Skip to content

Accessing the Clusters

Shell Access

All IT4Innovations clusters are accessed by the SSH protocol via login nodes at the address The login nodes may be addressed specifically, by prepending the loginX node name to the address.

Workgroups Access Limitation

Projects from the EUROHPC workgroup can only access the Karolina cluster.

Karolina and Barbora updated security requirements

Due to updated security requirements on Karolina and Barbora, only clients based on OpenSSH 7.4p1 and later can connect (including other SSH clients with compatible security algorithms). This means that starting with RHEL/Centos 7, Debian 9 or Ubuntu 18.04, you are good to go. Some users who still have DSA keys will be also unable to connect and are urged to update their keypairs, preferably to the Ed25519 format.

Karolina Cluster

Login address Port Protocol Login node 22 SSH round-robin DNS record for login{1,2,3,4}
login{1,2,3,4} 22 SSH login{1,2,3,4}

Barbora Cluster

Login address Port Protocol Login node 22 SSH round-robin DNS record for login{1,2}
login{1,2} 22 SSH login{1,2}


Authentication is available by private key only. Verify SSH fingerprints during the first logon:



Fingerprints are identical for all login nodes.

# login{1,2,3,4}:22 SSH-2.0-OpenSSH_7.4
2048 MD5:41:3a:40:32:da:08:77:51:79:04:af:53:e4:57:d0:7c (RSA)
2048 SHA256:Ip37d/bE6XwtWf3KnWA+sqA+zRGSFlf5vXai0v3MBmo (RSA)
256 MD5:e9:b6:8e:7d:f8:c6:8f:42:34:10:71:02:14:a6:7c:22 (ED25519)
256 SHA256:zKEtQMi2KRsxzzgo/sHcog+NFZqQ9tIyvJ7BVxOfzgI (ED25519)

Public Keys \ Known Hosts

Public Keys \ Known Hosts are identical for all login nodes.

login1,,login1.karolina, ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9Cp8/a3F7eOPQvH4+HjC778XvYgRXWmCEOQnE3clPcKw15iIat3bvKc8ckYLudAzomipWy4VYdDI2OnEXay5ba8HqdREJO31qNBtW1AXgydCfPnkeuUZS4WVlAWM+HDlK6caB8KlvHoarCnNj2jvuYsMbARgGEq3vrk3xW4uiGpS6Y/uGVBBwMFWFaINbmXUrU1ysv/ZD1VpH4eHykkD9+8xivhhZtcz5Z2T7ZnIib4/m9zZZvjKs4ejOo58cKXGYVl27kLkfyOzU3cirYNQOrGqllN/52fATfrXKMcQor9onsbTkNNjMgPFZkddufxTrUaS7EM6xYsj8xrPJ2RaN
login1,,login1.karolina, ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDkIdDODkUYRgMy1h6g/UtH34RnDCQkwwiJZFB0eEu1c
login2,,login2.karolina, ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9Cp8/a3F7eOPQvH4+HjC778XvYgRXWmCEOQnE3clPcKw15iIat3bvKc8ckYLudAzomipWy4VYdDI2OnEXay5ba8HqdREJO31qNBtW1AXgydCfPnkeuUZS4WVlAWM+HDlK6caB8KlvHoarCnNj2jvuYsMbARgGEq3vrk3xW4uiGpS6Y/uGVBBwMFWFaINbmXUrU1ysv/ZD1VpH4eHykkD9+8xivhhZtcz5Z2T7ZnIib4/m9zZZvjKs4ejOo58cKXGYVl27kLkfyOzU3cirYNQOrGqllN/52fATfrXKMcQor9onsbTkNNjMgPFZkddufxTrUaS7EM6xYsj8xrPJ2RaN
login2,,login2.karolina, ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDkIdDODkUYRgMy1h6g/UtH34RnDCQkwwiJZFB0eEu1c
login3,,login3.karolina, ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9Cp8/a3F7eOPQvH4+HjC778XvYgRXWmCEOQnE3clPcKw15iIat3bvKc8ckYLudAzomipWy4VYdDI2OnEXay5ba8HqdREJO31qNBtW1AXgydCfPnkeuUZS4WVlAWM+HDlK6caB8KlvHoarCnNj2jvuYsMbARgGEq3vrk3xW4uiGpS6Y/uGVBBwMFWFaINbmXUrU1ysv/ZD1VpH4eHykkD9+8xivhhZtcz5Z2T7ZnIib4/m9zZZvjKs4ejOo58cKXGYVl27kLkfyOzU3cirYNQOrGqllN/52fATfrXKMcQor9onsbTkNNjMgPFZkddufxTrUaS7EM6xYsj8xrPJ2RaN
login3,,login3.karolina, ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDkIdDODkUYRgMy1h6g/UtH34RnDCQkwwiJZFB0eEu1c
login4,,login4.karolina, ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9Cp8/a3F7eOPQvH4+HjC778XvYgRXWmCEOQnE3clPcKw15iIat3bvKc8ckYLudAzomipWy4VYdDI2OnEXay5ba8HqdREJO31qNBtW1AXgydCfPnkeuUZS4WVlAWM+HDlK6caB8KlvHoarCnNj2jvuYsMbARgGEq3vrk3xW4uiGpS6Y/uGVBBwMFWFaINbmXUrU1ysv/ZD1VpH4eHykkD9+8xivhhZtcz5Z2T7ZnIib4/m9zZZvjKs4ejOo58cKXGYVl27kLkfyOzU3cirYNQOrGqllN/52fATfrXKMcQor9onsbTkNNjMgPFZkddufxTrUaS7EM6xYsj8xrPJ2RaN
login4,,login4.karolina, ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDkIdDODkUYRgMy1h6g/UtH34RnDCQkwwiJZFB0eEu1c



