Posts Tagged ‘connection’

How to calculate connections from IP address with shell script and log to Zabbix graphic

Thursday, March 11th, 2021

We had to test the number of connections incoming IP sorted by its TCP / IP connection state.

For example:

TIME_WAIT, ESTABLISHED, LISTEN etc.


The reason behind is sometimes the IP address '192.168.0.1' does create more than 200 connections, a Cisco firewall gets triggered and the connection for that IP is filtered out. To be able to know in advance that this problem is upcoming. a Small userparameter script is set on the Linux servers, that does print out all connections from IP by its STATES sorted out.

 

The script is calc_total_ip_match_zabbix.sh is below:

#!/bin/bash
#  check ESTIMATED / FIN_WAIT etc. netstat output for IPs and calculate total
# UserParameter=count.connections,(/usr/local/bin/calc_total_ip_match_zabbix.sh)
CHECK_IP='192.168.0.1';
f=0; 

 

for i in $(netstat -nat | grep "$CHECK_IP" | awk '{print $6}' | sort | uniq -c | sort -n); do

echo -n "$i ";
f=$((f+i));
done;
echo
echo "Total: $f"

 

root@pcfreak:/bashscripts# ./calc_total_ip_match_zabbix.sh 
1 TIME_WAIT 2 ESTABLISHED 3 LISTEN 

Total: 6

 

root@pcfreak:/bashscripts# ./calc_total_ip_match_zabbix.sh 
2 ESTABLISHED 3 LISTEN 
Total: 5


images/zabbix-webgui-connection-check1

To make process with Zabbix it is necessery to have an Item created and a Depedent Item.

 

webguiconnection-check1

webguiconnection-check1
 

webgui-connection-check2-item

images/webguiconnection-check1

Finally create a trigger to trigger alarm if you have more than or eqaul to 100 Total overall connections.


images/zabbix-webgui-connection-check-trigger

The Zabbix userparameter script should be as this:

[root@host: ~]# cat /etc/zabbix/zabbix_agentd.d/userparameter_webgui_conn.conf
UserParameter=count.connections,(/usr/local/bin/webgui_conn_track.sh)

 

Some collleagues suggested more efficient shell script solution for suming the overall number of connections, below is less time consuming version of script, that can be used for the calculation.
 

#!/bin/bash -x
# show FIN_WAIT2 / ESTIMATED etc. and calcuate total
count=$(netstat -n | grep "192.168.0.1" | awk ' { print $6 } ' | sort -n | uniq -c | sort -nr)
total=$((${count// /+}))
echo "$count"
echo "Total:" "$total"

      2 ESTABLISHED
      1 TIME_WAIT
Total: 3

 


Below is the graph built with Zabbix showing all the fluctuations from connections from monitored IP. ebgui-check_ip_graph

 

KVM Virtual Machine RHEL 8.3 Linux install on Redhat 8.3 Linux Hypervisor with custom tailored kickstart.cfg

Friday, January 22nd, 2021

kvm_virtualization-logo-redhat-8.3-install-howto-with-kickstart

If you don't have tried it yet Redhat and CentOS and other RPM based Linux operationg systems that use anaconda installer is generating a kickstart file after being installed under /root/{anaconda-ks.cfg,initial-setup- ks.cfg,original-ks.cfg} immediately after the OS installation completes. Using this Kickstart file template you can automate installation of Redhat installation with exactly the same configuration as many times as you like by directly loading your /root/original-ks.cfg file in RHEL installer.

Here is the official description of Kickstart files from Redhat:

"The Red Hat Enterprise Linux installation process automatically writes a Kickstart file that contains the settings for the installed system. This file is always saved as /root/anaconda-ks.cfg. You may use this file to repeat the installation with identical settings, or modify copies to specify settings for other systems."


Kickstart files contain answers to all questions normally asked by the text / graphical installation program, such as what time zone you want the system to use, how the drives should be partitioned, or which packages should be installed. Providing a prepared Kickstart file when the installation begins therefore allows you to perform the installation automatically, without need for any intervention from the user. This is especially useful when deploying Redhat based distro (RHEL / CentOS / Fedora …) on a large number of systems at once and in general pretty useful if you're into the field of so called "DevOps" system administration and you need to provision a certain set of OS to a multitude of physical servers or create or recreate easily virtual machines with a certain set of configuration.
 

1. Create /vmprivate storage directory where Virtual machines will reside

First step on the Hypervisor host which will hold the future created virtual machines is to create location where it will be created:

[root@redhat ~]#  lvcreate –size 140G –name vmprivate vg00
[root@redhat ~]#  mkfs.ext4 -j -b 4096 /dev/mapper/vg00-vmprivate
[root@redhat ~]# mount /dev/mapper/vg00-vmprivate /vmprivate

To view what is the situation with Logical Volumes and  VG group names:

[root@redhat ~]# vgdisplay -v|grep -i vmprivate -A7 -B7
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  – currently set to     8192
  Block device           253:0

 

  — Logical volume —
  LV Path                /dev/vg00/vmprivate
  LV Name                vmprivate
  VG Name                vg00
  LV UUID                VVUgsf-FXq2-TsMJ-QPLw-7lGb-Dq5m-3J9XJJ
  LV Write Access        read/write
  LV Creation host, time lpgblu01f.ffm.de.int.atosorigin.com, 2021-01-20 17:26:11 +0100
  LV Status              available
  # open                 1
  LV Size                150.00 GiB


Note that you'll need to have the size physically available on a SAS / SSD Hard Drive physically connected to Hypervisor Host.

To make the changes Virtual Machines storage location directory permanently mounted add to /etc/fstab

/dev/mapper/vg00-vmprivate  /vmprivate              ext4    defaults,nodev,nosuid 1 2

[root@redhat ~]# echo '/dev/mapper/vg00-vmprivate  /vmprivate              ext4    defaults,nodev,nosuid 1 2' >> /etc/fstab

 

2. Second we need to install the following set of RPM packages on the Hypervisor Hardware host

[root@redhat ~]# yum install qemu-kvm qemu-img libvirt virt-install libvirt-client virt-manager libguestfs-tools virt-install virt-top -y

3. Enable libvirtd on the host

[root@redhat ~]#  lsmod | grep -i kvm
[root@redhat ~]#  systemctl enable libvirtd

4. Configure network bridging br0 interface on Hypervisor


In /etc/sysconfig/network-scripts/ifcfg-eth0 you need to include:

NM_CONTROLED=NO

Next use nmcli redhat configurator to create the bridge (you can use ip command instead) but since the tool is the redhat way to do it lets do it their way ..

