File Protection Using CHMOD

Files in the AFS distributed file system use access control lists for the directories they are in, and most protections are set on directories using the fs sa command (or pts command for groups). Files on a local disk, however, do not have access control lists, so the chmod (change file mode) command must be used to set access to an individual file.

Chmod allows you to control whether a file can be read or written at all. If you turn off writing for a file, you will prevent anyone, including yourself, from writing to that file; the same goes for reading a file. If you turn on writing for a file, you allow anyone write access to that file if they already have write access to the file's directory; the same goes for read and execute access. See the chmod help file for more information.

To turn off write access for a file

chmod -w filename

To turn off read access for a file

chmod -r filename

To turn off execute access for scripts and executable files

chmod -x filename

To turn on write access for a file

chmod +w filename

To turn on read access for a file

chmod +r filename

To turn on execute access for scripts and executable files

chmod +x filename

Most protections on Andrew are set on directories. Therefore, even if you change the protections on an individual file using the chmod command, other users may still have access rights (or regain access rights) to that file based on their access rights to the directory in which the file resides.

Last Updated: 6/27/05