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

USERADD(8)			    System Management Commands			       USERADD(8)

       useradd - create a new user or update default new user information

       useradd [options] LOGIN

       useradd -D

       useradd -D [options]

       useradd is a low level utility for adding users. On Debian, administrators should usually
       use adduser(8) instead.

       When invoked without the -D option, the useradd command creates a new user account using
       the values specified on the command line plus the default values from the system.
       Depending on command line options, the useradd command will update system files and may
       also create the new user's home directory and copy initial files.

       By default, a group will also be created for the new user (see -g, -N, -U, and

       The options which apply to the useradd command are:

       -b, --base-dir BASE_DIR
	   The default base directory for the system if -d HOME_DIR is not specified.  BASE_DIR
	   is concatenated with the account name to define the home directory. If the -m option
	   is not used, BASE_DIR must exist.

	   If this option is not specified, useradd will use the base directory specified by the
	   HOME variable in /etc/default/useradd, or /home by default.

       -c, --comment COMMENT
	   Any text string. It is generally a short description of the login, and is currently
	   used as the field for the user's full name.

       -d, --home HOME_DIR
	   The new user will be created using HOME_DIR as the value for the user's login
	   directory. The default is to append the LOGIN name to BASE_DIR and use that as the
	   login directory name. The directory HOME_DIR does not have to exist but will not be
	   created if it is missing.

       -D, --defaults
	   See below, the subsection "Changing the default values".

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

	   If not specified, useradd will use the default expiry date specified by the EXPIRE
	   variable in /etc/default/useradd, or an empty string (no expiry) by default.

       -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.

	   If not specified, useradd will use the default inactivity period specified by the
	   INACTIVE variable in /etc/default/useradd, or -1 by default.

       -g, --gid GROUP
	   The group name or number of the user's initial login group. The group name must exist.
	   A group number must refer to an already existing group.

	   If not specified, the behavior of useradd will depend on the USERGROUPS_ENAB variable
	   in /etc/login.defs. If this variable is set to yes (or -U/--user-group is specified on
	   the command line), a group will be created for the user, with the same name as her
	   loginname. If the variable is set to no (or -N/--no-user-group is specified on the
	   command line), useradd will set the primary group of the new user to the value
	   specified by the GROUP variable in /etc/default/useradd, or 100 by default.

       -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. The default is
	   for the user to belong only to the initial group.

       -h, --help
	   Display help message and exit.

       -k, --skel SKEL_DIR
	   The skeleton directory, which contains files and directories to be copied in the
	   user's home directory, when the home directory is created by useradd.

	   This option is only valid if the -m (or --create-home) option is specified.

	   If this option is not set, the skeleton directory is defined by the SKEL variable in
	   /etc/default/useradd or, by default, /etc/skel.

	   If possible, the ACLs and extended attributes are copied.

       -K, --key KEY=VALUE
	   Overrides /etc/login.defs defaults (UID_MIN, UID_MAX, UMASK, PASS_MAX_DAYS and

	   Example: -K PASS_MAX_DAYS=-1 can be used when creating system account to turn off
	   password ageing, even though system account has no password at all. Multiple -K
	   options can be specified, e.g.: -K UID_MIN=100 -K UID_MAX=499

       -l, --no-log-init
	   Do not add the user to the lastlog and faillog databases.

	   By default, the user's entries in the lastlog and faillog databases are resetted to
	   avoid reusing the entry from a previously deleted user.

	   For the compatibility with previous Debian's useradd, the -O option is also supported.

       -m, --create-home
	   Create the user's home directory if it does not exist. The files and directories
	   contained in the skeleton directory (which can be defined with the -k option) will be
	   copied to the home directory.

	   By default, if this option is not specified and CREATE_HOME is not enabled, no home
	   directories are created.

	   Do no create the user's home directory, even if the system wide setting from
	   /etc/login.defs (CREATE_HOME) is set to yes.

       -N, --no-user-group
	   Do not create a group with the same name as the user, but add the user to the group
	   specified by the -g option or by the GROUP variable in /etc/default/useradd.

	   The default behavior (if the -g, -N, and -U options are not specified) is defined by
	   the USERGROUPS_ENAB variable in /etc/login.defs.

       -o, --non-unique
	   Allow the creation of a user account with a duplicate (non-unique) UID.

	   This option is only valid in combination with the -u option.

       -p, --password PASSWORD
	   The encrypted password, as returned by crypt(3). The default is to disable the

	   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 system's password policy.

       -r, --system
	   Create a system account.

	   System users will be created with no aging information in /etc/shadow, and their
	   numeric identifiers are chosen in the SYS_UID_MIN-SYS_UID_MAX range, defined in
	   /etc/login.defs, instead of UID_MIN-UID_MAX (and their GID counterparts for the
	   creation of groups).

	   Note that useradd will not create a home directory for such an user, regardless of the
	   default setting in /etc/login.defs (CREATE_HOME). You have to specify the -m options
	   if you want a home directory for a system account to be created.