[root@redhat ~]# nmcli connection delete eno3
[root@redhat ~]# nmcli connection add type bridge autoconnect yes con-name br0 ifname br0
[root@redhat ~]# nmcli connection modify br0 ipv4.addresses 10.80.51.16/26 ipv4.method manual
[root@redhat ~]# nmcli connection modify br0 ipv4.gateway 10.80.51.1
[root@redhat ~]# nmcli connection modify br0 ipv4.dns 172.20.88.2
[root@redhat ~]# nmcli connection add type bridge-slave autoconnect yes con-name eno3 ifname eno3 master br0
[root@redhat ~]# nmcli connection up br0

5. Prepare a working kickstart.cfg file for VM


Below is a sample kickstart file I've used to build a working fully functional Virtual Machine with Red Hat Enterprise Linux 8.3 (Ootpa) .

#version=RHEL8
#install
# Run the Setup Agent on first boot
firstboot --enable
ignoredisk --only-use=vda
# Use network installation
#url --url=http://hostname.com/rhel/8/BaseOS
##url --url=http://171.23.8.65/rhel/8/os/BaseOS
# Use text mode install
text
#graphical
# System language
#lang en_US.UTF-8
keyboard --vckeymap=us --xlayouts='us'
# Keyboard layouts
##keyboard us
lang en_US.UTF-8
# Root password
rootpw $6$gTiUCif4$YdKxeewgwYCLS4uRc/XOeKSitvDJNHFycxWVHi.RYGkgKctTMCAiY2TErua5Yh7flw2lUijooOClQQhlbstZ81 --iscrypted
# network-stuff
# place ip=your_VM_IP, netmask, gateway, nameserver hostname 
network --bootproto=static --ip=10.80.21.19 --netmask=255.255.255.192 --gateway=10.80.21.1 --nameserver=172.30.85.2 --device=eth0 --noipv6 --hostname=FQDN.VMhost.com --onboot=yes
# if you need just localhost initially configured uncomment and comment above
##network В --device=lo --hostname=localhost.localdomain
# System authorization information
authconfig --enableshadow --passalgo=sha512 --enablefingerprint
# skipx
skipx
# Firewall configuration
firewall --disabled
# System timezone
timezone Europe/Berlin
# Clear the Master Boot Record
##zerombr
# Repositories
## Add RPM repositories from KS file if necessery
#repo --name=appstream --baseurl=http://hostname.com/rhel/8/AppStream
#repo --name=baseos --baseurl=http://hostname.com/rhel/8/BaseOS
#repo --name=inst.stage2 --baseurl=http://hostname.com ff=/dev/vg0/vmprivate
##repo --name=rhsm-baseos В  В --baseurl=http://172.54.8.65/rhel/8/rhsm/x86_64/BaseOS/
##repo --name=rhsm-appstream --baseurl=http://172.54.8.65/rhel/8/rhsm/x86_64/AppStream/
##repo --name=os-baseos В  В  В --baseurl=http://172.54.9.65/rhel/8/os/BaseOS/
##repo --name=os-appstream В  --baseurl=http://172.54.8.65/rhel/8/os/AppStream/
#repo --name=inst.stage2 --baseurl=http://172.54.8.65/rhel/8/BaseOS
# Disk partitioning information set proper disk sizing
##bootloader --location=mbr --boot-drive=vda
bootloader --append=" crashkernel=auto tsc=reliable divider=10 plymouth.enable=0 console=ttyS0 " --location=mbr --boot-drive=vda
# partition plan
zerombr
clearpart --all --drives=vda --initlabel
part /boot --size=1024 --fstype=ext4 --asprimary
part swap --size=1024
part pv.01 --size=30000 --grow --ondisk=vda
##part pv.0 --size=80000 --fstype=lvmpv
#part pv.0 --size=61440 --fstype=lvmpv
volgroup s pv.01
logvol / --vgname=s --size=15360 --name=root --fstype=ext4
logvol /var/cache/ --vgname=s --size=5120 --name=cache --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var/log --vgname=s --size=7680 --name=log --fstype=ext4 --fsoptions="defaults,nodev,noexec,nosuid"
logvol /tmp --vgname=s --size=5120 --name=tmp --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /home --vgname=s --size=5120 --name=home --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /opt --vgname=s --size=2048 --name=opt --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var/log/audit --vgname=s --size=3072 --name=audit --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var/spool --vgname=s --size=2048 --name=spool --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
logvol /var --vgname=s --size=7680 --name=var --fstype=ext4 --fsoptions="defaults,nodev,nosuid"
# SELinux configuration
selinux --disabled
# Installation logging level
logging --level=debug
# reboot automatically
reboot
###
%packages
@standard
python3
pam_ssh_agent_auth
-nmap-ncat
#-plymouth
#-bpftool
-cockpit
#-cryptsetup
-usbutils
#-kmod-kvdo
#-ledmon
#-libstoragemgmt
#-lvm2
#-mdadm
-rsync
#-smartmontools
-sos
-subscription-manager-cockpit
# Tune Linux vm.dirty_background_bytes (IMAGE-439)
# The following tuning causes dirty data to begin to be background flushed at
# 100 Mbytes, so that it writes earlier and more often to avoid a large build
# up and improving overall throughput.
echo "vm.dirty_background_bytes=100000000" >> /etc/sysctl.conf
# Disable kdump
systemctl disable kdump.service
%end

Important note to make here is the MD5 set root password string in (rootpw) line this string can be generated with openssl or mkpasswd commands :

Method 1: use openssl cmd to generate (md5, sha256, sha512) encrypted pass string

[root@redhat ~]# openssl passwd -6 -salt xyz test
$6$xyz$rjarwc/BNZWcH6B31aAXWo1942.i7rCX5AT/oxALL5gCznYVGKh6nycQVZiHDVbnbu0BsQyPfBgqYveKcCgOE0

Note: passing -1 will generate an MD5 password, -5 a SHA256 encryption and -6 SHA512 encrypted string (logically recommended for better security)

Method 2: (md5, sha256, sha512)

[root@redhat ~]# mkpasswd –method=SHA-512 –stdin

The option –method accepts md5, sha-256 and sha-512
Theoretically there is also a kickstart file generator web interface on Redhat's site here however I never used it myself but instead use above kickstart.cfg
 

6. Install the new VM with virt-install cmd


Roll the new preconfigured VM based on above ks template file use some kind of one liner command line  like below:
 

