Setting Up Serial Console Access on a Linux Server

If your server has a virtual serial port – like HP iLO, Dell iDRAC, or any BMC that exposes a serial console over SSH – this gets you keyboard-in-the-face access before the network stack is even up.

Useful for debugging boot issues, GRUB recovery, or just not having to walk to the machine room.

Find your serial port

sudo dmesg | grep tty

Look for something like ttyS0, ttyS1, etc. On many systems:

ttyS0 = COM1 (first serial port)
ttyS1 = COM2 (second serial port)

The iLO virtual serial port usually appears as ttyS1. Adjust the commands below to match your port.

Enable a serial getty

This lets you log in over the serial line.

sudo systemctl enable [email protected]
sudo systemctl start [email protected]

Replace ttyS1 with your port if different.

Configure GRUB for serial console

Edit the GRUB config:

sudo nano /etc/default/grub

Add or edit these lines. Adjust ttyS1 and --unit=1 to match your serial port (unit 0 = COM1, unit 1 = COM2, etc.):

GRUB_CMDLINE_LINUX="console=tty0 console=ttyS1,115200n8"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=1 --word=8 --parity=no --stop=1"
GRUB_TERMINAL_INPUT="console serial"
GRUB_TERMINAL_OUTPUT="gfxterm serial"

What each line does:

Setting	Effect
`GRUB_CMDLINE_LINUX`	Tells the kernel to send boot messages to the serial port
`GRUB_SERIAL_COMMAND`	Configures the serial port speed and parameters
`GRUB_TERMINAL_INPUT`	Lets you type into GRUB over serial
`GRUB_TERMINAL_OUTPUT`	Shows the GRUB menu on both screen and serial

Apply the changes:

sudo update-grub

Done

This enables console access at every stage:

Stage	What you see
GRUB menu	Boot options, recovery mode
Kernel boot	Boot messages, driver loading
Runtime	Login prompt, full shell access

The serial getty service gives you the login prompt after boot – you get a working shell over serial just like you would over SSH.

Reboot and connect from your BMC. Common connection commands:

BMC	Command
HP iLO	SSH to iLO, then type `VSP`
Dell iDRAC	`ssh iDRAC-ip -l root`, then `console com2`
Supermicro IPMI	`ipmitool -H BMC-ip sol activate`
QEMU/libvirt	`virsh console vm-name` or `virt-viewer`

You should see the full boot process and be able to log in.

From now on you can interact with GRUB, watch kernel boot messages, and drop into single-user mode – all over the serial link.