Folks,

I've been using dm-crypt in such a way with USB keys and it works fine:

[insert USB key]
cryptosetup create /dev/mapper/sda1 /dev/sda1
mount /dev/mapper/sda1 /mnt/usb

When I'm done copying files to the USB key, I do, to take the USB key out:

umount /mnt/usb

This effectively unmounts the device (eg. df does not show it anymore).

Problem is, if I re-insert the USB key and try to mount it again, it does not work. cryptosetup reports that the device already exists.

Fair enough. I do: cryptosetup remove sda1

But then I try to re-create and it issues an error:

cryptosetup create /dev/mapper/sda1 /dev/sda1
"Command failed: Block device required"

If the computer is rebooted, then I can start from top and it works again.

What is the proper procedure to unmount an encrypted USB key so it can be mounted again later without rebooting the computer (this isn't Windows after all !! ;-)

Thanks.

I believe you need to do cryptosetup remove, then umount. Always do things symmetrically, like matching parentheses. mount -> cryptosetup -> cryptosetup remove -> umount.

That's it. So simple after all. I tried it and it works. Here it is:

Start:

[insert USB key]
cryptosetup create /dev/mapper/sda1 /dev/sda1
mount /dev/mapper/sda1 /mnt/usb

[do stuff with USB key]

umount /mnt/usb
cryptosetup remove sda1

[disconnect USB key]

goto Start

Oops, yeah, I had mine backwards, thinking of a loopback mounted file. But you definitely have it there.