Archive for May, 2009
Umounting NFS Share After Deletion on the ‘Server Side’
Since I like to be an example to others of what not to do, I thought I’d share my fun today. Today I was doing a little cleanup on our systems and removed an empty directory that had been mounted by another system via NFS. (HINT: if you’re stuck in this position and need help fast, scroll to the end, otherwise I’m going to tell you the story) Not really realizing that I had done this, I went on with my day as normal. Later in the day, I was asked why all of a sudden certain operations were timing out on that system. The first thing I checked was disk space on the device which returned some mount points, but not all and “sat there doing nothing”. After a little while I closed the session and opened up a new one. Running a mount returned all the mount points that allegedly existed, but the list from my ‘df -h’ stopped at the mount right before the NFS mount point in question. Doing a ‘umount -f /mnt/point’ simply returned a “device is busy” error.
The particular directory that I had deleted was an old directory that we were using for Virtualmin to do its backups to and had moved. Since it was complaining I thought I’d just try doing a bounce of the Webmin/Virtualmin services quick to see if that helped since Virtualmin should’ve been the only application that needed to have files open in that directory. But, alas, didn’t make a difference. Then I had the bright idea of trying to find out what processes might’ve tried to have files open in that directory. I ran a ‘lsof | grep /mnt/point’ and it “sat there doing nothing” again..
After my failed attempts, I decided to try to recreate the directory on the other end, re-export the share and hopefully my system would pick back up where it left off. Unfortunately, I didn’t realize this, but my export had already been deleted from the /etc/exports file as well so recreating the directory and re-exporting the NFS shares did me no good.
A quick Google search led me to a post in the Ubuntu forums with a user saying they had to reboot. As this server is in production, a reboot was not an option at this point (or at least the worst possible scenario). For sure if the system was rebooted, the mount point wouldn’t be busy anymore but that’s no good. Later in the thread (after the unnecessary reboot) I found that one can let umount do a “lazy” umount. This lets the OS umount a mount point while still maintaining any references to files in that mount point until those processes lets go. Anyway, if you’re still with me, the command is:
sudo umount -l /mnt/point
Voila! No more timeouts checking disk space, lsof’s, and the mount point is no longer mounted.
Tags: linux, nfs, ubuntu
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May 29th, 2009
Failed New Zealand Deal With Microsoft Good News for Linux?
Microsoft’s recently failed contract renewal with the country of New Zealand is being hailed by blogs and news outlets as a big opportunity for other open source solutions to move in. I’m not quite ready to break out the champagne and streamers. Why would the country walk away from a deal? I don’t understand why the news outlets never mentioned this.. All we have to do is open up the front page of any major news site to see articles about the horrible state of our world’s economy. Of course they walked away from the deal. You don’t get steep licensing discounts from a vendor by jumping all over the first offer. It’s also car shopping 101. But you can just walk away for show. You have to walk away and mean it. Now, I’m not saying that New Zealand is not open to open source alternatives, but so far we haven’t been given evidence that they are moving in the open source direction. I guess only time will tell, but let’s not put the cart before the open source horse.
Tags: microsoft, open source
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May 28th, 2009
SATA 3.0 Standard Official
The Serial ATA International Organization has made its third generation of the SATA standard official. SATA 3 boasts a 6Gbps theoretical transfer rate from the storage controller to the storage device. Hardware manufacturers have already implemented some of the draft versions of the standard, so real world support should be soon to follow. While this new SATA standard doubles the amount of throughput on the line, traditional drives aren’t nearly fast enough to make use of this newly found speed. The new standard does contain a newer implementation of NCQ to allow SATA devices to make use of queuing optimizations, but the biggest improvement will be in drives with higher RPMs or solid state disks.
Tags: hardware
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May 27th, 2009
Cleaning Up After Safari 4
There’s been a few reports in the blogosphere of an issue with the Safari 4 beta not cleaning up after itself on OS X Leopard. Apparently this version of Safari leaves some data in the ~/Library/Caches/Metadata/Safari directory when clearing history as well as preview images of websites in /private/var/folders/
In the menu bar, go to Safari -> Reset Safari and select the webpage previews option. On my system this dumped the entirety of my webpages preview directory (as expected).
You can find out exactly which directory Safari is showing these previews in via the following command: ‘getconf DARWIN_USER_CACHE_DIR’
Tags: apple, safari
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May 27th, 2009
Once Again, Social Engineering Proves Much Easier Than Real Engineering
Whatever Twittercut was or wasn’t, it does seem to have proved an already-known fact once again surrounding computer security: sometimes it’s easier to just ask someone for their username/passwords than to try to steal them. Twittercut was a service that has been called a worm by several blogs and other methods because of its use of viral social techniques for spreading its popularity. The service was supposed to help one receive a large amount of Twitter followers after you entered your Twitter username and password into their service. This is no different than a lot of services out there for Twitter. However, when it started posting tweets in accounts, people got a little freaked out. Right or wrong, that’s what happened.
What’s important here, though, is the lessons learned. People, for some reason, seem to be all loosey goosey about their credentials to services such as Twitter. This is okay as long as one isn’t terribly concerned about those credentials being stolen. However, if one maintains a single password for all (or even a majority of accounts online) this can be a devastating problem. Once inside your Twitter account, a “thief” can get your email information. Once again, not a huge deal unless you share your password with your email account. If that is the case then things get interesting. Access to one’s email can potentially be key to breaking into other accounts that you hold. Why? Most online services allow you to fill in your username and send a password reset link to your email address.
Okay, so I took that much further than it was taken in this case, but often some of the most devastating worms are just that simple. Hopefully people who found themselves caught up in handing out usernames and passwords like they’re candy can get a little reality check after this scare.
Tags: security, twitter
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May 27th, 2009
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