Basic LINUX commands that a DBA should know

groupadd 

This is the command used to create new group. At OS level group is used to give and take  pivillages.

Syntax : groupadd <group name>

Ex : [root@rac5 ~]# groupadd group1

View : [root@rac5 ~]# cat /etc/group  -This command used to view which user belongs to which group.

Output: group1:x:607:

useradd 

This is the command used to create a new user in a group.

Syntax : useradd -g <group name> <user name>

Ex : [root@rac5 ~]# useradd -g group1 user1

passwd

This is the command used to give password for create use or to update the password.

Syntax : passwd <user name>

Ex: [root@rac5 ~]# passwd user1

Output :

[root@rac5 ~]# Changing password for user soufir.

New UNIX password:

BAD PASSWORD: it is based on a dictionary word

Retype new UNIX password:

passwd: all authentication tokens updated successfully.

date

a. This is the command used to view the current system date.

Syntax : date

Output : Wed Oct 27 21:55:36 IST 2010

b. In order to update the date we can give :

Syntax : [root@rac5 ~]# date -s "2 OCT 2010 14:00:00"  OR

[root@rac5 ~]# date --set="27 OCT 2010 21:56:00"

Output : Sat Oct  2 14:00:00 IST 2010

cal

This command shows the calender of current year or any.

Ex : [root@rac5 ~]#  Cal

Output : [root@rac5 ~]#    October 2010

                        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

pwd 

This command is to view the present working directory.

Ex : [root@rac5 ~]# pwd

Output : [root@rac5 ~]# /root.

cd

a.This is the command used to change a directory

Ex : [oracle@rac5 ~]$ ls

authorized_keys  file   file2  oraInventory  stand.ora

authorized-keys  file1  file3  soufir

[oracle@rac5 ~]$ cd soufir

[oracle@rac5 soufir]$

b.This is used to go back to parent directory

Ex : cd ..

mkdir
This command is used for make a new directory.

 Ex : mkdir dir1

rmdir

This commad is used for remove a directory.

 Ex : rmdir dir1

rm -rf

This command is used to forcefully remove a direcory.

Ex : rm -fr dir1

man

This command is used to show the online manual pages of related commands

Ex : man ls

ls

This command is used to list all contents of directories

Ex : ls

ls -lt

This command is used to list lot of information about contents of directories

Ex : ls -lt
The permissions are the first 10 characters of the line (-rwxrwx---) and can be broken down as follows.

-	rwx	r--	r--	1	root	root	765	Apr 23	file.txt
File type	Owner	Group	All	Links	Owner	Group	Size	Mod date	Filename

touch

This command is used create an empty file
Ex : touch file1

cat

This command is used to create and view files of directories

Ex : cat file1
cat file1 > newfile   // owerwrite newfile with file1
cat file1 >> newfile  // append newfile the contents with file1

cp

This command is used to copy a file from one to another 

Ex : cp file1 filenew 

mv

This command is used to rename the name of a file to other

Ex : mv file1 filenew

su

This command is used to switch one user to other. it doesnot change the current working directory. so you cant access the /usr/sbin  directories.

Ex : su soufir

su -

This command is used to switch one user with changing current working directory.

Ex : su - soufir