Admins eHow

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/*
cp LIST_OF_FILES .
tar jcf backup.tar.bz2 *
echo | mutt -a backup.tar.bz2 -s "my daily backup" -- adminsehow@gmail.com

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 adminsehow@gmail.com 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 time-nw.nist.gov && /sbin/hwclock --systohc

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'

June 16, 2009

How to mirror a website on linux ?

Filed under: General,HTML — Tags: , , — admin @ 2:34 pm

You almost certainly have wget already. Try wget –help at the command line. If you get an error message, install wget with your Linux distribution’s package manager. Or fetch it from the official wget page and compile your own copy from source.

Once you have wget installed correctly, the command line to mirror a website is:

wget -m -k -K -E http://url/of/web/site

See man wget or wget –help | more for a detailed explanation of each option.

If this command seems to run forever, there may be parts of the site that generate an infinite series of different URLs. You can combat this in many ways, the simplest being to use the -l option to specify how many links “away” from the home page wget should travel. For instance, -l 3 will refuse to download pages more than three clicks away from the home page. You’ll have to experiment with different values for -l. Consult man wget for additional workarounds.

June 7, 2009

Change Linux Password from PHP Script

Filed under: CentOS,Debian,General,PHP — Tags: , , , — admin @ 8:48 pm

There are a few scripts available on net which allow you to change a linux user password from PHP. but all of them are very complex and hard to implement , so after some hours of work , I’ve written this PHP script :) it is very simple , in order for this to work you need to allow your webserver to run sed command as root through sudoers , or allow your webserver to write on your /etc/shadow file.

$username='USERNAME';
$password='PASSWORD';  // New Password
$sed='/bin/sed'; //Path to sed command
$salt = substr($username, 0, 2);
$pass_crypt = crypt($password, $salt);
$pass_crypt=str_replace("/","\/",$pass_crypt);
system($sed." -i 's/".$username.":[a-zA-z0-9/$\.]*/".$username.":".$pass_crypt."/g' /etc/shadow",$retval);

May 12, 2009

Check Memory Usage in Linux

Filed under: CentOS,Debian,General — Tags: , — admin @ 5:39 pm

In order to check memory usage in Linux , there are several commands , but the most useful commands I have found are the following :

Check total memory usage :

# free -m
total       used       free     shared    buffers     cached
Mem:           512        490         21          0         16        160
-/+ buffers/cache:        314        197
Swap:         1023         76        947

what you are looking for is in front of “-/+ buffers/cache:” , in above example Total memory is 512MB , Used memory is 314MB and Free memory is 197MB.
it also shows the usage of Swap which is 76MB from 1023MB Total.

Check detailed processes memory usage :

# ps aux | awk '{print $4"\t"$11}' | sort | uniq -c | awk '{print $2" "$1" "$3}' | sort -nr
10.0 1 (squid)
2.7 1 python
1.5 1 /usr/sbin/pdns_recursor
1.3 1 sshd:
1.3 1 /usr/sbin/apache2
.........

This command is a little complex , we dont want to go into the details of command. we are only interested in the output.
The First column shows the percent of memory which this process is using , second column shows the number of instances of the process and the third column is the name of process. in the above example , process “squid” is using 10% of my server memory and python is using 2.7% of memory.

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