[Indimail-support] Neat trick to bypass /etc/resolv.conf, use your own custom resolv.conf to use dnscache

[Manvendra B. <mbh...@gm...>]

I had a situation where I am running dnscache on local laptop running
indimail. However my resolv.conf would get updated by NetworkManager
or by vpn client. There are solutions to modify have NetworkManager
scripts / dhclient scripts / interface startup scripts to have
nameserver as 127.0.0.1, but I found those solutions different for
different distros. Here is a neat solution using unshare command from
util-linux. This command is available on centos, rhel, debian, ubuntu.
This is how you do it

1. Modify svscanboot to call unshare --mount e.g.
    exec unshare --mount env - PATH=$PATH \
       SCANINTERVAL=$SCANINTERVAL SCANLOG="" \
        STATUSFILE=$STATUSFILE \
         /usr/sbin/svscan $SERVICEDIR

2. Modifed svscan to execute the following command before calling supervise
    /usr/bin/mount --bind /etc/indimail/resolv.conf /etc/resolv.conf

3. in /etc/indimail/control have the following entry
    nameserver 127.0.0.1

Now all services started by svscan will transparently use
/etc/indimail/resolv.conf as /etc/resolv.conf

There are many other things you can do with unshare. You can use a
totally different hostname, domain name on per process basis

you can find the mount point in /proc/$pid/mountinfo where pid is the
process id of svscan process.

Read more about unshare at
http://blog.endpoint.com/2012/01/linux-unshare-m-for-per-process-private.html

-- 
Regards Manvendra - http://www.indimail.org
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