Linux and Unix usermod command

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About usermod
Syntax
Examples
Related commands
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About usermod

Modifies a user account.

Syntax

usermod [options] LOGIN

Description

The usermod command is used by an administrator to change a user's system account settings, as listed in the options below:

Options

-a, --append Add the user to the supplementary group(s). Use only with the -G option.
-c COMMENT, --comment COMMENT The new value of the user's password file comment field. It is normally modified using the chfn utility.
-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.
-e EXPIRE_DATE, --expiredate EXPIRE_DATE The date on which the user account will be disabled. The date is specified in the format YYYY-MM-DD. An empty EXPIRE_DATE argument will disable the expiration of the account.

This option requires a /etc/shadow file. A /etc/shadow entry will be created if there were none.
-f INACTIVE, --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.

This option requires a /etc/shadow file. A /etc/shadow entry will be created if there were none.
-g GROUP, --gid GROUP The group name or number of the user's new initial login group. The group must exist.

Any file from the user's home directory owned by the previous primary group of the user will be owned by this new group.
-G, --groups GROUP1[,GROUP2,...[,GROUPN]] A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no intervening whitespace. 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.
-l NEW_LOGIN, --login NEW_LOGIN The name of the user will be changed from LOGIN to NEW_LOGIN. Nothing else is changed. In particular, the user's home directory or mail spool should probably be renamed manually to reflect the new login name.
-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 want to lock the account (not only access with a password), you should also set the EXPIRE_DATE to 1 using -e (see above).
-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.

usermod will try to adapt the ownership of the files and to copy the modes, ACL and extended attributes, but manual changes might be needed afterwards.
-o, --non-unique When used with the -u option, this option allows to change the user ID to a non-unique value.
-p PASSWORD, --password PASSWORD The encrypted password, as returned by crypt.

Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes (using the ps command, for instance).

The password will be written in the local /etc/passwd or /etc/shadow file. This might differ from the password database configured in your PAM (Pluggable Authentication Module) configuration.

You should make sure the password respects the system's password policy.
-R CHROOT_DIR, --root CHROOT_DIR Apply changes in the CHROOT_DIR chroot directory and use the configuration files from the CHROOT_DIR directory.
-s SHELL, --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.
-u, --uid UID The new numerical value of the user's ID.

This value must be unique, unless the -o option is used. The value must be non-negative.

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.

The ownership of files outside of the user's home directory must be fixed manually.

No checks will be performed with regard to the UID_MIN, UID_MAX, SYS_UID_MIN, or SYS_UID_MAX values from /etc/login.defs.
-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 want 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) using the -e option (see above).
-Z SEUSER, --selinux-user SEUSER The new SELinux user for the user's login.

A blank SEUSER will remove the SELinux user mapping for user LOGIN (if any).

Notes

You must make certain that the named user is not executing any processes when this command is being executed if the user's numerical user ID, the user's name, or the user's home directory is being changed. usermod checks this on Linux, but only check if the user is logged in according to the utmp file on other architectures.

You must change the owner of any crontab files or at jobs manually.

You must make any changes involving NIS (Network Information Service) on the NIS server.

Configuration

The following configuration variables in /etc/login.defs change the behavior of this tool:

Name Type Description
MAIL_DIR string The mail spool directory. This is needed to manipulate the mailbox when its corresponding user account is modified or deleted. If not specified, a compile-time default is used.
MAIL_FILE string Defines the location of the users' mail spool files relative to their home directory.
MAX_MEMBERS_PER_GROUP number Maximum members per group entry. When the maximum is reached, a new group entry (line) is started in /etc/group (with the same name, same password, and same GID).

The default value is 0, meaning that there are no limits in the number of members in a group.

This feature (split group) permits to limit the length of lines in the group file. This is useful to make sure that lines for NIS groups are not larger than 1024 characters.

If you need to enforce such limit, you can use 25.

Note: split groups may not be supported by all tools. You should not use this variable unless you really need it.

Files

usermod makes use of the following files:

/etc/group Group account information.
/etc/gshadow Secure group account information.
/etc/login.defs Shadow password suite configuration.
/etc/passwd User account information.
/etc/shadow Secure user account information.

Examples

usermod -d /home/exampleusernew exampleuser

Modifies the home directory for the exampleuser account, changing it to /home/exampleusernew.

Related commands

chsh — The C shell command interpreter.
useradd — Add a user to the system.
userdel — Remove a user from the system.