TranslateProject/sources/tech/20170910 Useful Linux Commands that you should know.md

translating by liuxinyu123   

Useful Linux Commands that you should know
======
If you are Linux system administrator or just a Linux enthusiast/lover, than
you love & use command line aks CLI. Until some years ago majority of Linux
work was accomplished using CLI only & even there are some limitations to GUI
. Though there are plenty of Linux distributions that can complete tasks with
GUI but still learning CLI is major part of mastering Linux.

To this effect, we present you list of useful Linux commands that you should
know.

 **Note:-** There is no definite order to all these commands  & all of these
commands are equally important to learn & master in order to excel in Linux
administration. One more thing, we have only used some of the options for each
command for an example, you can refer to 'man pages' for complete list of
options for each command.

### 1- top command

'top' command displays the real time summary/information of our system. It
also displays the processes and all the threads that are running & are being
managed by the system kernel.

Information provided by top command includes uptime, number of users, Load
average, running/sleeping/zombie processes, CPU usage in percentage based on
users/system etc, system memory free & used, swap memory etc.

To use top command, open terminal & execute the comamnd,

 **$ top**

To exit out the command, either press 'q' or 'ctrl+c'.

### 2- free command

'free' command is used to specifically used to get the information about
system memory or RAM. With this command we can get information regarding
physical memory, swap memory as well as system buffers. It provided amount of
total, free & used memory available on the system.

To use this utility, execute following command in terminal

 **$ free**

It will present all the data in kb or kilobytes, for megabytes use options
'-m' & '-g ' for gb.

#### 3- cp command

'cp' or copy command is used to copy files among the folders. Syntax for using
'cp' command is,

 **$ cp source destination**

### 4- cd command

'cd' command is used for changing directory . We can switch among directories
using cd command.

To use it, execute

 **$ cd directory_location**

### 5- ifconfig

'Ifconfig' is very important utility for viewing & configuring network
information on Linux machine.

To use it, execute

 **$ ifconfig**

This will present the network information of all the networking devices on the
system. There are number of options that can be used with 'ifconfig' for
configuration, in fact they are some many options that we have created a
separate article for it ( **Read it here ||[IFCONFIG command : Learn with some
examples][1]** ).

### 6- crontab command

'Crontab' is another important utility that is used schedule a job on Linux
system. With crontab, we can make sure that a command or a script is executed
at the pre-defined time. To create a cron job, run

 **$ crontab -e**

To display all the created jobs, run

 **$ crontab -l**

You can read our detailed article regarding crontab ( **Read it here ||[
Scheduling Important Jobs with Crontab][2]** )

### 7- cat command

'cat' command has many uses, most common use is that it's used to display
content of a file,

 **$ cat file.txt**

But it can also be used to merge two or more file using the syntax below,

 **$ cat file1 file2 file3 file4 > file_new**

We can also use 'cat' command to clone a whole disk ( **Read it here ||
[Cloning Disks using dd & cat commands for Linux systems][3]** )

### 8- df command

'df' command is used to show the disk utilization of our whole Linux file
system. Simply run.

 **$ df**

& we will be presented with disk complete utilization of all the partitions on
our Linux machine.

### 9- du command

'du' command shows the amount of disk that is being utilized by the files &
directories on our Linux machine. To run it, type

 **$ du /directory**

( **Recommended Read :[Use of du & df commands with examples][4]** )

### 10- mv command

'mv' command is used to move the files or folders from one location to
another. Command syntax for moving the files/folders is,

 **$ mv /source/filename /destination**

We can also use 'mv' command to rename a file/folder. Syntax for changing name
is,

 **$ mv file_oldname file_newname**

### 11- rm command

'rm' command is used to remove files\folders from Linux system. To use it, run

 **$ rm filename**

We can also use '-rf' option with 'rm' command to completely remove a
file\folder from the system but we must use this with caution.

### 12- vi/vim command

VI or VIM is very famous & one of the widely used CLI-based text editor for
Linux. It takes some time to master it but it has a great number of utilities,
which makes it a favorite for Linux users.

For detailed knowledge of VIM, kindly refer to the articles [**Beginner 's
Guide to LVM (Logical Volume Management)** & **Working with Vi/Vim Editor :
Advanced concepts.**][5]

### 13- ssh command

SSH utility is to remotely access another machine from the current Linux
machine. To access a machine, execute

 **$ ssh[[email protected]][6] OR machine_name**

Once we have remote access to machine, we can work on CLI of that machine as
if we are working on local machine.

### 14- tar command

'tar' command is used to compress & extract the files\folders. To compress the
files\folders using tar, execute

 **$ tar -cvf file.tar file_name**

where file.tar will be the name of compressed folder & 'file_name' is the name
of source file or folders. To extract a compressed folder,

 **$ tar -xvf file.tar**

For more details on 'tar' command, read [**Tar command : Compress & Decompress
the files\directories**][7]

###  15- locate command

'locate' command is used to locate files & folders on your Linux machines. To
use it, run

 **$ locate file_name**

### 16- grep command

'grep' command another very important command that a Linux administrator
should know. It comes especially handy when we want to grab a keyword or
multiple keywords from a file. Syntax for using it is,

 **$ grep 'pattern' file.txt**

It will search for 'pattern' in the file 'file.txt' and produce the output on
the screen. We can also redirect the output to another file,

 **$ grep 'pattern' file.txt > newfile.txt**

### 17- ps command

'ps' command is especially used to get the process id of a running process. To
get information of all the processes, run

 **$ ps -ef**

To get information regarding a single process, executed

 **$ ps -ef | grep java**

### 18- kill command

'kill' command is used to kill a running process. To kill a process we will
need its process id, which we can get using above 'ps' command. To kill a
process, run

 **$ kill -9 process_id**

### 19- ls command

'ls' command is used list all the files in a directory. To use it, execute

 **$ ls**

### 20- mkdir command

To create a directory in Linux machine, we use command 'mkdir'. Syntax for
using 'mkdir' is

 **$ mkdir new_dir**

These were some of the useful linux commands that every System Admin should
know, we will soon be sharing another list of some more important commands
that you should know being a Linux lover. You can also leave your suggestions
and queries in the comment box below.


--------------------------------------------------------------------------------

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[a]:http://linuxtechlab.com
[1]:http://linuxtechlab.com/ifconfig-command-learn-examples/
[2]:http://linuxtechlab.com/scheduling-important-jobs-crontab/
[3]:http://linuxtechlab.com/linux-disk-cloning-using-dd-cat-commands/
[4]:http://linuxtechlab.com/du-df-commands-examples/
[5]:http://linuxtechlab.com/working-vivim-editor-advanced-concepts/
[6]:/cdn-cgi/l/email-protection#bbcec8dec9d5dad6defbf2ebdadfdfc9dec8c8
[7]:http://linuxtechlab.com/tar-command-compress-decompress-files
[8]:https://www.facebook.com/linuxtechlab/
[9]:https://twitter.com/LinuxTechLab
[10]:https://plus.google.com/+linuxtechlab
[11]:http://linuxtechlab.com/contact-us-2/