On this page we describe the different launchers for experiments. It is possible to use the local machine or batch schedulers like Slurm or Oracle Grid Engine (formerly SGE) to run experiments. The launchers can be selected by adding further arguments to the simex experiments launch command or by setting up a launchers.yml file. The structure of this file will also be explained on this page.

In the following sections, we consider the sorting expample from the Quick Start guide.

Queue Launcher

The queue launcher is mainly useful in scenarios where no sophisticated batch scheduler (e.g. Slurm) is available, especially when launching experiments on a remote machine over ssh. In this case it does not require an active connection. As the name suggests, the queue launcher puts the jobs in a queue and executes them sequentially. It is possible to start a queue launcher as a daemon or interactively in a terminal. You can launch experiments and monitor/stop/kill the launcher.

Starting the Launcher

As Daemon

To start the queue launcher as a daemon you need to have the systemd service manager installed. Then, use simex queue daemon to start the launcher:

$ simex queue daemon
Running as unit run-rdc0128bd4cd343e393681898359e5c69.service. # systemd output


You can start the queue launcher in a terminal so that it is possible to directly see internal states of the launcher. You will then work from another terminal window in order to send commands to the launcher. To start the launcher, use simex queue interactive:

$ simex queue interactive
Serving on /home/username/.extl.sock  # internal message of the queue launcher


If the daemon was not closed properly via the stop or kill command, a UNIX socket remains on the file system. In this case you need to add the --force argument to the simex queue interactive or simex queue daemon command to start the launcher. Alternatively, you can delete the socket manually. The default path for the socket is ~/.extl.sock.

Launching Experiments

To launch experiments through the queue launcher we need to set up a launchers.yml file or add the --launch-through=queue argument to the simex experiments launch command:

$ simex experiments launch --launch-through=queue
Launching run bubble-sort/uniform-n1000-s1[0] on local machine
Launching run bubble-sort/uniform-n1000-s2[0] on local machine
Launching run bubble-sort/uniform-n1000-s3[0] on local machine
Launching run insertion-sort/uniform-n1000-s1[0] on local machine
Launching run insertion-sort/uniform-n1000-s2[0] on local machine
Launching run insertion-sort/uniform-n1000-s3[0] on local machine

Show the Status

It is possible to query the launcher for the current run, pending runs and the number of completed runs. To do that, you can use simex queue show:

$ simex queue show
Currently running:   bubble-sort/uniform-n1000-s3[0]
Pending runs:        insertion-sort/uniform-n1000-s1[0]
Completed runs:      2


The launcher can be terminated by using the stop or kill command. The differences of those commands are stated below.

  • simex queue stop: terminate the launcher after finishing all pending jobs
  • simex queue kill: terminate the launcher immediately

“launchers.yml” File

The launchers.yml file contains a list of launchers. By setting up a launchers.yml file we can omit additional arguments in the simex experiments launch command or select launchers, which are defined in it. In the following sections, we will see how to setup and use our launchers.yml. First, we need to create the launchers.yml file in the ~/.simexpal/ folder:

$ mkdir ~/.simexpal     # Create the ~/.simexpal/ folder if it does not exist already
$ cd ~/.simexpal        # Navigate into ~/.simexpal/
$ touch launchers.yml   # Create an empty launchers.yml file


To specify launchers in the launchers.yml file we need to set the

  • launchers: list of dictionaries, which contain launchers


Queue Launcher

To define a queue launcher we need to add a list entry to the launchers key, which contains a dictionary with the

  • name: name of the launcher
  • default: boolean (true/false) - whether this is the default launcher or not
  • scheduler: type of the launcher


How to specify a queue launcher in the launchers.yml file.
     - name: local-queue
       default: true
       scheduler: queue

In this way we created a queue launcher with the name local-queue. We also set it to be the default launcher.

Command Line Interface

Default Launcher

When setting default: true for a launcher, simex experiments launch will run experiments with this launcher.


There can only be one launcher with default: true. Having multiple launchers with default: true will lead to a RuntimeError.

Selecting the Launcher

When launching experiments using simex experiments launch, you can specify the --launcher option to select a certain launcher defined in the launchers.yml file. For example:

Assume you have a launchers.yml file set up as in the Queue Launcher section, then simex experiments launch --launcher local-queue will select the launcher named local-queue from the launchers.yml file to run experiments.