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Linux : understanding ifcfg-*** files  from directory  #/etc/sysconfig/network-scripts

Posted on 2016-07-28
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Last Modified: 2016-08-24
In my office one of the de-commissioned DB server hand over to me for the purpose of using other software like Apache.
when I see the details about network  in directory # /etc/sysconfig/network-scripts, I could see list below list

 # /etc/sysconfig/network-scripts
 ifcfg-bond0
 ifcfg-bond
 ifcfg-bond:
 ifcfg-bond2
 ifcfg-bond3
 ifcfg-bond4
 ifcfg-eth286_2.4
 ifcfg-eth646_.4
 ifcfg-ib0
 ifcfg-ib0.8004
 
 ifcfg-ib
 ifcfg-ib.8004

ifcfg-lo

=============
As typical Apche server admin, I know only files - ifcfg-lo & ifcfg-etho,
where usefully I edit for DNS server settings.

I have checked all files, could not find DNS- server details entries in neither of the files.

please let me know
- The importance of above files
- where to find DNS details in such scenario
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Question by:mac_g
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by:savone
savone earned 1000 total points
ID: 41732905
There are many different kind of ifcfg files.  Some of the ones you have listed are network bonds, you can good that to find out more about them.

My recommendation would be to reinstall Linux on the server.  Since you do not know what the previous configuration was, it will be an uphill battle to reconfigure it for your purpose.
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by:mac_g
ID: 41732988
@savOne, i am not looking advice to re-install.

But to understand when/why/how .. these kind of configurations are required for server.
what is it significance.
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by:savone
savone earned 1000 total points
ID: 41733744
Interface bonding is a very large topic for someone to teach you by typing here.  There is thousands and thousands of pages of documentation on the internet.  I told you what they were, and here are some links to help you learn more.

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/s2-networkscripts-interfaces-chan.html

http://www.enterprisenetworkingplanet.com/linux_unix/article.php/3850636/Understanding-NIC-Bonding-with-Linux.htm

That should get you started. As I said, it is way too much to type here, especially if you do not know anything about bonded interfaces.  It would take me days to type it all out.  I hope that helps.
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Author Comment

by:mac_g
ID: 41735198
thanks for your above links for basic understanding.

I could not find DNS IP details any of the above files.

typical it should be available in /../network-scripts/ ifcfg-eth0.


please advice where to find such details for the environment like this.
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Expert Comment

by:savone
ID: 41735261
I am not sure what distro your have, but look in /etc/resolv.conf
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by:mac_g
ID: 41735319
OS : Oracle Linux 6.5

resolve.conf anyway will have. this CONF file reflect the values which we have provided in -/../network-scripts/ ifcfg-eth0.

In my case I could not find the DNS server details any of the files in above dir.
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Accepted Solution

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savone earned 1000 total points
ID: 41735342
DNS settings do not have to be set in a ifcfg-xxx files.  They can be set globally in the /etc/resolv.conf file.
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Author Comment

by:mac_g
ID: 41735419
@SAvOne
for  your info..
if you edit resolv.conf with new DNS value, then, whenever the system rebooted the OLD DNS value will re-appear. for that the permanent changes to be done on ifcfg-xxx files.
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by:Duncan Roe
Duncan Roe earned 1000 total points
ID: 41735682
If the old ones are re-appearing, it may be that dhcpcd is doing that. Use pgrep dhcpcd to see if it is running
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Expert Comment

by:savone
ID: 41735774
@Mac_g

You said there are no DNS settings in the ifcfg files, now you saying the settings in the ifcfg files are overwriting /etc/resolv.conf.

Are you using DHCP?  Are you running network manager?  We need accurate information about your system to help you troubleshoot.
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Author Comment

by:mac_g
ID: 41735803
the explanation above I gave you <<if you edit resolv.conf with new DNS value, then, whenever the system rebooted the OLD DNS value will re-appear. for that the permanent changes to be done on ifcfg-xxx files>>>, this is general information the way Linux OS runs in any typical environment, this is just to share info for your understanding.

what I am looking is now, other than resolv.conf file, DNS values should be available in **eth0 file. in my case I could not find that. Where could I find ?

as u requested above info, 1) we are not using DHCP &  2) we are using Network mgr

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