Chmod Calculator
Calculate Unix file permissions instantly — toggle bits or enter an octal value
Permission Bits
Special Bits
Result
chmod 644 filenameowner can read, owner can write, group can read, others can read
Common Presets
What is chmod?
chmod (change mode) is a Unix command used to set or change the access permissions of files and directories. Each file has three permission groups: owner, group, and others.
Each group can independently be granted read (r = 4), write (w = 2), and execute (x = 1) permissions. The values are added together to form a single octal digit per group.
Octal vs Symbolic
Octal notation (e.g., 755) is the most common format used with the chmod command. Each digit represents the combined permission value for owner, group, and others respectively.
Symbolic notation (e.g., rwxr-xr-x) is displayed by ls -la and shows each permission as a letter or dash for easy reading.
Common Use Cases
Web Files (644)
Standard permission for HTML, CSS, and config files. Owner can edit; server reads them.
Scripts & Binaries (755)
Owner has full control; group and others can read and execute the script.
SSH Keys (600)
Private key files must be readable only by the owner to satisfy SSH security checks.
Shared Directories (775)
Group members can read and write; others can only read. Ideal for team collaboration.
Sticky Bit (/tmp)
Prevents users from deleting files they do not own in shared directories like /tmp.
SetUID Binaries
Programs like passwd run with the owner's privileges regardless of who executes them.