Posts Tagged ‘linux?’

Linux: Compress website images for better responsiveness with Trimage Graphical tool

Tuesday, March 10th, 2020

trimage-compress-reduce-lossless-encoding-of-pictures-for-seo-linux-screenshot0

If you run a Website or a Blog with images sooner or later you will end up with in looking for better ways to optimize the SEO of the website. I had a small discussion today with a friend of mine Mitko Ivanov who is working as SEO consultant expert,  we had a small discussion on the good practice of optimizing website pictures to reduce the website opening time. Ingeral part of Website responsiveness is the time the Browser needs to fetch all the page Images. Thus if your site is with multiple images, like this blog here, picture comperssion is definitely something that could make miracles in how website visualize for end user and increase rank in Search Engines. The easiest way to compress images of an amateur website of course is to use external picture compression service such as tinypng.com, this requires no knowledge at any computer technology and you can do it easy, but the problem is it shares your image to the remote website used for conversion and I personally think this is not the best idea.
For WordPress website owners of course there is plenty of plugins such as eWWW Image Optimizer that does realtime reduce of size of picture by chunking out the unnecessery bits.
Alternative to especially for people who have a little bit of technical knowledge is is to use some command line tool as optipng together with some kind of shell for loopfor details see my previous article Optimize PNG images by compressing on GNU / Linux, FreeBSD server to Improve Website overall Performance.
But for Many of Webmaster site owners this solution takes too much time as well many people just don't have even basic command line knowledge / are kinda of scared from the console but need to do image compression in a simple GUI way for those the good news are there is  Graphical cross-platform tool for losslessly optimizing PNG and JPG files for web. Trimage.
To use it it even unexperienced non enthusiast could simply roll out a new Virtual Machine on top of some VM Host machine such as Virtual Box and roll out some kind of Linux distribution via a graphical installer which is mega easy well guided and takes 15-20 minutes time.

Once machine is set-up either the Graphical Distribution tool for page management or via apt you can fetch Trimage. It is now existing in most Linux distributions so, to install it on any deb based distribution Debian / Mint / Ubuntu etc. do the usual:

# apt-get install –yes trimage


trimage-compress-reduce-lossless-encoding-of-pictures-for-seo-linux-screenshot1

Once you have it, just move the pictures you want to compress for losslessly optimizing from your website to your Computer with Linux. Trimage GUI on the background will run commands optipng, pngcrush, advpng or jpegoptim, imageoptim and depending on the filetype remove the unnecessery file data that are appended by the program with which image was produced Gimp / Photoshop / Camera software etc. All image files are losslessy compressed on the highest available compression levels, and EXIF and other metadata is removed so you just have to recopy ( upload ) the optimized images back to the website.

trimage-compress-reduce-lossless-encoding-of-pictures-for-seo-linux-screenshot2

That's all folks Enjoy ! 🙂

 

Fix eth changing network interface names from new Linux naming scheme ens, eno, em1 to legacy eth0, eth1, eth2 on CentOS Linux

Thursday, January 16th, 2020

Change-systemd-Linux-servers-network-interface-name-ensxx-to-eth0-copy

On CentOS / RHEL 7 / Fedora 19+ and other Linux distributions, the default network eth0, eth1 .. interface naming scheme has been changed and in newer Linux kernels OS-es to names such as – ens3 , eno1, enp5s2, em1 etc.,  well known old scheme for eth* is now considered a legacy.
This new Network card naming in Linux OS is due to changes made in Kernel / modules and udev  rules which resembles how Ethernet ifaces are named on other UNIX like systems.
The weird name is taken depending on the Hardware Network card vendor name and is a standard for years in FreeBSD and Mac OSX, however this was not so over the years,
so for old school sysadmins that's pretty annoying as, we're much used to the eth0 / eth1 / eth2 / eth3 naming standard which brought some clearness on the network card naming.

Also for systems which are upgraded from old Linux OS distro releases to a newer ones, that includes this great new "cool" feature, that fits so well the New age-of computing Cloud craziness.
That behaviour could create a number of problems, especially if the already Production working servers due to failure to bring up some of the network devices after the upgrade or, even if you fix that by editting the /etc/network* / etc/sysconfig/networking/* by hand still there is even more stuff that won't work properly, such as any custom made iptables / ipset firewalls rules, or any kind of custom used third party Shell / Perl scripts that depend on the old-school conventional and (convenient easy to remember!!!) eth0, eth2 etc. naming


For sysadmins who are using some kind of Application Clustering with something like corosync / pacemaker this new fuzzy improvement makes things even worse as having a changed interface name of the card will break the cluster …

 

1. Get list of the LAN Card Server hardware

 

To get a better view on the server installed and recognized LAN Cards use lspci / dmidecode commands:

 lspci |grep -i Ether -A1 -B1
01:00.4 USB controller: Hewlett-Packard Company Integrated Lights-Out Standard Virtual USB Controller (r                                                                                                           ev 03)
02:00.0 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
02:00.1 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
02:00.2 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
02:00.3 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
03:00.0 RAID bus controller: Hewlett-Packard Company Smart Array Gen9 Controllers (rev 01)
05:00.0 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
05:00.1 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
05:00.2 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
05:00.3 Ethernet controller: Broadcom Inc. and subsidiaries NetXtreme BCM5719 Gigabit Ethernet PCIe (rev                                                                                                            01)
7f:08.0 System peripheral: Intel Corporation Xeon E7 v3/Xeon E5 v3/Core i7 QPI Link 0 (rev 02)

 

lspci reports all attached LAN Cards to server which are plugged in on the Motherbord, since that specific server has a Motherboard integrated LAN Adapters too, we can see this one
via dmidecode.

# dmidecode |grep -i Ether -A 5 -B 5

Handle 0x00C5, DMI type 41, 11 bytes
Onboard Device
        Reference Designation: Embedded LOM 1 Port 3
        Type: Ethernet
        Status: Enabled
        Type Instance: 3
        Bus Address: 0000:XX:00.X

Handle 0x00C6, DMI type 41, 11 bytes
Onboard Device
        Reference Designation: Embedded LOM 1 Port 4
        Type: Ethernet
        Status: Enabled
        Type Instance: 4
        Bus Address: 0000:0X:00.X

Handle 0x00C7, DMI type 41, 11 bytes


       Strings:
                PciRoot(0x0)/Pci(0x2,0x0)/Pci(0x0,0x0)
                NIC.Slot.2.1
                HP Ethernet 1Gb 4-port 331T Adapter – NIC
                Slot 2

Handle 0x00E3, DMI type 203, 34 bytes
OEM-specific Type
        Header and Data:

 

The illustrate the eth0 changing name issue, here is example taken from server on how eth1 interface is named on a new CentOS install:
 

# ip addr show

…..
eno1: [BROADCAST,MULTICAST,UP,LOWER_UP] mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 6c:0b:84:6c:48:1c brd ff:ff:ff:ff:ff:ff
inet 10.10.9.5/24 brd 10.10.9.255 scope global eno1
inet6 2606:b400:c00:48:6e0b:84ff:fe6c:481c/128 scope global dynamic
valid_lft 2326384sec preferred_lft 339184sec
inet6 fe80::6e0b:84ff:fe6c:481c/64 scope link
valid_lft forever preferred_lft forever

 

 

2. Disable Network Manager on the server


To prevent potential problems for future with randomly changing Network card names order on reboots and other mess,
it is generally a good idea to disable Network Manager.

