find that gateway is missing you might want to add it with:

root@freak:~# ip route add default via 192.168.5.1

If you need to add a speicic network IP range via separate gateways, you can use commands like:

To add routing for 192.168.0.1/24 / 192.168.1.1/24 via 192.168.0.1 and 192.168.1.1

# /sbin/route add -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.1.1 dev eth1
# /sbin/route add -net 192.168.0.0 netmask 255.255.255.0 gw 192.168.0.1 dev eth1

If you need to delete a configured wrong route with ip command

# ip route del 192.168.1.0/24 via 0.0.0.0 dev eth1
# ip route del 192.168.0.0/24 via 0.0.0.0 dev eth1

5. Use ping (ICMP protocol) the Destionation IP

root@freak:~# ping -c 3 192.168.0.1
PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=0.219 ms
64 bytes from 192.168.0.1: icmp_seq=2 ttl=64 time=0.295 ms
64 bytes from 192.168.0.1: icmp_seq=3 ttl=64 time=0.270 ms

— 192.168.0.1 ping statistics —
3 packets transmitted, 3 received, 0% packet loss, time 2048ms
rtt min/avg/max/mdev = 0.219/0.261/0.295/0.031 ms
root@freak:~# ping -c 3 192.168.0.39
PING 192.168.0.39 (192.168.0.39) 56(84) bytes of data.
From 192.168.1.80: icmp_seq=2 Redirect Host(New nexthop: 192.168.0.39)
From 192.168.1.80: icmp_seq=3 Redirect Host(New nexthop: 192.168.0.39)
From 192.168.1.80 icmp_seq=1 Destination Host Unreachable

— 192.168.0.39 ping statistics —
3 packets transmitted, 0 received, +1 errors, 100% packet loss, time 2039ms
pipe 3

Note that sometimes you might get 100% traffic loss but still have connection to the destionation in case if the ICMP protocol is filtered for security.

However if you get something like Network is unreachable that is usually an indicator of some routing problem or wrongly configured network netmask.

root@freak:~# ping 192.168.0.5
ping: connect: Network is unreachable

Test network with different packet size. To send 8972 bytes of payload in a Ethernet frame without fragmentation, the following command can be used:

root@pcfreak:~# ping -s 8972 -M do -c 4 freak
PING xen (192.168.1.8) 8972(9000) bytes of data.
ping: local error: message too long, mtu=1500
ping: local error: message too long, mtu=1500
ping: local error: message too long, mtu=1500
^C
— xen ping statistics —
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2037ms

root@pcfreak:~#

-M pmtudisc_opt
Select Path MTU Discovery strategy. pmtudisc_option may be either do (prohibit fragmentation, even local one), want (do PMTU discovery, fragment locally when packet size is
large), or dont (do not set DF flag).

root@pcfreak:~# ping -s 8972 -M want -c 4 freak
PING xen (192.168.1.8) 8972(9000) bytes of data.
8980 bytes from xen (192.168.1.5): icmp_seq=1 ttl=64 time=2.18 ms
8980 bytes from xen (192.168.1.5): icmp_seq=2 ttl=64 time=1.90 ms
8980 bytes from xen (192.168.1.5): icmp_seq=3 ttl=64 time=2.10 ms
^C
— xen ping statistics —
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 1.901/2.059/2.178/0.116 ms
root@pcfreak:~#

-M do: prohibit fragmentation
-s 8972 8972 bytes of data
ICMP header: 8 bytes
IP header: 20 bytes (usually, it can be higher)
8980 bytes of bytes is the IP payload

These commands can be used to capture for MTU (maximum transmition units) related issues between hosts that are preventing for hosts to properly send traffic between themselves.
A common issue for Linux hosts to be unable to see each other on the same network is caused by Jumbo Frames (MTU 9000) packets enabled on one of the sides and MTU of 1500 on the other side.
Thus it is always a good idea to thoroughully look up all configured MTUs for all LAN Devices on each server.

6. Check traceroute path to host

If there is no PING but ip route get shows routing is properly configured and the routes existing in the Linux machine routing tables, next step is to check the output of traceroute / tracepath / mtr

raceroute to 192.168.0.1 (192.168.0.1), 30 hops max, 60 byte packets
1 pcfreak (192.168.0.1) 0.263 ms 0.166 ms 0.119 ms
root@freak:~# tracepath 192.168.1.1
1?: [LOCALHOST] pmtu 1500
1: vivacom-gigabit-router 0.925ms reached
1: vivacom-gigabit-router 0.835ms reached
Resume: pmtu 1500 hops 1 back 1

It might be useful to get a frequent output of the command (especially on Linux hosts) where mtr command is not installed with:

root@freak:~# watch -n 0.1 traceroute 192.168.0.1

root@freak:~# traceroute -4 google.com
traceroute to google.com (172.217.17.110), 30 hops max, 60 byte packets
1 vivacom-gigabit-router (192.168.1.1) 0.657 ms 1.280 ms 1.647 ms
2 213.91.190.130 (213.91.190.130) 7.983 ms 8.168 ms 8.097 ms
3 * * *
4 * * *
5 212-39-66-222.ip.btc-net.bg (212.39.66.222) 16.613 ms 16.336 ms 17.151 ms
6 * * *
7 142.251.92.65 (142.251.92.65) 18.808 ms 13.246 ms 209.85.254.242 (209.85.254.242) 15.541 ms
8 142.251.92.3 (142.251.92.3) 14.223 ms 142.251.227.251 (142.251.227.251) 14.507 ms 142.251.92.3 (142.251.92.3) 15.328 ms
9 ams15s29-in-f14.1e100.net (172.217.17.110) 14.097 ms 14.909 ms 142.251.242.230 (142.251.242.230) 13.481 ms
root@freak:~#

If you have MTR then you can get plenty of useful additional information such as the Network HOP name or the Country location of the HOP.

To get HOP name:

root@freak:~# mtr -z google.com

To get info on where (which Country) exactly network HOP is located physically:

root@freak:~# mtr -y 2 google.com

7. Check iptables INPUT / FORWARD / OUTPUT rules are messing with something

# iptables -L -n
…

# iptables -t nat -L -n
…

Ideally you would not have any firewall

# iptables -L -n

Chain INPUT (policy ACCEPT)
target prot opt source destination

Chain FORWARD (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

# iptables -t nat -L -n
Chain PREROUTING (policy ACCEPT)
target prot opt source destination

Chain INPUT (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

Chain POSTROUTING (policy ACCEPT)
target prot opt source destination

In case if something like firewalld is enabled as a default serviceto provide some modern Linux firewall as Ubuntu and Redhat / CentOS / Fedoras has it often turned on as a service stop and disable the service

# systemctl stop firewalld

# systemctl disable firewalld

8. Debug for any possible MAC address duplicates

root@pcfrxen:~# arp -an
? (192.168.1.33) at 00:16:3e:59:96:9e [ether] on eth0
? (192.168.1.1) at 18:45:93:c6:d8:00 [ether] on eth1
? (192.168.0.1) at 8c:89:a5:f2:e8:d9 [ether] on eth1
? (192.168.1.1) at 18:45:93:c6:d8:00 [ether] on eth0
? (192.168.1.11) at 7c:0a:3f:89:b6:fa [ether] on eth1
? (192.168.1.17) at <incomplete> on eth0
? (192.168.1.37) at 00:16:3e:ea:05:ce [ether] on eth0
? (192.168.1.80) at 8c:89:a5:f2:e7:d8 [ether] on eth0
? (192.168.1.11) at 7c:0a:3f:89:a5:fa [ether] on eth0
? (192.168.1.30) at 00:16:3e:bb:46:45 [ether] on eth1
? (192.168.0.210) at 00:16:3e:68:d9:55 [ether] on eth1
? (192.168.1.30) at 00:16:3e:bb:46:45 [ether] on eth0
? (192.168.1.18) at 00:16:3e:0d:40:05 [ether] on eth1
? (192.168.0.211) at 00:16:3e:4d:41:05 [ether] on eth1
? (192.168.1.35) at 00:16:3e:d1:8f:77 [ether] on eth0
? (192.168.1.18) at 00:16:3e:0d:43:05 [ether] on eth0
? (192.168.1.28) at 00:16:3e:04:12:1c [ether] on eth1
? (192.168.0.3) at 70:e2:84:13:43:12 [ether] on eth1
? (192.168.0.208) at 00:16:3e:51:de:9c [ether] on eth1
? (192.168.0.241) at 00:16:3e:0d:48:06 [ether] on eth1
? (192.168.1.28) at 00:16:3e:04:12:1c [ether] on eth0
? (192.168.1.33) at 00:16:3e:59:97:8e [ether] on eth1
? (192.168.0.241) at 00:16:3e:0d:45:06 [ether] on eth0
? (192.168.0.209) at 00:16:3e:5c:df:96 [ether] on eth1

root@pcfrxen:~# ip neigh show
192.168.1.33 dev eth0 lladdr 00:16:3e:59:96:9e REACHABLE
192.168.1.1 dev eth1 lladdr 18:45:93:c6:d8:00 STALE
192.168.0.1 dev eth1 lladdr 8c:89:a5:f2:e8:d9 REACHABLE
192.168.1.1 dev eth0 lladdr 18:45:93:c6:d9:01 REACHABLE
192.168.1.11 dev eth1 lladdr 7c:0a:3f:89:a6:fb STALE
192.168.1.17 dev eth0 FAILED
192.168.1.37 dev eth0 lladdr 00:16:3e:ea:06:ce STALE
192.168.1.80 dev eth0 lladdr 8c:89:a5:f2:e8:d9 REACHABLE
192.168.1.11 dev eth0 lladdr 7c:0a:3f:89:a7:fa STALE
192.168.1.30 dev eth1 lladdr 00:16:3e:bb:45:46 STALE
192.168.0.210 dev eth1 lladdr 00:16:3e:68:d8:56 REACHABLE
192.168.1.30 dev eth0 lladdr 00:16:3e:bb:45:46 STALE
192.168.1.18 dev eth1 lladdr 00:16:3e:0d:48:04 STALE
192.168.0.211 dev eth1 lladdr 00:16:3e:4d:40:04 STALE
192.168.1.35 dev eth0 lladdr 00:16:3e:d2:8f:76 STALE
192.168.1.18 dev eth0 lladdr 00:16:3e:0d:48:06 STALE
192.168.1.28 dev eth1 lladdr 00:16:3e:04:11:2c STALE
192.168.0.3 dev eth1 lladdr 70:e2:84:13:44:13 STALE
192.168.0.208 dev eth1 lladdr 00:16:3e:51:de:9c REACHABLE
192.168.0.241 dev eth1 lladdr 00:16:3e:0d:48:07 STALE
192.168.1.28 dev eth0 lladdr 00:16:3e:04:12:1c REACHABLE
192.168.1.33 dev eth1 lladdr 00:16:3e:59:96:9e STALE
192.168.0.241 dev eth0 lladdr 00:16:3e:0d:49:06 STALE
192.168.0.209 dev eth1 lladdr 00:16:3e:5c:dd:97 STALE
root@pcfrxen:~#

