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SSH Remote Calculator (ssh://)

The ssh:// calculator runs each case on a remote host over SSH. Input files are uploaded by SFTP, the command runs in a remote temporary directory, and result files are downloaded back before the outputs are parsed.

Requires the paramiko package (pip install paramiko).

URI Syntax

ssh://[user[:password]@]host[:port]/command [arguments]

# Key-based auth (recommended) — uses your ~/.ssh keys / agent
calculators = "ssh://john@compute.edu/bash /home/john/run.sh"

# Custom port
calculators = "ssh://john@server.edu:2222/bash /path/to/script.sh"

# Several remote nodes in parallel
calculators = [
    "ssh://user@node1.cluster.edu/bash /path/run.sh",
    "ssh://user@node2.cluster.edu/bash /path/run.sh",
]

Use absolute paths for remote commands

ssh://user@host/bash script.sh may not resolve on the remote side. Prefer ssh://user@host/bash /absolute/path/to/script.sh.

How It Works

  1. Open an SSH connection (key, agent, URI password, or interactive prompt).
  2. Create a remote temporary directory.
  3. SFTP-upload the compiled input files (and relative input_static files).
  4. Run the command remotely in that directory.
  5. SFTP-download the result files.
  6. Remove the remote temp directory.

Authentication

Method How
SSH key / agent ssh://user@host/... — keys from ~/.ssh/ are tried automatically (recommended)
Interactive password ssh://user@host/... — FZ prompts if key auth fails
Password in URI ssh://user:password@host/... — insecure, avoid in production

Host Key Verification

On first connection to an unknown host, FZ shows the fingerprint and asks whether to accept it. To skip the prompt (use with care):

export FZ_SSH_AUTO_ACCEPT_HOSTKEYS=1

Configuration

Variable Purpose Default
FZ_SSH_KEEPALIVE Keepalive interval, seconds 300
FZ_SSH_AUTO_ACCEPT_HOSTKEYS Auto-accept unknown host keys 0
FZ_RUN_TIMEOUT Per-case timeout, seconds 3600

Remote Script Example

/home/user/run.sh (on the server)
#!/bin/bash
source input.txt

module load gcc/11.2 openmpi/4.1
mpirun -np 16 ./simulation input.txt
# results written to output.txt, downloaded by FZ

See Also