Summary
This chapter discussed the command line commands you need to know to manage the Linux security on your system. Linux uses a system of user IDs and group IDs to protect access to files, directories, and devices. Linux stores information about user accounts in the /etc/passwd file and information about groups in the /etc/group file. Each user is assigned a unique numeric user ID, along with a text login name to identify the user in the system. Groups are also assigned unique numerical group IDs and text group names. A group can contain one or more users to allowed shared access to system resources.
Several commands are available for managing user accounts and groups. The useradd command allows you to create new user accounts, and the groupadd command allows you to create new group accounts. To modify an existing user account, use the usermod command. Similarly, use the groupmod command to modify group account information.
Linux uses a complicated system of bits to determine access...