Category Archives: Linux

Proxy/ReverseProxy and Apache2

I recently configured Apache2 to be a ReverseProxy/Proxy and thought I would share my experiences while it was still fresh. Having never configured any kind of proxy, I found this webpage very informative. The scenario I would like to use for my example is that I have three internal web servers called

Site Local IP Remote IP Port
www.reallycoolsite.com 192.168.1.102 10.15.22.1 80
www.justcoolsite.com 192.168.1.102 10.15.22.2 80
www.reallylamesite.com 192.168.1.44 10.15.22.3 80

Alright…pretty straight forward right? If you are in a situation that I was when I started, you haven’t done much more than install apache from source and added a few modules here and there occasionally. The way I solved the problem was to create name-based virtual host for each of the servers.
our example would look like


#you can listen on specific ports for requests if you like
#(ex->Listen 192.168.1.102:80)
#I use the below statement to listen on 80 for all requests
Listen *:80
#Because we have multiple names mapped to same ip
NameVirtualHost 192.168.1.102:80

<VirtualHost 192.168.1.102:80 >
ServerName www.reallycoolsite.com
ProxyRequests Off
ProxyPass / http://10.15.22.1/
ProxyReverse / http://www.reallycoolsite.com/
ProxyPreserveHost On
ErrorLog reallycoolsite_error_log
CustomLog reallycoolsite_access_logs
</VirtualHost >

<VirtualHost 192.168.1.102:80 >
ServerName www.justcoolsite.com
ProxyRequests Off
ProxyPass / http://10.15.22.2/
ProxyReverse / http://www.justcoolsite.com/
ProxyPreserveHost On
ErrorLog justcoolsite_error_log
CustomLog justcoolsite_access_logs
</VirtualHost >

<VirtualHost 192.168.1.44:80 >
ServerName www.reallylamesite.com
ProxyRequests Off
ProxyPass / http://10.15.22.3/
ProxyReverse / http://www.reallylamesite.com/
ProxyPreserveHost On
ErrorLog reallylamesite_error_log
CustomLog reallylamesite_access_logs
</VirtualHost >

If you receive errors during the communication of your proxy and your server, it may be a good idea to investigate if you have an http protocol error discussed at the bottom of this page
The following two lines are pulled from the reference and fixed a problem I had with one of my IIS servers using SSL(for more info about the issue, go here

SetEnv force-proxy-request-1.0 1
SetEnv proxy-nokeepalive 1

My apache configuration file(httpd.conf) was the file I used to edit my settings.. Your file may be different depending on how new your apache version is. I found that some implementations called the configuration file apache.conf…. I hope this blog entry is helpful you, Happy Configuring!

BarCamp Omaha

I have just been informed/invited to Omaha’s BarCamp! According to the site, this is a “unconference born from the desire for people to share and learn in an open environment.”

The list of topics that have been submitted thus far are already enough to get any developer’s inner geek super-charged. At this point I am not sure what I will talk about, but here are a few ideas.

  1. uploading/updating multiple models in one form (ROR)
  2. Groovy and flickr
  3. Action Script 3 concepts
  4. Linux Administration
  5. Setting up Twiki

Any suggestions or votes on what I could bring to the BarCamp would be awesome. If you can make it, I suggest checking this event out! After all, you don’t want to be sitting there listening to you fellow IT buddies raving about the great time they had learning at BarCamp…right?

File I/O Part 1

I love to learn and try new languages. Not only is learning a new language fun, many times it teaches me something new about a language that I am already familiar with. The only problem that I have with learning so many languages, is keeping them straight. I decided that I would take a few of the dynamic languages I use most often and compile a list of how to handle File I/O with each of them. If you have a Dynamic language(part 2 of this post will be on static languages) not represented below or have another method of File I/O with the represented languages, please add to the list with its respective File I/O code:D
Without further ado…

//Groovy open file for writing
def target ="filename"
File wf= new File(target)
wf.write( "I am in your file eating your space" )

//Groovy one liner
new File('filename.txt').text = 'First line of text!'

//Groovy open file for appending
def target ="filename"
File af= new File(target)
af.append("I have all of your base")

//Groovy read each line in file
new File("filename").eachLine{line-> println line}

//Groovy read whole document and put into List

List lines = new File("filename").readLines()
//lines contains two lines that we need
println "first line  $lines[0]"
println "second line $lines[1]"

//Groovy reading one line
File rf= new File("filename") //open for reading
//read first line, trim, assign to tmp
rf.withReader { line ->tmp = line.readLine().trim()}

//Groovy test if file exists
File src = new File(srcFile)
if (src.exists() ){ println "I exist"}
else{println "I don't exist"}

#Ruby openfile for reading
fh = File.new(path, "r")  # open file "path" for reading only
fh.close

