useradd (将用户添加到系统)

useradd is a low-level utility for adding users to a system. In general, the more friendly adduser should be used instead.

Your operating system may come with a slightly different version of useradd; check your documentation before using it to create new accounts. This documentation refers to some options frequently used on Debian-based variants of Linux, but is representative of useradd's general use.

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 the -g, -N, -U options, and the USERGROUPS_ENAB variable, below).

useradd [options] LOGIN

useradd -D

useradd -D [options]

When invoked with only the -D option, useradd displays 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:

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 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. The regular expression which describes a valid username is:

[a-z_][a-z0-9_-]*[$]?

The only constraints are that usernames must neither start with a dash ('-') nor plus ('+') nor tilde ('~') nor contain a colon (':'), a comma (','), or a whitespace (space: ' ', end of line: '\n', tab: '\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:

The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the user's mail spool.

useradd exits with the following status, depending on what occurred:

useradd -D

Displays the defaults for new users. Output resembles the following:

GROUP=1001
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=no

useradd newperson

Creates newperson as a new user. Once the new user has been added, you would need to use the passwd command to assign a password to the account.

Once a user has been created, you can modify any of the user settings, such as the user's home directory, using the usermod command.