Hint on applications hanging at startup - culprit is DNS

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Hint on applications hanging at startup - culprit is DNS

Unread postby kubatyszko » Fri Jan 13, 2012 2:38 am

Just came up with some insight into why my cvd was failing to start and wanted to share the findings:

Added to wiki:

http://www.nekochan.net/wiki/IRIX_Insta ... olve_Order

=== Important note about DNS settings ===
If you use a domain that you own (or not) and your hosts don't actually resolve to real IP addresses (say you use abc.com for your website and iris.abz.com for the irix host which does not resolve to any IP address publicly) - IRIX may fallback to your domain's default IP address - in this case IP address for abz.com.

This may cause problems with certain applications using tooltalk (you would then see instances of "ttsession" in your ps output).

Examples may be cvd or rapidapp - those will show up in "ps" along with ttsessions instances but not display anything and look as if it were frozen.

Try running such app using "par", look for "gethostname" system calls and you should see dns resolution results.
Inspect those in order, see if the lookup resolves to your local machine's hostname and IP address - if it doesn't, then fix your DNS to either use local server, correct your /etc/hosts and resolution order in /etc/nsswitch.conf, or add your machine to the real DNS server for your domain.

Another way to verify this issue is to simply "ping something_nonexistent" from your terminal - if it resovles to ANY IP address (for nonexisting hostname), then you do have this problem.

The explanation is simple:

Applications like cvd or rapidapp use tooltalk protocol which establishes some connection (possibly over IP) - so it launches hostname lookup for your machine, if this doesn't resolve back to your exact machine the app will keep waiting hoping the other side will respond and seem frozen.


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