Charliecloud

Charliecloud is similar to Singularity in that it is a software container service. However, it has one significant advantage over Singularity in that it does not require root privileges to install the Charliecloud software or to run Charliecloud containers. This can be a huge advantage, particularly on HPC systems where users generally do not have root privileges and where system administrators are often reluctant to install singularity because of security concerns.

Charliecloud was developed and is still maintained by software developers at Los Alamos National Laboratory. We refer you to to their Documentation pages for further information about the project, for instructions on how to build containers and other resources, and for troubleshooting any problems. Note in particular the Charliecloud command reference.

In the documentation that follows we focus only on what you need to know as a user of JEDI.

Warning

See the Charliecloud documenation (particularly the Installation and Tutorial sections) for tips and warnings about using Charliecloud. For example, there is a known bug on the Cray Linux Environment that causes nodes to crash just before exiting some Charliecloud jobs (they do have a workaround). Also, if you have a large number of MPI processes that each invokes the same Charliecloud container, it could overwhelm a network file system. For JEDI, we’ve run MPI jobs from within the container and have not yet noticed a problem with this (please let us know if you do!).

Installing Charliecloud

If you are using a Vagrant virtual machine that you created with the JEDI Vagrantfile as described on our Vagrant page, then you can skip this step: Charliecloud is already installed.

The Charliecloud Documentation pages have thorough Installation Instructions. This is the most up-to-date documentation available and if you have any problems with the procedure describe here we refer to you that page for troubleshooting.

Installing on Mac OS and Windows systems

Like Singularity, Charliecloud relies on Linux mount namespaces to control the set of filesystem mounts that are visible to a process. Neither Mac nor Windows operating systems currently support such mount namespaces.

So, if you are using a Mac or Windows laptop, we recommend that you install a virtual machine provider like Vagrant. Instructions on how to do so are provided on our JEDI Vagrant Page. This will allow you to create a Linux virtual machine on your computer where you can install Charliecloud and run JEDI.

You are free to choose what type of linux operating system you want to have for your Vagrant virtual machine. In much of what follows, we will use Ubuntu as as an example, and in particular Ubuntu 18.04. We recommend this environment for running Charliecloud, in part because it has a more up-to-date version of bash than the Ubuntu 16.04 bento box available from virtualbox. However, most recent Linux varieties (including Ubuntu 16.04) should be sufficient, as long at they support mount namespaces (see the linux installation section for further information.

Installing on Linux Systems

To install Charliecloud, you’ll need a relatively recent version of Linux that is capable of creating mount namespaces. Most Linux implementations from the last few years should be sufficient. If you want to check the version of the Linux kernel, you can enter:

uname -r

Charliecloud recommends a version of 4.4 or later.

You’ll also need a C compiler and some basic software tools. These may already be installed if you are using an HPC system or a linux PC. However, if you are starting from a bare installation, such as a Vagrant virtual machine or a cloud computing instance (e.g. Amazon EC2), you may need to install these yourself. On Ubuntu or Debian systems you can do this with:

sudo apt-get update
sudo apt-get install build-essential python

Or, on CentOS, Fedora, Amazon Linux, and similar systems, you might instead enter:

sudo yum update
sudo yum groupinstall "Development Tools"

These commands require root access. If you do not have root access, chances are good that the required software is already installed.

The next step is to clone the Charliecloud repository on GitHub, build it, and install it into a directory of your choice. Here we build and install the code into the user’s home directory:

mkdir ~/build
cd ~/build
git clone --recursive https://github.com/hpc/charliecloud.git
cd charliecloud
make
make install PREFIX=$HOME/charliecloud

Unless there were problems, Charliecloud should now be installed in the user’s home directory, in the subdirectory charliecloud. If you wish to test the installation (optional), run the Bats test suite as described in the Charliecloud Documentation.

Now add the Charliecloud executables to your path. You may wish to do this interactively when you install Charliecloud for the first time but we recommend that you also put it in a startup script such as .bash_profile.

export PATH=$PATH:$HOME/charliecloud/bin

Note

If you do decide to run the Charliecloud test suite you should be aware that some of these tests require root privileges. If you do not have root privileges, you can disable these tests by setting this environment variable before running make test:

export CH_TEST_PERMDIRS=skip

Building the JEDI environment

Once Charliecloud is installed on your system, the next step is to make a home for the JEDI Charliecloud container and download it as follows (you may also have to install wget if it’s not included in the developer tools mentioned above):

mkdir -p ~/jedi/ch-container
cd ~/jedi/ch-container
wget http://data.jcsda.org/containers/ch-jedi-latest.tar.gz

This looks like a normal gzipped tar file. However, you should not upack it with tar! Instead, unpack it with this command:

ch-tar2dir ch-jedi-latest.tar.gz .

