[PROBLEM]
Synaptic on Xubuntu 16.04.3:
Trying to install/upgrade some packages, I got the following error message:
W: Can't drop privileges for downloading as file '/root/.synaptic/tmp//tmp_cl' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
[SOLUTION]
Seems it's just a warning - and seems it's only generated after I accessed Changelogs of packages.