I don't have a 2013 N7, but I do have an N5 that I successfully rooted using linux after the 5.1 update. I installed android-tools-adb and android-tools-fastboot from
this ppa. I'm actually running Debian sid, but had no trouble with those packages. I have never been able to straight up install the Android SDK and have it recognize my Java and so on properly, so I went the lazy route and used those tools.
From there, you can go
here and start with "Check if you have permission for your device" (or you can ignore my entire first paragraph and follow that thread).
Once you can see your device using adb, you should be able to follow the directions to unlock your bootloader or root in
this thread. Only the prerequisite part of that post is for Windows only.
ETA: If you have a custom recovery already installed, you might be able to just flash SuperSu. That works on the N5. I'm not sure about the N7.