Linux assigns a unique user identifier (UID) to each user, and a group identifier (GID) to each group. A user can be a member of a single primary group, and multiple supplementary groups.
A user with sudo privileges can impersonate another user, such as the root user, to perform tasks that would normally be restricted.
The permissions that are set on a file or directory determine who can access the item and how they can interact with it. Permissions are defined for three user entities: the owner of the file, the group that owns the file, and any other user on the system.
A file or a directory in Linux has a single user owner and a single group owner.
The chown command modifies the user and group owner of a file.
The defined permissions can allow a user set to read, write, or execute the file.
File permissions are represented by letters or octal numbers.
The chmod command modifies permissions on files and directories.