Reorganize files to account for new "External" section

QubesOS/qubes-issues#4693

developer/debugging/mount-lvm-image.md

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+---
+layout: doc
+title: Mount LVM image
+permalink: /doc/mount-lvm-image/
+---
+
+# How to mount LVM image
+
+You want to read your LVM image (ex: you did some errors and can't start the VM ). 
+ 
+1: make the image available for qubesdb.
+
+```bash
+# Example: /dev/qubes_dom0/vm-debian-9-tmp-root
+[user@dom0]$ dev=$(basename $(readlink /dev/YOUR_LVM_VG/YOUR_LVM_IMAGE))
+[user@dom0]$ qubesdb-write /qubes-block-devices/$dev/desc "YOUR_LVM_IMAGE"
+```
+
+2: Create a new disposable VM
+
+```bash
+[user@dom0]$ qvm-run -v --dispvm=YOUR_DVM_TEMPLATE --service qubes.StartApp+xterm &
+```
+
+3: Attach the device to your newly created disp VM
+
+From the GUI, or from the command line: 
+```bash
+[user@dom0]$ qvm-block attach NEWLY_CREATED_DISPVM dom0:$dev
+```
+
+4: Mount the partition you want to, and do what you want with it
+
+```bash
+[user@dispXXXX]$ mount /dev/xvdiX /mnt/
+```
+
+5: Umount and kill the VM
+```
+[user@dispXXXX]$ umount /mnt/
+```
+
+6: Remove the image from qubesdb
+```
+[user@dom0]$ qubesdb-rm /qubes-block-devices/$dev/
+```
+
+# References
+
+https://github.com/QubesOS/qubes-issues/issues/4687#issuecomment-451626625