apt-mirror/apt-mirror — pull request #36 by georgemarselis (2014-09-05 12:37:32+00:00)
Title: flock() fails to establish a lock on remotely mounted directories.

apt-mirror uses flock() to establish a lock. as per http://perldoc.perl.org/functions/flock.html
"Note also that some versions of flock cannot lock things over the
network; you would need to use the more system-specific fcntl for that."

So I propose this try flock/then try fcntl approach, so apt-get can be used with network mounts