9. Check out with netstat / ss for any irregularities such as high amount of error of faulty ICMP / TCP / UDP network packs

For example check out the netstat network stack output

# netstat -s

root@pcfrxen:~# netstat -s
Ip:
Forwarding: 2
440044929 total packets received
1032 with invalid addresses
0 forwarded
0 incoming packets discarded
439988902 incoming packets delivered
396161852 requests sent out
3 outgoing packets dropped
100 dropped because of missing route
Icmp:
1025 ICMP messages received
540 input ICMP message failed
ICMP input histogram:
destination unreachable: 1014
timeout in transit: 11
519 ICMP messages sent
0 ICMP messages failed
ICMP output histogram:
destination unreachable: 519
IcmpMsg:
InType3: 1014
InType11: 11
OutType3: 519
Tcp:
1077237 active connection openings
1070510 passive connection openings
1398236 failed connection attempts
111345 connection resets received
83 connections established
438293250 segments received
508143650 segments sent out
42567 segments retransmitted
546 bad segments received
329039 resets sent
Udp:
1661295 packets received
278 packets to unknown port received
0 packet receive errors
1545720 packets sent
0 receive buffer errors
0 send buffer errors
IgnoredMulti: 33046
UdpLite:
TcpExt:
1 invalid SYN cookies received
1398196 resets received for embryonic SYN_RECV sockets
1737473 packets pruned from receive queue because of socket buffer overrun
1118775 TCP sockets finished time wait in fast timer
638 time wait sockets recycled by time stamp
656 packetes rejected in established connections because of timestamp
2218959 delayed acks sent
2330 delayed acks further delayed because of locked socket
Quick ack mode was activated 7172 times
271799723 packet headers predicted
14917420 acknowledgments not containing data payload received
171078735 predicted acknowledgments
52 times recovered from packet loss due to fast retransmit
TCPSackRecovery: 337
Detected reordering 1551 times using SACK
Detected reordering 1501 times using reno fast retransmit
Detected reordering 61 times using time stamp
9 congestion windows fully recovered without slow start
38 congestion windows partially recovered using Hoe heuristic
TCPDSACKUndo: 241
104 congestion windows recovered without slow start after partial ack
TCPLostRetransmit: 11550
1 timeouts after reno fast retransmit
TCPSackFailures: 13
3772 fast retransmits
2 retransmits in slow start
TCPTimeouts: 24104
TCPLossProbes: 101748
TCPLossProbeRecovery: 134
TCPSackRecoveryFail: 3
128989224 packets collapsed in receive queue due to low socket buffer
TCPBacklogCoalesce: 715034
TCPDSACKOldSent: 7168
TCPDSACKOfoSent: 341
TCPDSACKRecv: 16612
150689 connections reset due to unexpected data
27063 connections reset due to early user close
17 connections aborted due to timeout
TCPDSACKIgnoredOld: 158
TCPDSACKIgnoredNoUndo: 13514
TCPSpuriousRTOs: 9
TCPSackMerged: 1191
TCPSackShiftFallback: 1011
TCPDeferAcceptDrop: 699473
TCPRcvCoalesce: 3311764
TCPOFOQueue: 14289375
TCPOFOMerge: 356
TCPChallengeACK: 621
TCPSYNChallenge: 621
TCPSpuriousRtxHostQueues: 4
TCPAutoCorking: 1605205
TCPFromZeroWindowAdv: 132380
TCPToZeroWindowAdv: 132441
TCPWantZeroWindowAdv: 1445495
TCPSynRetrans: 23652
TCPOrigDataSent: 388992604
TCPHystartTrainDetect: 69089
TCPHystartTrainCwnd: 3264904
TCPHystartDelayDetect: 4
TCPHystartDelayCwnd: 128
TCPACKSkippedPAWS: 3
TCPACKSkippedSeq: 2001
TCPACKSkippedChallenge: 2
TCPWinProbe: 123043
TCPKeepAlive: 4389
TCPDelivered: 389507445
TCPAckCompressed: 7343781
TcpTimeoutRehash: 23311
TcpDuplicateDataRehash: 8
TCPDSACKRecvSegs: 17335
IpExt:
InMcastPkts: 145100
OutMcastPkts: 9429
InBcastPkts: 18226
InOctets: 722933727848
OutOctets: 759502627470
InMcastOctets: 58227095
OutMcastOctets: 3284379
InBcastOctets: 1756918
InNoECTPkts: 440286946
InECT0Pkts: 936

List all listening established connections to host

# netstat -ltne

List all UDP / TCP connections

# netstat -ltua

or if you prefer to do it with the newer and more comprehensive tool ss:

List all listening TCP connections

# ss -lt

List all listening UDP connections

# ss -ua

Display statistics about recent connections

root@pcfrxen:~# ss -s
Total: 329
TCP: 896 (estab 70, closed 769, orphaned 0, timewait 767)

Transport Total IP IPv6
RAW   0 0 0
UDP   40 36 4
TCP   127 118 9
INET   167 154 13
FRAG   0 0 0

If you need to debug some specific sport or dport filter out the connection you need by port number

# ss -at '( dport = :22 or sport = :22 )'

Debug for any possible issues with ICMP unreachable but ports reachable with NMAP / telnet / Netcat

# nc 192.168.0.1 -vz

root@pcfrxen:/ # nc 192.168.0.1 80 -vz
pcfreak [192.168.0.1] 80 (http) open

root@pcfrxen:/ # nc 192.168.0.1 5555 -vz
pcfreak [192.168.0.1] 5555 (?) : Connection refused

root@pcfrxen:/# telnet 192.168.0.1 3128
Trying 192.168.0.1…
Connected to 192.168.0.1.
Escape character is '^]'.
^]
telnet> quit
Connection closed.

root@pcfrxen:/# nmap -sS -P0 192.168.0.1 -p 443 -O
Starting Nmap 7.80 ( https://nmap.org ) at 2023-11-27 19:51 EET
Nmap scan report for pcfreak (192.168.0.1)
Host is up (0.00036s latency).

PORT STATE SERVICE
443/tcp open https
MAC Address: 8C:89:A5:F2:E8:D8 (Micro-Star INT'L)
Warning: OSScan results may be unreliable because we could not find at least 1 open and 1 closed port
Aggressive OS guesses: Linux 3.11 (96%), Linux 3.1 (95%), Linux 3.2 (95%), AXIS 210A or 211 Network Camera (Linux 2.6.17) (94%), Linux 2.6.32 (94%), Linux 3.10 (94%), Linux 2.6.18 (93%), Linux 3.2 – 4.9 (93%), ASUS RT-N56U WAP (Linux 3.4) (93%), Linux 3.16 (93%)
No exact OS matches for host (test conditions non-ideal).
Network Distance: 1 hop

OS detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 6.24 seconds
root@pcfrxen:/#

10. Add static MAC address to Ethernet Interface (if you find a MAC address being wrongly assigned to interface)

Sometimes problems with network unrechability between hosts is caused by wrongly defined MAC addresses on a Switch that did not correspond correctly to the ones assigned on the Linux host.
The easiest resolution here if you don't have access to Switch in work environment is to reassign the default MAC addresses of interfaces to proper MAC addresses, expected by remote router.

root@pcfrxen:/#  /sbin/ifconfig eth2 hw ether 8c:89:a5:f2:e8:d6

root@pcfrxen:/#  /sbin/ifconfig eth1 hw ether 8c:89:a5:f2:e8:d5

root@pcfrxen:/#  ifconfig eth0|grep -i ether
ether 8c:89:a5:f2:e8:d6 txqueuelen 1000 (Ethernet)

11. Check for Network Address Translation (NAT) misconfigurations

If you do use some NAT-ing between Linux host and the remote Network Device you cannot reach, make sure IP Forwarding is enabled (i.e. /etc/sysctl.conf was not mistakenly overwritten by a script or admin for whatever reason).

root@server:~# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1
root@server:~# sysctl net.ipv4.conf.all.forwarding
net.ipv4.conf.all.forwarding = 1

root@server:~# sysctl net.ipv6.conf.all.forwarding
net.ipv6.conf.all.forwarding = 0

12. Check for Resolving DNS irregularities with /etc/resolv.conf

If network connectivity is okay on TCP / IP , UDP Level but problems with DNS of course, check what you have configured inside /etc/resolv.conf

And if use newer Linux distributions and have resolving managed by systemd check status of resolvectl

root@server:~# cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND — YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "resolvectl status" to see details about the actual nameservers.

nameserver 127.0.0.1
search pc-freak.net
domain pc-freak.net
nameserver 8.8.8.8
nameserver 8.8.4.4
nameserver 109.104.195.2
nameserver 109.104.195.1
nameserver 208.67.222.222
nameserver 208.67.220.220
options timeout:2 rotate
root@pcfreak:~#

root@server:~# resolvectl status
Global
Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub

Link 2 (ens3)
Current Scopes: DNS
Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.5.1
DNS Servers: 192.168.5.1

As seen see, the systemd-resolved service is used to provide domain names resolution and we can modify its configuration file /etc/systemd/resolved.conf to add the DNS server – the following line is set (two DNS servers’ addresses are added):

For example …

DNS=8.8.8.8

13. Fix problems with wrongly configured Network Speed between hosts

It is not uncommon to have a Switch between two Linux hosts that is set to communicate on a certain maximum amount of Speed but a Linux host is set to communicate or lesser or more of Speed, this might create network issues so in such cases make sure either you use the Auto Negitionation network feature
or set both sides to be communicating on the same amount of network speed.

