How to get list of dns server of <network> on Linux - Documentation does not seem to cover this

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I need to retrieve the DNS servers in use, from a group of Linux boxes. Looking at the documentation https://support.bigfix.com/inspectors/Networking%20Objects_Lin.html DNS property does not seem to be present.
I did find the equivalent to this for Windows platforms: “dns server of , Plural: dns servers Returns a list of DNS servers used by the local computer”. However this property is not applicable to Linux.
I guess I could come up with a code to retrieve values from “/etc/resolv.conf”, but is there a BigFix way of doing this ?

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You can use BigFix relevance to retrieve the values from your file, what parts do you need to get and how do you want to use it ?

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I am writing a fixlet to update DNS settings for a group of RHEL6 servers, IEM platform version is 9.2.
The old DNS servers are XX.XX.XX.XX and XZ.XZ.XZ.XZ, and I have already wrote a bash script to update the settings to YY.YY.YY.YY and YZ.YZ.YZ.YZ, everything is working nice so far.

I would like my fixlet to become relevant (applicable) if only XX.XX.XX.XX or/and XZ.XZ.XZ.XZ are detected, so I would not have to apply this fixlet again over and over to all the clients.

A BigFix way like “concatenation “,” of (addresses of dns servers of adapters of network as string)” like for Windows would have been an elegant way of doing this.

4

You can do the replacement without having to use a shell script - you can do that directly through BigFix action script if you like.

But to answer your question something like this should work for applicability

Q: exists lines whose (it contains "XX.XX.XX.XX" or it contains "ZZ.ZZ.ZZ.ZZ") of file "/etc/resolv.conf"
A: True
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5

@ gearoid : Thank you for your reply.
The reason I am using bash is because when my script is doing more than to only update this file, it is actually a post install script.

The problem with retrieving values form “/etc/resolv.conf” is that in some cases there are multiple entries, some of them commented out. #XX.XX.XX.XX may be already present.

/etc/resolv.conf may look like this:

search www.myDomain.org
#nameserver XX.XX.XX.XX
#nameserver XZ.XZ.XZ.XZ
nameserver YY.YY.YY.YY
nameserver YZ.YZ.YZ.YZ

or like this
search www.myDomain.org
nameserver XX.XX.XX.XX
nameserver XZ.XZ.XZ.XZ
#nameserver YY.YY.YY.YY
#nameserver YZ.YZ.YZ.YZ

6

So you need to exclude lines that start with # from your search ?
Is that all ?

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yes, that is correct.

Something like this:
exists lines whose (it contains “XX.XX.XX.XX” or it contains “ZZ.ZZ.ZZ.ZZ” and (not starts with “#”)) of file “/etc/resolv.conf”

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Q: exists lines whose ((it contains "XX.XX.XX.XX" or it contains "ZZ.ZZ.ZZ.ZZ") and character 0 of it != "#") of file "/etc/resolv.conf"
A: True
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9

Thank you @gearoid !
Much appreciated.

1 Like
10

Hi! I am facing the same scenario almost. However I would like to use bigifx to change the DNS servers in resolve.conf. Any tips on how to proceed?

Thanks in advance

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lines starting with “nameserver” eliminates the “#”

Q: (lines starting with “nameserver” of file “/etc/resolv.conf”)
A: nameserver%09xx.xx.xx.xxx
A: nameserver%09xx.xx.xx.xxx
A: nameserver%09xx.xx.xx.xxx
T: 744

vs

Q: (lines containing “nameserver” of file “/etc/resolv.conf”)
A: #nameserver%09xx.xx.xx.xxx
A: nameserver%09xx.xx.xx.xxx
A: nameserver%09xx.xx.xx.xxx
A: nameserver%09xx.xx.xx.xxx
A: ##nameserver%09xx.xx.xx.xxx

Eventually it gets to this.

Q: if (exists file “/etc/resolv.conf”) then if exists (lines starting with “nameserver” of file “/etc/resolv.conf”) then (following texts of firsts “nameserver” of lines starting with “nameserver” of file “/etc/resolv.conf”) as trimmed string else (“nameserver not found in /etc/resolv.conf”) else ("/etc/resolv.conf not found")
A: 101.69.101.253
A: 101.69.111.254
A: 101.69.111.11

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hello,

/etc/resolv.conf file conains nameserver entries. You can add new nameserver entries and get list of nameservers from this file