Linux kernel upgrade failed to start, Kernel Panic-not syncing unable to mount Root fs on unknown block (0,0)

Cause: A kernel Upgrade that causes the system to fail to boot.

First enter the recovery mode: the boot interface Select-->ubuntu Advanced--and the options that appear, select the recovery mode that can be started (several kernel versions try each)--confirm that you can see a lot of options on the interface. Select the first recovery mode-->ok. (That's the way it is.)

And then it went into the system. Here's how to do this:

1. View the files under/boot/

Abi-4.4.0-31-generic Memtest86+.bin
Abi-4.4.0-98-generic memtest86+.elf
Config-4.4.0-31-generic Memtest86+_multiboot.bin
Config-4.4.0-98-generic System.map-4.4.0-31-generic
Grub System.map-4.4.0-98-generic
Initrd.img-4.4.0-31-generic Vmlinuz-4.4.0-31-generic
Initrd.img-4.4.0-98-generic Vmlinuz-4.4.0-98-generic

Found two versions of the kernel, the reason should be an automatic update?? I don't know

2, try to modify/boot/grub/grub.cfg

Navigate to a Menuentry (the one you need to boot yourself), and the following is the menuentry of the system I can't boot

Menuentry ' ubuntu '--class ubuntu--class gnu-linux--class GNU--class os $menuentry _id_option ' gnulinux-simple-c9ddf11a -a984-4854-91af-bcaed3e6c9b9 ' {
Recordfail
Load_video
Gfxmode $linux _gfx_mode
Insmod Gzio
Insmod Part_msdos
Insmod ext2
Set root= ' Hd0,msdos9 '
if [x$feature_platform_search_hint = xy]; Then
Search--no-floppy--fs-uuid--set=root--hint-bios=hd0,msdos9--hint-efi=hd0,msdos9--hint-baremetal=ahci0,msdos9 C9ddf11a-a984-4854-91af-bcaed3e6c9b9
Else
Search--no-floppy--fs-uuid--set=root c9ddf11a-a984-4854-91af-bcaed3e6c9b9
Fi
linux/boot/vmlinuz-4.4.0-31-generic root=uuid=c9ddf11a-a984-4854-91af-bcaed3e6c9b9 ro Quiet Splash $vt _ Handoff
Initrd/boot/initrd.img-4.4.0-31-generic
}

Red version, the high version of your system is modified to a lower version. If my system version is originally 31, do not know why upgrade to 98, modified back.

The reboot will start.

Linux kernel upgrade failed to start, Kernel Panic-not syncing unable to mount Root fs on unknown block (0,0)