useradd -D 可以呼出建立用户的默认值。
[root@localhost home]# useradd -D
GROUP=100 预设的群
HOME=/home 默认的家目录所在的目录
INACTIVE=-1 密码失效日
EXPIRE= 账号失效日
SHELL=/bin/bash 预设的shell
SKEL=/etc/skel 用户家目录的内容数据参考目录
CREATE_MAIL_SPOOL=yes 是否主动帮使用者建立邮箱
系统会默认建立用户的家目录是和 etc/login.defs 这个档案内的CREATE_HOME yes
[bobby@localhost ~]$ cat /etc/login.defs
# *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 99999
PASS_MIN_DAYS 0
PASS_MIN_LEN 5
PASS_WARN_AGE 7
#
# Min/max values for automatic uid selection in useradd
#
UID_MIN 500
UID_MAX 60000
#
# Min/max values for automatic gid selection in groupadd
#
GID_MIN 500
GID_MAX 60000
#
# 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 （在不加-M及-m时是否主动建立家目录）
# 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
# Use MD5 or DES to encrypt password? Red Hat use MD5 by default.
MD5_CRYPT_ENAB yes
[bobby@localhost ~]$
useradd -d /tmp/user user 创建用户后su - user 进去之后执行 pwd 显示出来的是这个
用户的家目录，和root家目录理解是不样的root进入家目录是cd ~