To turn on auto negotiation for ether interface

# ethtool -s eth1 speed 1000 duplex full autoneg on

For example to set a Linux network interface to communicate on 1 Gigabit speed and switch off autonegotiation off.

# ethtool -s eth1 speed 1000 duplex full autoneg off

14. Check arp and icmp traffic with tcpdump

On both sides where the IPs can't see each other we can run a tcpdump to check the ARP and ICMP traffic flowing between the hosts.

# tcpdump -i eth1 arp or icmp

cpdump: verbose output suppressed, use -v[v]… for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), snapshot length 262144 bytes
15:29:07.001841 IP freak-eth1 > pcfr_hware_local_ip: ICMP echo request, id 13348, seq 65, length 64
15:29:07.001887 IP pcfr_hware_local_ip > freak-eth1: ICMP echo reply, id 13348, seq 65, length 64
15:29:07.598413 ARP, Request who-has pcfr_hware_local_ip tell zabbix-server, length 46
15:29:07.598425 ARP, Reply pcfr_hware_local_ip is-at 8c:89:a5:f2:e8:d8 (oui Unknown), length 28
15:29:07.633055 ARP, Request who-has freak_vivacom_auto_assigned_dhcp_ip tell 192.168.1.1, length 46
15:29:08.025824 IP freak-eth1 > pcfr_hware_local_ip: ICMP echo request, id 13348, seq 66, length 64
15:29:08.025864 IP pcfr_hware_local_ip > freak-eth1: ICMP echo reply, id 13348, seq 66, length 64

# tcpdump -i eth1 -vvv
…

If you want to sniff for TCP protocol and specific port and look up for DATA transfered for SMTP you can use something like:

# tcpdump -nNxXi eth0 -s 0 proto TCP and port 25

If you need a bit more thorough explanation on what it would do check out my previous article How to catch / track mail server traffic abusers with tcpdump.

15. Debugging network bridge issues

Having bridge network interface is another brink where things could go totally wrong.
If you have network bridges configured, check out what is the status of the bridge.

root@freak:/etc/network# brctl show
bridge name   bridge id       STP enabled   interfaces
xenbr0       8000.70e284134411   yes       eno1
                           vif1.0
                           vif10.0
                           vif16.0
                           vif16.0-emu
                           vif2.0
                           vif3.0
                           vif4.0
                           vif5.0
                           vif6.0
                           vif9.0
                           vif9.0-emu
xenbr1       8000.70e284134412   yes       eno2
                           vif1.1
                           vif10.1
                           vif16.1
                           vif16.1-emu
                           vif2.1
                           vif3.1
                           vif4.1
                           vif5.1
                           vif6.1
                           vif9.1
                           vif9.1-emu

Check out any configurations such as /etc/sysconfig/network-scripts/ifcfg-* are not misconfigured if on Redhat / CentOS / Fedora.
Or if on Debian / Ubuntu and other deb based Linuxes look up for /etc/network/interfaces config problems that might be causing the bridge to misbehave.

For example one bridge network issue, I've experienced recently is related to bridge_ports variable configured as bridge_ports all.
This was causing the second bridge xenbr1 to be unable to see another local network that was directly connected with a cable to it.

The fix was bridge_ports none. Finding out this trivial issue caused by a restored network config from old backup took me days to debug.
As everything seemed on a network level to be perfect just like in Physical layer, same way and on Software level, routings were okay.
Checked everything multiple times and did not see anything irregular. ping was missing and hosts cannot see each other even though having the right netmask and
network configuration in place.

Below is my /etc/network/interfaces configuration with the correct bridge_ports none changed.

root@freak:/etc/network# cat /etc/network/interfaces
auto lo
iface lo inet loopback

auto eno1
allow-hotplug eno1
iface eno1 inet manual
dns-nameservers 127.0.0.1 8.8.8.8 8.8.4.4 207.67.222.222 208.67.220.220
auto eno2
allow-hotplug eno2
iface eno2 inet manual
dns-nameservers 127.0.0.1 8.8.8.8 8.8.4.4 207.67.222.222 208.67.220.220

auto xenbr0
allow-hotplug xenbr0
# Bridge setup
# fetching dhcp ip from 192.168.1.20 (vivacom fiber optics router) routing traffic via 1Gigabit network
iface xenbr0 inet dhcp
hwaddress ether 70:e2:84:13:44:11
# address 192.168.1.5/22
address 192.168.1.5
netmask 255.255.252.0
# address 192.168.1.8 if dhcp takes from vivacom dhcpd
bridge_ports eno1
gateway 192.168.1.20
bridge_stp on
bridge_waitport 0
bridge_fd 0
bridge_ports none
dns-nameservers 8.8.8.8 8.8.4.4

auto xenbr1
# fetching dhcp ip from pc-freak.net (192.168.0.1) bergon.net routing traffic through it
allow-hotplug xenbr1
iface xenbr1 inet dhcp
hwaddress ether 70:e2:84:13:44:11
## address 192.168.0.3/22
address 192.168.0.8
netmask 255.255.252.0
# address 192.168.0.8 if dhcp takes from vivacom dhcpd (currently mac deleted from vivacom router)
# address 192.168.0.9 if dhcp takes from pc-freak.net hware host
# hwaddress ether 70:e2:84:13:44:13
gateway 192.168.0.1
bridge_ports eno2
bridge_stp on
bridge_waitport 0
bridge_fd 0
bridge_ports none
dns-nameservers 8.8.8.8 8.8.4.4
root@freak:/etc/network#

root@freak:/etc/network# brctl showstp xenbr0
xenbr0
bridge id       8000.70e284134411
designated root   8000.70e284134411
root port       0           path cost       0
max age       20.00           bridge max age       20.00
hello time       2.00           bridge hello time   2.00
forward delay       15.00           bridge forward delay   15.00
ageing time       0.00
hello timer       1.31           tcn timer       0.00
topology change timer   0.00           gc timer       0.00
flags

eno1 (1)
port id       8001           state       forwarding
designated root   8000.70e284134411   path cost       19
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8001           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif1.0 (2)
port id       8002           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8002           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif10.0 (12)
port id       800c           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   800c           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif16.0 (13)
port id       800d           state       disabled
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   800d           forward delay timer   0.00
designated cost   0           hold timer       0.00
flags

vif16.0-emu (14)
port id       800e           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   800e           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif2.0 (4)
port id       8004           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8004           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif3.0 (5)
port id       8005           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8005           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif4.0 (3)
port id       8003           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8003           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif5.0 (6)
port id       8006           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8006           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif6.0 (7)
port id       8007           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   8007           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

vif9.0 (10)
port id       800a           state       disabled
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   800a           forward delay timer   0.00
designated cost   0           hold timer       0.00
flags

vif9.0-emu (11)
port id       800b           state       forwarding
designated root   8000.70e284134411   path cost       100
designated bridge   8000.70e284134411   message age timer   0.00
designated port   800b           forward delay timer   0.00
designated cost   0           hold timer       0.31
flags

root@freak:/etc/network#

Sum it up

We have learned how to debug various routing issues, how to add and remote default gateways, check network reachability with ICMP protocol with ping, traceroute as well check for DNS issues and given some hints how to resolve DNS misconfigurations.
We also learned how to check the configured Network interfaces certain settings and resolve issues caused by Network sides max Speed misconfigurations as well how to track and resolve communication issues caused by wrongly configured MAC addresses.
Further more learned on how to do a basic port and protocol debugging of state of Network packets with netstat and nc and check problems related to iptables Firewall and IP Forwarding misconfigurations.
Finally we learned some basic usage of tcpdump on how to track arp and MAC traffic and look up for a specific TCP / UDP protocol and its contained data.
There is certainly things this article is missing as the topic of debugging network connectivity issues on Linux is a whole ocean, especially as the complexity of Linux has grown dramatically these days.
I gues it is worthy to mention that unable to see remote network could be caused by wrong VLAN configurations on Linux or even buggy switches and router devices, due to hardware or software,
but I hope this article at least covers the very basics of network debugging and Linux.

Enjojy 🙂

Tags: article, broadcast, data, debugging, default, Display, fails, guide, histogram, ifconfig eth0, initial, internal, issues, link, linux?, loopback, mtr, MULTICAST, multiple times, network, network speed, Old, operating systems, ping, pipe, Present, running, RX, Settings, system administrators, tcp, time, Tx
Posted in Debian, Educational, Linux, Networking, System Administration | No Comments »

Megaraid SAS software installation on CentOS Linux

Saturday, October 20th, 2012

With a standard el5 on a new Dell server, it may be necessary to install the Dell Raid driver, otherwise the OMSA always reports an error and hardware monitoring is therefore obsolete:

Previously, the megaraid_sys package was now called mptlinux

For this we need the following packages in advance:

# yum install gcc kernel-devel
Now the driver stuff:

# yum install dkms mptlinux
That should have built the new module, better test it:

# modinfo mptsas

# dkms status
After a kernel update it may be necessary to build the driver for the new version:

# dkms build -m mptlinux -v 4.00.38.02

# dkms install -m mptlinux -v 4.00.38.02

Tags: based, better, called, Dell Raid, Display, Enable X11, gcc, Getting X11, installation, list, need, packages, somehost, ssh, standard, tell, update, working, xauth, yum
Posted in Linux, Linux and FreeBSD Desktop | No Comments »

LVM extend partition Linux howto and how to check if Logical Volume Manager partition is extendable

Thursday, February 13th, 2014

how-to-resize-extend-lvm-partitioned-hard-disks-logical_volume_manager_lvm_logo

Many Linux servers these days are using LVM (Logical Volume Manager) in order to allow disk drives and partitions to be easily managed (shrinked / resized). It is interesting fact LVM is successor of HP-UX's volume manager. LVM can be considered as a thin software layer on top of the hard disks and partitions, which creates an abstraction of continuity and ease-of-use for managing hard drive replacement, re-partitioning, and backup.

LVM is commonly used for the following purposes:

Managing large hard disk farms by allowing disks to be added and replaced without downtimes and services disruption (useful whenever hot-swapping is needed)
On small systems (like a desktop at home), instead of having to estimate at installation time how big a partition might need to be in the future.
– LVM lets file systems to be easily resized later as needed.
Performing consistent backups by taking snapshots of the logical volumes.
Creating single logical volumens of multiple physical volumes or entire hard disks (somewhat similar to RAID-0), ability to do dynamic volume resizing (in LVM partitions are volumes).

