Red Hat Bugzilla – Bug 490943
cups doesn't pick up printers on network change
Last modified: 2010-06-28 07:30:58 EDT
Every day I get on the vpn in the office, and when I want to print something, the print dialog shows my home printer (correctly marked as unplugged or offline), and none of the office printers. I do have the correct BrowsePoll entry in cupsd.conf. Restarting cups makes all the printers appear. It would be really nice if that wasn't necessary.
Can we make cups listen for network changes and be smart about this ?
Surely not bug #354071 *again*?
Hmm, I can't reproduce this here with the same recipe as for bug #354071. That bug was that we didn't reinitialise the resolver before a lookup if it failed last time, so lookups that failed before the correct nameserver was added to /etc/resolv.conf were still failing (our resolver doesn't watch for changes to that file).
Please attach /etc/cups/cupsd.conf.
Created attachment 336164 [details]
You should be able to see output from this:
grep '^E.*cups-polld' /var/log/cups/error_log
Can you let me know what the error messages are?
error_log has tons and tons of
E [23/Mar/2009:12:36:55 -0400] [cups-polld cups.bos.redhat.com:631] Unable to connect to cups.bos.redhat.com on port 631: Host name lookup failure
E [23/Mar/2009:12:37:25 -0400] [cups-polld cups.bos.redhat.com:631] Unable to connect to cups.bos.redhat.com on port 631: Host name lookup failure
E [23/Mar/2009:12:37:55 -0400] [cups-polld cups.bos.redhat.com:631] Unable to connect to cups.bos.redhat.com on port 631: Host name lookup failure
E [23/Mar/2009:12:38:25 -0400] [cups-polld cups.bos.redhat.com:631] Unable to connect to cups.bos.redhat.com on port 631: Host name lookup failure
E [23/Mar/2009:12:38:55 -0400] [cups-polld cups.bos.redhat.com:631] Unable to connect to cups.bos.redhat.com on port 631: Host name lookup failure
While at the same time, dig cups.bos.redhat.com finds it just fine.
What's going on in general here is that when cups-polld started, you didn't have nameservers for the VPN. At this point, resolving cups.bos.redhat.com fails. However, glibc will remember that there is no way to resolve that hostname and future calls will *also* fail.
Then, once the VPN is up and the nameserver added to /etc/resolv.conf, newly started applications can start to resolve VPN hosts. But cups-polld can't, because the glibc resolver still remembers not to try resolving that hostname.
The fix is to get cups-polld to call res_init() each time it resolves the hostname if it failed last time, and that's what we've done for Fedora 9 and 10.
However, it has now broken in Fedora 11. The reason seems to be that getaddrinfo() is no longer returning EAI_FAIL in this case, but EAI_AGAIN -- *and* it is still caching the failure.
It seems quite wrong to me that EAI_AGAIN is saying "try again, but reinitialise the resolver first" -- this is meant to be indicating a *temporary* failure and so the failure should not be cached. At least, that seems to be what common sense would dictate; perhaps the standard says something different.
So, holding off judgement for the moment on whether this is a cups bug or a glibc bug, I've built cups-1.4-0.b2.12.fc11 which will reinitalise the resolver if it sees EAI_AGAIN.
Changing component to glibc:
Is getaddrinfo() returning the wrong error code in this situation?
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.
More information and reason for this action is here:
This is still behaving in the same way: see bug #567353.
Is getnameinfo/getaddrinfo() returning the wrong error code in this situation?
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