Recently I was upgrading a stack of Catalyst 9300 switches and one switch ended up in rommon mode. Well, first of all, my stack was not healthy. The second switch had version mismatch so I thought upgrading them all together to a newer version will fix the issue. What happened was 1st switch got upgraded and 2nd did not. So I’ve added software auto-upgrade command thinking it will fix the 2nd switch. It started the process but something did not go as planned. And switch ended up in rommon.
Never upgrade switch stack if your stack is in version mismatch state
Luckily I had console access and after some research, I discovered a great command. Just need access to bin file on flash or USB flash drive.
switch: emergency-install flash:cat9k_iosxe.16.09.02.SPA.bin
Executing command started recovery sequence and after 10-15 minutes switch was back online.