UMASK in linux

What is Umask?

A umask (user file-creation mode mask) determines the default permissions assigned to new files and directories when they are created.
It works by subtracting these values from the maximum possible permissions.

Default Maximum Permissions

Files: 0022
Directories: 755

pavan@EPINHYDW1828:~$ touch EXAMPLE
pavan@EPINHYDW1828:~$ mkdir -p EXAMPLE2
pavan@EPINHYDW1828:~$ ls -ltr
-rw-r--r-- 1 pavan pavan    0 Mar 23 17:52 EXAMPLE
drwxr-xr-x 2 pavan pavan 4096 Mar 23 17:52 EXAMPLE2
pavan@EPINHYDW1828:~$ umask
0022
pavan@EPINHYDW1828:~$ umask -S
u=rwx,g=rx,o=rx

Commands Summary

Command	Description
`umask`	Check the current umask value in octal format.
`umask -S`	Check the current umask in symbolic format (e.g., `u=rwx,g=rx,o=rx`).
`umask`	Temporarily set a new umask value (e.g., `umask 0022`).
`source ~/.bashrc`	Apply changes to umask made in the `.bashrc` file immediately.

Examples

1. Checking Current Default Permissions

To see your current umask setting: umask
- Output example: 0022
To see the human-readable default permissions: umask -S
- Output example: u=rwx,g=rx,o=rx

2. Calculating File Permissions

If umask is 022, new files are calculated as 666 - 022 = 644.
- File Permissions: 644 (rw-r--r--)

3. Temporarily Changing Default Permissions

To remove write permissions for the group and others for new files: umask 0022

4. Permanently Changing Default Permissions

To make changes permanent, add the umask command to your shell configuration file (e.g., ~/.bashrc or ~/.profile).
1. Edit the file: nano ~/.bashrc
2. Add line at the end: umask 0077 (This makes files private to the user only).
3. Apply changes: source ~/.bashrc

5. Modifying Specific Permissions (Symbolic Mode)

Instead of calculating numbers, you can directly set permissions for users (u), groups (g), or others (o).
To remove read permissions for others for new files: umask o-r