Chmod Calculator
Calculate Linux and Unix file permissions visually. Get the octal value, symbolic notation, and ready-to-run chmod command.
| Entity | Read(4) | Write(2) | Execute(1) | Octal | Symbolic |
|---|---|---|---|---|---|
| Owner (u) | 6 | rw- | |||
| Group (g) | 4 | r-- | |||
| Others (o) | 4 | r-- |
Octal
644
Symbolic
-rw-r--r--
Command
chmod 644 filename
About the Chmod Calculator
The Chmod Calculator converts between visual permission checkboxes, octal notation, and symbolic notation for Linux and Unix file permissions. Toggle read, write, and execute for owner, group, and others — the octal value and chmod command update instantly. You can also type an octal value directly (e.g., 755) to see what it means.
Every file and directory on a Unix system has three permission sets: owner (the user who created the file), group (users in the file's assigned group), and others (everyone else). Each set has three bits: read (r = 4), write (w = 2), and execute (x = 1). The octal value is the sum of the bits for each set — for example, rwx = 4+2+1 = 7, r-x = 4+0+1 = 5.
Common values: 644 for regular files (owner can edit, others can read), 755 for executables and directories (owner can do everything, others can read and traverse), 600 for private files like SSH keys. All calculation runs locally in your browser.
Frequently Asked Questions
What does chmod 755 mean?
755 means: owner has read+write+execute (7 = 4+2+1), group has read+execute (5 = 4+0+1), others have read+execute (5 = 4+0+1). This is the standard permission for executable files and directories — the owner can modify them, while everyone else can read and execute/traverse them.
What does chmod 644 mean?
644 means: owner has read+write (6 = 4+2+0), group has read-only (4), others have read-only (4). This is the standard permission for regular files — the owner can edit the file, but others can only read it.
What is the execute bit for a directory?
For directories, the execute bit means “traverse” — the ability to cd into the directory and access files within it. A directory without the execute bit cannot be entered even if you have read permission. This is why directories typically need the execute bit set (e.g., 755 rather than 644).
What permissions should I set on SSH keys?
Private keys (~/.ssh/id_rsa, ~/.ssh/id_ed25519) should be 600 — readable and writable only by the owner. The ~/.ssh directory should be 700. SSH will refuse to use keys with overly permissive settings.
What is the difference between octal and symbolic notation?
Octal notation uses three digits (e.g., 755), one per entity. Symbolic notation uses letters (e.g., rwxr-xr-x), with a - for unset bits. Both represent the same permissions. The chmod command accepts both: chmod 755 file and chmod u=rwx,g=rx,o=rx file are equivalent.