[root@redhat ~]# virt-install -n RHEL8_3-VirtualMachine –description "CentOS 8.3 Virtual Machine" –os-type=Linux –os-variant=rhel8.3 –ram=8192 –vcpus=8 –location=/vmprivate/rhel-server-8.3-x86_64-dvd.iso –disk path=/vmprivate/RHEL8_3-VirtualMachine.img,bus=virtio,size=70 –graphics none –initrd-inject=/root/kickstart.cfg –extra-args "console=ttyS0 ks=file:/kickstart.cfg"

7. Use a tiny shell script to automate VM creation


For some clarity and better automation in case you plan to repeat VM creation you can prepare a tiny bash shell script:
 

#!/bin/sh
KS_FILE='kickstart.cfg';
VM_NAME='RHEL8_3-VirtualMachine';
VM_DESCR='CentOS 8.3 Virtual Machine';
RAM='8192';
CPUS='8';
# size is in Gigabytes
VM_IMG_SIZE='140';
ISO_LOCATION='/vmprivate/rhel-server-8.3-x86_64-dvd.iso';
VM_IMG_FILE_LOC='/vmprivate/RHEL8_3-VirtualMachine.img';

virt-install -n "$VMNAME" –description "$VM_DESCR" –os-type=Linux –os-variant=rhel8.3 –ram=8192 –vcpus=8 –location="$ISO_LOCATION" –disk path=$VM_IMG_FILE,bus=virtio,size=$IMG_VM_SIZE –graphics none –initrd-inject=/root/$KS_FILE –extra-args "console=ttyS0 ks=file:/$KS_FILE"


A copy of virt-install.sh script can be downloaded here

Wait for the installation to finish it should be visualized and if all installation is smooth you should get a login prompt use the password generated with openssl tool and test to login, then disconnect from the machine by pressing CTRL + ] and try to login via TTY with

[root@redhat ~]# virst list –all
 Id   Name        State
—————————
 2    
RHEL8_3-VirtualMachine   running

[root@redhat ~]#  virsh console RHEL8_3-VirtualMachine


redhat8-login-prompt

One last thing I recommend you check the official documentation on Kickstart2 from CentOS official website

In case if you later need to destroy the VM and the respective created Image file you can do it with:
 

[root@redhat ~]#  virsh destroy RHEL8_3-VirtualMachine
[root@redhat ~]#  virsh undefine RHEL8_3-VirtualMachine

Don't forget to celebreate the success and give this nice article a credit by sharing this nice tutorial with a friend or by placing a link to it from your blog 🙂

 

 

Enjoy !

Hack: Using ssh / curl or wget to test TCP port connection state to remote SSH, DNS, SMTP, MySQL or any other listening service in PCI environment servers

Wednesday, December 30th, 2020

using-curl-ssh-wget-to-test-tcp-port-opened-or-closed-for-web-mysql-smtp-or-any-other-linstener-in-pci-linux-logo

If you work on PCI high security environment servers in isolated local networks where each package installed on the Linux / Unix system is of importance it is pretty common that some basic stuff are not there in most cases it is considered a security hole to even have a simple telnet installed on the system. I do have experience with such environments myself and thus it is pretty daunting stuff so in best case you can use something like a simple ssh client if you're lucky and the CentOS / Redhat / Suse Linux whatever distro has openssh-client package installed.
If you're lucky to have the ssh onboard you can use telnet in same manner as netcat or the swiss army knife (nmap) network mapper tool to test whether remote service TCP / port is opened or not. As often this is useful, if you don't have access to the CISCO / Juniper or other (networ) / firewall equipment which is setting the boundaries and security port restrictions between networks and servers.

Below is example on how to use ssh client to test port connectivity to lets say the Internet, i.e.  Google / Yahoo search engines.
 

[root@pciserver: /home ]# ssh -oConnectTimeout=3 -v google.com -p 23
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to google.com [172.217.169.206] port 23.
debug1: connect to address 172.217.169.206 port 23: Connection timed out
debug1: Connecting to google.com [2a00:1450:4017:80b::200e] port 23.
debug1: connect to address 2a00:1450:4017:80b::200e port 23: Cannot assign requested address
ssh: connect to host google.com port 23: Cannot assign requested address
root@pcfreak:/var/www/images# ssh -oConnectTimeout=3 -v google.com -p 80
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to google.com [172.217.169.206] port 80.
debug1: connect to address 172.217.169.206 port 80: Connection timed out
debug1: Connecting to google.com [2a00:1450:4017:807::200e] port 80.
debug1: connect to address 2a00:1450:4017:807::200e port 80: Cannot assign requested address
ssh: connect to host google.com port 80: Cannot assign requested address
root@pcfreak:/var/www/images# ssh google.com -p 80
ssh_exchange_identification: Connection closed by remote host
root@pcfreak:/var/www/images# ssh google.com -p 80 -v -oConnectTimeout=3
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to google.com [172.217.169.206] port 80.
debug1: connect to address 172.217.169.206 port 80: Connection timed out
debug1: Connecting to google.com [2a00:1450:4017:80b::200e] port 80.
debug1: connect to address 2a00:1450:4017:80b::200e port 80: Cannot assign requested address
ssh: connect to host google.com port 80: Cannot assign requested address
root@pcfreak:/var/www/images# ssh google.com -p 80 -v -oConnectTimeout=5
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to google.com [142.250.184.142] port 80.
debug1: connect to address 142.250.184.142 port 80: Connection timed out
debug1: Connecting to google.com [2a00:1450:4017:80c::200e] port 80.
debug1: connect to address 2a00:1450:4017:80c::200e port 80: Cannot assign requested address
ssh: connect to host google.com port 80: Cannot assign requested address
root@pcfreak:/var/www/images# ssh google.com -p 80 -v
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to google.com [172.217.169.206] port 80.
debug1: Connection established.
debug1: identity file /root/.ssh/id_rsa type 0
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: identity file /root/.ssh/id_xmss type -1
debug1: identity file /root/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
debug1: ssh_exchange_identification: HTTP/1.0 400 Bad Request

