Brandon Purcell's Blog

Helpful command to see disk space usage on linux by directory

2010-03-30T19:48:43-07:00

I was running out of space on a server the other day and was wondering what directory was full and what files I could clean up. There is a simple command that is helpful to identify usage by directory. This works from within any directory so you can walk the path from / down through your largest directories and look for files to clean up.

[root@localhost]# du -hc --max-depth=1
4.0K ./misc
4.0K ./srv
576K ./root
29M ./sbin
16K ./tmp
2.0G ./usr
731M ./proc
12M ./boot
0 ./sys
379M ./appserver
28M ./opt
447M ./var
85M ./lib
8.0M ./etc
11M ./home
0 ./selinux
6.3M ./bin
16K ./lost+found
40K ./dev
24K ./mnt
3.7G .
3.7G total

Help with PostgreSQL commands

2010-01-06T08:14:10-07:00

We use PostgreSQL for SpatialKey and because of that I have learned a lot about system administration with PostgreSQL. While debugging an issue with tables that had ballooned up I ran into this article which has some great tips for isolating db and table size with a few quick commands. http://www.thegeekstuff.com/2009/05/15-advanced-postgresql-commands-with-examples/

Also check out 15 Practical PostgreSQL database administration commands and backup and restore PostGreSQL with pg dump and psql.

Keeping a session alive on ColdFusion using Jquery

2009-08-04T06:36:45-07:00

There is nothing more frustrating than taking 30 minutes filling out some text in a long form only to submit and have your session reset and lose all of your data. Here is a simple solution to keep a session open on forms where users may need an extended period of time for data entry. I included this code on any page where I need the session extended. You can remove the javascript include if JQuery is included on everyone of your pages already.

<!--- Include this file on any page where users may take a 
long time filling in text and you want to keep the session open --->
<cfparam name="variables.refreshrate" default="60000">

<cfoutput>
<script type="text/javascript" src="/js/jquery-1.3.2.min.js"></script>
<script language="JavaScript" type="text/javascript">
	$(document).ready(function(){
 					setTimeout("callserver()",#variables.refreshrate#); 
 				});
 	
 	function callserver()
 	{
 		var remoteURL = '/emptypage.cfm	';
			    $.get(remoteURL,  function(data){
			      //alert(data);
			      setTimeout("callserver()",#variables.refreshrate#);
			    });
 	}
</script>
</cfoutput>

Drunk on Software episode featuring members from the SpatialKey team

2009-07-30T12:09:35-07:00

James Ward and Jon Rose recently published the latest episode of Drunk on Software with members of the SpatialKey team, including myself, Tom Link, and Doug McCune.

In the video we talk about Universal Mind, how SpatialKey came to be, a lot about what SpatialKey is and how it works. I dive into the architecture a bit and how we leveraged the cloud to build out our infrastructure.

Thanks to Jon and James hosting us, we crashed Jon's house for the video. I think Doug tossed back the most beers I can't keep up with him and still talk.

Linux NFS mount: failed, reason given by server: Permission denied

2009-06-11T18:28:56-07:00

This issue drove me nuts today for several hours today, to be honest I was pretty close to breaking something! Earlier in the day I had the NFS mount working fine then I created an AMI and booted up another instance from the newly created AMI but in the new instance the mount kept failing. The error looks something like this:

[root@server]# mount -t nfs 192.168.2.1:/dbshare /mnt/dbshare
mount: 192.168.2.1:/dbshare failed, reason given by server: Permission denied

According to the error you would think that I have a configuration issue so I changed everything that I could think of within /etc/exports

My /etc/exports originally looked like this:

/dbshare 192.168.2.2(rw,sync) (where 192.168.2.2 is the client where I am performing the mount)

I changed it to something more open like this with no luck:

/dbshare 192.168.0.0/255.255.0.0(rw,sync)

I started looking around the logs on the server in /var/log/messages and found that it was authenticating fine
Jun 11 19:04:00 servername mountd[5222]: authenticated mount request from 192.168.2.2:736 for /dbshare (/dbshare)

I was really frustrated at this point and I had already spent an hour on Google looking for the answer. I found another answer but the website was down, luckily the cached version on Google came to the rescue.

