= Validation =

In BOINC, a '''validator''' is a program that decides whether results are correct.
You must supply a validator for each application in your project,
and include it in the <daemons> section of your [ProjectConfigFile project configuration file].

Depending on various factors, you may be able to use a standard validator that comes with BOINC,
or you may have to develop a custom validator.

 * If your application generates exactly matching results
  (either because it does no floating-point arithmetic,
  or because you use [HomogeneousRedundancy homogeneous redundancy])
  then you can use the 'sample bitwise validator' (see below).
 * If you are using BOINC for 'desktop grid' computing
  (i.e. you trust all the participating hosts) then you can use the 'sample trivial validator' (see below).
 * Otherwise, you'll need to [ValidationSimple develop a custom validator] for your application.

Two standard validators are supplied:

 * The '''sample_bitwise_validator''' requires a strict majority, and regards results as equivalent only if they agree byte for byte.
 * The '''sample_trivial_validator''' accepts all results as valid.
 * The '''sample_substr_validator''' accepts results whose stderr output includes a given string.

By default, a validator grants credit for valid results using a default mechanism (described [CreditNew here]).
There are several [CreditAlt alternative ways of granting credit].

=== Command-line arguments ===

A validator (either standard or custom) has the following command-line arguments:

 --app appname:: 	Name of the application
 [ --one_pass_N_WU N ]:: 	Validate at most N WUs, then exit
 [ --one_pass ]:: 	Make one pass through WU table, then exit
 [ --mod n i ]:: 	Process only WUs with (id mod n) == i. This option lets you run multiple instances of the validator for increased performance.
 [ --max_granted_credit X ]:: 	Grant no more than this amount of credit to a job.
 [ --update_credited_job ]:: For each valid result, create an entry in the credited_job database table.
  This lets you keep track of which user contributed to each WU, even if you use [DbPurge db_purge].

Options related to credit.
'''Don't use these options in general.  With no options,
validators will grant credit in a fair way.'''

 [ --no_credit ]:: Don't grant credit (use this if you [CreditAlt grant credit via trickle messages]).
 [ --credit_from_runtime ]:: Grant credit proportional to (runtime * CPU FLOPS).
  Use this if:
 * the app has only single-threaded CPU versions, and
 * the app's jobs do different amounts of computation on different hosts,
   e.g. if they exit after a fixed amount of time.
 * [CreditAlt Details].
 [ --credit_from_wu ]:: Grant credits written in WU template. See CreditAlt and JobSubmission.