Tag Archives: bash

Building a free Dynamic DNS client with rackspace Cloud


As a cloud server customer you get access to rackspace’s free DNS service.

When I fist saw this product I had an instance light-bulb moment, I could stop paying for a dynamic DNS service and build my own private one. As a broadband (DHCP) user I have a very basic requirement of needing to regularly update an A record so that I can find my pc :)

To bring my idea into fruition I began researching; I need a cli tool which I could run from cron on my linux box (to send the DNS update requests to rackspace). In my research I found rscurl, a cli tool to control cloud servers, as rackspace have a standard API for all their products I have been able to use rscurl to develop rsdns.

rsdns is a series of cli tools to adding/deleting/changing rackspace DNS records, as part of the tool development I have created a script called rsdns-dc.sh to run on my machine, below is a short how to:

How to get free dynamic dns from rackspace.

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Cisco ASA Firewalls and IP Ranges in ACLS

I’ve google’d and I cannot find a way of creating a firewall range style object in an ASA, you know the kind of thing whereby you want to allow IP addresses 192.168.1.10 thru 192.168.1.20 in an ACL.

In my frustration I have given up and created a shell script which converts a CSV into an ASA output, simply create a two column CSV with Col A containing your starting IP and Col B containing you end IP.

The script is a recursive loop so should support large outputs such as 10.1.2.10 to 10.2.1.20 howvere I’m not actually sure you’d want that in your firewall config but I wrote the computability for the fun it!

Have fun, click “more” below if you can’t see the script!

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GTD in your Shell

For the last few months I’ve felt better at managing my actions and tasks thanks to Steve Losh’s T. T is a simple python script that allows you to manage a simple task list from your shell prompt.

I use my shell all the time to ping stuff, renice processes and you know, whatever (like in the image below)…..

Screenshot of T in iTerm

… having my todo list right there in front of me has been really helpful (The numbers in the square brackets!). Steve’s website suggests a quick update to your shell profile to add your task list to your prompt but I found running a python script each time I do anything quite slow, especially since I have two lists.

Below is my bash .profile file, there you can see the rather OTT change(s) I’ve made to integrate my todo lists into my shell prompt. I have two lists (work & personal) the number of things to do shown in my shell prompt gets updated each time the lists change (thanks to md5)…. and I hide my work list over the weekend ;) 

alias p='python ~/bin/t/t.py --task-dir ~/Dropbox/Tasks --list personal.tasks --delete-if-empty'
alias w='python ~/bin/t/t.py --task-dir ~/Dropbox/Tasks --list work.tasks --delete-if-empty'

function nick_PS1 {

        if [ -e "/Users/nick/Dropbox/Tasks/Personal.tasks" ]
        then
                CurrentPersonalMD5=`md5 ~/Dropbox/Tasks/Personal.tasks | awk '{print $4}' | cat `

                if [ -e "~/.tasks.personal.md5" ]
                then
                        LastPersonalMD5=`cat ~/.tasks.personal.md5`
                fi

                if [ "$CurrentPersonalMD5" == "$LastPersonalMD5" ]
                then
                        if [ -e "~/.tasks.personal.no" ]
                        then
                                NumOfPersonal=`cat ~/.tasks.personal.no`
                        fi
                else
                        NumOfPersonal=`p | wc -l | sed -e's/ *//'`
                        echo $NumOfPersonal > ~/.tasks.personal.no
                        echo $CurrentPersonalMD5 > ~/.tasks.personal.md5
                fi

                if [ $NumOfPersonal -ne 0 ]
                then
                        LEFT='['
                        RIGHT=']'
                        Personal="p:$NumOfPersonal"
                fi

        else
                NumOfPersonal=0
        fi

DayOfWeek=`date "+%u"`
if [ $DayOfWeek -lt 6 ]
then
        if [ -e "/Users/nick/Dropbox/Tasks/Work.tasks" ]
        then
                CurrentWorkMD5=`md5 ~/Dropbox/Tasks/Work.tasks | awk '{print $4}'`

                if [ -e "~/.tasks.work.md5" ]
        then
                LastWorkMD5=`cat ~/.tasks.work.md5`
        fi

