For every target you define in your skamfile, a number of implicit targets exist - these are status targets, and they indicated the execution status of each target. By default, these status targets map to the filesystem.
status_ok(Target) - this status target is generated if Target was generated successfully (ie the exitcode of the run/srun was zero)
status_err(Target) - this status target is generated if Target was not generated successfully (ie the exitcode of the run/srun was non-zero). Note that Target may be present - however, it should not be trusted because the exitcode of the command which built it is non-zero. (not to be confused with stderr(Target) which is the output of standard error.
status_run(Target) - this status target is generated if Target is currently being generated, or if the job for generating Target has been submitted to a job queueing system.
submit_id(Target) - this status target contains an identifier, or list of identifiers, supplied by the job queueing system.