How to use the command `salloc` (with examples)

The salloc command is used to start an interactive shell session or execute a command by allocating one or more nodes in a cluster. It provides the ability to allocate resources on a cluster system and run commands or scripts within the allocated resources.

Use case 1: Start an interactive shell session on a node in the cluster

Code:

salloc

Motivation: Starting an interactive shell session is useful when you want to directly interact with the allocated node in the cluster. This allows you to run commands and perform tasks specific to that node without interfering with other nodes or processes in the cluster.

Explanation: By simply running salloc without any additional arguments, it requests an interactive shell session on a node in the cluster. This means that the user will be given access to a shell on a single node, which can be used to execute commands and perform tasks on that node.

Example output:

salloc: Granted job allocation ...
salloc: Waiting for resource configuration ...
salloc: Nodes computenode1 are ready for job
[user@computenode1 ~]$

Use case 2: Execute the specified command synchronously on a node in the cluster

Code:

salloc ls -a

Motivation: Executing a command synchronously on a node in the cluster is useful when you want to perform a specific task or run a script on a particular node without the need to start an interactive session. This is helpful for running one-time commands or scripts that don’t require user interaction.

Explanation: In this use case, the salloc command is used along with the command ls -a, which lists all files and directories (including hidden ones) in the current directory. The specified command is executed synchronously on a node in the cluster, and the output is displayed on the terminal.

Example output:

salloc: Granted job allocation ...
salloc: Waiting for resource configuration ...
salloc: Nodes computenode1 are ready for job
.
..
file1.txt
file2.txt
...

Use case 3: Only allocate nodes fulfilling the specified constraints

Code:

salloc --constraint=(amd|intel)&gpu

Motivation: When working with a cluster that has different types of compute nodes with varying capabilities, it is often useful to allocate nodes that fulfill certain constraints. For example, you might want to allocate nodes with either an AMD or Intel processor, along with a GPU.

Explanation: The salloc command supports using constraints to specify the desired characteristics of the allocated nodes. In this use case, the --constraint option is used with the (amd|intel)&gpu constraint, which means the allocated nodes should have either an AMD or Intel processor and a GPU. This ensures that only nodes fulfilling the specified constraints are allocated for the job.

Example output:

salloc: Granted job allocation ...
salloc: Waiting for resource configuration ...
salloc: Nodes computenode2 are ready for job

Conclusion:

In this article, we have explored different use cases of the salloc command. We have seen how to start an interactive shell session on a node in the cluster, execute commands synchronously, and allocate nodes fulfilling specific constraints. The salloc command provides a flexible and convenient way to allocate resources and run commands on a cluster system.