 

# systemctl disable NetworkManager
rm '/etc/systemd/system/multi-user.target.wants/NetworkManager.service'
rm '/etc/systemd/system/dbus-org.freedesktop.NetworkManager.service'
rm '/etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service'

 

3. Check and correct network configuration if necessery in  /etc/sysconfig/network-scripts/ifcfg-*


Either fix the naming across all files ifcfg-* to match eth0 / eth1 / ethXX or even better both change the NAME and DEVICE in files and completely rename the files ifcfg-eno1 to ifcfg-eth1 ..
ifcfg-enoXX to ifcfg-ethXX
 

server:~# cat /etc/sysconfig/network-scripts/ifcfg-eno1
……
NAME=eth0
DEVICE=eth0
……

 

4. Fix the interface scheme naming through passing a GRUB boot parameter to Kernel

 

a. Create backup of /etc/default/grub
 

cp -rpf /etc/default/grub /etc/default/grub_bak_date +"%Y_%m_%Y"


b. Edit /etc/default/grub

c. Find config parameter GRUB_CMDLINE_LINUX

d. Add net.ifnames=0 biosdevname=0 to the line

 

net.ifnames=0 biosdevname=0


After the change the line should look like

GRUB_CMDLINE_LINUX=" crashkernel=auto net.ifnames=0 biosdevname=0 rhgb quiet"

 

e. Regenerate GRUB loader to have included the new config

server:~# grub2-mkconfig -o /boot/grub2/grub.cfg

f. Reboot the sytem
 

server:~# shutdown -r now

 

5. Fix auto-generated inconvenient naming by modifying udev rules

The Mellanox Ehternet server card vendor's workaround to the ever changing eth names is modify udev rules to be able to have the ordinary eth0 / eth1 / eth2 … Lan card name scheme.
In short this is recommended for Mellanox but should work on any other Lan card device attached on a Linux powered server.
 

# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE="eth1"
BOOTPROTO="static"
HWADDR="7c:fe:90:cb:76:02"
IPADDR=10.10.9.2
NETMASK=255.255.255.0
ONBOOT="yes"

 

# cat /etc/sysconfig/network-scripts/ifcfg-eth2
DEVICE="eth1"
BOOTPROTO="static"
HWADDR="7c:fe:90:cb:76:02"
IPADDR=10.10.99.99
NETMASK=255.255.255.0
ONBOOT="yes"

 

# vi /etc/udev/rules.d/70-persistent-net.rules

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="7c:fe:90:cb:76:02", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="7c:fe:90:cb:76:03", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

 

Next step is to reboot.
 

# /sbin/reboot


After a while when the server boots check with ip or ifconfig the configuration to make sure the ethXX ordering is proper again.

interface-list-eth1-eth2-screenshot

# /sbin/ifconfig eth1
eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.0.99.99 netmask 255.255.255.0 broadcast 10.10.9.255
inet6 fe80::7efe:90ff:fecb:7602 prefixlen 64 scopeid 0x20<link>
ether 7c:fe:90:cb:76:02 txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 23 bytes 3208 (3.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
eth2: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether 7c:fe:90:cb:76:03 txqueuelen 1000 (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

On some Linux distributions, if it happens this udev extra configuration is not venerated, use net.ifnames=0 biosdevname=0 grub configuration.

6. Verify eth interfaces are present    

# ip addr show

…..

eth0: [BROADCAST,MULTICAST,UP,LOWER_UP] mtu 1500 qdisc pfifo_fast state UP qlen 1000

link/ether 6c:0b:84:6c:48:1c brd ff:ff:ff:ff:ff:ff

inet 10.10.9.5/24 brd 10.10.9.255 scope global eno1

inet6 2606:b400:c00:48:6e0b:84ff:fe6c:481c/128 scope global dynamic

valid_lft 2326384sec preferred_lft 339184sec

inet6 fe80::6e0b:84ff:fe6c:481c/64 scope link

valid_lft forever preferred_lft forever

That's all this should put an end to the annoying auto generated naming lan device naming.

 

Summary

 

So what was explained up was how to resolve problems caused by autogenerated ethernet interface cards by a new functionality in the Linux kernel, so Network cards are again visible via ip address show / ifconfig again in a proper order eth0 / eth1 / eth2 / eth3 etc. instead of a vendor generated cryptic names as ens / eno / em etc. This is possible via either by editing udev rules or grub configuration. Doing so saves nerves and makes sysadmin life better, at least it did mine.
That's all this should put an end to the annoying auto generated naming.
 

How to debug failing service in systemctl and add a new IP network alias in CentOS Linux

Wednesday, January 15th, 2020

linux-debug-failing-systemctl-systemd-service--add-new-IP-alias-network-cable

If you get some error with some service that is start / stopped via systemctl you might be pondering how to debug further why the service is not up then then you'll be in the situation I was today.
While on one configured server with 8 eth0 configured ethernet network interfaces the network service was reporting errors, when atempted to restart the RedHat way via:
 

service network restart


to further debug what the issue was as it was necessery I had to find a way how to debug systemctl so here is how:

 

How to do a verbose messages status for sysctlct?

 

linux:~# systemctl status network

linux:~# systemctl status network

 

Another useful hint is to print out only log messages for the current boot, you can that with:

# journalctl -u service-name.service -b

 

if you don't want to have the less command like page separation ( paging ) use the –no-pager argument.

 

# journalctl -u network –no-pager

Jan 08 17:09:14 lppsq002a network[8515]: Bringing up interface eth5:  [  OK  ]

    Jan 08 17:09:15 lppsq002a network[8515]: Bringing up interface eth6:  [  OK  ]
    Jan 08 17:09:15 lppsq002a network[8515]: Bringing up interface eth7:  [  OK  ]
    Jan 08 17:09:15 lppsq002a systemd[1]: network.service: control process exited, code=exited status=1
    Jan 08 17:09:15 lppsq002a systemd[1]: Failed to start LSB: Bring up/down networking.
    Jan 08 17:09:15 lppsq002a systemd[1]: Unit network.service entered failed state.
    Jan 08 17:09:15 lppsq002a systemd[1]: network.service failed.
    Jan 15 11:04:45 lppsq002a systemd[1]: Starting LSB: Bring up/down networking…
    Jan 15 11:04:45 lppsq002a network[55905]: Bringing up loopback interface:  [  OK  ]
    Jan 15 11:04:45 lppsq002a network[55905]: Bringing up interface eth0:  RTNETLINK answers: File exists
    Jan 15 11:04:45 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:45 lppsq002a network[55905]: Bringing up interface eth1:  RTNETLINK answers: File exists
    Jan 15 11:04:45 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth2:  ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth2 has different MAC address than expected, ignoring.
    Jan 15 11:04:46 lppsq002a network[55905]: [FAILED]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth3:  RTNETLINK answers: File exists
    Jan 15 11:04:46 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth4:  ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth4 does not seem to be present, delaying initialization.
    Jan 15 11:04:46 lppsq002a network[55905]: [FAILED]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth5:  RTNETLINK answers: File exists
    Jan 15 11:04:46 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth6:  RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:47 lppsq002a network[55905]: Bringing up interface eth7:  RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a systemd[1]: network.service: control process exited, code=exited status=1
    Jan 15 11:04:47 lppsq002a systemd[1]: Failed to start LSB: Bring up/down networking.
    Jan 15 11:04:47 lppsq002a systemd[1]: Unit network.service entered failed state.
    Jan 15 11:04:47 lppsq002a systemd[1]: network.service failed.
    Jan 15 11:08:22 lppsq002a systemd[1]: Starting LSB: Bring up/down networking…
    Jan 15 11:08:22 lppsq002a network[56841]: Bringing up loopback interface:  [  OK  ]
    Jan 15 11:08:22 lppsq002a network[56841]: Bringing up interface eth0:  RTNETLINK answers: File exists
    Jan 15 11:08:22 lppsq002a network[56841]: [  OK  ]
    Jan 15 11:08:26 lppsq002a network[56841]: Bringing up interface eth1:  RTNETLINK answers: File exists
    Jan 15 11:08:26 lppsq002a network[56841]: [  OK  ]
    Jan 15 11:08:26 lppsq002a network[56841]: Bringing up interface eth2:  ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth2 has different MAC address than expected, ignoring.
    Jan 15 11:08:26 lppsq002a network[56841]: [FAILED]
    Jan 15 11:08:26 lppsq002a network[56841]: Bringing up interface eth3:  RTNETLINK answers: File exists
    Jan 15 11:08:27 lppsq002a network[56841]: [  OK  ]


2020-01-15-15_42_11-root-server

 

Another useful thing debug arguments is the -xe to do:

# journalctl -xe –no-pager

 

  • -x (– catalog)
    Augment log lines with explanation texts from the message catalog.
    This will add explanatory help texts to log messages in the output
    where this is available.
  •  -e ( –pager-end )  Immediately jump to the end of the journal inside the implied pager
      tool.

