On Unix-like operating systems, the useradd command creates a new user or sets the default information for new users.
This document covers the Linux version of useradd.
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).
COMMENT can be 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
Set new default values. See the section on Changing New User Default Values, below.
-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 groups containing the user as a member. 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 a help message, and exit.
-k, --skel SKEL_DIR
SKEL_DIR is 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 ACL 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: -KPASS_MAX_DAYS=-1 can be used when creating system account to turn off password aging, even though system account has no password at all. Multiple -K options can be specified, for example: -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 versions of useradd, the -O option is also supported for this purpose.
-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.
-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. 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 (for example, with the ps command).
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.
-R, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.
-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 or equal to UID_MIN and greater than every other user.
See also the -r option and the UID_MAX description.
-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 New User Default Values
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:
-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.
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. 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.
Configuration
The following configuration variables in /etc/login.defs change the behavior of this tool:
name
type
description
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 line.
GID_MAX, GID_MIN
number
Range of group IDs used for the creation of regular groups by useradd, groupadd, or newusers.
The default value for GID_MIN is 1000; the default for GID_MAX is 60000.
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 group ID).
The default value is 0, meaning that there are no limits in the number of members in a group.
This feature (split group) can help 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 advanced tools like 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, SYS_GID_MIN
number
Range of group IDs used for the creation of system groups by useradd, groupadd, or newusers.
The default value for SYS_GID_MIN is 101; the default value for SYS_GID_MAX is GID_MIN minus 1.
SYS_UID_MAX, SYS_UID_MIN
number
Range of user IDs used for the creation of system users by useradd or newusers.
The default value for SYS_UID_MIN is 101; the default value of SYS_UID_MAX is UID_MIN minus 1.
UID_MAX, UID_MIN
number
Range of user IDs used for the creation of regular users by useradd or newusers.
The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).
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 Status
useradd exits with the following status, depending on what occurred:
0
Everything was completed successfully.
1
Couldn't update the password file.
2
The syntax of the command was invalid.
3
One or more options were given an invalid argument.
4
User ID is already in use, and -o was not specified.
useradd (將用戶添加到系統)
在類似Unix的操作系統上，useradd命令創建一個新用戶或為新用戶設置默認信息。 本文檔介紹了useradd的Linux版本。
On Unix-like operating systems, the useradd command creates a new user or sets the default information for new users. This document covers the Linux version of useradd.
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1 useradd 運行系統環境
2 useradd 描述
3 useradd 語法
4 useradd 示例
useradd 運行系統環境
Linux
useradd 描述
useradd是用于將用戶添加到系統的低級實用程序。 通常，應該使用更友好的adduser。
您的操作系統可能附帶稍微不同的useradd版本。 在使用它創建新帳戶之前，請先檢查您的文檔。 本文檔引用了一些經常在基于Debian的Linux變體上使用的選項，但它們代表了useradd的一般用法。
如果在不使用-D選項的情況下調用useradd命令，則會使用命令行上指定的值以及系統的默認值來創建新的用戶帳戶。 根據命令行選項，useradd命令將更新系統文件，并且還可以創建新用戶的主目錄并復制初始文件。
默認情況下，還將為新用戶創建一個組（請參見下面的-g，-N，-U選項和USERGROUPS_ENAB變量）。
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).
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useradd 語法
如果未指定，則useradd將使用/ etc / default / useradd中EXPIRE變量指定的默認到期日期，或者默認為空字符串（無到期）。
如果未指定，則useradd將使用/ etc / default / useradd中的INACTIVE變量指定的默認非活動期，或者默認為-1。
如果未指定，則useradd的行為將取決于/etc/login.defs中的USERGROUPS_ENAB變量。如果將此變量設置為yes（或在命令行上指定-U / --user-group），則將為該用戶創建一個與登錄名相同的組。如果變量設置為no（或在命令行上指定-N / --no-user-group），則useradd會將新用戶的主要組設置為GROUP所指定的值/ etc / default / useradd中的變量，或者默認為100。
僅當指定了-m（或--create-home）選項時，此選項才有效。
如果未設置此選項，則框架目錄由/ etc / default / useradd中的SKEL變量或默認情況下/ etc / skel中的SKEL變量定義。如果可能，將復制ACL和擴展屬性。
示例：-K PASS_MAX_DAYS = -1可以在創建系統帳戶以關閉密碼時限時使用，即使系統帳戶根本沒有密碼也是如此。可以指定多個-K選項，例如：-K UID_MIN = 100 -K UID_MAX = 499
默認情況下，將重置lastlog和faillog數據庫中的用戶條目，以避免重用先前刪除的用戶的條目。
