Linux Basic Commands

For those who are unsure how to use linux commands. We begin truly learning Linux. So, open a terminal, if you use windows, open PuTTY, and log in to the server.

First, we start with pwd command which means Print Working Directory. This command shows you where you are in the file system. It will help to knowing the file system and help to learn everything else.

pwd command
[root@linuxguideco home]# pwd
/home

man command
This command brings up the online unix manual. It can be used for each of the commands and can see the manual of the given command.

[root@linuxguideco /]# man ls (ls command manual)

cal command
cal commands shows the current month calendar

[root@linuxguideco /]# cal
     April 2013
Su Mo Tu We Th Fr Sa
    1  2  3  4  5  6
 7  8  9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30

‘cal ’ will display calendar for specified month and year.

[root@linuxguideco /]# cal 01 1990
    January 1990
Su Mo Tu We Th Fr Sa
    1  2  3  4  5  6
 7  8  9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31

date command
This command will display current date and time.

[root@linuxguideco /]# date
Mon Apr 29 13:01:31 PKT 2013

This command will only display current time.

[root@linuxguideco /]# date +%T
13:03:08

whoami command
This command shows current logged in user.

[root@linuxguideco /]# whoami
root

id command
id command shows user and groups (UID and GID) of current user.

[root@linuxguideco /]# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)

[root@linuxguideco bin]# id root
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)

du command
shows the total size used by the files.
[root@linuxguideco guide]# du -c /dev

shows the directory size
[root@linuxguideco guide]# du -s /dev
96      /dev

shows directory size with human understanding.
[root@linuxguideco guide]# du -hs /dev
96K      /dev

df command shows free disk space.
[root@linuxguideco guide]# df

ls command
To show the current directory list.

[root@linuxguideco /]# ls
bin  boot  dev  etc  home  lib  media  misc  mnt  net  opt  proc  root  sbin  selinux  srv  sys  tmp  usr  var

[root@linuxguideco /]# ls -l
drwxr-xr-x   2 root root  4096 Apr 12 10:13 bin

[root@linuxguideco /]# ls -al
drwxr-xr-x  23 root root  4096 Apr 30 14:51 .
drwxr-xr-x  23 root root  4096 Apr 30 14:51 ..
-rw-------   1 root root    19 Apr 12 17:53 .bash_history
drwxr-xr-x   2 root root  4096 Apr 12 10:13 bin

cd command
for changing the directory.

[root@linuxguideco /]# cd /usr/
[root@linuxguideco usr]#

one step back to the directory.

[root@linuxguideco usr]# cd ..
[root@linuxguideco /]#

go to previous working directory

[root@linuxguideco usr]# cd -
/
go to current login user home directory

[root@linuxguideco /]# cd ~
[root@linuxguideco ~]#

mkdir command
Create a folder on root partition.
[root@linuxguideco /]# mkdir /guide

create a folder in /guide
[root@linuxguideco /]# mkdir /guide/test

create multiple folder in multiple directories with single command
[root@linuxguideco /]# mkdir /usr/dir1 /var/dir2 /etc/dir3

create multiple folder in same directory
[root@linuxguideco /]# mkdir dir11 dir12 dir13

cp command
copy a file in directory
[root@linuxguideco guide]# cp file /guide2

copy a file from /guide/file to /guide2/dir
[root@linuxguideco guide]# cp /guide/file /guide2/dir

copy a directory with -r option
[root@linuxguideco guide]# cp -r dir6 dir7

copy a file from /guide/file1 paste in /usr with file2 name
[root@linuxguideco guide]# cp /guide/file1 /usr/file2

rm command
remove a file
[root@linuxguideco guide]# rm file

remove a file with forcefully option
[root@linuxguideco guide]# rm -f file

remove a directory without -r option, it will appear an error
[root@linuxguideco /]# rm guide
rm: cannot remove directory `guide': Is a directory

remove a directory with -r option
[root@linuxguideco /]# rm -r guide

remove a directory with -r option
[root@linuxguideco /]# rm -rf guide

move command
Move /usr/dir1 to /opt/ with different name
[root@linuxguideco /]# mv /usr/dir1 /opt/dir2

Rename the folder name mydir to dir
[root@linuxguideco /]# mv /usr/mydir /usr/dir

Rename the file1 name with file2
[root@linuxguideco /]# mv file1 file2

For reading a file on terminal

[root@linuxguideco etc]# cat /etc/grub.conf

commands
read a file page by page with less command
[root@linuxguideco /]# less /etc/grub.conf

read a file page by page with more command
[root@linuxguideco /]# more /etc/grub.conf

read first ten lines of grub.conf
[root@linuxguideco /]# head /etc/grub.conf

read last ten lines of grub.conf
[root@linuxguideco /]# tail /etc/grub.conf

read first 12 lines with -n option
[root@linuxguideco /]# head -n 12 /etc/grub.conf

read last 13 lines with -n option
[root@linuxguideco /]# last -n 13 /etc/grub.conf

copy the contents of /etc/grub.conf in /guide/file
[root@linuxguideco /]# cat /etc/grub.conf > /guide/file

Append the contents of /guide/file in /guide2/file
[root@linuxguideco /]# cat /guide/file >> /guide2/file

merging two commands with pipe sign output of the first command is input of second command
[root@linuxguideco /]# cat /usr/apache2/conf/httpd.conf | more

count the total lines of httpd.conf
[root@linuxguideco /]# cat /usr/apache2/conf/httpd.conf | wc -l
479

show only conf words in httpd.conf
[root@linuxguideco /]# cat /usr/apache2/conf/httpd.conf | grep conf

flush the contents of file
[root@linuxguideco /]# cat /dev/null > /guide/file
 
help commands
[root@linuxguideco guide]# man mkdir
[root@linuxguideco guide]# info mkdir
[root@linuxguideco guide]# mkdir --help
[root@linuxguideco guide]# apropos "partition"

I hope these basic commands will surely help out to Linux beginner users.