For the record, an other case has been fixed about _apt sandboxing https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=806406
oem@u64:~$ getent passwd ..... _apt:x:123:65534::/nonexistent:/bin/false ** Bug watch added: Debian Bug tracker #806406 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=806406 -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to apt in Ubuntu. https://bugs.launchpad.net/bugs/1522675 Title: Can't drop privileges for downloading : _apt user not allowed Status in apt package in Ubuntu: New Status in dpkg package in Ubuntu: Confirmed Status in synaptic package in Debian: New Bug description: Recently we got new versions for synaptic 0.82+build1 & apt 1.1.3, but now get that error when installing/upgrading some packages: Setting up libc6-dbg:amd64 (2.21-0ubuntu5) ... Processing triggers for libc-bin (2.21-0ubuntu5) ... 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) From nautilus, i'm seeing a /root/ folder locked (x on its icon) and the folder is empty (no /.synaptic/ sub-folder or file), so the above error. ======================================================================= The real problem is : there is no _apt user on the system (see #808802 MV comments) grep -B2 _apt /var/lib/dpkg/info/apt.postinst # add unprivileged user for the apt methods adduser --force-badname --system --home /nonexistent \ --no-create-home --quiet _apt || true # Fixup any mistake in the home directory of the _apt user if dpkg --compare-versions "$2" lt-nl 1.1~exp10~; then usermod --home /nonexistent _apt ====================================================================== and also a workaround: sudo chown _apt /var/lib/update-notifier/package-data-downloads/partial/ ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: synaptic 0.82+build1 ProcVersionSignature: Ubuntu 4.3.0-1.10-generic 4.3.0 Uname: Linux 4.3.0-1-generic x86_64 NonfreeKernelModules: nvidia ApportVersion: 2.19.2-0ubuntu8 Architecture: amd64 CurrentDesktop: GNOME Date: Fri Dec 4 05:23:25 2015 SourcePackage: synaptic UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1522675/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp