Chmod Permissions Calculator
Interactively calculate octal and symbolic Linux file permissions with an instant command generator.
| Class | Read (4) | Write (2) | Execute (1) | Octal Sum |
|---|---|---|---|---|
| Owner (u) | 7 | |||
| Group (g) | 5 | |||
| Others (o) | 5 |
How Linux Permissions Work
In Unix-like operating systems, file permissions are divided into three user categories:
User (u) / Owner
The specific user account that owns the file.
Group (g)
All members of the file's assigned group.
Others (o) / Public
Anyone else with access to the system.
Octal Bit Calculation
- 4 (Read - r): Permission to view file contents or list directory.
- 2 (Write - w): Permission to modify, delete, or create files.
- 1 (Execute - x): Permission to run as a binary/script or enter a directory.
Frequently Asked Questions
What do the three permission digits in chmod mean (e.g. 755)?
Each digit represents permissions for a different group: the first digit is the file owner, the second is the group, and the third is everyone else. Each digit is the sum of read (4), write (2), and execute (1) — so 7 means read+write+execute, 5 means read+execute.
What's the difference between chmod 644 and 755?
644 (rw-r--r--) is the standard permission for regular files — the owner can read/write, everyone else can only read. 755 (rwxr-xr-x) adds execute permission and is typically used for directories and scripts, since execute is what lets you enter a directory or run a script.
Why do directories need execute permission?
For directories, the execute bit controls whether a user can access files inside it (traverse the directory), not "run" it like a program. Without execute permission on a directory, you can't cd into it or open files inside it even with read access.
Is symbolic notation (rwxr-xr-x) or octal notation (755) better to use?
They're equivalent — octal is faster to type once memorized, while symbolic notation is easier to read at a glance since each character maps directly to a permission. Most sysadmins use octal for scripts and symbolic for quick visual checks.
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