2020-01-15-15_42_32-root-server

Finally after fixing the /etc/sysconfig/networking-scripts/* IP configuration issues I had all the 8 Ethernet interfaces to work as expected
 

# systemctl status network


2020-01-15-16_15_38-root-server

 

 

2. Adding a new IP alias to eth0 interface


Further on I had  to add an IP Alias on the CenOS via its networking configuration, this is done by editing /etc/sysconfig/network-scripts/ifcfg* files.
To create an IP alias for first lan interface eth0, I've had to created a new file named ifcfg-eth0:0
 

linux:~# cd /etc/sysconfig/network-scripts/
linux:~# vim ifcfg-eth0:0


with below content

NAME="eth0:0"
ONBOOT="yes"
BOOTPROTO="none"
IPADDR="10.50.10.5"
NETMASK="255.255.255.0"


Adding this IP address network alias works across all RPM based distributions and should work also on Fedora and Open SuSE as well as Suse Enterprise Linux.
If you however prefer to use a text GUI and do it the CentOS server administration way you can use nmtui (Text User Interface for controlling NetworkManager). tool.
 

linux:~# nmtui

 

centos7_nmtui-ncurses-network-configuration-sysadmin-tool

nmtui_add_alias_interface-screenshot

How to install jcmd on CentOS 7 to diagnose running Java Virtual Machine crashing applications

Tuesday, January 14th, 2020

how-to-install-jcmd-centos-jcdm-java-logo-1

jcmd utility is well known in the Brane New wonderful world of Java but if you're like me a classical old school sysadmins and non-java developer you probably never heard it hence before going straight into how to install it on CentOS 7 Linux servers, I'll shortly say few words on what it is.
jcmd is used to send diagnostic requests to running Java Virtual Machine (JVM) it is available in both in Oracle Java as well as OpenJDK.
The requests jcmd sends to VM are based on the running Java PID ID and are pretty useful for controlling Java Flight Recordings, troubleshoot, and diagnose JVM and Java Applications. It must be used on the same machine where the JVM is running.

 Used without arguments or with the -l option, jcmd prints the list of running Java processes with their process id, their main class and their command line arguments.
When a main class is specified on the command line, jcmd sends the diagnostic command request to all Java processes for which the command line argument is a substring of the Java process' main class.
jcmd could be useful if the JConsoleJMX (Java Management Extensions) can't be used for some reason on the server or together with Java Visual VM (visual interface for viewing detailed info about Java App).

In most Linux distributionsas as  of year 2020 jcmd is found in  java-*-openjdk-headless.

To have jcmd on lets say Debian GNU / Linux, you're up to something like:

 

apt-get install –yes openjdk-12-jdk-headless
 

or

apt-get install openjdk-11-jdk-headless
however in CentOS
7 jcmd is not found in java*openjdk*headless but instead to have it on server, thus it take me a while to look up where it is foundso after hearing
from some online post it is part of package java*openjdk*devel* to make sure this so true, I've used the  –download-only option
 

 yum install –downloadonly –downloaddir=/tmp java-1.8.0-openjdk-devel

 


So the next question was how to inspect the downloaded rpm package into /tmp usually, this is possible via Midnight Commander (mc) easily to view contents, however as this
server did not have installed mc due to security policies I had to do it differently after pondering a while on how to to list the RPM package file content come up using following command

 

 

 rpm2cpio java-1.8.0-openjdk-devel-1.8.0.232.b09-0.el7_7.x86_64.rpm |cpio -idmv|grep -i jcmd|less

 


To then install  java-1.8.0-openjdk-devel-1.8.0.232.b09-0.el7_7.x86_64.rpm to do so run:

 

 

 

yum -y install  java-1.8.0-openjdk-devel-1.8.0*


Once the jcmd, I've created the following bash script  that was set that was tracking for application errors and checking whether the JBoss application server pool-available-count is not filled up and hence jboss refuses to serve connections  through jboss-cli.sh query automatically launching jcmd to get various diagnostic data about Java Virtual Machine (e.g. a running snapshot) – think of it like the UNIX top for debugging or Windows System Monitor but run one time. 

 

 

 

# PID_OF_JAVA=$(pgrep -l java)
# jcmd $PID_OF_JAVA GC.heap_dump GC.heap_dump_file-$(date '+%Y-%m-%d_%H-%M-%S').jfr
# jcmd $PID_OF_JAVA Thread.print > Thread.print-$(date '+%Y-%m-%d_%H-%M-%S').jfr


The produced log files can then be used by the developer to visualize some Java specific stuff "Flight recordings" like in below screenshot:

jcmd-java-tool-dump-jfr-flight-recordings-visualized-java 

If you're interested on some other interesting tools that can be used to Monitor  and Debug a Running Java VM take a look at Java's official documentation Monitoring Tools.
So that's all Mission Accomplished 🙂 Now the Java Application developer could observe the log and tell why exactly the application crashed after the multitude of thrown Exceptions in the JBoss server.log.

How to clear ARP cache on Linux / Windows for a single IP address / Flush All IPs ARP cache

Wednesday, December 11th, 2019

linux-how-to-delete-modify-arp-cache-entries-after-IP-is-migrated-from-one-server-or-VPN-host-to-another-resized

On times of Public Internet IP migration or Local IPs between Linux servers or especially in clustered Linux Application Services running on environments like Pacemaker / Corosync / Heartbeat with services such as Haproxy.
Once an IP gets migrated due to complex network and firewall settings often the Migrated IP from Linux Server 1 (A) to Linux Server 2 (B) keeps time until a request to reload the Internet server IP ARP cache with to point to the new IP location, causing a disruption of accessibility to the Newly configured IP address on the new locations. I will not get much into details here what are the ARP (Address Resolution protocol) and Network ARP records on a Network attached Computer and how they correspond uniquely to each IP address assigned on Ethernet or Aliased network Interfaces (eth0 eth0:1 eth0:2) . But in this article, I'll briefly explain once IP Version 4 address is migrated from one server Data Center location to another DC, how the unique corresponding ARP record kept in OS system memory should be flushed in the ARP corresponding Operating System so called ARP table (of which you should think as a logical block in memory keeping a Map of where IP addresses are located physically on a Network recognized by the corresponding Unique MAC Address.
 

1. List the current ARP cache entries do

Arp is part of net-tools on Debian GNU / Linux and is also available and installed by default on virtually any Linux distribution Fedora / CentOS / RHEL / Ubuntu / Arch Linux and even m$ Windows NT / XP / 2000 / 10 / whatever, the only difference is Linux tool has a bit of more functionality and has a bit more complex use.
Easiest use of arp on GNU / Linux OS-es is.
 

# arp -an 

sample-IP-address-list-with-the-assigned-ARP-cache-mac-addresses
The -a lists all records and -n flag is here to omit IP resolving as some IPs are really slow to resolve and output of command could get lagged.

2. Delete one IP entry from the cache


Assuming only one IP address was migrated, if you want to delete the IP entry from local ARP table on any interface:
 

# arp -d 192.168.0.8


It is useful to delete an ARP cached entry for IP address only on a certain interface, to do so:
 

# /usr/sbin/arp -i eth1 -d 10.0.0.1

 

3. Create ARP entry MAC address with a static one for tightened security


A useful Hack is to (assign) / bind specific Static MAC addresses to be static in the ARP cache, this is very useful to improve security and fight an ARP poisoning attacks.
Doing so is pretty easy, to do so:

Above will staticly make IP 192.168.0.8 to always appear in the ARP cache table to the MAC 00:50:ba:85:85:ca. So even if we have another system with the same MAC
trying to spoof our location and thus break our real record location for the Hostname in the network holding in reality the MAC 00:50:ba:85:85:ca, poisoning us
trying to make our host to recognize 192.168.0.8 to a different address this will not happen as the static ARP will be kept unchanged in ARP caching table.

 

 # arp -s 192.168.0.8 00:50:ba:85:85:ca

 

4. Flush all ARP records only for specific Ethernet Interface


After the IP on interface was migrated run:

 

# ip link set arp off dev eth0 ; ip link set arp on dev eth0

 

5. Remove a set of few IPs only migrated ARP cache entries

 

# for i in 192.168.0.1 10.0.0.1 172.168.0.3; do sudo arp -d $i; done


Once old ARP entries are removed the arp command would return as:

 

linux:~$ arp
? (192.168.0.8) at <incomplete>  on eth1
? (172.168.0.3) at <incomplete>  on eth2


The 192.168.0.8 / 172.168.0.3 entry now shows as incomplete, which means the ARP entry will be refreshed when it is needed again, this would also depend
on the used network switches / firewalls in the network settings so often could take up to 1 minute or so..

