Improve error for DNS lookup failures

[Sergio Cazzolato]

I get this assertion when I run the command unity8-snap-install in my zesty vm.
This happens with the today's zesty daily image.

sudo snap install unity8-session --edge --devmode
error: cannot perform the following tasks:
- Fetch and check assertions for snap "unity8-session" (439) (Get https://assertions.ubuntu.com/v1/assertions/snap-revision/rjPkjvvl9AezpBRMi_cxP6yLUf7hychxwsOg7CT68Ygr9JnccHmvCfymWqUEZGTt?max-format=0: dial tcp: lookup assertions.ubuntu.com: no such host)

[Michał Sawicz (saviq)]

This looks like a network error on your side:

 host assertions.ubuntu.com
assertions.ubuntu.com has address 162.213.33.203
assertions.ubuntu.com has address 162.213.33.202

[Sergio Cazzolato (sergio-j-cazzolato)]

I changed the nameserver to 8.8.8.8, rebooted the machine and I ran again.

ubuntu@zesty-unity8-snap:~$ sudo snap install unity8-session --edge --devmode
[sudo] password for ubuntu:
error: cannot perform the following tasks:
- Fetch and check assertions for snap "unity8-session" (439) (Get https://assertions.ubuntu.com/v1/assertions/snap-revision/rjPkjvvl9AezpBRMi_cxP6yLUf7hychxwsOg7CT68Ygr9JnccHmvCfymWqUEZGTt?max-format=0: dial tcp: lookup assertions.ubuntu.com: no such host)

It is happening that I download the 100 % of the snap without any problem.

[Jean-Baptiste Lallement (jibel)]

I had the same error earlier this week and name resolution worked fine.

[Michael Vogt (mvo)]

I looked into this a bit and found some theories about leaking fds that can confuse the resolver. I wrote testcode that spawns 50k go routines and never had any issues und 16.10.

I also noticed you run zesty - maybe it is related to that?

[Sergio Cazzolato (sergio-j-cazzolato)]

Yes running in zesty, today I could install unity8-session snap.

[Daniel Manrique (roadmr)]

Hello, is this error still happening?

[Facundo Batista (facundo)]

Hello! The issue title is confusing.

I'm failing to understand how "max-format is not a positive integer assertion" relates to the (apparent) network problem explained in the description and subsequent comments.

Could you please clarify that? thanks!