tool / devops

chmod Calculator

Click checkboxes, type an octal number, or enter symbolic notation — all three stay in sync. Security warnings for dangerous permissions.

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Read (r) Write (w) Execute (x)
Owner
Group
Other
Presets:

Octal Reference

BitsOctalMeaning
0000---
0011--x
0102-w-
0113-wx
1004r--
1015r-x
1106rw-
1117rwx

Three digits: Owner · Group · Other. Each digit is the sum of r=4, w=2, x=1.

Common Permissions

  • 644 — files: readable by all, writable by owner only.
  • 755 — directories and executables: readable and executable by all, writable by owner.
  • 600 — private key files: only the owner can read or write.
  • 400 — read-only for owner, nothing for anyone else.

Security Notes

  • 777 is almost always wrong on production systems — any user can modify the file.
  • 666 lets anyone write to the file without needing execute permission.
  • SSH private keys must be 600 or SSH will refuse to use them.

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