Table of Contents

 

Name

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

Synopsis

useradd [options] LOGIN

useradd -D

useradd -D [options]

Description

 

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.

Options

The options which apply to the useradd command are:

-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.

-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.

-D, --defaults

See below, the subsection "Changing the default values".

-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.

-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. The default value is -1.

-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. The default group number is 1 or whatever is specified in /etc/default/useradd.

-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 in /etc/default/useradd or, by default, /etc/skel.

This option may not function correctly if the username has a / in it.

-K, --key KEY=VALUE

Overrides /etc/login.defs defaults (UID_MIN, UID_MAX, UMASK, PASS_MAX_DAYS and others).

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

Note: -K UID_MIN=10,UID_MAX=499 doesn’t work yet.

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

-l

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.

-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, no home directories are created.

-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 login.defs.

-o, --non-unique

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

-p, --password PASSWORD

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

-r, --system

Create a system account.

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

-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.

-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 login.defs.

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.

-e, --expiredate EXPIRE_DATE

The date on which the user account is disabled.

-f, --inactive INACTIVE

The number of days after a password has expired before the account will be disabled.

-g, --gid GROUP

The group name or ID for a new user’s initial group. The named group must exist, and a numerical group ID must have an existing entry.

-s, --shell SHELL

The name of a new user’s login shell.

Notes

The system administrator is responsible for placing the default user files in the /etc/skel/ directory.

Caveats

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

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, and are only followed by lower case letters, digits, underscores, dashes, and optionally terminated by 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.).

Usernames may only be up to 32 characters long.

Configuration

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

GID_MAX (number), GID_MIN (number)

Range of group IDs used for the creation of regular groups by useradd, useradd, or newusers.

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-timedefault 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 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 youneed 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 daysallowed 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 newusers.

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 permission mask is initialized to this value. If not specified, the permission mask will be initialized to 022.

USERGROUPS_ENAB (boolean)

Files

/etc/passwd

User account information.

/etc/shadow

Secure user account information.

/etc/group

Group account information.

/etc/default/useradd

Default values for account creation.

/etc/skel/

Directory containing default files.

/etc/login.defs

Shadow password suite configuration.

Exit Values

The useradd command exits with the following values:

0

success

1

can’t update password file

2

invalid command syntax

3

invalid argument to option

4

UID already in use (and no -o)

6

specified group doesn’t exist

9

username already in use

10

can’t update group file

12

can’t create home directory

13

can’t create mail spool

See Also

 

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

 


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