       -s, --shell SHELL
	   The name of the user's login shell. The default is to leave this field blank, which
	   causes the system to select the default login shell specified by the SHELL variable in
	   /etc/default/useradd, or an empty string by default.

       -u, --uid UID
	   The 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 default is to use the smallest ID value
	   greater than 999 and greater than every other user. Values between 0 and 999 are
	   typically reserved for system accounts.

       -U, --user-group
	   Create a group with the same name as the user, and add the user to this group.

	   The default behavior (if the -g, -N, and -U options are not specified) is defined by
	   the USERGROUPS_ENAB variable in /etc/login.defs.

       -Z, --selinux-user SEUSER
	   The SELinux user for the user's login. The default is to leave this field blank, which
	   causes the system to select the default SELinux user.

   Changing the default values
       When invoked with only the -D option, useradd will display the current default values.
       When invoked with -D plus other options, useradd will update the default values for the
       specified options. Valid default-changing options are:

       -b, --base-dir BASE_DIR
	   The path prefix for a new user's home directory. The user's name will be affixed to
	   the end of BASE_DIR to form the new user's home directory name, if the -d option is
	   not used when creating a new account.

	   This option sets the HOME variable in /etc/default/useradd.

       -e, --expiredate EXPIRE_DATE
	   The date on which the user account is disabled.

	   This option sets the EXPIRE variable in /etc/default/useradd.

       -f, --inactive INACTIVE
	   The number of days after a password has expired before the account will be disabled.

	   This option sets the INACTIVE variable in /etc/default/useradd.

       -g, --gid GROUP
	   The group name or ID for a new user's initial group (when the -N/--no-user-group is
	   used or when the USERGROUPS_ENAB variable is set to no in /etc/login.defs. The named
	   group must exist, and a numerical group ID must have an existing entry.

	   This option sets the GROUP variable in /etc/default/useradd.

       -s, --shell SHELL
	   The name of a new user's login shell.

	   This option sets the SHELL variable in /etc/default/useradd.

       The system administrator is responsible for placing the default user files in the
       /etc/skel/ directory (or any other skeleton directory specified in /etc/default/useradd or
       on the command line).

       You may not add a user to a NIS or LDAP group. This must be performed on the corresponding

       Similarly, if the username already exists in an external user database such as NIS or
       LDAP, useradd will deny the user account creation request.

       It is usually recommended to only use usernames that begin with a lower case letter or an
       underscore, followed by lower case letters, digits, underscores, or dashes. They can end
       with a dollar sign. In regular expression terms: [a-z_][a-z0-9_-]*[$]?

       On Debian, the only constraints are that usernames must neither start with a dash ('-')
       nor contain a colon (':') or a whitespace (space: ' ', end of line: '\n', tabulation:
       '\t', etc.). Note that using a slash ('/') may break the default algorithm for the
       definition of the user's home directory.

       Usernames may only be up to 32 characters long.

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

       CREATE_HOME (boolean)
	   Indicate if a home directory should be created by default for new users.

	   This setting does not apply to system users, and can be overridden on the command

       GID_MAX (number), GID_MIN (number)
	   Range of group IDs used for the creation of regular groups by useradd, groupadd, or

       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.

       PASS_MAX_DAYS (number)
	   The maximum number of days a password may be used. If the password is older than this,
	   a password change will be forced. If not specified, -1 will be assumed (which disables
	   the restriction).

       PASS_MIN_DAYS (number)
	   The minimum number of days allowed between password changes. Any password changes
	   attempted sooner than this will be rejected. If not specified, -1 will be assumed
	   (which disables the restriction).

       PASS_WARN_AGE (number)
	   The number of days warning given before a password expires. A zero means warning is
	   given only upon the day of expiration, a negative value means no warning is given. If
	   not specified, no warning will be provided.

       SYS_GID_MAX (number), SYS_GID_MIN (number)
	   Range of group IDs used for the creation of system groups by useradd, groupadd, or

       SYS_UID_MAX (number), SYS_UID_MIN (number)
	   Range of user IDs used for the creation of system users by useradd or newusers.

       UID_MAX (number), UID_MIN (number)
	   Range of user IDs used for the creation of regular users by useradd or newusers.

       UMASK (number)
	   The file mode creation mask is initialized to this value. If not specified, the mask
	   will be initialized to 022.

	   useradd and newusers use this mask to set the mode of the home directory they create

	   It is also used by pam_umask as the default umask value.

       USERGROUPS_ENAB (boolean)
	   If set to yes, userdel will remove the user's group if it contains no more members,
	   and useradd will create by default a group with the name of the user.

	   User account information.

	   Secure user account information.

	   Group account information.

	   Secure group account information.

	   Default values for account creation.

	   Directory containing default files.

	   Shadow password suite configuration.

       The useradd command exits with the following values:


	   can't update password file

	   invalid command syntax

	   invalid argument to option

	   UID already in use (and no -o)

	   specified group doesn't exist

	   username already in use

	   can't update group file

	   can't create home directory

	   can't create mail spool

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

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

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