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docs(zbm): Nudge user to work with Dropbear keepalives (#6)

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hygienic-books 2023-11-05 02:10:33 +01:00
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@ -230,11 +230,30 @@ The script takes the following installation steps.
1. Configure boot method 1. Configure boot method
- Either an EFI image with EFI boot order entries on a UEFI machine - Either an EFI image with EFI boot order entries on a UEFI machine
- Or Syslinux with `extlinux` for a legacy BIOS computer - Or Syslinux with `extlinux` for a legacy BIOS computer
1. If requested by user enable SSH in ZFSBootMenu
1. Add `pacman` hooks to keep ZFSBootMenu images (and `extlinux`) updated 1. Add `pacman` hooks to keep ZFSBootMenu images (and `extlinux`) updated
- [quico.space/quico-os-setup/zbm-regen-pacman-hook](https://quico.space/quico-os-setup/zbm-regen-pacman-hook) - [quico.space/quico-os-setup/zbm-regen-pacman-hook](https://quico.space/quico-os-setup/zbm-regen-pacman-hook)
- [quico.space/quico-os-setup/zbm-syslinux-pacman-hook](https://quico.space/quico-os-setup/zbm-syslinux-pacman-hook) - [quico.space/quico-os-setup/zbm-syslinux-pacman-hook](https://quico.space/quico-os-setup/zbm-syslinux-pacman-hook)
1. Exit into Arch Linux live CD ISO image shell for you to `reboot` and frolick 1. Exit into Arch Linux live CD ISO image shell for you to `reboot` and frolick
# SSH in ZFSBootMenu
Per [SSH](#ssh) and [Networking](#networking) this script will optionally add a Dropbear SSH daemon to ZFSBootMenu. While the mechanism of SSH-ing into a server isn't particularly noteworthy we humbly suggest that in this particular use case you let your SSH client listen for keepalive messages from the server.
```
ssh -o ServerAliveInterval=3 -o ServerAliveCountMax=0 <addr> -p <port>
```
A typical workflow with Dropbear is for your to SSH into it, issue `zfs` or `zfsbootmenu` commands and allow the Arch Linux boot process to commence. As soon as you're done the Dropbear SSH server will terminate as ZFSBootMenu hands its control off to your operating system's real kernel. Without your client listening to keepalive messages it may not realize that the connection's gone for quite some time until you harshly interrupt it.
The server defaults to sending keepalive messages to your client every second.
With `-o ServerAliveInterval=3` you instruct your client to send an are-your-still-there message to the server if your client ever stops getting keepalive messages from the server for 3 seconds. The server defaults to sending 1 keepalive ping per second so even on a somewhat lossy connection we can reasonably expect to get one message through to us within 3 seconds.
When it comes to the point that your SSH client sends an are-your-still-there message it expects a near-realtime response. It will accept `-o ServerAliveCountMax=0` failures from the server to comply.
This effectively configures your SSH client to remain connected even through somewhat lossy hops to the Dropbear daemon; and to cleanly disconnect 3 seconds and some change after you've executed whatever you needed to do in ZFSBootMenu.
# Flavor choices # Flavor choices
We make the following opinionated flavor choices. Feel free to change them to your liking. We make the following opinionated flavor choices. Feel free to change them to your liking.