Sending Desktop Notification from Cron

Usually when one wants to keep track of one’s cron jobs, one tells the cron daemon to email the output of the commands. While this is probably the best solution for servers, on desktop machines is problematic. Many ISPs block outgoing traffic on port 25 (SMTP), and if you want to send the emails via external SMTP server (such as GMail) this requires you to store authentication details in plain text. A better solution for the desktop would be to harness the desktop notifications available in Ubuntu.

There is a useful tool called notify-send which is able to send desktop notifications directly from the command line. However, there are few caveats:

  • notify-send expects its input on the command line, it can’t read from stdin.
  • If you run from cron you must tell it which display to use.

The first issue can be worked around by using cat to pick up the input. The second issue is handled by adding a DISPLAY environment variable to the crontab. So your crontab will look something like this:

DISPLAY=:0
10 1 * * sun some_cool_command | notify-send "Backup Documents" "$(cat)"

The first argument to notify-send is the title of the notification. The second is the actual text to appear in it, in our case it’s whatever comes in the stdin. If you want to store the output in a log file as well as displaying it in a desktop notification, you can use tee, which basically saves its input to a given file and also pipes it again to stdout.

DISPLAY=:0
10 1 * * sun some_cool_command | tee -a ~/some_log.log | notify-send "Backup Documents" "$(cat)"

Fixing virtualenv after Upgrading Your Distribution/Python

After you upgrade your python/distribution (specifically this happened to me after upgrading from Ubuntu 11.10 to 12.04), your existing virtualenv environments may stop working. This manifests itself by reporting that some modules are missing. For example when I tried to open a Django shell, it complained that urandom was missing from the os module. I guess almost any module will be broken.

Apparently, the solution is dead simple. Just re-create the virtualenv environment:

virtualenv /PATH/TO/EXISTING/ENVIRONMENT

or

virtualenv --system-site-packages /PATH/TO/EXISTING/ENVIRONMENT

(depending on how you created it in the same place). All the modules you’ve already installed should keep working as before (at least it was that way for me).

Creating a Deb for an Updated Version

Say you’ve an existing package like gitg and you want to use the new version of gitg or even apply your own patches. You could directly make install but you will probably regret it as soon as you’ll want to upgrade/uninstall, and you want to create a better package than the one created by checkinstall. Apperantly, creating a deb package for a new version of already packaged deb isn’t complicated.

Getting Started

Start by pulling the sources for the already available package. I’ll by using gitg as an example throughout this tutorial.

$ apt-get source gitg

This will create a folder according to the version of the package, something like gitg-0.2.4. Extract the new version besides it and cd into its directory. The next step is to copy the debian/ directory from the old source package the code you’ve just extracted.

$ cp -R ../gitg-0.2.4/debian/ .

Dependencies

There are some dependencies you’ll need:

$ sudo apt-get install devscripts
$ sudo apt-get install dpkg-dev

You’ll probably want to do:

$ sudo apt-get build-dep gitg

in order to make sure you’ve all the relevant build time dependencies.

Update debian/ Files

The next step is to update the files under the debian/ sub-directory.

$ DEBEMAIL="Guy Rutenberg <myemail@domain.com>" debchange --nmu

This will update the debian/changelog and set the new version. --nmu will create a new “non maintainer upload” version, meaning if the current version was 0.2.4-0ubuntu1, it will change it to 0.2.4-0ubuntu1.1. This will make sure that there won’t be any collision between your package and an official one. If you update to a new upstream version. It might be more suitable to use something like this:

$ debchange --newversion 0.2.5+20111211.git.20391c4

If necessary, update the Build-Depends and Depends sections of debian/control.

Building the Package

If your building a package directly from version control and not part of an official release, you may need to run

$ ./autogen

at this point.

Now to the actual building:

$ debuild -us -uc -i -I -b

-us -uc tells the script not to sign the .dsc and .changes files accordingly. -i and -I makes the script ignore common version control files. -b tells debuild to only create binary packages. You can also pass -j followed by the number of simultaneous jobs you wish to allow (e.g. -j3, like in make) which an significantly speed things up.

Installing the Package

The package will reside in the parent directory, for example:

../gitg_0.2.5+20111211.git.20391c4_amd64.deb

At this point you’re basically done. If you want to install the package you can use

sudo debi

while you’re still inside the build directory.

Creating Source Packages

If you want to go the extra mile and create source packages, it will make things easier for others to build their own packages based on yours.

You’ll need to create a an “orig” tarball

../gitg_0.2.5+20111211.git.20391c4.orig.tar.bz2

(note the underscore between the package-name and the version). The “orig” tarball should contain the original source-code without the debian specific patches.

Now you can run the debuild command like before but without the -b flag.
This will create the following files:

../gitg_0.2.5+20111211.git.20391c4.debian.tar.gz
../gitg_0.2.5+20111211.git.20391c4.dsc

References

  • UpdatingADeb
  • Man pages for debuild, dpgk-genchanges, dpgk-buildpackage.

Reinstall grub in Ubuntu

My brother asked me to repair his boot loader, after he accidentally erased his MBR. This can be done easily via LiveCD and the command line.

Boot the system using a LiveCD (I’ve used Ubuntu from USB stick) and do the following:

$ sudo mount /dev/sda /mnt
$ sudo mount --bind /usr/sbin /mnt/usr/sbin
$ sudo mount --bind /usr/lib /mnt/usr/lib
$ sudo mount --bind /dev/ /mnt/dev
$ sudo chroot /mnt

# grub-install /dev/sda

I hope it will be useful for others as well, as the Ubuntu community documentations offers a solution based on Boot-Repair, which seems an overkill for me.

Disable Touchpad Tapping in Kubuntu

In Ubuntu (gnome) there is an easy graphical way to disable tapping on the touchpad. However, KDE lacks such thing. But lacking graphical configuration doesn’t mean this should be difficult. All you need is the gsynaptics package. The package provides a small utility called synclient. Now you can disable tapping by doing

 synclient TapButton1=0

To disable the tapping permanently you should use the following to run the command at the start of every KDE session.

echo "synclient TapButton1=0" > ~/.kde/env/disable-tapping.sh

Blocking IP Range using UFW

Uncomplicated Firewall (ufw) is one of the greatest frontends to IPTables I’ve encountered. It is very simple to use and I just wish it was also available for Gentoo. Up until recently everything went smoothly for me and ufw, but we hit some rough waters when I’ve tried to block an IP range.

To block an IP or IP range in ufw you should do

sudo ufw deny from 188.162.67.197/21

Continue reading Blocking IP Range using UFW

Installing Lighttpd-1.4.22 on Ubuntu 8.04

I had some problems with the lighttpd-1.4.19 that comes with Ubuntu 8.04, mainly it’s problems of handling the HTTP header Expect: 100-continue (which older versions of Lighttpd return error 417). The problem was fixed in Lighttpd-1.4.21, but 1.4.22 is the newest version so I’ve decided to install it.

As I mentioned before, Ubuntu doesn’t have lighttpd-1.4.22 for 8.04, and it’s also not available in the updates or backports repositories. Fortunately, I’ve found that the package is available from Debuian Sid (unstable). Here are some instructions on how to install it.
Continue reading Installing Lighttpd-1.4.22 on Ubuntu 8.04