[리눅스 명령어] useradd

useradd

I. 개념

사용자 계정 생성 : useradd

• 계정 : 시스템에 ID(Identity)와 암호(Password)를 생성하여 사용권을 부여하는 것
  • useradd : 사용자의 ID를 생성하는 명령
  • adduser : root 권한자가 root 이외의 사용자를 생성할 때 사용하는 명령

사용법

# useradd [option] [사용자 계정 이름]

• -p
  • 사용자의 암호를 추가할 때 사용
• -d
  • 홈 디렉터리를 지정할 때 사용
  • 최종 디렉터리만 생성하므로 중간 경로가 있는 경우에는 미리 생성해야 함.
• -g
  • 그룹을 지정할 때 사용
  • 지정할 그룹이 미리 생성되어 있어야 함.
  • 이 옵션을 지정하지 않을 경우
    • 아이디와 동일한 그룹에 포함. (레드햇 계열)
• -G
  • 기본 그룹 이외에 추가로 그룹에 속하게 할 경우 사용.
  • --groups
• -c
  • 사용자 생성 시, 사용자에 대한 설명을 설정할 때 사용
• -s
  • 사용자 생성 시, 사용자가 사용할 셀을 지정할 때 사용
• -D
  • /etc/default/useradd에 설정된 유저 추가와 관련된 기본 사항들을 보여줌.
• -m
  • 사용자를 생성할 때 홈 디렉터리를 생성해주는 옵션
  • 레드햇 리눅스는 이 옵션을 사용하지 않아도 홈 디렉터리가 생성됨.
    • 다른 배포판에서는 홈 디렉터리가 생성되지 않으므로 이 옵션을 지정해야 함.
      • 보통 -k 옵션과 같이 사용하여 사용자 생성 시 기본적으로 부여되는 목록이 들어있는 skeldir을 지정할 때 사용
• -k
  • 사용자 생성 시에 제공되는 환경 파일들은 기본적으로 /etc/skel로 지정되어 있음.
  • /etc/skel 이외의 디렉터리를 지정할 때 사용
• -f
  • 사용자의 패스워드 만기일을 날짜수로 지정할 때 사용
• -e
  • 계정의 만기일을 YYYY-MM-DD 형식으로 지정할 때 사용
• -u
  • 사용자 추가 시에 UID 값 지정
• -h
  • useradd 명령의 사용법 및 주요 옵션을 화면에 출력함.
  • --help

 

사용 예

• starrykss 라는 계정 생성

# useradd starrykss

• marine이라는 사용자를 생성하면서 홈 디렉터리의 경로 및 그룹을 지정
  • 해당 디렉터리(/home/terran/marine)과 해당 그룹(terran)은 미리 생성되어 있어야 함.

# useradd marine -d /home/terran/marine -g terran

참고

• 위의 명령 실행 전에 아래와 같은 명령을 수행해서 미리 디렉터리와 그룹을 생성해야 함.

# mkdir /home/terran
# groupadd terran

• 사용자 생성시 기본적으로 적용되는 정보를 확인
  • 해당 정보 파일 : /etc/default/useradd

# useradd -D

GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel

 

---

II. MAN 명령어로 살펴보기

USERADD(8)                System Management Commands                USERADD(8)



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

SYNOPSIS
       useradd [options] LOGIN

       useradd -D

       useradd -D [options]

DESCRIPTION
       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).

OPTIONS
       The options which apply to the useradd command are:

       -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.

           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 login,
           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. The directory
           HOME_DIR does not have to exist but will not be created if it is
           missing.

       -D, --defaults
           See below, the subsection "Changing the default values".

       -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 aging, 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 reset 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, 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 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 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.

       -R, --root CHROOT_DIR
           Apply changes in the CHROOT_DIR directory and use the configuration
           files from the CHROOT_DIR directory.

       -P, --prefix PREFIX_DIR
           Apply changes in the PREFIX_DIR directory and use the configuration
           files from the PREFIX_DIR directory. 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
           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 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.

           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.

       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. In regular expression terms:
       [a-zA-Z0-9_.][a-zA-Z0-9_.-]*[$]?

       Usernames may only be up to 32 characters long.

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

       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 (number), 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 (resp.  GID_MAX) is 1000 (resp.
           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.

       If MAIL_CHECK_ENAB is set to yes, they are also used to define the MAIL
       environment variable.

       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.

       SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)
           If /etc/subuid exists, the commands useradd and newusers (unless
           the user already have subordinate group IDs) allocate SUB_GID_COUNT
           unused group IDs from the range SUB_GID_MIN to SUB_GID_MAX for each
           new user.

           The default values for SUB_GID_MIN, SUB_GID_MAX, SUB_GID_COUNT are
           respectively 100000, 600100000 and 65536.

       SUB_UID_MIN (number), SUB_UID_MAX (number), SUB_UID_COUNT (number)
           If /etc/subuid exists, the commands useradd and newusers (unless
           the user already have subordinate user IDs) allocate SUB_UID_COUNT
           unused user IDs from the range SUB_UID_MIN to SUB_UID_MAX for each
           new user.

           The default values for SUB_UID_MIN, SUB_UID_MAX, SUB_UID_COUNT are
           respectively 100000, 600100000 and 65536.

       SYS_GID_MAX (number), 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 (resp.  SYS_GID_MAX) is 101
           (resp.  GID_MIN-1).

       SYS_UID_MAX (number), 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 (resp.  SYS_UID_MAX) is 101
           (resp.  UID_MIN-1).

       UID_MAX (number), 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 login to define users' initial umask. Note that
           this mask can be overridden by the user's GECOS line (if
           QUOTAS_ENAB is set) or by the specification of a limit with the K
           identifier in limits(5).

       USERGROUPS_ENAB (boolean)
           Enable setting of the umask group bits to be the same as owner bits
           (examples: 022 -> 002, 077 -> 007) for non-root users, if the uid
           is the same as gid, and username is the same as the primary group
           name.

           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/subgid
           Per user subordinate group IDs.

       /etc/subuid
           Per user subordinate user IDs.

       /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

       14
           can't update SELinux user mapping

SEE ALSO
       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).

 

---

III. 예제

다음 조건에 맞게 사용자를 생성하려고 한다.

 

예제 1

• posein의 주 그룹을 insa로 설정한다.
• 홈 디렉터리는 /home/insa 디렉터리 안에 아이디와 동일하게 생성한다.
• 옵션과 관련된 인자값은 하나의 괄호로 처리한다. (예: -u posein)

# mkdir /home/insa
# groupadd insa
# useradd -g insa -d /home/insa/posein posein

• -g : 그룹을 지정할 때 사용
• -d : 홈 디렉터리를 지정할 때 사용

 

예제 2

• alin 및 joon 사용자의 홈 디렉터리는 /home/alba 디렉터리 안에 생성되도록 설정한다.
• 해당 계정들은 2016년 12월 31일까지만 로그인이 되도록 설정한다.
• 옵션과 관련된 인자값은 하나의 괄호로 처리한다. (예: -u posein)

# mkdir /home/alba
# useradd -D -b /home/alba -e 2016-12-31
# useradd alin
# useradd joon

• -D : "Changing the default values".
• -b : "The default base directory for the system if -d HOME_DIR is not specified. "