Admins eHow SysAdmin Tips & Tricks

August 27, 2009

How to clear all iptables rules

Filed under: CentOS,Debian,General,Security — Tags: , , , — admin @ 2:08 pm

In order to flush all iptables rules , Run the following commands :

iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT

August 7, 2009

DirectAdmin installation requirements on CentOS 5

Filed under: CentOS,General — Tags: , , — admin @ 10:00 pm

DirectAdmin guide only asks you to download their setup script and run it , but it doesn’t explain about requires packages before installation , so before installation run the following commands :

yum update
yum install perl gcc gcc-c++ make tar gzip bzip2 diffutils dbus quota

August 5, 2009

Install locate and updatedb on CentOS and Debian

Filed under: CentOS,Debian,General — Tags: , , , , — admin @ 3:55 pm

locate and updatedb commands are the best commands to search and find files in Linux. if you dont have them installed on your Linux , use the following commands :
Debian :

apt-get install locate

CentOS :

yum install mlocate

July 24, 2009

Delete Files Older Than x Days on Linux

Filed under: CentOS,Debian,General — Tags: , , , — admin @ 1:40 pm

The find utility on linux allows you to pass in a bunch of interesting arguments, including one to execute another command on each file. We’ll use this in order to figure out what files are older than a certain number of days, and then use the rm command to delete them.

Command Syntax

find /path/to/files* -mtime +5 -exec rm {} \;

Note that there are spaces between rm, {}, and \;


  • The first argument is the path to the files. This can be a path, a directory, or a wildcard as in the example above. I would recommend using the full path, and make sure that you run the command without the exec rm to make sure you are getting the right results.
  • The second argument, -mtime, is used to specify the number of days old that the file is. If you enter +5, it will find files older than 5 days.
  • The third argument, -exec, allows you to pass in a command such as rm. The {} \; at the end is required to end the command.

or you can use the following command :

find /path/to/files* -mtime +5 | xargs rm -f

This should work on Ubuntu, Suse, Redhat, or pretty much any version of linux.

July 14, 2009

Limit Connections per IP using mod_limitipconn on cPanel

Filed under: Apache,CentOS,cPanel,General,Security — Tags: , , , , , , — admin @ 9:41 am

one of the problems I had on one of my cPanel servers was that some people were using download managers to download files from server , so hundreds of connections were being ESTABLISHED to Apache and it was becoming like a dos attack and causing Apache to become non responsive.
so here is what I did to limit connections per IP in a cPanel hosting server :
there is an Apache module named mod_limitipconn which will take care of it for us.
first download the latest version of mod_limitipconn from this site :
decompress and install it.
at current time the latest version is 0.23.

tar jxvf mod_limitipconn-0.23.tar.bz2
cd mod_limitipconn-0.23
/usr/local/apache/bin/apxs -cia mod_limitipconn.c

next step is to add the required configuration to the Apache config file , we can add this directly to the end of httpd.conf file but the problem is that if we do this , the httpd.conf will be overwritten by easyapache so we will use include files to add our config.
login into your WHM panel , and follow the following menu items :
Main >> Service Configuration >> Apache Configuration >> Include Editor
on the Post VirtualHost Include section , choose All Versions from drop down menu and add the following config into it :

<IfModule mod_limitipconn.c>
<Location />
MaxConnPerIP 10
NoIPLimit images/*

then click on update and restart Apache server.
now We are all set 🙂

July 12, 2009

Backup Your Data in Linux by sending them to your GMail

Filed under: CentOS,Debian,General,Security — Tags: , , , — admin @ 8:33 am

A very effective way for backing up your data on a Linux server is to set a cron job on your box to mail your data to your GMail account. GMail servers are very reliable and give you a huge amount of space for free. so they are pretty suitable for backing up sensitive data.
In order to accomplish this , first create a directory named “backup” in the root directory of your box :

cd / && mkdir backup

then you need to create a script to do the backup and mail it for you.

nano /usr/bin/backup

copy and paste the following into the file :

cd /backup
rm -rf /backup/*
tar jcf backup.tar.bz2 *
echo | mutt -a backup.tar.bz2 -s "my daily backup" --

you have to change LIST_OF_FILES string to the list of the files you want to be backed up separated by space , and change to your own gmail account.
as you can see in the script we are compressing the data files to make them as small as possible.
also we are using “mutt” to send emails so you need to install it , in Debian you can install it by following command :

apt-get install mutt

make the script executable :

chmod +x /usr/bin/backup

lastly you need to set a cron job , so open the cron file by following command :

crontab -e

and copy and paste the following command into it :

0 0 * * * /usr/bin/backup

it will run your backup script once daily 🙂
also don’t forget you need to have a working smtp server on your Linux box.

June 29, 2009

How to synchronize Linux Time Daily

Filed under: CentOS,Debian,General — Tags: , , , , — admin @ 6:51 pm

First you need to install rdate package.
For Debian :

apt-get install rdate

For CentOS :

yum install rdate

After installing the rdate package , install a new cron job to be run daily to synchronize your machine time and date.

crontab -e

and enter the following line into the cron file :

0 0 * * * /usr/bin/rdate -s && /sbin/hwclock --systohc

June 26, 2009

bash: /bin/rm: Argument list too long

Filed under: CentOS,Debian,General — Tags: — admin @ 1:44 pm

Use the following command the directory to solve the problem :

ls | xargs rm

June 22, 2009

Remove comments and empty lines on linux using sed command

Filed under: CentOS,Debian,General — Tags: , , , , — admin @ 10:24 am
sed -e 's/#.*//' -e 's/[ ^I]*$//' -e '/^$/ d' filename

June 17, 2009

MySQL Backup/Restore from command line

Filed under: CentOS,Debian,General,MySQL — Tags: , , , — admin @ 2:48 pm


Dump ALL MySQL Databases

mysqldump --user=XXXXXXXX --password=XXXXXXX -A > /PATH/TO/DUMPFILE.SQL

Dump Individual or Multiple MySQL Databases


Dump only certain tables from a MySQL Database

mysqldump --user=XXXXXXXX --password=XXXXXXXX DB_NAME --tables TABLE_NAME > /PATH/TO/DUMPFILE.SQL


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