{subsubsection: Audience}
If you have a HTCondor pool that is *not* configured to use Partitionable slots and you wish to run Folding@home as backfill jobs on those slots using the recipe
{wiki:  HowToConfigureFoldingAtHome here}

{subsubsection: Strategy}
We will use HTCondor's "fetch work" configuration to run a script on each execute machine that periodically generates a job classad for Folding@Home work.  Those jobs will have a retirement time of 0 so that they can be pre-empted by jobs sent from a Schedd.  These jobs will all be run by a dedicated user named *backfill*, and the Startd will give negative RANK jobs from the *backfill* user.


The configuration fragment below can be customized by modifying =FAH_Owner=, =FAH_HOME= and =FAH_Executable= configuration variables near the top of the file.
{snip: backfill_folding_at_home.config}
# The local user to run FAH jobs as, you must create this user
#
FAH_Owner = backfill

# Folding at home settings, change to match your install path and work directory
# Each slot will use a subdirectory under this path named from the slotid of the slot
# e.g.  /opt/fah/slot2, /opt/fah/slot3, etc.
#
FAH_HOME = /opt/fah
FAH_Executable = /usr/bin/FAHClient

# Arguments to the Folding@Home client for each slot, change this to match
# the cpus and memory of your slots
#
# Checkpoint every N minutes, default is 15
FAH_CheckpointArg = 15
FAH_CpusArg       = 1
FAH_MemArg        = $(DETECTED_MEMORY)/$(DETECTED_CPUS)*1024*1024

FAH_Arguments = --config $(FAH_HOME)/config.xml \
                --data-directory . \
                --checkpoint $INT(FAH_CheckpointArg) \
                --client-threads $INT(FAH_CpusArg) \
                --memory $INT(FAH_MemArg) \
                --cpus $(FAH_CpusArg)

# the script that HTCondor will use to get FAH jobs, steal this script from HTCondor website
#
# this script extracts slot id from stdin and
# puts it into the environment as _CONDOR_BACKFILL_SLOTID=<SlotId>
# then runs
#    condor_config_val -macro '$(FAH_JOB)'
# to generate a job classad for that slot
#
FAH_HOOK_FETCH_WORK = $(FAH_HOME)/fetch_work

#
# Template for the Folding@Home job that the FAH_FETCH_SCRIPT will return
#
FAH_JOB @=end
  Cmd = "$(FAH_Executable)"
  Iwd = "$(FAH_HOME)/slot$(BACKFILL_SLOTID)"
  Owner = "$(FAH_Owner)"
  User = "$(FAH_Owner)@$(UID_DOMAIN)"
  JobUniverse = 5
  Arguments = "$(FAH_Arguments)"
  Out = "fah.out"
  Err = "fah.err"
  NiceUser = true
  Requirements = (State == "Unclaimed") && ($(StateTimer) > 1200)
  MaxJobRetirementTime = 0
  JobLeaseDuration = 604800
  RequestCpus = $INT(FAH_CpusArg)
  RequestMemory = $INT(FAH_MemArg)
@end

#
# Enable work fetch for Folding@Home jobs and rank them
# lower than normal jobs
#
STARTD_JOB_HOOK_KEYWORD = FAH
RANK = $(RANK:0) - (Owner == "$(FAH_Owner)")


{endsnip}