Comment 5 for bug 1547984

same cause of this bugs:

https://bugs.launchpad.net/ubuntu/+source/update-notifier/+bug/1570141
https://bugs.launchpad.net/ubuntu/+source/pepperflashplugin-nonfree/+bug/1551511

I install a new ppa and run apt-get update and get this error:

W: Can't drop privileges for downloading as file '/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_xenial_InRelease' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permissão negada)

I am using Ubuntu 16.0 Beta Final, with all the updated packages

The permissions:

fabio@luzfcb:~$ ls -dl /var/cache/apt/archives/partial/
drwx------ 2 _apt root 4096 Abr 11 21:13 /var/cache/apt/archives/partial/

fabio@luzfcb:~$ ls -dl /var/cache/apt/archives/
drwxr-xr-x 4 root root 28672 Abr 13 19:57 /var/cache/apt/archives/

fabio@luzfcb:~$ 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

fabio@luzfcb:~$ sudo apt-get update
Atingido:1 http://repo.steampowered.com/steam precise InRelease
Obter:2 http://archive.ubuntu.com/ubuntu xenial InRelease [247 kB]
Ign:3 http://dl.google.com/linux/chrome/deb stable InRelease
Atingido:5 http://archive.canonical.com/ubuntu xenial InRelease
Atingido:6 http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease
Atingido:7 http://dl.google.com/linux/chrome/deb stable Release
Atingido:9 http://ppa.launchpad.net/gregory-hainaut/pcsx2.official.ppa/ubuntu xenial InRelease
Atingido:10 http://ppa.launchpad.net/gwendal-lebihan-dev/hexchat-stable/ubuntu xenial InRelease
Atingido:11 http://ppa.launchpad.net/indicator-brightness/ppa/ubuntu xenial InRelease
Ign:4 http://toolbelt.heroku.com/ubuntu ./ InRelease
Atingido:12 http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu xenial InRelease
Atingido:14 http://ppa.launchpad.net/saiarcot895/myppa/ubuntu xenial InRelease
Obter:15 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial InRelease [17,5 kB]
Atingido:13 http://toolbelt.heroku.com/ubuntu ./ Release
Obter:17 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial/main amd64 Packages [2.840 B]
Atingido:18 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Obter:19 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial/main i386 Packages [2.840 B]
Obter:20 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial/main Translation-en [1.260 B]
Atingido:21 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Atingido:22 http://archive.ubuntu.com/ubuntu xenial-security InRelease
Obter:23 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages [1.184 kB]
Obter:24 http://archive.ubuntu.com/ubuntu xenial/main i386 Packages [1.179 kB]
Obter:25 http://archive.ubuntu.com/ubuntu xenial/main amd64 DEP-11 Metadata [635 kB]
Obter:26 http://archive.ubuntu.com/ubuntu xenial/main DEP-11 64x64 Icons [404 kB]
Obter:27 http://archive.ubuntu.com/ubuntu xenial/universe amd64 Packages [7.543 kB]
Obter:28 http://archive.ubuntu.com/ubuntu xenial/universe i386 Packages [7.524 kB]
Obter:29 http://archive.ubuntu.com/ubuntu xenial/universe Translation-en [4.361 kB]
Obter:30 http://archive.ubuntu.com/ubuntu xenial/universe amd64 DEP-11 Metadata [1.846 kB]
Obter:31 http://archive.ubuntu.com/ubuntu xenial/universe DEP-11 64x64 Icons [7.482 kB]
Baixados 32,4 MB em 2min 19s (233 kB/s)
AppStream cache update completed, but some metadata was ignored due to errors.
Lendo listas de pacotes... Pronto
W: Can't drop privileges for downloading as file '/var/lib/apt/lists/partial/archive.ubuntu.com_ubuntu_dists_xenial_InRelease' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permissão negada)
W: http://dl.google.com/linux/chrome/deb/dists/stable/Release.gpg: Signature by key 4CCA1EAF950CEE4AB83976DCA040830F7FAC5991 uses weak digest algorithm (SHA1)
W: http://toolbelt.heroku.com/ubuntu/./Release.gpg: Signature by key 150C6249147592DE6D91981CC927EBE00F1B0520 uses weak digest algorithm (SHA1)