 


debug1: ssh_exchange_identification: Content-Type: text/html; charset=UTF-8


debug1: ssh_exchange_identification: Referrer-Policy: no-referrer


debug1: ssh_exchange_identification: Content-Length: 1555


debug1: ssh_exchange_identification: Date: Wed, 30 Dec 2020 14:13:25 GMT


debug1: ssh_exchange_identification:


debug1: ssh_exchange_identification: <!DOCTYPE html>

debug1: ssh_exchange_identification: <html lang=en>

debug1: ssh_exchange_identification:   <meta charset=utf-8>

debug1: ssh_exchange_identification:   <meta name=viewport content="initial-scale=1, minimum-scale=1, width=device-width">

debug1: ssh_exchange_identification:   <title>Error 400 (Bad Request)!!1</title>

debug1: ssh_exchange_identification:   <style>

debug1: ssh_exchange_identification:     *{margin:0;padding:0}html,code{font:15px/22px arial,sans-serif}html{background:#fff;color:#222;padding:15px}body{margin:7% auto 0;max-width:390px;min-height:180px;padding:30px 0 15px}* > body{background:url(//www.google.com/images/errors/robot.png) 10
debug1: ssh_exchange_identification: 0% 5px no-repeat;padding-right:205px}p{margin:11px 0 22px;overflow:hidden}ins{color:#777;text-decoration:none}a img{border:0}@media screen and (max-width:772px){body{background:none;margin-top:0;max-width:none;padding-right:0}}#logo{background:url(//www.g
debug1: ssh_exchange_identification: oogle.com/images/branding/googlelogo/1x/googlelogo_color_150x54dp.png) no-repeat;margin-left:-5px}@media only screen and (min-resolution:192dpi){#logo{background:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) no-repeat 0
debug1: ssh_exchange_identification: % 0%/100% 100%;-moz-border-image:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) 0}}@media only screen and (-webkit-min-device-pixel-ratio:2){#logo{background:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_
debug1: ssh_exchange_identification: color_150x54dp.png) no-repeat;-webkit-background-size:100% 100%}}#logo{display:inline-block;height:54px;width:150px}

debug1: ssh_exchange_identification:   </style>

debug1: ssh_exchange_identification:   <a href=//www.google.com/><span id=logo aria-label=Google></span></a>

debug1: ssh_exchange_identification:   <p><b>400.</b> <ins>That\342\200\231s an error.</ins>

debug1: ssh_exchange_identification:   <p>Your client has issued a malformed or illegal request.  <ins>That\342\200\231s all we know.</ins>

ssh_exchange_identification: Connection closed by remote host

 

Here is another example on how to test remote host whether a certain service such as DNS (bind) or telnetd is enabled and listening on remote local network  IP with ssh

[root@pciserver: /home ]# ssh 192.168.1.200 -p 53 -v -oConnectTimeout=5
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to 192.168.1.200 [192.168.1.200] port 53.
debug1: connect to address 192.168.1.200 port 53: Connection timed out
ssh: connect to host 192.168.1.200 port 53: Connection timed out

[root@server: /home ]# ssh 192.168.1.200 -p 23 -v -oConnectTimeout=5
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1g  21 Apr 2020
debug1: Connecting to 192.168.1.200 [192.168.1.200] port 23.
debug1: connect to address 192.168.1.200 port 23: Connection timed out
ssh: connect to host 192.168.1.200 port 23: Connection timed out


But what if Linux server you have tow work on is so paranoid that you even the ssh client is absent? Well you can use anything else that is capable of doing a connectivity to remote port such as wget or curl. Some web servers or application servers usually have wget or curl as it is integral part for some local shell scripts doing various operation needed for proper services functioning or simply to test locally a local or remote listener services, if that's the case we can use curl to connect and get output of a remote service simulating a normal telnet connection like this:

host:~# curl -vv 'telnet://remote-server-host5:22'
* About to connect() to remote-server-host5 port 22 (#0)
*   Trying 10.52.67.21… connected
* Connected to aflpvz625 (10.52.67.21) port 22 (#0)
SSH-2.0-OpenSSH_5.3

Now lets test whether we can connect remotely to a local net remote IP's Qmail mail server with curls telnet simulation mode:

host:~#  curl -vv 'telnet://192.168.0.200:25'
* Expire in 0 ms for 6 (transfer 0x56066e5ab900)
*   Trying 192.168.0.200…
* TCP_NODELAY set
* Expire in 200 ms for 4 (transfer 0x56066e5ab900)
* Connected to 192.168.0.200 (192.168.0.200) port 25 (#0)
220 This is Mail Pc-Freak.NET ESMTP

Fine it works, lets now test whether a remote server who has MySQL listener service on standard MySQL port TCP 3306 is reachable with curl

host:~#  curl -vv 'telnet://192.168.0.200:3306'
* Expire in 0 ms for 6 (transfer 0x5601fafae900)
*   Trying 192.168.0.200…
* TCP_NODELAY set
* Expire in 200 ms for 4 (transfer 0x5601fafae900)
* Connected to 192.168.0.200 (192.168.0.200) port 3306 (#0)
Warning: Binary output can mess up your terminal. Use "–output -" to tell
Warning: curl to output it to your terminal anyway, or consider "–output
Warning: <FILE>" to save to a file.
* Failed writing body (0 != 107)
* Closing connection 0
root@pcfreak:/var/www/images#  curl -vv 'telnet://192.168.0.200:3306'
* Expire in 0 ms for 6 (transfer 0x5598ad008900)
*   Trying 192.168.0.200…
* TCP_NODELAY set
* Expire in 200 ms for 4 (transfer 0x5598ad008900)
* Connected to 192.168.0.200 (192.168.0.200) port 3306 (#0)
Warning: Binary output can mess up your terminal. Use "–output -" to tell
Warning: curl to output it to your terminal anyway, or consider "–output
Warning: <FILE>" to save to a file.
* Failed writing body (0 != 107)
* Closing connection 0

As you can see the remote connection is returning binary data which is unknown to a standard telnet terminal thus to get the output received we need to pass curl suggested arguments.

host:~#  curl -vv 'telnet://192.168.0.200:3306' –output –
* Expire in 0 ms for 6 (transfer 0x55b205c02900)
*   Trying 192.168.0.200…
* TCP_NODELAY set
* Expire in 200 ms for 4 (transfer 0x55b205c02900)
* Connected to 192.168.0.200 (192.168.0.200) port 3306 (#0)
g


The curl trick used to troubleshoot remote port to remote host from a Windows OS host which does not have telnet installed by default but have curl instead.

Also When troubleshooting vSphere Replication, it is often necessary to troubleshoot port connectivity as common Windows utilities are not available.
As Curl is available in the VMware vCenter Server Appliance command line interface.

