nf-core/bamtofastq
Converts bam or cram files to fastq format and does quality control.
Introduction
Bamtofastq is a workflow designed to convert one or multiple bam/cram files into fastq format.
Samplesheet input
You will need to create a samplesheet with information about the samples you would like to analyse before running the pipeline. Use this parameter to specify its location. It has to be a comma-separated file with 3 columns, and a header row as shown in the examples below.
--input '[path to samplesheet file]'
Full samplesheet
The pipeline will auto-detect whether a sample is single- or paired-end. The samplesheet can have as many additional columns as you desire, however, the samplesheet must include the required columns listed in the table below (sample_id
, mapped
, file_type
). If index files are not available, the index
column should be omitted. In this case, the files will be automatically indexed during the pipeline run. This can have an effect on the runtime.
sample_id,mapped,index,file_type
test1,test1.cram,test1.cram.crai,cram
test2,test2.cram,test2.cram.crai,cram
Column | Description | Required? |
---|---|---|
sample_id | Custom sample name. | Yes |
mapped | Absolute path to input BAM/CRAM file. Allowed file extensions: “.bam” or “.cram”. | Yes |
index | If available, provide full path to input BAI/CRAI index file. File extensions must be “.bam.bai” or “.cram.crai”. | No |
file_type | Type of input file. Options: “bam” or “cram”. | Yes |
An example samplesheet has been provided with the pipeline.
Running the pipeline
The typical command for running the pipeline is as follows:
nextflow run nf-core/bamtofastq --input ./samplesheet.csv --outdir ./results -profile docker
This will launch the pipeline with the docker
configuration profile. See below for more information about profiles.
Note that the pipeline will create the following files in your working directory:
work # Directory containing the nextflow working files
<OUTDIR> # Finished results in specified location (defined with --outdir)
.nextflow_log # Log file from Nextflow
# Other nextflow hidden files, eg. history of pipeline runs and old logs.
If you wish to repeatedly use the same parameters for multiple runs, rather than specifying each flag in the command, you can specify these in a params file.
Pipeline settings can be provided in a yaml
or json
file via -params-file <file>
.
Do not use -c <file>
to specify parameters as this will result in errors. Custom config files specified with -c
must only be used for tuning process resource specifications, other infrastructural tweaks (such as output directories), or module arguments (args).
The above pipeline run specified with a params file in yaml format:
nextflow run nf-core/bamtofastq -profile docker -params-file params.yaml
with params.yaml
containing:
input: './samplesheet.csv'
outdir: './results/'
fasta: './reference.fasta'
<...>
You can also generate such YAML
/JSON
files via nf-core/launch.
Updating the pipeline
When you run the above command, Nextflow automatically pulls the pipeline code from GitHub and stores it as a cached version. When running the pipeline after this, it will always use the cached version if available - even if the pipeline has been updated since. To make sure that you’re running the latest version of the pipeline, make sure that you regularly update the cached version of the pipeline:
nextflow pull nf-core/bamtofastq
Reproducibility
It is a good idea to specify a pipeline version when running the pipeline on your data. This ensures that a specific version of the pipeline code and software are used when you run your pipeline. If you keep using the same tag, you’ll be running the same version of the pipeline, even if there have been changes to the code since.
First, go to the nf-core/bamtofastq releases page and find the latest pipeline version - numeric only (eg. 1.3.1
). Then specify this when running the pipeline with -r
(one hyphen) - eg. -r 1.3.1
. Of course, you can switch to another version by changing the number after the -r
flag.
This version number will be logged in reports when you run the pipeline, so that you’ll know what you used when you look back in the future. For example, at the bottom of the MultiQC reports.
To further assist in reproducbility, you can use share and re-use parameter files to repeat pipeline runs with the same settings without having to write out a command with every single parameter.
If you wish to share such profile (such as upload as supplementary material for academic publications), make sure to NOT include cluster specific paths to files, nor institutional specific profiles.
Core Nextflow arguments
These options are part of Nextflow and use a single hyphen (pipeline parameters use a double-hyphen).
-profile
Use this parameter to choose a configuration profile. Profiles can give configuration presets for different compute environments.
Several generic profiles are bundled with the pipeline which instruct the pipeline to use software packaged using different methods (Docker, Singularity, Podman, Shifter, Charliecloud, Apptainer, Conda) - see below.
We highly recommend the use of Docker or Singularity containers for full pipeline reproducibility, however when this is not possible, Conda is also supported.
The pipeline also dynamically loads configurations from https://github.com/nf-core/configs when it runs, making multiple config profiles for various institutional clusters available at run time. For more information and to see if your system is available in these configs please see the nf-core/configs documentation.
