# Explore the cluster environment in AWS PCS
<a name="getting-started_explore"></a>

 After you have logged into the cluster, you can run shell commands. For instance, you can change users, work with data on shared filesystems, and interact with Slurm. 

## Change user
<a name="getting-started_explore_change-user"></a>

 If you have logged in to the cluster using Session Manager, you may be connected as `ssm-user`. This is an special user that is created for Session Manager. Switch to the default user on Amazon Linux 2 using the following command. You will not need to do this if you connected using SSH.

```
sudo su - ec2-user
```

## Work with shared file systems
<a name="getting-started_explore_fs"></a>

You can confirm that the EFS filesystem and FSx for Lustre file systems are available with the command `df -h`. Output on your cluster should resemble the following:

```
[ec2-user@ip-10-3-6-103 ~]$ df -h
Filesystem                 Size  Used Avail Use% Mounted on
devtmpfs                   3.8G     0  3.8G   0% /dev
tmpfs                      3.9G     0  3.9G   0% /dev/shm
tmpfs                      3.9G  556K  3.9G   1% /run
tmpfs                      3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/nvme0n1p1              24G   18G  6.6G  73% /
127.0.0.1:/                8.0E     0  8.0E   0% /home
10.3.132.79@tcp:/zlshxbev  1.2T  7.5M  1.2T   1% /shared
tmpfs                      780M     0  780M   0% /run/user/0
tmpfs                      780M     0  780M   0% /run/user/1000
```

 The `/home` filesystem mounts 127.0.0.1 and has a very large capacity. This is the EFS file system that you created earlier in the tutorial. Any files written here will be available under `/home` on all nodes in the cluster. 

 The `/shared` filesystem mounts a private IP and has a capacity of 1.2 TB. This is the FSx for Lustre file system that you created earlier in the tutorial. Any files written here will be available under `/shared` on all nodes in the cluster. 

## Interact with Slurm
<a name="getting-started_explore_slurm"></a>

**Contents**
+ [List queues and nodes](#getting-started_explore_slurm_queues)
+ [Show jobs](#getting-started_explore_slurm_jobs)

### List queues and nodes
<a name="getting-started_explore_slurm_queues"></a>

 You can list the queues and the nodes they are associated with using `sinfo`. Output from your cluster should resemble the following: 

```
[ec2-user@ip-10-3-6-103 ~]$ sinfo
PARTITION AVAIL  TIMELIMIT  NODES  STATE NODELIST
demo         up   infinite      4  idle~ compute-1-[1-4]
[ec2-user@ip-10-3-6-103 ~]$
```

 Note the partition named `demo`. Its status is `up` and it has a maximum of 4 nodes. It is associated with nodes in the `compute-1` node group. If you edit the compute node group and increase the maximum number of instances to 8, the number of nodes would read `8` and the node list would read `compute-1-[1-8]`. If you created a second compute node group named `test` with 4 nodes, and added it to the `demo` queue, those nodes would show up in the node list as well. 

### Show jobs
<a name="getting-started_explore_slurm_jobs"></a>

 You can list all jobs, in any state, on the system with `squeue`. Output from your cluster should resemble the following: 

```
[ec2-user@ip-10-3-6-103 ~]$ squeue
JOBID PARTITION NAME USER ST TIME NODES NODELIST(REASON)
```

Try running `squeue` again later, when you have a Slurm job pending or running.