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Quickstart: Cluster


Accessing the cluster

NB! To access the cluster, user must have an active Uni-ID account. For people who are neither students nor employees of Taltech Uni-ID non-contractual account should be created by the head of a structural unit.

To get access to HPC contact us by email (hpcsupport@taltech.ee) or Taltech portal (Help centre -> Teadusarvutuste keskus (HPC centre)). We need the following information: uni-ID, department, project that pays the costs.

The login-node of the cluster can be reached by SSH. SSH (the Secure SHell) is available using the command ssh in Linux/Unix, Mac and Windows-10. A guide for Windows users using PuTTY (an alternative SSH using a graphical user interface (GUI)) is here.

For accessing the cluster base.hpc.taltech.ee use command:

ssh uni-ID@base.hpc.taltech.ee

where uni-ID should be changed to user’s uni-ID.

The cluster is accessible from inside the university and from major Estonian network providers. If you are traveling (or not on one of the major networks), the access requires FortiVPN (with previously shown command) or a two-step login using a jump-host:

ssh -l uni-ID@intra.ttu.ee uni-ID@proksi.intra.ttu.ee
ssh uni-ID@base.hpc.taltech.ee

where all uni-ID should be changed to user’s uni-ID.

For using graphical applications add the -X switch to the SSH command, and for GLX (X Window System) forwarding additionally the -Y switch, so to be able to start a GUI program that uses GLX the connection command would be:

ssh -X -Y uni-ID@base.hpc.taltech.ee

NB! The login-node is for some light interactive analysis. For heavy computations, request a (interactive) session on a compute node with the resource manager SLURM or submit job for execution by SLURM sbatch script!

We strongly recommend to use SSH-keys for logging to the cluster.

SSH fingerprints of host-keys

SSH key fingerprint is a security feature for easy identification/verification of the host, user is connecting to. This option allows to connect to the server without a password. On first connect, user is shown a fingerprint of a host-key, and asked if it should be added to the list of known hosts.

Please compare the fingerprint to the ones below, if one matches, the host can be added, if the fingerprint does not match, then there is a problem (e.g. man-in-the-middle-attack).

SSH host keys of our servers

base.hpc.taltech.ee

  • ECDSA SHA256:OEfQiOB/eIG8hYoQ25sQk9T5tx9EtQbhi6sNM4C8mME

  • ED25519 SHA256:t0CSTU0AnSsJThzuM68tucrcfnn2wLKabjSnuRKX8Yc

  • RSA SHA256:qYrmOw/YN7wf640yBHADX3wnAOPu0OOXlcu4LKBxzG8

.

amp.hpc.taltech.ee

  • ECDSA SHA256:yl6+VaKow6qDZAXL3rQY8+3d3pcH0kYg7MjGgNVTWZs

  • ED25519 SHA256:YOjtpcEL2+AWm6vDFjVl0znYuQPMSVCkyFGvdO5fm8o

  • RSA SHA256:4aaOxumH1ATNfiIA4mZSNMefvxfdFm5zZoUj6VR7TYo

.

viz.hpc.taltech.ee

  • ECDSA SHA256:z2/bxleZ3T3vErkg4C7kvDPKKEU0qaoR8bL29EgMfGA

  • ED25519 SHA256:9zRBmS3dxD7BNISZKwg6l/2+6p4HeqlOhA4OMBjD9mk

  • RSA SHA256:Q6NDm88foRVTKtEAEexcRqPqMQNGUzf3rQdetBympPg

How to get SSH keys.



Structure and file tree

By accessing the cluster, the user gets into his home directory or $HOME (/gpfs/mariana/home/$USER/).

In the home directory, the user can create, delete, and overwrite files and perform calculations (if slurm script does not force program to use $SCRATCH directory). The home directory is limited in size of 500 GB and backups are performed once per week.

The home directory can be accessed from console or by GUI programs, but it cannot be mounted. For mounting was created special smbhome and smbgroup folders (/gpfs/mariana/smbhome/$USER/ and /gpfs/mariana/smbgroup/, respectively). More about smb folders can be found here.

Some programs and scripts suppose that files will be transfer to $SCRATCH directory at compute node and calculations will be done there. If job will be killed due to the time limit back transfer will not occur. In this case, user needs to know at which node this job was running (see slurm-$job_id.stat), to connect to exactly this node (in example it is green11). $SCRATCH directory will be in /state/partition1/ and corresponds to jobID number.

srun -w green11 --pty bash
cd /state/partition1/

Please note that the scratch is not shared between nodes, so parallel MPI jobs that span multiple nodes cannot access each other’s scratch files.



