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Linux 2.6 - man page for usermod (linux section 8)

USERMOD(8)			    System Management Commands			       USERMOD(8)

       usermod - modify a user account

       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.

       -c, --comment COMMENT
	   The new value of the user's password file comment field. It is normally modified using
	   the chfn(1) 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, --expiredate EXPIRE_DATE
	   The date on which the user account will be disabled. The date is specified in the
	   format YYYY-MM-DD.

       -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.

       -g, --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.

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

       -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 user's home directory name should probably be changed 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 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 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

       -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.

	   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 configuration.

	   You should make sure the password respects the system's password policy.

       -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.

       -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. Values between 0 and 999 are typically reserved for system accounts.

	   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.

       -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

       -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.

       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 utmp on other architectures.

       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:

       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 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 user's mail spool.

       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

	   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

	   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.

	   Group account information.

	   Secure group account information.

	   User account information.

	   Secure user account information.

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

System Management Commands		    06/24/2011				       USERMOD(8)

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