Technology Blog

So today I ran into an svn problem: Svn: Path ’somedirectory’ not present  I spend a good hour trying to fix it.  It turned out to be left over garbage from moving folders around – something I wish svn was better able to do.  You can move folders around fluidly without causing havoc on your repo.

So Follow me I had a structure like this:

site.com

-www

-includes

-js

-css

I wound up renaming the www folder to “sliced” and created a new www folder.  I installed wordpress and did everything I needed to do.  I went to check it in and bamn – got the above error.  After trying several things online – with no good direction I realized all I had to do was create a folder includes that contained js and css folders and an add and checkin:

mkdir -p includes/css

mkdir -p includes/js

svn add includes

svn ci -m "my error is gone"

svn remove includes

svn ci -m "now my extra empty folder is gone as well"

A colleague of mine recently came over to discuss HTML 5 the next major revision of HTML! He wondered what new and beneficial features were in store. The few noticeable ones are:

• New “nav” and “footer” elements
• Canvas tag for immediate bitmap rendering – this is so cool!  No more using gd libraries on servers – use the clients web browser!
• Drag and Drop capability.  If you’ve ever created a website that had users uploading files we know this is a HUGE feature!  Gmail attachments will be so much easier now too!
• Cross Document Messaging – not too much discussion on this one – are two pages going to be communicate with each other?
• Timed media playback.
• Video tag allows in browser playback – cool in theory but they dropped a specific codec, so now this is going to get messy!  Users will need to have codec’s installed or users uploading will need to take care!

These are the highlights.  In my opinion the drag and drop is by far going to be the most anticipated and highly used feature – next to video.  But regular end users won’t notice the video tag as they are use to flash.  So many users won’t even notice a difference.

Unfortunately, we’ll probably have about 10 years to go until we’re able to use these features.  Microsoft IE 6 is still lingering around, so we have to wait for that beast to die (2014)…..and with some hope and luck, we’ll be happy coding in html 5 within 10 years!

Grub Booting

The servers I work on are almost never in front of me. Instead they are in dark rooms humming away gracefully. When I need to do a kernel upgrade or recompile I need to reconfigure grub to reboot into the new kernel. So normally you would just edit /etc/grub.conf and change –save-default=X to be the correct number.

Well what happens if you change that and your new kernel doesn’t boot? Your left black screened with no one looking at the server to tell you what’s wrong with it. This leaves you calling the data center (or your host) asking for a technician to take a look at the server, at the very least reboot login to single user mode, edit the config, and then restart into the old kernel. Sounds time consuming huh?

Yup, and then you still have to figure out what you did wrong, reboot, and pray again. With more and more host offering instant reboots in their control panels, you could do this whole operation without ever bothering anyone at the data center.

Instead of changing /etc/grub.conf just type in the following at the command line:

grub
savedefault --default=X --once
quit

X of course being the number kernel you would like to boot into.

Now if your server doesn’t boot properly into the new kernel you only need to power cycle it to get it to boot into the old working kernel. Host doesn’t offer power cycling? At the very least the data center staff will appreciate the joy of not having to log into your server and fix things. They are usually much quicker at handling simple reboot request than configuration changes. If they are busy they can at least have the janitor go over and power cycle the server, instead of someone who is a grub expert! Point taken?

Today I went to do a checkin on svn and got the following:

svn: Base checksum mismatch on '/trunk/sites/mysite.com/framework/application/views/main_layout_header.php':
expected: 481f0430e5f320350e138b96c59141de
actual: 3b42d820bf099c3995f4acc02aabe991

This means my local svn db info has been corrupted. I tried removing the file, doing an svn up and then a checkin thinking this would work. This does not!

SOLUTION: What you need to do is remove the entire parent directory (WORKING_DIR/sites/mysite.com/framework/application/views). In my specific instance I made a local copy of the file main_layout_header.php and then deleted it with “rm main_layout_header.php”. I did an svn up, then a checking. This checked in all my modified files with an unmodified original version of main layout_header.php. Then I deleted the directory (WORKING_DIR/sites/mysite.com/framework/application/views), did an svn up. Then immediately do a check in to make sure it works! At this point I copied back my modified main_layout_header back into the views directory and performed an svn up!

Today I was moving some stuff to a live server and Whaamm my code was giving me the following error:

Access denied for user: 'apache@localhost' (Using password: NO)

I debugged it to be the line containing mysql_real_escape_string. But why did it work on the dev server and not the live? My memory immediately kicked in and remembered having similar problems. The code on live was not using persistent connections (not an issue) and the call to mysql_real_escape_string requires a connection to mysql to be open at the time of call. Since the line of code came before any connection to the database was being made, it caused this error.

Make sure you have a connection to mysql open before calling this method!

On a local server I have for testing I need to use my isp’s mail server for sending emails. They block port 25 so all mail has to be routed through their server. Luckily they do not require authentication, they use ip based ACL’s so setting up sendmail was a breeze!

All it tooke was opening

/etc/mail/sendmail.mc

adding/changing:

define(`SMART_HOST',`[mail.bellsouth.net]')

and then reseeting the sendmail config via:

m4 sendmail.mc > sendmail.cf
service sendmail restart

Now any mail sent from my machine (system status, php’s mail function, etc) will be routed through my isp’s mail server.

