前言：

man useradd　　　　man  groupadd　　　　info useradd　　　　info  groupadd 都可以获取相关命令的用法信息。

个人比较喜欢读英文解释文档，没有你想象的那么complicated！😜

 

 

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 -dHOME_DIR is not specified. BASE_DIR is concatenated with the account name to define the home directory.
The BASE_DIR must exist otherwise the home directory cannot be created.

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.

-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 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.

-m, --create-home


-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
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.

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

 

 

 

 

 

GROUPADD(8) System Management Commands GROUPADD(8)

NAME
groupadd - create a new group

SYNOPSIS
groupadd [options] group

DESCRIPTION
The groupadd command creates a new group account using the values specified on the command line plus the default values from the system. The new group will
be entered into the system files as needed.

OPTIONS
The options which apply to the groupadd command are:

-f, --force
This option causes the command to simply exit with success status if the specified group already exists. When used with -g, and the specified GID
already exists, another (unique) GID is chosen (i.e. -g is turned off).

-g, --gid GID
The numerical value of the group'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 GID_MIN and greater than every other group.

See also the -r option and the GID_MAX description.

-h, --help
Display help message and exit.

-K, --key KEY=VALUE
Overrides /etc/login.defs defaults (GID_MIN, GID_MAX and others). Multiple -K options can be specified.

Example: -K GID_MIN=100-K GID_MAX=499

Note: -K GID_MIN=10,GID_MAX=499 doesn't work yet.

-o, --non-unique
This option permits to add a group with a non-unique GID.

-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.

Manual page groupadd(8) line 1 (press h for help or q to quit)