用户名的需求

Specifies the user name. Requirements:

• 必须开始with a lowercase letter.

• Can contain numbers and lowercase letters.

• Can include only these three special characters: hyphens ( - ), dots ( . ), and underscores ( _ ).

• Can have a maximum of 32 characters.

• Cannot be empty.

• Cannot contain uppercase letters.

• Cannot be:admin,root, orremote_user.

• Cannot be Linux reserved names such as:

  daemon,bin,sys,sync,proxy,www-data,备份,list,irc,gnats,nobody,systemd-bus-proxy,sshd,messagebus,rpc,systemd-journal-gateway,systemd-journal-remote,systemd-journal-upload,systemd-timesync,systemd-coredump,systemd-resolve,rpcuser,vagrant,opsd,rdanet,_lldpd,rdaadmin,rdaweb,docker_container,tss.