Julien and other MAT coders, perhaps you could subscribe to the Debian
package if not done already? 
http://packages.qa.debian.org/m/mat.html
(bottom left)
Package: mat
Version: 0.3.2-1
Usertags: goto-cc
In an attempt to build mat in a chroot (using pbuilder and cowbuilder), the
subsequent umount failed. This is due to the following process tree still left
running until after the build had completed:
20573 ?        S      0:00 /usr/bin/perl -w /usr/bin/exiftool
20610 ?        S      0:00  \_ /bin/sh /usr/bin/perldoc /usr/bin/exiftool
Please make sure that any subprocesses have exited properly.
Best,
Michael
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