#Ruby open file for writing
fout   = File.new(path, "w")  # open file "path" for writing only
fout.puts "Up, Up, Down, Down, Left, Right, Left, Right, B, A, Select, Start"
fout.close

#Ruby open file for apending
fa= File.new("DeleteMe.txt","a")
fa.puts "I am at the end of file"
fa.close

#Ruby read eachline in a file
File.open("file").each { |line| p line}

#Ruby read entire file to string
fh = File.new(filename)
str = fh.read

#Ruby read entire file into array(each line is an element in the array)
fh = File.new(filename)
str = fh.readlines

#Python Write a file
fout = open("DeletMe.txt", "w")
fout.write("Writing to fout\nCheck it out!")
fout.close()

#Python Read an entire file
fin = open("ReadingTest.txt", "r")
fin_text =  fin.read()
fin.close()
print fin_text

#Python read entire file into list
fin = open("ReadingTest.txt", "r")
txt= fin.readlines()
fin.close()
print txt[0]

#Python append to a file
fh= open ( 'DeleteMe.txt', 'a' )
fh.write ( '\n\n\nBottom line.' )
fh.close()

#Perl reading a file
open(FILE,  '<', $file) or die "Can't read $file: $!\n";
while(<FILE>)
{
print ;
}

#Perl append to a file
open(FILE, '>>', $file) or    die "Can't append to $file: $!\n";
print FILE "text";
close(FILE);

#Perl read and write to a file
#+< allows reading and writing, and keeps the data that was
#already in the file.  open() will fail if file doesn't exist.
open(FILE, "+<$file" ) or die ("Can't  read|write: $file\n");
close(FILE);

#Perl read and write to a file
#+>allows writing and reading, but replaces/overwrites the
#data in the file if the file exists. Creates it if it doesn't exist.
open(FILE, "+>$file" ) or die ("Can't write or read:$file \n");

close(FILE);

PHP code doesn’t display properly within WordPress, so here is an image of the code

PHP File I/O

Handling Ruby’s String.each_char Iterator

Ahh the joys of iterators. I can’t say enough about how much they make my life easier. They are just so darn handy. Life was good in my Ruby world until I needed to iterate through the characters in a string. Thinking to myself, “there has got to be a method that does this,” I looked up Ruby’s String class and saw just what the doctor ordered… each_char.

Feeling pretty proud that my favorite language had this baked right in, I was only to happy to inject it into my code and test it out. That is until I recieved the dreaded NoMethodError: undefined method `each_char’ . Eeek, what did I do wrong? Did I mispell the method…..Nope, did I call it correctly…..Yep. Well, what the heck is going on?

After multiple attempts to find the answer on Google, I finally posted my problem to the ruby-talk group. I was told that the Ruby 1.8 String implementation that I was using only understood bytes and that I could use require ‘jcode’ to get the iterator to work the way I wanted. I did some looking around and I am not sure this is a great solution, after all, I could have easily used the each_byte{|f| f.chr} to iterate through and convert accordingly. I don’t understand why something that is documented as part of the class, does not work.

It would really help if there was an easy to search area on the net dedicated to language quirks for people trying to get a better grasp of their programming language of choice. Maybe that will be my next ROR project.

As it turns out, my Ruby 1.8.7 installation on my Fedora core 9 works as advertised.

su vs. “su -” The Mystery Revealed

Inquiring minds want to know, what is this su - and why is it different than su? Well, if you are like me, you didn’t even know that su - existed. I ran into this problem when I was trying to add a new user to a new Linux machine. Remote root login was disabled(for obvious reasons:D) and I was logged in with my regular non-privileged user account. Well, normally the story goes like this…

  1. su
  2. Authenticate
  3. useradd account
  4. set password
  5. log out of privileged account
  6. Take coffee break from all the hard work and call it a day

No so today:( . When I attempted to run step three(useradd), I received a command not found error. “That’s weird” I thought. How could a machine not have this basic command. I looked in the bin directory to see if it was some kind of path error I was having. Thinking that this was the case, I was shocked to see that none of the user commands(adduser, usermod, deluser) where there.

After a few minutes of scratching my head, I asked someone more versed in Linux than I what they thought. After walking through each of the steps I had taken, my mistake was easily spotted. I hadn’t added the ‘-‘ to the su command. Thinking that the explanation was weird, I checked with google for the su - command. Sure enough, the link to Wikipedia had this to say about it,

Optionally, you can use a hyphen with su to invoke a login shell and assume the target user’s complete user environment:

I am glad I had someone to point this out to me… It could have been a longer and very frustrating ordeal. It was also a lesson for me to refer more to the man pages(it had the answer there too). I hope this blog entry helps someone else who is confronted with this situation.