September 2010 – Sol's blog

Apache reverse proxy using mod_proxy

Sep 212010

I recently set up this blog on a virtual machine which is running on my home computer. Since soljerome.com was already running elsewhere, I decided to serve up the content using the existing apache instance at soljerome.com by setting up apache using a reverse proxy.

This particular setup is on Ubuntu 8.04 as that is the distribution running on my web server. My web server is able to view the virtual machine using an internal IP address of 10.10.10.34. Here is the /etc/hosts entry

10.10.10.34 www.solnet www blog.solnet blog

So, I am able to view the blog from the web server by browsing to http://blog.solnet. Therefore, I needed to tell Apache was to take a URL like http://soljerome.com/blog, internally request http://blog.solnet, and give the result back to the viewer.

The first thing I needed to do was install the Apache mod_proxy module

aptitude install libapache2-mod-proxy-html

Then I enabled the proxy module by running

a2enmod proxy_html

After the module was enabled, I added the following lines to /etc/apache2/sites-available/default

    ProxyRequests off    

    <Proxy *>
        AddDefaultCharset off
        Order deny,allow
        Allow from all
    </Proxy>
    ProxyPass /blog http://blog.solnet
    ProxyVia off

Once I restarted Apache, I was able to browse to http://soljerome.com/blog successfully. There are still a few things that I have yet to get working properly (although I think most are due to bugs in WordPress). Some of the wp-admin links work but redirect to the internal address which forces me to have to click the back button on my browser (annoying). Also, trying to setup the admin interface to use SSL has proved to be a problem.

Python lists in reverse

Python No Responses »

Sep 142010

I was recently converting a bash script to python. I had a need to grab the last item (and only the last item) off the end of a list in order to implement bash’s basename function since Python’s basename function is not quite the same. The bash script had a line like the following
tmpbase=`basename $0`
I was able to get the information I needed by using the __file__ attribute in the script itself. From this, I was able to split the full pathname like this:

solj@abbysplaything $ cat foo.py
#!/usr/bin/env python3
print(__file__.split('/'))

solj@abbysplaything $ python /home/solj/foo.py
['', 'home', 'solj', 'foo.py']

As you can tell, the length of this path could vary depending on where the user runs the script from. Therefore, I needed to grab the first item from the end of the list in order to properly emulate the basename function of bash. I ended up being able to do the following:
tmpbase = __file__.split('/')[-1:]
The negative index allows you to count from the end of the list (I love Python). However, as it turns out, I am blind and didn’t finish fully reading the os.path documentation. This particular problem was solved in a much more elegant way using os.path.split() although I find the negative index to be an extremely useful thing to know.

Using LVM volumes with VirtualBox

Linux, VirtualBox 1 Response »

Sep 072010

I have been used to using KVM when doing virtualization. However, I ran into some performance issues when trying to setup my home machine to run KVM as a normal user. Therefore, I decided to try out VirtualBox again. One issue I had was trying to use an lvm volume as a physical device for the virtual machine. Here is how I solved the problem.

First, I created the lvm volume

lvcreate --name www --size 10G images

Next, I created a vmdk file which describes the disk properties using the VBoxManage command:

VBoxManage internalcommands createrawvmdk -filename /vbox/www.vmdk -rawdisk /dev/images/www

Here are the contents of the vmdk file after running that command:

# Disk DescriptorFile
version=1
CID=e5ee218c
parentCID=ffffffff
createType="fullDevice"

# Extent description
RW 20971520 FLAT "/dev/images/www" 0

# The disk Data Base
#DDB

ddb.virtualHWVersion = "4"
ddb.adapterType="ide"
ddb.geometry.cylinders="16383"
ddb.geometry.heads="16"
ddb.geometry.sectors="63"
ddb.uuid.image="46527bd3-f962-43cc-8a43-11aafd3425aa"
ddb.uuid.parent="00000000-0000-0000-0000-000000000000"
ddb.uuid.modification="00000000-0000-0000-0000-000000000000"
ddb.uuid.parentmodification="00000000-0000-0000-0000-000000000000"
ddb.geometry.biosCylinders="1024"
ddb.geometry.biosHeads="255"
ddb.geometry.biosSectors="63"

Lastly, I made sure the permissions were set so my user could read the file

chown solj. /vbox/www.vmdk

After this, I was able to add the file as a storage device as if I were adding the lvm volume itself. This is great since now I can grow the volume as needed if I end up storing more on the machine than initially planned.

tmux — a better terminal multiplexer

Linux No Responses »

Sep 052010

Update: I have created a new github repository which contains all my various dotfiles. You can now find my latest tmux.conf at https://github.com/solj/dotfiles/blob/master/.tmux.conf

I recently made the switch from GNU Screen to tmux. It took some time to get used to it, but it has turned out to be a pleasant experience. I had heard things a few things about tmux before making the switch, but none of them really made me want to switch away from screen. My screenrc took me weeks of time to get “just right” and I didn’t want to lose all that time. It doesn’t look like much, but the hardstatus/caption lines are extremely cryptic and non-intuitive.

One of the issues I had with screen was that it didn’t come with vertical splits by default (I had to patch it in). Even then, once patched, it was almost unusable over the slightly slow network I was using at the time. The claim that tmux handled this better was intriguing. When I also read that tmux used way less memory, I had to try it out.

The first difference I noticed when trying tmux was that when I started it up, the default layout was actually reasonable (I still remember my cluelessness when I first starting using screen). It most definitely uses less RAM

$ tmux ls
0: 20 windows (created Fri Jul 16 19:21:20 2010) [157x50] (attached)

This was a tmux session with 20 windows. Here is the ps output

solj     16390  0.0  0.0  23668  1192 pts/0    S+   15:48   0:00 tmux attach -d

That’s approximately 23MB of RAM. Here is the number of windows in use for a screen session I have open on another machine

Num Name                                                                                                                                                Flags

0 bash                                                                                                                                                    $
1 bash                                                                                                                                                    $
2 bash                                                                                                                                                    $
3 bash                                                                                                                                                    $

..and here is that machine’s ps output

solj      3230  0.0  0.0  24888   348 pts/1    S+   Aug27   0:00 screen -U

That’s approximately 24 MB of RAM which is slightly higher than the tmux session with 20 windows.

I decided to attempt to get my tmux sessions looking similar to my screen sessions. This turned out to be surprisingly easy after reading through the tmux man page. As opposed to the weeks it took me to get my screenrc just right, modifying my tmux.conf with the same options only took about half a day. Not only that, there are subtle improvements made possible by using tmux (such as highlighting the current window and the upcoming window-status-alert options) which improve the visibility of my session.

One issue I did come across was that I was trying to use the #(date) syntax to set the date in my tmux status line, however, this caused my session to become unresponsive after spawning off too many processes. After reading the man page, I realized this was unnecessary as it clearly states

string will be passed through strftime(3) before being used

I am now a happy tmux user and cannot see myself ever switching back to something that is not at all actively developed and which is unable to meet my current needs.