15+ switches of usermod command with example – Unix/Linux

The Unix/Linux command “usermod” is a useful one to alter the already created user via command line.

The command Useradd or adduser is for creating a user in Linux system/server from its command prompt. The basic syntax for creting a user is simply type the username after the command useradd.

It will create a user with defined settings. In some situations we need to alter the parameters of a user, in this case we can use the command usermod. See the syntax explained below.

User information are stored in /etc/passwd file.

The important user information are Username, UID(User ID), GID(Group ID), a comment, home directory location, shell details etc. With the command usermod, a lot of switches are available to change those parameters.

Example, you can change the comment of a user in the file /etc/passwd by using the switch “-c” similarly you can change the home directory by using the switch “d”.

Syntax

# usermod [options] USERNAME

See the default values to compare the usermod output

[[email protected] ~]# useradd me
[[email protected] ~]# grep -w me /etc/passwd
me:x:502:502::/home/me:/bin/bash

Switches with example

1, -a, –append

Add the user to the supplementary group(s). Use only with the -G option.

2, -c, –comment COMMENT

The new value of the user´s password file comment field.

Example:

[[email protected] ~]# usermod -c "I'm usermod" me
[[email protected] ~]# grep -w me /etc/passwd
me:x:502:502:I'm usermod:/home/me:/bin/bash

Comment field changed to “I’m usermod”

3, -d, –home HOME_DIR

The user´s new login directory.

If the -m option is given, the contents of the current home directory will be moved to the new home directory, which is created if it does not already exist.

Example:

[[email protected] ~]# usermod -d /home/meusermod  me
[[email protected] ~]# grep -w me /etc/passwd
me:x:502:502:I'm usermod:/home/meusermod:/bin/bash

4, -e, –expiredate EXPIRE_DATE

The date on which the user account will be disabled. The date is specified in the format YYYY-MM-DD.

5, -f, –inactive INACTIVE

The number of days after a password expires until the account is permanently disabled. A value of 0 disables the account as soon as the password has expired, and a value of -1 disables the feature.

6, -g, –gid GROUP

The group name or number of the user´s new initial login group. The group must exist.

Example:

[[email protected] ~]# usermod -g 0  me
[[email protected] ~]# grep -w me /etc/passwd
me:x:502:0:I'm usermod:/home/meusermod:/bin/bash

7, -G, –groups GROUP1[,GROUP2,…[,GROUPN]]]

A list of supplementary groups which the user is also a member of. Separated from the next by a comma without space. The groups are subject to the same restrictions as the group given with the -g option.

If the user is currently a member of a group which is not listed, the user will be removed from the group. This behaviour can be changed via the -a option, which appends the user to the current supplementary group list.

Example:

[[email protected] ~]# usermod -G crybit  me
[[email protected] ~]# groupmems -g crybit -l
me

8, -l, –login NEW_LOGIN

The name of the user will be changed from LOGIN to NEW_LOGIN. In particular, the user´s home directory name should probably be changed manually to reflect the new login name.

Example:

[[email protected] ~]# usermod -l namechange me
usermod: warning: /var/spool/mail/me not owned by me
[[email protected] ~]# grep -w me /etc/passwd
[[email protected] ~]# tail -n2 /etc/passwd
crybit:x:501:501::/home/crybit:/bin/bash
namechange:x:502:0:I'm usermod:/home/meusermod:/bin/bash

Login name changed to “namechange”

9, -L, –lock

Lock a user´s password. This puts a ´!´ in front of the encrypted password, effectively disabling the password. You can´t use this option with -p or -U.

Note: if you wish to lock the account (not only access with a password), you should also set the EXPIRE_DATE to 1.

Example:

[[email protected] ~]# usermod -L me
[[email protected] ~]# grep -w me /etc/shadow
me:!$6$E6bjJlI1$Phbo3rhsWNoHBwkRyGgPZV0BBM8.okQyJZifbHNzrGsmBsREmcxfNLv9TrKIX34zA7e3Hv/J0LxzxEIOTTt7n/:16101:0:99999:7:::

10, -U, –unlock

Unlock a user´s password. This removes the ´!´ in front of the encrypted password. You can´t use this option with -p or -L.

Note: if you wish to unlock the account (not only access with a password), you should also set the

EXPIRE_DATE (for example to 99999, or to the EXPIRE value from /etc/default/useradd).

[[email protected] ~]# usermod -U me
[[email protected] ~]# grep -w me /etc/shadow
me:$6$E6bjJlI1$Phbo3rhsWNoHBwkRyGgPZV0BBM8.okQyJZifbHNzrGsmBsREmcxfNLv9TrKIX34zA7e3Hv/J0LxzxEIOTTt7n/:16101:0:99999:7:::

11, -m, –move-home

Move the content of the user´s home directory to the new location. This option is only valid in combination with the -d (or –home) option.

12, -o, –non-unique

When used with the -u option, this option allows to change the user ID to a non-unique value.

13, -p, –password PASSWORD

The encrypted password, as returned by crypt(3).

Not recommended. The password (or encrypted password) will be visible by users listing the processes. You should make sure the password respects the system´s password policy.

14, -s, –shell SHELL

The name of the user´s new login shell. Setting this field to blank causes the system to select the default login shell.

Example:

[[email protected] ~]# usermod -s /bin me
[[email protected] ~]# grep -w me /etc/passwd
me:x:502:0:I'm usermod:/home/meusermod:/bin

15, -u, –uid UID

The new numerical value of the user´s ID. Set uniq number. The value must be non-negative. The UID 0 to 999 are system reserved.

The user´s mailbox, and any files which the user owns and which are located in the user´s home directory will have the file user ID changed automatically.

Change ownerships outside of the user ´s home directory manually.

[[email protected] ~]# usermod -u 100000 me
[[email protected] ~]# grep -w me /etc/passwd
me:x:100000:0:I'm usermod:/home/meusermod:/bin

16, -Z, –selinux-user SEUSER

The SELinux user for the user´s login. The default is to leave this field the blank, which causes the system to select the default SELinux user.

Thanks!! 🙂 🙂

Related Links:
groupdel, groupmems, groupmod, useradd

More:
ls, head, tail, top, ps, find, crontab

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Arunlal Ashok

Linux Systems Architect at Endurance International Group. I know her (Linux) since many years. Linux lover. Like to play on Linux console. I started this blog to share and discuss Linux thoughts.

Always happy for an open discussion! Write to arun (@) crybit (dot) com. Check about me for more details. About this blog and our strong members, check The team CryBit.com

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