As a Linux system administrator you'll have to know how to manage
user accounts. User account management involves creating, modifying and
deleting user accounts, setting up and modifying users' system privileges,
the ever-popular chore of changing forgetful users' passwords, etc.
User accounts (i.e., accounts used by human beings) aren't the only accounts on
your Linux system. The accounts with UIDs (User IDentification) from 0 through
a certain system-dependent number (e.g., 99, 499) are reserved for the root user
and for system processes that run under their own UIDs (instead of running as
root, which is a security risk). You don't want to delete or modify these
accounts unless you know what you're doing.