Using bash, how do you get alerts when a file stops being updated?

Question

I want to be alerted, say by email, if a file does not change for x minutes.

For context, an application is running 24/7 collecting tweets on an unattended system. If the file storing the tweets doesn't change for x minutes, I need to go and check the application hasn't terminated unexpectedly.

Any ideas please? I considered watch but I am new to bash and Linux in general.

Answer 1

Use inotifywait

#!/usr/bin/env sh

MONITOREDFILE=/path/to/monitoredfile

TIMEOUT=600 # 600s or 10 minutes

EMAIL=user@example.com

lastmodified="monitoring started on $(date -R)"
while inotifywait \
  --quiet \
  --timeout $TIMEOUT \
  --event 'MODIFY' \
  "$MONITOREDFILE"
do
  printf '%s has been modified before %s seconds timeout\n' \
  "$MONITOREDFILE" $TIMEOUT
  lastmodified=$(date -R)
done
printf '!!! ALERT !!!\nFile %s has not been modified since %s seconds\n' \
    "$MONITOREDFILE" $TIMEOUT >&2
mailx -s "Stalled file $MONITOREDFILE" "$EMAIL" <<ENDOFMAIL
Monitored file $MONITOREDFILE has not been modified since $lastmodified.
ENDOFMAIL

A different approach to get file last modification with GNU date, and having the loop empty:

#!/usr/bin/env sh

MONITOREDFILE=/path/to/monitoredfile
TIMEOUT=600 # 600s or 10 minutes
EMAIL=user@example.com

while inotifywait --quiet --timeout $TIMEOUT --event 'MODIFY' "$MONITOREDFILE"
do :;done
lastmodified=$(date --utc --iso-8601=seconds --reference="$MONITOREDFILE")
mailx -s "Stalled file $MONITOREDFILE" "$EMAIL" <<ENDOFMAIL
Monitored file $MONITOREDFILE has not been modified since $lastmodified.
ENDOFMAIL