This may take a few minutes so be patient. When done, it should give you a message like ./ch-jedi-latest unpacked ok and it should have created a directory by that same name. In our example, this directory would be located in ~/jedi/ch-container/ch-jedi-latest.

This is the JEDI Charliecloud container. It’s functionally equivalent to a Singularity image file but it appears as a directory rather than a single file. Furthermore, that directory contains a complete, self-contained Linux filesystem, complete with its own system directories like /usr/local, /bin, and /home.

To enter the Charliecloud container, type:

ch-run -c $HOME ~/jedi/ch-container/ch-jedi-latest -- bash

Let’s reconstruct this command to help you understand it and customize it as you wish.

The ch-run command runs a command in the Charliecloud container.

The -c $HOME option tells Charliecloud to enter the container in the user’s home directory, which is the same inside and outside the container. If this option is omitted, you will enter the container in the root directory. Typing cd will then place you in your home directory.

The ~/jedi/ch-container/ch-jedi-latest argument is the name of the container you want Charliecloud to run. This is the name of the directory created by the ch-tar2dir command above. If you run this from the container’s parent directory, in this case ~/jedi/ch-container, then you can omit the path.

Finally, we have to tell ch-run what command we want it to run. The command (including options and arguments) that comes after the double hyphen -- will be executed within the container. If you were to run a single command, like -- ls -alh, then ch-run will enter the container, execute the command, and exit. However, in this example, we started up a bash shell, with -- bash. So, all commands that follow will be executed inside the container. In order to exit the container, you have to explicitly type exit. This brings us to this important warning:

Warning

When you enter the Charliecloud container, your prompt may not change!! So, it can be very difficult to tell whether or not you are in the Charliecloud container or not. One trick is to enter the command eckit-version. If you do not have eckit installed on the host system (which may be a vagrant virtual machine or an amazon EC2 instance), then this command will only return a valid result if you are indeed inside the Charliecloud container. Note that this is different from Singularity, which does change your prompt when you enter the container.

Now, since you are in the container, you have access to all the software libraries that support JEDI. You can now proceed to build and run JEDI as described elsewhere in this documentation.

For example, to run and test ufo-bundle, you can proceed as follows:

git config --global credential.helper 'cache --timeout=3600'
mkdir -p ~/jedi/src
cd ~/jedi/src
git clone https://github.com/JCSDA/ufo-bundle.git
mkdir -p ~/jedi/build
cd ~/jedi/build
export FC=mpifort
ecbuild ../src/ufo-bundle
make -j4
ctest

Warning

On some systems (notably Cheyenne) it may be necessary to explicitly add /usr/local/lib to your LD_LIBRARY_PATH environment variable within the Charliecloud container, as follows:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib

General Charliecloud Tips

If you’re running a Charliecloud container from within Vagrant, the most important tip when using Charliecloud (because it is easy to forget) is to remember to type exit twice when you are finished working; once to leave the Charliecloud container and a second time to leave Vagrant.

Another important thing to realize (whether you are running Charliecloud from Vagrant, from AWS, from an HPC system, or from anywhere else), is that many directories on the host are still visible to you from within the container. This includes your home directory. So, it is easy to access files from within the container - you should be able to see and edit everything in your home directory.

In addition to the user’s home directory, a few system directories are also mounted and accessible from within the container. This includes /dev, /proc, and /sys. But, notably, it does not include /usr/local; This is the whole point of the container - to re-define the software that is installed on your system without conflicting with what you have installed already.

These mounted directories should be sufficient for many users. However, you have the option to also mount any additional directories of your choice. An important example is for Mac or Windows users who run Charliecloud from within a Vagrant virtual machine. The Vagrant home directory is visible from within the Charliecloud container but this directory is typically not accessible from the host operating system, e.g. MacOS.

In our Vagrant documentation we describe how you can set up a directory that is shared between the host system (Mac OS) and the virtual machine (Vagrant). From within Vagrant, we called this directory /home/vagrant/vagrant_data. Since this is in our home directory, it should be visible already from within the Charliecloud container so no explicit binding is necessary.

