Easier strace of scripts with pidof -x

Here’s a one minute read, about a trick which I discovered today:

When running an strace, it’s common to do something like:

strace -p<pid>

Smarter hackers know that they can use some bash magic and do:

strace -p`pidof <process name>`

However, if you’re tracing a script named foo.py, this won’t work because the real process is the script’s interpreter, and pidof python, might return other unrelated python scripts.

strace -p`pidof foo.py` # won't work
[failure]
[user sifting through ps output for real pid]
[computer explodes]

The trick is to use the -x flag of pidof. This will let you pass in your script’s name, and pidof will take care of the rest:

strace -p`pidof -x foo.py` # works!
[user cheering]
[normal strace noise]

Awesome!

Happy hacking,

James

 

first release of puppet-shorewall

Oh, hi there.

In case you’re interested, I’ve just made a first release of my puppet-shorewall module. This isn’t meant as an exhaustive shorewall module, but it does provide most of the usual functionality that most users need.

In particular, it’s the module dependency that I use for many of my other puppet modules that provide firewalling. This is probably where you’re most likely to consume it.

In general most modules just implement shorewall::rule, so if you really don’t want to use this code, you can implement that signature yourself, or not use automatic firewalling. The shorewall::rule type has two main signatures, so have a look at the source, or a simple example if you want to get more familiar with the specifics. Using this module is highly recommended, specifically with puppet-gluster.

Please keep in mind that since I mostly use this module to open ports and to keep my other modules happy, I probably don’t have advanced traffic control features on my roadmap. If you’re looking for something that I haven’t added, contact me with the details and consider sponsoring some features.

Happy hacking,

James

Desktop Notifications for Irssi in Screen through SSH in Gnome Terminal

I’m usually on IRC, but I don’t often notice incoming pings until after the fact. I had to both write, and modify various scripts to get what I wanted, but now it’s all done, and you can benefit from my hacking by following along…

The Setup

Laptop -> Gnome-Terminal -> SSH -> Screen -> Irssi

This way, I’m connected to IRC, even when my laptop isn’t. I run irssi in a screen session on an SSH server that I manage, and I use gnome-terminal on my laptop. If you don’t understand this setup, then you’ll need to get more comfortable with these tools first.

Fnotify

The first trick is getting irssi to store notifications in a uniform way. To do this, I modified an irssi script called fnotify. My changed version is available here. Installation is easy:

# on your ssh server:
cd /tmp; wget https://dl.dropboxusercontent.com/u/48553683/irssi/fnotify.pl
cp /tmp/fnotify.pl ~/.irssi/scripts/
# in irssi:
irssi> /load perl
irssi> /script load fnotify

When someone sends you a direct message, or highlights your nick on IRC, this script will append a line to the ~/.irssi/fnotify file on the SSH server.

Watching fnotify

On your local machine, we need a script to tail the fnotify file. This was surprisingly hard to get right. The fruit of my labour is available here. You’ll want to copy this script to your local ~/bin/ directory. I’ve named this script irssi-fnotify.sh. This script watches the remote fnotify file, and runs notify-send and paplay locally to notify you of any incoming messages, each time one comes in.

SSH Activation

We want the irssi-fnotify.sh script to run automatically when we connect to our SSH server. To do this, add the following lines to your ~/.ssh/config file:

# home
Host home
    HostName home.example.com
    PermitLocalCommand yes
    LocalCommand ~/bin/irssi-fnotify.sh --start %r@%h

You might also want to have other directives listed here as well, but that is outside the scope of this article. Now each time you run:

ssh home

The irssi-fnotify.sh command will automatically run.

Magic

I’ve left out some important details:

• The LocalCommand that you use, must return before ssh will continue. As a result, it daemonizes itself into the background when you invoke it with –start.
• My irssi-fnotify.sh program watches the parent ssh $PID. When it exits, it will run a cleanup routine to purge old notifications from the fnotify file. This requires a brief SSH connection back to the server. This is a useful feature!
• You may wish to modify irssi-fnotify.sh to paplay a different alert sound, or to avoid making noise entirely. The choice is yours.
• When irssi-fnotify.sh runs, it will tail the fnotify file over ssh. If there are “unread” messages, tail will try to “download” up to ten. You can edit this behaviour in irssi-fnotify.sh if you want a larger initial backlog.
• The irssi-notify.sh script doesn’t attempt to prevent flooding, nor does it filter weird characters from incoming messages. You may want to add this yourself, and or /kb users who cause you to need these features.

Here’s a little screenshot (with shameless plug) of the result in action:

Here’s an example of how this helps me to be more responsive in channel:

helping out in #gluster

I hope you found this useful.

Happy Hacking,

James

GNOME Montreal Summit

This October 12th to 14th Montreal hosted the GNOME boston summit. Many thanks to Canonical for sponsoring breakfast, Savoir Faire Linux for hosting a great 6 à 10 with fancy snacks, and RedHat for sponsoring a pool night. What follows is some technical commentary about stuff that went on.

