Same here [Ubuntu 12.04 - GTX460 - Driver 310 ("experimental" for Ubuntu-"recommended" for Steam)]. Also some rare times, loads the map and crashes just after you click left click to take a character (already started game/map). I don't get any crash or error message after the crash. Reoppening the Steam app didn't help. Rebooting some times solves the problem.

I think it's due to video ads in the MOTDs. Something known as Pinion, that a lot of servers use.
I had the same crashes, and I checked netstat right after the crash.
An interesting IP was 216.52.92.45
216.52.92.45 resolves to ads.adap.tv
I thought it must be Pinion, since those are known for their video ads.
Searching adap.tv pinion on google finds a nice pastebin http://pastebin.com/0WaMsf29 that shows that Pinion is indeed using that ad provider.

Valve, I know people have a right to put ads on their servers, and I know that you guys work with Pinion as seen on http://www.l4d.com/blog/post.php?id=10534
Can you please do something about this crash?

Hi All,
Glad to ehre that I am not alone with this issue :D
@pizzadude Thank you for tracking down the issue :P I have noticed as well some additional errors on the logs file: apparently some library (.so files) are missing: the matchmaking.so and client.so , but I do'nt know if there are critical error that lead to the segfault or jsut some errors that the game can cope with. In all case for the libraries issue I am not alone xD https://github.com/ValveSoftware/Source-1-Games/issues/450

@verdegr I have "almost" the same setup: GTX 560, and Ubuntu 13.04. But at this time it is not sure that the issue is related to hardware but let's wait for investigatiosn results :P

Just adding the log file as a gist ==> https://gist.github.com/elthommy/6053250

Sounds like https://github.com/ValveSoftware/Source-1-Games/issues/827 to me.

I can confirm L4D2 crashing this way after loading the map. My server's motd.txt content was http://hehoe.de/mcs/. The host.txt contained http://hehoe.de/mcs/l4d2server/banner.png. I emptied the files and all is well again. However, the server's message Dropped client (No Steam logon) was somewhat misleading.

I think I have the same issue. Maps load fine Single Player mode but online Campaign game crashes after loading map. Turning secure mode off in Launch Options "-insecure" and I can play online Campaign with no crashes.

"-insecure" will only alllow you to join non VAC (cheat protected) servers though.

• I should also note my VAC status is "In good standing" and online Campaign works fine in Windows.

AMD Phenom II X6 1100T 3300 Mhz
RAM: 7989 Mb
3.10.3-1-ARCH Linux (64 bit)
steam-runtime-release-i386_2013-06-28
Driver: NVIDIA Corporation GeForce GTX 560/PCIe/SSE2
Driver Version: 4.3.0 NVIDIA 319.32

I get this crash too, (Arch x64, AMD GPU with 13.8-1 drivers, installed from AUR). My friends confirmed the motd contained some kind of video ads. Can supply more info if needed, but it seems as if it has been provided by previous posts.

Tested further and the reason insecure servers work for me is none of the insecure servers seem to have any videos/ads in their MOTD, at least I didn't run into any in a day and a half of playing. Today about half the secure servers have video ads and half don't so its basically a gamble each time I play online Campaign with secure servers. 50/50 chance to crash. Yesterday every single secure server was a crash. I tried installing lib32-flashplugin but it didn't do anything and I already had libflashplayer.so inside ~/.steam/bin/plugins folder. I think we need "cl_disablehtmlmotd" added, and working, to this game to prevent this crashing. But for now i'll just play in insecure mode instead of gambling each time I start a new Campaign level, just playing with friends so I'm not worried about any cheaters.

Hey guys; I think I might have found a solution but I would like for people to try it out.

1. I created a syslink from libflashplayer.so and put it in ~./steam/ubuntu12_32/plugins

2. I then from root gave me the user the permissions to use it (the syslink).

3. Make it executable

I have been jumping around servers and haven't crashed yet; but I need to test this on a larger scale you know?

I'll be checking back in and hopefully it will be good news.

So, I followed the instructions from some posts in here, and found out something... it looks like I made a mistake when installing steam, and put a symlink to the 64bits version of libflashplayer.so (I'm using linux amd64) in the ubuntu12_32 folder... which seems to be the reason l4d2 crashed when loading (flash) ads, I guess...
There seem to other similar reports too, just google "linux l4d2 crashes online site:github.com/ValveSoftware" and you'll find them.
And btw, isn't it kind of dangerous to put flash ads? Vulnerabilities in flash could be used to install malware on our machines...
I hope this helps :)

A couple months ago, L4D2 on linux never had this instant-crash-on-load behavior for multiplayer matches, but now it occurs more than 95% of the time if I attempt to join any online match as soon as the program loads. However, if I load a single player campaign match, I am then able to disconnect from that any join any multiplayer match without issue. I have not investigated any correlation between that and the presence of motd's (iirc, there's a way to disable html motd's anyway), but based on the behavior I'm seeing, in my case, it's likely some other issue.