 

6. Flush all ARP table records on Linux

flush-all-arp-cache-addresses-on-linux-howto-with-ip-command

 

# ip -s -s neigh flush all

 

7. Delete ARP Cache on FreeBSD and other BSDs

# arp -d -a 

 

8.  Flush arp cache on Windows

Run command prompt as Administrator -> (cmd.exe)  and do:

C:\> ipconfig /all
netsh interface ip delete arpcache

 

9. Monitoring the arp table


On servers with multiple IP addresses, where you expect a number of IP addresses migrated to change it is useful to use watch + arp like so:
 

# watch -n 0.1 'arp -an'

The -n 0.1 will make the arp -an be rerun every 10 miliseconds and by the way is a useful trick to monitor stuff returned by commands that needs a higher refresh frequency.
 

Conclusion


In short in this article, was explained how to list your arp cache table.The arp command is also available both on Linux and Windows) and as integral part of OS networking it is useful to check thoroghfully to its man page (man arp).
Explained was how to create Static ARP table records to prevent ARP poisoning attacks on a server.
I went through how to delete only a single ARP records (in case if) only certain IPs on a host are changed and an ARP cache entry reload is needed, as well as how to flush the complete set of ARP records need to get refreshed, sometimes useful on networks with Buggy Network Switches or when completely changing the set of IP-addresses assigned on a server host.

How to change default Text editor in Linux

Saturday, August 31st, 2019

This is a very trivial question but, as I thought someone that is starting with Linux basics Operating might be interested I will shortly explain in this small article how to change default text editor on Linux.

Changing default text editor is especially helpful if you have to administer a newly purchased dedicated servers, that comes with default Operating System preinstalled.

By default many Linux distributions versions such as Debian / Ubuntu comes with nano comes with a default text editor nano (ANOther enhanced free Pico editor clone) many people as me are irritated and prefer to use instead vim (Vi Improved), mcedit (the Midnight Commander), joe or emacs as a default.
 

1. Changing default console text editor on Debian based Linux


On Debian / Ubuntu / Mint and other deb based distributions the easiest way to change text editor is with update-alternatives cmd.
 

update-alternatives –config editor


changing-default-text-editor-in-linux

Using Debian update-alternatives is useful as it makes the change OS global wide and the default mc viewer program mcview will also understand the change in the default text editor, which makes it the preferrable way to do it on deb based OS family.

An alternative way to set the default programs for the OS system wide is to create the respective symbolic link in /etc/alternatives actually what update-alternatives wrapper script does is exactly this it creates the required symlink.

2. Changing default text editor on any Linux


To change the text editor for only a single system existing user in /etc/passwd you need to edit $HOME/.bashrc, e.g. ~/.bashrc on Debian based Linux or on Fedora / RHEL / CentOS by adding to ~/.bash_profile
 

vim ~/.bashrc


And add

alias editor=vim

or

export EDITOR='/path/to/text-editor/program'
export VISUAL='/path/to/text-editor/program'

To change to mcedit for example when opening in any program that triggers to run default text editor

export EDITOR='/usr/bin/mcedit'
export VISUAL='/usr/bin/mcedit'


To make the change system wide on any Linux distribution you have to add the export EDITOR / export VISUAL at the end of /etc/bash.bashrc

To load the newly included .bashrc* instructions use source command
 

source ~/.bashrc

 

3. Changing the default text editor for mcview if all else fails

 

Once mc is running, use following menu keys order (also visible from Midnight Commander) menus:
 

    F9 Activates the top menu.
    o Selects the Option menu.
    c Opens the configuration dialog.
    i Toggles the use internal edit option.
    s Saves your preferences.

mcview-how-to-change-default-text-editor-screenshot

That's all folks Enjoy !

 

Check weather forecast from console (terminal) on GNU / Linux and FreeBSD howto

Friday, August 23rd, 2019

how to get weather forecast prognosis from command line text terminal / console on Linux and FreeBSD

Doing everything in Linux console / terminal is a question perhaps every Linux / BSD hacker wants to do as Graphical user interface and using web search or using Graphical Environment plugins is an unneded complexity + googling or duckduckgoing for weather to check your next vacation destination city has been more and more of a terrible experience (for me) as I'm not a big fan of using the OS in a GUI.
In that manner of thoughts, as a Linux console geek and hard core ASCII art fan. I was recently happy to find that  possible to check weather forecast in tty console or Linux terminal in a beautiful ascii art way easily through a Web wttr.in service – a web application weather forecast service that supports displaying the current and few days in future, weather forecast either in browser as a plain text or from the command line by simply accessing it with your favourite web access / transfer tool such as;
wget / curl or any of your favourite text browser elinks / lynx / w3m or if on *BSDs use fetch command.

 

Install Curl data transfer tool if it is not already


Wget is installed by default across most Linux distributions and fetch is present by default on BSDs, displaying it in text browser would perhaps be never used but if you decide to give it a try maybe try with elinks (to get colorful output), w3m and lynx will display a black and white results.

In case if you miss curl, install it:

On Debian distro

 

aptitude install -y curl


or Fedora

yum install -y curl


Of course to use wttr.in as it is Internet based Weather Forecast service the minimum you need to have is to have Internet connection to your Linux / BSD desktop computer.

Text based Weather Forecast Web App currently supports:

display the current weather as well as a 3-day weather forecast, split into morning, noon, evening and night

  • Temperature is displayed for morning, noon, evening and night (includes temperature range, wind speed and direction, viewing distance, precipitation amount and probability)
  • Provide results for Weather based on City / town / village location
  • Supports display of Moon Phases Forecast in calendar days
  • Supports multilingual names (Bulgarian Phonetic cyrillic / Russian and other exotic UTF-8 encodings such as Chineese and Japanese),  50+ languages are currently supported
  • Has ability for prognosis for hostname (domain) location based on an its IP GeoIP location on the Globe
  • Geographical locations / landmarks such as Lakes / Mountains etc. can be easily queried
  • Query results metrics could be configured, e.g. USCS units or EU and rest of world accepted ones (SI) metric
  • Displayed result could be either in ANSI (if from terminal / console / HTML if queried from browser or in PNG – if needed)

 

Where wttr.in could be useful ?

The best applications use, I can think of are for server (shell) / perl scripting automation purposes, it could be useful especially in TOO HOT, TOO, COLD, TOO WET location in Small and Middle sized Data Centers Green Energy (Sun Panel) Parks / Wind Energy situated Linux monitoring hosts to track possible problems of overheats or overcolding of servers due to abnormal excessive temperatures such as the ones we experienced this summer here All across in Europe or in too Cold DC locations such as heat locations Deserts in African Countries, Saudi Arabia or Chukotka or Siberia in Russia.
Other application is as a backup option to other normal Weather report services by PHP or Python scripts that fetch data, from multiple places.
Of course since this is a third party controlled service, the downtime is due to excessive connection requests, the service could get flooded and stopped working, but I guess for any Commercial use, wttr.in creator Igor Chubin would be happy to sell a specific crafted service for any end user candidates.


Here is few examples of the beautiful returned ASCII art formatted output of wttr.in.
 

1. Getting a three days Weather Forecast prognosis for city / town location

To get what is current weather in my current city of Living, Sofia Bulgaria just pass the city to the URL address

curl http://wttr.in/Sofia

text-console-wttr.in-Weather-forecast-Sofia-for-Linux

 

links http://wttr.in/Dobrich

 

curl-Linux-show--Dobrich-Weather-forecast-in-lynx-text-browser


Default links (Linux) www text browser produces ugly black and white

2. Displaying Weather forecast with wget

 

wget -O- -q http://wttr.in


getting-weather-forecast-on-linux-terminal-console-with-wget-command

If you're lazy you can even omit the http:// as wget will look for HyperText Transmission Protocol by itself

 

wget -O- -q wttr.in

 

3. Getting Forecast results for a Tourist Destination


Lets get the weather forecast for the popular tourist Bulgarian destination of the Seven Rila Lakes (near Rila Monastery), situated in the Rila Mountain BG.

