How to setup Proxmox to redirect console

This is an example that works on my Dell Poweredge R630 and will probably work on many other servers (provided they use the same serial settings, like baud rate 115200).

Prerequisites

1. Your server is using systemd-boot (and not GRUB).
   • This is easy to check in the OS, like this:

$ efibootmgr -v
BootCurrent: 000A
BootOrder: 000A,0008,0007,0009,0005
[SNIP]
Boot0007* EFI DVD/CDROM 1       PciRoot(0x0)/Pci(0x1f,0x2)/Sata(5,0,0)
Boot0008* Linux Boot Manager    HD(2,GPT,<SNIP>)/File(\EFI\systemd\systemd-bootx64.efi)
Boot0009* Integrated NIC 1 Port 1 Partition 1   VenHw(<SNIP>)
Boot000A* Linux Boot Manager    HD(2,GPT,<SNIP>)/File(\EFI\systemd\systemd-bootx64.efi)

You can see that the system is using the \EFI\systemd\systemd-bootx64.efi file to boot the system. My system is using UEFI but it should not matter for this setup, Legacy BIOS should work as well.

Procedure

1. Find the file to edit for systemd-boot options. On Proxmox, it’s in /etc/kernel/cmdline.
2. Insert console=ttyS0,115200n8 into the file, keeping it a one-line if you already have options in there. My example:

root=ZFS=rpool/ROOT/pve-1 boot=zfs console=ttyS0,115200n8

1. Update the bootloader settings. You will need root privilege for this.

   $ proxmox-boot-tool refresh
   

2. Reboot the system.

Result

You can see if this has worked by opening the serial console on the server. On Dell servers you can ssh into the iDRAC and run this command:

/admin1-> console com2

After the reboot and the kernel selection screen, you should see your OS boot and get you to the login prompt.