Chmod Calculator
MathConvert between octal and rwx Unix permission notation with special bits support, showing the owner, group and other bits for secure file permissions.
0755rwxr-xr-xRelated Tools
About Chmod Calculator
Can never remember exactly what chmod 755 grants to whom, or which number maps to sticky and setuid?This tool makes Linux/Unix file permissions visual: tick read/write/execute for owner, group, and others to instantly get the octal value (like 755) and the symbolic form (like rwxr-xr-x), and typing an octal back restores the checkboxes immediately. It also supports the three special bits — setuid, setgid, and sticky — with common presets for quick reference. For example, ticking owner rwx, group r-x, others r-x instantly gives 755 and rwxr-xr-x side by side.
How to Use
- Open the Chmod Calculator tool
- Enter the values to calculate
- Adjust the output options as needed
- Click the Calculate button; results appear in real time
- Copy or export the result
Use Cases
- Deploy scripts — Confirm which number your chmod command needs, avoiding stray write access on a directory.
- Debug permissions — Reverse an rwx string from a failing file into octal to see who lacks the execute bit.
- SSH keys — Verify the 600 a private key needs so ssh does not refuse to load it for being too open.
- Shared folders — Use the sticky bit (1777) for a public temp directory so users cannot delete each other files.
- Read symbolics — Map the rwx string from ls -l output to its equivalent numeric permission.
- Dockerfile permissions — Check the correct octal values for COPY and RUN commands in Dockerfiles to ensure containers run with least privilege.
- Git hook scripts — Verify that pre-commit or pre-push hook scripts have the correct executable permissions (755) without excessive access.
FAQ
Is 755 different from 0755?
Numerically equivalent. The leading 0 means the special bits (setuid/setgid/sticky) are 0. The tool shows both the three-digit form and the four-digit form with special bits for different needs.
What do s and t mean in the rwx string?
s marks a setuid or setgid bit with execute present; uppercase S means no execute. t/T marks the sticky bit. They appear in the execute position.
Is setuid useful on directories?
Generally no. setuid mainly affects executables, running a program as its owner, and is usually ignored on directories. setgid on a directory is meaningful: new files inherit the group.
How do I pick common permissions?
Directories often use 755, regular files 644, executable scripts 755, and secrets like keys 600. The tool ships these presets for one-tap use.
Can it change file permissions on my server?
No. It only computes permissions visually, outputting values to copy into a chmod command; it never connects to or alters any real filesystem.