The umask command in Linux is used to set or view the file mode creation mask, which determines the default permissions for newly created files or directories². The umask command specifies the permissions that the user does not want to be given out to the new files or directories³.

Here is an example of using the umask command:

The umask value is an octal number that represents the bitwise complement of the desired permissions¹. For example, a umask value of 0022 means that the user does not want to give write permissions to the group and others. Therefore, the default permissions for files are 644 (read and write for owner, read for group and others) and for directories are 755 (read, write and execute for owner, read and execute for group and others).

You can change the umask value temporarily by using the umask command with a new value as an argument. This will affect only the current shell session and any processes spawned from it². To make the umask change permanent, you need to add the umask command to your shell configuration file, such as ~/.bashrc or ~/.profile.

You can also use symbolic notation to set or view the umask value. For example, you can use u=rwx,g=rx,o=rx to specify that you want to give read, write and execute permissions to the owner, and read and execute permissions to the group and others³. To use symbolic notation, you need to add the -S option to the umask command. For example: