In this morning, I updated my CentOS 7 running with old kernel 3.0.xx to latest stable kernel verison 5.0 from elrepo-kernel. Then, I rebooted the VM but didn't boot up correctly and entered into emergency mode. I checked with journalctl -xb
. I found "Dependency failed for /boot" in journalctl result. How can I sort it out to normal operational state.

Kernel 3.x --> 5.x is an awfully big jump. Kernel-3.x is vintage 2014. As a first move, I would check the docs for kernel 4.x & 5.x to find the minimum software versions required.

You don't say what hypervisor you're using (Xen, vmware, KVM, Virtualbox, etc) but with VB (the one I have experience with) you need to recompile the kernel modules for the new kernel, which means you need the kernel source. You'll also need the Module.symvers, and may have to compile the config just to get it.

Post again, giving a lot more information. What's your glibc version? Did you install the 5.x kernel headers? What's your gcc? what's your exact error? Check all logs for scraps of information.

I suspect your boot image might need updated. Try using something like dracut to generate a new one. I don't do this often, so I don't remember off hand the command line options.

Is /boot on a separate partition, or on the root file system? Because it sounds like it failed to mount /boot, which will be a big problem, as this is where the kernel is stored.

Also, did you post this thread on serverfault?

elrepo provides kernel packages with the kernel already built, so they didn't build it to begin with. So this information isn't relevant. CentOS uses kernel 3.x by default, so if you wanted a higher version then unless you build it yourself, you would use elrepo's kernel packages on CentOS.