This bug was initially created as a copy of Bug #1983000

I am copying this bug because: 

Same code in RHEL8. Even though PPC64 isn't supported anymore, the code is exactly the same on PPC64le so I would expect it also fails here, even if not tested myself.

Description of problem:

When recovering a PPC64+multipath system, the ofpathname binary may fail executing due to not having /sys mounted in the chroot:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
Installing for powerpc-ieee1275 platform.
/sbin/ofpathname: line 411: cd: /sys/class/*/dm-2: No such file or directory
/usr/bin/find: warning: Unix filenames usually don't contain slashes (though pathnames do).  That means that '-name '/'' will probably evaluate to false all the time on this system.  You might find the '-wholename' test more useful, or perhaps '-samefile'.  Alternatively, if you are using GNU grep, you could use 'find ... -print0 | grep -FzZ '/''.
/usr/bin/find: missing argument to `-name'
ofpathname: Could not retrieve Open Firmware device path
            for logical device "/dev/mapper/mpathf".
/vdevice/v-scsi@300000e2/disk@8200000000000000 /vdevice/v-scsi@3000007e/disk@8200000000000000
Installation finished. No error reported.
2021-06-04 13:42:33.207523277 GRUB2 installed on /dev/mapper/mpathf1
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

The ofpathname binary is called by grub2-install but additionally grub2-install doesn't detect the error, which doesn't make ReaR fail.

The result is an unbootable system.


Version-Release number of selected component (if applicable):

rear-2.4


How reproducible:

Always on the customer system


Additional info:

rear-2.6 has code to mount /sys automatically.

The following fix in /usr/share/rear/finalize/Linux-ppc64/620_install_grub2.sh is known to work on customer's systems:

Original lines (with numbers)
---------------------------------------------------
23 LogPrint "Installing GRUB2 boot loader"
24 mount -t proc none $TARGET_FS_ROOT/proc
25
:
75 umount $TARGET_FS_ROOT/proc
---------------------------------------------------

Modified lines:
---------------------------------------------------
23 LogPrint "Installing GRUB2 boot loader"
24 mount -t proc none $TARGET_FS_ROOT/proc
25 mount -t sysfs sys $TARGET_FS_ROOT/sys
26
:
76 umount $TARGET_FS_ROOT/sys
77 umount $TARGET_FS_ROOT/proc
---------------------------------------------------