However, what if we were to instead mount the shared directory in /vagrant_data (as viewed from Vagrant)? This is the default behavior in the Vagrantfile as created by the vagrant init command. Since this branches off of the root directory, it would not be visible by default from within the Charliecloud container. However, You can still mount this (or nearly any other directory of your choice) in the Charliecloud container using the -b (or --bind) option:

ch-run -b /vagrant_data -c $HOME ch-jedi-latest -- bash

By default, this is mounted in the Charliecloud container as the directory /mnt/0. You can change the mount point provided that the target directory already exists within the container.

For example, if you create a directory called /home/vagrant/vagrant_data before entering the container, then you can identify that directory as the target for the mount:

ch-run -b /vagrant_data:/home/vagrant/vagrant_data ch-jedi-latest -- bash

Then, when you are inside the container, any files that you put in /home/vagrant/vagrant_data will be accessible from Mac OS.

Tips for HPC Systems

By default, Charliecloud does not change environment variables (with a few exceptions). The JEDI Charliecloud container does explicitly set a few variables such as NETCDF, FC, PIO, etc. (for bash shells) but it’s still good practice to clean your environment by purging other modules before you enter your ch-run command. Most HPC systems use some form of environment modules to load software packages. So “cleaning your environment” usually just looks like this:

module purge

Another common practice on HPC systems is to run applications in designed work or scratch directories instead of one’s home directory. This is often required to have access to sufficient disk space. The JEDI Charliecloud and Singularity containers includes a /worktmp directory that can be used as a mount point for a system work space. For example, on Cheyenne one may wish to do this:

ch-run -b/glade/work/`whoami`:/worktmp <path>/ch-jedi-latest -- bash

This is good, but for substantial parallel applications there is an approach that is even better for MPI jobs. System administrators at HPC centers spend a lot of time and effort configuring their MPI implementations to take full advantage of the system hardware. If you run the mpi implementation inside the container (currently openmpi), you won’t be able to take advantage of these site-specific configurations and optimizations. Fortunately, there is a way out of this dilemma: you can invoke the parallel process manager, mpirun or mpiexec outside the container and then have each MPI process enter its own container. Again using Cheyenne as an example, you can do this in a batch script like this:

#!/bin/bash
#PBS -N multicon
#PBS -A <account-number>
#PBS -l walltime=00:10:00
#PBS -l select=4:ncpus=36:mpiprocs=36
#PBS -q regular
#PBS -j oe
#PBS -m abe
#PBS -M <email-address>

module purge
module load gnu/7.3.0 openmpi/3.1.3

export CHDIR=$HOME/ch-jedi
export WORK=/glade/work/`whoami`
export RUNDIR=/worktmp/myrundir
export BINDIR=/worktmp/jedi/fv3-gnu-openmpi/build/bin

### Run the executable
mpirun -np 144 ch-run -b $WORK:/worktmp -c $RUNDIR $CHDIR/ch-jedi-latest -- $BINDIR/fv3jedi_var.x -- testinput/3dvar_c48.yaml

There are a few things to note about this example. First, mpirun is called from outside the container to start up 144 mpi tasks. Each task then starts its own Charliecloud container by running ch-run, mounting a work disk that is accessed through /worktmp in the container, as described above. The -c $RUNDIR option tells Charliecloud to cd to the $RUNDIR directory to run the command (note that this is the path as viewed from within the container). As before, the command appears after the --. But instead of entering the container by invoking a bash script, we enter a single command, which is here enclosed by double quotes ". So, in short, we are telling each MPI task to run this command in the container, from the $RUNDIR directory.

Important This will only work if the MPI implementations inside and outside the container are compatible. Since the MPI implementation inside the container is openmpi compiled with gnu compilers, we load the gnu/7.3.0 and openmpi/3.1.3 modules before calling mpirun.

This is usually more efficient than the alternative of running a single container with multiple mpi jobs:

export TMPDIR=/worktmp/scratch
ch-run -b $WORK:/worktmp -c $WORKDIR $CHDIR/ch-jedi-latest -- mpirun -np 144 $BINDIR/fv3jedi_var.x -- testinput/3dvar_c48.yaml

This example illustrates another important tip to keep in mind. Openmpi uses the directory $TMPDIR to store temporary files during runtime. On Cheyenne, this is set to /glade/scratch/$(whoami) by default. But this directory is not accessible from the container so, unless we do something about this, our executable will fail. Redefining it as /worktmp/scratch as shown here does the trick, provided that associated external directory $WORK/scratch exists. Recall that Charliecloud does not change environment variables so we can set it outside the container as shown. A similar workaround may also be required on other HPC systems.