From 71a1cc9b9872b2c16220f3634422547ed11bbb81 Mon Sep 17 00:00:00 2001
From: Jan-Erik Rediger <badboy@archlinux.us>
Date: Tue, 15 Jan 2013 13:21:19 +0100
Subject: [PATCH] new post: Problems after disconnecting LUKS device

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+---
+layout: post
+title: Problems after disconnecting LUKS device
+date: 14.01.2013 23:28
+---
+
+Yesterday I got my 2TB backup disk. I formatted it and then used [LUKS][] to encrypt it and [LVM][] for the Volume Management.
+After I copied some files to the new disk, I unmounted the disk, unplugged it and ...
+
+### ... Oh, shit.
+
+I forgot to `cryptsetup luksClose` it.
+
+That's not a good thing to do. __Always remember to luksClose! It's so much easier__
+
+So after reconnecting the device, you can't really decrypt and mount it, because it did not get unmapped (`/dev/mapper/name` still exists and so do `/dev/name/*`)
+
+### No problem, we fix that!
+
+_(in the following my mapping name is `extern`, change accordingly)_
+
+First see current status, especially `Open count`
+
+    dmsetup info
+
+Now remove each mapped device (`-backup` and `-media` for me, I have 2 partiions on the disk):
+
+    dmsetup remove extern-backup
+    dmsetup remove extern-media
+
+Once again check `Open count`, it should be `0` now. If so, go on and remove the mapping:
+
+    dmsetup remove extern
+
+Now you got rid of all old mappings. Let's try to mount the disk again. Plug it in, then do:
+
+    cryptsetup luksOpen /dev/sdb2 extern
+
+Type your password.
+If the Volume Groups are missing, use:
+
+    vgscan
+    vgchange -ay extern
+
+Now you can mount your partitions:
+
+    mount /dev/extern/backup /mnt/backup
+
+Once you're done, deactivate the volume groups and close the crypt device:
+
+    vgchange -an extern
+    cryptsetup luksClose extern
+
+Now remember to always use these two commands after unmounting the device and use the following to open it:
+
+    vgchange -ay extern
+    cryptsetup luksOpen /dev/sdb2 extern
+
+I wrote a little helper script which does exactly these steps as needed. I'll include it in my next post, when I talk about how I use the setup for backups.
+
+[luks]: https://wiki.archlinux.org/index.php/LUKS
+[lvm]: https://wiki.archlinux.org/index.php/LVM