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.
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
切换 ROOT 登录
配置 SSH 远程访问
# 关键在以下几个配置项 Port 22 ListenAddress 0.0.0.0 PermitRootLogin yes PasswordAuthentication yes