Free Chmod Calculator (File Permissions)
Tick permissions or type an octal or rwx string to get the matching chmod command — with a plain-English explanation.
| Class | Read (4) | Write (2) | Execute (1) |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
chmod 755 filename- The owner can read, write and execute.
- The group can read and execute.
- Everyone else can read and execute.
How to use / FAQ
How do the numbers map to permissions?
Each class (owner, group, others) gets one digit: read = 4, write = 2, execute = 1, added together. So 7 is read+write+execute, 5 is read+execute, 0 is nothing — 755 means the owner can do everything and everyone else can read and execute.
What do 755 and 644 mean, and when do I use each?
755 (rwxr-xr-x) is the standard mode for directories and executable scripts — everyone can enter/run, only the owner can modify. 644 (rw-r--r--) is the standard for ordinary files like HTML or config — everyone can read, only the owner can write. Web servers typically want exactly these two.
What are setuid, setgid, and the sticky bit?
A fourth, leading digit. Setuid (4) makes an executable run with its owner's privileges; setgid (2) does the same for the group, and on directories makes new files inherit the directory's group; the sticky bit (1) on a shared directory (like /tmp, mode 1777) means only a file's owner can delete it.
Why does the symbolic form sometimes show s, S, t, or T?
Special bits are displayed in the execute position. Lowercase (s, t) means the execute bit is also set; uppercase (S, T) means the special bit is set but execute is not — usually a mistake worth double-checking.
Is 777 safe?
Almost never the right answer. It lets every user on the system modify the file, which on shared hosting includes other compromised accounts. If something "only works with 777", the real problem is usually file ownership — fix that instead.