[student@station10-101 ~]$ passwd student
passwd: Only root can specify a user name.
# 這種指令下達方式只有 root 可以使用，因此 student 下達這種指令方式，就會失敗！
# 也就是說，這個指令根本沒有被執行啦！
[student@station10-101 ~]$ passwd
Changing password for user student.
Current password: <==這裡則是按下 [ctrl]+c 結束！
[student@station10-101 ~]$
[root@station10-101 ~]# passwd student
Changing password for user student.
New password: <==直接輸入 mystdgo 即可！
BAD PASSWORD: The password is shorter than 8 characters
Retype new password: <==再次輸入 mystdgo
passwd: all authentication tokens updated successfully.
看吧！ root 很萬能，所以，如果耳根子太軟，幫人家設計比較不良的密碼，很容易出狀況！
例題 4.2.1-2：
建立新用戶的帳號與密碼，兩個動作：
[root@station10-101 ~]# useradd myuser2
[root@station10-101 ~]# passwd myuser2
Changing password for user myuser2.
New password:
BAD PASSWORD: The password fails the dictionary check - it is based on a dictionary word
Retype new password:
passwd: all authentication tokens updated successfully.
建立另外一個新的用戶，方式也一樣：
[root@station10-101 ~]# useradd myuser3
[root@station10-101 ~]# passwd myuser3
Changing password for user myuser3.
New password:
BAD PASSWORD: The password fails the dictionary check - it is based on a dictionary word
Retype new password:
passwd: all authentication tokens updated successfully.
現在，觀察一下兩個帳號的 id 顯示狀況：
[root@station10-101 ~]# id myuser2
uid=1001(myuser2) gid=1001(myuser2) groups=1001(myuser2)
[root@station10-101 ~]# id myuser3
uid=1002(myuser3) gid=1002(myuser3) groups=1002(myuser3)
[root@station10-101 ~]# useradd myuser2
useradd: warning: the home directory already exists.
Not copying any file from skel directory into it.
Creating mailbox file: File exists
[root@station10-101 ~]# passwd myuser2
Changing password for user myuser2.
New password:
BAD PASSWORD: The password fails the dictionary check - it is based on a dictionary word
Retype new password:
passwd: all authentication tokens updated successfully.
[root@station10-101 ~]# ll -d /home/myuser* /var/spool/mail/myuser*
drwx------. 3 1001 1001 78 Feb 22 10:00 /home/myuser2
drwx------. 3 myuser3 myuser3 78 Feb 22 10:00 /home/myuser3
-rw-rw----. 1 1001 mail 0 Feb 22 10:00 /var/spool/mail/myuser2
-rw-rw----. 1 myuser3 mail 0 Feb 22 10:00 /var/spool/mail/myuser3
# 檔案並沒有正常的恢復！看起來 UID/GID 的部份有問題！來查看看：
[root@station10-101 ~]# id myuser2
uid=1003(myuser2) gid=1003(myuser2) groups=1003(myuser2)
[root@station10-101 ~]# userdel -r myuser3<==確實可以刪除 myuser3
[root@station10-101 ~]# userdel -r myuser2
userdel: user myuser2 is currently used by process 20486
# 因為剛剛在 tty4 登入 myuser2，尚未登出！趕緊去登出！
[root@station10-101 ~]# userdel -r myuser2
userdel: /var/spool/mail/myuser2 not owned by myuser2, not removing
userdel: /home/myuser2 not owned by myuser2, not removing
# 意思是說，上面的兩個檔名並不屬於 myuser2，所以自然不能隨意刪除！
[root@station10-101 ~]# ll -d /home/myuser* /var/spool/mail/myuser*
drwx------. 3 1001 1001 78 Feb 22 10:00 /home/myuser2
-rw-rw----. 1 1001 mail 0 Feb 22 10:00 /var/spool/mail/myuser2
# 確實存在不同的 UID 之故！
[root@station10-101 ~]# id myuser3
id: ‘myuser3’: no such user
[root@station10-101 ~]# id myuser2
id: ‘myuser2’: no such user
# 但是，事實上，這兩個帳號確實刪除了！
上述的留存的錯誤檔案，只好自己手動移除了！
[root@station10-101 ~]# rm -rfv /home/myuser2 /var/spool/mail/myuser2
[root@station10-101 ~]# ll -d /home/myuser* /var/spool/mail/myuser*
ls: cannot access '/home/myuser*': No such file or directory
ls: cannot access '/var/spool/mail/myuser*': No such file or directory
例題 4.2.2-1：
直接使用 usermod 修改次要群組支援時，錯誤的動作：
[root@station10-101 ~]# id prouser1
uid=1001(prouser1) gid=1002(prouser1) groups=1002(prouser1),1001(progroup)
[root@station10-101 ~]# usermod -G student prouser1
[root@station10-101 ~]# id prouser1
uid=1001(prouser1) gid=1002(prouser1) groups=1002(prouser1),1000(student)
[root@station10-101 ~]# usermod --help
Usage: usermod [options] LOGIN
Options:
......
-G, --groups GROUPS new list of supplementary GROUPS
-a, --append append the user to the supplemental GROUPS
mentioned by the -G option without removing
the user from other groups
......
看起來，說是使用 -a 搭配 -G 的話，會有效的達成我們想要的需求！就是『累加額外的次要群組支援』之意！
使用正確的手段來處理：
[root@station10-101 ~]# id prouser1
uid=1001(prouser1) gid=1002(prouser1) groups=1002(prouser1),1000(student)
[root@station10-101 ~]# usermod -a -G progroup prouser1
[root@station10-101 ~]# id prouser1
uid=1001(prouser1) gid=1002(prouser1) groups=1002(prouser1),1000(student),1001(progroup)
