Oracle Tips by Burleson

Setting default permissions using a file mask

By default, Linux permissions for new directories are set to 777 allowing read, write, and execute permissions to user, group, and other users. Conversely, file permissions default to 666 allowing read and write access to user, group, and others. The
System Administrator will often change the Linux default permissions by using the umask command in a login script.

You can use the umask command without specifying any arguments to determine what your current default permissions are. The value displayed by umask must be subtracted from the defaults of 777 (directories) and 666 (files) to determine your current defaults. Use the –S option to see the current default permissions displayed in the alpha symbolic format. You can
change your default permissions by specifying the mode argument to umask within your shell profile (.bash_profile) script.

Here are some examples.

Using umask to set default permissions

$ umask

0022

$ umask -S

u=rwx,g=rx,o=rx

$ umask 033

$ umask

0033

$ umask -S

u=rwx,g=r,o=r

You’ll notice that umask displays a 4-digit permissions mask, but only the last 3 digits represent the mask for owner, group, and others.

The above book excerpt is from:

Easy Linux Commands
Working Examples of Linux Command Syntax

ISBN: 0-9759135-0-6   

Terry Clark 

http://www.rampant-books.com/book_2005_1_linux_commands.htm