title: "Debugging a Crunch script"
...
-To test changes to a script by running a job, the change must be pushed into @git@, the job queued asynchronously, and the actual execution may be run on any compute server. As a result, debugging a script can be difficult and time consuming. This tutorial demonstrates using @arv-crunch-job@ to run your job in your local VM. This avoids the job queue and allows you to execute the script from your uncomitted git tree.
+To test changes to a script by running a job, the change must be pushed to your hosted repository, and the job might have to wait in the queue before it runs. This cycle can be an inefficient way to develop and debug scripts. This tutorial demonstrates an alternative: using @arv-crunch-job@ to run your job in your local VM. This avoids the job queue and allows you to execute the script directly from your git working tree without committing or pushing.
-*This tutorial assumes that you are "logged into an Arvados VM instance":{{site.baseurl}}/user/getting_started/ssh-access.html#login, and have a "working environment.":{{site.baseurl}}/user/getting_started/check-environment.html*
+{% include 'tutorial_expectations' %}
This tutorial uses *@you@* to denote your username. Replace *@you@* with your user name in all the following examples.
h2. Create a new script
-Change to your git directory and create a new script in @crunch_scripts/@.
+Change to your Git working directory and create a new script in @crunch_scripts/@.
<notextile>
<pre><code>~$ <span class="userinput">cd <b>you</b>/crunch_scripts</span>
#!/usr/bin/env python
print "hello world"
+print "this script will fail, and that is expected!"
EOF</span>
~/<b>you</b>/crunch_scripts$ <span class="userinput">chmod +x hello-world.py</span>
</code></pre>
h2. Using arv-crunch-job to run the job in your VM
-Instead of a git commit hash, we provide the path to the directory in the "script_version" parameter. The script specified in "script" will actually be searched for in the @crunch_scripts/@ subdirectory of the directory specified "script_version". Although we are running the script locally, the script still requires access to the Arvados API server and Keep storage service. The job will be recorded in the Arvados job history, and visible in Workbench.
+Instead of a Git commit hash, we provide the path to the directory in the "script_version" parameter. The script specified in "script" is expected to be in the @crunch_scripts/@ subdirectory of the directory specified "script_version". Although we are running the script locally, the script still requires access to the Arvados API server and Keep storage service. The job will be recorded in the Arvados job history, and visible in Workbench.
<notextile>
<pre><code>~/<b>you</b>/crunch_scripts$ <span class="userinput">cat >~/the_job <<EOF
2013-12-12_21:36:42 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 child 29834 started on localhost.1
2013-12-12_21:36:42 qr1hi-8i9sb-okzukfzkpbrnhst 29827 status: 0 done, 1 running, 0 todo
2013-12-12_21:36:42 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 stderr hello world
+2013-12-12_21:36:42 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 stderr this script will fail, and that is expected!
2013-12-12_21:36:43 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 child 29834 on localhost.1 exit 0 signal 0 success=
2013-12-12_21:36:43 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 failure (#1, permanent) after 0 seconds
2013-12-12_21:36:43 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 output
</code></pre>
</notextile>
-This is the line of interest:
+These are the lines of interest:
bc. 2013-12-12_21:36:42 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 stderr hello world
+2013-12-12_21:36:42 qr1hi-8i9sb-okzukfzkpbrnhst 29827 0 stderr this script will fail, and that is expected!
The script's output is captured in the log, which is useful for print statement debugging. However, although this script returned a status code of 0 (success), the job failed. Why? For a job to complete successfully scripts must explicitly add their output to Keep, and then tell Arvados about it. Here is a second try:
projects / arvados.git / blobdiff