Unix Permissions Calculator
Build chmod permissions visually. Click to toggle bits, type a numeric value, or pick a common preset.
Symbolic notation
chmod 755 filenamechmod u=rwx,g=rx,o=rx filenamechmod -R 755 directory/find . -type f -exec chmod 755 {} \;Common Presets
Quick answer
Unix permissions use a 3-digit octal number where each digit represents owner, group, and others. Each digit is the sum of: read (4) + write (2) + execute (1). So 755 = owner:rwx (7), group:r-x (5), others:r-x (5).
Unix permission bits explained
| Value | Binary | Permission | Meaning |
|---|---|---|---|
| 0 | 000 | --- | No permissions |
| 1 | 001 | --x | Execute only |
| 2 | 010 | -w- | Write only |
| 3 | 011 | -wx | Write + execute |
| 4 | 100 | r-- | Read only |
| 5 | 101 | r-x | Read + execute |
| 6 | 110 | rw- | Read + write |
| 7 | 111 | rwx | Full permissions |
Common chmod values
| chmod | Symbolic | Use case |
|---|---|---|
| 755 | rwxr-xr-x | Directories, executables |
| 644 | rw-r--r-- | Regular files, web files |
| 600 | rw------- | SSH private keys |
| 700 | rwx------ | Private directories |
| 777 | rwxrwxrwx | ⚠️ Avoid — full access |
| 400 | r-------- | Read-only, backups |
| 775 | rwxrwxr-x | Group collaboration |
| 440 | r--r----- | Shared read-only files |
chmod command examples
chmod 755 script.sh # make executable chmod 600 ~/.ssh/id_rsa # secure SSH key chmod -R 755 /var/www/ # recursive on directory chmod +x script.sh # add execute for all chmod u+w,g-w file.txt # symbolic modification chmod =644 file.txt # set exact permissions
How to check file permissions
ls -la filename # show permissions stat filename # detailed file info find . -perm 777 # find files with specific perms find . -perm /111 # find executable files
Special permission bits
SetUID (4000): When set on an executable, the process runs with the owner user's effective UID — classic example: passwd must write shadow files owned by root while invoked by normal users.
SetGID (2000): For executables, runs with the group's GID; for directories, new files inherit the directory's group (useful for team-shared folders).
Sticky bit (1000): On directories (e.g. /tmp), only the file owner, directory owner, or root may remove or rename files — not everyone with write access.
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