https://bugzilla.redhat.com/show_bug.cgi?id=2364963 

 
Description of problem: Azure rhui images affected by double prompt and double echo characters in grub command line.

Version-Release number of selected component (if applicable):
Rhel 7, 8 and 9

How reproducible:
Every time

Steps to Reproduce:
1.From serial console escape to grub menu on boot.
2.press "c" to enter grub command line

Actual results:
You will then see grub>grub>. Input shows double characters and other unexpected behavior like moving the cursor.

Expected results:
One grub> command prompt and being able to type text into the command line.

Additional info: attached images. what fixes it:

Broken:
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console" <--
GRUB_CMDLINE_LINUX="debug=all loglevel=3 crashkernel=auto console=tty1 console=ttyS0 earlyprintk=ttyS0 rootdelay=300"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true
GRUB_TIMEOUT_STYLE=countdown
GRUB_TERMINAL="serial console" <--
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

Fixed:
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="serial" <--
GRUB_TERMINAL_INPUT="console" <--
GRUB_CMDLINE_LINUX=GRUB_CMDLINE_LINUX="debug=all loglevel=3 crashkernel=auto console=tty1 console=ttyS0 earlyprintk=ttyS0 rootdelay=300"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true
GRUB_TIMEOUT_STYLE=countdown
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

Removed "GRUB_TERMINAL="serial console"" entirely.