show changes for a certain revision in svn

In order to show the source code changes for a certain revision "RVSN", use the following command:
> svn diff -c RVSN

hide tab in Thunderbird

In order to hide the tab in Thunderbird and increase the useful window area, set the option "mail.tabs.autoHide" to "true" by using the Config Editor (accessible from Preferences > Advanced > General). If more that one tab are created, then the area is displayed again.

map Alt key in Linux when logging from Mac OS X

When logging from Mac OS X in Linux via ssh, the Alt key seems not to be mapped correctly, and it cannot be used in emacs. The solution seems to be to run this command on the Mac OS X machine from which you connect:
xmodmap -e "keycode 66 = Meta_L"

fix create INBOX folder problem in Thunderbird

When using Thunderbird with IMAP folders, you may encounter the fact that INBOX folders are created in the IMAP directory when moving messages to Trash.
One way to fix this is to use the Config Editor (Preferences > General menu) and search for "trash_folder_name". The value of can be something like INBOX/Trash, and it should be changed to Trash.
You should restart Thunderbird for the changes to take effect.
Reference: http://superuser.com/questions/278745/thunderbird-creates-a-folder-called-inbox-on-imap

prevent updates in ubuntu

To prevent the update of certain packages in Ubuntu, you can use Synaptic to lock those packages. This is accomplished by selecting the package and then choosing Package > Lock version from the menu.

For example, in order to prevent kernel updates, the following packages should be locked:
- linux-headers-generic
- linux-image-generic
- linux-headers-generic-pae
- linux-generic