Unmounting disks in Ubuntu is a bit more challenging than it should be. Say you have an external drive mounted on /media/disk. Trying the standard
sudo umount /media/disk
will often result in an error such as
umount: /media/drive: device is busy.
It is advisable to check what files may be open on the drive with
lsof | grep /media/disk
If something important is still open on the disk, make sure to close the files or programs using the disk. If nothing else should be keeping the disk busy, you can usually achieve an unmount with
sudo umount -vl /mnt/external_disk
This performs a verbose, lazy unmount – i.e. Ubuntu unmounts the disk drive when the device is no longer busy, showing any errors in the unmount if there are any.
To confirm [...]
How to unmount a disk drive in Ubuntu (device is busy)?
Securely erase hard drive on Ubuntu (unrecoverable shred command)
Did you ever want to securely erase a hard disk on your server so the data is unrecoverable? Maybe you are selling the drive or the computer and want to be sure that no sensitive data can be recovered by a future owner. Ubuntu has a command line tool for just that purpose. If you want to completely erase the drive your system is on, first boot your computer using a Ubuntu LiveCD or the server install disk. Then, from the terminal (located in Applications->Accessories->Terminal if you use the Desktop LiveCD) enter the shred:
sudo shred -vfz -n [times] [your hard drive]
For example, you could type
sudo shred -vfz -n 5 /dev/sda
This would overwrite the data on the drive in /dev/sda with [...]
CSS Grid Systems (960 gs and blueprint)
CSS Grid Systems have become the latest Web design trend. While controversial among the HTML purists because grids violate the strict separation between content and presentation through the insertion of CSS classes such as class=”grid_4″, designers big and small are falling in love with them. Grids certainly streamline, simplify and sometimes even inspire the design process.
While there are many grid systems available today, two have attained particular popularity:
960 Grid System
Blueprint CSS Framework
And not much time has passed until they were picked up as base themes for our favorite CMS Drupal:
NineSixty base theme for Drupal
Blueprint base theme for Drupal
While we prefer to build our own themes from scratch, these base themes are a good starting point for anyone just starting out with grids and [...]
‘Shutdown’ versus ‘poweroff’ versus ‘halt’ on Ubuntu server
There seems to be a lot of confusion around how to properly restart or shut down your server under Ubuntu. The are several commands out there: halt, shutdown, poweroff and reboot. Which are the right ones to use and what are the differences?
Historically, halt, poweroff and reboot were fairly low-level commands that would do exactly what their command name implies. However, they would not gracefully take down your server – it was presumed that the server administrator would do that him- or herself before invoking these commands. Many newer Linux users were not familiar with the right usage scenarios and, as a result, the commands were changed to invoke shutdown, a gentler command that gracefully terminates any open processes by [...]
Augmented reality away from the iPhone or computer
Augmented reality has been a popular topic for the iPhone as well as computers or game consoles. Now it appears that next year we are going to see more compelling products from the AR field outside of just iPhone applications, sales materials, and PC/console games:
Recon Instruments is getting ready to launch ski googles with build-in heads-up display. Utilizing various sensors to display real-time information on speed, slope angle, weather, altitude, and more, the googles also use a GPS to show you your friends’ locations on the slope! All this technology takes up space but since ski goggles are naturally pretty bulky, it’s not as intrusive. I can’t wait for similar technology to make it into sunglasses in the next decade.
Google adds ‘Site Performance’ to Webmaster Tools – ready for Caffeine?
Google just added a new performance feature to the Labs section of its Google Webmaster tools. The ‘Site Performance’ feature displays a historical overview of your site performance (see picture below) as well as Page Speed suggestions for your slowest pages underneath.
The suggestions take the form of some stats on the page as well as suggestions to improve performance:
[Link to the page]
Details: Save up to [xxx] KB, [xxx] requests, [xxx] DNS lookups
Enable gzip compression
Combine external JavaScript
Minimize DNS lookups
Combine external CSS
Much has been blogged about Google’s new Caffeine engine and its effect on SEO and SERPS rankings. Google certainly seem to be pushing for faster page loading. I doubt Google will take this to the extreme though. If a feature doesn’t improve [...]
Has your mail server has been blacklisted for spam?
We used a shared host for one of our projects and recently noticed a lot of emails not making it to their intended destinations. It turns out that someone else on our shared host was using it to send spam and, as a result, everyone’s email from that IP address was marked as spam as well.
How can you find out if your mail server has been blacklisted for spamming? Use these tools below:
Spamhaus SBL Blacklist
MX Toolbox Spam Blacklist lookups
Also, if you have your own dedicated server (or rather dedicated IP address, which is a good thing), make sure you get a reverse DNS entry for your IP address from your provider – this helps a lot in avoiding overly aggressive spam filtering since [...]
ChromeOS and the “Cloud” – where did my desktop go?
Google recently showed off their upcoming ChromeOS and released parts of the project into open source.
ArsTechnica published a very good overview of what the OS does and does not offer. I certainly don’t even want to attempt to replicate their effort. The most interesting part about the ChromeOS is what it doesn’t do: to achieve its advantages in (startup) performance and security, it basically does away with your local file system. Like workstations running off servers of an era past, ChromeOS basically is said to be a thin-client for the “Cloud” and the Internet.
Now, the “Cloud” is a much abused term lately. Some good explanations of the concept can be found in There’s Grid in them thar Clouds and also [...]
SSL Vulnerability
This may be a bit worrisome if you have valuable data to protect online:
HTTPS, SSL attack vector discovered; fix is on the way
A fix is on the way and hopefully this gets resolved quickly before hackers start taking advantage of it. Or maybe they have known about this for a while before security researchers found it? I’ll update this story when the fix has been released.
Cheap circuits on non-silicon – Xerox breakthrough
The next few years should get interesting. Xerox has announced the availability of silver-based inks that can print circuits on materials other than silicon; for example plastic, film or textiles.
The implications of these silver circuits are interesting. We will be able to embed electronics more cheaply and in much more useful materials. No one wants to walk around wearing a silicon board. But what if regular clothing could become ‘intelligent?’
One immediate application would be RFID tags. This breakthrough will lower their cost dramatically paving the way for huge efficiency gains in warehousing and shipping logistics. I wouldn’t be surprised if RFID readers start making their way into consumer electronics in the next few years, allowing consumers to scan all [...]