So if you're sysadmin it is quite likely that some LVM volume starts being filled up (because of bad initial planning), so the customer asks you to resize a LVM (volume), here is how to do it:

1. Check whether LVM configured on server has free disk space that can be relocated
First lets list all LVM configured volumes on server:

# vgscan Reading all physical volumes. This may take a while... Found volume group "web_log" using metadata type lvm2 Found volume group "web_all" using metadata type lvm2 Found volume group "rootvg" using metadata type lvm2

vgscan – scan all disks for volume groups and rebuild caches
Then lets display the volume group information.

This is done with vgdisplay cmd
# vgdisplay --- Volume group --- VG Name rootvg System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 13 VG Access read/write VG Status resizable MAX LV 0 Cur LV 11 Open LV 11 Max PV 0 Cur PV 1 Act PV 1 VG Size 136.56 GB PE Size 8.00 MB Total PE 17480 Alloc PE / Size 7329 / 57.26 GB Free PE / Size 10151 / 79.30 GB VG UUID 27z2w0-Ku0H-y6M0-QFCR-3Rp6-c1HX-OTinzn

[root@lupus ~]# vgs
VG #PV #LV #SN Attr VSize VFree
VolGroup00 1 3 0 wz–n- 695.44G 0
[root@lupus ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda3 VolGroup00 lvm2 a– 695.44G 0

Important line from above command output is (Free PE / Size 10151 / 79.30 GB). Indicating that server's LVM had 79.30 GB Free which can be used to extend any of the server LVM existing volumes.

Here are one of servers managed by me existing volumes:

# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/rootvg-root 5.0G 301M 4.4G 7% / udev 18G 144K 18G 1% /dev tmpfs 42G 0 42G 0% /dev/shm /dev/cciss/c0d0p1 122M 28M 88M 24% /boot /dev/mapper/rootvg-home 512M 268M 219M 56% /home /dev/mapper/rootvg-opt 2.5G 484M 1.9G 21% /opt /dev/mapper/rootvg-Tivoli 3.0G 895M 2.0G 32% /opt/Tivoli /dev/mapper/rootvg-uc4 3.0G 289M 2.6G 11% /opt/uc4 /dev/mapper/rootvg-sysadm 3.0G 69M 2.8G 3% /sysadm /dev/mapper/rootvg-tmp 1.3G 35M 1.2G 3% /tmp /dev/mapper/rootvg-usr 4.0G 1.2G 2.6G 32% /usr /dev/mapper/rootvg-var 5.0G 500M 4.2G 11% /var /dev/mapper/rootvg-webservices 9.9G 4.0G 5.9G 41% /webservices

For instance lets say the task is to extend LVM (volume) partition:

/dev/mapper/rootvg-webservices 9.9G 4.0G 5.9G 41% /webservices

Lets say we want to extend /dev/mapper/rootvg/rootvg-webserices with 20 Gygabytes:

# lvextend -L20G /dev/mapper/rootvg-webservices

Then we we would like to add some extra 10GB:

# lvextend -L10G /dev/mapper/rootvg-webservices

In order to add all available LVM free space to a volume use:

# lvextend -l +100%FREE /dev/mapper/rootvg-webservices

Whether you had to do it on Linux with kernel 2.4.x and ext2 / ext3 FS:

# umount /dev/mapper/rootvg-webservices # resize2fs /dev/mapper/rootvg-webservices # mount /dev/mapper/rootvg /webservices

To resize ext4 filesystem with LVM above umount / resize2fs and mount commands can be safely skipped.

On other file systems to raise the size of the filesystem there are different tools to use also on some umount and mount is not necessary example for dynamicly resizable filesystem is reiserfs (though I don't recommend this FS to anyone as the creator of ReiserFS killed his family – moreover my personal experience with ReiserFS in past was quite bitter – I lost personal data because of ReiserFS break ups).

Here is how to dynamicly resize FS after lvextend on Reiserfs filesystem:

# resize_reiserfs -f /dev/myvg/homevol

XFS also supports resize of filesystem with no need to re-mount on server with XFS LVM resize after lvextend run:

# xfs_growfs /webservices

Tags: check, disk space, Display, filesystem, Filesystem Size Used Avail Use Mounted, FS, hard disks, howto, information, kernel 2, linux?, Logical Volume Manager, LVM, mapper, metadata, Metadata Areas, mount dev, partition, partitions, resize, server, servers, top, type
Posted in Linux, System Administration | No Comments »

Display Content of SSL certificate .pem file with openssl command

Thursday, October 11th, 2018

display-content-of-pem-der-and-scr-file-how-to-view-pem-file-linux

If you have generated a .pem formatted SSL certificate or you have multiple .pem SSL certificates and you're not sure which .pem file is generated for which domain / subdomain it is useful to Display content of SSL Certificate .PEM file with openssl command.

Viewing certificate's content is also very useful if you have hosted multiple websites hosted on a server and you want to check which of the SSLs assigned in the Virtualhosts has Expired (for example if you have domains that expire in short term period (365 days).

1. How to Display Content of SSL certificate .pem file?

root@pcfreak:~# openssl x509 -in cert.pem -text
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            04:d1:ad:55:91:f3:f9:ef:3e:53:ea:2c:3a:f4:5f:e6:ce:c1
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C = US, O = Let's Encrypt, CN = Let's Encrypt Authority X3
        Validity
            Not Before: Oct 10 17:49:34 2018 GMT
            Not After : Jan 8 17:49:34 2019 GMT
        Subject: CN = mail.www.pc-freak.net
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:bb:b0:c9:1c:83:82:61:47:f9:c2:73:60:c0:48:
                    e6:0c:f2:a1:ff:db:ae:f1:84:17:14:5d:fc:a3:b2:
                    e4:00:3a:d1:85:42:90:da:41:a9:e9:a8:af:20:3d:
                    12:ef:8e:ca:61:a1:71:f2:cc:43:bf:40:0d:fa:08:
                    7d:d9:61:2b:ea:5d:30:e0:52:43:db:18:30:92:0c:
                    2c:ce:87:93:84:ea:91:61:b7:70:db:11:7c:b6:a4:
                    33:de:d8:3f:d6:61:47:42:f2:36:12:7f:3d:e3:f7:
                    5b:11:3e:1c:f0:af:96:cd:61:8a:1a:a0:f0:b5:23:
                    65:73:b6:b4:9c:19:a7:09:dd:43:96:37:ac:48:fc:
                    21:07:02:52:67:26:2c:81:24:f4:d7:10:e6:f4:12:
                    69:53:ef:91:2a:15:6a:21:06:22:ea:fe:31:38:82:
                    b4:5a:b5:9b:67:90:16:b8:31:e8:27:38:f2:41:b9:
                    19:02:8f:c7:6e:e1:2c:84:75:19:6d:bb:30:3b:d2:
                    02:f0:65:f1:76:82:15:9c:ce:31:3a:d4:7c:83:ca:
                    d1:f9:e1:b7:76:f6:78:93:47:d2:00:f9:63:aa:94:
                    41:d4:78:d0:ee:bc:e6:e9:14:14:e4:ae:54:31:88:
                    f8:58:8d:7b:3e:9f:87:5c:f2:04:e5:07:e0:4c:9a:
                    81:eb
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Key Usage: critical
                Digital Signature, Key Encipherment
            X509v3 Extended Key Usage:
                TLS Web Server Authentication, TLS Web Client Authentication
            X509v3 Basic Constraints: critical
                CA:FALSE
            X509v3 Subject Key Identifier:
                DB:AB:81:E3:14:5F:6D:BE:B4:78:7B:5E:7D:FB:66:BF:56:37:C5:1D
            X509v3 Authority Key Identifier:
                keyid:A8:4A:6A:63:04:7D:DD:BA:E6:D1:39:B7:A6:45:65:EF:F3:A8:EC:A1

            Authority Information Access:
                OCSP – URI:http://ocsp.int-x3.letsencrypt.org
                CA Issuers – URI:http://cert.int-x3.letsencrypt.org/

            X509v3 Subject Alternative Name:
                DNS:mail.www.pc-freak.net
            X509v3 Certificate Policies:
                Policy: 2.23.140.1.2.1
                Policy: 1.3.6.1.4.1.44947.1.1.1
                  CPS: http://cps.letsencrypt.org
                  User Notice:
                    Explicit Text: This Certificate may only be relied upon by Relying Parties and only in accordance with the Certificate Policy found at https://letsencrypt.org/repository/

            CT Precertificate SCTs:
                Signed Certificate Timestamp:
                    Version   : v1 (0x0)
                    Log ID    : E2:69:4B:AE:26:E8:E9:40:09:E8:86:1B:B6:3B:83:D4:
                                3E:E7:FE:74:88:FB:A4:8F:28:93:01:9D:DD:F1:DB:FE
                    Timestamp : Oct 10 18:49:34.453 2018 GMT
                    Extensions: none
                    Signature : ecdsa-with-SHA256
                                30:46:02:21:00:D6:DE:47:AD:D2:32:BE:BE:DD:B3:EB:
                                EE:84:9E:02:8A:4F:33:E2:63:21:D5:F7:4D:47:82:92:
                                AB:B9:0A:49:62:02:21:00:E8:7D:17:81:32:E3:4F:CF:
                                2D:79:8C:97:46:E1:EF:5E:99:F4:8A:8B:B5:6D:23:5F:
                                05:84:E2:14:6A:56:8E:A0
                Signed Certificate Timestamp:
                    Version   : v1 (0x0)
                    Log ID    : 29:3C:51:96:54:C8:39:65:BA:AA:50:FC:58:07:D4:B7:
                                6F:BF:58:7A:29:72:DC:A4:C3:0C:F4:E5:45:47:F4:78
                    Timestamp : Oct 10 18:49:34.451 2018 GMT
                    Extensions: none
                    Signature : ecdsa-with-SHA256
                                30:44:02:20:6C:8E:E7:E2:70:AD:33:A6:5C:E0:89:84:
                                FB:0B:F6:E1:5C:05:06:0A:A8:DB:8B:1C:7A:D0:52:99:
                                5F:3F:A2:64:02:20:4B:CD:0B:E7:A0:27:04:31:19:18:
                                58:99:51:73:49:6B:77:25:A7:E7:5B:10:8C:BD:ED:54:
                                03:DD:40:E4:2D:31
    Signature Algorithm: sha256WithRSAEncryption
         9c:86:b3:34:64:af:ac:9d:c4:d3:a7:cc:fc:8a:32:18:75:95:
         95:47:9b:9c:3c:0e:3b:61:f9:88:61:38:1a:a6:92:69:3d:14:
         6a:53:13:14:65:e6:ca:fa:b9:8e:48:c9:d4:73:f6:e4:74:8a:
         1f:2b:f2:14:86:f1:18:55:26:1b:a0:97:89:15:0b:62:c6:2b:
         27:81:6f:60:af:55:68:b3:2c:5b:10:56:a2:7d:28:cb:8e:fc:
         f0:21:65:78:9b:3a:52:d3:9d:27:ff:d7:24:95:de:0f:d8:3d:
         a2:43:6e:fc:a5:2d:f2:ad:37:e9:ea:db:b5:75:b8:7c:ad:23:
         45:1d:bd:fe:4e:36:c7:f4:e2:3d:47:c9:06:fc:cb:75:ba:d4:
         0a:90:17:ea:e1:7f:49:e6:68:27:97:8a:70:c7:50:e9:19:4a:
         8a:21:18:26:79:a3:61:ff:1b:26:9e:fe:85:8f:20:ed:c6:4d:
         c1:0e:04:21:a8:05:d4:29:69:99:53:63:81:c7:d5:58:71:df:
         02:b5:94:c9:36:48:c9:35:80:ab:71:78:d9:12:f6:f5:10:25:
         3d:38:c5:40:75:25:b1:95:18:d8:1c:96:f1:c6:1a:d2:c4:99:
         f5:01:2e:f4:e1:4a:1f:10:42:0e:34:ed:92:8e:53:9f:c2:7b:
         11:51:78:6a
—–BEGIN CERTIFICATE—–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—–END CERTIFICATE—–

