Chapter 6. Managing system upgrades with snapshots

Procedure

1. Create a snapshot of your root logical volume:

   • If your root file system uses thin provisioning, create a thin snapshot:

     # lvcreate -s rhel/root -kn -n root_snapshot_before_changes
      Logical volume "root_snapshot_before_changes" created.

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     Here:

     • -s creates the snapshot.
     • rhel/root copies the file system to the logical volume.
     • -kn automatically activates LV at boot time.

     • -n root_snapshot_before_changes shows the name of the snapshot.

       While creating a thin snapshot, do not define the snapshot size. The snapshot is allocated from the thin pool.

   • If your root file system uses thick provisioning, create a thick snapshot:

     # lvcreate -s rhel/root -n root_snapshot_before_changes -L 25g
      Logical volume "root_snapshot_before_changes" created.

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     In this command:

     • -s creates the snapshot.
     • rhel/root copies the file system to the logical volume.
     • -n root_snapshot_before_changes shows the name of the snapshot.

     • -L 25g is the snapshot size. Make a size estimate based on the size of the original installation.

       While creating a thick snapshot, define the snapshot size that can hold all the changes during the upgrade.

       Important

       The created snapshot does not include any additional system changes.

2. Enable boom by using the GRUB boot loader

   # grub2-mkconfig > /boot/grub2/grub.cfg
   Generating grub configuration file ...
   Found linux image: /boot/vmlinuz-3.10.0-1160.118.1.el7.x86_64
   Found initrd image: /boot/initramfs-3.10.0-1160.118.1.el7.x86_64.img
   Found linux image: /boot/vmlinuz-3.10.0-1160.el7.x86_64
   Found initrd image: /boot/initramfs-3.10.0-1160.el7.x86_64.img
   Found linux image: /boot/vmlinuz-0-rescue-f9f6209866c743739757658d1a4850b2
   Found initrd image: /boot/initramfs-0-rescue-f9f6209866c743739757658d1a4850b2.img
   done

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3. Create the profile:

   # boom profile create --from-host --uname-pattern el7
   Created profile with os_id f150f3d:
     OS ID: "f150f3d6693495254255d46e20ecf5c690ec3262",
     Name: "Red Hat Enterprise Linux Server", Short name: "rhel",
     Version: "7.9 (Maipo)", Version ID: "7.9",
     Kernel pattern: "/vmlinuz-%{version}", Initramfs pattern: "/initramfs-%{version}.img",
     Root options (LVM2): "rd.lvm.lv=%{lvm_root_lv}",
     Root options (BTRFS): "rootflags=%{btrfs_subvolume}",
     Options: "root=%{root_device} ro %{root_opts}",
     Title: "%{os_name} %{os_version_id} (%{version})",
     Optional keys: "grub_users grub_arg grub_class id", UTS release pattern: "el7"

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4. Create a snapshot boot entry of the original system using backup copies of the original boot images:

   # boom create --backup --title "Root LV snapshot before changes" --rootlv rhel/root_snapshot_before_changes
   Created entry with boot_id bfef767:
     title Root LV snapshot before changes
     machine-id 7d70d7fcc6884be19987956d0897da31
     version 3.10.0-1160.114.2.el7.x86_64
     linux /vmlinuz-3.10.0-1160.114.2.el7.x86_64.boom0
     initrd /initramfs-3.10.0-1160.114.2.el7.x86_64.img.boom0
     options root=/dev/rhel/root_snapshot_before_changes ro rd.lvm.lv=rhel/root_snapshot_before_changes
     grub_users $grub_users
     grub_arg --unrestricted
     grub_class kernel

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   Here:

   • --title "Root LV snapshot before changes" is the name of the boot entry, that shows in the boot entry list during system startup.

   • --rootlv is the root logical volume that corresponds to the new boot entry.

     After you complete the previous step, you have a boot entry that enables access to the original system, before the upgrade.

5. Upgrade to Red Hat Enterprise Linux 8 using the Leapp utility:

   # leapp upgrade
   ==> Processing phase `configuration_phase`
   ====> * ipu_workflow_config
           IPU workflow config actor
   ==> Processing phase `FactsCollection`
   ...
   ============================================================
                         REPORT OVERVIEW
   ============================================================
   
   Upgrade has been inhibited due to the following problems:
       1. Btrfs has been removed from RHEL8
       2. Missing required answers in the answer file
   
   HIGH and MEDIUM severity reports:
       1. Packages available in excluded repositories will not be installed
       2. GRUB core will be automatically updated during the upgrade
       3. Difference in Python versions and support in RHEL 8
       4. chrony using default configuration
   
   Reports summary:
       Errors:                      0
       Inhibitors:                  2
       HIGH severity reports:       3
       MEDIUM severity reports:     1
       LOW severity reports:        3
       INFO severity reports:       4
   
   Before continuing consult the full report:
       A report has been generated at /var/log/leapp/leapp-report.json
       A report has been generated at /var/log/leapp/leapp-report.txt
   
   ============================================================
                      END OF REPORT OVERVIEW
   ============================================================

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   Review and resolve any blockers indicated by the leapp upgrade command report. For detailed instructions on the report, see Assessing upgradability from the command line.

6. Reboot into the upgrade boot entry:

   # leapp upgrade --reboot
   ==> Processing phase `configuration_phase`
   ====> * ipu_workflow_config
           IPU workflow config actor
   ==> Processing phase `FactsCollection`
   ...

