Linux account Management with ACL rights settings

1. Linux Accounts and Groups
1.1 User identification: UID and GID
1.2 User account:/etc/passwd,/etc/shadow
1.3 About groups: Effective with initial group, groups, NEWGRP
2. Account Management:
2.1 New and removed users: Useradd, related profiles, passwd, Usermod, Userdel
2.2 User features: Chsh, CHFN, finger, id
2.3 New and removed groups: Groupadd, Groupmod, Groupdel, GPASSWD, NEWGRP
2.4 Password Management: passwd
3. User Identity switch:
3.1 su
3.2 sudo, Visudo (/etc/sudoers)
4. User's special shell and PAM module
4.1 Special shell,/sbin/nologin
4.2 PAM module:/etc/nologin,/etc/securetty,/etc/security/*
5. Use of chat and mail for users on Linux systems:
4.1 Users: W, who, last, Lastlog
4.2 Users talking: Talk, MESG, wall
4.3 User email: Mail
6. Manually added users:
5.1 Some inspection tools: Pwck, Pwconv, Pwunconv, chpasswd
5.2 Special accounts, such as the establishment of a pure digital account:
5.3 Non-open terminal login account (Ex>mail acccount)
5.4 An example of a large number of built-in accounts:

Linux account Management and ACL permissions setting