[dm-crypt] cryptsetup luksClose

Marc Schwarzschild ms at TheBrookhavenGroup.com
Thu Jan 19 16:30:26 CET 2012

Thank you.

--- January 18, 2012 Milan Broz sent: ---

  On 01/17/2012 10:31 PM, Marc Schwarzschild wrote:
  > Thank you.  I gather from this that I can safely halt or reboot
  > while a disk is mounted, right?
   From the LUKS metadata point of view yes (there will be still
  encryption key in memory but that's different problem).
   From the filesystem POV above LUKS - it depends. If it is remounted
  read-only, there should be no data loss on [un]expected reboot.
  (If you reboot while some write IOs are in-flight, of course you get
  some corruption.)
  Anyway, distro initscripts should handle this during controlled
  shutdown for all mounted devices.
  > --- January 17, 2012 Milan Broz sent: ---
  >    On 01/16/2012 03:48 PM, Marc Schwarzschild wrote:
  >    >  I am setting up an external USB encrypted drive. I can mount it
  >    >  manually after I boot the computer. I understand that I must
  >    >  issue the 'cryptsetup luksClose' after I umount the disk. How do
  >    >  I arrange for this as part of the Debian halt process so it
  >    >  happens automatically when the server is shutdown?
  >    It is not cryptsetup job, it should be part of initscripts/systemd
  >    to correctly unmap active devices on shutdown.
  >    (Usually it tries to unmap all crypto disks except device
  >    with root fs which is just remounted read-only. Recent systemd is able
  >    to unmouteven root device properly.)
  >    For hot-plugged disks it is usually handled by some GUI service,
  >    usually based on udisks.
  >    >  What happens
  >    >  if there is a power failure and 'cryptsetup luksClose' was not
  >    >  executed?
  >    For LUKS, no need to worry after power failure - luksClose
  >    just remove kernel mapping (kernel state) it doesn't touch
  >    on-disk metadata at all.
  >    (Of course there can be some filesystem damage after power failure,
  >    but that's not LUKS related, it can happen even for unencrypted fs.)
  >    Milan


Marc Schwarzschild 212-580-1175 The Brookhaven Group, LLC

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