39:55:e2:b9:2a:a2:c4:9e:b1:8e:f0:f7:b1:66:a8:73 (RSA)
40:67:03:26:d3:6c:a0:7f:0a:df:0e:e7:a0:52:cc:4e (ED25519)

ZQzFTJVDdZa3I0ics9ME2qz4v5a3QzXugvyVioaH6tI (ED25519)

Public Keys \ Known Hosts, ssh-rsa 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, ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOmUm4btn7OC0QLIT3xekKTTdg5ziby8WdxccEczEeE1


Barbora has identical SSH fingerprints on all login nodes.

Private Key Authentication:

On Linux or Mac, use:

local $ ssh -i /path/to/id_rsa

If you see a warning message UNPROTECTED PRIVATE KEY FILE!, use this command to set lower permissions to the private key file:

local $ chmod 600 /path/to/id_rsa

On Windows, use the PuTTY SSH client.

After logging in, you will see the command prompt with the name of the cluster and the message of the day.


The environment is not shared between login nodes, except for shared filesystems.

Data Transfer

Serial Transfer

Data in and out of the system may be transferred by SCP and SFTP protocols.

Cluster Port Protocol
Karolina 22 SCP, SFTP
Barbora 22 SCP

Authentication is by private key only.

On Linux or Mac, use an SCP or SFTP client to transfer data to the cluster:

local $ scp -i /path/to/id_rsa my-local-file
local $ scp -i /path/to/id_rsa -r my-local-dir


local $ sftp -o IdentityFile=/path/to/id_rsa

You may request the cipher for more efficient ssh based transfer:

local $ scp -c -i /path/to/id_rsa -r my-local-dir

The -c argument may be used with ssh, scp and sftp, and is also applicable to sshfs and rsync below.

A very convenient way to transfer files in and out of the cluster is via the fuse filesystem SSHFS.

local $ sshfs -o IdentityFile=/path/to/id_rsa mountpoint

Using SSHFS, the user's home directory will be mounted on your local computer, just like an external disk.

Learn more about SSH, SCP, and SSHFS by reading the manpages:

local $ man ssh
local $ man scp
local $ man sshfs

The rsync client uses ssh to establish connection.

local $ rsync my-local-file
local $ rsync -r my-local-dir

Parallel Transfer


The data transfer speed is limited by the single TCP stream and single-core ssh encryption speed to about 250 MB/s (750 MB/s in case of cipher) Run multiple streams for unlimited transfers

Many Files

Parallel execution of multiple rsync processes utilizes multiple cores to accelerate encryption and multiple tcp streams for enhanced bandwidth. First, set up ssh-agent single sign on:

local $ eval `ssh-agent`
local $ ssh-add
Enter passphrase for /home/user/.ssh/id_rsa:

Then run multiple rsync instances in parallel, f.x.:

local $ cd my-local-dir
local $ ls | xargs -n 2 -P 4 /bin/bash -c 'rsync "$@"' sh

The -n argument detemines the number of files to transfer in one rsync call. Set according to file size and count (large for many small files). The -P argument determines number of parallel rsync processes. Set to number of cores on your local machine.

