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Chmod Permissions Calculator

Calculate Linux and Unix file permissions with an interactive 3x3 matrix, octal, and symbolic codes.

Runs in your browser. Nothing you add is uploaded.

What the Chmod Permissions Calculator does

Unix and Linux file permissions determine who can read, modify, or execute files and directories on a server. Remembering octal numbers, symbolic representations, and special bits (SUID, SGID, Sticky) can be error-prone. This interactive calculator synchronizes a 3x3 permission grid with octal codes and generates exact chmod commands.

How to calculate chmod permissions

  1. Toggle Read (4), Write (2), and Execute (1) checkboxes for Owner, Group, and Others.
  2. Enable SUID, SGID, or Sticky Bit if configuring shared directories or special binaries.
  3. Watch the Octal number (e.g. 755 or 644) and Symbolic string (-rwxr-xr-x) update in real time.
  4. Select from common server presets like SSH keys (600), web directories (755), or scripts.
  5. Copy the ready-to-run chmod command or recursive directory fix script.

The Chmod Permissions Calculator runs entirely in your browser — nothing you enter is uploaded, stored, or logged.

When to use it

Securing SSH Key Files

OpenSSH strictly refuses private keys with loose permissions. Use chmod 600 (read/write for owner only) to fix 'WARNING: UNPROTECTED PRIVATE KEY FILE!'.

Web Server File and Directory Security

Fix web server permission issues by setting directories to 755 (drwxr-xr-x) and files to 644 (-rw-r--r--) with the provided find command.

Shared Directory Collaboration with Sticky Bit

Configure /tmp or team folders with chmod 1777 (drwxrwxrwt) so team members can create files without deleting each other's work.

Good to know

  • Directories always require the execute bit (x) for users to cd into them or list their contents.
  • Avoid chmod 777 on production servers; it gives every local user write access to critical files.
  • SUID (4000) causes an executable to run with the privileges of the file owner rather than the calling user.

Frequently asked questions

What does chmod 755 mean?

Chmod 755 gives the Owner full Read, Write, and Execute permissions (7), while Group and Others can only Read and Execute (5). It is the standard permission for directories and executable scripts.

What is the Sticky Bit used for?

The Sticky bit (octal 1000, symbolic 't') is used on shared directories like /tmp. It allows multiple users to write files, but only the file owner or root can delete or rename them.

How do octal permissions add up?

Read = 4, Write = 2, Execute = 1. Add the numbers for each role: Read + Write = 6, Read + Execute = 5, Read + Write + Execute = 7.

What is SGID on a directory?

When SGID (2000) is set on a directory, all newly created files inherit the directory's group ownership rather than the primary group of the user who created them.

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