Chmod Calculator

Chmod Calculator — What It Does

Select read, write, and execute permissions for the file owner, group, and others. The tool instantly shows the corresponding octal value (e.g. 755), the symbolic notation (e.g. rwxr-xr-x), and the complete chmod command to run on your server.

How Unix File Permissions Work

Every file and directory on a Unix/Linux system has three permission groups: owner (the user who created it), group (a shared user group), and others (everyone else). Each group can have up to three permissions:

• Read (r = 4) — View file contents or list directory contents
• Write (w = 2) — Modify file contents or create/delete files in a directory
• Execute (x = 1) — Run a file as a program, or enter (cd into) a directory

Most Common Permission Values

• 755 (rwxr-xr-x) — Directories and executable scripts: owner full, others read+execute
• 644 (rw-r--r--) — Regular files: owner read+write, everyone else read-only
• 600 (rw-------) — Private files like SSH keys: only owner can read/write
• 700 (rwx------) — Private scripts: only owner can read, write, execute
• 777 (rwxrwxrwx) — World-writable: dangerous, avoid on servers

Frequently Asked Questions

How does Unix file permission work?

Unix permissions are split into three groups: owner, group, and others. Each group has three bits: read (r=4), write (w=2), and execute (x=1). Add the values for each group to get the octal digit. Three octal digits form the complete permission (e.g. 755).

What does chmod 755 mean?

chmod 755 means: owner has read+write+execute (7), group has read+execute (5), others have read+execute (5). This is the most common permission for executable scripts and web directories accessible to all users.

What does chmod 644 mean?

chmod 644 means: owner has read+write (6), group has read-only (4), others have read-only (4). This is standard for non-executable files like HTML, CSS, config files — readable by everyone but writable only by the owner.

Why should I avoid chmod 777?

chmod 777 (rwxrwxrwx) gives full read, write, and execute access to everyone including other users and processes on the system. This is a major security risk — if exploited, any user could modify or execute the file.

What is the execute bit on a directory?

On a directory, the execute bit means the ability to enter (cd into) the directory and access its contents. Without execute permission on a directory, you cannot traverse it even if you have read permission on its files.