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chmod Permissions Cheat Sheet: Numeric Table and Common Modes

A quick chmod reference — what each octal digit means, the read/write/execute bit values, and a table of common modes like 777, 755, 644, and 600.

How chmod Numbers Work

A chmod mode is three octal digits — one each for owner, group, and others. Each digit is the sum of three bits:

Bit Value Meaning
read (r) 4 view file / list directory
write (w) 2 modify file / add-remove entries
execute (x) 1 run file / enter directory

Add the bits you want per role. 7 = 4+2+1 = rwx, 6 = 4+2 = rw-, 5 = 4+1 = r-x, 4 = r--.

Single-Digit Reference

Octal Binary Symbolic Permissions
0 000 --- none
1 001 --x execute
2 010 -w- write
3 011 -wx write + execute
4 100 r-- read
5 101 r-x read + execute
6 110 rw- read + write
7 111 rwx read + write + execute

Common Modes

Mode Symbolic Typical use
777 rwxrwxrwx Everyone full access — avoid; almost never correct
755 rwxr-xr-x Executables, directories, web content
700 rwx------ Private scripts/dirs (owner only)
644 rw-r--r-- Regular files (owner edits, others read)
640 rw-r----- Config readable by group, not world
600 rw------- Private files (SSH keys, secrets)
444 r--r--r-- Read-only for everyone

Files vs Directories

The execute bit means different things:

  • On a file, x lets you run it as a program/script.
  • On a directory, x lets you cd into it and access its contents. A directory with r but no x lets you list names but not open anything — usually a mistake. That's why directories are typically 755, not 644.

Quick Tips

  • Web servers usually want 755 for directories and 644 for files.
  • SSH is strict: ~/.ssh must be 700 and private keys 600, or it refuses them.
  • chmod -R applies recursively — be careful applying file modes to directories (you'll strip the needed x).

Frequently Asked Questions

What does chmod 777 mean? Read, write, and execute for owner, group, and others — full access for everyone. It's a security risk and rarely the right answer; prefer 755 or 644.

What is the difference between 755 and 644? 755 (rwxr-xr-x) includes the execute bit, used for directories and executables. 644 (rw-r--r--) has no execute, used for regular files.

Why do SSH keys need chmod 600? SSH refuses to use a private key that other users can read. 600 (rw-------) restricts it to the owner only.

Compute any mode visually with the chmod calculator, and learn the model in depth in Linux File Permissions Explained.