User Administration

Type of Users:

Root user                -           Default user highly privileged UID is 0. This will create while installing the operating system

System users         -           is nothing but services, at the time of installing particular package. UID starts from 1 to 499.

Local users            -           after installing of the operating system admin user will create these users. UID starts from 500 to 65534.

Ø  After creating a user, user home directory will be created in default path /home.

Ø  One group is will be created with same user name (primary group)

Ø  Files from /etc/skel will be copied automatically to user home directory

Ø  /etc/passwd file is updated with user information

Ø  /etc/group file is update with primary group information

Important files

/etc/passwd     User Information

/etc/shadow     User Passwords

/etc/group      Group Information

/etc/gshadow    Group Passwords

User Administration Commands:

# useradd <user name>     -           To create specified local user

# useradd –d <home directory> <user name>  - create a user with specified home path

[root@sankar ~]# useradd -d /users/ san

 

[root@sankar ~]# cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin

# useradd –u <UID> <user name>         - create user with specific UID.

# passwd <user name>      -           change the user password

# userdel <user name>      -           delete user

# userdel <user name>      -           delete user including home directory

# finger <user name>         -           See user properties

# chfn <user name>            -           Change user information




 
[root@sankar ~]# chfn root
Changing finger information for root.
Name [root]:




 # chage –l <user name> - to check user password expiry and account expiry information



 chage -l  root
Last password change                                    : May 02, 2015
Password expires                                        : never
Password inactive                                       : never
Account expires                                         : never
Minimum number of days between password change          : 0
Maximum number of days between password change          : 99999
Number of days of warning before password expires       : 7
 

 

# su - <user name> -           Switch to other user account

# id <user name>    -           it will show the user id

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

# system-config-users         -           create and manage user account in GUI

Usermod command options:

-c = We can add comment field for the user account.

-d = To modify the directory for any existing user account.

-e = Using this option we can make the account expiry in specific period.

-g = Change the primary group for a User.

-G = To add a supplementary groups.

-a = To add anyone of the group to a secondary group.

-l = To change the login name from tecmint to tecmint_admin.

-L = To lock the user account. This will lock the password so we can’t use the account.

-m = moving the contents of the home directory from existing home dir to new dir.

-p = To Use un-encrypted password for the new password. (NOT Secured).

-s = Create a Specified shell for new accounts.

-u = Used to Assigned UID for the user account between 0 to 999.

-U = To unlock the user accounts. This will remove the password lock and allow us to use the user account.

Creating Groups:

Group information is located/stored on /etc/group file.

# groupadd <group name>           - Create a group with specified name

# usermod –G <group name> <user name> - Add user to group

# gpasswd –a san Administrators – Adds the user ravi to the group Administrators

# gpasswd –A san  Administrators – give user ravi administrative rights to the group

# gpasswd –d san  Administrators – remove user ravi from the group Administrators

# groupdel <group name> - Delete group name

# groupmod –n <new group name> <old group name> - change group name

# newgrp - <group name> - Login into the group if successful, re-initializes the user environment