| Class | Read | Write | Execute |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
— — About this tool
Unix permissions control who can read, write and execute a file. Each of the three groups — owner, group and others — has those three bits, written as an octal digit (rwx = 7) or symbolic letters (rwxr-xr-x). This calculator keeps a checkbox grid, the octal value and the symbolic notation in sync, so changing any one updates the others.
It also covers the special bits — setuid, setgid and the sticky bit — which add a fourth leading octal digit (as in 4755) and change the execute letters to s, S, t or T. Copy the ready-to-run chmod command, or paste an octal value to see exactly what it grants.
All calculation is local — nothing is uploaded.
Frequently asked questions
What does chmod 755 mean?
Owner gets read, write and execute (7); group and others get read and execute (5). It is the common mode for directories and executable scripts that everyone may run but only the owner may change.
How do I calculate Unix file permissions?
Add the bits for each role: read = 4, write = 2, execute = 1. Sum them per role (owner, group, others) to get one octal digit each — so rwx is 4+2+1 = 7 and r-x is 4+1 = 5, giving 755. Toggle the checkboxes above and the octal, symbolic and chmod command update together.
What are setuid, setgid and the sticky bit?
They're special permission bits in a fourth octal digit. setuid/setgid run a file with its owner's or group's privileges; the sticky bit on a directory lets only a file's owner delete it. In symbolic form they replace the execute letter with s, S, t or T.
What's the difference between octal and symbolic notation?
They describe the same permissions two ways. Octal (755) is compact; symbolic (rwxr-xr-x) spells out each bit. chmod accepts both — this tool generates each from the checkbox grid.