用户管理

1. useradd 新增用户

   [root@localhost ~]# useradd john
   [root@localhost ~]# useradd -u 555 user1 # 指定UID
   [root@localhost ~]# useradd -g user1 user2 # 指定GID
   [root@localhost ~]# useradd -d /home/mydir3 user3 #指定home目录
   

2. passwd 设置密码

   root用户
   bash [root@localhost ~]# passwd john Changing password for user john. New password: BAD PASSWORD: The password is a palindrome Retype new password: passwd: all authentication tokens updated successfully. [root@localhost ~]#
   > 普通用户
   bash [john@localhost ~]$ passwd Changing password for user john. Changing password for john. (current) UNIX password: New password: Retype new password: passwd: all authentication tokens updated successfully. [john@localhost ~]$

3. usermod 修改用户

   [root@localhost ~]# useradd alice
   [root@localhost ~]# passwd alice
   Changing password for user alice.
   New password:
   BAD PASSWORD: The password is a palindrome
   Retype new password:
   passwd: all authentication tokens updated successfully.
   [root@localhost ~]# cat /etc/passwd | grep alice
   alice:x:1002:1002::/home/alice:/bin/bash
   # 修改用户alice home目录
   [root@localhost ~]# usermod -d /home/alice_new -m alice
   [root@localhost ~]# cat /etc/passwd | grep alice
   alice:x:1002:1002::/home/alice_new:/bin/bash
   

4. userdel 删除用户

   [root@localhost ~]# userdel alice
   [root@localhost ~]#
   

5. groupadd 新增用户组

   [root@localhost home]# groupadd group1
   [root@localhost home]#
   

6. groupdel 删除用户组

   [root@localhost home]# groupdel group1
   

7. users who w 查看用户

   [root@localhost home]# users
   root test
   [root@localhost home]# who
   root     pts/0        2019-01-08 01:57 (192.168.56.1)
   test     pts/1        2019-01-08 01:16 (192.168.56.1)
   [root@localhost home]# w
   02:24:09 up  4:24,  2 users,  load average: 0.00, 0.01, 0.05
   USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
   root     pts/0    192.168.56.1     01:57    1.00s  0.09s  0.01s w
   test     pts/1    192.168.56.1     01:16   30:09   0.03s  0.03s -bash
   

   w命令
   * 第一行显示 当前时间 系统运行时间 已登录用户数 系统负载
   * 下面信息分为8列：
   + 登录用户的用户名
   + 用户登录终端
   + 如果用户从网络登录，显示远程主机的主机名或IP
   + 用户登录时间
   + 用户闲置时间
   + 与终端相关的当前所有运行进程消耗的CPU时间总量
   + 当前WHAT列所对应的进程消耗的CPU时间总量
   + 用户当前运行的进程

8. finger 调查用户

   [root@localhost ~]# finger
   Login     Name       Tty      Idle  Login Time   Office     Office Phone   Host
   root      root       pts/1          Jan  8 04:14                           (192.168.56.1)
   test                 pts/0      24  Jan  8 04:14                           (192.168.56.1)
   [root@localhost ~]# finger test
   Login: test                             Name:
   Directory: /home/test                   Shell: /bin/bash
   On since Tue Jan  8 04:14 (EST) on pts/0 from 192.168.56.1
   25 minutes 18 seconds idle
   No mail.
   No Plan.
   [root@localhost ~]#
   

9. su 切换用户

   切换用户
   bash [test@localhost ~]$ su Password: [root@localhost test]# pwd /home/test [root@localhost test]# exit exit [test@localhost ~]$
   > 切换用户环境
   bash [test@localhost ~]$ su - Password: Last login: Tue Jan 8 04:22:09 EST 2019 on pts/0 [root@localhost ~]# pwd /root [root@localhost ~]# exit logout [test@localhost ~]$

10. sudo 用其他用户身份执行命令

    [root@localhost ~]# visudo
    
    [john@localhost test]$ sudo passwd user1
    
    We trust you have received the usual lecture from the local System
    Administrator. It usually boils down to these three things:
    
        #1) Respect the privacy of others.
        #2) Think before you type.
        #3) With great power comes great responsibility.
    
    [sudo] password for john:
    Changing password for user user1.
    New password:
    BAD PASSWORD: The password is a palindrome
    Retype new password:
    passwd: all authentication tokens updated successfully.
    

11. at 单一时刻执行一次任务

    at atq atrm

12. cron 周期性执行任务