On servers where curl is not there but you have wget is installed you can use it also to test a remote port

 

# wget -vv -O /dev/null http://google.com:554 –timeout=5
–2020-12-30 16:54:22–  http://google.com:554/
Resolving google.com (google.com)… 172.217.169.206, 2a00:1450:4017:80b::200e
Connecting to google.com (google.com)|172.217.169.206|:554… failed: Connection timed out.
Connecting to google.com (google.com)|2a00:1450:4017:80b::200e|:554… failed: Cannot assign requested address.
Retrying.

–2020-12-30 16:54:28–  (try: 2)  http://google.com:554/
Connecting to google.com (google.com)|172.217.169.206|:554… ^C

As evident from output the port 554 is filtered in google which is pretty normal.

If curl or wget is not there either as a final alternative you can either install some perl, ruby, python or bash script etc. that can opens a remote socket to the remote IP.

Start Stop Restart Microsoft IIS Webserver from command line and GUI

Thursday, April 17th, 2014

start-stop-restart-microsoft-iis-howto-iis-server-logo
For a decomissioning project just recently I had the task to stop Microsoft IIS  on Windows Server system.
If you have been into security for a while you know well how many vulnerabilities Microsoft (Internet Information Server) Webserver used to be. Nowadays things with IIS are better but anyways it is better not to use it if possible …

Nomatter what the rason if you need to make IIS stop serving web pages here is how to do it via command line:

At Windows Command Prompt, type:

net stop WAS

If the command returns error message to stop it type:

net stop W3SVC

stop-microsoft-IIS-webservice
Just in case you have to start it again run:

net start W3SVC

start-restart-IIS-webserver-screenshot

For those who prefer to do it from GUI interface, launch services.msc command from Windows Run:

> services.msc

services-msc-stop-microsoft-iis-webserver

In list of services lookup for
IIS Admin Service and HTTP SSL
a) (Click over it with right mouse button -> Properties)
b) Set Startup type to Manual
c) Click Stop Button

You're done now IIS is stopped to make sure it is stopped you can run from cmd.exe:

telnet localhost 80

when not working you should get 'Could not open connection to the host. on port 80: Connection failed' like shown up in screenshot.

New World Order, Secret Societies and the Bible Prophecies a movie research on secret societies and Bible Prophecies

Monday, April 30th, 2012

I've just completed watching a movie I found on youtube

 

NWO: Secret Societies and Biblical Prophecy Vol. 1

The movie is quite intriguing research on the topic of Secret Societies and connection of what happened in the world so far. The movie points at what is about to happen in the future and how there are certain groups of people who has interest for the New Wolrd Order to come.

 

The movie says how the Biblical  Prophecies, we can read in the bible has clearly foretold many of the things that happened like the re-creation of  Jewish Country (Israel). All this events to occur was foretold many hundred years ago in the Holy Bible (scriptures). The movie director is called Leonard Ulrich a person who graduated with double degree in Winnepig University  and University of Minnetoba Caneda. This presentational material is as it the author points himself a 5 years of research on secret societies and the New Wolrd Order. The movie discuss the major secret societies (occult) organizations existing of today and claims there is a connection between the different secret societies. As Ulrich's point is there is a clear connection between the major globalism, secret societies and ancient occult teachings. The movie can be classified under a conspiracy theory and some of the facts might be considered by many sceptical people a wild imagination, however all those who  took the time to research on the movie's stand points will assure the movie is based on hard truths. As the presentation wents through history and turns back to the modern days it exposes how connections between a numerous of FreeMasonry organizations, dictatorship regimes like Communism, Nazism, Hitler Stalin and the rest of the key figures in modern day history somehow had a connection with the occult / sorceries / magicians  or secret societies. All the America Founders, communism, nazism and the world wars the author claims, were initiated by this same secret soecities. The movie reveals shocking facts about the United Nations  anti-christian character as well as the facts that many of the modern day turns the major world leaders of this day are orchestrated based on ancient non-christian belief systems like Kabalah  I will stop here with my review and let you alone watch it and discern if the facts in the movie can be considered trustable. For me personally as a Christian, I'm pretty much convinced what the movie retells is pure facts. Unfortunately nowdays, most people are so deluded, so they can't see the pure facts, but prefer to believe the lie that the world is governed towards its destination by money only.  Well, I clearly see it myself how most people nowdays are blindly led to bow down in front of technology which is just a major tool for the building of this unrightous (unjustice) system proclaimed under the fuzzy name New World Order. I truly enjoyed the movie and I believe watching the movie will help many to realize that Christianity is not just some old tales but a religion based on facts and truths.

 

Fix FTP active connection issues “Cannot create a data connection: No route to host” on ProFTPD Linux dedicated server

Tuesday, October 1st, 2019

proftpd-linux-logo

Earlier I've blogged about an encounter problem that prevented Active mode FTP connections on CentOS
As I'm working for a client building a brand new dedicated server purchased from Contabo Dedi Host provider on a freshly installed Debian 10 GNU / Linux, I've had to configure a new FTP server, since some time I prefer to use Proftpd instead of VSFTPD because in my opinion it is more lightweight and hence better choice for a small UNIX server setups. During this once again I've encounted the same ACTIVE FTP not working from FTP server to FTP client host machine. But before shortly explaining, the fix I find worthy to explain briefly what is ACTIVE / PASSIVE FTP connection.

 

1. What is ACTIVE / PASSIVE FTP connection?
 

Whether in active mode, the client specifies which client-side port the data channel has been opened and the server starts the connection. Or in other words the default FTP client communication for historical reasons is in ACTIVE MODE. E.g.
Client once connected to Server tells the server to open extra port or ports locally via which the overall FTP data transfer will be occuring. In the early days of networking when FTP protocol was developed security was not of such a big concern and usually Networks did not have firewalls at all and the FTP DATA transfer host machine was running just a single FTP-server and nothing more in this, early days when FTP was not even used over the Internet and FTP DATA transfers happened on local networks, this was not a problem at all.

In passive mode, the server decides which server-side port the client should connect to. Then the client starts the connection to the specified port.

But with the ever increasing complexity of Internet / Networks and the ever tightening firewalls due to viruses and worms that are trying to own and exploit networks creating unnecessery bulk loads this has changed …

active-passive-ftp-explained-diagram
 

2. Installing and configure ProFTPD server Public ServerName

I've installed the server with the common cmd:

 

apt –yes install proftpd

 

And the only configuration changed in default configuration file /etc/proftpd/proftpd.conf  was
ServerName          "Debian"

I do this in new FTP setups for the logical reason to prevent the multiple FTP Vulnerability Scan script kiddie Crawlers to know the exact OS version of the server, so this was changed to:

 

ServerName "MyServerHostname"

 

Though this is the bad security through obscurity practice doing so is a good practice.
 

