How To Create User In Red Hat

User and Group Management :

1. USER : All linux user have a used ID and a unique numeric identification number called User Id (UID).

Every user of the system is assigned a unique User ID number. User’s name and UID are stored in /etc/passwd.

User are assigned a home directory and a program that is run when they log in (usually called shell).

Users can not read, write or execute each other files and directory without permission

Group :

2. GROUP : All Linux users have a group ID and a unique numeric identification number called Group Id (GID). Users are assigned to group with unique Group ID number. GID are stored in /etc/group file. Each user is given their own private group, they can also be added to other groups to gain the additional access of a particular file or directory. All users in a group can share files that belong to the same group.

When a user is get created in linux its entry is recorded in the following files.

• 1. /home(user directory)

• 2. /etc/passwd (uid and gid)

• 3. /etc/shadow(password )

• 4. /etc/group(user group)

• 5. /etc/default/useradd (command)

User creation :

Normal User

Root=admin, root has 0 pid, user has low pid is power full then the other users.

#useradd Mark (or)
#adduser Tony

How to create a user with pid 510 in red hat?

#useradd –u 510 Mark

#passwd Mark
New password:*******
Conform password:*******

#system-config-users

Note:- when you create a user then it’s home- directory create in /home
:- it’s mail box is also create in /var/spool/mail/username

Delete user in Red Hat :

#userdel is used for user delete

#userdel Mark

#userdel -r Mark

#ls /home
#cat /etc/passwd
#ls /var/spool/mail/username

Su (switch user) in Red Hat :

How to switch user in Red Hat?

[root@localuser~]#su  -  Mark
[sumit@localuser~]$ ------------(normal user)
[sumit@localuser~]$su - Mark 
Password:*********----------  (give password of Mark)
[raj@localuser~]$

Note : Normal user can not login in to other user they have to give the password.

[Mark@localuser~]$su 
Password:----------(give password of root)
[root@localhost Mark]#

User components :

When you create the user then It’s components create.

#cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
damone:x:2:2:damone:/damone:/sbin/nologin
Mark:x:500:500::/home/mark:/bin/bash
--------------------------------------------------------------

• (root:) : Username

• (x:) : password

• (0:) : uid

• (0:) : gid

• (root:) : comment

• (/root:) : home directory

• (/bin/bash) : shell

Create a user with uid “700”, comment "sales” home dir in “/tmp/mark”, shell “/bin/ksh”

#useradd -u 700 -c sales -d /tmp/mark -s /bin/ksh mark

Check in the passwd file.

#cat /etc/passwd
Mark:x:700:700:sales: /mp/mark:/bin/ksh

User modification :

# usermod –L username

#usermod -U username

# usermod -c username

# usermod -s /bin/ksh username

#usermod –l new-username old-username

#usermod  -e