What is UMASK?

UMASK is a Unix environment variable which automatically sets file permissions on newly created files.

The UMASK variable can be confusing to use, because it does work as a mask. In other words, you set the permissions that you do not want in the UMASK.

To calculate permissions which will result from specific UMASK values, subtract the UMASK from 666 for files and from 777 for directories.

If you want all files created with permissions of 666, set your UMASK to 000. Alternatively, if you want all files created with permissions of 000, set your UMASK to 666.

A reasonable value for UMASK is 022, which will cause files to be created with permissions of 644 (rw-r--r--) and directories to be created with permissions of 755 (rwxr-xr-x).

A more secure value for UMASK is 066, which will cause files to be created with permissions of 600 (rw-------) and directories to be created with permissions of 700 (rwx------).

UMASK is nomally defined in the .profile or .login user startup files.