Death, taxes, and exit codes

If there’s one thing I’m learning, it’s that I can always find a new way to create an error message. I recently discovered a situation where I had some paired end samples I was importing (as manifest file) and trimming (with cutadapt plugin) and then merging (with vsearch plugin). When making the manifest file, I typically run a command on the directory of fastq files to check that there is some data in each .fastq file:

find . -type f -name "*.gz" -empty -delete

For whatever reason, this failed to recognize that several of my fastq files apparently had zero reads. At first, this didn’t seem to matter (and I didn’t notice because I didn’t get any error!). The import function worked without any error being flagged. Then cutadapt worked without issue. But interestingly, vsearch fails when it tries to merge an empty file.

Command: vsearch --fastq_mergepairs /tmp/qiime2-archive-s1v74pfi/53390f42-dd28-451b-9205-9c77e4dbf7b2/data/nau1304194_264_L001_R1_001.fastq.gz --reverse /tmp/qiime2-archive-s1v74pfi/53390f42-dd28-451b-9205-9c77e4dbf7b2/data/nau1304194_265_L001_R2_001.fastq.gz --fastqout /tmp/q2-SingleLanePerSampleSingleEndFastqDirFmt-1_6mf45b/nau1304194_129_L001_R1_001.fastq --fastq_ascii 33 --fastq_minlen 1 --fastq_minovlen 10 --fastq_maxdiffs 10 --fastq_qmin 0 --fastq_qminout 0 --fastq_qmax 41 --fastq_qmaxout 41 --fastq_allowmergestagger

vsearch v2.7.0_linux_x86_64, 251.7GB RAM, 24 cores

Fatal error: File too small
Traceback (most recent call last):
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/site-packages/q2cli/", line 274, in __call__
    results = action(**arguments)
  File "<decorator-gen-130>", line 2, in join_pairs
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/site-packages/qiime2/sdk/", line 231, in bound_callable
    output_types, provenance)
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/site-packages/qiime2/sdk/", line 362, in _callable_executor_
    output_views = self._callable(**view_args)
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/site-packages/q2_vsearch/", line 57, in join_pairs
    qmax, qmaxout)
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/site-packages/q2_vsearch/", line 141, in _join_pairs_w_command_output
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/site-packages/q2_vsearch/", line 33, in run_command, check=True)
  File "/mnt/lustre/macmaneslab/devon/.conda/envs/qiime2-2018.11/lib/python3.5/", line 398, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['vsearch', '--fastq_mergepairs', '/tmp/qiime2-archive-s1v74pfi/53390f42-dd28-451b-9205-9c77e4dbf7b2/data/nau1304194_264_L001_R1_001.fastq.gz', '--reverse', '/tmp/qiime2-archive-s1v74pfi/53390f42-dd28-451b-9205-9c77e4dbf7b2/data/nau1304194_265_L001_R2_001.fastq.gz', '--fastqout', '/tmp/q2-SingleLanePerSampleSingleEndFastqDirFmt-1_6mf45b/nau1304194_129_L001_R1_001.fastq', '--fastq_ascii', '33', '--fastq_minlen', '1', '--fastq_minovlen', '10', '--fastq_maxdiffs', '10', '--fastq_qmin', '0', '--fastq_qminout', '0', '--fastq_qmax', '41', '--fastq_qmaxout', '41', '--fastq_allowmergestagger']' returned non-zero exit status 1

This got me to wondering a couple of things:

  1. Any idea why the find command isn’t flagging these empty files? I ended up adding on a -size parameter to ensure it ditches the empty files, but can’t figure out why the bash shell isn’t thinking these files are empty.
  2. I know we can filter sequences and features in QIIME, but is there a way to remove samples from the initial demux.seqs.qza artifact I generate from the manifest importing step? That’s a SampleData[PairedEndSequencesWithQuality] type… It would be great to have the same basic feature where you can just drop entire samples from that file if there was a way to count the number of sequences for each sample.
  3. Because our compute cluster uses SLURM, I end up generating my .log files via the program’s SBATCH --output= command. Perhaps it’s just the nature of our cluster, but I can’t ever access the temporary files it generates in the .log to look at. If I run the same command on the head node, then I capture the message and can access the /tmp/pathtomessage to see what really went wrong. Any idea if this is a SLURM thing, or something about the setup of our compute cluster?


Hi @devonorourke!

I suspect the problem was you have a compressed file (.gz). Compression usually takes a little bit of overhead to explain what kind of compression it is and to set up any initial structures used by the algorithm (wasting space for very small files). This means even an empty file ends up with a few bytes (in the case of gzip, these bytes are the original filename and timestamp (I have no idea why, it makes md5sum hard as well)).

I agree, that would be very useful (and simple to implement)!

That’s a pretty common gotcha on most clusters. In this case your sbatch is sending the job to a node as determined by your other arguments for memory, walltime, etc. and the schedulers configuration.

That node will have its own filesystem and thus /tmp directory. This is a good thing as it means QIIME 2 can write stuff quickly without going over a network while it’s working. The downside is the path that q2cli will report will always be specific to the node the scheduler picked. Typically your sysadmin will not want you rooting around the different cluster nodes, so what I recommend would be setting the --verbose flag always, that way it is captured by slurm into your .log files.

In the future we’d like to be more aware of the scheduler, but that’s a hard problem as there’s lots of schedulers in the world.

Hope that helps!

1 Like

Very much appreciate the insights @ebolyen:

Compression usually takes a little bit of overhead to explain what kind of compression it is and to set up any initial structures used by the algorithm

:rainbow: the more you know…

what I recommend would be setting the --verbose flag always

Will do. Awesome stuff!