Tar

I’ve avoided the tar command for some time now, only to find there’s nothing to be afraid of.  My Windows background always led to pkzip for compression and archiving.  Knowing that zip shipped with OS X there wasn’t really a need to look any further.

But sometimes you’re sent things in the tar format.  Or the even more mysterious tar.gz.  If you have no experience with Linux or Unix the tar command and tar.gz files might leave you confused. Before OS X the only experience Murphy had with Linux was hacking a Directv TiVo so he could install a bigger drive.

Anyway - OS X makes tar and tar.gz files simple to work with.  Double-click one in the Finder and its contents are extracted.  But what if you want to create one?  Or see what’s inside before you open it?  We’ll do both of those things in the screencast, but here’s a quick overview of some tar basics.

tar -cvf irl08.tar Pictures/ireland_08

That command will create an archive called irl08.tar in the current directory.  All the files inside the ireland_08 directory will be placed inside, without compression.  The c creates the archive, the v displays progress as files are added, and the f specifies a file as the destination.  (tar stands for tape archive)

tar -zcvf irl08.tar.gz Pictures/ireland_08

This command is almost exactly the same, but the z option compresses the archive so we’ve added the customary gz to the file name.

Here’s how to view the contents of a tar archive:

tar -tvf irl08.tar

The t option lists the files.  If your archive is compressed add a z option too.

How does tar compare to zip?  Murphy isn’t sure what all the differences are.  He compressed a directory with dozens of screencasts in it using both utilities.  The resulting archive was about the same size for each.  The screencasts were already compressed themselves, so they might not be the best test subject.

A little research shows that extracting a single file from a very large archive might be quicker with zip than with tar.  A zip file includes a table of contents that makes locating an included file more direct.  And a zip file compresses the included files individually as they’re added.  A tar.gz file creates the archive first and then compresses the whole thing at once.  That can make single file extraction more time consuming as the entire large archive must be opened up.

There’s also gzip for compressing files.  But gzip deletes your original file, replacing it with the compressed one.   That makes Murphy a little nervous.  tar leaves your original files in place, so you can delete them if you need to.

tar.  One less thing to be afraid of.

You might find these posts interesting:

zip
command line encryption

Get More From Hotel Wifi

Using multiple devices with paid hotel Internet access.

This weekend I used the Internet at a hotel that charged for access. I signed up using my iPod, then later tried to access the service using a laptop. The sign-on page didn’t provide a place to sign in using my name or room number - it seemed like I might be charged again if I went any further. I had never seen the particular service before, so I couldn’t tell what would happen.

I didn’t feel like calling the front desk, and chances are I wouldn’t have had much faith in whatever they told me. Sounds cold, but it’s true. The solution I found was probably faster anyway.

I assumed the hotel tracked my iPod by its MAC address. If you’re not familiar with a MAC address, it’s a unique identifier assigned to network devices like your wired Ethernet port or a wifi card. (MAC addresses are not to be confused with Macs) Some software interfaces provide a simple way to change the MAC address your device presents to the network. I didn’t see a simple way in System Preferences.

A quick Google search landed me at OS X Daily. There you’ll find the exact command to enter in Terminal to change your MAC address. You may have to tweak the command a little if you’re using multiple network interfaces on your Mac, like wired and wireless.

So, I took the MAC address of my iPod and assigned it to the laptop. I didn’t try to use both at once, and both worked just fine. As soon as the MAC was changed on the laptop it was on the Internet, without having to access any special sign-up page for the service.

At some point hotels will probably update their services to help with a situation like this, but in the meantime OS X Daily helped me out in less than two minutes. Nice.

Disable Windows XP Notification Bubbles / Balloons

If you use Windows you might not be overly fond of the little bubbles that pop up down on your Task Bar. You know the ones — warnings about your firewall and unused items on your desktop?

A simple registry edit will stop the bubbles, for all applications. You can watch the screencast to see two ways to make the change. You can either make the edit manually using regedit, a registry editor that comes with Windows. Or you can download a file from Murphy and double-click it. The file will make the change.

You don’t have much to worry about. In fact, you can right-click the file (after unzipping it), select Edit, and you’ll see it’s just a couple lines of text. The change is easily undone. Simply delete the entry from your registry.

The balloons will stop appearing for all applications - only for the user you’re logged in as when you make the change. Log out and back in to test your results.

If you’re comfortable in the registry go ahead and make this entry:

Add a DWORD value in the following key, and name it EnableBalloonTips. Set its hex value to zero.

HKEY_CURRENT_USER\Software\Microsoft\Windows\

CurrentVersion\Explorer\Advanced

Not a registry person? Watch the screencast.

I don’t even know if they have bubbles in Vista…

Archive Your Mobile Phone Voicemail

Do you have messages on your phone that you save every time you review your voicemail? A call from your daughter announcing your first grandchild? Mary Pat McBride saying she does love you and she will go to the prom with you after all? Your boss calling - fully intoxicated - and promising you the Penske account?

If you’d like to get these messages off your phone and store them somewhere else Murphy has a solution. Run Audio Hijack while calling your mobile phone via Skype. Save the recording on your computer and you can delete it from your phone.

To call a mobile phone from your Skype account you’ll need Skype credit. Maybe you have a free-of-charge way to call your mobile from your computer. Let us know in the comments.

If you’re not familiar with Audio Hijack you can watch the screencast for details on how to capture your voicemail.

It really works.  Here’s a success story based on the experience of Jean MacDonald from Smile On My Mac.  (textexpander and more)

Related Post: You can make Skype always start in invisible mode. Or whatever mode you choose.

Set a Hardware Password For Your Mac

Many PC users are familiar with the idea of a firmware password that needs to be entered before the computer will load the OS. For PC power-users the BIOS or CMOS interface is familiar territory - and it’s the place where they set such a password.

Murphy Mac commenter Brian posted information on something similar for your Mac. Here’s the rundown.

Using the Open Firmware Password utility you can set a password on your Mac that will stop someone from resetting a user account password using the method described in this previous post. Essentially, it prevents unauthorized users from using a disk other than the machine’s internal drive to boot. The utility comes on the install disk that ships with your Mac.

Keep in mind this isn’t much additional security. It might slow down a casual attacker, but a determined foe with physical access to your machine can bypass this security. Your best bet for security that lasts is to encrypt your sensitive files using one of the methods described previously.