Alternatively, use HyperQueue. First get HyperQueue binary, then run:

local $ hq server start &
local $ hq worker start &
local $ find my-local-dir -type f | xargs -n 2 > jobfile
local $ hq submit --log=/dev/null --progress --each-line jobfile \
        bash -c 'rsync -R $HQ_ENTRY'

Again, the -n argument detemines the number of files to transfer in one rsync call. Set according to file size and count (large for many small files).

Single Very Large File

To transfer single very large file efficienty, we need to transfer many blocks of the file in parallel, utilizing multiple cores to accelerate ssh encryption and multiple tcp streams for enhanced bandwidth.

First, set up ssh-agent single sign on as described above. Second, start the HyperQueue server and HyperQueue worker:

local $ hq server start &
local $ hq worker start &

Once set up, run the hqtransfer script listed below:

local $ ./hqtransfer mybigfile outputpath/outputfile

The hqtransfer script:

#Read input
if [ -z $1 ]; then echo Usage: $0 'input_file ssh_destination [output_path/output_file]'; exit; fi

if [ -z $2 ]; then echo Usage: $0 'input_file ssh_destination [output_path/output_file]'; exit; fi

if [ ! -z $3 ]; then OUTFILE=$3; fi

#Calculate transfer blocks
SIZE=$(($(stat --printf %s $INFILE)/1024/1024/1024))
echo Transfering $(($SIZE+1)) x 1GB blocks

hq submit --log=/dev/null --progress --array 0-$SIZE /bin/bash -c \
        "dd if=$INFILE bs=1G count=1 skip=\$HQ_TASK_ID | \
         ssh -c $DEST \
         dd of=$OUTFILE bs=1G conv=notrunc seek=\$HQ_TASK_ID"


Copy-paste the script into hqtransfer file and set executable flags:

local $ chmod u+x hqtransfer

The hqtransfer script is ready for use.

Data Transfer From Windows Clients

On Windows, use the WinSCP client to transfer data. The win-sshfs client provides a way to mount the cluster filesystems directly as an external disc.

Connection Restrictions

Outgoing connections from cluster login nodes to the outside world are restricted to the following ports:

Port Protocol
22 SSH
873 Rsync


Use SSH port forwarding and proxy servers to connect from cluster to all other remote ports.

Outgoing connections from cluster compute nodes are restricted to the internal network. Direct connections from compute nodes to the outside world are cut.

Port Forwarding

Port Forwarding From Login Nodes


Port forwarding allows an application running on cluster to connect to arbitrary remote hosts and ports.

It works by tunneling the connection from cluster back to the user's workstations and forwarding from the workstation to the remote host.

Select an unused port on the cluster login node (for example 6000) and establish the port forwarding:

$ ssh -R

In this example, we establish port forwarding between port 6000 on the cluster and port 1234 on the By accessing localhost:6000 on the cluster, an application will see the response of The traffic will run via the user's local workstation.

Port forwarding may be done using PuTTY as well. On the PuTTY Configuration screen, load your cluster configuration first. Then go to Connection > SSH > Tunnels to set up the port forwarding. Click the Remote radio button. Insert 6000 to the Source port textbox. Insert Click Add, then Open.

Port forwarding may be established directly to the remote host. However, this requires that the user has an SSH access to

$ ssh -L 6000:localhost:1234


Port number 6000 is chosen as an example only. Pick any free port.

Port Forwarding From Compute Nodes

Remote port forwarding from compute nodes allows applications running on the compute nodes to access hosts outside the cluster.

First, establish the remote port forwarding from the login node, as described above.

Second, invoke port forwarding from the compute node to the login node. Insert the following line into your jobscript or interactive shell:

$ ssh  -TN -f -L 6000:localhost:6000 login1

In this example, we assume that port forwarding from login1:6000 to has been established beforehand. By accessing localhost:6000, an application running on a compute node will see the response of

Using Proxy Servers

Port forwarding is static; each single port is mapped to a particular port on a remote host. Connection to another remote host requires a new forward.


Applications with inbuilt proxy support experience unlimited access to remote hosts via a single proxy server.

To establish a local proxy server on your workstation, install and run the SOCKS proxy server software. On Linux, SSHD demon provides the functionality. To establish the SOCKS proxy server listening on port 1080 run:

local $ ssh -D 1080 localhost

On Windows, install and run the free, open source Sock Puppet server.

Once the proxy server is running, establish the SSH port forwarding from cluster to the proxy server, port 1080, exactly as described above:

local $ ssh -R 6000:localhost:1080

Now, configure the applications proxy settings to localhost:6000. Use port forwarding to access the proxy server from compute nodes, as well.