usermod

Change a username

$ sudo usermod --login [new_username] [username]

$ sudo usermod --uid [id] [username]

$ sudo usermod --shell [path/to/shell] [username]

$ sudo usermod --append --groups [group1,group2,...] [username]

$ sudo usermod --move-home --home [path/to/new_home] [username]

usermod [options] LOGIN

The usermod command modifies the system account files to reflect the changes that are specified on the command line.

The options which apply to the usermod command are:

-a, --append

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

-b, --badnames

Allow names that do not conform to standards.

-c, --comment COMMENT

The new value of the users password file comment field. It is normally modified using the chfn(1) utility.

-d, --home HOME_DIR

The users 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. If the current home directory does not exist the new home directory will not be created.

-e, --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

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, --gid GROUP

The group name or number of the users new initial login group. The group must exist.

Any file from the users home directory owned by the previous primary group of the user will be owned by this new group.

The group ownership of files outside of the users home directory must be fixed manually.

The change of the group ownership of files inside of the users home directory is also not done if the home dir owner uid is different from the current or new user id. This is a safety measure for special home directories such as /.

-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. This behaviour can be changed via the -a option, which appends the user to the current supplementary group list.

-l, --login NEW_LOGIN

The name of the user will be changed from LOGIN to NEW_LOGIN. Nothing else is changed. In particular, the users home directory or mail spool should probably be renamed manually to reflect the new login name.

-L, --lock

Lock a users password. This puts a ! in front of the encrypted password, effectively disabling the password. You cant 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.

-m, --move-home

Move the content of the users home directory to the new location. If the current home directory does not exist the new home directory will not be created.

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

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

Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes.

You should make sure the password respects the systems password policy.

-r, --remove

Remove the user from named supplementary group(s). Use only with the -G option.

-R, --root CHROOT_DIR

Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.

-P, --prefix PREFIX_DIR

Apply changes in the PREFIX_DIR directory and use the configuration files from the PREFIX_DIR directory. This option does not chroot and is intended for preparing a cross-compilation target. Some limitations: NIS and LDAP users/groups are not verified. PAM authentication is using the host files. No SELINUX support.

-s, --shell SHELL

The path of the users 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 users ID.

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

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

The ownership of files outside of the users home directory must be fixed manually.

The change of the user ownership of files inside of the users home directory is also not done if the home dir owner uid is different from the current or new user id. This is a safety measure for special home directories such as /.

No checks will be performed with regard to the UID_MIN, UID_MAX, SYS_UID_MIN, or SYS_UID_MAX from /etc/login.defs.

-U, --unlock

Unlock a users password. This removes the ! in front of the encrypted password. You cant 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).

-v, --add-subuids FIRST-LAST

Add a range of subordinate uids to the users account.

This option may be specified multiple times to add multiple ranges to a users account.

No checks will be performed with regard to SUB_UID_MIN, SUB_UID_MAX, or SUB_UID_COUNT from /etc/login.defs.

-V, --del-subuids FIRST-LAST

Remove a range of subordinate uids from the users account.

This option may be specified multiple times to remove multiple ranges to a users account. When both --del-subuids and --add-subuids are specified, the removal of all subordinate uid ranges happens before any subordinate uid range is added.

No checks will be performed with regard to SUB_UID_MIN, SUB_UID_MAX, or SUB_UID_COUNT from /etc/login.defs.

-w, --add-subgids FIRST-LAST

Add a range of subordinate gids to the users account.

This option may be specified multiple times to add multiple ranges to a users account.

No checks will be performed with regard to SUB_GID_MIN, SUB_GID_MAX, or SUB_GID_COUNT from /etc/login.defs.

-W, --del-subgids FIRST-LAST

Remove a range of subordinate gids from the users account.

This option may be specified multiple times to remove multiple ranges to a users account. When both --del-subgids and --add-subgids are specified, the removal of all subordinate gid ranges happens before any subordinate gid range is added.

No checks will be performed with regard to SUB_GID_MIN, SUB_GID_MAX, or SUB_GID_COUNT from /etc/login.defs.

-Z, --selinux-user SEUSER

The new SELinux user for the users login.

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

You must make certain that the named user is not executing any processes when this command is being executed if the users numerical user ID, the users name, or the users home directory is being changed. usermod checks this on Linux. On other platforms it only uses utmp to check if the user is logged in.

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

You must make any changes involving NIS on the NIS server.

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

LASTLOG_UID_MAX (number)

Highest user ID number for which the lastlog entries should be updated. As higher user IDs are usually tracked by remote user identity and authentication services there is no need to create a huge sparse lastlog file for them.

No LASTLOG_UID_MAX option present in the configuration means that there is no user ID limit for writing lastlog entries.

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. The parameter CREATE_MAIL_SPOOL in /etc/default/useradd determines whether the mail spool should be created.

MAIL_FILE (string)

Defines the location of the users mail spool files relatively to their home directory.

The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the users mail spool.

If MAIL_CHECK_ENAB is set to yes, they are also used to define the MAIL environment variable.

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 (even in the Shadow toolsuite). You should not use this variable unless you really need it.

SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)

If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate group IDs) allocate SUB_GID_COUNT unused group IDs from the range SUB_GID_MIN to SUB_GID_MAX for each new user.

The default values for SUB_GID_MIN, SUB_GID_MAX, SUB_GID_COUNT are respectively 100000, 600100000 and 65536.

SUB_UID_MIN (number), SUB_UID_MAX (number), SUB_UID_COUNT (number)

If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate user IDs) allocate SUB_UID_COUNT unused user IDs from the range SUB_UID_MIN to SUB_UID_MAX for each new user.

The default values for SUB_UID_MIN, SUB_UID_MAX, SUB_UID_COUNT are respectively 100000, 600100000 and 65536.

/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.

/etc/subgid

Per user subordinate group IDs.

/etc/subuid

Per user subordinate user IDs.

chfn(1), chsh(1), passwd(1), crypt(3), gpasswd(8), groupadd(8), groupdel(8), groupmod(8), login.defs(5), subgid(5), subuid(5), useradd(8), userdel(8).