File ownership and user groups

Initially, a file's owner is identified by the user ID of the person who created the file.

The owner of a file determines who may read, write (modify), or execute the file. Ownership can be changed with the chown command.

Every user ID is assigned to a group with a unique group ID. The system manager creates the groups of users when setting up the system. When a new file is created, the operating system assigns permissions to the user ID that created it, to the group ID containing the file owner, and to a group called others, consisting of all other users. The id command shows your user ID (UID), group ID (GID), and the names of all groups you belong to.

In file listings (such as the listings shown by the ls command), the groups of users are always represented in the following order: user, group, and others. If you need to find out your group name, the groups command shows all the groups for a user ID.