3. Create iptable firewall rules to allow ACTIVE FTP mode


But anyways, next step was to configure the firewall to be allowed to communicate on TCP PORT 21 and 20 to incoming source ports range 1024:65535 (to enable ACTIVE FTP) on firewal level with iptables on INPUT and OUTPUT chain rules, like this:

 

iptables -A INPUT -p tcp –sport 1024:65535 -d 0/0 –dport 21 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s 0/0 –sport 1024:65535 -d 0/0 –dport 20 -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s 0/0 –sport 21 -d 0/0 –dport 1024:65535 -m state –state ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s 0/0 –sport 20 -d 0/0 –dport 1024:65535 -m state –state ESTABLISHED,RELATED -j ACCEPT


Talking about Active and Passive FTP connections perhaps for novice Linux users it might be worthy to say few words on Active and Passive FTP connections

Once firewall has enabled FTP Active / Passive connections is on and FTP server is listening, to test all is properly configured check iptable rules and FTP listener:
 

/sbin/iptables -L INPUT |grep ftp
ACCEPT     tcp  —  anywhere             anywhere             tcp spts:1024:65535 dpt:ftp state NEW,ESTABLISHED
ACCEPT     tcp  —  anywhere             anywhere             tcp spts:1024:65535 dpt:ftp-data state NEW,ESTABLISHED
ACCEPT     tcp  —  anywhere             anywhere             tcp dpt:ftp
ACCEPT     tcp  —  anywhere             anywhere             tcp dpt:ftp-data

netstat -l | grep "ftp"
tcp6       0      0 [::]:ftp                [::]:*                  LISTEN    

 

4. Loading nf_nat_ftp module and net.netfilter.nf_conntrack_helper (for backward compitability)


Next step of course was to add the necessery modules nf_nat_ftp nf_conntrack_sane that makes FTP to properly forward ports with respective Firewall states on any of above source ports which are usually allowed by firewalls, note that the range of ports given 1024:65535 might be too much liberal for paranoid sysadmins and in many cases if ports are not filtered, if you are a security freak you can use some smaller range such as 60000-65535.

 

Here is time to say for sysadmins who haven't recently had a task to configure a new (unecrypted) File Transfer Server as today Secure FTP is almost alltime used for file transfers for the sake of security might be puzzled to find out the old Linux kernel ip_conntrack_ftp which was the standard module used to make FTP Active connections work is substituted nowadays with  nf_nat_ftp and nf_conntrack_sane.

To make the 2 modules permanently loaded on next boot on Debian Linux they have to be added to /etc/modules

Here is how sample /etc/modules that loads the modules on next system boot looks like

cat /etc/modules
# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
softdog
nf_nat_ftp
nf_conntrack_sane


Next to say is that in newer Linux kernels 3.x / 4.x / 5.x the nf_nat_ftp and nf_conntrack-sane behaviour changed so  simply loading the modules would not work and if you do the stupidity to test it with some FTP client (I used gFTP / ncftp from my Linux desktop ) you are about to get FTP No route to host errors like:

 

Cannot create a data connection: No route to host

 

cannot-create-a-data-connection-no-route-to-host-linux-error-howto-fix


Sometimes, instead of No route to host error the error FTP client might return is:

 

227 entering passive mode FTP connect connection timed out error


To make the nf_nat_ftp module on newer Linux kernels hence you have to enable backwards compatibility Kernel variable

 

 

/proc/sys/net/netfilter/nf_conntrack_helper

 

echo 1 > /proc/sys/net/netfilter/nf_conntrack_helper

 

To make it permanent if you have enabled /etc/rc.local legacy one single file boot place as I do on servers – for how to enable rc.local on newer Linuxes check here

or alternatively add it to load via sysctl

sysctl -w net.netfilter.nf_conntrack_helper=1

And to make change permanent (e.g. be loaded on next boot)

echo 'net.netfilter.nf_conntrack_helper=1' >> /etc/sysctl.conf

 

5. Enable PassivePorts in ProFTPD or PassivePortRange in PureFTPD


Last but not least open /etc/proftpd/proftpd.conf find PassivePorts config value (commented by default) and besides it add the following line:

 

PassivePorts 60000 65534

 

Just for information if instead of ProFTPd you experience the error on PureFTPD the configuration value to set in /etc/pure-ftpd.conf is:
 

PassivePortRange 30000 35000


That's all folks, give the ncftp / lftp / filezilla or whatever FTP client you prefer and test it the FTP client should be able to talk as expected to remote server in ACTIVE FTP mode (and the auto passive mode) will be not triggered anymore, nor you will get a strange errors and failure to connect in FTP clients as gftp.

Cheers 🙂

How to configure VIVACOM 3g USB ( internet ) modem HUAWEI Mobile broadband E173 on Debian and Ubuntu GNU / Linux

Wednesday, July 4th, 2012

sakis3g-configure-usb-modem-kdialog-shot

I've been given a HUAWEI Mobile Broadband E173 USB 3g model. The USB modem contains a flash USB Storage segment storing a little install program dedicated to make the modem work fine on Microsoft Windows XP / Vista / 7 and probably other M$ OSes. I'm a long time DebianGNU / Linux user and as a free software enthusiast I ofcourse wanted to be able to use Vivacom's 3G USB Modem on my Linux powered notebook.

Thanksfully as I've red on Vivacom's website the modem supports Linux OS 🙂

For those unaware in Bulgaria there are currently 3 major GSM network providers providing 3G internet this are;;;
 

  • VIVACOM – The ex Government ran national company BTC (Bulgarian Telecommunication Company)
  • M-Tel – The first GSM network provider that entered Bulgaria around year 1995
  • GLOBUL – The 3rd and last GSM mobile and net provider entered last and not so much used by Bulgarians today

Until today I had no experience in running any 3G modems on Linux, neither I had used the 3 networks 3G internet to determine which one is best, however I've been given for temporal use a VIVACOM 3G internet modem today so I proceeded to try installing it on my Debian host.

My Linux system is a bit strangely configured as I use wicd network connection manager -( wicd-gtk ) to manage wireless and LAN connections instead of the standard installed GNOME network manager – available through package ( network-manager-gnome ).

The reason I use wicd is not that it is so much better than GNOME network manger but rather for historical reasons because few years past I had impression it works better in connecting me to wireless networks. Another reason why I choosed wicd back then was the nice looking stats …

I tried plugging in the Vivacom USB 3G modem stick and checked in wicd to see if I can see a possibility to connect to the mobile opeartor 3G network but unfortunately nothing appeared.

