用户相关

禁用密码长度限制

Ok, I will answer my question :)

I've found that pam_unix module performs password complexity check and it can be configured.

man pam_unix:

   minlen=n
       Set a minimum password length of n characters. The default value is
       6. The maximum for DES crypt-based passwords is 8 characters.

   obscure
       Enable some extra checks on password strength. These checks are
       based on the "obscure" checks in the original shadow package. The
       behavior is similar to the pam_cracklib module, but for
       non-dictionary-based checks.

Solution:
Alter the line in the pam_unix module in the /etc/pam.d/common-password file to:

password    [success=1 default=ignore]  pam_unix.so minlen=1 sha512

It allows you to set any password with minimal length of 1.

启用 ROOT 远程访问

设置 ROOT 密码

sudo passwd

切换 ROOT 登录

su root

配置 SSH 远程访问 vim /etc/ssh/sshd_config

# 关键在以下几个配置项
Port 22
ListenAddress 0.0.0.0
PermitRootLogin yes
PasswordAuthentication yes