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(Posting here rather than the Ubuntu subsite because I don't think it's specifically related to Ubuntu...)

I've previously been successfully using kexec-reboot -lr from the exceptionally useful page here.

After an upgrade from 18.04 to 20.04, running this command still reboots the system, but it now does a 'hard' reboot where it drops all the way to EFI/firmware instead of just reloading and restarting the kernel. This adds several minutes to the boot time on my server (and defeats the whole point of using this invocation...)

The command that's being run according to the verbose output of kexec-reboot is:

Running /sbin/kexec -l /boot/vmlinuz-5.4.0-54-generic --append='root=UUID=69a4d39e-361f-41e7-9ad3-866cb9dae202 ro intel_iommu=on' --initrd=/boot/initrd.img-5.4.0-54-generic

Running that command directly (i.e. not from the kexec-reboot convenience script) gives the same behavior.

I've checked syslog and dmesg for messages that seem relevant and I can't find anything, but I'm also likely not aware of all the various places I could look. Other than just the verbose flag, what other things can I use to troubleshoot this?

Update 11/26: If I manually build the kexec line as describe above and then run kexec -e (As described here) it does indeed just boot the kernel directly. Looking at the kexec-reboot code shows that the final call there is shutdown -r now, so I'm now trying to figure out why shutdown -r now is different behavior than it was before...

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From Kernel 5.4 onwards Linux Security Module enabled Lockdown feature. This will disable the kexec reboot feature and doesn't allow bypassing hard reset. By default Lockdown feature is disabled in 5.4. But confirm in your case it is not enabled. You can check u-boot variables or kernel source.

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  • On this machine, if I use kexec -e the system DOES reboot immediately and skips the hard reset. I was under the impression that this meant things were OK for kexec... ? – ljwobker Nov 30 '20 at 23:46

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