Though the 3G adsl modem was unavailable straing in wicd, checking about it in the list of attached USB devices I could see it detected, e.g.:

noah:~# lsusb |grep -i huawei
Bus 001 Device 007: ID 12d1:1c05 Huawei Technologies Co., Ltd.

This was at least a good sign pointing me to the thoughts that the modem is probably gonna work.

I did a quick Google search to see if other people succeded running the device on a Linux host and came across a few blog posts in Bulgarian explaining a "success story" on Ubuntu Linux through using a tweakened shell script – sakis3g. For more on how the script works and script download check out Sakis3g

Here is a quote from sakis3g's website describing the script:
 

It automagically setups your USB or Bluetooth™ modem, and may even detect operator settings.
You should try it when anything else fails!

Sakis3g has different versions designed for for plenty of spacific hware architectures i.e. for (i386, amd64, armv4t, armv5t).
There is also a version of the script which by the way contains a combination of bash shell scripting instruction and some binary exec data.

To run sakis3g on my laptop I did:

1. Download sakis3g

My notebook architecture is 64 bit so I download and used the amd64 version of the script;;;

hipo@noah:~$ mkdir sakis3g
hipo@noah:~$ cd sakis3g
hipo@noah:~/sakis3g$ wget http://www.sakis3g.org/versions/latest/amd64/sakis3g.gz

I've made also a mirror of sakis3g i386, 64 bit and all architecture the mirrors just in case it disappears in future. The mirror versions of sakis3g are here:

a. sakis3g i386 b. sakis3g amd64 c. sakis3g all architectures source

2. Unarchive and make it executable

After downloading it as it is in gzip I had to do the usual de-gzipping and making the file executable;;;

hipo@noah:~/sakis3g$ /bin/gzip -d sakis3g.gz
hipo@noah:~/sakis3g$ chmod +x sakis3g

The script is then ready to run by either clicking twice on it or (as I prefer for debugging reasons to run it in terminal):

hipo@noah:~$ ./sakis3g

Something that I have wondered a bit was the dialog where I had to fill in some data of some variable APN abbreviation for – (Access Point Name)

The APN host for VIVACOM mobile internet is;;;
APN: internet.vivacom.bg

I've used the Windows configuration progrma to gather also the following data that I thought might be important for configuring the 3G adsl modem on the Linux host;;;

Auth: *99#
User: VIVACOM
pass: VIVACOM

Here are all the configuration screenshots I've taken from sakis3g and all the data that I filled in.
Next the following tiny window appeared on screen:

Sakis3g configure usb modem kdialog shot 1 VIVACOM USB Modem Sakis 3g Shot 2 sakis 3g usb modem vivacom connect screenshot 2 vivacom 3g modem linux sakis3g enter pin dialog shot 4 Sending pin screenshot 5 sakis3g APN Dialog sakis3g screenshot 6sakis3g Internet Linux VIVACOM screenshot 7sakis3g Debian GNU Linux VIVACOM 3g Internet screenshot 8sakis3g initializing modem screenshot 9sakis3g successful connect to VIVACOM mobile 3g usb adls modem shot 10

Well that's all folks, now sakis3g succesfully connected to the I_net via an (PPP) VPN connection tunnel here is data from ifconfig command showing the succesful 3G connection to VIVACOM;;;

noah:~# /sbin/ifconfig ppp0
ppp0 Link encap:Point-to-Point Protocol
inet addr:10.58.146.232 P-t-P:10.64.64.64 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:2066 errors:1 dropped:0 overruns:0 frame:0
TX packets:1609 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:2232058 (2.1 MiB) TX bytes:341693 (333.6 KiB)

The internet via the 3G connection is not blazing fast but good enough to check your mail or read some webpages. VIVACOM currently has different (traffic limited packages) for their 3G internet, I'm not sure which package exactly is the 3G USB stick modem but probably the "quick" internet connection that is now would slow down once the traffic limit is reached …
Hope this post helps someone to configure 3G internet on VIVACOM in Debian and Ubuntu Linux. Though I've tested sakis3g on Debian it should work with no hassles on any other GNU Linux distribution that has bash installed.

How to connect to WiFi network using console or terminal on GNU / Linux

Wednesday, November 2nd, 2011

iwlist-screenshot-howto-connect-to-wifi-in-text-console-linux-wpasupplicant

Sometimes its useful to connect to Wireless Networks using console . The reasons for that might be many, one possible reason is to be able to debug, Wireless connection failures or simply omit the use of the many available GUI wifi connection programs.

As a first step before connecting in terminal is to look up for the wifi networks available for connection, this is done with cmd:

linux:~# iwlist wlan0 scanning
wlan0 Scan completed :
Cell 01 - Address: 00:24:01:90:8F:38
Channel:7
Frequency:2.442 GHz (Channel 7)
Quality=70/70 Signal level=-39 dBm
Encryption key:on
ESSID:"magdanoz"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=000000034f5c786b
Extra: Last beacon: 68ms ago
IE: Unknown: 00086D616764616E6F7A
IE: Unknown: 010482848B96
IE: Unknown: 030107
IE: Unknown: 32080C1218602430486C
IE: Unknown: CC0700CC020000018A
IE: Unknown: CC0700CC0300000100
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (2) : TKIP CCMP
Authentication Suites (1) : PSK
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : TKIP
Pairwise Ciphers (2) : TKIP CCMP
Authentication Suites (1) : PSK
Cell 02 - Address: 00:1E:2A:60:5E:DC
Channel:1
...

