Calculate Unix and Linux file permissions visually. Toggle checkboxes or type an octal number to instantly see symbolic notation, the chmod command, and a human-readable description of each permission set.
Last updated: March 2026| Read (4) | Write (2) | Execute (1) | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
chmod (change mode) is a Unix/Linux command that modifies file and directory permissions. Permissions are organized into three classes: Owner (user who owns the file), Group (users in the file's group), and Others (everyone else). Each class can have Read (value 4), Write (value 2), and Execute (value 1). These values are summed per class to produce an octal digit — for example, chmod 755 means Owner=rwx(7), Group=r-x(5), Others=r-x(5).chmod 755 sets Owner to read+write+execute (7), Group to read+execute (5), and Others to read+execute (5). This is the standard permission for web server directories and executable scripts — the owner can fully manage files while group members and the public can read and execute but not modify them.755 or 644 to set all permissions at once. Symbolic mode uses letter notation like u+x (add execute for user), g-w (remove write for group), or o=r (set others to read-only). Symbolic mode is ideal for changing specific permissions without affecting others, while numeric mode is faster when you need to set exact permissions from scratch.