Note that multiple profiles can be loaded, for example: -profile test,docker
- the order of arguments is important!
They are loaded in sequence, so later profiles can overwrite earlier profiles.
If -profile
is not specified, the pipeline will run locally and expect all software to be installed and available on the PATH
. This is not recommended, since it can lead to different results on different machines dependent on the computer enviroment.
test
- A profile with a complete configuration for automated testing
- Includes links to test data so needs no other parameters
docker
- A generic configuration profile to be used with Docker
singularity
- A generic configuration profile to be used with Singularity
podman
- A generic configuration profile to be used with Podman
shifter
- A generic configuration profile to be used with Shifter
charliecloud
- A generic configuration profile to be used with Charliecloud
apptainer
- A generic configuration profile to be used with Apptainer
wave
- A generic configuration profile to enable Wave containers. Use together with one of the above (requires Nextflow
24.03.0-edge
or later).
- A generic configuration profile to enable Wave containers. Use together with one of the above (requires Nextflow
conda
- A generic configuration profile to be used with Conda. Please only use Conda as a last resort i.e. when it’s not possible to run the pipeline with Docker, Singularity, Podman, Shifter or Charliecloud.
--input
Use this to specify the location of your input BAM/CRAM files. For example:
--input 'path/to/samplesheet.csv'
--fasta
When converting a CRAM file the fasta file specified in the CRAM header should be used to decompress the file. If that file is not available, you will need to specify an alternative path using the --fasta
option.
You can check which reference FASTA file should be used by inspecting the CRAM file with the following command:
samtools view -H path/to/sample.cram | grep '@SQ'.
To specify a reference genome FASTA you can follow the command below:
--input 'path/to/samplesheet.csv' --fasta 'ftp://ftp.broadinstitute.org/pub/seq/references/Homo_sapiens_assembly19.fasta'
--chr
(optional)
Use to only obtain reads mapping to a specific chromosome or region.
It is important to specify the chromosome or region name exactly as set in the bam/cram file. Otherwise no reads may be extracted!
For example:
--chr 'X chrX'
This extracts reads mapping to X
as well as chrX
.
To check beforehand which chromosome notation is used in your bam/cram file you can use samtools.
samtools idxstats your_input.[bam|cram] | head -n 25
--no_read_QC
(optional)
Use to skip FastQC
on obtained reads. This is useful, when the reads are used as input in another pipeline, which runs QC
on its input data as well.
--no_read_QC
--samtools_collate_fast
(optional)
Use to specify the fast mode for the samtools collate
command in the processes COLLATE_FASTQ_MAP
, COLLATE_FASTQ_UNMAP
and SAMTOOLS_COLLATEFASTQ_SINGLE_END
. This option relies on the samtools command line flags -f -r INT
and will output primary alignments only. For full documentation of this mode please refer to the samtools documentation.
--reads_in_memory
(optional)
Only relevant in combination with --samtools_collate_fast
. It specifies how many alignment reads are kept in memory [default = ‘100000’]. This is useful for speeding up the processes COLLATE_FASTQ_MAP
, COLLATE_FASTQ_UNMAP
and SAMTOOLS_COLLATEFASTQ_SINGLE_END
.
Example:
--samtools_collate_fast --reads_in_memory '1000000'
--no_stats
(optional)
Use to skip FastQC
on both input bam/cram and output reads, as well as all processes that compute statistics samtools flagstat
, samtools idxstats
, and samtools stats
. This is useful for large datasets, since the quality metrics processes require a significant amount of time and resources.
❗ Use this at own risk. You won’t be able to quickly sanity check the results.
--no_stats
Job resources
Automatic resubmission
Each step in the pipeline has a default set of requirements for number of CPUs, memory and time. For most of the steps in the pipeline, if the job exits with an error code of 143
(exceeded requested resources) it will automatically resubmit with higher requests (2 x original, then 3 x original). If it still fails after three times then the pipeline is stopped.
Custom resource requests
Wherever process-specific requirements are set in the pipeline, the default value can be changed by creating a custom config file. See the files hosted at nf-core/configs
for examples.
If you are likely to be running nf-core
pipelines regularly it may be a good idea to request that your custom config file is uploaded to the nf-core/configs
git repository. Before you do this please can you test that the config file works with your pipeline of choice using the -c
parameter (see definition below). You can then create a pull request to the nf-core/configs
repository with the addition of your config file, associated documentation file (see examples in nf-core/configs/docs
), and amending nfcore_custom.config
to include your custom profile.
