LINUX BASIC COMMON COMMANDS

Filter result:

grep

ex: filter all processes and ports of java

ps -e | grep java
netstat -tunap | grep java

Process and infomation :

Information about process

$ls -l /proc/$PID/exe
OR
$ps -p PID -o comm=
OR
$cat /proc/PID/cmdline

Kill process

sudo kill -9 PID

User and Group:

Login

#su - {user-name}

Login as root

#su -

check username

#whoami

logout

#logout

Extract & Compress file:

Extract

#tar -zxvf {file.tar.gz}
#tar -xf {file.tar.gz} -C /target/directory
#tar -xzf backup.tar.gz -C /target/directory
#unzip file.zip -d destination_folder

Download

#wget http://ftp.gnu.org/gnu/wget/wget-1.5.3.tar.gz  -P /target/directory

Restating the network service:

To restart the network service under RHEL / CentOS based systems, enter:

service network restart

OR

/etc/init.d/network restart

Check linux kernel version number :

Open a shell prompt (or a terminal) and type the following command to see your current Linux kernel version:

uname -r

Or type the following command

uname -mrs

To print all information, enter

uname -a

Type the following command to see Linux version info

cat /proc/version

Find Distribution Version :

Type the following command

cat /etc/*release

OR

lsb_release -a

Port & Firewall :

Port and process command

netstat -tunap

If you want to open a single port

open iptables file

vi /etc/sysconfig/iptables

Add below line to open port.

-A INPUT -m state --state NEW -m tcp -p tcp --dport 143 -j ACCEPT

For multiple, you can use the following instead (or repeat the above line multiple times):

-A INPUT -m state --state NEW -m tcp -p tcp -m multiport --dports 22,80,143 -j ACCEPT

service iptables save

Disable / Turn off Linux Firewall (Red hat/CentOS/Fedora Core)

Type the following two commands (you must login as the root user)

/etc/init.d/iptables save

/etc/init.d/iptables stop

Turn off firewall on boot

chkconfig iptables off

Enable / Turn on Linux Firewall (Red hat/CentOS/Fedora Core)

Type the following command to turn on iptables firewall

/etc/init.d/iptables start 

Turn on firewall on boot

chkconfig iptables on 

Linux / Unix - Checking Free Disk Space:

df command examples - to check free disk space

Type df -h or df -k to list free disk space

df -h

OR

df -k

Find Files and Folders in Linux :

find / -name "java" 

/: meaning is the root folder. hold systems
-name "java": all files have name is java.