/etc/login.defs 是设置用户帐号限制的文件。该文件里的配置对root用户无效。

如果/etc/shadow文件里有相同的选项，则以/etc/shadow里的设置为准，也就是说/etc/shadow的配置优先级高于/etc/login.defs

# *REQUIRED* 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
#创建用户时，要在目录/var/spool/mail中创建一个用户mail文件
#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   99999
#密码最大有效期
PASS_MIN_DAYS   0
#两次修改密码的最小间隔时间
PASS_MIN_LEN    5
#密码最小长度，对于root无效
PASS_WARN_AGE   7
#密码过期前多少天开始提示
#
# Min/max values for automatic uid selection in useradd
#创建用户时不指定UID的话自动UID的范围
UID_MIN                   500
#用户ID的最小值
UID_MAX                 60000
#用户ID的最大值
#
# Min/max values for automatic gid selection in groupadd
#自动组ID的范围
GID_MIN                   500
#组ID的最小值
GID_MAX                 60000
#组ID的最大值
#
# 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
#当删除用户的时候执行的脚本
#
# 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
#使用useradd的时候是够创建用户目录
# The permission mask is initialized to this value. If not specified,
# the permission mask will be initialized to 022.
UMASK           077
# This enables userdel to remove user groups if no members exist.
#
USERGROUPS_ENAB yes
#用MD5加密密码