What is umask? How to set it permanently for a user?

November 14, 2019 720 views
Linux Commands Linux Basics

Recently I’ve been seeing this question quite a lot so I decided to shade some light about what a umask is, how to set it permanently for a user and explain what’s the differences between the following umask values: 000, 002, 022, 027, 077 and 277.

1 Answer

On Linux and Unix operating systems, new files are created with a default set of permissions. According to the official man page the description of umask is:

umask() sets the calling process’s file mode creation mask (umask) to mask & 0777 (i.e., only the file permission bits of mask are used), and returns the previous value of the mask.

The umask is used by open(2), mkdir(2), and other system calls that create files to modify the permissions placed on newly created files or directories. Specifically, permissions in the umask are turned off from the mode argument to open(2) and mkdir(2).

This might be a bit confusing, so essentially what this means is that when a new file or directory is created it is restricted in a specific way by applying permissions “mask” called the umask. The umask command basically sets the default permission or base permissions to the newly created files or folders on a Linux machine. Most of the Linux distros give 022 (0022) as default UMASK.

So for example, if your umask is set to 0022, when you create a new file it would be created with 0644 permissions, if you create a directory it would be created with 755 permissions. So essentially you subtract the umask from the default 666 file and 777 folder permissions.

The umask command is used to set this mask, or to show you its current value.

To make things a bit clearer, here’s a table with a few examples:

Umask File result Directory result
000 666 rw- rw- rw- 777 rwx rwx rwx
002 664 rw- rw- r– 775 rwx rwx r-x
022 644 rw- r– r– 755 rwx r-x r-x
027 640 rw- r– — 750 rwx r-x —
077 600 rw—- — 700 rwx — —
277 400 r– — — 500 r-x — —

Here’s that in action:

umask linux

To permanently change your umask you need to update your shell profile:

~/.profile
~/.bashrc
~/.zshrc
~/.cshrc

Hope that this helps!
Regards,
Bobby

Have another answer? Share your knowledge.