Steam won't download games on Ubuntu (why and how to fix)

[2Weak2Live]

I had a persistent problem with Steam not downloading games on Ubuntu, even on the same machine and same network where it worked fine under Windows (both 7 and 10). Here's an explanation of why and how to fix it, since most people will not be able to diagnose it.

Background:

Like most big data providers, Steam has a lot of servers hosted at various ISPs. When you download a game, you're directed to servers that are topologically closer to you--usually ones hosted by the ISP you use. In my case, this is Comcast, and Steam uses the host name cdn.comcast.cs.steampowered.com.

Ubuntu Desktop uses a caching DNS server called dnsmasq. Besides providing caching services, it captures advertised hostnames on the network, allowing you to refer to other machines by name without having to set up DNS.

Symptom:

You'll get dialog windows and messages in the Steam log file saying that connections timed out. No downloads will actually work.

Interestingly, nowhere does it explicitly tell you that it's actually the DNS query that's timing out, as opposed to the connection to the actual content server. This confused me quite a bit.

The problem:

Steam's DNS and dnsmasq don't get along. The list of DNS records for cdn.comcast.cs.steampowered.com is long enough that the response doesn't fit in a UDP packet. Normally this is retried transparently over TCP and works fine. However, dnsmasq stalls and times out on this request. (Don't ask me why. I haven't debugged it--yet.) As a result, all attempts to connect to the Steam content servers fail, and no downloads occur.

Note: I've only run the Steam client on Ubuntu 14.10 and 15.04. I do not know whether this problem affects other versions.

Workaround:

The obvious workaround is to stop using dnsmasq. However, it's somewhat hardwired into Ubuntu. Here's what I did:

# apt-get install unbound # do this first or you'll be sad
# cd /etc/NetworkManager
# service NetworkManager stop
# vi NetworkManager.conf # or whatever editor you want; I don't care
[change "dns=dnsmasq" to "dns=unbound"]
# rm /etc/resolv.conf # don't forget this
# service NetworkManager start

Now all your DNS queries should go through your local unbound server (at 127.0.0.1 a.k.a. localhost), retries over TCP should work as expected, and Steam should be able to download just fine. You can test it with:

# nslookup cdn.comcast.cs.steampowered.com

If that hangs or returns SERVFAIL or REFUSED, you still have a problem.

[DrGrant]

I had a similar problem: my ubuntu's steam WAS actually downloading games, but only few megabytes per hour (a peak of 4/5 MB for a few seconds, and then nothing and nothing for many minutes), the only workaround was to pause and restart the download everytime (so to kick start a brief peak), but this solution you provided fixed it completely! Many thanks! :)

[2Weak2Live]

Originally posted by Vgnrchst:

I had a similar problem: my ubuntu's steam WAS actually downloading games, but only few megabytes per hour (a peak of 4/5 MB for a few seconds, and then nothing and nothing for many minutes), the only workaround was to pause and restart the download everytime (so to kick start a brief peak), but this solution you provided fixed it completely! Many thanks! :)

What version of Ubuntu? They recently closed my ticket due to inactivity, and because they theorize it's "probably" fixed in a later version. For several reasons, I've generally given up and play games under Windows now.

[Forcen]

You should post this here: http://steamcommunity.com/app/221410/discussions/ then the linux people might see it.

Or post it here: https://github.com/ValveSoftware/steam-for-linux/issues?q=is%3Aopen
https://wiki.ubuntu.com/Valve

Are you sure this is not an issue with the comcast CDN? Tried another steam content server?