Chmod Calculator
Toggle Unix file permission bits to see the octal value, symbolic representation, and the chmod command.
Presets
Read (r)
Write (w)
Execute (x)
Owner
Group
Other
Special
Octal
000
Symbolic
---------
Command
chmod 000 path/to/file
Type an octal (3 or 4 digits) or a 9-character symbolic string to update the grid above.
About the Chmod Calculator
Unix file permissions control who can read, write, and execute files and directories. The octal notation (755, 644, 777) is compact but opaque — most developers have to look up what each number means every time. This calculator converts between octal notation, symbolic notation (rwxr-xr-x), and a visual checkbox interface, with explanations of what each permission combination means in practice.
Permission reference
Common file permissions
644— regular files (config, HTML, CSS)755— executables and directories600— private files (SSH keys, .env)400— read-only (backups, certificates)
Permission bits
4= read (r)2= write (w)1= execute (x)7= read+write+execute
Security notes
- Never use
777in production — it gives everyone full access - SSH private keys must be
600or SSH will refuse to use them - Web server files should be
644(files) and755(directories) - Use
chmod -Rcarefully — recursive permission changes are hard to undo
Frequently asked
- What does chmod stand for?
- chmod stands for "change mode". It is the Unix/Linux command for changing the access permissions of files and directories. Permissions control who can read, write, and execute a file.
- What does 755 mean in chmod?
- 755 means: owner has read+write+execute (7), group has read+execute (5), others have read+execute (5). This is the standard permission for executable files and directories that should be publicly readable but only owner-writable.
- What does 644 mean in chmod?
- 644 means: owner has read+write (6), group has read-only (4), others have read-only (4). This is the standard permission for regular files like configuration files and web assets.
- What is the difference between octal and symbolic notation?
- Octal notation uses three digits (e.g. 755) where each digit represents the permissions for owner, group, and others as a sum of read(4)+write(2)+execute(1). Symbolic notation uses letters (e.g. rwxr-xr-x) which is more readable but harder to calculate mentally.
- What does the execute bit mean on a directory?
- On a directory, the execute bit means "traverse" — the ability to enter the directory (cd into it) and access files within it. Without the execute bit on a directory, you cannot access its contents even if you have read permission.