Description of problem:
For an unknown reason, customer had a missing line feed at the end of /etc/default/grub:
~~~
[root@localhost ~]# cat /etc/default/grub 
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=vg_system/root rd.lvm.lv=vg_system/swap rhgb quiet transparent_hugepage=never processor.max_cstate=1 intel_idle.max_cstate=1 elevator=noop"
GRUB_DISABLE_RECOVERY="true"[root@localhost ~]# 
~~~

After running `leapp upgrade` and rebooted twice, the grub entry corresponding to the new RHEL 8 kernel was not present.
The userspace was fully updated, but some final leapp routines were not executed.

Additionally, the run of grubby was not stored in leapp-upgrade.log, but another related issue is visible in the journal upon reboot (done by the leapp.service, it's an obvious side effect):
~~~
Mar 10 12:33:57 localhost.localdomain leapp3[1413]: ============================================================
Mar 10 12:33:57 localhost.localdomain leapp3[1413]:                            ERRORS
Mar 10 12:33:57 localhost.localdomain leapp3[1413]: ============================================================
Mar 10 12:33:57 localhost.localdomain leapp3[1413]: 2021-03-10 12:30:27.027232 [ERROR] Actor: kernelcmdlineconfig
Mar 10 12:33:57 localhost.localdomain leapp3[1413]: Message: Failed to append extra arguments to kernel command line.
Mar 10 12:33:57 localhost.localdomain leapp3[1413]: Summary:
Mar 10 12:33:57 localhost.localdomain leapp3[1413]:     Details: Command ['grubby', '--update-kernel=/boot/vmlinuz-4.18.0-193.28.1.el8_2.x86_64', '--args=net.ifnames=0'] failed with exit code 1.
~~~

The resulting /etc/default/grub is wrong:
~~~
# cat /etc/default/grub 
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto spectre_v2=retpoline rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet"
GRUB_DISABLE_RECOVERY="true"GRUB_ENABLE_BLSCFG=true
~~~

And the BLS entries in /boot/loader/entries only contain the RHEL 7 kernels.


Version-Release number of selected component (if applicable):
leapp-repository-0.13.0-2.el7_9.noarch

How reproducible:
100%

Steps to Reproduce:
1. truncate -s -1 /etc/default/grub
2. leapp upgrade
3. reboot twice

Expected result:
A small check and/or fix to prevent this issue (even if ultimately the issue resides in grub postinst rpm, I didn't check).