ssh_login.md

Connecting via Terminal (Linux, Mac, Windows)

Connecting via terminal works on every operating system. For Linux and Mac operating systems no additional software is required. For users of a Windows OS a recent version of Windows is required (Windows 10, Build 1809 and higher). It is possible to use Command Prompt or PowerShell). Ensure that OpenSSH is installed on the system.

SSH establishes secure connections using authentication and encryption. The login nodes accept the following encryption algorithms: aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, aes256-gcm@openssh.com, chacha20-poly1305@openssh.com, chacha20-poly1305@openssh.com.

Before Your First Connection

We suggest to create an SSH key pair before you work with the ZIH systems. This ensures high connection security.

marie@local$ mkdir -p ~/.ssh
marie@local$ ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519
Generating public/private ed25519 key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
[...]

Type in a passphrase for the protection of your key. The passphrase should be non-empty. Copy the public key to the ZIH system (Replace placeholder marie with your ZIH login):

marie@local$ ssh-copy-id -i ~/.ssh/id_ed25519.pub marie@login2.barnard.hpc.tu-dresden.de
The authenticity of host 'barnard.hpc.tu-dresden.de (141.30.73.104)' can't be established.
RSA key fingerprint is SHA256:HjpVeymTpk0rqoc8Yvyc8d9KXQ/p2K0R8TJ27aFnIL8.
Are you sure you want to continue connecting (yes/no)?

Compare the shown fingerprint with the documented fingerprints. Make sure they match. Then you can accept by typing yes.

!!! note "One ssh-copy-id command for all clusters"

Since your home directory, where the file `.ssh/authorized_keys` is stored, is available on all HPC
systems, this task is only required once and you can freely choose a target system for the
`ssh-copy-id` command. Afterwards, you can access all clusters with this key file.

??? info "ssh-copy-id is not available"

If `ssh-copy-id` is not available, you need to do additional steps:

```console
marie@local$ scp ~/.ssh/id_ed25519.pub marie@login2.barnard.hpc.tu-dresden.de:
The authenticity of host 'barnard.hpc.tu-dresden.de (141.30.73.104)' can't be established.
RSA key fingerprint is SHA256:Gn4n5IX9eEvkpOGrtZzs9T9yAfJUB200bgRchchiKAQ.
Are you sure you want to continue connecting (yes/no)?
```

After that, you need to manually copy the key to the right place:

```console
marie@local$ ssh marie@login2.barnard.hpc.tu-dresden.de
[...]
marie@login.barnard$ mkdir -p ~/.ssh
marie@login.barnard$ touch ~/.ssh/authorized_keys
marie@login.barnard$ cat id_ed25519.pub >> ~/.ssh/authorized_keys
```

Configuring Default Parameters for SSH

After you have copied your key to the ZIH system, you should be able to connect using:

marie@local$ ssh marie@login2.barnard.hpc.tu-dresden.de
[...]
marie@login.barnard$ exit

However, you can make this more comfortable if you prepare an SSH configuration on your local workstation. Navigate to the subdirectory .ssh in your home directory and open the file config (~/.ssh/config) in your favorite editor. If it does not exist, create it. Put the following lines in it (you can omit lines starting with #):

Host barnard
  #For login (shell access)
  HostName login1.barnard.hpc.tu-dresden.de
  #Put your ZIH-Login after keyword "User":
  User marie
  #Path to private key:
  IdentityFile ~/.ssh/id_ed25519
  #Don't try other keys if you have more:
  IdentitiesOnly yes
  #Enable X11 forwarding for graphical applications and compression. You don't need parameter -X and -C when invoking ssh then.
  ForwardX11 yes
  Compression yes
Host dataport
  #For copying data without shell access
  HostName dataport1.hpc.tu-dresden.de
  #Put your ZIH-Login after keyword "User":
  User marie
  #Path to private key:
  IdentityFile ~/.ssh/id_ed25519
  #Don't try other keys if you have more:
  IdentitiesOnly yes

Afterwards, you can connect to the ZIH system using:

marie@local$ ssh barnard

If you want to copy data from/to ZIH systems, please refer to the documentation Dataport Nodes: Transfer Data to/from ZIH's Filesystems for more information on Dataport nodes.

!!! note "Gernalization to all HPC systems"

In the above `.ssh/config` file, the HPC system `Barnard` is chosen as an example.
The very same settings can be made for individuall or all ZIH systems, e.g. `Alpha`, `Julia`,
`Romeo` etc.

X11-Forwarding

If you plan to use an application with graphical user interface (GUI), you need to enable X11-forwarding for the connection. If you use the SSH configuration described above, everything is already prepared and you can simply use:

marie@local$ ssh barnard

If you have omitted the last two lines in the default configuration above, you need to add the option -X or -XC to your SSH command. The -C enables compression which usually improves usability in this case:

marie@local$ ssh -XC barnard

!!! info

Also consider to use a [DCV session](desktop_cloud_visualization.md) for remote desktop
visualization at ZIH systems.