How to use the Chmod Calculator tool
- Tick the permissions, or type a mode like 644 or rwxr-x---.
- Add setuid, setgid or the sticky bit if needed.
- Copy the chmod command.
How Unix permissions work
Every file and directory has three sets of permissions: for the owner, the group and others. Each set has read (4), write (2) and execute (1). Add the numbers to get one digit per set: read and write is 6, read and execute is 5, all three is 7. So 754 means owner rwx, group r-x, others r--.
On directories the meaning shifts: read lists the names, write creates and deletes files inside, and execute lets you enter the directory and reach files in it. A directory without execute is effectively closed, even if it is readable.
Sensible defaults
- 644: regular files (web pages, configs). Owner edits, everyone reads.
- 755: directories and scripts.
- 600: private keys and files with passwords, such as ~/.ssh/id_ed25519 or .env.
- 700: private directories like ~/.ssh.
- 775 / 664: shared project folders where a group collaborates.
- 1777: shared temp directories like /tmp: anyone writes, only the owner deletes.
From server administration: if someone suggests chmod 777 to “fix” an error, find the real cause instead. It is almost always the wrong owner (fix with chown) or a missing group, and 777 lets any process on the server change the file.
Special bits
setuid (4xxx) runs a program with its owner’s rights, as passwd does. setgid (2xxx) on a directory makes new files inherit its group, which is perfect for shared folders. The sticky bit (1xxx) on a directory allows only owners to delete their files. Capital S or T in ls -l means the special bit is set but execute is not.
Privacy
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Frequently asked questions
What does chmod 755 mean?
Owner can read, write and execute; group and others can read and execute.
What permissions should a WordPress site have?
Typically 755 for directories, 644 for files and 600 or 640 for wp-config.php, with files owned by the web server user or a deploy user.
How do I apply permissions recursively?
chmod -R applies the same mode to everything. To treat files and directories differently use find: find . -type d -exec chmod 755 {} + and find . -type f -exec chmod 644 {} +.
Why does SSH refuse my key?
SSH rejects private keys that others can read. Set chmod 600 on the key and 700 on ~/.ssh.