I'm getting this choker on my newly-built Linux Mint 18.2 desktop after several attempts this week:

[bash]
clive@climate ~ $ sudo apt-get install texlive-latex-extra texlive-fonts-recommended texlive-fonts-extra git

[...]

clive@climate ~ $ git clone git://git.code.sf.net/p/gretl/git gretl-git
Cloning into 'gretl-git'...
remote: Counting objects: 153006, done.
remote: Compressing objects: 100% (32161/32161), done.
remote: Total 153006 (delta 123847), reused 148682 (delta 120378)
Receiving objects: 100% (153006/153006), 174.65 MiB | 2.76 MiB/s, done.
Resolving deltas: 100% (123847/123847), done.
Checking connectivity... done.
clive@climate ~ $ cd gretl-git
clive@climate ~/gretl-git $ sudo apt-get build-dep gretl
[sudo] password for clive:
Reading package lists... Done
E: Unable to find a source package for gretl
clive@climate ~/gretl-git $ apt-get build-dep gretl
E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied)
E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?

[/bash]