chmod Calculator

About this tool

Unix file permissions are three groups (owner, group, everyone else) of three switches (read, write, execute). Each switch is a number: read 4, write 2, execute 1, added together per group, so rwxr-xr-x is 755. Tick the boxes to get the octal number and symbolic form, or type either one and the boxes update. A fourth leading digit sets setuid (4), setgid (2) and the sticky bit (1). The result is also written out in plain English, with warnings for risky choices such as world-writable files. Pasting the first column of ls -l output works too. Everything runs in your browser.

How to use it

1. Tick the read, write and execute boxes for owner, group and everyone else, or type a number like 755.
2. Read the plain-English summary and any warnings.
3. Press Copy command and run it on your file or directory.
4. For a directory and everything inside it, add -R, but check what that will change first.

Common problems

Permission denied even though the mode looks right

Check the directories above the file: you need execute permission on every directory in the path. Also check who owns the file.

Should I use 777 to fix an error?

Almost never. It lets every user change the file. Find out which user needs access and give only that user or group the permission.

The capital S or T in symbolic form

It means the setuid, setgid or sticky bit is set but the matching execute bit is not.