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folderitems:
- title: Merlin7 Infrastructure
url: /merlin7/slurm-configuration.html
- title: Running Slurm Interactive Jobs
url: /merlin7/interactive-jobs.html
- title: Slurm Batch Script Examples
url: /merlin7/slurm-examples.html
- title: Software Support

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---
title: Running Interactive Jobs
#tags:
keywords: interactive, X11, X, srun, salloc, job, jobs, slurm, nomachine, nx
last_updated: 07 August 2024
summary: "This document describes how to run interactive jobs as well as X based software."
sidebar: merlin7_sidebar
permalink: /merlin7/interactive-jobs.html
---
## Running interactive jobs
There are two different ways for running interactive jobs in Slurm. This is possible by using
the ``salloc`` and ``srun`` commands:
* **``salloc``**: to obtain a Slurm job allocation (a set of nodes), execute command(s), and then release the allocation when the command is finished.
* **``srun``**: is used for running parallel tasks.
### srun
Is run is used to run parallel jobs in the batch system. It can be used within a batch script
(which can be run with ``sbatch``), or within a job allocation (which can be run with ``salloc``).
Also, it can be used as a direct command (in example, from the login nodes).
When used inside a batch script or during a job allocation, ``srun`` is constricted to the
amount of resources allocated by the ``sbatch``/``salloc`` commands. In ``sbatch``, usually
these resources are defined inside the batch script with the format ``#SBATCH <option>=<value>``.
In other words, if you define in your batch script or allocation 88 tasks (and 1 thread / core)
and 2 nodes, ``srun`` is constricted to these amount of resources (you can use less, but never
exceed those limits).
When used from the login node, usually is used to run a specific command or software in an
interactive way. ``srun`` is a blocking process (it will block bash prompt until the ``srun``
command finishes, unless you run it in background with ``&``). This can be very useful to run
interactive software which pops up a Window and then submits jobs or run sub-tasks in the
background (in example, **Relion**, **cisTEM**, etc.)
Refer to ``man srun`` for exploring all possible options for that command.
<details>
<summary>[Show 'srun' example]: Running 'hostname' command on 3 nodes, using 2 cores (1 task/core) per node</summary>
<pre class="terminal code highlight js-syntax-highlight plaintext" lang="plaintext" markdown="false">
caubet_m@login001:~> srun --clusters=merlin7 --ntasks=6 --ntasks-per-node=2 --nodes=3 hostname
cn001.merlin7.psi.ch
cn001.merlin7.psi.ch
cn002.merlin7.psi.ch
cn002.merlin7.psi.ch
cn003.merlin7.psi.ch
cn003.merlin7.psi.ch
</pre>
</details>
### salloc
**``salloc``** is used to obtain a Slurm job allocation (a set of nodes). Once job is allocated,
users are able to execute interactive command(s). Once finished (``exit`` or ``Ctrl+D``),
the allocation is released. **``salloc``** is a blocking command, it is, command will be blocked
until the requested resources are allocated.