The ANSWER:

The problem was that the special nfsd file system that mounts to /proc/fs/nfsd wasn't mounted. I'm not sure how it gets mounted (maybe rc.sysinit does it?), but I tool the advice from the forum entry and added an entry to /etc/fstab

none /proc/fs/nfsd nfsd auto,defaults 0 0

then ran mount -a

After this the mount worked fine. I hope that someone finds this helpful.

Recursively deleting .svn directories

2009-05-27T10:15:32-07:00

I often need to copy code from a SVN repository to a location where I have files deployed or I may pull code from an SVN repository on the web and want to check it in locally. Both of these actions require the stripping out of all .svn directories spread throughout the directory structure. On Linux or Mac this is pretty simple with the following command

sudo find -d . -name '.svn' -exec rm -rf '{}' \; -print

Slick Example of JQuery Selectors

2009-05-14T22:50:11-07:00

I ran across this today. Examples are great when trying to understand JQuery selectors.

CFDUMP for PHP and Javascript

2009-05-14T11:34:24-07:00

In recent months I have been using PHP to extend functionality inside of WordPress for the SpatialKey site and working with JQuery as well. After working with ColdFusion for so long I have gotten spoiled by the CFDUMP tag . Here are a few options similar to CFDUMP for both PHP and Javascript.

CFDUMP for PHP - dBug

CFDUMP for Javascript

Sending SMTP messages from your EC2 instances

2009-04-29T13:27:05-07:00

One challenge I have encountered with Amazon Ec2 is the sending of email from our web applications. If you try to send directly from sendmail or postfix then you might as well forget about guranteed delivery. A large amount of your email will end up in spam folders if it is even delivered at all.

There are a few problems with delivering email from Ec2

MX record will not map to your IP and you are using dynamic IPs (you can address this with elastic IP's) adding a SPF DNS record can help as well
Reverse DNS will map back to Amazon and not back to your Hostname
Many of the Ec2 IP's have been blacklisted due to abusers of the service sending spam.

There are a few solutions to this problem and I will propose two of them.

Using a google apps account:

If you are using a solution like Google Apps and have them host your email accounts then you can use gmail as your SMTP server. You will need to create an account donotreply@mydomain.com and use authentication in your applications to send the email. With Google apps you cannot override the "from" address when you send email it wil always become whatever you account you are sending from. For example if you create the account donotreply@mydomain.com and attempt to set the "from" in your code to send from brandon@mydomain.com google will override it and send from donotreply. The only option is to set "replyto" in your code and when a user replys they will send to your replyto account. With google apps you are limited to a maximum amount of 500 emails a day per account as well and if you are sending a lot of emails this can quickly become a problem. This is a great solution for small volumes of email and you delivery rates are very good.

Relay from localhost through a third party:

This blog post outlines a set of steps to relay through a local Postfix instance to a third party SMTP service. The great thing about this solution is that you can send email from your application to localhost without storing the authentication parameters in your applications code and have Postfix handle it all. If you have many applications sending email this can greatly simplify things. Also it allows your application to hand off the emails quickly to another service that can handle queuing in case the third party email service is down at any time. You could combine the approach above with this one but you would still have the 500 email limitation. I am searching for a good third party SMTP service that is reliable, the author of the blog post recommends AuthSMP. I have not tried them and their prices are not too high but not cheap either. I am going to do a little more digging and test some of the options and will report back to this posting.

Running applications at startup on Linux with chckconfig

2009-04-29T12:13:53-07:00

This is common knowledge if you have been using Linux for a while but I still find it a helpful resource to understand how you set what programs are running when Linux starts. This is mainly specific to Red Hat or CentOS which I use on a regular basis.

Running level
Running level is the current running functional level of the operation system, from level 1 to 6, possessing different functions.
Here are the different running levels:

0 - downtime or halt
1 single user mode
2 multi-userno NFS
3 entire multi-user mode(standard running level)
4 not available
5 - X11 multi-user graphic modexwindow)
6 - restart never set initdefault 6

These levels are specified in the file /etc/inittab., which is the main file that the program init looks for, and the first running service is placed under the directory /etc/rc.d. For most Linux releases, startup scripts are all located in /etc/rc.d/init.d, which are all linked to the directory /etc/rc.d/rcn.d by ln command (here the n is the running level 0-6).

Setting services/applications to run at startup using chkconfig

chkconfig command (under redhat and centos)

Linux provides the command chkconfig to update and query system services of different running levels allowing you to set when certain process are started.

