Chmod Calculator — Linux File Permissions
Build Unix and Linux file permissions without memorizing octal. Tick the boxes or type a number like 644 and get the symbolic form and the exact chmod command.
| Read (4) | Write (2) | Execute (1) | |
|---|---|---|---|
| Owner (user) | |||
| Group | |||
| Others | |||
| Special |
Permissions
How to use the chmod calculator
- Tick read, write and execute for the owner, group and others, or type an octal value like 644 or 2775.
- The symbolic form (like -rwxr-xr-x) and the chmod command update instantly.
- Use the presets for the most common settings, then copy the command into your terminal.
How Unix permissions work
Every file and folder has three sets of permissions: for its owner, for its group, and for everyone else. Each set has read (4), write (2) and execute (1), and the digits add up: 7 is rwx, 6 is rw-, 5 is r-x, 4 is r--. So 755 means the owner can do everything while group and others can read and execute, the standard for scripts and directories. 644 is the standard for regular files.
For directories, execute means permission to enter the folder and access files inside it, and read means permission to list its contents. A folder usually needs execute wherever it has read. Private keys and credentials should be 600 (owner read/write only); SSH refuses to use keys that are readable by others.
The optional fourth (leading) digit holds special bits: setuid (4) runs a program as its owner, setgid (2) runs as the group or makes new files in a directory inherit its group, and the sticky bit (1) on a shared directory like /tmp lets only a file's owner delete it. Avoid 777: it lets anyone modify the file.
Need a different tool? Suggest it here — we read every message.
Frequently asked questions
What does chmod 755 mean?
Owner: read, write, execute. Group and others: read and execute. Shown as rwxr-xr-x.
What does chmod 644 mean?
Owner: read and write. Group and others: read only. Shown as rw-r--r--. The default for most files.
Why is chmod 777 dangerous?
It gives every user on the system permission to modify or replace the file, a common security hole on web servers.
How do I apply permissions to a whole folder?
Add -R (chmod -R 755 folder), but be careful: files and folders usually need different permissions. find with -type f and -type d lets you set them separately.