Running jobs with the SLURM

SLURM is a management and job scheduling system at Linux clusters. SLURM quick reference can be found here.

Examples of slurm scripts are usually given on the program’s page with some recommendations for optimal use of resources for this particular program. List of the programs installed at HPC is given on our software page. At software page or program’s page also can be found information about licenses, since for programs installed at HPC have varying licence agreement. o use some licensed programs (for example, Gaussian), the user must be added to the appropriate group. For this contact us email (hpcsupport@taltech.ee) or Taltech portal.

The most often used SLURM commands are:

  • srun - to start a session or an application (in real time)

  • sbatch - to start a computation using a batch file (submit for later execution)

  • squeue - to check the load of the cluster and status of own jobs

  • sinfo - to check the state of the cluster and partitions

  • scancel - to delete a submitted job (or stop a running one).


For more parameters see the man-pages (manual) of the commands srun, sbatch, sinfo and squeue. For this use the command man followed by the program-name whose manual you want to see, e.g.:

man srun

Requesting resources with SLURM can be done either with parameters to srun or in a batch script invoked by sbatch.

The following defaults are used if not otherwise specified:

  • default memory – is 1 GB/thread (for larger jobs request more memory)

  • short partition – default time limit is 10 min and max time limit is 4 hours (longer jobs need to be submitted to partitions common or one of the infiniBand partitions)

  • common partition – default time is 10 min and max time limit is 8 days.

  • long partition – default time is 10 min and time limit 15 days.

  • green-ib partition – default time is 10 min and max time limit is 8 days

  • gray-ib partition – default time is 10 min and max time limit is 8 days

  • mem1tb partition – default time is 10 min and max time limit is 8 days

  • gpu partition – default time is 10 min and max time limit is 5 days


Running an interactive session longer than default 10 min. (here 1 hour):

srun -t 01:00:00 --pty bash

This logs you into one of the compute nodes, there you can load modules and run interactive applications, compile your code, etc.

With srun is reccomended to use CLI (command-line interface) instead of GUI (Graphical user interface) programs if it is possible. For example, use octave-CLI or octave instead of octave-GUI.

Running a simple non-interactive single process job that lasts longer than default 4 hours (here 5 hours):

srun --partition=common -t 05:00:00 -n 1 ./a.out

NB! Environment variables for OpenMP are not set automatically, e.g.

srun  -N 1 --cpus-per-task=28 ./a.out

would not set OMP_NUM_THREADS to 28, this has to be done manually. So usually, for parallel jobs it is recommended to use scripts for sbatch.

Below is given an example of batch slurm script (filename: myjob.slurm) with explanation of the commands.

#!/bin/bash
#SBATCH --partition=common    ### Partition
#SBATCH --job-name=HelloOMP   ### Job Name           -J
#SBATCH --time=00:10:00       ### WallTime           -t
#SBATCH --nodes=4             ### Number of Nodes    -N 
#SBATCH --ntasks-per-node=7   ### Number of tasks (MPI processes)
#SBATCH --cpus-per-task=4     ### Number of threads per task (OMP threads)
#SBATCH --account=hpcrcf      ### In case of several accounts, specifies account used for job submission
#SBATCH --mem-per-cpu=100     ### Min RAM required in MB
#SBATCH --array=13-18         ### Array tasks for parameter sweep

export OMP_NUM_THREADS=$SLURM_CPUS_PER_TASK		### setup environment
module load gcc						### setup environment
./hello_omp $SLURM_ARRAY_TASK_ID			### only for arrays, setup output files with system information
mpirun -n 28 ./hello_mpi 				### run program

In this example are listed some of the more common submission parameters. There are many more possible job-submission options, moreover, some of the options listed above are not useful to apply together. An explanation of the variables used inside SLURM/SBATCH can be found here. In contrast to e.g. GridEngine, SLURM allows fine-grained resource requests, using parameters like --ntasks-per-core or --ntasks-per-node.

An example script for submitting:

  • a single process job

  • an OpenMP parallel job

  • an MPI parallel job (OpenFOAM)

  • an array (parameter sweep) job

  • a GPU job

  • a job using the scratch partition (sequential or OpenMP parallel)


The job is then submitted to SLURM by

sbatch myjob.slurm

and will be executed when the requested resources become available.

Output of applications and error messages are by default written to a slurm-$job_id.out file. More about SLURM finished job statistics can be found here.

Some useful online resources:


SLURM accounts

In SLURM exist accounts for billing, these are different from the login account!

