---
layout: default
navsection: installguide
title: Install the Crunch dispatcher

...



The dispatcher normally runs on the same host/VM as the API server.

h4. Perl SDK dependencies

Install the Perl SDK on the controller.

* See "Perl SDK":{{site.baseurl}}/sdk/perl/index.html page for details.

h4. Python SDK dependencies

Install the Python SDK and CLI tools on controller and all compute nodes.

* See "Python SDK":{{site.baseurl}}/sdk/python/sdk-python.html page for details.

h4. Likely crunch job dependencies

On compute nodes:

* @pip install --upgrade pyvcf@

h4. Crunch user account

On compute nodes and controller:

* @adduser crunch@

The crunch user should have the same UID, GID, and home directory on all compute nodes and on the controller.

h4. Repositories

Crunch scripts must be in Git repositories in the directory configured as @git_repositories_dir@/*.git (see the "API server installation":install-api-server.html#git_repositories_dir).

Once you have a repository with commits -- and you have read access to the repository -- you should be able to create a new job:

<pre>
read -rd $'\000' newjob <<EOF; arv job create --job "$newjob"
{"script_parameters":{"input":"f815ec01d5d2f11cb12874ab2ed50daa"},
 "script_version":"master",
 "script":"hash",
 "repository":"arvados"}
EOF
</pre>

Without getting this error:

<pre>
ArgumentError: Specified script_version does not resolve to a commit
</pre>

h4. Running jobs

* @services/api/script/crunch-dispatch.rb@ must be running.
* @crunch-dispatch.rb@ needs @services/crunch/crunch-job@ in its @PATH@.
* @crunch-job@ needs @sdk/perl/lib@ and @warehouse-apps/libwarehouse-perl/lib@ in its @PERLLIB@
* @crunch-job@ needs @ARVADOS_API_HOST@ (and, if necessary in a development environment, @ARVADOS_API_HOST_INSECURE@)

Example @/var/service/arvados_crunch_dispatch/run@ script:

<pre>
#!/bin/sh
set -e

rvmexec=""
## uncomment this line if you use rvm:
#rvmexec="/usr/local/rvm/bin/rvm-exec 2.1.1"

export PATH="$PATH":/path/to/arvados/services/crunch
export ARVADOS_API_HOST={{ site.arvados_api_host }}
export CRUNCH_DISPATCH_LOCKFILE=/var/lock/crunch-dispatch

fuser -TERM -k $CRUNCH_DISPATCH_LOCKFILE || true

## Only if your SSL cert is unverifiable:
# export ARVADOS_API_HOST_INSECURE=yes

cd /path/to/arvados/services/api
export RAILS_ENV=production
exec $rvmexec bundle exec ./script/crunch-dispatch.rb 2>&1
</pre>