                if [ "$CurrentWorkMD5" == "$LastWorkMD5" ]
        then
                        if [ -e "~/.tasks.work.no" ]
                        then
                                NumOfWork=`cat ~/.tasks.work.no`
                        fi
                else
                                        NumOfWork=`w | wc -l | sed -e's/ *//'`
                                        echo $NumOfWork > ~/.tasks.work.no
                                        echo $CurrentWorkMD5 > ~/.tasks.work.md5
                fi

                if [ $NumOfWork -ne 0 ]
                then
                        LEFT='['
                        RIGHT=']'
                        Work="w:$NumOfWork"
                fi

        else
                NumOfWork=0
        fi
else
 NumOfWork=0
fi

        if [ $NumOfPersonal -ne 0 ]
        then
                if [ $NumOfWork -ne 0 ]
                then
                        SEP="|"
                fi
         fi

        RESULT="$LEFT$Personal$SEP$Work$RIGHT"

        if [ -z $RESULT ]
        then
                RESULT="linickx@macbookpro"
        fi

        echo $RESULT
}

export PS1="\$(nick_PS1) \W \$"

… I think my next stop will be using geektool show the list/reminders on my desktop.

Lowing VirtualBox priorities

One of the things I’d really like is process priorities for virtual box. In the forum I posted a couple of shell commands that I regularly type… which gets a bit tedious, following a recent article on lifehacker reviewing mac text expanding I’ve been prompted to automate a few things… below is a little shell script to lower the priority (renice) of all running virtual machines.

The advantage of doing this is that your host machine stays snappy, responsive and won’t get too over-loaded by jobs on your VMs!

#!/bin/bash
ps -xo pid,command | grep -v grep | grep startvm | while read line ;
do
        procID=`echo $line | awk '{print $1}'`
        sudo renice +10 -p $procID
done

The above code works on a mac; although I haven’t tested it, I recon to get it running on Linux you need to update the PS command, by swapping the x for an e… like this…. 

#!/bin/bash
ps -eo pid,command | grep -v grep | grep startvm | while read line ;
do
        procID=`echo $line | awk '{print $1}'`
        sudo renice +10 -p $procID
done

Have fun, suggestions and improvements welcome.

Bash script to fix file permissions recursively

I love the redhat implementation of cron, simply drop a shell script into /etc/cron.daily/ and your script will be executed every day (by default at 4am).

Recently I’ve been having a small problem with mediatomb, further investigation lead me to a “Inotify thread caught exception” error which can be fixed by recursively resetting your file permissions.

What I have done to fix the issue is save the following code as /etc/cron.daily/fix_mt.sh and ‘jobs a gooden’ :cool: 

#!/bin/bash
# Load up your mediatomb directories...
MediaTombDirectories[0]="/home/me/Videos"
MediaTombDirectories[1]="/home/me/Music"
# add more if needbe
# MediaTombDirectories[2]="/home/me/files"

# Setup find correctly.
export IFS=$'\n'

# Loop through our array.
for x in ${MediaTombDirectories[@]}
	do
		# Find all directories & subdirectories
		for i in $(find $x -type d)
			do
				# Fix Permissions
				chmod -c 775 $i
				chown -c me:user $i
			done

		# Find all Files
		for i in $(find $x -type f)
			do
				# Fix Permissions
				chmod -c 664 $i
				chown -c me:user $i
			done
	done


Quick tip: You (or root) will get e-mailed every time this executes, you can make the script more verbos by changing all “-c” to “-v“, or make it silent by removing the “-c” altogether.

Enjoy!

History Meme – What’s your shell top 10?

Planet gnome have started a trend…

$ history | awk '{a[$2]++}END{for(i in a){print a[i] " " i}}' | sort -rn | head
114 ping
107 sudo
82 ssh
71 top
71 cd
68 iwconfig
56 ls
46 usbkey.sh
43 ps
33 evolution

The output shows what commands you type the most, usbkey.sh is a script to unlock the secret-keys held on my usb key-fob, sudo is high up probably cause I use sudo to bounce services (the intel wireless drive crashes quite alot and both it and Network Manager then need restarting) and evolution needs a shutdown every now and again :( The other commands are fairly self-explanatory.

So what’s your history?