Home Page

Category: sysadmin

POODLE: SSLv3 bug summary

Yet Another SSL bug: This time a problem with SSLv3. Most browsers and web servers support SSLv3. Many don't use it by default; instead opting for higher versions of SSL such as TLS v1.0+. The problem is that attackers can force a downgrade of the negotiated protocol, which will result in the SSLv3 protocol being used […]

Pydocmd: Generate Markdown from python source files

I've created pydocmd. It generates Python Module / script documentation in the Markdown (md) format. It was written to automatically generate documentation that can be put on Github or Bitbucket. It is as of yet not very complete and is more of a Proof-of-concept than a fully-fledged tool. Markdown is also a very restricted format and […]

Work around insufficient remote permissions when SCPing

Here's a problem I often run into: I need to copy files from a remote system to my local system. I have root access to the remote system via sudo or su, but not directly via SSH. I don't have enough permissions to read the remote files as a normal user; I need to be […]

How to REALLY test for Bash Shellshock (CVE-2014-6271)

Like always in a crisis, many things go wrong. Everyobody starts chattering, and start deteriorating the signal-to-noise level. I'll keep this brief. There are a bunch of sites out there that are telling you how to test for the Bash Shellshock vulnerability. Many of the tests are WRONG: # WROOOOOOOOOOOOOOOOONG $ env x=’() { ;;}; […]

SSH port forwarding: bind: Cannot assign requested address

Just now I tried seting up an SSH tunnel. Something I must have done for at least a few tens of thousands of times in my career. But suddenly, it didn't work anymore: $ ssh -L 8080:127.0.0.1:80 dev.local bind: Cannot assign requested address After checking that the local port was free, and the remote port […]

Scripting a Cisco switch with Python and Expect

In the spirit of "Automate Everything" I was tasked with scripting some oft needed tasks on Cisco Switches. It's been a while since I've had to do anything even remotely related to switches, so I thought I'd start by googling for some ways to automate tasks on switches. What I found: http://ciobota.web.cern.ch/ciobota/project/sw_script/ https://trigger.readthedocs.org/en/latest/ Both seemed […]

Multi-column data plotting with Gnuplot

In my previous post I showed how to generate good looking charts with Gnuplot. Those were simple bar charts with a single bar. In this post I want to show you how to plot bar charts with multiple bars. Such charts take multiple columns of data and plot them grouped in the chart. We'll be working with […]

Generating good-looking charts with Gnuplot

Gnuplot is a tool for plotting graphs. It was originally created to allow scientists and students to visualize mathematical functions and data interactively, but has grown to support many non-interactive uses such as web scripting. It is excellent for generating all kinds of charts. Unfortunately, the defaults for Gnuplot don't generate very appealing charts: set terminal […]

Upload a file by command line via sftp.

If you want to upload a file by commandline via SFTP, you may end up on this StackOverflow page. The answer there is WRONG. Those are not using the SFTP subsystem, they use SSH and process output redirection. Using scp will result in an error if the server only allows the SFTP subsystem:  This service […]

Various databases and how they scale

By chance I stumbled upon an article about databases and how they scale. It's a great read and does an excellent job describing the various stengths and weaknesses regarding different kinds of scaling for databases. Especially the images really capture the essence.