Same way a .der files content / encryption algorithm and domain name could be grasped.

root@pcfreak:~# openssl x509 -in cert.der -inform der -text
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            ad:c2:96:6f:4b:db:31:5c
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: CN = example.com
        Validity
            Not Before: Jun 22 04:00:37 2015 GMT
            Not After : Jul 22 04:00:37 2015 GMT
        Subject: CN = example.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (512 bit)
                Modulus:
                    00:ac:75:73:b4:51:ed:1f:dd:ae:70:52:43:fc:df:
                    c7:5b:d0:2c:75:1b:14:b8:75:01:04:10:e5:1f:03:
                    65:45:dd:df:a7:9f:34:ae:fd:be:e9:05:84:df:47:
                    16:81:d9:89:4b:ce:8e:6d:1c:fa:95:44:e8:af:84:
                    74:4f:ed:c2:e5
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                26:CF:C8:ED:4B:D7:94:B2:E4:25:03:58:24:8F:04:C0:74:D5:97:8A
            X509v3 Authority Key Identifier:
                keyid:26:CF:C8:ED:4B:D7:94:B2:E4:25:03:58:24:8F:04:C0:74:D5:97:8A

            X509v3 Basic Constraints:
                CA:TRUE
    Signature Algorithm: sha256WithRSAEncryption
         0c:8b:ff:12:80:9e:4c:90:bc:26:b0:96:20:ab:76:0c:64:71:
         d2:15:48:a5:33:f6:47:e4:03:df:76:5e:0f:cd:e1:1b:5e:d1:
         4d:c2:1f:8d:b8:63:2f:c9:7d:6e:5c:3b:cb:cd:a3:d0:d8:27:
         74:66:a3:76:06:a5:fb:81:3a:b6
—–BEGIN CERTIFICATE—–
MIIBdTCCAR+gAwIBAgIJAK3Clm9L2zFcMA0GCSqGSIb3DQEBCwUAMBYxFDASBgNV
BAMMC2V4YW1wbGUuY29tMB4XDTE1MDYyMjA0MDAzN1oXDTE1MDcyMjA0MDAzN1ow
FjEUMBIGA1UEAwwLZXhhbXBsZS5jb20wXDANBgkqhkiG9w0BAQEFAANLADBIAkEA
rHVztFHtH92ucFJD/N/HW9AsdRsUuHUBBBDlHwNlRd3fp580rv2+6QWE30cWgdmJ
S86ObRz6lUTor4R0T+3C5QIDAQABo1AwTjAdBgNVHQ4EFgQUJs/I7UvXlLLkJQNY
JI8EwHTVl4owHwYDVR0jBBgwFoAUJs/I7UvXlLLkJQNYJI8EwHTVl4owDAYDVR0T
BAUwAwEB/zANBgkqhkiG9w0BAQsFAANBAAyL/xKAnkyQvCawliCrdgxkcdIVSKUz
9kfkA992Xg/N4Rte0U3CH424Yy/JfW5cO8vNo9DYJ3Rmo3YGpfuBOrY=
—–END CERTIFICATE—–

2. How to display content and info about .CSR (Certificate Signing request)

root@pcfreak:~# openssl req -in cert.csr -noout -text

Certificate Request:
    Data:
        Version: 1 (0x0)
        Subject: C = BG, ST = BG, L = Dobrich, O = Pc Freak, CN = mail.www.pc-freak.net, emailAddress = hipo@www.pc-freak.net
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:b1:83:a7:07:62:19:d4:60:95:58:49:de:b3:48:
                    a8:39:31:fa:5a:bd:2b:d6:73:94:50:36:72:74:18:
                    58:b6:27:d3:0b:26:75:15:a8:ba:1b:77:a7:c9:54:
                    96:1f:c7:8d:da:bd:c9:17:91:53:85:9e:0a:f4:71:
                    3c:fb:d6:e4:75:41:c1:95:32:e1:22:fc:7b:1f:36:
                    23:12:00:ca:37:27:d5:f9:9b:29:48:4a:51:95:d1:
                    40:d0:ea:94:51:98:98:6b:d3:d9:79:1d:a1:65:bb:
                    a9:d1:ab:c9:46:6e:03:ee:24:45:e5:f2:73:e5:f4:
                    82:4a:08:57:b1:06:52:c3:cc:42:9a:02:5b:7a:7c:
                    bd:34:d5:5f:d7:ba:ef:27:d5:3d:97:16:69:06:c7:
                    c1:06:5e:d9:07:16:3f:a3:61:50:9d:dd:ea:95:32:
                    f1:ee:93:82:48:df:20:8b:ae:d2:95:89:05:e4:3d:
                    0c:d7:e1:cf:07:ae:55:84:11:06:92:be:34:b4:a2:
                    a1:ce:07:06:bf:21:bc:80:e2:03:d2:85:b4:64:02:
                    8d:cd:d2:86:1c:49:41:52:43:a8:12:f8:ef:2c:f4:
                    be:a0:dc:ac:ea:27:3a:f9:ab:ab:27:da:28:63:1d:
                    10:5a:4f:b8:51:42:40:ae:be:c0:2d:e9:a3:5a:5a:
                    23:7f
                Exponent: 65537 (0x10001)
        Attributes:
            a0:00
    Signature Algorithm: sha256WithRSAEncryption
         47:f0:54:cd:5e:46:6f:2c:cc:48:7e:85:f0:a8:96:10:ca:a3:
         15:98:77:d3:02:95:8c:67:84:e3:55:d2:0c:e8:d5:a7:ba:82:
         95:fb:ce:73:4c:bc:8f:da:85:97:0c:a8:59:32:b3:a4:af:0a:
         80:4c:78:7f:62:cd:1b:00:01:e8:51:27:9c:eb:75:29:80:e9:
         99:24:fc:86:e2:09:28:be:47:5a:1d:bf:b1:b4:c4:29:4e:6e:
         f3:70:b4:58:f8:d9:a6:63:03:8b:a1:ef:ee:6d:1a:35:33:1e:
         b2:32:25:c1:33:37:3d:46:82:37:9b:0d:4c:40:20:ae:ff:e0:
         cc:51:a2:6b:dd:74:26:d6:93:26:89:c7:76:29:13:cf:6e:5a:
         0f:7c:1b:f5:80:be:3b:6a:a3:c0:10:cd:07:1e:a2:31:8b:49:
         94:d7:63:cf:93:8d:80:03:75:4a:76:b4:cd:14:fe:96:62:61:
         6b:96:8f:c0:a5:ef:67:c7:5e:c0:a5:4b:4f:95:57:b6:43:03:
         8b:6d:10:5f:ab:f2:95:54:ba:85:8e:8b:c1:99:ea:fd:3f:5e:
         23:01:d4:27:f3:e9:20:37:c4:05:47:30:67:94:53:f0:87:27:
         48:73:57:55:f2:70:04:b1:e9:29:eb:2e:2c:9a:cc:55:f4:cc:
         a4:71:c2:5a

That's all folks 🙂

Tags: AA, csr, DB, DER, Display, Display Content, encryption algorithm, f2, f7, get cert info, How to, mail, none, Oct, openssl, pcfreak, pem, SSL
Posted in System Administration, Web and CMS | 1 Comment »

Find all running hosts, used IPs and ports on your local wireless / ethernet network or how to do a basic network security audit with nmap

Monday, September 4th, 2017

Find all running hosts / used IPs on your local wireless or ethernet network

If you're using a Free Software OS such as GNU / Linux or some other proprietary OS such as Mac OS X or Windows and you need a quick way to check all running IPs hosts / nodes locally on your current connected Ethernet or Wireless network, here is how to do it with nmap (Network exploration and security tool port scanner).

So why would you do scan that?

Well just for fun, out of curiousity or just because you want to inspect your local network whether someone unexpected cracker did not break and is not using your Wi-Fi or Ethernet local network and badly snoring your network listening for passwords.

Before you start you should have installed NMAP network scanner on your GNU / Linux, to do so on

Redhat Based Linux (Fedora / CentOS / Redhat Enterprise RHEL):

yum -y install nmap
…

On Deb based GNU / Linux-es such as Ubuntu / Mint / Debian etc.

apt-get install –yes nmap
…

To install nmap on FreeBSD / NetBSD / OpenBSD OS issue from console or terminal:

cd /usr/ports/security/nmap
make install clean
…

or if you prefer to install it from latest binary instead of compiling

pkg_add -vr nmap
…

On a proprietary Mac OS X (I don't recommend you to use this obnoxious OS which is designed as a proprpietary software to steal your freedom and control you, but anyways for Mac OS victims), you can do it to with Macs equivalent tool of apt-get / yum called homebrew:

Open Mac OS X terminal and to install homebrew run:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
brew install nmap
brew search nmap
brew info nmap

If you want to do it system wide become root (super user) from Mac terminal with

su root

and run above commands as administrator user.

