DevOps & Dev Utilities

Chmod Permission Calculator

Click through read, write, and execute permissions visually and get the matching octal notation, symbolic notation, and chmod command.

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Octal notation

chmod command

Octal0644

Symbolicrw-r--r--

Commandchmod 644 filename

Unix File Permissions Guide

Unix-like operating systems (Linux, macOS, FreeBSD) control access to files and directories through a permission system based on three classes: owner, group, and others.

The three permission classes

Owner: The user who created the file (or was explicitly set as owner). Group: Any user belonging to the file's associated group. Others (world): Everyone else on the system. Permissions are evaluated in order: if you are the owner, only owner permissions apply — group and world permissions are ignored.

Octal shorthand

Each permission triplet (rwx) maps to a 3-bit binary number. r=4, w=2, x=1. Add them together: rwx=7, rw-=6, r-x=5, r--=4. Common modes: 755 (owner can do everything; others can read and execute) is standard for public directories and executables. 644 is standard for readable data files.

Special bits: SUID, SGID, Sticky

The setuid bit (4xxx) makes an executable run as the file owner, not the caller. The setgid bit (2xxx) makes new files inherit the directory's group. The sticky bit (1xxx) on directories prevents users from deleting files they don't own — essential for shared directories like /tmp.

Security implications

Never set 777 (world-writable) permissions on files accessible by a web server. This allows any process on the server to overwrite your files. Web application files should typically be 644 (files) and 755 (directories). Sensitive config files with database credentials should be 600 (owner-read-only).

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How it works

Three steps, no setup

Toggle permissions

Set read, write, and execute independently for owner, group, and others.

Read the notations

Octal (like 755) and symbolic (like rwxr-xr-x) update together.

Copy the chmod command

Ready to paste straight into a terminal.

Common questions

Frequently asked questions

What does 755 actually mean?

It grants the owner full read/write/execute access, while group and others get read and execute only — a common setting for scripts and executables.

Why avoid 777 permissions?

It gives every user on the system full read, write, and execute access, which is rarely necessary and a common security misconfiguration.

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Chmod Permission Calculator

Unix File Permissions Guide

The three permission classes

Octal shorthand

Special bits: SUID, SGID, Sticky

Security implications

Three steps, no setup

Toggle permissions

Read the notations

Copy the chmod command

Frequently asked questions

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Unix File Permissions Guide

The three permission classes

Octal shorthand

Special bits: SUID, SGID, Sticky

Security implications