dnsmasq - improper handling of resolv.conf

[rmcgonegal@…]

The symptom is quite often than name lookup fails.

Because the dnsmasq start() command appears to mishandle the sym link /tmp/resolv.conf, the nemserver entries end up in the wrong file and are not accessible to dnsmasq while running.

/etc/init.d/boot has

touch /tmp/resolv.conf.auto
ln -sf /tmp/resolv.conf.auto /tmp/resolv.conf

This creates /tmp/resolv.conf.auto as the actual file, and /tmp/resolv.conf.auto as the sym link to it

/etc/config/dhcp has

option 'resolvfile' '/tmp/resolv.conf.auto'

/etc/init.d/dnsmasq has

append_parm "$cfg" "resolvfile" "-r"

which results the following added to the runstring of dnsmasq

-r /tmp/resolv.conf.auto

which is defined as
-r, --resolv-file=path Specify path to resolv.conf (defaults to /etc/resolv.conf)

So dnsmasq uses /tmp/resolv.conf.auto as the file with the nameservers in it

However, in the /etc/init.d/dnsmasq file itself

In the stop command it does

[ -f /tmp/resolv.conf ] && {

rm -f /tmp/resolv.conf
ln -s /tmp/resolv.conf.auto /tmp/resolv.conf

}

which deletes the sym link and then re-creates it, which does nothing to the contents of the file.

In the start command it does

rm -f /tmp/resolv.conf
DNS_SERVERS="$DNS_SERVERS 127.0.0.1"
for DNS_SERVER in $DNS_SERVERS ; do

echo "nameserver $DNS_SERVER" >> /tmp/resolv.conf

done

which deletes the sym link and then creates a real file with the nameservers in it

Net result is that there are two files, however the one with the nameservers in it is not used by dnsmasq

The fix is to replace the line in dnsmasq start()

rm -f /tmp/resolv.conf

with the line

echo -n "" > /tmp/resolv.conf

This will result in one file and a sym link to it, and the file contents will be removed during a start.

[anonymous]

Actually, after testing this, it is an incomplete fix. Because udhcpc only runs when the interface comes up, but you can do a dnsmasq restart anytime, the above fix ends up correct after a reboot, but a subsequent dnsmasq restrart wipes out the nameserver information in resolv.conf from udhcpc. However each restart of dnsmasq will rewrite the nameserver information that it enters multiple times.

A better fix is as follows:

/usr/sbin/dnsmasq $args --log-queries --log-facility=/tmp/dns.log && {

# rm -f /tmp/resolv.conf

DNS_SERVERS="$DNS_SERVERS 127.0.0.1"
for DNS_SERVER in $DNS_SERVERS ; do

grep -q "nameserver $DNS_SERVER" /tmp/resolv.conf \

echo "nameserver $DNS_SERVER" >> /tmp/resolv.conf

done

This checks whether the nameserver line is already in resolv.conf and does not modify it.

You can check this by issuing "ifup wan" and looking at the contents of /tmp/resolv.conf and then issue a "/etc/init.d/dnsmasq restart" and look again.

[anonymous]

For some reason the wiki deleted the "

" that was in front of the echo command on the continuation line - it should be

grep -q "nameserver $DNS_SERVER" /tmp/resolv.conf \
||echo "nameserver $DNS_SERVER" >> /tmp/resolv.conf

[monte <peabody.bb4wtmzci8qj@…>]

I'm fairly new to OpenWRT, but this is working for me with snapshot r19759
(2/20/2010).

What use case are you trying to solve?

If I configure wan as dhcp, /tmp/resolv.conf.auto is populated with nameservers
when it gets it's lease.

If I configure wan as static, I have to go into /etc/config/dhcp and add
"option cachelocal 0" under "config dnsmasq" and go into /etc/config/network
and add "option dns 8.8.8.8" under "config interface lan" (or wan).
This leaves /tmp/resolv.conf.auto blank, but populates /tmp/resolv.conf.

In both cases, I can resolve hostnames.

[jow]

Milestone Attitude Adjustment 12.09 deleted