How to grant or change user permissions in the Linux operating system?

In Linux, user permissions are managed using the commands chmod, chown, and usermod.

• chmod changes the access rights to files and directories (read, write, execute) for the owner, group, and others. Example: chmod 755 file — the owner can read, write, and execute; others can read and execute.

• chown changes the owner and group of a file or directory. Example: chown user:group file — sets the owner and group.

• usermod modifies user parameters, including their groups. Example: usermod -aG group user — adds the user to an additional group.

You can also use groups to view user groups and id for detailed information.

For more fine-grained permission control, ACLs (Access Control Lists) are used with the commands setfacl and getfacl.