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inotify-tools (inotifywait)

The inotify-tools package comes with several tools that can be used to watch files for changes.

inotifywait

The inotifywait tools comes with the inotify-tools package.

It waits for changes to files (using inotify or fanotify, the latter from C) and can be used inside shell scripts to execute arbitrary code whenever the watched files are modified.

inotifywait Output

Whenever the watched file changes, it outputs an "event."
By default the event uses the format: 

watched_filename EVENT_NAMES event_filename

  • watched_filename: The name of the file that the change occurred in.
  • EVENT_NAMES: Comma-separated inotify events that occurred.
  • event_filename: Only outputs when the event occurred on a directory.
    • This will hold the name of the file inside that directory which caused the "event."

inotifywait Usage

while read -r event; do
    printf "Event: %s\n" "$event"
done < <(inotifywait -m -r -e create,modify,delete "$WATCH_FILE")
  • -m: Monitor mode. Execute indefinitely. The default is to exit after the first event.
    • You'll probably want to use this inside scripts.

  • -r: Recursive. Watch all subdirectories of any dirs being watched.

  • -d: Daemon. Same as --monitor but runs in the background.

    • Logs events to a file (--outfile required).
    • Also implies --syslog.

  • -s: Syslog. Outputs errors to system log module rather than stderr.

    • man 3 syslog

  • -e: Event. Listen for specific events only.

    • Common events:
      • access
      • modify
      • create
      • delete
    • man://inotifywait /^\s*EVENTS