Find the total number of httpd processes running at a particular instance on your server

ps -ef | grep http | wc -l

How to check if ports have got open after IPTables rules

Verify that port is open

Run following command:
netstat -tulpn | less
Make sure iptables is allowing port 80 / 110 / 143 connections:
iptables -L -n

Refer to iptables man page for more information about iptables usage and syntax:
man iptables

IPTables CentOS5.6 - port 80, 143, 443 allowed or open

I had my webserver setup perfectly and it was working fine but it was not accessible from outside. It was IPtables blocking the same. I read on internet about the rules for IpTables to allow access to port 80,443,143. below mentioned are the rules.

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 143 -j ACCEPT

But even after applying these rules things were not working because I was appending these rules after the rule

-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited


-------------------------------------------------------------------------------
I think (I don't know for sure) the rule for icmp shall always be at the last. Any rule after that to allow access to network resources will not get effective.

If I am wrong please correct.

You can refer to http://www.cyberciti.biz/faq/howto-rhel-linux-open-port-using-iptables/ for more information on IPTables.

How to find the Linux Distro Name and version

Some distros put a '*-release' or '*-version' file 
in /etc. Here are some examples: 

/etc/redhat-release 
/etc/debian_version 
/etc/SuSE-release 
/etc/slackware-version 
/etc/gentoo-release 

You could do 'cat /etc/*-release' or 'cat /etc/*-version'. 

IPtables the play is dangerous and frustrating...yet find the way how to enable outbound traffic for port 3306 mysql

1. vi /etc/sysconfig/iptables 
To allow inbound traffic add this rule:  -A INPUT -p tcp -m tcp --dport 3306 -j ACCEPT
To allow outbound traffic add this rule:  -A OUTPUT -p tcp -m tcp --dport 3306 -j ACCEPT 

Now restart IPtables:  /etc/init.d/iptables restart

tail command to see the access log details created by a particular IP

tail -f /var/log/httpd/access_log | grep "122.176.44.144"

How to send alert message for SWAP Usage

here is a shell script which will Alert by send mail if the system started to use more than 20% of swap area and 80% of hard disk space.

$ vim swap-use.sh

#!/bin/sh
free -m | grep Swap | while read output;
do
  swap=$(echo $output | awk '{print $2}' )
  used=$(echo $output | awk '{ print $3 }' )
  freed=$(echo $output | awk '{ print $4 }' )
  echo "Swap : $swap"
  echo "Used : $used"
  echo "Free : $freed"
  usep=`expr $used \* 100 / $swap`
  echo $usep
  if [ $usep -ge 20 ]; then
    echo "Swap Usage Alert Total Swap: \"$swap\" Used: \"$used ($usep%)\" Free:
\"$freed\" on $(hostname) as on $(date)" |
     mail -s "Alert: Swap Usage space $usep%" mail1@example.com,mail2@example.com
  fi
done

Then schedule it in cron

--

How to add existing users in existing groups in linux and see which user is in which group

Add to group:

[root@288832-web3 ~]# usermod -a -G group1 user1
[root@288832-web3 ~]# usermod -a -G group2 user2

View which group which user belongs:
[root@288832-web3 ~]# groups user1
user1 : user1 apache group1

[root@288832-web3 ~]# groups user2
user2 : user2 apache group2

Run a command in background example: wget

Run the command in background on Linux:
$> nohup wget URL


This is true for running any command in background. Also, the command
generates a file called nohup.out, which might grow as the command
proceeds. So if you are downloading something using wget in
background, you can see the status by

cd <download_folder>
tail -f nohup.out

Find and delete files recursively

find ./ -name '*.html' -print0 | xargs -0 rm -rf

Setting up liferay/tomcat as service on suse linux

1. Copy the attached file to /etc/init.d
2. Modify the paths
3. Run the following command to add the script as service
chkconfig --add liferay
---------------------------------
Filename: liferay



#!/bin/sh
#
# /etc/init.d/tomcat
#
# This is the init script for starting up the
#  Jakarta Tomcat server
#
# description: Starts and stops the Tomcat daemon.
#


tomcat=/media/Resources/data/www/liferay-portal-6.0.6/tomcat-6.0.29
startup=$tomcat/bin/startup.sh
shutdown=$tomcat/bin/shutdown.sh


start() {
  echo -n $"Starting Tomcat service: "
  sh $startup
  echo $?
}


stop() {
  echo -n $"Stopping Tomcat service: "
  sh $shutdown
  echo $?
}


restart() {
  stop
  start
}


status() {
  #ps -aef | grep liferay | grep -v tomcat6 | grep -v grep
  numproc=`ps -ef | grep liferay | grep -v "grep liferay" | wc -l`
  if [ $numproc -gt 0 ]; then
    echo "Liferay is running..."
  else
    echo "Liferay is stopped..."
  fi
}


# Handle the different input options
case "$1" in
start)
  start
  ;;
stop)
  stop
  ;;
status)
  status
  ;;
restart)
  restart
  ;;
*)
  echo $"Usage: $0 {start|stop|restart|status}"
  exit 1
esac


exit 0

Add a new user to SVN for UKSS

Login as root via SSH on UKSS

Here we are adding a new user with the username: user1

Add new user: useradd user1

Add Password for the new user: passwd user1

Add user to groups: 

gpasswd -a user1 svn

gpasswd -a user1 apache

How to get list of files greater than 512MB in linux

find / -type f -size +512000k -exec du -hs {} \;

How to zip or archive or tar a directory and exclude one directory

tar -czpf /path/to/backups/my_backup.tar.gz --exclude path/to/images/tmp path/to/images/

How to see disk space utilization in Linux

Listing size and % usage of each partition.

[root@288832-web3 ~]# df -H
Filesystem Size Used Avail Use% Mounted on
/dev/sda5 279G 265G 0 100% /
/dev/sda2 2.1G 355M 1.7G 18% /tmp
/dev/sda1 104M 26M 73M 26% /boot
tmpfs 13G 0 13G 0% /dev/shm
------------------------------------------------------------------

Find How Much Disk Space Is Being Used Show Display
Login as root
then cd /
then execute: du -hc --max-depth=1
Output:
[root@hostname /]# du -hc --max-depth=1
0 ./net


1.6G ./usr
16K ./lost+found
515M ./proc
8.0K ./misc
648M ./var
112K ./dev
8.0K ./mnt
66M ./lib
8.0K ./selinux
7.3M ./bin
77M ./root
4.2M ./boot
28K ./tmp
2.7M ./backups
20M ./sbin
8.0K ./media
8.0K ./srv
0 ./sys
43M ./etc
42M ./home
8.0K ./opt
3.0G .
3.0G total

Taken from: http://www.wallpaperama.com/forums/linux-command-to-find-how-much-disk-space-is-being-used-show-display-t713.html