Default Permissions (umask)

umask decides the default permissions when you create:

1. New files
2. New directories

It removes permissions from Linux defaults.

Simple meaning:

Default permission = System default - umask

Check Current umask

Run:

umask

Example:

0022

Linux Default Permissions

Before umask, Linux starts with:

Type	Default
File	666
Directory	777

Why files are 666:

• read + write
• no execute by default

Why directories are 777:

• read + write + execute

Example: umask 022

File:

666 - 022 = 644

Result:

• rw-r--r--

Directory:

777 - 022 = 755

Result:

drwxr-xr-x

Example in Terminal

Check:

umask

Create file:

touch notes.txt

ls -l notes.txt

Result:

• rw-r--r--

Create folder:

mkdir project

ls -ld project

Result:

drwxr-xr-x

Common umask Values

umask	File	Directory	Use
022	644	755	most Linux systems
002	664	775	team/shared servers
077	600	700	private/secure

Example: 002

Set:

umask 002

Create file:

touch app.txt

Result:

• rw-rw-r--

Good for team collaboration.

Example: 077

Set:

umask 077

Create:

touch secret.txt

Result:

• rw-------

Only owner can access.

Temporary Change

umask 027

Works for current shell only.

Open new terminal = old value returns.

Permanent Change

Bash:

nano ~/.bashrc

Add:

umask 022

Reload:

source ~/.bashrc

System-wide:

/etc/profile

Real-World Examples

Web server

Use:

umask 022

Files readable by web server.

Shared DevOps team

Use:

umask 002

Team can edit files.

Private SSH/security

Use:

umask 077

For sensitive files.

Useful Commands

Check:

umask

Set:

umask 022

Test:

touch demo.txt

ls -l