Windows users might take a look at Nmap for Windows or use the M$ Windows native portqry command line port scanner

Test whether nmap is properly installed and ready to use with command:

nmap –help
Nmap 6.00 ( http://nmap.org )
Usage: nmap [Scan Type(s)] [Options] {target specification}
TARGET SPECIFICATION:
Can pass hostnames, IP addresses, networks, etc.
Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254
-iL <inputfilename>: Input from list of hosts/networks
-iR <num hosts>: Choose random targets
–exclude <host1[,host2][,host3],…>: Exclude hosts/networks
–excludefile <exclude_file>: Exclude list from file
HOST DISCOVERY:
-sL: List Scan – simply list targets to scan
-sn: Ping Scan – disable port scan
-Pn: Treat all hosts as online — skip host discovery
-PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports
-PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
-PO[protocol list]: IP Protocol Ping
-n/-R: Never do DNS resolution/Always resolve [default: sometimes]
–dns-servers <serv1[,serv2],…>: Specify custom DNS servers
–system-dns: Use OS's DNS resolver
–traceroute: Trace hop path to each host
SCAN TECHNIQUES:
-sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
-sU: UDP Scan
-sN/sF/sX: TCP Null, FIN, and Xmas scans
–scanflags <flags>: Customize TCP scan flags
-sI <zombie host[:probeport]>: Idle scan
-sY/sZ: SCTP INIT/COOKIE-ECHO scans
-sO: IP protocol scan
-b <FTP relay host>: FTP bounce scan
PORT SPECIFICATION AND SCAN ORDER:
-p <port ranges>: Only scan specified ports
Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
-F: Fast mode – Scan fewer ports than the default scan
-r: Scan ports consecutively – don't randomize
–top-ports <number>: Scan <number> most common ports
–port-ratio <ratio>: Scan ports more common than <ratio>
SERVICE/VERSION DETECTION:
-sV: Probe open ports to determine service/version info
–version-intensity <level>: Set from 0 (light) to 9 (try all probes)
–version-light: Limit to most likely probes (intensity 2)
–version-all: Try every single probe (intensity 9)
–version-trace: Show detailed version scan activity (for debugging)
SCRIPT SCAN:
-sC: equivalent to –script=default
–script=<Lua scripts>: <Lua scripts> is a comma separated list of
directories, script-files or script-categories
–script-args=<n1=v1,[n2=v2,…]>: provide arguments to scripts
–script-args-file=filename: provide NSE script args in a file
–script-trace: Show all data sent and received
–script-updatedb: Update the script database.
–script-help=<Lua scripts>: Show help about scripts.
<Lua scripts> is a comma separted list of script-files or
script-categories.
OS DETECTION:
-O: Enable OS detection
–osscan-limit: Limit OS detection to promising targets
–osscan-guess: Guess OS more aggressively
TIMING AND PERFORMANCE:
Options which take <time> are in seconds, or append 'ms' (milliseconds),
's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).
-T<0-5>: Set timing template (higher is faster)
–min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
–min-parallelism/max-parallelism <numprobes>: Probe parallelization
–min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
probe round trip time.
–max-retries <tries>: Caps number of port scan probe retransmissions.
–host-timeout <time>: Give up on target after this long
–scan-delay/–max-scan-delay <time>: Adjust delay between probes
–min-rate <number>: Send packets no slower than <number> per second
–max-rate <number>: Send packets no faster than <number> per second
FIREWALL/IDS EVASION AND SPOOFING:
-f; –mtu <val>: fragment packets (optionally w/given MTU)
-D <decoy1,decoy2[,ME],…>: Cloak a scan with decoys
-S <IP_Address>: Spoof source address
-e <iface>: Use specified interface
-g/–source-port <portnum>: Use given port number
–data-length <num>: Append random data to sent packets
–ip-options <options>: Send packets with specified ip options
–ttl <val>: Set IP time-to-live field
–spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
–badsum: Send packets with a bogus TCP/UDP/SCTP checksum
OUTPUT:
-oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
and Grepable format, respectively, to the given filename.
-oA <basename>: Output in the three major formats at once
-v: Increase verbosity level (use -vv or more for greater effect)
-d: Increase debugging level (use -dd or more for greater effect)
–reason: Display the reason a port is in a particular state
–open: Only show open (or possibly open) ports
–packet-trace: Show all packets sent and received
–iflist: Print host interfaces and routes (for debugging)
–log-errors: Log errors/warnings to the normal-format output file
–append-output: Append to rather than clobber specified output files
–resume <filename>: Resume an aborted scan
–stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
–webxml: Reference stylesheet from Nmap.Org for more portable XML
–no-stylesheet: Prevent associating of XSL stylesheet w/XML output
MISC:
-6: Enable IPv6 scanning
-A: Enable OS detection, version detection, script scanning, and traceroute
–datadir <dirname>: Specify custom Nmap data file location
–send-eth/–send-ip: Send using raw ethernet frames or IP packets
–privileged: Assume that the user is fully privileged
–unprivileged: Assume the user lacks raw socket privileges
-V: Print version number
-h: Print this help summary page.
EXAMPLES:
nmap -v -A scanme.nmap.org
nmap -v -sn 192.168.0.0/16 10.0.0.0/8
nmap -v -iR 10000 -Pn -p 80
SEE THE MAN PAGE (http://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES

Most local router local networks are running under an IP range of 192.168.0.1/24 (192.168.0.1.254) or 192.168.1.1/24 or at some weird occasions depending on how the router is configured it might be something like 192.168.10.0/24 to be sure on what kind of network your computer is configured, you can check with ifconfig command, what kind of network IP has the router assigned to your computer, here is output from my Debian GNU / Linux /sbin/ifconfig

hipo@noah:~$ /sbin/ifconfig
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:336 errors:0 dropped:0 overruns:0 frame:0
TX packets:336 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:26656 (26.0 KiB) TX bytes:26656 (26.0 KiB)

wlan0 Link encap:Ethernet HWaddr 00:1c:bf:bd:27:59
inet addr:192.168.0.103 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::21c:bfff:ffbd:2759/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:112836 errors:0 dropped:0 overruns:0 frame:0
TX packets:55363 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:141318655 (134.7 MiB) TX bytes:7391330 (7.0 MiB)

As evident from above output my router assigns IPs via DHCP once authenticated into the Wi-Fi router under standard IP range of 192.168.0.0/24

So under this IP range case, to inspect my small local networkconnected computer I had to run from gnome-terminal or under a /dev/ttyX virtual console:

hipo@noah:~$ nmap -sn 192.168.0.0/24

Starting Nmap 6.00 ( http://nmap.org ) at 2017-09-04 12:45 EEST
Nmap scan report for pcfreak (192.168.0.1)
Host is up (0.011s latency).
Nmap scan report for 192.168.0.103
Host is up (0.00011s latency).
Nmap done: 256 IP addresses (2 hosts up) scanned in 2.53 seconds

-sn argument instructs nmap to do the so called ping scan, e.g. not to do a port s
can after host discovery but just print available hosts that are responding

Some bigger corporate networks are configured to run a couple of local networks simultaneously such as 192.168.168.0.0/24, 192.168.1.0/24, 192.168.2.0/24 etc.

So if that's the case you can add more virtual IPs to your ifconfig after becoming root super user with:

hipo@noah:~$ su root
Password:
root@noah:/home/hipo#

And then run:

/sbin/ifconfig wlan0:0 192.168.1.110 netmask 255.255.255.0
/sbin/ifconfig wlan0:1 192.168.2.110 netmask 255.255.255.0

etc.

Note that here I purposefully choose .110 IP because often the 192.168.1.1 is an IP assigned to the router and that might cause some IP conflicts and trigger alarms in the router security which I want to avoid.

To check just added extra Virtual IPs on wlan0 wireless interface (note that depending on your Wi-Fi card and your driver this interface might come under a different name on your computer):

root@noah# /sbin/ifconfig |grep -i wlan0 -A 1
wlan0 Link encap:Ethernet HWaddr 00:1c:bf:bd:25:59
inet addr:192.168.0.103 Bcast:192.168.0.255 Mask:255.255.255.0
—
wlan0:0 Link encap:Ethernet HWaddr 00:1c:bf:bd:25:59
inet addr:192.168.1.110 Bcast:192.168.1.255 Mask:255.255.255.0
—
wlan0:1 Link encap:Ethernet HWaddr 00:1c:bf:bd:27:59
inet addr:192.168.2.110 Bcast:192.168.2.255 Mask:255.255.255.0

If you're scanning not on your own network but on a public connected network you might prefer to not use the ping scan as this might identify you in router's firewall as possible intruder and could cause you headaches, besides that some network connected nodes are connected to not respond on a ping scan (some networks purposefully disable pings at all) to avoid possibility of the so called ping flood that might overload a router buffer or bring down hosts on the network beinf flooded.

If you have doubts that a network has ping disabled and it shows no result you can give a try to the so called SYN / FIN Stealth packet scan with added requirement to scan for UDP open ports (-sS) argument

root@noah:/~# nmap -sS -sU -sT 192.168.0.1-255

Starting Nmap 6.00 ( http://nmap.org ) at 2017-09-04 13:31 EEST
Nmap scan report for pcfreak (192.168.0.1)
Host is up (0.012s latency).
Not shown: 998 closed ports
PORT STATE SERVICE
80/tcp open http
1900/tcp open upnp
MAC Address: 10:FE:ED:43:CF:0E (Unknown)

Nmap scan report for 192.168.0.100
Host is up (0.0036s latency).
Not shown: 998 closed ports
PORT STATE SERVICE
625/tcp open apple-xsrvr-admin
49153/tcp open unknown
MAC Address: 84:38:35:5F:28:75 (Unknown)

Nmap scan report for 192.168.0.103
Host is up (0.000012s latency).
Not shown: 999 closed ports
PORT STATE SERVICE
22/tcp open ssh

You might also like to add some verbosy (that would generate a lot of output so be careful):

In case if above scan fails due to firewalls and you have a ping scan disabled on the network too you might also try out the so called nmap connect TCP connect scan (-sT), that would avoid the SYN scan. The -sT is useful also if you're not possessing root superprivileges on nmap running host.

nmap -sS -sU 192.168.0.1-255

Note that connect scan could take ages as nmap tries to connect every port from default port scanned ranged on remote found hosts that are reporting as up and running.

