Linode Dynamic DNS Bash Script

So Mark Walling was working on an ash script for his router running OpenWRT to update Linode's DNS Manager with his IP address. I liked the idea of a simple shell script to update without needing to install libraries for Perl or Python.  I took his script and tried to adapt it to get the DOMAINID and RESOURCEID using sed or awk.  Those utilities seem great for manipulating multiline files of text, but I wasn't getting anywhere trying to parse one line of JSON from wget.  So I used perl to extract the id numbers.  I believe OpenWRT has some sort of perl with limited functionality, so maybe this will work with that or at least be easily adapted.  This could also be easily modified to use curl instead of wget. I suspect someone out there will find this useful.

#!/bin/bash
#
# Script to update Linode's DNS Manager for a given name.
#

# Things you need to change.
APIKEY=$(cat ~/.linode-apikey)
LASTIP="/tmp/lastip"
DOMAIN="domain.com"
SOAEMAIL="hostmaster@domain.com"
STATUS="1"
RRTYPE="A"
RRNAME="home"
IFACE="eth0"

# Shouldn't need to change anything below here.

WGET="wget -qO - https://api.linode.com/api/"
NEWIP=$(ifconfig $IFACE | head -n2 | tail -n1 | cut -d: -f2 | cut -d' ' -f1)
test -e $LASTIP && OLDIP=$(cat $LASTIP) || OLDIP=""

if [ x"$OLDIP" = x"$NEWIP" ]; then
  logger "No IP address change detected. Keeping $NEWIP"
else
   DOMAINID=$($WGET --post-data "api_key=$APIKEY&action=domainList" | 
        perl -e 'if ( =~ /"DOMAIN":"'"$DOMAIN"'","DOMAINID":([0-9]+),/) { print $1; }')
   RESOURCEID=$($WGET --post-data "api_key=$APIKEY&action=domainResourceList&DomainID=$DOMAINID" | 
        perl -e 'if ( =~ /"RESOURCEID":([0-9]+),"DOMAINID":'"$DOMAINID"',"TYPE":"'"$RRTYPE"'","NAME":"'"$RRNAME"'"/) { print $1; }')
   $WGET --post-data "api_key=$APIKEY&action=domainResourceSave&ResourceID=$RESOURCEID&DomainID=$DOMAINID&Name=$RRNAME&Type=$RRTYPE&Target=$NEWIP"; echo
   $WGET --post-data "api_key=$APIKEY&action=domainSave&DomainID=$DOMAINID&Domain=$DOMAIN&Type=master&Status=$STATUS&SOA_Email=$SOAEMAIL"; echo
   echo $NEWIP > $LASTIP
   logger "Updated IP address to $NEWIP"
fi

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One Response to “Linode Dynamic DNS Bash Script”

  1. Mike Says:

    Thanks for the nice script. Yours was one of the few I found that obtains the remote IP internally rather than depending on an external website.

    Just a note. People using this script may need to put in full path of ifconfig if running from cron, otherwise it will fail. E.g., change

    NEWIP=$(ifconfig $IFACE | head -n2 | tail -n1 | cut -d: -f2 | cut -d' ' -f1)

    to

    NEWIP=$(/sbin/ifconfig $IFACE | head -n2 | tail -n1 | cut -d: -f2 | cut -d' ' -f1)

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