remote unlocking via ssh: interactive vs passphrase piping

Vincent Lefevre <[email protected]> Mon, 6 Jul 2026 16:11:11 +0200

Newsgroups	gmane.linux.debian.user
Message-ID	<[email protected]>

About remote unlocking of a LUKS partition,
/usr/share/doc/cryptsetup/README.Debian.gz says

 You can then unlock the disk remotely via SSH with

    ssh -tF ~/.luks/ssh.conf [email protected] cryptroot-unlock

 Or, using a local gpg-encrypted key file:

    gpg --decrypt ~/.luks/remote.key.gpg | ssh -TF ~/.luks/ssh.conf [email protected] cryptroot-unlock

In my case, "ssh -t ..." works fine:

X11 forwarding request failed on channel 0
Please unlock disk nvme0n1p3_crypt: 
cryptsetup: nvme0n1p3_crypt set up successfully

But if I do

  cat file | ssh -T ...

where "file" is a text file just containing the passphrase,
I get an error:

X11 forwarding request failed on channel 0
Please unlock disk nvme0n1p3_crypt
cryptsetup: cryptsetup failed, bad password or options?

What could be the cause?