Chmod Calculator
Work out Unix file permissions as a chmod number or in rwx form.
About this tool
Converts between permission checkboxes, the three-digit octal number used by chmod and the symbolic rwx string shown by ls -l. Each digit adds 4 for read, 2 for write and 1 for execute.
On Linux, macOS and other Unix systems, every file and folder has read, write and execute permissions for its owner, its group and everyone else. The chmod command sets them with a three-digit number such as 755 or 644, which is hard to read at a glance. Tick the permissions you want to get the number and the rwx form, or type a number to see what it allows.
How to use the Chmod Calculator
- Tick read, write and execute for the owner, the group and others.
- Or type a three-digit number such as 644 to fill in the boxes.
- Read the chmod number and the symbolic form.
- Copy the command and replace filename with your file or folder.
What 755 and 644 mean
In 755, the owner digit 7 is 4 + 2 + 1 (read, write, execute), and each 5 is 4 + 1 (read and execute), so it shows as rwxr-xr-x. It is typical for folders and scripts. In 644, the owner has 6 (read and write) and everyone else 4 (read only), shown as rw-r--r--, which is typical for web pages and documents.
How Unix permissions work
Read lets you open a file or list a folder, write lets you change a file or add and delete files in a folder, and execute lets you run a file as a program or enter a folder. Permissions are set separately for the file’s owner, its group and all other users. Each set becomes a digit from 0 to 7 by adding 4 for read, 2 for write and 1 for execute, giving the familiar three-digit code. The ls -l command shows the same thing as letters, with a dash for each missing permission and a leading character for the file type. A fourth leading digit can set special bits (setuid, setgid and sticky), which this tool leaves at 0. Avoid 777 on servers: it lets anyone change the file.
Frequently asked questions
What does chmod 777 do?
It gives read, write and execute permission to everyone. It is a security risk on shared systems and web servers.
What permissions should a website use?
Commonly 755 for folders and 644 for files, with configuration files that hold passwords set more tightly.
Why do SSH keys need 600?
SSH refuses to use a private key that other users can read, so the owner must be the only one with access.
How do I apply permissions to a whole folder?
Use chmod -R with care, because it applies the same mode to files and folders alike.