# Frequently asked questions

## Installation errors

To compile this package a fully C++11 compliant compiler is required. This is implicit for CRAN packages since `R=3.6.2` and is hence not listed in SystemRequirements. If you encounter an error saying that that no matching function call to `zmq::message_t::message_t(std::string&)` exists, your compiler does not (fully) support this and the automated check failed for some reason.

    In file included from CMQMaster.cpp:2:0:
    CMQMaster.h: In member function ‘void CMQMaster::proxy_submit_cmd(SEXP, int)’:
    CMQMaster.h:146:40: error: no matching function for call to ‘zmq::message_t::message_t(std::string&)’
             mp.push_back(zmq::message_t(cur));

This happens for instance for old versions of the `gcc` compiler (default on most Linux distributions). You can check your version in the terminal using:

    # the minimum required gcc version is 5.5 for full C++11 support (3.3 for clang)
    cc --version

In this case, it is very likely that your HPC system already has a newer compiler installed that you need to add to your `$PATH` or load as a module. Once this is set, you can install the package from R that was started in a terminal that has this module/path active.

## Session gets stuck at “Running calculations”

Your R session may be stuck at something like the following:

    > clustermq::Q(identity, x=42, n_jobs=1)
    Submitting 1 worker jobs (ID: cmq8480) ...
    Running 1 calculations (5 objs/19.4 Kb common; 1 calls/chunk) ...

You will see this every time your jobs are queued but not yet started. Depending on how busy your HPC is, this may take a long time. You can check the queueing status of your jobs in the terminal with e.g. `qstat` (SGE), `bjobs` (LSF), or `sinfo` (SLURM).

If your jobs are already finished, this likely means that the `clustermq` workers can not connect to the main session. You can confirm this by passing `log_worker=TRUE` to `Q` and inspect the logs created in your current working directory. If they state something like:

    > clustermq:::worker("tcp://my.headnode:9091")
    2023-12-11 10:22:58.485529 | Master: tcp://my.headnode:9091
    2023-12-11 10:22:58.488892 | connecting to: tcp://my.headnode:9091:
    Error: Connection failed after 10016 ms
    Execution halted

the submitted job is indeed unable to establish a network connection with the head node. This can happen if your HPC does not allow incoming connections, but more likely happens because there are multiple network interfaces, only some of which have access to the head node.

You can list the available network interfaces using the `ifconfig` command in the terminal. Find the interface that shares a subnetwork with the head node and add the R option `clustermq.host=<interface>`. If this is unclear, contact your system administrators to see which interface to use.

## SSH not working

Before trying remote schedulers via SSH, make sure that the scheduler works when you first connect to the cluster and run a job from there.

If the terminal is stuck at

    Connecting <user@host> via SSH ...

make sure that each step of your SSH connection works by typing the following commands in your local terminal and make sure that you don’t get errors or warnings in each step:

    # test your ssh login that you set up in ~/.ssh/config
    # if this fails you have not set up SSH correctly
    ssh <user@host>

    # test port forwarding from 54709 remote to 6687 local (ports are random)
    # if the fails you will not be able to use clustermq via SSH
    ssh -R 54709:localhost:6687 <user@host> R --vanilla

If you get an `Command not found: R` error, make sure your `$PATH` is set up correctly in your `~/.bash_profile` and/or your `~/.bashrc` (depending on your cluster config you might need either). You may also need to modify your SSH template to load R as a module or conda environment.

If you get a SSH warning or error try again with `ssh -v` to enable verbose output. If the forward itself works, run the following in your local R session (ideally also in command-line R, not only in RStudio):

    options(clustermq.scheduler = "ssh",
            clustermq.ssh.log = "~/ssh_proxy.log")
    Q(identity, x=1, n_jobs=1)

This will create a log file on the remote server that will contain any errors that might have occurred during `ssh_proxy` startup.

If the `ssh_proxy` startup fails on your local machine with the error

    Remote R process did not respond after 5 seconds. Check your SSH server log.

but the server log does not show any errors, then you can try increasing the timeout:

    options(clustermq.ssh.timeout = 30) # in seconds

This can happen when your SSH startup template includes additional steps before starting R, such as activating a module or conda environment, or having to confirm the connection via two-factor authentication.

## Running the master inside containers

If your master process is inside a container, accessing the HPC scheduler is more difficult. Containers, including singularity and docker, isolate the processes inside the container from the host. The R process will not be able to submit a job because the scheduler cannot be found.

Note that the HPC node running the master process must be allowed to submit jobs. Not all HPC systems allow compute nodes to submit jobs. If that is the case, you may need to run the master process on the login node, and discuss the issue with your system administrator.

If your container is binary compatible with the host, you may be able to bind in the scheduler executable to the container.

For example, PBS might look something like:

    #PBS directives ...

    module load singularity

    SINGULARITYENV_APPEND_PATH=/opt/pbs/bin
    singularity exec --bind /opt/pbs/bin r_image.sif Rscript master_script.R

A working example of binding SLURM into a CentOS 7 container image from a CentOS 7 host is available at https://groups.google.com/a/lbl.gov/d/msg/singularity/syLcsIWWzdo/NZvF2Ud2AAAJ

Alternatively, you can create a script that uses SSH to execute the scheduler on the login node. For this, you will need an SSH client in the container, keys set up for password-less login, and create a script to call the scheduler on the login node via ssh (e.g. `~/bin/qsub` for SGE/PBS/Torque, `bsub` for LSF and `sbatch` for Slurm):

    #!/bin/bash
    ssh -i ~/.ssh/<your key file> ${PBS_O_HOST:-"no_host_not_in_a_pbs_job"} qsub "$@"

Make sure the script is executable, and bind/copy it into the container somewhere on `$PATH`. Home directories are bound in by default in singularity.

    chmod u+x ~/bin/qsub
    SINGULARITYENV_APPEND_PATH=~/bin