# Other types of jobs

```{instructor-note}
Total: 75min
(Teaching:45Min | Discussion:0min | Breaks:0min | Exercises:30Min)
```

```{objectives}
- Objectives
   - Interactive jobs for testing

```

Up to this point, we've focused on running jobs in batch mode. SLURM
also provides the ability to start an interactive session.

There are very frequently tasks that need to be done interactively. Creating an entire job
script might be overkill, but the amount of resources required is too much for a login node to
handle. A good example of this might be building a genome index for alignment with a tool like
[HISAT2](https://ccb.jhu.edu/software/hisat2/index.shtml). Fortunately, we can run these types of
tasks as a one-off with `srun`.

## Interactive jobs

Instead of running on a login node, you can ask the queue system to allocate compute resources 
for you, and once assigned, you can run commands interactively for as long as requested. 
The below is an example.

```{warning}
  Interactive jobs require that you maintain a stable/uninterupted connection to the cluster.
  There for we use terminal multiplexer like `tmux` or `screen`
 
```

`````{tabs}
  ````{tab} SAGA/Fram/Betzy

    ```{literalinclude} snippets/saga/13-interactive.txt
       :language: bash
    ```

  ````
  ````{tab} FOX

    ```{literalinclude} snippets/fox/13-interactive.txt
       :language: bash
    ```

  ````
`````

````{exercise} Find out available resources on a compute node

 User interactive login to access a compute node and find out 
 number of cores and amount of memory. How much of it is at your 
 disposal ? 
  
 ```{solution}
    nproc --all

    free -h

    echo `$SLURM_MEM_PER_NODE`

    echo `$SLURM_NTASKS`
 
 ```
````


## Keeping interactive jobs alive

Interactive jobs stop when you disconnect from the login node either by
choice or by internet connection problems. To keep a job alive you can
use a terminal multiplexer like `tmux`.

`tmux` allows you to run processes as usual in your standard bash shell

You start `tmux` on the login node before you get an interactive Slurm
session with `srun` and then do all the work in it. In case of a
disconnect you simply reconnect to the login node and attach to the `tmux`
session again by typing:
```
$ tmux attach
```
Or in case you have multiple session running:
```
$ tmux list-session
$ tmux attach -t SESSION_NUMBER
```

As long as the `tmux` session is not closed or terminated (e.g. by a
server restart) your session should continue. One problem with our
systems is that the `tmux` session is bound to the particular login server
you get connected to. So if you start a `tmux` session on login-1 on SAGA
and next time you get randomly connected to login-2 you first have to
connect to login-1 again by:

```
$ ssh login-1
```

To log out a `tmux` session without closing it you have to press Ctrl-B
(that the Ctrl key and simultaneously "b", which is the standard `tmux`
prefix) and then "d" (without the quotation marks). To close a session
just close the bash session with either Ctrl-D or type exit. You can get
a list of all `tmux` commands by Ctrl-B and the ? (question mark). See
also [this
page](https://www.hamvocke.com/blog/a-quick-and-easy-guide-to-tmux/) for
a short tutorial of `tmux`. Otherwise, working inside a `tmux` session is
almost the same as a normal bash session.