root@katerina-XPS:~# apt-get source criu 
Reading package lists... Done
NOTICE: 'criu' packaging is maintained in the 'Git' version control system at:
https://anonscm.debian.org/git/collab-maint/criu.git
Please use:
git clone https://anonscm.debian.org/git/collab-maint/criu.git
to retrieve the latest (possibly unreleased) updates to the package.
Need to get 745 kB of source archives.
Get:1 http://archive.ubuntu.com/ubuntu xenial/universe criu 2.0-2ubuntu3 (dsc) [2068 B]
Get:2 http://archive.ubuntu.com/ubuntu xenial/universe criu 2.0-2ubuntu3 (tar) [733 kB]
Get:3 http://archive.ubuntu.com/ubuntu xenial/universe criu 2.0-2ubuntu3 (diff) [9512 B]
Fetched 745 kB in 0s (1073 kB/s)
gpgv: Signature made Τετ 30 Μάρ 2016 06:52:20 μμ EEST using RSA key ID 64792D67
gpgv: Can't check signature: public key not found
dpkg-source: warning: failed to verify signature on ./criu_2.0-2ubuntu3.dsc
dpkg-source: info: extracting criu in criu-2.0
dpkg-source: info: unpacking criu_2.0.orig.tar.gz
dpkg-source: info: unpacking criu_2.0-2ubuntu3.debian.tar.xz
dpkg-source: info: applying 4f609883a3a37946a2f8ab0957232a3e67cd9ddf.patch
dpkg-source: info: applying 7cf22c17fe08f71c2019cfcc73b1274d53bcfc36.patch
dpkg-source: info: applying 5c700c3e3999f1518941de679a9146fb215003f0.patch
dpkg-source: info: applying 5691a6b38c84d23707008d465bbb25ef3c8a57eb.patch
dpkg-source: info: applying 20f5024ac9cca9c5ea3faa694e89342ff0bb7661.patch
W: Can't drop privileges for downloading as file 'criu_2.0-2ubuntu3.dsc' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)