 

curl http://wttr.in/Seven+Rila+Lakes

 

Console-terminal-Weather-forecast-Linux-Seven-Rila-Lakes

 

 

4. Display Forecast for a specific server IP


Displaying information on specific server IP address current situated in GeoIP database, of course could be not really true, as the IP could be just a Load Balancer a router that does NAT to some internal DMZ-ed location server, but anyways it is a cool feature.

Lets get information on what is the weather on Google Global's Public DNS server IP 8.8.8.8 so commonly used to guarantee a Windows and Linux Desktop client machines Internet connectivity.
 

curl wttr.in/@8.8.8.8

 

wttr.in-Linux-text--forecast-service-curl-screenshot Google Public DNS location weather forecast

5. Download PNG image picture from wttr.in service

 


Lets say you want to get a 3 days standard Weather forecast for the popular Black Sea Resort town in Bulgaria Pomorie (a beautiful sea city which has even a functioning 5 Monks Monastery Pomorie Monastery situated near sea coast)

 

curl http://wttr.in/Pomorie.png
 

 

–2019-08-22 20:15:51–  http://wttr.in/Pomorie.png
Resolving wttr.in (wttr.in)… 5.9.243.187
Connecting to wttr.in (wttr.in)|5.9.243.187|:80… connected.
HTTP request sent, awaiting response… 200 OK
Length: 42617 (42K) [image/png]
Saving to: ‘Pomorie.png’

Pomorie.png                                     100%[=======================================================================================================>]  41.62K  –.-KB/s    in 0.07s   

2019-08-22 20:15:52 (586 KB/s) – ‘Pomorie.png’ saved [42617/42617]

 

Note: The generated .png is again the ASCII art produced by a direct text fetch bug in pic format

 

6. Displaying Current Moon Phase


If you want to enjoy a text based Moon phase picture through wttr.in 🙂

wget -O- -q wttr.in/Moon


Display-current-Phase-of-Moon-in-terminal-console-Linux-wttr.in-service

You can also get a Moon Phase prognosis for a current future date or get a previous date phase

 

curl wttr.in/moon@2019-09-15

Full-Moon-Weather-forecast-text-console-reporting-via-wttr.in-on-Gnu_Linux


Full Moon Madness !! – Vampires are out beaware and Enjoy the ultra kewl ASCII Colorful Art 🙂
 

7. Getting help for wttr.in terminal Waether Forecast results

 

 

$ curl wttr.in/:help
Usage:

 

    $ curl wttr.in          # current location
    $ curl wttr.in/muc      # weather in the Munich airport

Supported location types:

    /paris                  # city name
    /~Eiffel+tower          # any location
    /Москва                 # Unicode name of any location in any language
    /muc                    # airport code (3 letters)
    /@stackoverflow.com     # domain name
    /94107                  # area codes
    /-78.46,106.79          # GPS coordinates

Special locations:

    /moon                   # Moon phase (add ,+US or ,+France for these cities)
    /moon@2016-10-25        # Moon phase for the date (@2016-10-25)

Units:

    m                       # metric (SI) (used by default everywhere except US)
    u                       # USCS (used by default in US)
    M                       # show wind speed in m/s

View options:

    0                       # only current weather
    1                       # current weather + 1 day
    2                       # current weather + 2 days
    A                       # ignore User-Agent and force ANSI output format (terminal)
    F                       # do not show the "Follow" line
    n                       # narrow version (only day and night)
    q                       # quiet version (no "Weather report" text)
    Q                       # superquiet version (no "Weather report", no city name)
    T                       # switch terminal sequences off (no colors)

PNG options:

    /paris.png              # generate a PNG file
    p                       # add frame around the output
    t                       # transparency 150
    transparency=…        # transparency from 0 to 255 (255 = not transparent)

Options can be combined:

    /Paris?0pq
    /Paris?0pq&lang=fr
    /Paris_0pq.png          # in PNG the file mode are specified after _
    /Rome_0pq_lang=it.png   # long options are separated with underscore

Localization:

    $ curl fr.wttr.in/Paris
    $ curl wttr.in/paris?lang=fr
    $ curl -H "Accept-Language: fr" wttr.in/paris

Supported languages:

    af da de el et fr fa hu id it nb nl pl pt-br ro ru tr uk vi (supported)
    az be bg bs ca cy cs eo es fi ga hi hr hy is ja jv ka kk ko ky lt lv mk ml nl fy nn pt pt-br sk sl sr sr-lat sv sw th te uz zh zu he (in progress)

Special URLs:

    /:help                  # show this page
    /:bash.function         # show recommended bash function wttr()
    /:translation           # show the information about the translators

 


 

 

8. Comparing two cities weather from command line

 


One useful use of wttr.in if you plan to travel from Location city A to Location city B is to compare the temperatures with a simple bash one liner script:

 

 

 

diff -Naur <(curl -s http://wttr.in/Sofia ) <(curl -s http://wttr.in/Beograd )

 

 

9. Using ansiweather command to get Weather Temperature / Wind / Humidity in one line beuatiful text

 


If you go and install answeather Linux package

 

apt-get install –yes ansiweather


You will get a shell script wrapper with ANSI colors and Unicode symbols support. Weather data comes from OpenWeatherMap, this is useful if wttr.in is not working due to some URL malfunction (due to service is DoS-ed) etc.

 

ansiweather -l Atina

 

ansiweather-Atina-weather-forecast-result-linux-text-console

Lets use ansiweather to print the weather prognosis for upcoming 5 days for near port of Burgas, BG
 

ansiweather -F -l Burgas

ansiweather-print-weather-forecast-prognosis-for-5-days-in-Linux-text-terminal

 

10. Get all Weather current forecast for each Capital in the world


You can download and use this simple plain text file list of All Country Capitals in the World (country-capitals-all-world.txt) with ansiweather and a bash loop to get displayed each and every current day Weather Forecast in the World, here is how:

 

while read line; do ansiweather -l $line; sleep 3; done < country-capitals-all-world.txt


ansiweather-all-countires-capitals-result

As you can see some of the very exotic third world capitals does not return data so 'ERROR: Cannot fetch weather data' is returned.


You can also substitute ansiweather with curl wttr.in/$line to do get the beautiful ASCII art 3 days weather forecast via wttr.in

 

while read line; do curl http://wttr.in/$line; sleep 3; done < country-capitals-all-world.txt


I'll be happy to know other nice ASCII Art supporting Web service to enjoy from text terminal on Linux (nomatter useful or) just funny joyful prank maniacal pranks such as Watching text ASCII version remake of Star Wars Classic Movie by simply telnetting to towel.blinkenlights.nl (if you haven't so just telnet and enjoy the streamed ASCIIs ! 🙂

 

telnet towel.blinkenlights.nl

 

watch-star-wars-ascii-art-version-remake-online-with-telnet-on-linux-console-terminal

 

Talking about fun and ASCII, its worthy to mention hollywood Linux package

hipo@jeremiah:~/Desktop$ apt-cache show hollywood|grep -i desc -A 3
Description-en: fill your console with Hollywood melodrama technobabble
 This utility will split your console into a multiple panes of genuine
 technobabble, perfectly suitable for any Hollywood geek melodrama.
 It is particularly suitable on any number of computer consoles in the


Description-md5: 768f44c76220ea2b35f855ea34c8bc35
Homepage: http://launchpad.net/hollywood
Section: games
Priority: optional


Once installed on Debian with:

aptitude install -y hollywood

You can get in a rapid manner plenty of tmux (screen like – virtual console emulator) split screen statistics about your notebook / workstation / server CPU usage, mlocate.db status, info about plugged in machine voltage, Speedometer (statistics about Network bandwidth usage), System load avarage (CPU Count, Memory Utilization) and some other random info coming out of dmesg kernel log and more. The information displayed in splitted windows changes rapidly and (assuming you run it at home Desktop with a soundblaster) and not remotely, a james bond Agent 007 soundtrack is played on the back, that brings up one's adrenaline and makes it look even cooler.

hollywood-melodrama-technobubble-split-console-multiple-panes-for-genuine-technobubble

To give you an idea what to expect, here is shot of /usr/games/hollywood (the program start binary location) on Debian GNU / Linux running, Enjoy! 🙂
 

What is inode and how to find out which directory is eating up all your filesystem inodes on Linux, Increase inode count on a ext3 ext4 and ufs filesystems

Tuesday, August 20th, 2019

what-is-inode-find-out-which-filesystem-or-directory-eating-up-all-your-system-inodes-linux_inode_diagram

If you're a system administrator of multiple Linux servers used for Web serving delivery / Mail server sysadmin, Database admin or any High amount of Drives Data Storage used for backup servers infra, Data Repository administrator such as Linux hosted Samba / CIFS shares, etc. or using some Linux Hosting Provider to host your website or any other UNIX like Infrastructure servers that demands a storage of high number of files under a Directory  you might end up with the common filesystem inode depletion issues ( Maximum Inode number for a filesystem is predefined, limited and depending on the filesystem configured size).

