Linux Permissions Cheatsheet

Linux permissions control who can read, write, and execute files. The Linux permissions cheatsheet provides fast access to the most common chmod, chown, and chgrp patterns.

Step 1: Understand the three-part permission string

The output of ls -la shows permissions like -rwxr-xr-x. The first character is the file type (- for regular, d for directory, l for symlink). The next nine characters are three sets of rwx (read/write/execute) for owner, group, and others.

Step 2: Use octal notation for reliable chmod

Octal notation is unambiguous: each digit is the sum of r=4, w=2, x=1. Common patterns: chmod 755 for executables and directories (rwxr-xr-x), chmod 644 for regular files (rw-r--r--), chmod 600 for private keys (rw-------).

Step 3: Use symbolic notation for targeted changes

Symbolic notation adds or removes permissions without affecting others: chmod +x script.sh adds execute for all, chmod o-w file removes write from others, chmod g+r file adds read for group.

Step 4: Recursive permission changes

Use chmod -R 755 /var/www/ to recursively set permissions on a directory tree. Be careful with recursive changes — applying 755 to all files makes them executable, which is usually wrong for regular files. A better pattern: set directories to 755 and files to 644 using find: find /path -type d -exec chmod 755 {} \; && find /path -type f -exec chmod 644 {} \;