When running **``salloc``**, once the resources are allocated, *by default* the user will get
a ***new shell on one of the allocated resources*** (if a user has requested few nodes, it will
prompt a new shell on the first allocated node). However, this behaviour can be changed by adding
a shell (`$SHELL`) at the end of the `salloc` command. In example:
```bash
# Typical 'salloc' call
salloc --clusters=merlin7 -N 2 -n 2
# Custom 'salloc' call
# - $SHELL will open a local shell on the login node from where ``salloc`` is running
salloc --clusters=merlin7 -N 2 -n 2 $SHELL
```
<details>
<summary>[Show 'salloc' example]: Allocating 2 cores (1 task/core) in 2 nodes (1 core/node) - <i>Default</i></summary>
<pre class="terminal code highlight js-syntax-highlight plaintext" lang="plaintext" markdown="false">
caubet_m@login001:~> salloc --clusters=merlin7 -N 2 -n 2
salloc: Granted job allocation 161
salloc: Nodes cn[001-002] are ready for job
caubet_m@login001:~> srun hostname
cn002.merlin7.psi.ch
cn001.merlin7.psi.ch
caubet_m@login001:~> exit
exit
salloc: Relinquishing job allocation 161
</pre>
</details>
<details>
<summary>[Show 'salloc' example]: Allocating 2 cores (1 task/core) in 2 nodes (1 core/node) - <i>$SHELL</i></summary>
<pre class="terminal code highlight js-syntax-highlight plaintext" lang="plaintext" markdown="false">
caubet_m@login001:~> salloc --clusters=merlin7 --ntasks=2 --nodes=2 $SHELL
salloc: Granted job allocation 165
salloc: Nodes cn[001-002] are ready for job
caubet_m@login001:~> srun hostname
cn001.merlin7.psi.ch
cn002.merlin7.psi.ch
caubet_m@login001:~> exit
exit
salloc: Relinquishing job allocation 165
</pre>
</details>
## Running interactive jobs with X11 support
### Requirements
#### Graphical access
[NoMachine](/merlin7/nomachine.html) is the official supported service for graphical
access in the Merlin cluster. This service is running on the login nodes. Check the
document [{Accessing Merlin -> NoMachine}](/merlin7/nomachine.html) for details about
how to connect to the **NoMachine** service in the Merlin cluster.
For other non officially supported graphical access (X11 forwarding):
* For Linux clients, please follow [{How To Use Merlin -> Accessing from Linux Clients}](/merlin7/connect-from-linux.html)
* For Windows clients, please follow [{How To Use Merlin -> Accessing from Windows Clients}](/merlin7/connect-from-windows.html)
* For MacOS clients, please follow [{How To Use Merlin -> Accessing from MacOS Clients}](/merlin7/connect-from-macos.html)
### 'srun' with x11 support
Merlin6 and merlin7 clusters allow running any windows based applications. For that, you need to
add the option ``--x11`` to the ``srun`` command. In example:
```bash
srun --clusters=merlin7 --x11 sview
```
will popup a X11 based slurm view of the cluster.
In the same manner, you can create a bash shell with x11 support. For doing that, you need
to add the option ``--pty`` to the ``srun --x11`` command. Once resource is allocated, from
there you can interactively run X11 and non-X11 based commands.
```bash
srun --clusters=merlin7 --x11 --pty bash
```
<details>
<summary>[Show 'srun' with X11 support examples]</summary>
<pre class="terminal code highlight js-syntax-highlight plaintext" lang="plaintext" markdown="false">
caubet_m@login001:~> srun --clusters=merlin7 --x11 sview
caubet_m@login001:~>
caubet_m@login001:~> srun --clusters=merlin7 --x11 --pty bash
caubet_m@cn003:~> sview
caubet_m@cn003:~> echo "This was an example"
This was an example
caubet_m@cn003:~> exit
exit
</pre>
</details>
### 'salloc' with x11 support
**Merlin6** and **merlin7** clusters allow running any windows based applications. For that, you need to
add the option ``--x11`` to the ``salloc`` command. In example:
```bash
salloc --clusters=merlin7 --x11 sview
```
will popup a X11 based clock.
In the same manner, you can create a bash shell with x11 support. For doing that, you need
to add to run just ``salloc --clusters=merlin7 --x11``. Once resource is allocated, from
there you can interactively run X11 and non-X11 based commands.
```bash
salloc --clusters=merlin7 --x11
```
<details>
<summary>[Show 'salloc' with X11 support examples]</summary>
<pre class="terminal code highlight js-syntax-highlight plaintext" lang="plaintext" markdown="false">
caubet_m@login001:~> salloc --clusters=merlin7 --x11 sview
salloc: Granted job allocation 174
salloc: Nodes cn001 are ready for job
salloc: Relinquishing job allocation 174
caubet_m@login001:~> salloc --clusters=merlin7 --x11
salloc: Granted job allocation 175
salloc: Nodes cn001 are ready for job
caubet_m@cn001:~>
caubet_m@cn001:~> sview
caubet_m@cn001:~> echo "This was an example"
This was an example
caubet_m@cn001:~> exit
exit
salloc: Relinquishing job allocation 175
</pre>
</details>