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User Accounts: To use the Unix operating system you must have a user account that consists of user name (login) and password (password). User accounts are created by the administrator in Unix is a special user called root.
User Groups: All users belong to at least one group that is the main user group, also called user's primary group but can belong to more groups. If you belong to more groups, these are secondary groups.
Root: The root user, sometimes called root, is the user administrator. Is identified with the user number zero (uid = 0) and has permissions on the entire system without any restrictions. The root user can access any file, run, install and uninstall any application, modify the system configuration files and manage users.

• Creating users / useradd
• Modifying user / usermod
• Deleting users / userdel
• Team Building / groupadd / / Add a group # groupadd students
• Modification of groups / groupmod
• Elimination of groups / groupdel / / Deleting a group # groupdel teachers
• Add users to a group / adduser
• Remove users from a group / deluser

/ / Set the user's password
# Passwd fred

Types of permits: Reading When a user has permission to read a file means that you can read it or display it, either by application or by command. • Permit writing: When a user has write permission on a file means that can modify its content, and even delete it. It also entitles you to change file permissions using the chmod command and change its owner and group. • Driving performance: When a user has execute permission on a file means that you can run. If the user does not have execute permission, you can not even run an application.

ToWho can issue permits? Permits can only be awarded to three types or groups of users: • The user owns the file
• The group owns the file • When other users of the system (all except the user who owns and users who are in the group owner)

Show permissions for a file or folder with the command ls-l can see the permissions of files or folders.

The SUID bit is an extension of the permit ejecución.Para activate the SUID, you can run the command chmod u + s filename.