名字
       useradd - 创建一个新的用户，或者更新一个已有用户的信息

简介

       useradd [options] LOGIN


       useradd -D


       useradd -D [options]


描述
       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 USERGROUPS_ENAB).


选项
       The options which apply to the useradd command are:


       -b, --base-dir BASE_DIR

           所有用户的主目录存放的绝对路径，BASE_DIR将在HOME_DIR参数没有设定的情况下组合用户名生成新建用户的主目录。如果-m参数不指定，BASE_DIR必须存在。

           默认为/home或是/etc/default/useradd里的HOME变量。

       -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

用户的主目录的绝对路径。默认值是将LOGIN NAME和ABSE_DIR组合起来作为新建用户的主目录的绝对路径。用户的绝对主目录不一定必须存在但是如果一旦被删掉，主目录将不会再被创建。

       -D, --defaults

       -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 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


       -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, 创建用户家目录

创建用户家目录，如果不存在，将会把模板文件夹（有-K参数指定）中的文件和文件夹拷贝到用户新创建的家目录中。

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


       -M
           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 password.


           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.


改变文件默认值

       使用-D不加任何参数时，将会显示出useradd的默认值；当使用-D并且加上一些参数时，useradd将会更新对应的默认值。-D可以使用的参数如下：

       -b, --base-dir BASE_DIR

       -e, --expiredate EXPIRE_DATE

账号过期时间，这个选项将会改变/etc/default/useradd里的EXPIRE变量。

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

账号过期后，还可以继续使用的huan

           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.


NOTES
       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
       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, 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.


CONFIGURATION
       下面的这些变量设定了useradd的一些默认值。他们保存在/etc/login.defs文件中。

       CREATE_HOME (boolean)
          创建新的用户时是否创建对应的主目录。只适用于普通用户，不用于系统用户。此参数可以通过命令行设置。


       GID_MAX (number), GID_MIN (number)
           GID的取值范围，将会被useradd,groupadd,newusers使用。

       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 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.


       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 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 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.


FILES
       /etc/passwd
           User account information.


       /etc/shadow
           Secure user account information.


       /etc/group
           Group account information.


       /etc/gshadow
           Secure 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).