In case a directory stored files end up exceding the amount of possible addressable inodes could prevent any data to be further assiged and stored on the Filesystem.

When a device runs out of inodes, new files cannot be created on the device, even though there may be plenty free space available and the first time it happened to me very long time ago I was completely puzzled how this is possible as I was not aware of Inodes existence  …

Reaching maximum inodes number (e.g. inode depletion), often happens on Busy Mail servers (receivng tons of SPAM email messages) or Content Delivery Network (CDN – Website Image caching servers) which contain many small files on EXT3 or EXT4 Journalled filesystems. File systems (such as Btrfs, JFS or XFS) escape this limitation with extents or dynamic inode allocation, which can 'grow' the file system or increase the number of inodes.

 

Hence ending being out of inodes could cause various oddities on how stored data behaves or communicated to other connected microservices and could lead to random application disruptions and odd results costing you many hours of various debugging to find the root cause of inodes (index nodes) being out of order.

In below article, I will try to give an overall explanation on what is an I-Node on a filesystem, how inodes of FS unit could be seen, how to diagnose a possible inode poblem – e.g.  see the maximum amount of inodes available per filesystem and how to prepare (format) a new filesystem with incrsed set of maximum inodes.

 

What are filesystem i-nodes?

 

This is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory.
The data structure described in the inodes might vary slightly depending on the filesystem but usually on EXT3 / EXT4 Linux filesystems each inode stores the index to block that contains attributes and disk block location(s) of the object's data.
– Yes for those who are not aware on how a filesystem is structured on *nix it does allocate all stored data in logical separeted structures called data blocks. Each file stored on a local filesystem has a file descriptor, there are virtual unit structures file tables and each of the inodes that are a reference number has a own data structure (inode table).

Inodes / "Index" are slightly unusual on file system structure that stored the access information of files as a flat array on the disk, with all the hierarchical directory information living aside from this as explained by Unix creator and pioneer- Dennis Ritchie (passed away few years ago).

what-is-inode-very-simplified-explanation-diagram-data

Simplified explanation on file descriptors, file table and inode, table on a common Linux filesystem

Here is another description on what is I-node, given by Ken Thompson (another Unix pioneer and father of Unix) and Denis Ritchie, described in their paper published in 1978:

"    As mentioned in Section 3.2 above, a directory entry contains only a name for the associated file and a pointer to the file itself. This pointer is an integer called the i-number (for index number) of the file. When the file is accessed, its i-number is used as an index into a system table (the i-list) stored in a known part of the device on which the directory resides. The entry found thereby (the file's i-node) contains the description of the file:…
    — The UNIX Time-Sharing System, The Bell System Technical Journal, 1978  "


 

What is typical content of inode and how I-nodes play with rest of Filesystem units?


The inode is just a reference index to a data block (unit) that contains File-system object attributes. It may include metadata information such as (times of last change, access, modification), as well as owner and permission data.

 

On a Linux / Unix filesystem, directories are lists of names assigned to inodes. A directory contains an entry for itself, its parent, and each of its children.

Structure-of-inode-table-on-Linux-Filesystem-diagram

 

Structure of inode table-on Linux Filesystem diagram (picture source GeeksForGeeks.org)

  • Information about files(data) are sometimes called metadata. So you can even say it in another way, "An inode is metadata of the data."
  •  Inode : Its a complex data-structure that contains all the necessary information to specify a file. It includes the memory layout of the file on disk, file permissions, access time, number of different links to the file etc.
  •  Global File table : It contains information that is global to the kernel e.g. the byte offset in the file where the user's next read/write will start and the access rights allowed to the opening process.
  • Process file descriptor table : maintained by the kernel, that in turn indexes into a system-wide table of files opened by all processes, called the file table .

The inode number indexes a table of inodes in a known location on the device. From the inode number, the kernel's file system driver can access the inode contents, including the location of the file – thus allowing access to the file.

  •     Inodes do not contain its hardlink names, only other file metadata.
  •     Unix directories are lists of association structures, each of which contains one filename and one inode number.
  •     The file system driver must search a directory looking for a particular filename and then convert the filename to the correct corresponding inode number.

The operating system kernel's in-memory representation of this data is called struct inode in Linux. Systems derived from BSD use the term vnode, with the v of vnode referring to the kernel's virtual file system layer.


But enough technical specifics, lets get into some practical experience on managing Filesystem inodes.
 

Listing inodes on a Fileystem


Lets say we wan to to list an inode number reference ID for the Linux kernel (files):

 

root@linux: # ls -i /boot/vmlinuz-*
 3055760 /boot/vmlinuz-3.2.0-4-amd64   26091901 /boot/vmlinuz-4.9.0-7-amd64
 3055719 /boot/vmlinuz-4.19.0-5-amd64  26095807 /boot/vmlinuz-4.9.0-8-amd64


To list an inode of all files in the kernel specific boot directory /boot:

 

root@linux: # ls -id /boot/
26091521 /boot/


Listing inodes for all files stored in a directory is also done by adding the -i ls command flag:

Note the the '-1' flag was added to to show files in 1 column without info for ownership permissions

 

root@linux:/# ls -1i /boot/
26091782 config-3.2.0-4-amd64
 3055716 config-4.19.0-5-amd64
26091900 config-4.9.0-7-amd64
26095806 config-4.9.0-8-amd64
26091525 grub/
 3055848 initrd.img-3.2.0-4-amd64
 3055644 initrd.img-4.19.0-5-amd64
26091902 initrd.img-4.9.0-7-amd64
 3055657 initrd.img-4.9.0-8-amd64
26091756 System.map-3.2.0-4-amd64
 3055703 System.map-4.19.0-5-amd64
26091899 System.map-4.9.0-7-amd64
26095805 System.map-4.9.0-8-amd64
 3055760 vmlinuz-3.2.0-4-amd64
 3055719 vmlinuz-4.19.0-5-amd64
26091901 vmlinuz-4.9.0-7-amd64
26095807 vmlinuz-4.9.0-8-amd64

 

To get more information about Linux directory, file, such as blocks used by file-unit, Last Access, Modify and Change times, current External Symbolic or Static links for filesystem object:
 

root@linux:/ # stat /etc/
  File: /etc/
  Size: 16384         Blocks: 32         IO Block: 4096   catalog
Device: 801h/2049d    Inode: 6365185     Links: 231
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-08-20 06:29:39.946498435 +0300
Modify: 2019-08-14 13:53:51.382564330 +0300
Change: 2019-08-14 13:53:51.382564330 +0300
 Birth: –

 

Within a POSIX system (Linux-es) and *BSD are more or less such, a file has the following attributes[9] which may be retrieved by the stat system call:

   – Device ID (this identifies the device containing the file; that is, the scope of uniqueness of the serial number).
    File serial numbers.
    – The file mode which determines the file type and how the file's owner, its group, and others can access the file.
    – A link count telling how many hard links point to the inode.
    – The User ID of the file's owner.
    – The Group ID of the file.
    – The device ID of the file if it is a device file.
    – The size of the file in bytes.
    – Timestamps telling when the inode itself was last modified (ctime, inode change time), the file content last modified (mtime, modification time), and last accessed (atime, access time).
    – The preferred I/O block size.
    – The number of blocks allocated to this file.