Each user has his/her own personal SLURM-account, which will have a monthly limit and at least one project account for larger calculations.

SLURM user-accounts start with user_ and project accounts with project_ and course accounts with course_, followed by uniID/projectID/courseID. You can check which SLURM accounts you belong to, by sacctmgr show associations format=account%30,user%30 | grep uniID . Currently (almost) all users belong to the SLURM-account “vaikimisi” (default), it is possible to submit jobs under this account, especially if no user_ or project account has been created for you yet, however, “vaikimisi” will be discontinued in the near future.

When submitting a job, it is important to use the correct SLURM-account --account=SLURM-ACCOUNT, as this is connected to the financial source.




Monitoring jobs & resources

Monitoring a job on the node

Status of a job

User can check the status his jobs (whether they are running or not, and on which node) by the command:

squeue -u $USER

squeue

Load of the node

User can check the load of the node his job runs on, status and configuration of this node by command

scontrol show node <nodename>

the load should not exceed the number of hyperthreads (CPUs in SLURM notation) of the node.

scontrol

In case of MPI parallel runs statistics of several nodes can be monitored by specifying nodes names. For example:

scontrol show node=green[25-26]

Node features for node selection using --constraint=:

feature what it is
A100-40 has A100 GPU with 40GB
A100-80 has A100 GPU with 80GB
L40 has L40 GPU with 48GB
nvcc80 GPU has compute capability 8.0 (A100, L40)
nvcc89 GPU has compute capability 8.9 (L40)
nvcc35 GPU has compute capability 3.5 (K20Xm, A100, L40)
zen2 AMD Zen CPU architecture 2nd generation (amp1)
zen3 AMD Zen CPU architecture 3rd generation (amp2)
zen4 AMD Zen CPU architecture 4th generation (ada*)
avx512 CPU has avx512 (skylake, zen4)
skylake Intel SkyLake CPU architecture (green*)
sandybridge Intel SandyBridge CPU architecture (mem1tb, viz)
ib InfiniBand network interface

Monitoring with interactive job

It is possible to submit a second interactive job to the node where the main job is running, check with squeue where your job is running, then submit

srun -w <nodename> --pty htop

Note that there must be free slots on the machine, so if you cannot use -n 80 or --exclusive for your main job (use -n 79).

htop

Press q to exit.

You can also add a column that shows the CPU number of the program (for more details click here).

For Linux F1-F10 keys should be used, for Mac - just click on the corresponding buttons.

htop-1

Will appear a new column, showing the CPU number of the program.

htop-2


Monitoring jobs using GPUs

Log to amp or amp2. Command

echo ${SLURM_STEP_GPUS:-$SLURM_JOB_GPUS}

shows the GPU IDs allocated to your job.

GPUs load can be checked by command:

nvidia-smi

nvidia-smi

Press control+c to exit.

Another option is to logging to amp or amp2, check which GPUs are allocated to your job, and give command:

nvtop

nvtop

Press q to exit.

An alternative method on Linux computers, if you have X11. Logging to base/amp with --X key:

ssh --X UniID@base.hpc.taltech.ee

then submit your main interactive job

srun --x11 -n <numtasks> --cpus-per-task=<numthreads> --pty bash

and start an xterm -e htop & in the session.

In sbatch the option --x11=batch can be used, note that the ssh session to base needs to stay open!

Monitoring resource usage

Default disc quota for home (that is backed up weekly) is 500 GB and for smbhome (that is not backed up) – 2 TB per user. For smbgroup there is no limits and no backup.

The easiest way to check your current disk usage is to look at the table that appears when you log in to HPC.

disk_usage

You can also monitor your resource usage by taltech-lsquota.bash script and sreport command.

Current disk usage:

taltech-lsquota.bash

usage

CPU usage during last day:

sreport -t Hours cluster UserUtilizationByAccount Users=$USER

CPUhours

CPU usage in specific period (e.g. since beginning of this year):

sreport -t Hours cluster UserUtilizationByAccount Users=$USER start=2024-01-01T00:00:00 end=2024-12-31T23:59:59

Where start= and end= can be changed depending on the desired period of time.

CPUhours_1

For convenience, a tool taltech-history was created, by default it shows the jobs of the current month, use taltech-history -a to get a summary of the useh hours and costs of the current month.



Copying data to/from the clusters

Since HPC disk quota is limited, it is recommended to have your own copy of important calculations and results. Data from HPC can be transferred by several commands: scp, sftp, sshfs or rsync.