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   Select the Red Hat Enterprise Linux Upgrade Initramfs entry from the GRUB boot screen.

   Note

   The Snapshots submenu from the GRUB boot screen is not available in Red Hat Enterprise Linux 8.

Procedure

1. Reboot the system:

   # reboot

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2. Select the required boot entry from the GRUB boot loader screen.

Procedure

1. Boot into Red Hat Enterprise Linux 8 from the GRUB boot loader screen.

2. After the system loads, view the available boot entries. The following output shows the snapshot boot entry in the list of boom boot entries:

   # boom list
   WARNING - Options for BootEntry(boot_id=cae29bf) do not match OsProfile: marking read-only
   BootID  Version                      Name                            RootDevice
   e0252ad 3.10.0-1160.118.1.el7.x86_64 Red Hat Enterprise Linux Server /dev/rhel/root_snapshot_before_changes
   611ad14 3.10.0-1160.118.1.el7.x86_64 Red Hat Enterprise Linux Server /dev/mapper/rhel-root
   3bfed71- 3.10.0-1160.el7.x86_64 Red Hat Enterprise Linux Server /dev/mapper/rhel-root _cae29bf 4.18.0-513.24.1.el8_9.x86_64 Red Hat Enterprise Linux        /dev/mapper/rhel-root

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   The warning is expected, you cannot change or delete these entries by using boom because the kernel and grubby packages manage them.

3. Delete the snapshot entry by using the BootID value:

   # boom delete --boot-id e0252ad
   Deleted 1 entry

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   This deletes the boot entry from the GRUB menu.

4. Remove the LV snapshot:

   # lvremove rhel/root_snapshot_before_changes
   Do you really want to remove active logical volume rhel/root_snapshot_before_changes? [y/n]: y
         Logical volume "root_snapshot_before_changes" successfully removed

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5. Complete the remaining post-upgrade tasks. For details, see Upgrade from RHEL 7 to RHEL 8.

Procedure

1. Merge the snapshot with the original volume:

   # lvconvert --merge rhel/root_snapshot_before_changes
     Logical volume rhel/root_snapshot_before_changes contains a filesystem in use.
     Delaying merge since snapshot is open.
     Merging of thin snapshot rhel/root_snapshot_before_changes will occur on next activation of rhel/root.

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   Warning

   After you merge the snapshot, you must continue with all the remaining steps in this procedure to prevent data loss.

2. Create a rollback boot entry for the merged snapshot:

   # boom create --backup --title "RHEL Rollback" --rootlv rhel/root
   Created entry with boot_id 1e6d298:
     title RHEL Rollback
     machine-id f9f6209866c743739757658d1a4850b2
     version 3.10.0-1160.118.1.el7.x86_64
     linux /vmlinuz-3.10.0-1160.118.1.el7.x86_64.boom0
     initrd /initramfs-3.10.0-1160.118.1.el7.x86_64.img.boom0
     options root=/dev/rhel/root ro rd.lvm.lv=rhel/root
     grub_users $grub_users
     grub_arg --unrestricted
     grub_class kernel

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3. Reboot your machine to restore the operating system state:

   # reboot

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   • After the system reboots, select the RHEL Rollback boot entry from the GRUB screen.

   • When the root logical volume is active, the system automatically starts the snapshot merge operation.

     Important

     When the merge operation starts, the snapshot volume is no longer available. After successfully booting the RHEL Rollback boot entry, the Root LV snapshot boot entry no longer works. Merging the snapshot logical volume destroys the Root LV snapshot and restores the prior state of the original volume.

4. After you complete the merge operation, remove the unused entries and restore the original boot entry:

   1. Remove the unused Red Hat Enterprise Linux 8 boot entries from the /boot file system and rebuild the grub.cfg file for the changes to take effect:

      # rm -f /boot/loader/entries/*.el8*

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      # rm -f /boot/*.el8*

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      # grub2-mkconfig -o /boot/grub2/grub.cfg
      Generating grub configuration file ...
      Found linux image: /boot/vmlinuz-3.10.0-1160.118.1.el7.x86_64.boom0
      ....
      done

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   2. Restore the original Red Hat Enterprise Linux boot entry:

      # new-kernel-pkg --update $(uname -r)

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5. After a successful rollback to the system, delete the boom snapshot and rollback boot entries:

   # boom list -o+title
   BootID  Version                      Name                            RootDevice                             Title
   a49fb09 3.10.0-1160.118.1.el7.x86_64 Red Hat Enterprise Linux Server /dev/mapper/rhel-root                  Red Hat Enterprise Linux (3.10.0-1160.118.1.el7.x86_64) 8.9 (Ootpa)
   1bb11e4 3.10.0-1160.el7.x86_64       Red Hat Enterprise Linux Server /dev/mapper/rhel-root                  Red Hat Enterprise Linux (3.10.0-1160.el7.x86_64) 8.9 (Ootpa)
   e0252ad 3.10.0-1160.118.1.el7.x86_64 Red Hat Enterprise Linux Server /dev/rhel/root_snapshot_before_changes Root LV snapshot before changes
   1e6d298 3.10.0-1160.118.1.el7.x86_64 Red Hat Enterprise Linux Server /dev/rhel/root                         RHEL Rollback

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   # boom delete e0252ad
   Deleted 1 entry
   # boom delete 1e6d298
   Deleted 1 entry

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