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Hands-on tutorial on Nextflow and Containers (Docker and Singularity). Paris 2018.
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test1 Minor improvements Mar 27, 2018
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C4LWG-2018 C4LWG-2018

Hands-on tutorial on Nextflow and Containers (Docker and Singularity). Paris 2018. For this tutorial we need to install Nextflow (, Singularity ( and Docker (

Virtual appliance

For sake of simplicity we provide a virtual appliance in OVA format. They can be imported in a virtual machine system such as Virtualbox (video instructions).

It is a Debian Stretch machine from OSBoxes project (ref: Java, Docker, Singularity and Nextflow are already installed.

Check appliances download

Take care that files downloaded correctly (around 6GB). You can check with MD5 utilites from the terminal

In Linux:

$ md5sum -c C4LWG-2018-full.ova.md5 
C4LWG-2018-full.ova: OK

In Mac:

$ md5 C4LWG-2018-full.ova 
$ cat C4LWG-2018-full.ova.md5

Check both outputs show the same string.

User login

  • User: osboxes
  • Password:

If you need to use the root user (e.g. via su -l), it has the same password.

Manual installation

Software requirements

  • For installing NextFlow we need Java version 1.8. You can check with "java -version". Then just type "curl -s | bash" for installing a local copy in your current directory. Finally type "./nextflow run hello" for testing.
  • Mac OS X users can consider installing Homebrew and Homebrew-Cask.
  • Docker (Community Edition): . Download and install last stable version in your system.
    • Cask users: brew cask install docker
  • Singularity:
    • Linux
    • Mac (Homebrew and Homebrew-Cask are needed)
      • If using Vagrant with Singularity, Vagrant shared folder with the host is /vagrant. That would be the best location to place generated images.

Installing nextflow

curl -s | bash

Container installation

You can retrieve Docker image with all used software by doing:

docker pull biocorecrg/c4lwg-2018

Alternately, you can always modify and build a Docker image yourself in your computer by doing:

docker build -t myimagename .

Converting Docker image into Singularity image

singularity build c4lwg-2018.simg docker://biocorecrg/c4lwg-2018
  • If you experience problems executing the generated image, e.g., ERROR : No valid /bin/sh in container, try to change your umask (e. g., umask 000) Ref

Generating a Singularity image from a Singularity recipe

There are other ways to generate Singularity images from other recipe approaches. As a example, using Debootstrap (being root is required in these cases)

singularity build c4lwg-2018.xenial.simg Singularity.xenial

Nextflow usage

We can reach the first folder test0

cd test0; ls


We can have a look at the code and launch it:

nextflow run

Nextflow creates a directory named work with different subfolders. Each one contains the input, output and some hidden files:

  • .exitcode
  • .command.log
  • .command.out
  • .command.err
  • .command.begin

In this case there is neither input nor output file.

Second example where we read a fasta file, split it in several ones and tests on them.

cd test1; ls


nextflow run In the work folder we have subfolders containing this time a link to the input and the output file. In output folder we have links to the final results.

Third example where we launch two fastQC analysis and we run multiQC on their result: cd test2; ls

  • params.config: with parameters
  • nextflow.config: with information about resources needed for each task and the container to be used

We can inspect the different files and launch te pipeline.

nextflow run -bg We can inspect the results in the different folders.

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