26

While I was away from my computer, my encrypted USB drive got accidentally unmounted somehow (although it was still physically connected at the time). I haven't been able to recover (haven't tried a reboot yet). I have now completely disconnected the device, but I still get "Device or resource busy" when I try to remove the dangling entry in /dev/mapper. Can I reconnect and mount the drive without a reboot?

Here's what I have tried (long name changed to "xxxxx")...

$ sudo dmsetup ls
luks-xxxxx (252:1)
luks-yyyyy (252:0)

$ sudo umount /dev/mapper/luks-xxxxx
umount: /dev/mapper/luks-xxxxx: not mounted

$ sudo fuser --kill /dev/mapper/luks-xxxxx
$ echo $?
1

$ sudo dmsetup info -c luks-xxxxx
Name       Maj Min Stat Open Targ Event  UUID
luks-xxxxx 252   1 L--w    1    1      0 CRYPT-LUKS1-xxxxx-luks-xxxxx

$ sudo dmsetup remove luks-xxxxx
device-mapper: remove ioctl on luks-xxxx failed: Device or resource busy
Command failed

After reconnecting the device...

$ sudo cryptsetup luksOpen "/dev/sde1" "luks-xxxxx"
Device luks-xxxxx already exists.

[EDIT] I solved the problem, this time, by closing a GUI text editor which had no open files, but had been launched from a folder on the device in question. So the question becomes more specific: How can you identify which application is holding the device open?

Bear in mind that lsof doesn't seem to present an easy solution because, once the device is disconnected, the associated names provided by lsof no longer include the name of the disconnected device.

  • Running into the same problem but on CentOS. Found this link: krenel.org/… but I don't show the device mounted – Lars Nordin Jun 9 '14 at 11:48
  • Seems remarkably similar to this closed-as-fixed bug report: bugs.debian.org/cgi-bin/bugreport.cgi?bug=574126 – nobar Mar 9 '16 at 20:50
  • Word of warning: Mounting with sudo, as shown here, may prevent you from ejecting normally using the user-space file-manager. – nobar Jun 11 '17 at 22:31
23

After two years of fighting with this, I think I've finally cracked it completely!

dmsetup ls gives you the data you need:

$ sudo dmsetup ls
luks-xxxxx (252:1)

then

sudo lsof |grep 252,1

It seems that sudo may be critical here -- at least in some cases.


This should give you the information necessary to close all open files on the device -- including names of open files and process IDs for the offending applications. You may be able to simply go to those apps and close them, but a brute force approach might be something like:

kill -9 (process ID)

Once you've closed all the files, some of the command-line tools shown in the question may be necessary in order to close down the existing mount before it can be reopened normally.

  • 4
    Notice the slight translation required: (252:1) becomes 252,1. – nobar Aug 17 '16 at 23:04
11

Try to stop LVM group prior to stop cypher:

lvchange -a n [LVM_Group_name]

then

cryptsetup -v luksClose [LUKS_name]

Sample:

lvchange -a n My_vg_crypt
cryptsetup -v luksClose My_Crypt
  • 1
    Use @nobar's answer first (but try kill before kill -9). However @nobar's solution wasn't sufficient for me - it seems that the kernel itself had the device open because of the LVM device mappings - which this answer resolved. – Tom Hale Nov 15 '16 at 9:27
  • +1 In my case the accepted answer's grep didn't find any matches, but this worked. – user000001 Jan 18 at 9:52
4

next time try a lazy umount

umount -l /<folder>

This works for me most of the times, especially useful with hung-up NFS-drives.

  • I tried this, but didn't help for the problem at hand. I'm assuming that you can't actually use LUKS over NFS, and that this was just a shot-in-the-dark suggestion. – nobar May 9 '16 at 13:38
  • this was exactly my problem, i forgot that i need to unmount mapped storage first :D – holms Dec 18 '16 at 10:25
2

Here is how I manage to solve this problem on Linux Mint 17.3 (~Ubuntu Trusty):

  1. remove the device from device-mapper

    $ sudo dmsetup remove luks-xxyyzz
    
  2. map it back

    $ sudo cryptsetup open /dev/sdc1 luks-xxyyzz
    Enter passphrase for /dev/sdc1:
    

Now the devices is accessible.

  • 2
    This post might be helpful to someone, but as noted in the question -- sometimes dmsetup remove reports "Command failed". – nobar Mar 8 '16 at 23:36
0

I was in a similar situation but could not solve the problem by removing the luks-xxxx device. Instead I had to remove ubuntu--vg-root.

My situation was:

  • I accidentally removed the device before it was locked.
  • Trying to lock or remove the luks device after the fact failed with a busy error message.
  • Unlocking the same device failed because a device with the same name already existed.
  • lsof did not show any open handles for the device.

What did help was to unplug the physical device and remove the ubuntu--vg-root device with the following command:

sudo dmsetup remove ubuntu--vg-root

At that point I was able to normally activate and decrypt the external device again with my usual setup:

udisksctl unlock -b /dev/sda3
sudo lvchange --activate y ubuntu-vg/root

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