-The naive way to do this is to know, a-priori, which machines have the software, and constrain the requirements expression so that your job only matches those machines. This is often problematic and hard to maintain. A better solution involves a two-step process.
+The naive way to do this is to know ahead of time exactly which machines have the software, and then constrain the =Requirements= expression of the job so that it only matches those machines. Knowing ahead of time is problematic and difficult to maintain as the pool changes. A better solution uses this two-step process.
-First, you need to tell the machines to report that they have special
-software installed, and second, you need to tell the jobs to require
-machines that have that software.
+First, each machine that has the special software installed needs to advertise its availability in its machine ClassAd. Second, the job identifies in its submit description file that it requires a machine that has the special software.
-To tell the machines to report the presence of special software, first
-add a parameter to their configuration files like so:
+A machine advertises the presence of special software in its local configuration file, as in this example:
{code}
HAS_MY_SOFTWARE = True
{endcode}
-And then, if there are already STARTD_ATTRS defined in that file, add
-HAS_MY_SOFTWARE to them, or, if not, add the line:
+Also, if =STARTD_ATTRS= is already defined in that file, add
+=HAS_MY_SOFTWARE= to the list. If =STARTD_ATTRS= is not already in
+that local configuration file, add the line:
{code}
STARTD_ATTRS = HAS_MY_SOFTWARE, $(STARTD_ATTRS)
{endcode}
-Note For these changes to take effect, each condor_startd you update
-needs to be reconfigured with condor_reconfig -startd.
+For this configuration change to take effect, the condor_startd on that machine
+needs to be reconfigured. Use =condor_reconfig -startd=. Each machine with
+the configuration change must be reconfigured.
-You can double-check that this has been correctly added by running the condor_status command:
+Double check that this has been correctly implemented by running the condor_status command:
{code}
condor_status -constraint HAS_MY_SOFTWARE
{endcode}
-Next, to tell your jobs to only run on machines that have this
-software, add a requirements statement to their submit files like so:
+Jobs that need to run on the machines with the special software installedadd a =Requirements= command to their submit description file:
{code}
Requirements = (HAS_MY_SOFTWARE =?= True)
{endcode}
-Note Be sure to use =?= instead of == so that if a machine doesn't have
-the HAS_MY_SOFTWARE parameter defined, the job's Requirements
-expression will not evaluate to ``undefined'', preventing it from
-running anywhere!
+Be sure to use =?= instead of ==, so that if a machine does not have
+the =HAS_MY_SOFTWARE= configuration variable defined, the job's =Requirements=
+expression will not evaluate to =Undefined=, preventing the job from
+running anywhere.
