RHEL/Centos/OL 7.X

Baremetal
<code>
cat  /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
#GRUB_TERMINAL_OUTPUT="console"
GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
GRUB_CMDLINE_LINUX="crashkernel=auto console=tty1 console=ttyS0,115200"
GRUB_DISABLE_RECOVERY="true"
GRUB_GFXPAYLOAD_LINUX=text
</code>

VM
<code>

</code>

Ubuntu VM(qemu kvm)
<code>
$ cat /proc/cmdline 
BOOT_IMAGE=/vmlinuz-4.4.0-93-generic root=/dev/mapper/ubuntu--vg-root ro console=tty1 console=ttyS0
ubuntu@ubuntu:~$ cat /etc/default/grub
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'

GRUB_DEFAULT=0
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="console=tty1 console=ttyS0"
GRUB_CMDLINE_LINUX=""
</code>