Redirect port 80 to 9000 in linux

/sbin/iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 80 -j REDIRECT –to-port 9000
/sbin/iptables -t nat -A OUTPUT -o lo -p tcp –dport 80 -j REDIRECT –to-port 9000

Mysql and replication

Last week, we ran into an issue of mysql getting stuck in a replication.  Turned out, one of the transaction that failed in the master, failed in the slave with a different error.  That had halted the replication.

This is how we fixed it.

mysql -p

Subversion filter

As developers, we use some versioning system.  We also come under situation, where we dont want to keep every files in the repo.  Especially those that are created at runtime, as logs.  We can create filters in the repo, so that we can ensure that these files are not saved in the repository.  Here is how we do it in subversion:

svn propset svn:ignore "*.log" log

What this means is, we are telling subversion to ignore all the *.log files inside the log directory that is situated in the current folder.  You run this command from within the repo.

You can run the following command to see what all properties are set in the current folder.

svn proplist

How to iterate through list of filenames in linux

Today, somebody asked me how to iterate through a list of filenames given in a text file, and do something with it.  So, I did, and then thought i would put it here, so it might help somebody else.

So, the script goes like this:

for f in `cat x` ; do
  if ! test -e $f
  then
    echo $f
  fi
done

How to set timezone in linux – Ubuntu Hardy

Now with the proliferation of Cloud computing, we often come across the necessity to configure the linux server to run in a particular timezone other than where it is running.  I had to do this in some of our servers, so I thought, I would share this information with others.

The server’s current timezone is defined by the file /etc/timezone.  The timezone files for other zones are located in the folder /usr/share/zoneinfo.

First save your current timezone file.  Rename this file as a backup.  You can also delete the same.

mv /etc/timezone /etc/timezone.backup

Now lets take a look at the collection of timezone files.

cd /usr/share/zoneinfo

Take a look at the files.  Each file pertains to a particular timezone.  The filename’s are quite explanatory.  For countries with multiple timezone, like US, Canada etc,   you will see a folder named by the country.  Inside this folder you will see these files.  Choose the timezone file you want to use.  For eg.  lets say, I want to set the timezone to US – PST.  The timezone file for this is /usr/share/zoneinfo/US/Pacific

Just run,

cp /usr/share/zoneinfo/US/Pacific /etc/timezone

All set.  Run the date command to see the server’s timezone is now set to PST.

Have fun.

PGError: Server closed connection unexpectedly

I’ve been struggling with this error for sometime lately.  The issue goes like this:

I have a web based application developed using Ruby on Rails, that uses PostgreSQL as database.    It works perfectly fine for functions, which retrieves less data.  But for others which has more data, the client (RoR) fails with this error.   And the server log says, Client disconnected prematurely.  But if I keep hitting F5 (Browser Refresh), sometimes the page loads successfully.  Isn’t that awesome?

Google didn’t have any answer for this either.  I could see a lot of people posting this error in many blogs, but I didn’t see any solution that pertains to my problem.

If you have any solution for this, please let me know.

mysqldump and stored procedures

Today I found out something interesting.  Well, probably its only for me.  Mysqldump does not dump the stored procedures by default.   Default option for mysql dump is to exclude stored procedures.  Where as triggers are include by default.

So, in order to include stored procedures, you have to use option –routines. So, the command goes like:

mysqldump [other options of mysql dump] –routines > out_filename

How to change root password in mysql

You can use the mysqladmin tool to change the root password like this:

mysqladmin -u root -p'OLDPASSWORD' password NEWPASSWORD

How to set root password for mysql

mysql root password can be set by using the mysqladmin tool.

mysqladmin -u root password NEWPASSWORD

How to configure nginx to serve the images

Add this to your server configuration to configure nginx to serve the static contents like images, css etc.

location ~* ^.+\.(jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|pdf|txt|tar|wav|bmp|rtf|js|flv|swf|html|htm)$
{
root /path/to/static/assets;
}