 

Getting more extensive information on a mounted filesystem


Most Linuxes have the tune2fs installed by default (in debian Linux this is through e2fsprogs) package, with it one can get a very good indepth information on a mounted filesystem, lets say about the ( / ) root FS.
 

root@linux:~# tune2fs -l /dev/sda1
tune2fs 1.44.5 (15-Dec-2018)
Filesystem volume name:   <none>
Last mounted on:          /
Filesystem UUID:          abe6f5b9-42cb-48b6-ae0a-5dda350bc322
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file
Filesystem flags:         signed_directory_hash
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              30162944
Block count:              120648960
Reserved block count:     6032448
Free blocks:              13830683
Free inodes:              26575654
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      995
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Filesystem created:       Thu Sep  6 21:44:22 2012
Last mount time:          Sat Jul 20 11:33:38 2019
Last write time:          Sat Jul 20 11:33:28 2019
Mount count:              6
Maximum mount count:      22
Last checked:             Fri May 10 18:32:27 2019
Check interval:           15552000 (6 months)
Next check after:         Wed Nov  6 17:32:27 2019
Lifetime writes:          338 GB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:              256
Required extra isize:     28
Desired extra isize:      28
Journal inode:            8
First orphan inode:       21554129
Default directory hash:   half_md4
Directory Hash Seed:      d54c5a90-bc2d-4e22-8889-568d3fd8d54f
Journal backup:           inode blocks


Important note to make here is file's inode number stays the same when it is moved to another directory on the same device, or when the disk is defragmented which may change its physical location. This also implies that completely conforming inode behavior is impossible to implement with many non-Unix file systems, such as FAT and its descendants, which don't have a way of storing this invariance when both a file's directory entry and its data are moved around. Also one inode could point to a file and a copy of the file or even a file and a symlink could point to the same inode, below is example:

$ ls -l -i /usr/bin/perl*
266327 -rwxr-xr-x 2 root root 10376 Mar 18  2013 /usr/bin/perl
266327 -rwxr-xr-x 2 root root 10376 Mar 18  2013 /usr/bin/perl5.14.2

A good to know is inodes are always unique values, so you can't have the same inode number duplicated. If a directory is damaged, only the names of the things are lost and the inodes become the so called “orphan”, e.g.  inodes without names but luckily this is recoverable. As the theory behind inodes is quite complicated and is complicated to explain here, I warmly recommend you read Ian Dallen's Unix / Linux / Filesystems – directories inodes hardlinks tutorial – which is among the best academic Tutorials explaining various specifics about inodes online.

 

How to Get inodes per mounted filesystem

 

root@linux:/home/hipo# df -i
Filesystem       Inodes  IUsed   IFree IUse% Mounted on

 

dev             2041439     481   2040958   1% /dev
tmpfs            2046359     976   2045383   1% /run
tmpfs            2046359       4   2046355   1% /dev/shm
tmpfs            2046359       6   2046353   1% /run/lock
tmpfs            2046359      17   2046342   1% /sys/fs/cgroup
/dev/sdb5        1221600    2562   1219038   1% /usr/var/lib/mysql
/dev/sdb6        6111232  747460   5363772  13% /var/www/htdocs
/dev/sdc1      122093568 3083005 119010563   3% /mnt/backups
tmpfs            2046359      13   2046346   1% /run/user/1000


As you see in above output Inodes reported for each of mounted filesystems has a specific number. In above output IFree on every mounted FS locally on Physical installed OS Linux is good.


Here is an example on how to recognize a depleted Inodes on a OpenXen Virtual Machine with attached Virtual Hard disks.

linux:~# df -i
Filesystem         Inodes     IUsed      IFree     IUse%   Mounted on
/dev/xvda         2080768    2080768     0      100%    /
tmpfs             92187      3          92184   1%     /lib/init/rw
varrun            92187      38          92149   1%    /var/run
varlock            92187      4          92183   1%    /var/lock
udev              92187     4404        87783   5%    /dev
tmpfs             92187       1         92186   1%    /dev/shm

 

Finding files with a certain inode


At some cases if you want to check all the copy files of a certain file that have the same i-node pointer it is useful to find them all by their shared inode this is possible with simple find (below example is for /usr/bin/perl binary sharing same inode as perl5.28.1:

 

ls -i /usr/bin/perl
23798851 /usr/bin/perl*

 

 find /usr/bin -inum 435308 -print
/usr/bin/perl5.28.1
/usr/bin/perl

 

Find directory that has a large number of files in it?

To get an overall number of inodes allocated by a certain directory, lets say /usr /var

 

root@linux:/var# du -s –inodes /usr /var
566931    /usr
56020    /var/

To get a list of directories use by inode for a directory with its main contained sub-directories sorted from 1 till highest number use:
 

du -s –inodes * 2>/dev/null |sort -g

 

Usually running out of inodes means there is a directory / fs mounts that has too many (small files) that are depleting the max count of possible inodes.

The most simple way to list directories and number of files in them on the server root directory is with a small bash shell loop like so:
 

for i in /*; do echo $i; find $i |wc -l; done


Another way to identify the exact directory that is most likely the bottleneck for the inode depletion in a sorted by file count, human readable form:
 

find / -xdev -printf '%h\n' | sort | uniq -c | sort -k 1 -n


This will dump a list of every directory on the root (/) filesystem prefixed with the number of files (and subdirectories) in that directory. Thus the directory with the largest number of files will be at the bottom.

 

The -xdev switch is used to instruct find to narrow it's search to only the device where you're initiating the search (any other sub-mounted NAS / NFS filesystems from a different device will be omited).

 

Print top 10 subdirectories with Highest Inode Usage

 

Once identifed the largest number of files directories that is perhaps the issue, to further get a list of Top subdirectories in it with highest amount of inodes used, use below cmd:

 

for i in `ls -1A`; do echo "`find $i | sort -u | wc -l` $i"; done | sort -rn | head -10

 

To list more than 10 of the top inodes used dirs change the head -10 to whatever num needed.

N.B. ! Be very cautious when running above 2 find commands on a very large filesystems as it will be I/O Excessive and in filesystems that has some failing blocks this could create further problems.

To omit putting a high I/O load on a production filesystem, it is possible to also use du + very complex regular expression:
 

cd /backup
du –inodes -S | sort -rh | sed -n         '1,50{/^.\{71\}/s/^\(.\{30\}\).*\(.\{37\}\)$/\1…\2/;p}'


Results returned are from top to bottom.

 

How to Increase the amount of Inodes count on a new created volume EXT4 filesystem

Some FS-es XFS, JFS do have an auto-increase inode feature in case if their is physical space, whether otheres such as reiserfs does not have inodes at all but still have a field reported when queried for errors. But the classical Linux ext3 / ext4 does not have a way to increase the inode number on a live filesystem. Instead the way to do it there is to prepare a brand new filesystem on a Disk / NAS / attached storage.

The number of inodes at format-time of the block storage can be as high as 4 billion inodes. Before you create the new FS, you have to partition the new the block storage as ext4 with lets say parted command (or nullify the content of an with dd to clean up any previous existing data on a volume if there was already existing data:
 

parted /dev/sda


dd if=/dev/zero of=/dev/path/to/volume


  then format it with this additional parameter:

 

mkfs.ext4 -N 3000000000 /dev/path/to/volume

 

Here in above example the newly created filesystem of EXT4 type will be created with 3 Billion inodes !, for setting a higher number on older ext3 filesystem max inode count mkfs.ext3 could be used instead.

Bear in mind that 3 Billion number is a too high number and if you plan to have some large number of files / directories / links structures just raise it up to your pre-planning requirements for FS. In most cases it will be rarely anyone that want to have this number higher than 1 or 2 billion of inodes.

On FreeBSD / NetBSD / OpenBSD setting inode maximum number for a UFS / UFS2 (which is current default FreeBSD FS), this could be done via newfs filesystem creation command after the disk has been labeled with disklabel:

 

freebsd# newfs -i 1024 /dev/ada0s1d

 

Increase the Max Count of Inodes for a /tmp filesystem

 

Sometimes on some machines it is necessery to have ability to store very high number of small files (e.g. have a very large number of inodes) on a temporary filesystem kept in memory. For example some web applications served by Web Server Apache + PHP, Nginx + Perl-FastCGI are written in a bad manner so they kept tons of temporary files in /tmp, leading to issues with exceeded amount of inodes.
If that's the case to temporary work around you can increase the count of Inodes for /tmp to a very high number like 2 billions using:

 

mount -o remount,nr_inodes=<bignum> /tmp

To make the change permanent on next boot if needed don't forget to put the nr_inodes=whatever_bignum as a mount option for the temporary fs to /etc/fstab

Eventually, if you face this issues it is best to immediately track which application produced the mess and ask the developer to fix his messed up programs architecture.

