I have an audio recording script file that runs for slightly over an hour. I want it to start the job on the top of each hour. There will be a brief moment when two jobs will overlap, but that should not be a problem - I can run two of the same script on the console without any errors. However, the problem is, the cron is invoking the job only once every 2 hours, not every hour. The jobs that are invoked, run to completion without any errors. I am piping stdout and stderr to file, and there are no error messages. This is on Slackware 14.1 64-bit. Crond is obviously running - '/usr/sbin/crond -l notice'.


/home/myuserid/myscript:

#!/bin/bash

STP=$(date +%s)
arecord -D plug:dsnoop -d 3600 -r 11025 -f S16_LE sounds/$STP.wav
sox -q sounds/$STP.wav sounds/$STP-1.wav silence -l 1 0.1 0.1% -1 1 0.1%
lame --quiet sounds/$STP-1.wav $STP.mp3

---------------------
crontab entry:
0 * * * * /home/myuserid/myscript >> /tmp/myscript_err 2>&1

I think the reason is that the script takes more than one our to run. Cron will not start the script when it's already running. Maybe add & at the end?

Here is a little more info. I ran the following script (mydate_sleep.sh) every minute
#!/bin/bash
date
sleep 65

Crontab entry is this:
* * * * * mydate_sleep.sh >> /tmp/mydate_sleep

The output file /tmp/mydate_sleep looks like this:
Sat Jul 4 20:10:01 EDT 2015
Sat Jul 4 20:12:01 EDT 2015
Sat Jul 4 20:13:01 EDT 2015
Sat Jul 4 20:15:01 EDT 2015
Sat Jul 4 20:17:01 EDT 2015
Sat Jul 4 20:19:01 EDT 2015
Sat Jul 4 20:21:01 EDT 2015
Sat Jul 4 20:23:01 EDT 2015
Sat Jul 4 20:25:01 EDT 2015
Sat Jul 4 20:27:01 EDT 2015
Sat Jul 4 20:29:01 EDT 2015
Sat Jul 4 20:31:01 EDT 2015
Sat Jul 4 20:33:01 EDT 2015
Sat Jul 4 20:35:01 EDT 2015
Sat Jul 4 20:37:01 EDT 2015
Sat Jul 4 20:39:01 EDT 2015
Sat Jul 4 20:41:01 EDT 2015
Sat Jul 4 20:42:01 EDT 2015
Sat Jul 4 20:44:01 EDT 2015
Sat Jul 4 20:46:01 EDT 2015
Sat Jul 4 20:48:01 EDT 2015
Sat Jul 4 20:50:01 EDT 2015
Sat Jul 4 20:52:01 EDT 2015
Sat Jul 4 20:54:01 EDT 2015
Sat Jul 4 20:56:01 EDT 2015
Sat Jul 4 20:58:01 EDT 2015


Notice that the script run every two minutes (instead of one minute), but not always. Sometimes it runs every minute. Check the 3rd and 18th outputs. Those are one minute apart. I am confused by this unpredictable behavior. If I remove the "sleep 65" from the script, then it runs every minute.

This is on dillon's cron daemon 4.5.