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тАО11-25-2010 07:04 AM
тАО11-25-2010 07:04 AM
I have changed the IPs and hosts name of DNS servers on all of our HP-UX servers and Linux servers by modified configure files /etc/resolv.conf.
After DNS change, some servers didn't work properly, they still looking for the old DNS IPs and hostanmes. I need manually to flush DNS cache on Linux servers. But on HP-UX server, there is no cache for DNS, right?
Someone said, after DNS change, we need restart some processes to make the change take effect without system reboot. What's the processes and how to retart?
Someone said there is daemon pwgrd on HP-UX the same like Linux/solaris's nscd, we need run pwgrd to do some thing like "flush the DNS cache". If so, how? Just # /usr/sbin/pwgrd?
I know, this kind of question has been asked here so many times, but so far I didn't find a answer to fit my case. I don't wanna reboot server.
Thanks a lot. Any answers will be very appreciate.
-GL
Solved! Go to Solution.
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тАО11-25-2010 07:46 AM
тАО11-25-2010 07:46 AM
SolutionWhat exactly is failing or what is looking for the old server? Did you try a nslookup to some name/IP that are in the DNS tables?
I am not aware of DNS caching at the OS level when it comes to DNS clients, it is always a lookup. It is possible that you have a running application that has made a lookup when it started up and it is still using the name/IP of that first lookup. If that's the case you have to restart the application.
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тАО11-25-2010 07:52 AM
тАО11-25-2010 07:52 AM
Re: After change IPs and hostname of DNS server
Thanks a lot for your fast reply.
For the error "not work properly, still look for old DNS servers", I got this alert from our network support team, they sent me a bunch list of not working properly servers, some are linux servers and some a HP-UX servers. I have fished the linux server part via flush DNS cache by restart nscd daemond. But have no idea how to fix the problem on HP-UX servers. In ITRC, lots of people said, if you change the IPs of DNS server by modify /etc/resolv.conf, you have to restart some processes to make the change work. But they didn't mentiond which processes need be restarted and how?
-GL
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тАО11-25-2010 08:22 AM
тАО11-25-2010 08:22 AM
Re: After change IPs and hostname of DNS server
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тАО11-25-2010 08:28 AM
тАО11-25-2010 08:28 AM
Re: After change IPs and hostname of DNS server
You don't know which processes/daemond need be restarted after DNS change? If not, would you please provide me how to restart to make the change take effect without system reboot. If so, then would you please provide me how to use nslookup to check it's working or not AND how to fix if find incorrect one. BTW, /etc/resolv.conf is configured correct.
But, I'm sure there are bunch of HP-UX servers are not working properly, they are still lookup for the old DNS server, network team has show me the report.
Thanks.
-Gary
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тАО11-25-2010 08:49 AM
тАО11-25-2010 08:49 AM
Re: After change IPs and hostname of DNS server
And if my psychic powers were not so weak,
then _I _might be able to see that report,
too. As usual, showing actual evidence, that
is, actual commands with their actual output,
can be more helpful than vague descriptions
and interpretations, especially hearsay.
(Some people consider secret hearsay to be
especially unreliable.)
> [...] HP-UX servers [...]
Not a very detailed description of anything.
uname -a
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тАО11-25-2010 09:20 AM
тАО11-25-2010 09:20 AM
Re: After change IPs and hostname of DNS server
If your HP-UX server is only a ***DNS client***, there is nothing that you need to restart.
You may have read in other threads that you need to restart the pwgr daemon but that is only needed if you use NIS, it is not DNS related.
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тАО11-25-2010 02:46 PM
тАО11-25-2010 02:46 PM
Re: After change IPs and hostname of DNS server
-G
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тАО11-25-2010 05:13 PM
тАО11-25-2010 05:13 PM
Re: After change IPs and hostname of DNS server
Alternatively, you could ask the network team to turn off the old DNS servers (after all, everyone should be using the new ones, right?). Anything in your HP-UX boxes that rely upon those particular DNS servers will soon stop working!
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тАО11-26-2010 01:15 AM
тАО11-26-2010 01:15 AM
Re: After change IPs and hostname of DNS server
In HP-UX (at least 11.11 and older), each process will read /etc/resolv.conf once when it's starting up and then never again. If you modified resolv.conf while applications are running, those applications will still be using the old settings until they are restarted.
This behaviour is coded into the system's standard libraries (/usr/lib/libc.*), which are used by practically all programs, so essentially all programs will behave the same.
(The function that actually reads resolv.conf is called res_init(); if you want, you can use truss or a similar tool to verify e.g. whether a daemon re-executes this function or not if you send it a HUP signal. If you're a programmer and have never heard of this function, it is probably because the libc initialization code calls it for you before entering the main() function of your program.)
So it's not a matter of restarting one process or just a few processes; you must restart *all* long-running processes that use network hostnames in any way. The easiest way to do this is to reboot the system.
Because nslookup is a process, it will read the current resolv.conf settings whenever you start it. It will tell you how any new processes will do DNS lookups, but not what the old processes are doing.
MK