To just list the ESSID s of the wifi networks:

linux:~# iwlist wlan0 scanning|grep -i 'essid'
ESSID:"magdanoz"
ESSID:"default"
ESSID:"todorov"
ESSID:"BTC-ADSL"
ESSID:"Zahari"
ESSID:"Drago"

1. Connecting to Open Wireless Network

Now from the above output it is clear 6 wifi networks are available for connection. The default wifi network from the list is an Open network (e.g. without pass). To connect to it I use cmd:

linux:~# /sbin/iwconfig wlan0 essid 'default'
linux:~# /sbin/iwconfig wlan0 key open

After connected to configure IP, Gateway and DNS from a DHCP server running on the WIFI router, dhclient cmd is used:

linux:~# /sbin/dhclient wlan0

2. Connecting to WEP 64bit / 128bit encrypted network

linux:~# /sbin/iwconfig wlan0 key 1234-5678-9101-1213

3. Connecting to WPA / WPA2 encrypted wifi network

To connect to WPA or WPA2 encrypted network its necessery to have installed wpasupplicant package. The name of the package might vary in different distributions on Debian and Ubuntu, the name of the package is wpasupplicant, on Fedora, CentOS and RHEL the package that has to be in is wpa_supplicant :
After having installed the wpa_supplicant to connect to the network with ESSID name magdanoz , wpa_passphrase is used first:

linux:~# /usr/bin/wpa_passphrase magdanoz Secret_Wifi_Password | tee -a /etc/wpa_supplicant.conf
network={
ssid="magdanoz"
#psk="Secret_Wifi_Password"
psk=6f7590250c4496ff7bf8dd25199ac3bb5a614d4bc069975aa884bcf084da73bc
}

As you see in above command the secret password key is generated printed on the screen and then added to /etc/wpa_supplicant.conf , necessery to establish the wireless connection with wpa_supplicant with cmd:

linux:~# /sbin/wpa_supplicant wpa_supplicant -d wext -i wlan0 -c /etc/wpa_supplicant.conf -B

-d wext instructs wpa_supplicant to use (Linux wireless extension driver).
-B tells wpa_supplicant to background the connection to prevent the wireless connection to drop off, if the console / terminal from which it is launched gets closed.

In case of succesful connection with wpa_supplicant , once again IP, Gateway and DNS is configured fetching the settings from the wifi hotspot dhcp server:

linux:~# /sbin/dhclient wlan0

General information about the wireless network and info related to the established connection can be obtained with /usr/bin/iwconfig :

linux:~# /sbin/iwconfig
lo no wireless extensions.
eth0 no wireless extensions.
wlan0 IEEE 802.11abg ESSID:"magdanoz"
Mode:Managed Frequency:2.442 GHz Access Point: 00:24:00:90:8F:38
Bit Rate=54 Mb/s Tx-Power=15 dBm
Retry long limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=70/70 Signal level=-39 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0

To configure the exact channel over which the wireless connection will be established again is done with iwconfig, for instance to configure wlan0 wifi connection established to be on wifi channel 7:

linux:~# /sbin/iwconfig wlan0 channel 11

By default iwconfig is set to automatically set the channel based on connected network ESSID , if the channel is modified to some specific number to revert it back use:

linux:~# /sbin/iwconfig wlan0 channel auto
 

Optimizing Linux TCP/IP Networking to increase Linux Servers Performance

Tuesday, April 8th, 2008

optimize-linux-servers-for-network-performance-to-increase-speed-and-decrease-hardware-costs-_tyan-exhibits-hpc-optimized-server-platforms-featuring-intel-xeon-processor-e7-4800-v3-e5-2600-supercomputing-15_full

Some time ago I thought of ways to optimize my Linux Servers network performance.

Even though there are plenty of nice articles on the topic on how to better optimize Linux server performance by tunning up the kernel sysctl (variables).

Many of the articles I found was not structed in enough understandable way so I decided togoogle around and  found few interesting websites which gives a good overview on how one can speed up a bit and decrease overall server loads by simply tuning few basic kernel sysctl variables.

Below article is a product of my research on the topic on how to increase my GNU / Linux servers performance which are mostly running LAMP (Linux / Apache / MySQL / PHP) together with Qmail mail servers.

The article is focusing on Networking as networking is usual bottleneck for performance.
Below are the variables I found useful for optimizing the Linux kernel Network stack.

Implementing the variables might reduce your server load or if not decrease server load times and CPU utilization, they would at lease increase thoroughput so more users will be able to access your servers with (hopefully) less interruptions.
That of course would save you some Hardware costs and raise up your Servers efficiency.

Here are the variables themselves and some good example:
 

# values.net.ipv4.ip_forward = 0 ( Turn off IP Forwarding )

net.ipv4.conf.default.rp_filter = 1

# ( Control Source route verification )
net.ipv4.conf.default.accept_redirects = 0

# ( Disable ICMP redirects )
net.ipv4.conf.all.accept_redirects = 0 ( same as above )
net.ipv4.conf.default.accept_source_route = 0

# ( Disable IP source routing )
net.ipv4.conf.all.accept_source_route = 0
( - || - )net.ipv4.tcp_fin_timeout = 40

# ( Decrease FIN timeout ) - Useful on busy/high load
serversnet.ipv4.tcp_keepalive_time = 4000 ( keepalive tcp timeout )
net.core.rmem_default = 786426 - Receive memory stack size ( a good idea to increase it if your server receives big files )
net.ipv4.tcp_rmem = "4096 87380 4194304"
net.core.wmem_default = 8388608 ( Reserved Memory per connection )
net.core.wmem_max = 8388608
net.core.optmem_max = 40960
( maximum amount of option memory buffers )

# like a homework investigate by yourself what the variables below stand for :)
net.ipv4.tcp_max_tw_buckets = 360000
net.ipv4.tcp_reordering = 5
net.core.hot_list_length = 256
net.core.netdev_max_backlog = 1024

 

# Below are newly added experimental
#net.core.rmem_max = 16777216
#net.core.wmem_max = 16777216
##kernel.msgmni = 1024
##kernel.sem = 250 256000 32 1024
##vm.swappiness=0
kernel.sched_migration_cost=5000000

 

Also a good sysctl.conf file which one might want to substitite or use as a skele for some productive server is ready for download here


Even if you can't reap out great CPU reduction benefits from integrating above values or similar ones, your overall LAMP performance to end customers should increase – at some occasions dramatically, at others little bit but still noticable.

If you're unsure on exact kernel variable values to use check yourself what should be the best values that fits you according to your server Hardware – usually this is done by experimenting and reading the kernel documentation as provided for each one of uplisted variables.

Above sysctl.conf is natively created to run on Debian and on other distributions like CentOS, Fedora Slackware some values might either require slight modifications.

Hope this helps and gives you some idea of how network optimization in Linux is usually done. Happy (hacking) tweakening !

Sermon on how the Christian can live without Fear – Repent ! Pope Shenouda II Coptic Patriarch

Tuesday, April 9th, 2013

I'm a Christian and even though I'm trying to live as a Christian it is not always working. I'm a human and as all of us I have my fears. Thus by God's grace today by looking on Youtube on what the Coptic Christian say on Fear. I've ended in Sermon from his Holiness Pope Shenoda II. He explains very well the connection of Fear and the lack of Christian repentance. Below is the video I hope some Christian out there can earn by watching this video.
 

HH pope Shenouda Sermon Old ''A Life Without Fear''