GNU Parallel以交互方式在脚本中运行，但不能通过crontab在同一脚本中运行

Question

I'm using GNU Parallel version 20141122 to curl 100 IP addresses in parallel within a larger script.

When I execute the script interactively, Parallel produces the expected results in a log file.

When I run the same script via a crontab job, no entries are added to the log file although the remainder of the script produces expected results for all of the non-Parallel-related tasks.

The line in the script that executes Parallel is

parallel -j30 < contactdevices.input

The file contactdevices.input contains 100 lines like this:

./contactdevice.sh  155.156.157.158

contactdevice.sh curls the IP address and appends a one line result to a log file.

My Amazon AMI environment supports more than 40 such simultaneous jobs.

Why does Parallel work within my script when run interactively but appears not to run at all when the identical script is executed via crontab?

Thanks for your help. I'm pretty much a linux and bash neophyte.

Answer 1

Usually the problem with cron is that you have a limited $PATH. Try setting that:

PATH=/usr/bin:/bin:/the/dir/containing/contactdevice

and then remove the ./

Answer 2

The parallel utility was installed in the the user's bin folder rather than /usr/bin . Installing the utility in /usr/bin solved the problem. Alternatively, we could have solved the problem by specifying the location of parallel when invoking it.