USERADD(8)

名称
useradd - 创建一个新用户或更新默认新用户信息

大纲

useradd [options] LOGIN

useradd -D

useradd -D [options]

描述

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 USERGROUPS_ENAB).

选项

The options which apply to the useradd command are:

--badname
    Allow names that do not conform to standards.

-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 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 account, and is currently used as the field for the user's full name.

-d, --home-dir 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. If the directory HOME_DIR does not exist, then it will be created unless the -M option is specified.

-D, --defaults
    看下边，“更改默认值”子节。

-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
    defines the number of days after the password exceeded its maximum age where the user is expected to replace this password. The value is stored in the shadow password file. An input of 0 will disable an expired password with no delay. An input of -1 will blank the respective field in the shadow password file. See shadow(5)for more information.

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

-F, --add-subids-for-system
    Update /etc/subuid and /etc/subgid even when creating a system account with -r option.

-g, --gid GROUP
    The name or the number of the user's primary 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 the 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 1000 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. In addition to passing in the -G flag, you can add the option GROUPS to the file /etc/default/useradd which in turn will add all users to those supplementary groups.

-h, --help
    显示帮助信息并退出。

-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.

    Absolute symlinks that link back to the skel directory will have the /etc/skel prefix replaced with the user's home directory.

    如果可以，也复制 ACL 和扩展属性。

-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 an account to turn off password aging. Multiple -K options can be specified, e.g.: -K UID_MIN =100 -K UID_MAX=499

-l, --no-log-init
    不要将用户添加到最近登录和登录失败数据库。

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

    If this option is not specified, useradd will also consult the variable LOG_INIT in the /etc/default/useradd if set to no the user will not be added to the lastlog and faillog databases.

-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.

    The directory where the user's home directory is created must exist and have proper SELinux context and permissions. Otherwise the user's home directory cannot be created or accessed.

-M, --no-create-home
    Do not 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
    allows the creation of an account with an already existing UID.

    This option is only valid in combination with the -u option. As a user identity serves as key to map between users on one hand and permissions, file ownerships and other aspects that determine the system's behavior on the other hand, more than one login name will access the account of the given UID.

-p, --password PASSWORD
    defines an initial password for the account. PASSWORD is expected to be encrypted, as returned by crypt (3). Within a shell script, this option allows to create efficiently batches of users.

    Without this option, the new account will be locked and with no password defined, i.e. a single exclamation mark in the respective field of /etc/shadow. This is a state where the user won't be able to access the account or to define a password himself.

    Note:Avoid this option on the command line because the password (or encrypted password) will be visible by users listing the processes.

    您应该确保密码符合系统的密码政策。

-r, --system
    创建一个系统账户。

    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 a 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.

    Note that this option will not update /etc/subuid and /etc/subgid. You have to specify the -F options if you want to update the files for a system account to be created.

-R, --root CHROOT_DIR
    Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory. Only absolute paths are supported.

-P, --prefix PREFIX_DIR
    Apply changes to configuration files under the root filesystem found under the directory PREFIX_DIR. 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
    sets the path to the user's login shell. Without this option, the system will use the SHELL variable specified in /etc/default/useradd, or, if that is as well not set, the field for the login shell in /etc/passwd remains empty.

-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 or equal to UID_MIN and greater than every other user.

    See also the -r option and the UID_MAX description.

-U, --user-group
    创建一个和用户同名的组，并将用户添加到组中。

    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
    defines the SELinux user for the new account. Without this option, SELinux uses the default user. Note that the shadow system doesn't store the selinux-user, it uses semanage(8) for that.

--selinux-range SERANGE
    defines the SELinux MLS range for the new account. Without this option, SELinux uses the default range. Note that the shadow system doesn't store the selinux-range, it uses semanage(8) for that.

    This option is only valid if the -Z (or --selinux-user) option is specified.

  更改默认值

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
    sets 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
    sets the date on which newly created user accounts are disabled.

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

-f, --inactive INACTIVE
    defines the number of days after the password exceeded its maximum age where the user is expected to replace this password. See shadow(5)for more information.

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

-g, --gid GROUP
    sets the default primary group for newly created users, accepting group names or a numerical group ID. The named group must exist, and the GID must have an existing entry.

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

-s, --shell SHELL
    defines the default login shell for new users.

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

注意：

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).

CAVEATS

您可能不能想 NIS 组或 LDAP 组添加用户。这只能在相应服务器上进行。

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

Usernames may contain only lower and upper case letters, digits, underscores, or dashes. They can end with a dollar sign. Dashes are not allowed at the beginning of the username. Fully numeric usernames and usernames . or .. are also disallowed. It is not recommended to use usernames beginning with . character as their home directories will be hidden in the ls output.

用户名不能超过 256 个字符长。

配置文件

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

文件

/etc/passwd
    用户账户信息。

/etc/shadow
    安全用户账户信息。

/etc/group
    组账户信息。

/etc/gshadow
    安全组账户信息。

/etc/default/useradd
    账户创建的默认值。

/etc/shadow-maint/useradd-pre.d/*, /etc/shadow-maint/useradd-post.d/*
    Run-part files to execute during user addition. The environment variable ACTION will be populated with useradd and SUBJECT with the username. useradd-pre.d will be executed prior to any user addition. useradd-post.d will execute after user addition. If a script exits non-zero then execution will terminate.

/etc/skel/
    包含默认文件的目录。

/etc/subgid
    Per user subordinate group IDs.

/etc/subuid
    Per user subordinate user IDs.

/etc/login.defs
    Shadow 密码套件配置。

退出值

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 or group name already in use

10
    can't update group file

12
    can't create home directory

14
    can't update SELinux user mapping

19
    invalid user or group name

参见

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