Common Linux Commands

The Basics – The command line

When you log in to a Linux system using SSH or open a terminal window from a Linux desktop, you are running a “shell” program.  Basically, a shell is a program that processes the commands you type.  It is very common to use Linux by entering commands in a shell.  This is called “working from the command line”.  In this brief guide, we’ll cover a number of useful commands and tools that will help you become more proficient at using the command line.

There are two common shells in Linux:  bash and tcsh.  Since bash has become the most common shell, we’ll be using bash in all the examples that follow.

The Shell Prompt

When the shell is ready for you to enter a command, it displays a “prompt”.  Usually, the prompt will be something simple like:

bash$

To enter a command, you just type it after the prompt and hit <return>.  For instance, you can find out today’s date and the current time by typing the command date like so:

bash$ date

Wed Jan 13 22:10:52 CST 2016

Basic Shell Commands – Changing Directories

In Linux, a “directory” is what Windows users usually call a “folder”.  It’s basically a location in the file system for storing files.  Directories are organized hierarchically starting with the directory called / at the top of the “directory tree”.  There several common directories you should be aware of:

/usr/bin – This is where the most common user programs are located.

/home/{username} – Home directories are usually found under /home.  For most Linux users, their home directory is /home/{username}, where {username} is the account name.

/tmp – this is a temporary directory where you can put files that you don’t intend to keep.

/etc – This is a path to where most of the configuration files that Linux uses are stored.

The cd Command

The cd command is one of the most common commands you will use. It allows you to different directories. It’s pretty simple, just type cd {destination} where {destination} is the path you want to move to. Here are some examples:

cd /tmp – Move to the /tmp directory.
cd .. – Move to the directory above your current directory.
cd ../docs – Move up one level, then down to the directory called “docs”.

The pwd Command

The pwd goes hand in hand with the cd. The pwd command shows you where you currently are located in the directory tree. For example, to see what directory you are in type:

bash$ pwd
/home/johnd
bash$ cd ..
pwd
/home

Using ssh

Using SSH

[bash]ssh username@hostname[/bash]

Display manual pages

[bash]man <command>[/bash]

Examples

[bash] man yum
man chkconfig
[/bash]

Run a command as root

[bash]sudo <command>[/bash]

Update system

[bash]sudo yum update[/bash]

List all available pages

[bash]sudo yum list[/bash]

Install one or more packages

[bash]sudo yum install <package1> [<package2>] […][/bash]

Add a local user account

[bash]sudo useradd <username>[/bash]

Change Password

[bash]passwd[/bash]

or

[bash]sudo passwd [<username>][/bash]

Edit firewall

[bash]system-config-securitylevel[/bash]

List all services

[bash]sudo chkconfig –list[/bash]

Set a service to start on boot

chkconfig <name> on

Examples

[bash]sudo chkconfig httpd on
sudo chkconfig mysqld on[/bash]

Set up a LAMP Stack (Linux Apache MySQL PHP )

[bash]sudo yum install httpd mysql mysql-server php php-mysql
sudo chkconfig httpd on
sudo chkconfig mysqld on
system-config-securitylevel # Open port port in firewall for http
reboot[/bash]