Mac crash / Mac blue screen flash during use (not at startup)

A few days ago my MacBook Pro (running OSX 10.6.6) starting having some weird issues. I would be working on the computer, and all of a sudden the screen would flash blue, and then a few seconds later show my blank desktop background, and then finally the dock would come back. All within a few seconds. All of my applications would be closed as if it had restarted.

This has happened about five times, all when I was using different programs. The first time it happened, it was after I dragged a file to trash; after that it happened while using iPhoto and it had frozen up on me; and another time while using Safari. Most recently, the blue screen flash occurred after waking the computer from sleep and trying to close the browser windows in Google Chrome.

I've researched a lot of Mac forums and apparently this is a common problem, and I saw posts from 2007 that were never resolved; I still haven't found a forum with a clear answer.

Anyways, I reviewed the console from the crash this morning, and saw that there was quite a bit of activity all occurring around the time of the blue screen flash, like "windowserver port death" and a whole lot of errors and warnings. This narrowed it down to a possible problem with the window server. I took it in to the Apple store nearby and spoke with a Mac Genius. I showed him the console with the errors, and he suspected it might be a permissions error causing the system to crash and then reboot (looks like it is logging out and then re-logging in at rapid pace).

The Mac Genius attached an external hard drive and rebooted from that and ran permissions repair. He recommended doing this every 3 months or so since it is easy to corrupt permissions. I had never done this before, and it took about 12 minutes. He also said he would recommend doing this at home by booting from the Install DVD I got with the computer. To do this, you have to press the 'option' key during startup in order to have the option to boot from the DVD. (I guess this is a change from pressing "C" with older models.)

Here's how to reboot and repair permissions from the OSX install DVD:

• Insert install DVD, restart computer, and hold down the 'option' key during startup.
  
• This will give the options of booting from the hard drive or the DVD – select DVD
  
• The reboot could take up to 5 minutes or so.
  
• When install screen comes up, go to "utilities" in the top menu bar and select "Disk Utility."
  
• Click on the main hard drive (not the subfolder/partition), and click on "repair disk permission" button, allowing the process to complete. This could take a while, especially if never done before. (It could take up to 3 hours, but mine took 12 minutes.)
  
• Quit Mac OSX installer from the menu bar and restart.
  

We were thinking this should clear up the problem, but if not, the second resort is to archive & reinstall OSX (archive will save all your data), and a third resort is to erase and install (after full backup of all data, of course). We'll see what happens! Hopefully it will work. That would be nice, since it is rather annoying to get the blue screen flash in the middle of doing something, and loosing any data you were working on.  

Update 5/17/11
Well, after many months, many disk permissions repairs and many more blue screen crashes, we decided to go back to the Genius Bar. It was evident that the problem was not fixed. When we returned they ran a test on the hard drive. It apparently failed the test to some degree because they replaced the hard drive. Perhaps it was a hardware problem all along? We'll see.

-- This is a guest post by my wife Susan

VSFTPD & SELinux

This can be a fun combo to work with. SELinux, or Security Enhanced Linux, is the life of any party. And Google searches about SELinux-related problems makes it pretty evident that very few people have taken the time to understand how this program works. I ran across numerous people simply suggesting that you turn off SELinux if it is getting in the way.

Well, I didn't buy into this wholesale approach to getting things to work. Besides, I want a secure system and if SELinux is going to help me in the long run, I want it enabled.

VSFTPD, or Very Secure FTP Daemon, is a pretty standard FTP server. You can install it on CentOS systems (or RHEL, for that matter) by running "yum install vsftpd" from the command line. Once you get it installed you can make changes to the configuration file at "/etc/vsftpd/vsftpd.conf" using a file editor. Also, to make sure it is always running in the background run "chkconfig vsftpd on" and "service vsftpd restart" from the command line.

Make sure the configuration file is set up properly. Only give FTP access to a limited number of users (never include root), disable anonymous access and make sure users can only access the files they need (I recommend chroot-ing them).

This is only half the battle. Now that VSFTPD is running, how do you allow users to access their home directories? SELinux usually will get in the way of this. Well, there is a SELinux setting for this called "ftp_home_dir" and this will allow users to access their home directory via FTP. To set this, from the command line run

setsebool -P ftp_home_dir 1

Be sure to also check file permissions and file ownership, if you run into problems. A file must be writable for everyone if they do not specifically own it.

If this fails to grant you FTP access where you need it, or your set-up is slightly different, you can always allow the FTP daemon full access to all files by running

setsebool -P allow_ftpd_full_access 1

This is granting a bit more power to the FTP daemon than is necessary, but it is much better than just disabling SELinux all-together.

By the way, here is a great intro to CentOS & SELinux.

Calculating Popularity

I am working on a new site that will have a sort of ranking system. It will be used to list a series of resources that visitors can rate and score. This scoring will then drive what resources are listed first and what resources are listed last.

Well, how in the world do you calculate ratings? I want to make sure new sites get a chance to rank high (so that old sites don't stay at the top forever). I also want to make sure that sites with a low number of votes are put at the top, just because all of the 2 people voted the max. And the list goes on, the more you think about it, the more there is to it.

Well, this blog entry does a great job of explaining different ranking algorithims and how they work. I give it a great score and a high rank. ;)

Database connection (mysql_connect) taking a long time

After setting up a new database, the connection from the web servers was really slow. We had enough combined traffic to slow down the response of the PHP function mysql_connect() to between 5 and 20 seconds. But the current load on the MySQL server wasn't that high... something fishy was going on.

What I found was that the database server was trying to do a reverse look-up on every connection using the IP. It was slowing down every connection for this. You can disable this by using the following option, as explained here.

--skip-name-resolve

"Do not resolve host names when checking client connections. Use only IP addresses. If you use this option, all Host column values in the grant tables must be IP addresses or localhost. See Section 7.9.8, "How MySQL Uses DNS"." --> http://dev.mysql.com

Anyway, you can make this change in the configuration file to be loaded at start-up (it doesn't have to be a command-line option). Simply add "skip-name-resolve" on a new line in the /etc/my.cnf file and restart your DB server. Voilà!

Good Design

I've been thinking about good design for the past few months. Apple always seems like the best example of good design because of the simplicity, ease of use and rugged product designs.

I came across this article today about Dieter Rams, a product designer that has influenced many, including Apple.

Here are 10 principles of good design attributed to him:

• Good design is innovative.

  
• Good design makes a product useful.

  
• Good design is aesthetic.

  
• Good design helps us to understand a product.

  
• Good design is unobtrusive.

  
• Good design is honest.

  
• Good design is durable.

  
• Good design is consequent to the last detail.

  
• Good design is concerned with the environment.

  
• Good design is as little design as possible.
  

Happy New Year!

It is here: 2011. To begin this new year my wife and I will be moving to Seattle. We are excited and are looking forward to the change in seasons, again. It has also been over one year since I began web development full-time (I had done it part-time for many years prior). Things have gone very well for a first year, a blessing for sure. So many adventures.

Happy New Year!

Pure-FTPd and Passwords

I use pure-ftpd as my FTP server, mostly because it was on the first server I managed and I got used to it. I've been having a little difficultly with setting it up on two new cloud computers and I came across this helpful note.

I set up new linux users and then when I tried to connect via FTP I would get a 530 Login authentication failed.

For whatever reason, if you create a new user and want to use it for FTP, the user must have a shell assigned. You can check the shell by looking at the /etc/passwd file and looking at the last parameter. If the user has no valid shell assigned, you can set this with a command like this:

chsh -s /bin/bash theusername