What are umask bits and How to Use Them in Linux?

In Linux, every file and directory has some permissions that help to manage the access level of every user on the system. User file creation mode mask bits set the permissions for newly created files or directories. Linux umask consists of nine bits: three bits for the user(owner), group, and other users. The umask changes the default permission of newly created files to prevent other users from accessing them. We can change these permissions by using umask commands.

Getting Started

List the permissions assigned to the files and directories, as follows:

Permissions in Linux

Every file created in Linux has certain properties associated with it, like ownership and permission. The ownership of each file and directory involves a user(owner) and a group. Similarly, the options for setting file and directory permissions are shown below:

• r is for read permission with a value of 4
• w is for write permission with a value of 2
• x is for execute permission with a value of 1

We can combine these permissions to assign a varying level of access to files or directories:

• rwx: it has full read, write, and execute permission with a value of 7
• rw-: it has only read and write permission with a value of 6
• r–: it has only read permission with a value of 4
• r-x: it has only read and execute permission with a value of 5

So, whenever we want to permit a certain file or folder for the owner, group, or other users, we must change the default mask. We can find out the default mask by this command.

In order to assign permission to a file or directory, we give it the umask value. Following are the permissions for directories against their umask values:

Permissions values umask value

To verify the permissions against the umask value, set the umask value to 0022 and create a directory such that every new directory has a default permission value of 755:

Following are the permissions for files against their umask values:

Permissions values umask value

Now set the umask value to 0022 and create a new file. The file will have 644 permissions:

Permission Assignment via Octal Notation

Now create a file & directory using the 0777 umask value. The directory and file created will have no permissions:

For full permission assignment to the new files and directories, set the umask value to 0000.

Permission Assignment via Symbolic Notation

Set file permissions using the symbolic options instead of the octal values. To set the full permissions using the symbolic options, run the following command.

To set the rw permissions for the user(owner), use the following command:

Set the umask permissions for the group as follows:

Set the umask permissions for others using the command below:

View the current umask in its symbolic form:

Umask configuration

The permission in umask remains only for the current session or directory. To implement changes permanently, set the changes in its configuration settings. The configuration settings of the umask may vary for each distribution; however, to add the umask values permanently in Ubuntu, make changes to the bash.bashrc file. Open the file in your favorite editor to include the changes as shown below:

Conclusion

Umask is a useful tool to assign specific default permission to the newly created files and directories. The article shows how to use umask bits, and the values against read/write/execute permissions. We also demonstrate how to assign permissions via umask bits using octal and symbolic notations.