与useradd命令相关的两个默认配置文件

  Configuration Files for User Management Defaults  

When working with tools as useradd, some default values are assumed. These default values are set in two configuration files: /etc/login.defs and /etc/default/ useradd.

[root@rhel7 ~]# cat /etc/default/useradd
# useradd defaults file
GROUP=
HOME=/home
INACTIVE=-
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes

the /etc/default/useradd file contains some default values that are applied when using useradd.

In the file /etc/login.defs, different login-related variables are set. This file is used by different commands, and it relates to setting up the appropriate environment for new users.

[root@rhel7 ~]# cat /etc/login.defs
#
# Please note that the parameters in this configuration file control the
# behavior of the tools from the shadow-utils component. None of these
# tools uses the PAM mechanism, and the utilities that use PAM (such as the
# passwd command) should therefore be configured elsewhere. Refer to
# /etc/pam.d/system-auth for more information.
#
 
# *REQUIRED*
#   Directory where mailboxes reside, _or_ name of file, relative to the
#   home directory.  If you _do_ define both, MAIL_DIR takes precedence.
#   QMAIL_DIR is for Qmail
#
#QMAIL_DIR      Maildir
MAIL_DIR        /var/spool/mail
#MAIL_FILE      .mail
 
# Password aging controls:
#
#       PASS_MAX_DAYS   Maximum number of days a password may be used.
#       PASS_MIN_DAYS   Minimum number of days allowed between password changes.
#       PASS_MIN_LEN    Minimum acceptable password length.
#       PASS_WARN_AGE   Number of days warning given before a password expires.
#
PASS_MAX_DAYS
PASS_MIN_DAYS
PASS_MIN_LEN
PASS_WARN_AGE   
 
#
# Min/max values for automatic uid selection in useradd
#
UID_MIN
UID_MAX
# System accounts
SYS_UID_MIN
SYS_UID_MAX               
 
#
# Min/max values for automatic gid selection in groupadd
#
GID_MIN
GID_MAX
# System accounts
SYS_GID_MIN
SYS_GID_MAX               
 
#
# If defined, this command is run when removing a user.
# It should remove any at/cron/print jobs etc. owned by
# the user to be removed (passed as the first argument).
#
#USERDEL_CMD    /usr/sbin/userdel_local
 
#
# If useradd should create home directories for users by default
# On RH systems, we do. This option is overridden with the -m flag on
# useradd command line.
#
CREATE_HOME     yes
 
# The permission mask is initialized to this value. If not specified,
# the permission mask will be initialized to .
UMASK           
 
# This enables userdel to remove user groups if no members exist.
#
USERGROUPS_ENAB yes
 
# Use SHA512 to encrypt password.
ENCRYPT_METHOD SHA512 

Here is a list of some of the most significant properties that can be set from /etc/login.defs:

■    MOTD_FILE:     Defines the file that is used as “message of the day” file. In this file, you can include messages to be displayed after the user has successfully logged in to the server.    
 ■    ENV_PATH:     Defines the $PATH variable, a list of directories that should be searched for executable files after logging in.    
 ■    PASS_MAX_DAYS, PASS_MIN_DAYS, and PASS_WARN_AGE:     Define the default password expiration properties when creating new users.    
 ■    UID_MIN:     The first UID to use when creating new users.    
 ■    CREATE_HOME:     Indicates whether or not to create a home directory for new users.    
 ■    USERGROUPS_ENAB:     Set to yes to create a private group for all new users. That means that a new user has a group with the same name as the user as its default group. If set to no, all users are made a member of the group users.