OK I managed to fix the issue by using this method:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1734147. The
problem had probably occurred in 17.10, but since there was no need for
an update to EFI entries and I haven't tried to access the BIOS setup
for a long time, I didn't notice it.
-
*** This bug is a duplicate of bug 1767025 ***
https://bugs.launchpad.net/bugs/1767025
** This bug has been marked a duplicate of bug 1767025
package shim-signed 1.34.9+13-0ubuntu2 failed to install/upgrade: installed
shim-signed package post-installation script subprocess returned error e
*** This bug is a duplicate of bug 1767025 ***
https://bugs.launchpad.net/bugs/1767025
** This bug has been marked a duplicate of bug 1767025
package shim-signed 1.34.9+13-0ubuntu2 failed to install/upgrade: installed
shim-signed package post-installation script subprocess returned error e
I got a similar problem after upgrading to 18.04 (kernel 4.15.0-20). In
my case the error returned by the efibootmgr is "Could not add entry to
BootOrder: Interrupted system call". Also, BIOS is not accessible. I
realize that the problem might be really major and it may be related to
the problem ca