If you have any questions or issues please send us a message on Slack.
AWS Batch specific parameters
Running the pipeline on AWS Batch requires a couple of specific parameters to be set according to your AWS Batch configuration. Please use the -awsbatch
profile and then specify all of the following parameters.
--awsqueue
The JobQueue that you intend to use on AWS Batch.
--awsregion
The AWS region to run your job in. Default is set to eu-west-1
but can be adjusted to your needs.
Please make sure to also set the -w/--work-dir
and --outdir
parameters to a S3 storage bucket of your choice - you’ll get an error message notifying you if you didn’t.
Other command line parameters
--outdir
The output directory where the results will be saved.
--email
Set this parameter to your e-mail address to get a summary e-mail with details of the run sent to you when the workflow exits. If set in your user config file (~/.nextflow/config
) then you don’t need to specify this on the command line for every run.
--email_on_fail
This works exactly as with --email
, except emails are only sent if the workflow is not successful.
-name
Name for the pipeline run. If not specified, Nextflow will automatically generate a random mnemonic.
This is used in the MultiQC report (if not default) and in the summary HTML / e-mail (always).
NB: Single hyphen (core Nextflow option)
-resume
Specify this when restarting a pipeline. Nextflow will use cached results from any pipeline steps where the inputs are the same, continuing from where it got to previously. For input to be considered the same, not only the names must be identical but the files’ contents as well. For more info about this parameter, see this blog post.
You can also supply a run name to resume a specific run: -resume [run-name]
. Use the nextflow log
command to show previous run names.
-c
Specify the path to a specific config file (this is a core Nextflow command). See the nf-core website documentation for more information.
Custom configuration
Resource requests
Whilst the default requirements set within the pipeline will hopefully work for most people and with most input data, you may find that you want to customise the compute resources that the pipeline requests. Each step in the pipeline has a default set of requirements for number of CPUs, memory and time. For most of the steps in the pipeline, if the job exits with any of the error codes specified here it will automatically be resubmitted with higher requests (2 x original, then 3 x original). If it still fails after the third attempt then the pipeline execution is stopped.
To change the resource requests, please see the max resources and tuning workflow resources section of the nf-core website.
Custom Containers
In some cases you may wish to change which container or conda environment a step of the pipeline uses for a particular tool. By default nf-core pipelines use containers and software from the biocontainers or bioconda projects. However in some cases the pipeline specified version maybe out of date.
To use a different container from the default container or conda environment specified in a pipeline, please see the updating tool versions section of the nf-core website.
Custom Tool Arguments
A pipeline might not always support every possible argument or option of a particular tool used in pipeline. Fortunately, nf-core pipelines provide some freedom to users to insert additional parameters that the pipeline does not include by default.
To learn how to provide additional arguments to a particular tool of the pipeline, please see the customising tool arguments section of the nf-core website.
nf-core/configs
In most cases, you will only need to create a custom config as a one-off but if you and others within your organisation are likely to be running nf-core pipelines regularly and need to use the same settings regularly it may be a good idea to request that your custom config file is uploaded to the nf-core/configs
git repository. Before you do this please can you test that the config file works with your pipeline of choice using the -c
parameter. You can then create a pull request to the nf-core/configs
repository with the addition of your config file, associated documentation file (see examples in nf-core/configs/docs
), and amending nfcore_custom.config
to include your custom profile.
See the main Nextflow documentation for more information about creating your own configuration files.
If you have any questions or issues please send us a message on Slack on the #configs
channel.
Azure Resource Requests
To be used with the azurebatch
profile by specifying the -profile azurebatch
.
We recommend providing a compute params.vm_type
of Standard_D16_v3
VMs by default but these options can be changed if required.
Note that the choice of VM size depends on your quota and the overall workload during the analysis. For a thorough list, please refer the Azure Sizes for virtual machines in Azure.
Running in the background
Nextflow handles job submissions and supervises the running jobs. The Nextflow process must run until the pipeline is finished.
The Nextflow -bg
flag launches Nextflow in the background, detached from your terminal so that the workflow does not stop if you log out of your session. The logs are saved to a file.
Alternatively, you can use screen
/ tmux
or similar tool to create a detached session which you can log back into at a later time.
Some HPC setups also allow you to run nextflow within a cluster job submitted your job scheduler (from where it submits more jobs).
Nextflow memory requirements
In some cases, the Nextflow Java virtual machines can start to request a large amount of memory.
We recommend adding the following line to your environment to limit this (typically in ~/.bashrc
or ~./bash_profile
):
NXF_OPTS='-Xms1g -Xmx4g'