If the shown results lead you find some unknown computer / tablet / mobile / phone device connected to your network, then connect to your router and thoroughfully inspect the traffic flowing through it, if you find intruder cut him off and change immediately your router passwords and monitor your network periodically to make sure the unwanted guest did not go back in future.

There is much more you can do with nmap so if you have some extra time and interest into penetration testing I recommend you check out Nmap Book (The Official Nmap project guide to Network Discovery and Security Scanning)

Tags: addr, CB, default port, Display, due, ethernet network, EXAMPLES, howto, ICMP, MISC, Output, pcfreak, port scanner, ports, Print, requirement, tcp, terminal, windows users
Posted in Computer Security, Curious Facts, FreeBSD, Linux, Linux and FreeBSD Desktop | No Comments »

How to show country flag, web browser type and Operating System in WordPress Comments

Wednesday, February 15th, 2012

!!! IMPORTANT UPDATE COMMENT INFO DETECTOR IS NO LONGER SUPPORTED (IS OBSOLETE) AND THE COUNTRY FLAGS AND OPERATING SYSTEM WILL BE NOT SHOWING INSTEAD,

!!!! TO MAKE THE COUNTRY FLAGS AND OS WP FUNCTIONALITY WORK AGAIN YOU WILL NEED TO INSTALL WP-USERAGENT !!!

I've come across a nice WordPress plugin that displays country flag, operating system and web browser used in each of posted comments blog comments.
Its really nice plugin, since it adds some transperancy and colorfulness to each of blog comments 😉
here is a screenshot of my blog with Comments Info Detector "in action":

Comments Info Detector as of time of writting is at stable ver 1.0.5.
The plugin installation and configuration is very easy as with most other WP plugins. To install the plugin;

1. Download and unzip Comments Info Detector

linux:/var/www/blog:# cd wp-content/plugins linux:/var/www/blog/wp-content/plugins:# wget http://downloads.wordpress.org/plugin/comment-info-detector.zip ... linux:/var/www/blog/wp-content/plugins:# unzip comment-info-detector.zip ...

Just for the sake of preservation of history, I've made a mirror of comments-info-detector 1.0.5 wp plugin for download here
2. Activate Comment-Info-Detector

To enable the plugin Navigate to;
Plugins -> Inactive -> Comment Info Detector (Activate)

After having enabled the plugin as a last 3rd step it has to be configured.

3. Configure comment-info-detector wp plugin

By default the plugin is disabled. To change it to enabled (configure it) by navigating to:

Settings -> Comments Info Detector

Next a a page will appear with variout fields and web forms, where stuff can be changed. Here almost all of it should be left as it is the only change should be in the drop down menus near the end of the page:

Display Country Flags Automatically (Change No to Yes) Display Web Browsers and OS Automatically (Change No to Yes

After the two menus are set to "Yes" and pressing on Save Changes the plugin is enabled it will immediately start showing information inside each comment the GeoIP country location flag of the person who commented as well as OS type and Web Browser 🙂

Tags: action, Auto, blog, Browsers, change, Comment, Comments, configured, country flag, country location, Detector, Display, downloads, Draft, drop, drop down menus, flag web, How to, Inactive, information, installation, Linux, location, mirror, operating system, os type, page, person, plugin, plugin installation, quot, sake, Save Changes, screenshot, show, Stable, time, transperancy, type, unzip, web browser type, web browsers, web forms, wget, Wordpress, Wordpress Comments, writting, www, zip linux
Posted in Web and CMS, Wordpress | 1 Comment »

Text Monitoring of connection server (traffic RX / TX) business in ASCII graphs with speedometer / Easy Monitor network traffic performance

Friday, May 4th, 2012

While reading some posts online related to MS-Windows TcpView – network traffic analyzing tool. I've came across very nice tool for tracking connection speed for Linux (Speedometer). If I have to compare it, speedometer is somehow similar to nethogs and iftop bandwidth network measuring utilities .

What differentiates speedometer from iftop / nethogs / iptraf is it is more suitable for visualizing a network file or data transfers.
The graphs speedometer draws are way easier to understand, than iftop graphs.

Even complete newbies can understand it with no need for extraordinary knowledge in networking. This makes Speedometer, a top tool to visually see the amount of traffic flowing through server network interface (eth0) … (eth1) etc.

What speedometer shows is similar to the Midnight Commander's (mc) file transfer status bar, except the statistics are not only for a certain file transfer but can show overall statistics over server passing network traffic amount (though according to its manual it can be used to also track individual file transfers).

The simplicity for basic use makes speedometer nice tool to track for network congestion issues on Linux. Therefore it is a must have outfit for every server admin. Below you see a screenshot of my terminal running speedometer on a remote server.

Speedometer ascii traffic track server network business screenshot in byobu screen like virtual terminal emulator

1. Installing speedometer on Debian / Ubuntu and Debian derivatives

For Debian and Ubuntu server administrators speedometer is already packaged as a deb so its installation is as simple as:

debian:~# apt-get --yes install speedometer ....

2. Installing speedometer from source for other Linux distributions CentOS, Fedora, SuSE etc.

Speedometer is written in python programming language, so in order to install and use on other OS Linux platforms, it is necessery to have installed (preferably) an up2date python programming language interpreter (python ver. 2.6 or higher)..
Besides that it is necessary to have installed the urwid -( console user interface library for Python) available for download via excess.org/urwid/

Hence to install speedometer on RedHat based Linux distributions one has to follow these steps:

a) Download & Install python urwid library

[root@centos ~]# cd /usr/local/src [root@centos src]# wget -q http://excess.org/urwid/urwid-1.0.1.tar.gz [root@centos src]# tar -zxvvf urwid-1.0.1.tar.gz .... [root@centos src]# cd urwid-1.0.1 [root@centos urwid-1.0.1]# python setup.py install running install running build running build_py creating build creating build/lib.linux-i686-2.4 creating build/lib.linux-i686-2.4/urwid copying urwid/tests.py -> build/lib.linux-i686-2.4/urwid copying urwid/command_map.py -> build/lib.linux-i686-2.4/urwid copying urwid/graphics.py -> build/lib.linux-i686-2.4/urwid copying urwid/vterm_test.py -> build/lib.linux-i686-2.4/urwid copying urwid/curses_display.py -> build/lib.linux-i686-2.4/urwid copying urwid/display_common.py -> build/lib.linux-i686-2.4/urwid ....

b) Download and install python-setuptools

python-setuptools is one other requirement of speedometer, happily on CentOS and Fedora the rpm package is already there and installable with yum:

[root@centos ~]# yum -y install python-setuptools ....

c) Download and install Speedometer

[root@centos urwid-1.0.1]# cd /usr/local/src/ [root@centos src]# wget -q http://excess.org/speedometer/speedometer-2.8.tar.gz [root@centos src]# tar -zxvvf speedometer-2.8.tar.gz ..... [root@centos src]# cd speedometer-2.8 [root@centos speedometer-2.8]# python setup.py install Traceback (most recent call last): File "setup.py", line 26, in ? import speedometer File "/usr/local/src/speedometer-2.8/speedometer.py", line 112 n = n * granularity + (granularity if r else 0) ^

While running the CentOS 5.6 installation of speedometer-2.8, I hit the
"n = n * granularity + (granularity if r else 0)"
error.

After consultation with some people in #python (irc.freenode.net), I've figured out this error is caused due the outdated version of python interpreter installed by default on CentOS Linux 5.6. On CentOS 5.6 the python version is:

[root@centos ~]# python -V Python 2.4.3

As I priorly said speedometer 2.8's minimum requirement for a python to be at v. 2.6. Happily there is quick way to update python 2.4 to python 2.6 on CentOS 5.6, as there is an RPM repository maintained by Chris Lea which contains RPM binary of python 2.6.

To update python 2.4 to python 2.6:

[root@centos speedometer-2.8]# rpm -Uvh http://yum.chrislea.com/centos/5/i386/chl-release-5-3.noarch.rpm[root@centos speedometer-2.8]# rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-CHL[root@centos speedometer-2.8]# yum install python26

Now the newly installed python 2.6 is executable under the binary name python26, hence to install speedometer:

[root@centos speedometer-2.8]# python26 setup.py install [root@centos speedometer-2.8]# chown root:root /usr/local/bin/speedometer [root@centos speedometer-2.8]# chmod +x /usr/local/bin/speedometer

[root@centos speedometer-2.8]# python26 speedometer -i 1 -tx eth0

The -i will instruct speedometer to refresh the screen graphs once a second.

3. Using speedometer to keep an eye on send / received traffic network congestion

To observe, the amount of only sent traffic via a network interface eth0 with speedometer use:

debian:~# speedometer -tx eth0

To only keep an eye on received traffic through eth0 use:

debian:~# speedometer -rx eth0

To watch over both TX and RX (Transmitted and Received) network traffic:

debian:~# speedometer -tx eth0 -rx eth0

If you want to watch in separate windows TX and RX traffic while running speedometer you can run in separate xterm windows speedometer -tx eth0 and speedometer -rx eth0, like in below screenshot:

Monitor Received and Transmitted server Network traffic in two separate xterm windows with speedometer ascii graphs

4. Using speedometer to test network maximum possible transfer speed between server (host A) and server (host B)

The speedometer manual suggests few examples one of which is:

How fast is this LAN?

host-a$ cat /dev/zero | nc -l -p 12345
host-b$ nc host-a 12345 > /dev/null
host-b$ speedometer -rx eth0

When I red this example in speedometer's manual, it wasn't completely clear to me what the author really meant, but a bit after when I thought over the example I got his point.

The idea behind this example is that a constant stream of zeros taken from /dev/zero will be streamed over via a pipe (|) to nc which will bind a port number 12345, anyone connecting from another host machine, lets say a server with host host-b to port 12345 on machine host-a will start receiving the /dev/zero streamed content.

Then to finally measure the streamed traffic between host-a and host-b machines a speedometer is started to visualize the received traffic on network interface eth0, thus measuring the amount of traffic flowing from host-a to host-b …

I give a try to the exmpls, using for 2 test nodes my home Desktop PC, Linux running arcane version of Ubuntu and my Debian Linux notebook.