  1. scp is available on all Linux systems, Mac and Windows10 PowerShell. There are also GUI versions available for different OS (like PuTTY).

    Copying to the cluster with scp:

    scp local_path_from_where_copy/file uni-id@base.hpc.taltech.ee:path_where_to_save

    scp

    Copying from the cluster with scp:

    scp uni-id@base.hpc.taltech.ee:path_from_where_copy/file local_path_where_to_save

    scp

    Path to the file at HPC can be checked by pwd command.

  2. sftp is the secure version of the ftp protocol vailable on Linux, Mac and Windows10 PowerShell. This command starts a session, in which files can be transmitted in both directions using the get and put commands. File transfer can be done in “binary” or “ascii” mode, conversion of line-endings (see below) is automatic in “ascii” mode. There are also GUI versions available for different OS (FileZilla, gFTP and WinSCP (Windows))

    sftp uni-id@base.hpc.taltech.ee

    sftp

  3. sshfs can be used to temporarily mount remote filesystems for data transfer or analysis. Available in Linux. The data is tunneled through an ssh-connection. Be sware that this is usually not performant and can creates high load on the login node due to ssh-encryption.

    sshfs uni-id@base.hpc.taltech.ee:remote_dir/ /path_to_local_mount_point/

  4. rsync can update files if previous versions exist without having to transfer the whole file. However, its use is recommended for the advanced user only since one has to be careful with the syntax.

SMB/CIFS exported filesystems

One of the simple and convenient ways to control and process data based on HPC is mounting. Mounting means that user attaches his directory placed at HPC to a directory on his computer and can process files as if they were on this computer. These can be accessed from within university or from EduVPN.

Each user automatically has a directory within smbhome. It does not match with $HOME directory, so calculations should be initially done at smbhome directory to prevent copying or files needed should be copied from home directory to the smbhome directory by commands:

pwd	### look path to the file 
cp path_to_your_file/your_file /gpfs/mariana/smbhome/$USER/	### copying

To get a directory for group access, please contact us (a group and a directory need to be created).

The HPC center exports two filesystems as Windows network shares:

local path on cluster Linux network URL Windows network URL
/gpfs/mariana/smbhome/$USER smb://smb.hpc.taltech.ee/smbhome \\smb.hpc.taltech.ee\smbhome
/gpfs/mariana/smbgroup smb://smb.hpc.taltech.ee/smbgroup \\smb.hpc.taltech.ee\smbgroup
/gpfs/mariana/home/$USER not exported not exported

This is the quick-access guide, for more details, see here

Windows access

The shares can be found using the Explorer “Map Network Drive”.

server >>> \\smb.hpc.taltech.ee\smbhome
username >>> INTRA\<uni-id>

From Powershell:

 net use \\smb.hpc.taltech.ee\smbhome /user:INTRA\uni-id
 get-smbconnection

Linux access

On Linux with GUI Desktop, the shares can be accessed with the nautilus browser.

From commandline, the shares can be mounted as follows:

dbus-run-session bash
gio mount smb://smb.hpc.taltech.ee/smbhome/

you will be asked for “User” (which is your UniID), “Domain” (which is “INTRA”), and your password.

To disconnect from the share, unmount with

gio mount -u smb://smb.hpc.taltech.ee/smbhome/

Special considerations for copying Windows - Linux

Microsoft Windows is using a different line ending in text files (ASCII/UTF8 files) than Linux/Unix/Mac: CRLF vs. LF When copying files between Windows-Linux, this needs to be taken into account. The FTP (File Transfer Protocol) has ASCII and BINARY modes, in ASCII-mode the line-end conversion is automatic.

There are tools for conversion of the line-ending, in case the file was copied without line conversion: dos2unix, unix2dos, todos, fromdos, the stream-editor sed can also be used.



Backup

There are 2 major directories where users can store data:

  • /gpfs/mariana/home/ default home directory which is limited to 500GB and is backed up, excluding specific directories: [*/envs/, */.cache/, */pkgs/].

  • /gpfs/mariana/smbhome/ has a limit of 2TB and is not backed up.

The home directory is meant for critical data like configurations and scripts, whereas smbhome is meant for data.

The backup will run weekly. If the home directory is larger than 500GB [usage is displayed upon login to the cluster] it will not be backed up.

If your home directory is larger than 500G please move the data to smbhome.

At HPC are installed programs with varying licence agreement. To use some licensed programs (for example, Gaussian), the user must be added to the appropriate group. For this contact us email (hpcsupport@taltech.ee) or Taltech portal. More about available programs and licenses can be found at software page.