Syntax:
chkconfig --list [name]
chkconfig --add name
chkconfig --del name
chkconfig [--level levels] name
chkconfig [--level levels] name

example:

[user@server]# chkconfig --list
anacron        	0:off	1:off	2:on	3:on	4:off	5:on	6:off
atd            	0:off	1:off	2:off	3:on	4:on	5:on	6:off
autofs         	0:off	1:off	2:off	3:on	4:off	5:on	6:off
conman         	0:off	1:off	2:off	3:off	4:off	5:off	6:off
crond          	0:off	1:off	2:on	3:on	4:on	5:on	6:off
dc_client      	0:off	1:off	2:off	3:off	4:off	5:off	6:off
dc_server      	0:off	1:off	2:off	3:off	4:off	5:off	6:off
getsshkey      	0:off	1:off	2:off	3:off	4:on	5:off	6:off
haldaemon      	0:off	1:off	2:off	3:on	4:on	5:on	6:off
haproxy        	0:off	1:off	2:off	3:on	4:on	5:on	6:off
httpd          	0:off	1:off	2:off	3:off	4:off	5:off	6:off
ibmasm         	0:off	1:off	2:off	3:off	4:off	5:off	6:off
ip6tables      	0:off	1:off	2:on	3:on	4:on	5:on	6:off
iptables       	0:off	1:off	2:on	3:on	4:on	5:on	6:off
jexec          	0:on	1:on	2:on	3:on	4:on	5:on	6:on

chkconfig has five functions: add service, delete service, list service, change startup info and check the start state of specified service.

Option overview:

--level levels
specify running level, which is a character string composed of the number 0 to 7. For example:
--level 35 means to specify running level 3 and 5.
To stop the service nfs during running level 3,4,5, use the command next: chkconfig --level 345 nfs off

--add name
This option adds a new service, chkconfig ensures every running level an entrance to start (S) or to kill (K). if it is absent, then it would auto establish from default init script.

--del name
To delete service and delete related sign connections from /etc/rc[0-6].d.

--list name
List, if name is specified, then it only displays specified service name, otherwise, to list the state of all service at different running levels.

Usage examples:

As an example if you wanted mysql to run when the os starts you just need to do the following

/etc/init.d/mysqld must exist and needs to be an executable (chmod +x)
Add mysql - chkconfig --add mysqld
setting the start level - chkconfig --level 345 mysqld on

This example applies to any server and to validate that it worked you can use chkconfig --list | grep mysql to see the changes

.htaccess tips and tricks

2009-04-29T09:36:28-07:00

I ran across this article while debugging some .htaccess issues on our SpatialKey server and found some helpful information on .htaccess.

Monitoring in Linux

2009-04-23T10:01:26-07:00

This is a good article on some monitoring tools for Linux. I had already used several of them before but found 'htop' and 'atop' in the comments and they are great

JBoss - Generating a thread dump with twiddle

2009-04-23T08:20:49-07:00

I had been looking for a simple way to get a thread dump from JBoss to see what was happening on each of the SpatialKey servers without actually logging onto any of them. After all reading through thread dumps is one of my favorite past times. I found a simple way to do that writes an HTML file containing the thread dump and I can access it by hitting the webserver directory at a hidden URL.

The command is rather simple to generate a thread dump:

/jboss/bin/twiddle.sh invoke "jboss.system:type=ServerInfo" listThreadDump > /dump.html

I modified the /etc/crontab file to create this file every minute

*/1 * * * * root //jboss/bin/twiddle.sh invoke "jboss.system:type=ServerInfo" listThreadDump > /apachewebroot/subdir/dump.html 2>&1

It is pretty simple but it worked for what I needed.

Searching through many files for a specific string in Linux

2009-04-07T14:33:40-07:00

I found a helpful command today to help me search through many different file in linux. I have a bunch of log files and want to find a certain occurrence of an error.

for i in `find ./`; do grep -H "string to search" $i; done

Putting your Excel Data on the Map - Data Visualization and Reporting with SpatialKey

2009-03-27T21:22:42-07:00

Excel is a powerfull tool for sorting and analyzing data but what if you want to look at your data from another angle. What if you want to see the geographic aspect and understand the trends both over time and geographically? Geocoding your data can be a challenging task and getting it on a map can be even more of a pain. SpatialKey takes the pain out of mapping your excel data and makes it simple to get your data into a map and build engaging reports.

I have outlined this process in an article explaining how to take your excel data and get it into SpatialKey