+# we want to run if any of the following things is true
+# - we have never run before
+# - var/lib/dpkg/status has been touched since the last run
+# - var/cache/apt/pkgcache.bin has been touched since the last run
+# - our last run ended with 'apt-get update failed'
+# - our last run has been more than MAX_AGE (23hrs) ago