Here are a series of commands to get Ubuntu 18.04 to boot into terminal mode, with various extras on how to get an automatic menu on boot up.

Skipping Graphical Boot

If you want to skip the graphical login screen, hit [Shift] or [Esc] before you see the grub menu to get to the grub menu. Add these features to the linux command:
systemd.unit=multi-user.target
Then hit Ctrl-X.

Changing the Default Boot Target

Become root. In /lib/systemd/system, change the default.target symlink:

# rm default.target; ln -s multi-user.target default.target
# systemctl daemon-reload

Checking the Filesystem Every Boot

If you do the first command above with a semicolon, you can still use tab-completion. Next, we go to /etc/default and update the grub settings:

# cd /etc/default
# vim grub
Change GRUB_CMDLINE_LINUX_DEFAULT to this value:
"fsck.mode=force fsck.repair=yes"

Run update-grub2:
# update-grub2

Reinforce this behavior by using tune2fs to make each file system run a check each boot. What file systems are you running?

# lsblk -o NAME,MOUNTPOINT # will produce output kinda like:
sda   
  sda1  /boot
  sda2  /
  sda3 [SWAP]
  sda4 /home

Running these command will make sda1, sda2, sda4 all check every mount:

# tune2fs -c1 /dev/sda1
# tune2fs -c1 /dev/sda2
# tune2fs -c1 /dev/sda4

Reboot:
# reboot

That shouldn’t take too long. You have a tty login now.

Creating an Automatic Menu

I’m disabling a few things:

systemctl disable snapd.service wpa_supplicant.service unattended-upgrades.service cups-browserd.service cups.service
systemctl daemon-reload

There will be lots of snaps you don’t want:

snap list --all | awk '/gnome|gtk/{print $1, $2}' | while read snapname snaprevision; do snap remove "$snapname" --revision="$snaprevision"; done
This didn't work well, maybe snap remove "$snapname" is enough

You are logged in on tty1 by default. (I don't know why tty0 exists.) Following this guide, create this directory:
# cd /etc/systemd/system
# mkdir getty@tty1.service.d
# cd getty@tty1.service.d
# vim override.conf
[Service]
ExecStart=
ExecStart=-/root/onboot.bash
StandardInput=tty
StandardOutput=tty

# vim /root/onboot.bash

#!/bin/bash
echo "This is a sound recorder appliance. Hit a key to start recording."
RECORDING=0
while true; do
  read -sn1 KEY
  if [[ $RECORDING = 0 ]]; then
    RECORDING=1
    echo "Now recording"
    /root/start-recording.bash
  else
    RECORDING=0
    echo "Recording stopped"
    /root/stop-recording.bash
  fi
done

# chmod +x /root/onboot.bash
# systemd daemon-reload
# reboot

All you have to do then is record things with the start-recording.bash and stop-recording.bash scripts.