Linux File Permission (chmod) Calculator
Tick the read, write and execute boxes for owner, group and others to generate the octal chmod code, the symbolic notation and the full chmod command; you can also type an octal code and have the checkboxes filled in for you.
FreeOnline Tool
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How to Use
- In the permission table, tick read (4), write (2) and execute (1) separately for "Owner", "Group" and "Others".
- The octal code (such as 755), the symbolic notation (such as rwxr-xr-x) and the full chmod command appear below and update live.
- If you already have an octal code, type it into the "Reverse lookup" box (for example 755) and click "Parse and tick"; the tool ticks the matching permission checkboxes for you.
- Click "Load sample data" to see the complete output for 755 permissions.
Features
- Tick read (4), write (2) and execute (1) visually for owner, group and others, each set independently.
- Calculates and displays the three-digit octal code (such as 755), the symbolic notation (such as rwxr-xr-x) and the complete command (such as chmod 755 file) in real time.
- Reverse lookup: enter any valid three-digit octal code made of digits 0-7 and the matching checkboxes are ticked automatically; an invalid code produces an error message instead.
- Pure front-end calculation that updates the moment you tick a box, with no extra button to press.
Use Cases
Setting permissions on a server
Sysadmins tick the boxes to settle on the right chmod value for a file or directory instead of adding the numbers up by hand.
Learning the Linux permission model
Beginners can tick read, write and execute and watch how octal codes and rwx notation correspond to each other.
Decoding a permission code you have seen
When you meet a number such as 644 or 755 and are not sure what it grants, use reverse lookup to see the permissions laid out as checkboxes.
Checking commands before writing a deploy script
Confirm the exact octal code and full command for the permissions you want before putting chmod into a Dockerfile or shell script.
FAQ
What do the three digits of a chmod code mean?
They stand, in order, for the owner, the group and other users. Each digit is the sum of read (4), write (2) and execute (1), so it ranges from 0 to 7.
What happens if I enter an invalid code in reverse lookup?
If the input is not three digits in the 0-7 range, for example 888, abc or only two digits, the tool shows a message asking for a three-digit octal code made of digits 0-7 and ticks nothing.
What are 755 and 644 typically used for?
755 (rwxr-xr-x) is common for executables and directories: the owner can read, write and execute, while group and others can only read and execute. 644 (rw-r--r--) is common for ordinary files: the owner can read and write, and everyone else can only read.
Will this tool actually change my file permissions?
No. It only calculates and converts permission codes locally in your browser, with no connection to any server or file system. You still have to run the generated chmod command in your own terminal to change permissions for real.