Chmod Master
Convert Linux permissions between octal, symbolic notation and a visual grid.
Permissions grid
| Read | Write | Execute | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
Values
How Linux permissions work
Every file or directory carries three permission sets — owner, group and others — each with read, write and execute. In octal notation, each set is a single digit that sums read (4), write (2) and execute (1):
754 → owner 7 = 4+2+1 = rwx → group 5 = 4+0+1 = r-x → others 4 = 4+0+0 = r-- → symbolic: rwxr-xr--
An optional 4th digit in front (e.g. 4755) sets the special bits: setuid (4), setgid (2) and the sticky bit (1), following the POSIX IEEE Std 1003.1 permission model. This tool computes all three representations — octal, symbolic and the checkbox grid — from each other entirely in your browser, plus the exact chmod command to copy and run.
Frequently asked questions
How do I read an octal permission like 755?
Each digit is the sum of read (4), write (2) and execute (1) for owner, group and others in that order. 755 means owner=rwx (4+2+1=7), group=r-x (4+0+1=5), others=r-x (4+0+1=5).
What do setuid, setgid and the sticky bit do?
They're an optional 4th octal digit. Setuid (4) makes a program run with its owner's privileges. Setgid (2) makes new files in a directory inherit the directory's group. The sticky bit (1) on a directory means only a file's owner can delete or rename it, even if others have write access — this is how /tmp is usually configured.
Why does the symbolic notation show an uppercase S or T sometimes?
A lowercase s or t means the special bit is set AND the matching execute bit is also set. An uppercase S or T means the special bit is set but execute is off for that category — which is usually a configuration mistake, since setuid/setgid have no effect without execute permission.
Does this tool actually change permissions on my files?
No. It only computes the octal value, symbolic string and the exact chmod command — nothing runs on a server or touches your filesystem. Copy the generated command and run it yourself.