The Linux Experiment

Five new Listener Feedback podcast episodes have been released in case you missed them:

• Episode 11: Chasing Eidolon – Chasing Eidolon (Pop Punk)
• Episode 12: Christopher Squier – Beneath the Ashes (Indie Rock, Bar Rock)
• Episode 13: Drop-Zone – Drop-Zone’s The Red Album MixTape CA V1 (Rap, Hip-hop, Mixtape)
• Episode 14: Tenpenny Joke – Ambush On All Sides (Rock, Punk)
• Episode 15: Trick Seventeen – Spot On (Pop Punk)

And as always you can grab the MP3 or Ogg version of this Creative Commons podcast.

Ever wanted your computer to be on when you need it but automatically put itself to sleep (suspended) when you don’t? Or maybe you just wanted to create a really elaborate alarm clock?

I stumbled across this very useful command a while back but only recently created a script that I now run to control when my computer is suspended and when it is awake.

#!/bin/sh
t=`date –date “17:00″ +%s`
sudo /bin/true
sudo rtcwake -u -t $t -m on &
sleep 2
sudo pm-suspend

This creates a variable, t above, with an assigned time and then runs the command rtcwake to tell the computer to automatically wake itself up at that time. In the above example I’m telling the computer that it should wake itself up automatically at 17:00 (5pm). It then sleeps for 2 seconds (just to let the rtcwake command finish what it is doing) and runs pm-suspend which actually puts the computer to sleep. When run the computer will put itself right to sleep and then wake up at whatever time you specify.

For the final piece of the puzzle, I’ve scheduled this script to run daily (when I want the PC to actually go to sleep) and the rest is taken care of for me. As an example, say you use your PC from 5pm to midnight but the rest of the time you are sleeping or at work. Simply schedule the above script to run at midnight and when you get home from work it will be already up and running and waiting for you.

I should note that your computer must have compatible hardware to make advanced power management features like suspend and wake work so, as with everything, your mileage may vary.

This post originally appeared on my personal website here.

A new episode of the Listener Feedback podcast has been released. This episode features the folk rock artist Bill Borman with his Creative Commons album In Our Dreams We’re Flying. Download it here.

A new episode of the Listener Feedback podcast has been released. This episode features the German rock band DirtyOldSpice with their Creative Commons album Follow The Traveler. Download it here.

It is a pretty common practice to use the command dd to make backup images of drives and partitions. It’s as simple as the command:

dd if=[input] of=[output]

A while back I did just that and made a dd backup of not just a partition but of an entire hard drive. This was very simple (I just used if=/dev/sda instead of something like if=/dev/sda2). The problem came when I tried to mount this image. With a partition image you can just use the mount command like normal, i.e. something like this:

sudo mount -o loop -t [filesystem] [path to image file] [path to mount point]

Unfortunately this doesn’t make any sense when mounting an image of an entire hard drive. What if the drive had multiple partitions? What exactly would it be mounting to the mount point? After some searching I found a series of forum posts that dealt with just this scenario. Here are the steps required to mount your whole drive image:

1) Use the fdisk command to list the drive image’s partition table:

fdisk -ul [path to image file]

This should print out a lot of useful information. For example you’ll get something like this:

foo@bar:~$ fdisk -ul imagefile.img
You must set cylinders.
You can do this from the extra functions menu.

Disk imagefile.img: 0 MB, 0 bytes
32 heads, 63 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x07443446

        Device Boot      Start         End      Blocks   Id  System
imagefile.img1   *          63      499967      249952+  83  Linux
imagefile.img2          499968      997919      248976   83  Linux

2) Take a look in what that command prints out for the sector size (512 bytes in the above example) and the start # for the partition you want to mount (let’s say 63 in the above example).

3) Use a slightly modified version of the mount command (with an offset) to mount your partition.

mount -o loop, offset=[offset value] [path to image file] [path to mount point]

Using the example above I would set my offset value to be sector size * offset, so 512*63 = 32256. The command would look something like this:

mount -o loop, offset=32256 image.dd /mnt/point

That’s it. You should now have that partition from the dd backup image mounted to the mount point.

I recently re-built an older PC from a laundry list of Frankenstein parts. However before installing anything to the hard drive I found I wanted to check it for physical errors and problems as I couldn’t remember why I wasn’t using this particular drive in any of my other systems.

From an Ubuntu 12.04 live CD I used GParted to to delete the old partition on the drive. This let me start from a clean slate. After the drive had absolutely nothing on it I went searching for an easy way to test the drive for errors. I stumbled across this excellent article and began using badblocks to scan the drive. Basically what this program does is write to every spot on the drive and then read it back to ensure that it still holds the data that was just written.

Here is the command I used. NOTE: This command is destructive and will damage the data on the hard drive. DO NOT use this if you want to keep the data that is already on the drive. Please see the above linked article for more information.

badblocks -b 4096 -p 4 -c 16384 -w -s /dev/sda

What does it all mean?

• -b sets the block size to use. Most drives these days use 4096 byte blocks.
• -p sets the number of passes to use on the drive. When I used the option -p 4 above it means that it will write/read from each block on the drive 4 times looking for errors. If it makes it through 4 passes without finding new errors then it will consider the process done.
• -c sets the number of blocks to test at a time. This can help to speed up the process but will also use more RAM.
• -w turns on write mode. This tells badblocks to do a write test as well.
• -s turns on progress showing. This lets you know how far the program has gotten testing the drive.
• /dev/sda is just the path to the drive I’m scanning. Your path may be different.

A new episode of the Listener Feedback podcast has been released. This episode features the Internet nerdcore gangster rap super group Futuristic Sex Robotz with their album Hotel Coral Essex. Download it here.

A new episode of the Listener Feedback podcast has been released. This episode features the industrial group Fresh Body Shop with their album Doctor X. Download it here.

A new episode of the Listener Feedback podcast has been released. This episode features the extremely talented acoustic rock artist Josh Woodward with his album Dirty Wings. Download it here.

A new episode of the Listener Feedback podcast has been released. This episode features the extremely talented one-man rock band Slim with his album Interstate Medicine. Download it here.