ssh Command Reference for CI Scripts

ssh gives an encrypted connection to run commands on a remote host.

ssh underlies deploys, git over SSH, and remote runners. Most CI failures are host-key prompts and key permissions, both of which have deterministic fixes.

Common flags/usage

• -i FILE: use a specific identity (private key)
• -o KEY=VALUE: set a config option inline
• -p PORT: connect to a non-default port
• -o BatchMode=yes: never prompt, fail instead
• -o StrictHostKeyChecking=accept-new: trust an unknown host once

Example

chmod 600 "${HOME}/.ssh/id_ed25519"
ssh-keyscan -H "${DEPLOY_HOST}" >> "${HOME}/.ssh/known_hosts"
ssh -i "${HOME}/.ssh/id_ed25519" -o BatchMode=yes \
  "deploy@${DEPLOY_HOST}" "cd /srv/app && ./pull-and-restart.sh"

In CI

"Host key verification failed" means the host is not in known_hosts and there is no TTY to accept it; pre-seed it with ssh-keyscan or use -o StrictHostKeyChecking=accept-new. "Permissions 0644 are too open" needs chmod 600. BatchMode=yes makes ssh fail fast instead of hanging on a password prompt.

Key takeaways

• Pre-seed known_hosts with ssh-keyscan to avoid the host-key prompt.
• chmod 600 the private key or ssh refuses to use it.
• BatchMode=yes makes ssh fail instead of hanging on a prompt.

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