PDFs in the linux commandline

I was recently faced with the task of scanning a lot of documents and wanted to preserve them as multi-page pdfs. Converting the raw jpegs to pdfs proved to be quite easy using ImageMagick's convert that I got from http://stackoverflow.com/questions/8955425/how-can-i-convert-a-series-of-images-to-a-pdf-from-the-command-line-on-linux. But, the file sizes of the pdfs was really large when using convert to create multi-page documents. A little bit of googling and I found pdfunite which was perfect and I was able to create reasonably sized multi-page pdfs from a set of single page pdfs :)

Mounting VM images with multiple partitions

Of late, I have been playing around with the eucalyptus cloud project. I have a pretty basic setup with a single cloud-controller/cluster-controller and 2 nodes (using xen on centos 5.4). Usually the simplest way to mount a vm image file is as follows (find a more detailed description here)

$ # associate image file with a loop device
$ losetup /dev/loop0 jaunty.img
$ # create a mount point
$ mkdir mnt
$ # mount it :)
$ mount -t ext3 /dev/loop0 mnt
$ # chroot to navigate easily
$ chroot mnt

Then I found the jboss CirrAS project that gives a vm image with a clustered jboss setup (both for ec2 and xen/kvm). So, out of curiosity I downloaded the images and since my eucalyptus cloud is operating in SYSTEM, I have to setup the vm instance such that it pings the CLC a few times so that the IP address gets updated. When I tried the tried and tested method above...boom nothing happened I kept getting

$ mount -t ext3 /dev/loop0 mnt
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

So, after some googling and some very helpful hints from #stormgrind turns out the CirrAS images have 2 partitions and if there are multiple partitions the loop device must be given an offset from which the actual image starts and the partition table ends :|. Thankfully mgoldmann in the irc channel suggested some sites that worked like a charm :)

$ # associate image file with a loop device with offset
$ losetup -o 32256 /dev/loop0 back-end-sda.raw
$ # create a mount point
$ mkdir mnt
$ # mount it :)
$ mount -t ext3 /dev/loop0 mnt
$ # w00t

How did I arrive at 32256? Simple. For images created by bximage you must use the value 32256 words of wisdom from here References http://bochs.sourceforge.net/doc/docbook/user/loop-device-usage.html http://varghese85-cs.blogspot.com/2008/11/mouting-partitions-with-losetup.html

iptables-fu

I've had a love hate relationship with iptables. I love the control it offers but, am quite confounded by all the low-level networking concepts at play. Today, I had to do some simple stuff, like blocking pings and block ssh from a particular IP. Here is my humble attempt at both

# reject all ping requests
iptables -A INPUT -p icmp -j REJECT
# drop all ssh (tcp:22) requests from 10.0.0.37
# DROP means that whoever is trying to connect from 37 will not get a connection refused...devious >(
iptables -A INPUT -p tcp --sport 22 -s 10.0.0.37 -j DROP