Chmod Calculator
Tick permissions or type a numeric (755) or symbolic (rwxr-xr-x) mode — everything stays in sync.
| Read (4) | Write (2) | Execute (1) | |
|---|---|---|---|
| Owner (user) | |||
| Group | |||
| Others |
How Linux file permissions work
Every file has three permission sets — for the owner, the group and others — and each set has
read (4), write (2) and execute (1) bits. Adding the bits gives one octal digit per set:
rwx = 4+2+1 = 7, r-x = 4+1 = 5, r-- = 4. So rwxr-xr-x is 755.
Common permission modes
| Mode | Symbolic | Typical use |
|---|---|---|
644 | rw-r--r-- | Regular files, web pages, configs readable by everyone |
755 | rwxr-xr-x | Directories, scripts and programs |
600 | rw------- | Private files: SSH keys, .env, credentials |
700 | rwx------ | Private directories such as ~/.ssh |
664 / 775 | rw-rw-r-- / rwxrwxr-x | Files/directories shared by a team group |
777 | rwxrwxrwx | Everyone can write — avoid, especially on web servers |
Special bits
- setuid (4000) — an executable runs with the file owner’s privileges (e.g.
/usr/bin/passwd). Shown assin the owner’s execute slot. - setgid (2000) — runs with the group’s privileges; on a directory, new files inherit the directory’s group.
- sticky (1000) — on a directory, only a file’s owner can delete or rename it (e.g.
/tmpis1777). Shown ast.
A capital S or T means the special bit is set but the underlying execute bit is not.
Frequently asked questions
What does chmod 755 mean?
Owner can read, write and execute (7); group and others can read and execute (5). Symbolic: rwxr-xr-x. It is the usual mode for directories and scripts.
What is the difference between 644 and 755?
755 adds the execute permission for everyone. Use 644 for ordinary files and 755 for directories and executable scripts.
Why is chmod 777 dangerous?
It lets every user on the system modify or replace the file. On a web server that can allow attackers to change your code. Grant only the permissions you need.
How do I apply permissions recursively?
Use chmod -R, but be careful: files and directories usually need different modes. A common pattern is find . -type d -exec chmod 755 {} + and find . -type f -exec chmod 644 {} +.