 

Conclusion

 

It was explained on the very common issue of having maximum amount of inodes on a filesystem depleted and the unpleasent consequences of inability to create new files on living FS.
Then a general overview was given on what is inode on a Linux / Unix filesystem, what is typical content of inode, how inode addressing is handled on a FS. Further was explained how to get basic information about available inodes on a filesystem, how to get a filename/s based on inode number (with find), the well known way to determine inode number of a directory or file (with ls) and get more extensive information on a FS on inodes with tune2fs.
Also was explained how to identify directories containing multitudes of files in order to determine a sub-directories that is consuming most of the inodes on a filesystem. Finally it was explained very raughly how to prepare an ext4 filesystem from scratch with predefined number to inodes to much higher than the usual defaults by mkfs.ext3 / mkfs.ext4 and *bsds newfs as well as how to raise the number of inodes of /tmp tmpfs temporary RAM filesystem.

Helpful Hints For Starting A Small WordPress Website or Ecomerce Business

Wednesday, August 14th, 2019

hints-for-starting-wordpress-site

Wordpress is the web application collection of PHP program behind thirty four percent (43%) of the internet’s websites, and fifteen percent (50%) of the top one hundred websites in the world, so if you’re considering it for your website then you’re perhaps thinking in the right direction. Small start-up projects a community website or even a small personal owned blog or mid to even large business presentation site  can benefit greatly from setting up their Web Platrform or Ecommerce shops on a WordPress website platform (that of itself depends just on a small number of technologies such as a Linux server with a Web Server installed on it to serve PHP as well as some kind of Linux host installed Database  backend engine such as MYSQL / PostgreSQL etc. …

But if you really want to create a successful ecommerce website on WordPress, that can seem a little intimidating at first as the general complexity to start up with WordPress looks very scary in the beginning. However in this article I’ll point to fewhelpful hints should get you off on the right foot, and make your entry into the world of Wodpress / WP Ecommerce a little easier and less scary.

This article is to be less technical than expected and in that will contrast slightly with many of the articles on this blog, the target audience is more of Web Marketing Manager or a Start-up Search Engine Optimization person at a small personal project or employed in the big bad corporate world.This is no something new that is going to be outlined in this article but a general rules that are known for the professional SEO Gurus but is most likely to be helpful for the starting persons.

If you happen to be one of these you should know you have to follow a set of well known rules on the website structure text, descriptions, text, orientation, ordering of menus and data etc. in order to have the WordPress based website running at full speed attracting more visitors to your site.
 

Photos
 

 

Importance of Photos on a Webiste
Although the text for your website is very important – more on that later – when a user first opens up your website in their browser, their eyes are going to be caught by the images that you have laid out on your website. Not using images is a big mistake, since it bores users’ eyes and makes your website seem amateur and basic, but using low quality images or irrelevant images can also harm your chances of appearing authentic to a user (yes here on this blog there are some of this low quality pictures but this is due to fact this website is more of information blog and not ecommerce. Thus at best case always make sure that you find the best, high-quality images for your website – make sure that you have the correct rights to use the images as well (as copyright infrignmenets) could cause you even a law suits ending in hundred or thousand dollar fines or even if this doesn't happen any publicity of such would reduce your website indexing rating. The images placed should always be relevant to your website. If you find a breath-taking sunset or tech-gadget picture, that’s great, but maybe not for your healthy food ecommerce store, but for your personal ranting or describing a personal experience.

 

Product Photos


Assuming that sooner or later even if you have a community website you will want to monerize it to bring back to yourself in material form at least part of the many years effort to bring the site to the web rank gained.
Leading on from that point, you’re going to be selling or advertise items – that’s the whole point of ecommerce. But users often find ads / online shopping frustrating due to not being able to properly see and understand what they’re buying before they make their purchase. This can lead to ‘buyer’s remorse’, and, consequently, refunds galore, which is not what you want. Make sure that images of your products are always available and of a high quality – investing in a fairly high quality camera might be a good idea – and consider many pictures for different angles or even rotating images so that the user can decide for themself which angle they want to look at.

 

Engaging Descriptions


“I can guarantee that you can’t remember the last five product descriptions you read – not even word-for-word, but the general ideas and vocabulary used will have been tossed into your short-term memory and forgotten in an instant. This is where your website can shine, and become better than ninety percent of those lingering on the internet,” Matthew Kelly, a project manager at WriteMyX and NextCoursework, suggests, “since putting effort into writing your product descriptions and making them lively and engaging will make your website memorable, and your subscribers will turn helpfully soon loyal customers will be more likely to come back time and time again and become repeat business, as well as mention you to their friends (social mounth to mouth marketing) and that way working as free advertising for you and making your website incredibly effective.”

 

Mobile-Friendly

 

Which device is most used to check email Laptop / PC or Mobile statistics as of year 2019

These days with the bloom of Mobile Devices that are currently overrunning the user of normal Desktop PCs, Laptops and Tablets and this trend is likely to stay and even increase, “If your website isn’t mobile-friendly in this day and age, then you won’t get anywhere with it.” Anne Baker, a marketer at BritStudent and Australia2Write, states. “Most people use their phones when they access websites, especially when they go shopping on the internet.

Statistics on user stay (secs / mins) stay on a website from Desktop PC and Mobile devices

On WordPress, this means finding a more recent theme – an older theme, maybe four-five years old, will probably not support mobile, and you just can’t afford to lose out on the mobile market.” In short, find yourself a mobile-friendly theme or install the right WordPress Pluguin that will enable you to have a Mobile Friendly theme in case if blog is accessed from a Mobile Dev or many of your customers will become frustrated with the badly formatted ‘mobile’ version of your website that they end up using, which might be for instance meant for a much larger screen. It can also ruin the atmosphere (experience) created at the accessed user site and have negative impact on your audience opion of your site or business. This is even more the case  if your website or webapp is targetting to be modern and keeping with the times – or especially if it deals with IT and electronics (where the competition is huge)!

 

Registration

 

Registration Ecommerce website

Registration form (Sign Up) on a website and the overall business cycle idea behind web product or business is of critical importance as this is the point that will guarantee intimidation with the customer, failing to have the person be engaged will quickly make your website rank lower and your producs less wanted. The general rule here is to make your registration be an easy (to orientate for the user) and be present on a very visible place on the site.

Registration steps should be as less as possible as this might piss off the user and repel him out of the site before the registration is completed. Showing oportunity to register with a Pop-Up window (while the user clicks on a place showing interest for the produce might be useful in some cases but generally might also push the user back so if you decide to implement it do it with a lot of care (beware of too much aggressive marketing on our site).

An example


The registration process should be as intimidating as possible to leave joy in the user that might later return and log in to your site or ecommerce platform, e.g. be interested to stay for a longer time. The marketing tactic aiming to make the user stay for a longer time on the website (dragging his attention / interest to stuff)  is nothing new by the way as it is well known marketing rule integrated in every supermarket you buy groceries, where all is made to keep you in the shop for as longer as possible. Research has shown that spending longer time within the supermarket makes the user buy more.

 

Returning customers can be intimidated with membership or a free gift (be it even virtual picture gift – free email whatever) or information store place could be given or if products are sold, registration will be obligatory to make them use their payment method or delivery address on next login to easify the buy out process. But if registration is convoluted and forced (e.g. user is somehow forced to become meber) then many customers will turn away and find another website for their shopping needs. Using a method like Quora’s ‘login to see more’ in that case might be a good idea even though for me this is also a very irritating and irritating – this method however should never be used if you run a ecommerce selling platform, on ecommerce site gatekeeping will only frustrate customers. Login is good to be implmeneted as a popup option (and not taking too much of the screen). Sign up and Login should be simplistic and self-explanatory – always not required but optioned and user should get the understanding of the advantage to be a member of the website if possible before the sign up procedure. Then, customers are more likely to sign up and won’t feel like they’ve been pushed into the decision – or pushed away, as the case may be.

Katrina Hatchett works as a lifestyle blogger at both Academic Brits and Assignment Help, due to a love of literature and writing, which she has had since youth. Throughout her career, she has become involved with many projects, such as writing for the PhD Kingdom blog.