tips

Share any website in Google Reader

Sun, 04 Sep 2011 13:53:31 +1000

Share any website in Google Reader

I read a lot of feeds and Google reader makes this easier.
It also allows me to 'share' the ones I find useful/interesting as an RSS feed for others to read.
One thing I found is that I sometimes come across a great site or blog post from a source other than Google Reader
that I want to share. This small Chrome/chromium bookmarklet allows you to share any website you visit.
You just create a bookmark on the Chrome toolbar with the URL set to the following javascript snippet.

javascript:var%20b=document.body;var%20GR________bookmarklet_domain='http://www.google.com';if(b&&!document.xmlVersion){void(z=document.createElement('script'));void(z.src='http://www.google.com/reader/ui/link-bookmarklet.js');void(b.appendChild(z));}else{}

openssh and X11 forwarding

Thu, 29 Jan 2009 22:17:00 +1100

Occasionally you may come across times where you need to run an X application on a remote, headless server.
Today was one of those occasions for me.
Installing xorg etc to add X to the server is a reasonable amount of work and not really a choice.
openssh has an option to tunnel X11 connections and auto setup the $DISPLAY environment variable on the remote host.
This can be done either on the fly with a switch to the ssh client or a permenant setup by changing the config file for openssh.

[lunix@godzilla ~]$ ssh -Y admin@10.20.1.254
admin@10.20.1.254's password:
Last login: Fri Jan 30 00:22:23 2009 from dynamic-20.home.lunix.com.au
/usr/bin/xauth:  creating new authority file /home/admin/.Xauthority
[admin@gateway01 ~]$ echo $DISPLAY
localhost:10.0
[admin@gateway01 ~]$

This extract of ~/.ssh/config shows how to make the X11 forwarding more permenant.

Host remotehost
ForwardX11 yes

Once this has been done and the $DISPLAY env. variable is set you should be able to fire up an application that displays its output via X.

[lunix@godzilla ~]$ wireshark

This will then fire up wireshark sending its output to X via localhost:10.0 which will tunnel it across ssh to your local screen.
Remeber this may be a bit slower than running it locally but it works.

I ran into problems this morning the first time I logged in with ssh -Y with the $DISPLAY env variable not being set.
To diagnose this I retried the ssh command with the extra options of -vv. Here is a snippet of the output.

[lunix@godzilla ~]$ ssh -vv -Y admin@10.20.1.254
admin@10.20.1.254's password:
...
debug2: x11_get_proto: /usr/bin/xauth  list :0 2>/dev/null
debug1: Requesting X11 forwarding with authentication spoofing.
..
..
debug1: Remote: No xauth program; cannot forward with spoofing.
..
Last login: Fri Jan 30 06:48:28 2009 from dynamic-20.home.lunix.com.au
[admin@gateway01 ~]$ echo $DISPLAY

[admin@gateway01 ~]$

$DISPLAY wasn't set. In my case the debug1: line mentioning a missing xauth program was the problem.
A simple yum install xorg-x11-xauth fixed this. ( centos 5 )

Hope this helps.

Usefull strace primer

Fri, 09 Jan 2009 15:09:00 +1100

I'm posting this here for both future use by myself and in the hope it's usefull to anyone else.

Have you ever racked your brain to find that bug? You know, the bug that you can't find in the source code,
but which appears with deliberate consistency when your code is compiled and run.
Hacker, meet strace.
strace is a utility that allows you to trace system calls and signals for a given command and its arguments.

Full article is over at the Redhat Magazine

Simple portscanning with bash and netcat

Wed, 31 Dec 2008 12:05:00 +1100

Today I was presented with the need to find all the machines on a network that have port 22 open.
This can easily be achieved with nmap.

sudo nmap -sS -p22 192.168.1.0/24

However the only box I had was a 'linux router' with a minimalistic linux install and no access to install extra packages.
What I ended up using was a very simple shell script with nothing more than a for loop and netcat.

    #!/bin/bash
    for h in {2..254};
    do
            nc -z 192.168.111.$h 22;
            if [ $? -eq 0 ]; then
                    echo -e "192.168.111.$h\n";
            fi
    done

The -z flag to nc ( netcat ) tells it 'no io' then I just test for the exit code it gives.
Simple.

Searching ~/.bash_history the easy way with tagging and ctrl-r

Sun, 06 Jul 2008 17:54:00 +1000

I use the bash hotkey of <ctrl-r> alot to search my ~/.bash_history and then re-use the commands.
When I learnt about this key sequence it saved me a lot of effort.
Now I have found out about one little addition to this thanks to a Tech Tip in issue #170 (June 2008) of Linux Journal.

Edit your ~/.bash_history and place tags at the end of each command you use regularly by using bash comments, ala #foo.

cd /home/httpd/html #webroot
firefox & #web
tail -f /var/log/everything.log #logall

Now a simple <ctrl-r> web will search my ~/.bash_history for #web and hitting enter will run that command again.
Not exactly a documented feature ( that i am aware of ) but a handy little hack.