First on the Ubuntu PC I issued

hipo@hip0-desktop:~$ cat /dev/zero | nc -l -p 12345

Note that I have previously had installed the netcat, as nc is not installed by default on Ubuntu and Debian. If you, don't have nc installed yet, install it with:

apt-get –yes install netcat

"cat /dev/zero | nc -l -p 12345" will not produce any output, but will display just a blank line.

Then on my notebook I ran the second command example, given in the speedometer manual:

hipo@noah:~$ nc 192.168.0.2 12345 > /dev/null

Here the 192.168.0.2 is actually the local network IP address of my Desktop PC. My Desktop PC is connected via a normal 100Mbit switch to my routing machine and receives its internet via NAT. The second test machine (my laptop), gets its internet through a WI-FI connection received by a Wireless Router connected via a UTP cable to the same switch to which my Desktop PC is connected.

Finally to test / get my network maximum thoroughput I had to use:

hipo@noah:~$ speedometer -rx wlan0

Here, I monitor my wlan0 interface, as this is my (laptop) wireless card interface over which I have connectivity to my local network and via which through the the WI-FI router I get connected to the internet.

Below is a snapshot captured showing approximately what is the max network thoroughput from:

Desktop PC -> to my Thinkpad R61 laptop

Using Speedometer to test network thorougput between two network server hosts screenshot Debian Squeeze Linux

As you can see in the shot approximately the maximum network thoroughput is in between:
2.55MB/s min and 2.59MB/S max, the speed is quite low for a 100 MBit local network, but this is normal as most laptop wireless adapters hardly transfer traffic in more than 10 to 20 MBits per sec.

If the same nework thoroughput test is conducted between two machines both connected to a same 100 M/bit switch, the traffic should be at least a 8 MB/sec.

There is something, else to take in consideration that probably makes the provided example network thoroughput measuring a bit inaccurate. The fact that the /dev/zero content is stremed over is slowing down the zeroes sent over network because of the pipe ( | ) use slows down the stream.

5. Using speedometer to visualize maximum writting speed to a local hard drive on Linux

In the speedometer manual, I've noticed another interesting application of this nifty tool.

speedometer can be used to track and visualize the maximum writing speed a hard disk drive or hard drive partition can support on Linux OS:

A copy paster from the manual text is as follows:

How fast can I write data to my filesystem? (with at least 1GB free) dd bs=1000000 count=1000 if=/dev/zero of=bigfile & speedometer bigfile

However, when I tried copy/pasting the example in terminal, to test the maximum writing speed to an external USB hard drive, only dd command was started and speedometer failed to initialize and display graphs of the file creation speed.

I've found a little "hack" that makes the man example work by adding a 3 secs sleep like so:

debian:/media/Expansion Drive# dd bs=1000000 count=1000 if=/dev/zero of=bigfile & sleep 3; speedometer bigfile

Here is a screenshot of the bigfile created by dd and tracked "in real time" by speedometer:

How fast is writting data to local USB expandable hard disk Debian Linux speedometer screenshot

Actually the returned results from this external USB drive are, quite high, the possible reason for that is it is connected to my laptop over an USB protocol verion 3.

6. Using Speedometer to keep an eye on file download in progress

This application of speedometer is mostly useless especially on Linux where it is used as a Desktop.

However in some occasions if files are transferred over ssh or in non interactive FTP / Samba file transfers between Linux servers it can come handy.

To visualize the download and writing speed of lets say FTP transferred .AVI movie (during the actual file transfer) on the download host issue:

# speedometer Download-Folder/What-goes-around-comes-around.avi

7. Estimating approximate time for file transfer

There is another section in the speedometer manual pointing of the program use to calculate the time remaining for a file transfer.

The (man speedometer) provided example text is:

How long it will take for my 38MB transfer to finish? speedometer favorite_episode.rm $((38*1024*1024))

At first glimpse it hard to understand (like the other manual example). A bit of reasoning and I comprehend what the man author meant by the obscure calculation:

$((38*1024*1024))

This is a formula used in which 38 has to be substituted with the exact file size amount of the transferred file. The author manual used a 38MB file so this is why he put $((38* … in the formula.

I give it a try – (just for the sake to see how it works) with a file with a size of 2500MB, in below two screenshot pictures I show my preparation to copy the file and the actual copying / "real time" transfer tracking with speedometer's status percentage completion bar.

xterm terminal copy file and estimate file copying operation speed on linux with speedometer preparation

Two xterm terminals one is copying a file the other one uses speedometer to estimate the time remaining to complete the file transfer from expansion USB hard drive to my laptop harddrive

Tags: amount, Ascii, Auto, avi, bandwidth network, CentOS, connection server, data transfers, Desktop, Display, Draft, Easy Monitor, eth, eye, granularity, hipo, host, import, Installing, iptraf, language interpreter, laptop, Linux, linux distributions, machine, midnight commander, monitor network, nbsp, necessery, network congestion, network interface, network traffic, noah, os linux, os platforms, package, python, python interpreter, python programming language, quot, remote server, root, rpm, server admin, server administrators, server network, server traffic, speedometer, test, text monitoring, traffic performance, Ubuntu, user interface library, yum
Posted in Monitoring, System Administration, Various | No Comments »

How to reset a forgotten WORDPRESS blog admin password (via MySQL)

Sunday, July 24th, 2011

Wordpress lost your password prompt screen My sister has forgotten the administrator account for her wordpress blog as she did not blogged for a while.
I decided to help her and reset the WORDPRESS blog password to another one.
The easiest way of course in normal circumstances is to use wordpress's Lost your password password reset via email.

However with this blog it seems I used an email address which I forgot so I couldn't really use this as a mean to reset the blog password.

Therefore as I'm addicted to command line 😉 I decided to do it straight via connecting to mysql server with mysql cli and change the encrypted password value directly there. Here is how I did it:

1. First I logged in to the mysql server with my root user/pass

pcfreak# mysql -u root -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 39263 Server version: 5.0.83-log FreeBSD port: mysql-server-5.0.83

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

2. Then I checked current set user and password for the wp-admin admin user

3. Used a query to reset the current encrypted password you see below shown under the user_pass column

mysql> UPDATE wp_users SET user_pass= MD5('my_new_wordpress_password_to_reset') where ID = '1';

4. I've changed the email set for user_email to which mail is sent, in case of forgotten password again

I've done this to prevent my sister to bother me again, if she forgets her password once again 😉

mysql> UPDATE wp_users SET user_email='invoke_@abv.bg' where ID = '1';

One important note here is that in step 3
I've used the MD5(); mysql embedded function to generate the MD5 crypted password which is inserted in above's sql query, however the MD5 function is only available in MySQL servers version 5.x, therefore in older releases of MySQL e.g. ver 4.x, one will have to first generate the md5 password with let's say md5sum linux command or bsd's md5 cmd like so:

a. On Linux
hipo@noah:~$ echo 'my_new_wordpress_password_to_reset' | md5sum f0ed1489e6d9e7eae8b363b1b5e4a864 -

b. On FreeBSD

pcfreak# echo 'my_new_wordpress_password_to_reset' | md5 f0ed1489e6d9e7eae8b363b1b5e4a864

Afterwards the SQL query that can be used with the above generated string to issue on the MySQL 4.x server or earlier versions would be:

mysql> UPDATE wp_users SET user_pass='f0ed1489e6d9e7eae8b363b1b5e4a864' where ID = '1';

That's all now the password is set to the newly generated my_new_wordpress_password_to_reset pass string.
Cheers 😉

Tags: administrator account, circumstances, cli, com, Commands, connection, connection id, course, Display, eae, email address, encrypted password, function, help, input statement, login, monitor, mysql connection, password, pcfreak, reset, root, root user, row, server version, status, update, url, value, wordpress blog, wp, ztywLp
Posted in FreeBSD, Linux, MySQL, System Administration, Wordpress | 7 Comments »

Make your Debian Linux and FreeBSD terminal / console display daily verse from KJV Bible

Saturday, September 26th, 2009

Since I am a Christian and I want to daily be in touch with the Holy Scriptures and I am most of the time spending on my Linux system. I have came to the conclusion that itâ€™s beneficial to
have a daily bible displaying everytime after login in console or terminal in X.

Therefore I thought it might be helpful to somebody out there who would wish to have short sentece of bible on each Linux / FreeBSD machine login.

Here is how to set bible quote to appear everytime after login in Debian Linux:
First install the verse program through:

# apt-get install verse
Next if you want to make the verse display global for the system put :

if [ -f /usr/bin/verse ]; thenecho/usr/bin/verse fi

in /etc/bash.bashrc
On the other hand if youâ€™d like to make it local for your account or a setnumber of accounts on your system append

if [ -f /usr/bin/verse ]; thenecho/usr/bin/verse fi
to your user ~/.bashrc as well as to the home directories of the users youâ€™d like to display a bible verse (if for several users).

If you decide to do that be aware that your login via sftp wonâ€™t work anymore – forget about sftp transfers ….

Every time you attempt to login youâ€™ll experience the error message:

â€œReceived message too longâ€. However that ainâ€™t a real problem for me since I use my system as a desktop and donâ€™t sftp or ssh remotely to my desktop.
In order to prevent this issue where sftp interactivity gets broken it is better to add verse app to execute via /etc/profile i. e. in /etc/profile on top of file add:

if [ -f /usr/bin/verse ]; then echo /usr/bin/verse fi

On FreeBSD the same is achieved a bit differently. Here is how to install it in FreeBSD:

First install fortune program and then install the fortune bible module; In FreeBSD bible quotes are only available via the good old fortune program:
cd /usr/ports/misc/fortune-mod-bible; make install clean

Next open:the /etc/profile file and insert in the end of it:
echo /usr/games/fortune /usr/local/share/games/fortune/bible

On your next login your FreeBSD should be showing a bible
sentence (quotation) after each and every login.
What is different with Debianâ€™s verse program is that verse keeps displaying one exact quote of the bible during every login for the whole day,
where in FreeBSD the fortune-mod-bible does show a different (random) bible sentence on each and every user login.

Tags: console, Debian, Display, freebsd, Linux, terminal
Posted in Christianity, Entertainment, Linux and FreeBSD Desktop, System Administration | 1 Comment »

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