JHBuild

JHBuild is a tool to make it easy to download/clone (from git) and compile all the GNOME modules and applications. It was easy to get going. I (mostly) followed the steps listed on the JHBuild HowDoI wiki page. I kept my .jhbuildrc in my home directory instead of ~/.config/. On my Fedora 19 machine, I found certain unlisted dependencies were missing to build everything. You can figure these out yourself when your builds fail, or just run the following command to install them beforehand:

# yum install /usr/bin/{g++,a2x,gnome-doc-prepare} python-rdflib lua-devel

The abridged list of commands that I ran includes:

$ git clone git://git.gnome.org/jhbuild
$ ./autogen.sh --simple-install
$ make
$ make install
$ ln -s ~/.local/bin/jhbuild ~/bin/jhbuild
$ jhbuild sysdeps --install
$ jhbuild buildone gnome-themes-standard    # i was impatient to get this early
$ jhbuild update                            # at home on fast network
$ jhbuild build --no-network                # can be run offline if you like
$ jhbuild run gedit
$ jhbuild shell                             # then run `env` inside the shell

You want to properly understand the context and working directory for each of these, but it should help get you to understand the process more quickly. One thing to realize is that the jhbuild run actually just runs a command from your $PATH, but from within the jhbuild environment, with modified $PATH and prefix variables. Run:

$ jhbuild run env

to get a better understanding of what changes. When patching, I recommend you clone locally from the mirrored git clones into your personal ~/code/ hacking directory. This way JHBuild can continue to do its thing, and keep the checkouts at master without your changes breaking the process.

Boxes

Boxes is a simple virtual machine manager for the GNOME desktop.

Zeeshan talked about some of the work he’s been doing in boxes. William Jon McCann reviewed some of the UI bugs, and I proposed the idea of integrating puppet modules so that a user could pick a module, and have a test environment running in minutes. This could be a way for users to try GlusterFS or FreeIPA.

GNOME Continuous

GNOME continuous (formerly known as GNOME-OSTree) is a project by Colin Walters. It is amazing for two reasons in particular:

1. It does continuous integration testing on a running OS image built from GNOME git master. This has enabled Colin to catch when commits break apps. It even takes screenshots so that you see what the running apps look like.
2. It provides bootable GNOME images that you can run locally in a vm. The images are built from GNOME git master. While there are no security updates, and this is not recommended for normal use, it is a great way to test out the bleeding edge of GNOME and report bugs early. It comes with an atomic upgrade method to keep your image up to date with the latest commits.

My goal is to try to run the bootable image for an hour every month. This way, I’ll be able to catch GNOME bugs early before they trickle down into Fedora and other GNOME releases.

Abiword 3.0

Hubert Figuière released AbiWord 3.0 which supports GTK+ 3. Cool.

A11y

Some of the A11y team was present and hacking away. I learned more about how the accessibility tools are used. This is an important technology even if you aren’t using them at the moment. With age, and accident, the current A11y technologies might one day be useful to you!

Hacking Hearts

Karen Sandler was kind enough to tell me about her heart condition and the proprietary software inside of her pacemaker defibrillator. Hopefully hackers can convince manufacturers that we need to have access to the source.

Yorba and Geary

Jim Nelson is a captivating conversationalist, and it was kind of him to tell me about his work on Geary and Vala, and to listen to my ideas about GPG support in email clients. I look forward to seeing Geary’s future. I also learned a bit more about IMAP.

Future?

I had a great time at the summit, and it was a pleasure to meet and hangout with the GNOME hackers. You’re always welcome in Montreal, and I hope you come back soon.

Happy Hacking,

James

Show current git branch in PS1 when branch is not master

Short post, long command…

I’ve decided to start showing the current git branch in my PS1. However, since I don’t want to know when I’m on master, I had to write a new PS1 that I haven’t yet seen anywhere. Add the following to your .bashrc:

PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
if [ -e /usr/share/git-core/contrib/completion/git-prompt.sh ]; then
    . /usr/share/git-core/contrib/completion/git-prompt.sh
    PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w$([ "$(__git_ps1 %s)" != "" -a "$(__git_ps1 %s)" != "master" ] && (echo -e " (\[33[32m\]"$(__git_ps1 "%s")"\[33[0m\])") || echo "")\$ '
fi

This keeps my PS1 short for when I’m hacking on personal repositories that only have a single branch. Keep in mind that you might have to change the path to git-prompt.sh depending on what OS you’re using.

Example:

james@computer:~/code/puppet$ cd puppet-gluster
james@computer:~/code/puppet/puppet-gluster$ git checkout -b cool-new-feature
Switched to a new branch 'cool-new-feature'
james@computer:~/code/puppet/puppet-gluster (cool-new-feature)$ # tada !

The branch name is coloured to match the default colours that git uses to colour branches.

Happy hacking,

James