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Description of problem:
When passing DNS to dracut via "nameserver=x.x.x.x",
the dns provided may be duplicated, so there can be duplicated DNS items in the "/etc/resolv.conf".


Version-Release number of selected component (if applicable):
kexec-tools-2.0.7-38

How reproducible:


Steps to Reproduce:
1. In static network environment, pass the same DNS to dracut via nameserver=x.x.x.x" several times through "/proc/cmdline" or other ways like specified using directive DNS1/DNS2 in "/etc/sysconfig/network-scripts/ifcfg-<config>".

2. Configure /etc/kdump.conf to use network dump target(either nfs or ssh)
   Configure /etc/kdump.conf to enable "default shell". 
   kdumpctl restart

3. After crash, let the kdump progress fail(for example: shutdown remote network), then it will enter a shell. 

4. In the shell, "cat /etc/resolv.conf", and will find the duplicated DNS items passed in 1).


Actual results:


Expected results:
"/etc/resolv.conf" generated by dracut doesn't contain duplicated DNS items passed through "nameserver=x.x.x.x".

Additional info:
"/etc/resolv.conf" have some restrictions on the number of DNS items
effective, so it'd be better that this file contains no duplicated DNS items.

There is a patch("network/net-lib.sh: delete duplicated DNS items from "/etc/resolv.conf") posted:
https://github.com/dracutdevs/dracut/compare/master...dracut-mailing-devs:1461665111-7385-2-git-send-email-xlpang%40redhat.com

https://errata.devel.redhat.com/advisory/24112

dracut-033.436.el7 already contains:

commit a3204225884ba63aee94db345d5c38f1c872d6b7
Author: Xunlei Pang <xlpang>
Date:   Tue Apr 26 18:05:11 2016 +0800

    network/net-lib.sh: delete duplicated DNS items from "/etc/resolv.conf"

Reproduced with RHEL-7.2 GA.
Verified on RHEL-7.3 Alpha with dracut-033-450.el7, duplicate nameservers are not present in /etc/resolv.conf created by dracut.

Moving to VERIFIED.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-2530.html