Liferea stores a lot of information in an sqlite database. If sqlite databases aren’t vacuumed every now and then, they bloat and slow down.

Most people know about speeding up Firefox by vacuuming the sqlite databases every now and then. Well, the same can be done with Liferea.
Close Liferea and paste the following in a bash terminal.

sqlite3 ~/.liferea_1.4/liferea.db "VACUUM;"

Open up Liferea and you should notice it load much faster. Unless of course, it was fast to begin with.

It is better to use > log_file.log as that will allow the file system to free the space that is used by the open file.

df -h Shows how much disk space is available. The -h means that you get G for gigabytes, M for megabytes etc.

sudo du -k / | sort -n Shows which directories are biggest (starting at the root directory /). The biggest ones will be printed at the bottom of the list. The sudo allows du to check directories that your user doesn’t have permission for. To check your home directory only use du -k ~ | sort -n

du -ka | sort -n Shows the size of all the files and sub-directories of the current directory. The biggest ones at the bottom of the list.

watch 'du -ka | sort -nr' Shows the size of all the files and sub-directories of the current directory. The biggest ones at the top of the list. The list is updated every 2 seconds. This is useful for watching disk usage in a particular directory, such as an upload directory on a web server.

Hope this helps someone…

It turns out that I had enabled bash completion on one machine but not on the other.

To enable it for all users on your system you need to edit  /etc/bash.bashrc and uncomment lines 32 – 34 (in the default file) so it looks like:

# enable bash completion in interactive shells
if [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
fi

Open a new terminal and auto-completion should now work.

tail -f query.log | grep "thing I'm interested in" --color

Now you will see any new lines added to query.log that contain “thing I’m interested in” highlighted. Any other lines will be ignored.

In this post, I will cover what forward and reverse tunneling of ports through SSH is.  Why you would want to do it, and how to do it.  Port tunneling is also known as port forwarding.

Forward Tunneling

Port forwarding allows a specific port to be mapped between one computer and another.  A forward tunnel allows you to have a remote port appear as a local one.

This can be useful if you need to connect your MySQL query browser to a remote database, but the database only listens to localhost.  Although this section only talks about MySQL, it is applicable to almost any other piece of client/server software that uses specific ports.

To forward port 3306 (MySQL’s default port) to your local systems port 3306 use the following command:
ssh user@remote-hostname -L 3306:remote-hostname:3306

If you are running MySQL locally on port 3306, or want to use a different local port to the remote port, change the port before the first colon:
ssh user@remote-hostname -L 3305:remote-hostname:3306

Then you can connect to your remote MySQL server as if it was a local one.  Use the usual username, password and database name as you would to connect to the database, but change the host to 127.0.0.1 and the port to 3305.  You should now be able to access the remote database as if it was a local one.

Reverse Tunneling

Reverse tunneling allows you to have a port on a remote machine work as if it is a port on your local machine. It’s the exact opposite of a forward tunnel.
You could use this when working on code that needed to be accessed by a service that is outside of your firewall, but not ready to be deployed on a server. For example, developing a payment gateway for a shop, when the payment gateway needs to talk to the code that is on your development machine and you don’t want to (or can’t) make modifications to your firewall.

To reverse tunnel port 8080 on a remote server to port 80 on the local machine use the following command:
ssh username@remote-hostname -R 8080:127.0.0.1:80
This will let you, or anyone else, visit http://remote-hostname:8080 and see what is visible on http://127.0.0.1:80. In this case, your local web server is available to anyone who can see remote-hostname. If remote-hostname is a server available to the whole internet, the whole internet can see into your local machine that is usually hidden behind your firewall.

Some notes

• This guide is for OpenSSH, other implementations may vary.
• You will need to set GatewayPorts to yes in /etc/ssh/sshd_config (Don’t forget to restart sshd after the change).
• When you close your ssh session,  the port forwarding stops.

For more information, read the OpenSSH documentation and Frequently Asked Questions

Being fairly geeky, Jude and I thought we might be able to recover some of the photos. Never tried it before, but thought it should be possible.  If they can do it on CSI, it must be possible.  Right?

When you delete a file on a computer, usually the contents of the file remain on the disk but the information that tells the computer where the file is is deleted. Knowing this, we decided the best thing to do was to remove the memory card and take photos using a different one. This would stop us from overwriting any data that might still be on the card.

To reduce the chance of corrupting any data on the card, I made a copy of the entire disk. Using the command ‘dd’ I made an image of the disk.

dd if=/dev/disk/by-label/EOS_DIGITAL of=/home/toeknee/cf/backup.img bs=512 conv=notrunc

This made a 2 gigabyte file on my computer containing all the data from the compact flash card.

Fairly happy that I had a copy of the card, I unmounted and removed it and put it in a safe place. I looked around google for a while trying to find other examples of people recovering images, but I didn’t find much of use. I thought I have a quick look in the ol’ package manager for programs that could recover files from FAT file systems (FAT is the file system used by most cameras). I came across a program called PhotoRec in the package testdisk.

PhotoRec is described as “file data recovery software designed to recover lost pictures from digital camera memory or even Hard Disks.”

Sounds good to me. photorec /home/toeknee/cf/backup.img

Enter the directory that the photos should be restored to, start it up and wait.

15 minutes later I had 200-odd pictures of the wedding and some that I had deleted months ago.

Very happy Tony, Very happy Jude. Very happy group photo…

Edit: Added conv=notrunc to the dd command as suggested by docatomic