Linux Umask : Permission Set When New File / Folder Created

April 15, 2013 | By in HOWTOS, LINUX COMMANDS
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UMASK in Linux is actually known as User Mask or it is also called User File creation MASK. This is a kind of base permission or default permission given when new file or folder is created in Linux box. Most of the distribution of Linux gives 022 as default UMASK. We can say, it is default permissions to the file and folders by the system.
When we create any file or directory in Linux, they are governed by umask setting. In case, any system administrator does not set the default umask will be 0000. This means that the new files created will have read and write permissions for each user and new directories will have read, write and execute permissions.

How can we calculate UMASK in Linux?

One thing is umask value is generally same for files and folders but the calculation of these values based on the permissions on files and directories are different.

Minimum UMASK value for directory : 000 and Maximum : 777
Minimum UMASK value for file: 000 and Maximum : 666

Here, the reason of keeping maximum value 666 for files is because script files and binary files in Linux should only have execute permissions. Normal files in Linux should only have read and write permissions. Normally, umask are calculated through bitwise AND operator. Some of the common octal notations are:

0 -- Read, Write and Execute
1 – Read and Write
2 – Read and Execute
3 – Read Only
4 –Write and Execute
5 –Write Only
6 –Execute Only
7 –No Permissions

Now, we can easily make use of the above mentioned table to calculate permission for files. For instance, if an umask is set to 077 means the permission is generally calculated as below:

0 – Owner – Read, Write and Execute
7 – Group – No Permissions
7 – Others – No Permissions

To set the above umask, you should type the command

$ umask 077
$ mkdir folder1
$ touch testfile
$ ls –ld folder1 testfile

drwx------ 2 demo demo 4096 2013-07-04 01:34 folder1
-rw------- 2 demo demo 0 2013-07-04 01:34 testfile

Display current umask value

If you run umask command without any argument it will display the current mask value.

$ umask

How can we set umask with Symbolic Values?

Below mentioned are the symbolic values we can use:
r: read, w: write, x: execute, u: user ownership, g: group ownership and o: other ownership


$ umask u=rwx, g=, o=
$ mkdir folder1
$ touch testfile
$ ls –ld folder1 testfile

What are the Limitations of umask?

1. umask command can be used to restrict permissions.
2. We can’t grant additional permissions beyond what is normally specified by any program used to create files and folders. If you want to make changes then you should use chmod command instead.
3. Many operating systems do not have a file that should be created with execute permission. In such environments, the new files will always have execute permissions disabled.
4. Mask is only applied to those functions which creates a new file.

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