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| -rw-r--r-- | modules.d/80lvmmerge/README.md | 61 |
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diff --git a/modules.d/80lvmmerge/README.md b/modules.d/80lvmmerge/README.md new file mode 100644 index 0000000..5e3e05f --- /dev/null +++ b/modules.d/80lvmmerge/README.md @@ -0,0 +1,61 @@ +# lvmmerge - dracut module + +## Preparation +- ensure that the lvm thin pool is big enough +- backup any (most likely /boot and /boot/efi) device with: +``` +# mkdir /restoredev +# dev=<device>; umount $dev; dd if="$dev" of=/restoredev/$(systemd-escape -p "$dev"); mount $dev +``` +- backup the MBR +``` +# dev=<device>; dd if="$dev" of=/restoredev/$(systemd-escape -p "$dev") bs=446 count=1 +# ls -l /dev/disk/by-path/virtio-pci-0000\:00\:07.0 +lrwxrwxrwx. 1 root root 9 Jul 24 04:27 /dev/disk/by-path/virtio-pci-0000:00:07.0 -> ../../vda +``` +- backup some partitions +``` +# dev=/dev/disk/by-path/virtio-pci-0000:00:07.0 +# dd if="$dev" of=/restoredev/$(systemd-escape -p "$dev") bs=446 count=1 +# umount /boot/efi +# dev=/dev/disk/by-partuuid/687177a8-86b3-4e37-a328-91d20db9563c +# dd if="$dev" of=/restoredev/$(systemd-escape -p "$dev") +# umount /boot +# dev=/dev/disk/by-partuuid/4fdf99e9-4f28-4207-a26f-c76546824eaf +# dd if="$dev" of=/restoredev/$(systemd-escape -p "$dev") +``` +Final /restoredev +``` +# ls -al /restoredev/ +total 1253380 +drwx------. 2 root root 250 Jul 24 04:38 . +dr-xr-xr-x. 18 root root 242 Jul 24 04:32 .. +-rw-------. 1 root root 209715200 Jul 24 04:34 dev-disk-by\x2dpartuuid-4fdf99e9\x2d4f28\x2d4207\x2da26f\x2dc76546824eaf +-rw-------. 1 root root 1073741824 Jul 24 04:34 dev-disk-by\x2dpartuuid-687177a8\x2d86b3\x2d4e37\x2da328\x2d91d20db9563c +-rw-------. 1 root root 446 Jul 24 04:38 dev-disk-by\x2dpath-virtio\x2dpci\x2d0000:00:07.0 +``` +- make a thin snapshot +``` +# lvm lvcreate -pr -s rhel/root --name reset +``` + +- mark the snapshot with a tag +``` +# lvm lvchange --addtag reset rhel/reset +``` + +- remove /restoredev +``` +# rm -fr /restoredev +``` + +## Operation + +If a boot entry with ```rd.lvm.mergetags=<tag>``` is selected and there are LVs with ```<tag>``` +dracut will +- make a copy of the snapshot +- merge it back to the original +- rename the copy back to the name of the snapshot +- if /restordev appears in the root, then it will restore the images + found in that directory. This can be used to restore /boot and /boot/efi and the + MBR of the boot device |