eCryptfs is a cryptographic stacked Linux filesystem. eCryptfs stores
cryptographic metadata in the header of each file written, so that encrypted
files can be copied between hosts; the file will be decrypted with the proper
key in the Linux kernel keyring. There is no need to keep track of any
additional information aside from what is already in the encrypted file
itself. You may think of eCryptfs as a sort of "gnupgfs", or "gnupg as a
filesystem".

On Slackware, the Slackbuild script does not install the mount helper binaries
into /sbin, but to /usr/sbin. Because of this, using `mount -t ecryptfs` won't
work, and you must call the `[u]mount.ecryptfs*` binaries explicitly.

For an unprivileged user to use the `[u]mount.ecryptfs_private` executables,
it is necessary to set the suid bit on them, which the Slackbuild script also
does not do.