為了與以前版本的兼容性useradd的，在-O選項也支持這一目的。
默認情況下，如果未指定此選項并且未啟用CREATE_HOME，則不會創建主目錄。
該選項僅與-u選項結合使用才有效。
注意：不建議使用此選項，因為列出進程的用戶（例如，使用ps命令）將看到密碼（或加密密碼）。
您應該確保密碼遵守系統的密碼策略。
將在/ etc / shadow中創建不帶任何老化信息的系統用戶，并在/etc/login.defs中定義的SYS_UID_MIN-SYS_UID_MAX范圍內選擇其數字標識符，而不是UID_MIN-UID_MAX（及其創建時使用的GID副本）組）。請注意，useradd命令不會創建這樣一個用戶的主目錄，而不管默認設置的/etc/login.defs的（CREATE_HOME）。如果要創建系統帳戶的主目錄，則必須指定-m選項。
另請參見-r選項和UID_MAX描述。
缺省行為（如果未指定-g，-N和-U選項）由/etc/login.defs中的USERGROUPS_ENAB變量定義。
僅使用-D選項調用時，useradd將顯示當前默認值。與-D和其他選項一起調用時，useradd將更新指定選項的默認值。
有效的默認更改選項為：
此選項在/ etc / default / useradd中設置EXPIRE變量。
此選項在/ etc / default / useradd中設置INACTIVE變量。
此選項在/ etc / default / useradd中設置SHELL變量。
系統管理員負責將默認用戶文件放置在/ etc / skel /目錄（或在/ etc / default / useradd或命令行中指定的任何其他框架目錄）中。
注意事項您不能將用戶添加到NIS或LDAP組。這必須在相應的服務器上執行。
同樣，如果用戶名已經存在于NIS或LDAP等外部用戶數據庫中，則useradd將拒絕用戶帳戶創建請求。
通常建議僅使用以小寫字母或下劃線開頭，后接小寫字母，數字，下劃線或破折號的用戶名。它們可以以美元符號結尾。描述有效用戶名的正則表達式為：
[a-z _] [a-z0-9 _-] * [$]？
唯一的限制是用戶名既不能以破折號（' - '）或加號（' + '）或代字號（' ? '）開頭，也不能包含冒號（' ： '），逗號（' ， '）或空格（空格：“”，行尾：“ \ n ”，制表符：“ \ t ”，等等）。請注意，使用斜杠（' / '）可能會破壞用于定義用戶主目錄的默認算法。
用戶名最多只能包含32個字符。
組態/etc/login.defs中的以下配置變量更改了此工具的行為：
此設置不適用于系統用戶，可以在命令行上覆蓋。
作為默認值GID_MIN是1000 ; GID_MAX的默認值為60000。
該MAIL_DIR和MAIL_FILE變量由useradd的，usermod命令，和則userdel創建，移動或刪除用戶的郵件池。
默認值為0，表示組中的成員數沒有限制。
此功能（拆分組）可以幫助限制組文件中的行長。確保NIS組的行不超過1024個字符非常有用。
如果您需要強制執行此限制，則可以使用25。
注意：并非所有工具都支持拆分組，即使陰影工具套件等高級工具也不支持。除非確實需要，否則不應使用此變量。
作為默認值SYS_GID_MIN是101 ; 默認值SYS_GID_MAX是GID_MIN減1。
作為默認值SYS_UID_MIN是101 ; 默認值SYS_UID_MAX是UID_MIN減1。
的默認值為1000（分別為60000）。
useradd退出時具有以下狀態，具體取決于發生的情況：
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.
If not specified, useradd will use the default inactivity period specified by the INACTIVE variable in /etc/default/useradd, or -1 by default.
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.
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 ACL and extended attributes are copied.
Example: -K PASS_MAX_DAYS=-1 can be used when creating system account to turn off password aging, even though system account has no password at all. Multiple -K options can be specified, for example: -K UID_MIN=100 -K UID_MAX=499
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 versions of useradd, the -O option is also supported for this purpose.
By default, if this option is not specified and CREATE_HOME is not enabled, no home directories are created.
The default behavior (if the -g, -N, and -U options are not specified) is defined by the USERGROUPS_ENAB variable in /etc/login.defs.
This option is only valid in combination with the -u option.
Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes (for example, with the ps command).
You should make sure the password respects the system's password policy.
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.
See also the -r option and the UID_MAX description.
The default behavior (if the -g, -N, and -U options are not specified) is defined by the USERGROUPS_ENAB variable in /etc/login.defs.
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:
This option sets the HOME variable in /etc/default/useradd.
This option sets the EXPIRE variable in /etc/default/useradd.
This option sets the INACTIVE variable in /etc/default/useradd.
This option sets the GROUP variable in /etc/default/useradd.
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).
CaveatsYou 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.
ConfigurationThe following configuration variables in /etc/login.defs change the behavior of this tool:
This setting does not apply to system users, and can be overridden on the command line.
The default value for GID_MIN is 1000; the default for GID_MAX is 60000.
The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the user's mail spool.
The default value is 0, meaning that there are no limits in the number of members in a group.
This feature (split group) can help 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 advanced tools like the Shadow toolsuite. You should not use this variable unless you really need it.
The default value for SYS_GID_MIN is 101; the default value for SYS_GID_MAX is GID_MIN minus 1.
The default value for SYS_UID_MIN is 101; the default value of SYS_UID_MAX is UID_MIN minus 1.
The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).
useradd exits with the following status, depending on what occurred:
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useradd 示例
顯示新用戶的默認值。輸出類似于以下內容：
創建newperson新用戶。添加新用戶后，您將需要使用passwd命令為該帳戶分配密碼。
創建用戶后，您可以使用usermod命令修改任何用戶設置，例如用戶的主目錄。
Displays the defaults for new users. Output resembles the following:
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.
為了使這些命令起作用，您必須具有root特權。
For these commands to work you must have root privileges.
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其他命令行
userdel | usermod | ul | umask | unalias | uname | uncompress | unhash | uniq | until | unlink | unpack | uptime | unzip |