删除用户ftp123后，重新添加用户ftp123失败，显示：
useradd: warning: the home directory already exists.
Not copying any file from skel directory into it.Creating mailbox file: File exists
解决方案：
userdel ftp123
rm -rf /home/ftp123
rm -rf /var/spool/mail/ftp123
useradd ftp123
passwd ftp123
输入密码两次，成功