Which of the following commands is used to change file access permissions in Linux?

chgrp changes the group ownership of a file, not its permission bits.

chperm is not a valid Linux command and does not exist in standard distributions.

chmod (change mode) is the POSIX-standard Linux command used to set or modify read, write, and execute permissions on files and directories for the owner, group, and others. It accepts both symbolic (e.g., chmod u+x) and octal (e.g., chmod 755) notation. It is the only command specifically designed to alter permission bits on the filesystem.

chown changes the user and/or group ownership of a file, not the permission bits.