Concatenating PDFs

Concatenating PDF files should be pretty straightforward.  On Linux, there are several tools that can do this, including pdftk, pdf2ps and convert, which is a wrapper for Ghostscript.  Unfortunately, I had a batch of files that I wanted to concatenate for ease of use on my tablet, and none of these tools were working.  pdftk failed repeatedly with the useful error message:


Error: Failed to open PDF file: 

   input.pdf

Using pdf2ps did create a merged copy of the input files, but it was HUGE, consisting of bitmap images of the pages, losing the text in the process.  ImageMagick convert never ran to completion, since I terminated it after it had eaten over 3GB of memory, presumably rendering the text into images.

Ultimately, I was able to successfully create a high quality, merged copy of my files by resorting to manually invoking Ghostscript:

gs -q -sPAPERSIZE=letter -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=output.pdf *.pdf

The resulting file is actually smaller than the combined total of the input files, storing text as text, rather than horrid, pre-rendered bitmaps.  Ghostscript used a sane amount of memory, and it ran to completion in a sensible amount of time.

To Ghostscript, bravo!  To the others, a big "Why"?

Ubuntu branding #fail

Install Ubuntu 11.10 Server, add Xfce4 desktop environment and reboot.  Result?  Debian space theme branding on the grub and boot screens.  Quality Assurance, anyone?  Perhaps images from upstream packages need a little more vetting before importing...

debian space-themed boot screen/grub menu on Ubuntu 11.10 "Oneiric"

Linux ICMP redirects

It seems that Ubuntu 11.10 ships with a sample /etc/sysctl.conf which contains the following statement, intended to tell the system not to originate ICMP redirects when acting as a router:

# Do not send ICMP redirects (we are not a router)
net.ipv4.conf.all.send_redirects = 0

Unfortunately, (at least) with kernel 3.0 as shipped with Oneiric, even after setting this and activating with 'sysctl -p', it doesn't work.  Symptoms are noisy kernel log records such as:

[611513.083432] host 192.168.0.100/if2 ignores redirects for 8.8.8.8 to 192.168.0.1.

If you actually want to disable sending ICMP redirects, you have to explicitly set this per interface in /etc/sysctl.conf, by doing:

# Do not send ICMP redirects (we are not a router)

net.ipv4.conf.eth0.send_redirects = 0

net.ipv4.conf.eth1.send_redirects = 0

net.ipv4.conf.eth2.send_redirects = 0

etc.