useradd具体参数
[root@yhwang ~] useradd -h
Usage: useradd [options] LOGIN
useradd -D
useradd -D [options] Options:
-b, --base-dir BASE_DIR base directory for the home directory of the
new account
-c, --comment COMMENT GECOS field of the new account
-d, --home-dir HOME_DIR home directory of the new account
-D, --defaults print or change default useradd configuration
-e, --expiredate EXPIRE_DATE expiration date of the new account
-f, --inactive INACTIVE password inactivity period of the new account
-g, --gid GROUP name or ID of the primary group of the new
account
-G, --groups GROUPS list of supplementary groups of the new
account
-h, --help display this help message and exit
-k, --skel SKEL_DIR use this alternative skeleton directory
-K, --key KEY=VALUE override /etc/login.defs defaults
-l, --no-log-init do not add the user to the lastlog and
faillog databases
-m, --create-home create the user's home directory
-M, --no-create-home do not create the user's home directory
-N, --no-user-group do not create a group with the same name as
the user
-o, --non-unique allow to create users with duplicate
(non-unique) UID
-p, --password PASSWORD encrypted password of the new account
-r, --system create a system account
-R, --root CHROOT_DIR directory to chroot into
-s, --shell SHELL login shell of the new account
-u, --uid UID user ID of the new account
-U, --user-group create a group with the same name as the user
-Z, --selinux-user SEUSER use a specific SEUSER for the SELinux user mapping
useradd创建的账户的默认值
[root@yhwang ~]# useradd -D
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes
1）新用户添加到GID为100的公共组
2）新用户的HOME目录将会位于/home/username
3）新用户账户密码在过期后不会被禁用
4）新用户账户未被设置为某个日期后就过期
5）新用户账户将bash shell作为默认shell
6）系统会将/etc/skel目录下的内容复制到用户的HOME目录下
7）系统为该用户账户在mail目录下创建一个用于接收邮件的文件
userdel具体参数
[root@yhwang ~]# userdel -h
Usage: userdel [options] LOGIN Options:
-f, --force force some actions that would fail otherwise
e.g. removal of user still logged in
or files, even if not owned by the user
-h, --help display this help message and exit
-r, --remove remove home directory and mail spool
-R, --root CHROOT_DIR directory to chroot into
-Z, --selinux-user remove any SELinux user mapping for the user
useradd添加账户和userdel删除账户
[root@yhwang ~]# useradd tom
useradd: warning: the home directory already exists.
Not copying any file from skel directory into it.
Creating mailbox file: File exists
[root@yhwang ~]# tail -1 /etc/passwd
tom:x:500:500::/home/tom:/bin/bash
[root@yhwang ~]# userdel -r tom
[root@yhwang ~]# useradd tom
[root@yhwang ~]# tail -1 /etc/passwd
tom:x:500:500::/home/tom:/bin/bash
passwd具体参数
[root@yhwang ~]# passwd --help
Usage: passwd [OPTION...] <accountName>
-k, --keep-tokens keep non-expired authentication tokens
-d, --delete delete the password for the named account (root only)
-l, --lock lock the password for the named account (root only)
-u, --unlock unlock the password for the named account (root only)
-e, --expire expire the password for the named account (root only)
-f, --force force operation
-x, --maximum=DAYS maximum password lifetime (root only)
-n, --minimum=DAYS minimum password lifetime (root only)
-w, --warning=DAYS number of days warning users receives before
password expiration (root only)
-i, --inactive=DAYS number of days after password expiration when an
account becomes disabled (root only)
-S, --status report password status on the named account (root
only)
--stdin read new tokens from stdin (root only) Help options:
-?, --help Show this help message
--usage Display brief usage message
passwd设置修改账户密码
[root@yhwang ~]# passwd tom
Changing password for user tom.
New password:
BAD PASSWORD: it is WAY too short
BAD PASSWORD: is a palindrome
Retype new password:
passwd: all authentication tokens updated successfully. [root@yhwang ~]# echo "tom"|passwd --stdin tom
Changing password for user tom.
passwd: all authentication tokens updated successfully.
赋予root权限
方法一
修改 /etc/sudoers 文件，找到下面一行，把前面的注释（#）去掉
## Allows people in group wheel to run all commands
%wheel ALL=(ALL) ALL
然后修改用户，使其属于root组（wheel），命令如下：
[root@yhwang ~] usermod -g root tom
修改完毕，现在可以用tom帐号登录，然后用命令 su - ，即可获得root权限进行操作。
方法二
修改 /etc/sudoers 文件，找到下面一行，在root下面添加一行，如下所示：
## Allow root to run any commands anywhere
root ALL=(ALL) ALL
tom ALL=(ALL) ALL
修改完毕，现在可以用tom帐号登录，然后用命令 su - ，即可获得root权限进行操作。
方法三
修改 /etc/passwd 文件，找到如下行，把用户ID修改为 0 ，如下所示：
## 修改前 tom:x:500:500:tom:/home/tom:/bin/bash ## 修改后 tom:x:0:500:tom:/home/tom:/bin/bash
保存，用tom账户登录后，直接获取的就是root帐号的权限。
参考资料
http://www.centoscn.com/CentOS/config/2014/0810/3471.html