Chmod & Glob Coach

Paste a chmod command and find out what it does before you run it — plus builders for chmod, umask and glob patterns. On-device.

The three octal digits are owner, group and others, each summing read as 4, write as 2 and execute as 1 — so 755 stops needing memorisation once you read it as bits. Execute means something different on a directory: traversable rather than runnable, which is why a readable directory without it lists names you cannot open.

Checking before running is the point. chmod 777 is the reflexive fix that makes a problem disappear by making a file world-writable, and recursive permission changes on the wrong path are among the more effective ways to break a system. umask is the same arithmetic inverted — it subtracts from the default rather than setting it.