So I am putting the final touches on a program. It is completely web based and needs to be protected as if it were an intranet but have the portability of a regular website. The best solution I could come up with was a vpn. But do I really want to explain or document cases for end uses to set up ptpp or ipsec vpn’s on their computers? This would be an ABSOLUTE headache. Instead the best solution would be a web based SSL vpn. Well after some googling two options come up: SSL Explorer – and Barracuda (http://www.barracudanetworks.com/ns/products/sslvpn_overview.php).

Well guess what? Barracuda bought SSLExplorer and that’s what’s on their appliance you pay $2,000 USD for. Unfortunately, this means SSLExplorer is no longer supported and developed. I tried to compile and install it finding out it was originally compiled in java 1.5 and my machine has java 1.6.
This failed miserably:
class file has wrong version 50.0, should be 49.0

Well version 49.0 means java version 1.5.0. (Maybe some kind of internal version numbers – who knows?)
Version 50 means Java 1.6.0 -> now this error makes sense!

So is their a work around? I found a neat trick for updating this:

mv /usr/local/src/sslexplorer-0.2.14_01/sslexplorer/lib/tools.jar /usr/local/src/sslexplorer-0.2.14_01/sslexplorer/lib/tools.jar.old
cp /usr/lib/jvm/java-6-sun-1.6.0.00/lib/tools.jar /usr/local/src/sslexplorer-0.2.14_01/sslexplorer/lib/tools.jar
cd /usr/local/src/sslexplorer-0.2.14_01
ant install

Apparently, sslexplorer is shipped with tools.jar from a 1.5 java distribution, so you only need to replace it with the version you installed.

Finally, after some more headaches and research I found out about Adito (sourceforge.net/projects/adito/). Adito is a fork of SSLExplorer and is actively maintained. I figured it would be best using a package that is still updated regularly, so I switched over to adito and followed pretty much the same installation instructions that SSLExplorer provided.

This proved to give me another error which would result in roughly 3 hours being devoted to fixing:

load: class com.adito.agent.client.launcher.AgentLauncher not found.
java.lang.ClassNotFoundException: com.adito.agent.client.launcher.AgentLauncher
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(Unknown Source)
at java.net.PlainSocketImpl.connectToAddress(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at sun.net.NetworkClient.doConnect(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.protocol.https.HttpsClient.(Unknown Source)
at sun.net.www.protocol.https.HttpsClient.New(Unknown Source)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at java.net.HttpURLConnection.getResponseCode(Unknown Source)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.access$000(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
... 7 more
Exception: java.lang.ClassNotFoundException: com.adito.agent.client.launcher.AgentLauncher


Googling this error gives no clues (except this blog entry once it gets indexed). Well the problem was a simple one to fix. I was using a proxy to access my adito server as it was on a different network than me. When the client opened on my local machine it no longer had access to the server to properly launch. This resulted in the above error.

I dmz’ed the server, and accessed it via its public ip address and all works well now! I have connected and used it on my vista pc and on my Mac!

Thought I would share this for whatever unlucky soul gets this undocumented error again in the future!

In dealing with a decent sized website property there were a few times we needed to bring down the site to the public and do a few roll outs. We didn’t want the public coming to the site and seeing a broken page, or getting any response at all. So we decided to forward all port 80 traffic and send them to a different server that hosted an under construction page for them.

The script is as follows:


/sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -A OUTPUT -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -A FORWARD -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

#We don’t want to forward our development team Replace your dev team’s ips with the xxx;s
/sbin/iptables -t nat -A PREROUTING -p tcp –dport 80 -s xxx.xxx.xxx.xxx -j REDIRECT –to-ports 80
/sbin/iptables -t nat -A PREROUTING -p tcp –dport 80 -s xxx.xxx.xxx.xxx -j REDIRECT –to-ports 80

#forward everyone else to destination ip yyy.yyy.yyy.yyy
for IP in `/sbin/ifconfig | grep ‘inet addr:’| grep -v ‘127.0.0.1′ | cut -d: -f2 | awk ‘{ print $1}’`;
do

/sbin/iptables -A FORWARD -i eth0 -o eth0 -p tcp –dport 80 -d $IP -m state –state NEW,ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 80 -d $IP -j DNAT –to-destination yyy.yyy.yyy.yyy
/sbin/iptables -t nat -A POSTROUTING -p tcp –dport 80 -d yyy.yyy.yyy.yyy -j SNAT –to $IP

done
echo 1 > /proc/sys/net/ipv4/ip_forward

When we were done and ready for the public to start vising the site again we simply stopped and restarted iptables.

You done some development with svn and now your at revision 300 and you realize you didn’t do things right. You want to go back to revision 290, since that’s what the live server is running gracefully.

To revert to 123 you just need to do this:

$ svn merge -rHEAD:290 .

This will undo the changes you have made since 290. Now you need to do a check in and you have a revision 301 that is exactly the same as revision 290.

Blast! I hate when this happens. It’s always when one of the biggest clients has a problem and I am debugging. How the heck am I suppose to help them now? My best search tool isn’t even working.

Well thankfully for the following snippet:


find . -type f -print0 | xargs -0 grep "search string here"