Cannot set SSH UserKnownHostsFile using `--ssh-option`

[stefankreutz]

Prerequisites

• I have updated to the latest version using nix run --refresh github:nix-community/nixos-anywhere
• I have reproduced the issue with the --debug flag
• I have searched existing issues to make sure this isn't a duplicate

Bug Description

When supplying --ssh-option "UserKnownHostsFile=foo" to nixos-anywhere as described in the CLI usage help, it still uses /dev/null.

I think this is because the value of the --ssh-option gets appended to the default SSH arguments.

OpenSSH uses the first UserKnownHostsFile setting on the command-line, and ignores the second. Thus, one cannot override the default UserKnownHostsFile=/dev/null.

The same applies to the other default arguments, notably StrictHostKeyChecking=no.

I think this could be fixed by prepending the --ssh-option values to the default SSH arguments.

Steps to Reproduce

1. Run nixos-anywhere --ssh-option "UserKnownHostsFile=$HOME/foo" ....
2. Confirm "$HOME/foo" is empty.

Debug Logs

N/A

Command Used

nixos-anywhere --ssh-option "UserKnownHostsFile=$HOME/foo" ...

Target System

Virtual machine

NixOS Version

unstable

Environment Information

• Host OS:
• Nix version:
• Target architecture:

Configuration Files

Additional Context

No response

[stefankreutz]

Sorry for not including a debug log, but I think it's pointless in this case 😃