29Aug 2012 by Asim Zeeshan 1 Comment

How to find zombie processes on linux

CentOS, Linux, Tips and Tricks, Ubuntu
My NAGIOS monitor alerted me that of my dedicated server has 10 Zombie processes, how to find Zombie processes via command line on Linux especially CentOS? [code] ps aux | awk '{ print $8 " " $2 }' | grep -w Z [/code] So it returns state (Z = Zombie) and the process id (PID) [code]root@sirius [~]# ps aux | awk '{ print $8 " " $2 }' | grep -w Z Z 4399 Z 4435 Z 4868 Z 5143 Z 5400 Z 5834 Z 7584 Z 11943 Z 16286 Z 24365[/code] Technically, you cannot kill a zombie process since its already dead but the entry in the process table is not removed because the parent will access the result via the PID in the process table.
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27May 2012 by Asim Zeeshan No Comments

How to find specific files and send alerts

CentOS, How to, Linux, Tips and Tricks, Ubuntu
Maintaining a shared hosting server is a full time job but tools and proper checks and balances can help make this burden lot less. I manage a shared hosting server for one of my friends and numerous times the scripts that people have installed over on their websites have vulnerabilities and hackers exploit it to upload stuff that mass-email or do other nasty stuff. Luckily, most of these exploits have common patterns like files names or other signatures that make them traceable (most of the time the so called hackers are just kiddy scripts) Create a file and put this in it [code]#!/bin/bash find /home -name 'paypal.com*' | mail -s '[Woodcrest] Phishing Alert!' me@mydomain.com find /home -name 'rout.php' | mail -s '[Woodcrest] Phishing Alert - Mail Bomber!' me@mydomain.com[/code] This is…
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26May 2012 by Asim Zeeshan 2 Comments

package-cleanup: command not found

CentOS, How to, Linux, Tips and Tricks
I tried to do package-cleanup and found this [code highlight="2"]root@ns1 [~]# package-cleanup --problems -bash: package-cleanup: command not found[/code] If I was on Ubuntu, I would have done "apt-get install package-cleanup" but it does not work that way on CentOS, its actually available in yum-utils package, install it by typing [code]yum install yum-utils[/code] Enjoy!!
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25May 2012 by Asim Zeeshan No Comments

How to configure repos to not overwrite base packages?

CentOS, How to, Linux
The greatest fear with adding additional and especially third party repos such as EPEL (we did a blog post on how to install EPEL earlier) is that it MAY overwrite base packages and bring the system to an unstable state. We can fix this issue by installing Yum Priorities plugin on CentOS 5: [code]yum install yum-priorities[/code] on CentOS 4 or CentOS 6: [code]yum install yum-plugin-priorities[/code] Then make sure that the plugin is enabled [code]nano /etc/yum/pluginconf.d/priorities.conf[/code] Now there are two ways to do it, either set HIGHEST priority to CentOS repos OR set lowest priority to other repos. This is done by adding the line [code highlight="3"] # N=1 highest priority # N=99 lowest priority priority=N [/code] In this blog post, I will set 1 as the priority (highest) for my…
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23May 2012 by Asim Zeeshan No Comments

How to change time and/or timezone in CentOS

CentOS, How to, Linux
Generically, I use this Change directory to /etc [code] [root@testbed ~]# cd /etc [/code] Now create a symbolic link (aka symlink) to the timezone e.g. Asia/Karachi (for Pakistan standard time) [code highlight="1"] [root@testbed etc]# ln -sf /usr/share/zoneinfo/Asia/Karachi localtime [root@testbed etc]# date Mon Jan 16 19:26:52 PKT 2012 [/code] Please note that the timezone is following a directory-structure so if you want EST time, you should use [code highlight="1"] [root@testbed etc]# ln -sf /usr/share/zoneinfo/EST localtime [/code]
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22May 2012 by Asim Zeeshan No Comments

How to disable SELinux

CentOS, How to, Linux, Tips and Tricks
SELINUX is a security feature on CentOS but some software such as SolusVM will require that SELINUX be disabled [code] Installation log : /tmp/install.log Add this slave to your SolusVM master using the following details: ID Key .......... : ABC ID Password ..... : XYZ IMPORTANT!! You need to setup a network bridge before you can use KVM on this server. Please see the following link: http://wiki.solusvm.com/index.php/KVM_Network_Bridge_Setup Please set SELINUX=disabled in /etc/selinux/config before rebooting. Thankyou for choosing SolusVM. [/code] The solution? 1) Edit /etc/selinux/config using your favourite editor [code][root@kvm ~]# nano /etc/selinux/config[/code] and set SELINUX=disabled [code highlight="6"]# This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings…
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20May 2012 by Asim Zeeshan 2 Comments

Freshclam daemon not running

CentOS, How to, Linux
Normally, I have two things on every Linux box so that I know whats going on NAGIOS monitoring (nrpe) Logwatch Today, I got something in my logwatch email and it was strange because just the other day, I upgraded the clamav to latest version using epel reo. [code title="This is what I got in logwatch today" highlight="3,4,5"] --------------------- clam-update Begin ------------------------ The ClamAV update process (freshclam daemon) was not running! If you no longer wish to run freshclam, deleting the freshclam.log file will suppress this error message. ---------------------- clam-update End ------------------------- [/code] It appears that the latest version has some permission issues on the log file because when I try to run freshclam on command line I get this [code]root@cpanel [~]# freshclam ERROR: Can't open /var/log/clamav/freshclam.log in append mode (check…
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19May 2012 by Asim Zeeshan No Comments

Install htop

CentOS, How to, Linux, Reviews, Tips and Tricks, Ubuntu
[caption id="attachment_1147" align="aligncenter" width="300" caption="htop - an alternative to linux top"][/caption] htop is a sleek utility that allows you to interactively view processes running in a linux box. I can safely say its a good alternate to 'top' To install htop just run this after installing epel repo [code]yum install htop[/code]
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19May 2012 by Asim Zeeshan No Comments

Installing EPEL repo

CentOS, How to
Installing EPEL repo in CentOS is simple, if you do not know what EPEL is, read more about it here. [code]rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-4.noarch.rpm[/code] To configure epel or disable it use [code]nano /etc/yum.repos.d/epel.repo[/code] and then switch the config enabled to 0 (or vice versa) Don't forget to do the following [code]yum clean all[/code]
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28Mar 2011 by Asim Zeeshan 2 Comments

Find memory consumed by currently running processes on Linux?

CentOS, How to, Linux, OpenSource, Resources, Reviews, Tips and Tricks, Tutorials, Ubuntu, Virtual Private Server
I always had the question (when I am running plenty of scripts on a linux box as to what is eating up all the memory? Finding memory consumed by current running processes in your favorite linux distro. Luckily, I found a great Python utility (scriplet to be exact). (more…)
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