Linux - Usermod

This command is used modify the user attributes like user id, group, name etc. 

Syntax:

Usermod [options] username

The following are the list of options to modify already existing user attributes.

-d  this option is used to change the working directory of the user

-g  this option is used to change the primary group of the user

-G this option is used to change the secondary group of the user

-L  this option is used to lock the user account.

-U this option is used to unlock the user account.

-s  this option is used to assign shell to the user.

-e  this option is used to assign specific expiry date to the particular user.

-u  this option is used to modify the user id of the user.

-l   this option is used to modify the login name of the user.

-c  this option is used to change the comment or assign the comment to the particular user.

Let us see some examples to understand more on this topic.

Example-1:

Assigning comment to a user:

So we are going to assign a comment to the user john by using “-c” option.

[root@sys1 ~]# grep --color DB2admin /etc/passwd
john:x:501:501:DB2admin:/home/john:/bin/bash

Example -2:

Changing working directory of the user:

To change working directory of the user we use ‘-d’ option with usermod command.

[root@sys1 ~]# usermod -d /repo john
[root@sys1 ~]# grep --color /repo /etc/passwd
john:x:501:501:DB2admin:/repo:/bin/bash

Example-3:

Changing primary group of the user:

To change primary group of the user we use ‘-g’ option with usermod command.

[root@sys1 ~]# usermod -g OracleDB steve
[root@sys1 ~]# id steve
uid=503(steve) gid=504(OracleDB) groups=504(OracleDB)

Example-4:

Changing secondary group of the user:

We use “-G” option with usermod command to change the secondary group of a particular user. To understand more observe the following scenario.

[root@sys1 ~]# id steve
uid=503(steve) gid=504(OracleDB) groups=504(OracleDB)

Now I am going to add SQL as the secondary group of the user steve.

[root@sys2 ~]# usermod -G SQL steve

Now check whether the secondary group has assigned or not using id command.

[root@sys2 ~]# id steve
uid=502(steve) gid=504(OracleDB) groups=504(OracleDB),510(SQL)

Example-5:

Locking and unlocking the user account:

By locking the user account the user was not able to login to the server. To lock the user account we use ‘-L’ option with user mod command. Have a look on the following scenario to understand more.

[root@sys2 ~]# usermod -L steve

From the above command, we locked the user steve. Now try to login with the credentials of steve.

login as: steve
steve@192.168.0.17's password:
Access denied

Hence, the user account was successfully locked. Now my question is how to check locked user account?

Simply use passwd command with –s option as shown below.

[root@sys2 ~]# passwd -S steve
steve LK 2016-01-26 0 99999 7 -1 (Password locked.)

From the above output the user account was successfully locked .

Now, I am going to unlock the user steve by using ‘-U’ with usermod command. After unlocking the user can be able to login to the server.

[root@sys2 ~]# usermod -U steve
[root@sys2 ~]# passwd -S steve
steve PS 2016-07-31 0 99999 7 -1 (Password set, SHA512 crypt.)
From the above scenario we are successfully unlocked the user account steve. Now I am trying to login as steve as follows.
login as: steve
steve@192.168.0.4's password:
[steve@sys2 ~]$

From the above view the steve account was successfully unlocked.

Example-6:

Assigning a shell to the user:

To change or assign ashell to the user we use “-s” option with usermod command. To know more about the Shell go through the topic shell in the introduction 

[root@sys2 ~]# grep steve /etc/passwd
steve:x:502:509::/home/steve:/bin/bash

From the above command the shell assigned to the steve is bash. Now I am going ro change the shell to c-shell.

[root@sys2 ~]# grep steve /etc/passwd
steve:x:502:509::/home/steve:/bin/csh

From the above lines the shell is successfully updated to the user steve.

Example-7:

Modifying the username of the user account:

Using ‘-l’ option with usermod command we can change the user name of a particular account. To understand more observe the following.

[root@sys2 ~]# grep --color steve /etc/passwd
steve:x:502:509::/home/steve:/bin/csh
[root@sys2 ~]# usermod -l steveJobs steve
[root@sys2 ~]# grep --color steveJobs /etc/passwd
steveJobs:x:502:509::/home/steve:/bin/csh

This is how we can change the user name of a particular account.

Example-8:

Assigning an expiry date to a user account:

By using ‘-e’ option with the usermod command we can assign the expiry date to a particular user account.

Let us see practically,

Check the expiry date of the user steve using chage –l command. We can change the expiry date of a user using chage command also click here to view that.

[root@sys2 ~]# chage -l steve
Last password change : Jul 31, 2016
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

From the above output we understood that there is no account expiry date to the user steve.

Now assign an expiry date to the user steve as follows.

[root@sys2 ~]# usermod -e 2018-01-01 steve

Now check weather expiry date has assigned or not.

[root@sys2 ~]# chage -l steve
Last password change : Jul 31, 2016
Password expires     : never
Password inactive    : never
Account expires      : Jan 01, 2018
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

Hence we assigned an expiry date to the user account steve.

Example-9:

Modifying the user id of an user account:

To change the user id of an user we use ‘-u’ option with usermod command. Observe the following to understand more.

Now I am going to change the user id of steve.

Check the user id of steve.

[root@sys2 ~]# id steve
uid=502(steve) gid=509(OracleDB) groups=509(OracleDB),510(SQL)

Change the user id of steve from 502 to 520.

[root@sys2 ~]# id steve
uid=520(steve) gid=509(OracleDB) groups=509(OracleDB),510(SQL)

Hence the user id of steve has changed successfully.

You can change different attributes of the user account within single command also.