Understanding umask 022 — The Linux Default

What Is umask?

The umask (user file-creation mode mask) controls the default permissions assigned to newly created files and directories. It works by removing permission bits from the maximum defaults.

How umask 022 Works

The system starts with maximum defaults:

• Files: 666 (rw-rw-rw-)
• Directories: 777 (rwxrwxrwx)

The umask is then subtracted (technically, bitwise AND with the complement):

Files:       666 & ~022 = 644 (rw-r--r--)
Directories: 777 & ~022 = 755 (rwxr-xr-x)

Breaking Down 022

0 = Owner:  no bits removed (keeps rw for files, rwx for dirs)
2 = Group:  write bit removed (r-x for dirs, r-- for files)
2 = Others: write bit removed (r-x for dirs, r-- for files)

Checking Current umask

# Display current umask (octal)
umask
# 0022

# Display in symbolic form
umask -S
# u=rwx,g=rx,o=rx

Setting umask

# Temporary (current session only)
umask 022

# Permanent for a user (add to shell profile)
echo "umask 022" >> ~/.bashrc

# System-wide default
# Edit /etc/login.defs: UMASK 022
# Or /etc/profile: umask 022

Why 022 Is the Default

umask 022 provides a practical balance:

• Files are readable by everyone but only writable by the owner
• Directories are traversable by everyone but only modifiable by the owner
• This works well for most single-user and multi-user systems

Common umask Values

umask	File	Directory	Use Case
022	644	755	Standard default
002	664	775	Group collaboration
077	600	700	Maximum privacy
027	640	750	Production servers