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Ubuntu Open Week - How to fix bugs in Ubuntu - James Westby and Daniel Holbach - Thu, Nov 5, 2009

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<< ... continued

(11:00:35 AM) dholbach: james_w: ready for part 2?
(11:00:44 AM) james_w: yes
(11:00:50 AM) dholbach: alrighty
(11:00:55 AM) dholbach: do have a bug we could get started with?
(11:01:41 AM) dholbach: just to answer a quick question first:
(11:01:42 AM) dholbach: <jtniehof> QUESTION: (if you're not going to get to gpg later): is the Ubuntu WoT same as Debian? (i.e. do I need to get my keys signed by two different sets of people?)
(11:01:50 AM) dholbach: jtniehof: it's very strongly encouraged
(11:01:59 AM) dholbach: but as far as I know not enforced
(11:02:25 AM) dholbach: also... if your gpg run is done now, please head to https://launchpad.net/people/+me/+editpgpkeys and add it to Launchpad
(11:02:35 AM) dholbach: (that's not necessary for the example now, but very useful :-))
(11:03:04 AM) dholbach: james_w: you have a bug we can start with?
(11:03:43 AM) james_w: want to start with https://bugs.launchpad.net/ubuntu/+source/xtux/+bug/454115 ?
(11:04:10 AM) dholbach: sounds good :)
(11:04:37 AM) dholbach: james_w: want to kick off the bug fixing frenzy? :)
(11:05:30 AM) james_w: ok
(11:05:46 AM) james_w: so, we first need to get the source package so that we can examine it and change it
(11:06:08 AM) james_w: so, please move to a temporary directory and run:
(11:06:12 AM) james_w: apt-get source xtux
(11:06:20 AM) james_w: that will go off and download the source package for you
(11:07:14 AM) james_w: you will see some messages about what it is doing
(11:08:31 AM) james_w: but it basically leaves you with the unpacked source package in
(11:08:56 AM) james_w: xtux-0.2.030306
(11:08:59 AM) james_w: so run:
(11:09:02 AM) james_w: cd xtux-0.2.030306
(11:09:50 AM) james_w: and you can see a whole bunch of files that make up this package
(11:10:06 AM) james_w: the packaging itself lives in the ./debian directory
(11:10:22 AM) james_w: and there are a whole bunch more files there
(11:10:33 AM) james_w: we won't look at what each of them do now
(11:10:37 AM) james_w: just a couple
(11:10:41 AM) james_w: so, debian/changelog
(11:10:47 AM) james_w: this is the changelog of the packaging
(11:11:19 AM) james_w: you can see changes that have been made
(11:11:45 AM) james_w: debian/control is some information about the package
(11:12:45 AM) james_w: it has things like the description, dependencies and the list
(11:12:48 AM) james_w: and the like
(11:13:15 AM) james_w: debian/copyright contains information on the license of the pakcage
(11:13:44 AM) james_w: so, let's look at the bug
(11:14:58 AM) james_w: so, the problem is:
(11:15:00 AM) james_w: Removing xtux-client ...
(11:15:00 AM) james_w: dpkg: error processing xtux-client (--remove):
(11:15:00 AM) james_w:  subprocess installed post-removal script returned error exit status 1
(11:15:08 AM) james_w: what does this mean?
(11:16:45 AM) james_w: the "post-removal script" that it refers to is one that a set of scripts
(11:17:04 AM) james_w: that a package can provide
(11:17:40 AM) james_w: these scripts are run by dpkg as the package is installed or removed
(11:17:59 AM) james_w: so, let's look at the one that is failing
(11:17:59 AM) dholbach: a lot of stuff is done during that step
(11:18:17 AM) dholbach: like updating the docs database, updating icon caches etc.
(11:18:38 AM) dholbach: in most cases you don't need them, unless you want anything special to happen during the installation or removal
(11:18:49 AM) dholbach: if you do want that to happen, you need to be extremely careful
(11:18:52 AM) james_w: yes
(11:19:02 AM) dholbach: everything else will botch the installation of your users
(11:19:04 AM) dholbach: like this case
(11:19:24 AM) dholbach: (all the regular steps are added automatically :))
(11:19:53 AM) james_w: open the file debian/xtux-client.postrm
(11:20:25 AM) dholbach: the real beef of the file is:
(11:20:27 AM) dholbach:    rmdir /etc/ggz/clients /etc/ggz >/dev/null 2>&1
(11:20:29 AM) james_w: "postrm" means "post rm", or "post removal"
(11:20:38 AM) james_w: so we know it is the script that we want
(11:20:54 AM) dholbach: everything else is stuff you need in there to get the "regular actions" taking after the removal of packages
(11:21:11 AM) dholbach: the call I mentioned above is problematic for a few reasons
(11:21:32 AM) dholbach: 1) it suppresses any output which makes it harder for us to figure what the problem is ( >/dev/null 2>&1)
(11:21:44 AM) dholbach: 2) it does not check if those directories are available
(11:22:00 AM) dholbach: 3) rmdir will fail if those directories are not empty
(11:22:07 AM) dholbach: james_w: anything I forgot?
(11:22:57 AM) james_w: it should perhaps only does it's work on purge as well?
(11:23:04 AM) dholbach: ah, good point
(11:23:33 AM) dholbach: (the difference between    apt-get remove <pkg>   and    apt-get remove --purge <pkg>   (or dpkg -P))
(11:23:47 AM) dholbach: james_w: what do we do to fix it?
(11:24:33 AM) james_w: so, to fix 1)
(11:24:51 AM) james_w: we need to to change the redirection
(11:24:59 AM) james_w: instead of rmdir /etc/ggz/clients /etc/ggz >/dev/null 2>&1
(11:25:09 AM) james_w: do rmdir /etc/ggz/clients /etc/ggz 2>&1 >/dev/null
(11:25:23 AM) james_w: or just rmdir /etc/ggz/clients /etc/ggz >/dev/null
(11:25:43 AM) james_w: to fix 2)
(11:25:56 AM) james_w: we need to guard this by a check for the existence of the directory
(11:26:08 AM) james_w: and 3) change the way we run rmdir
(11:26:21 AM) james_w: so something like:
(11:26:22 AM) james_w: for dir in /etc/ggz/clients /etc/ggz; do
(11:26:31 AM) james_w:     if [ -d $dir ]; then
(11:26:39 AM) james_w:       rmdir --ignore-fail-on-non-empty $dir;
(11:26:47 AM) james_w:    fi;
(11:26:53 AM) james_w: done
(11:27:29 AM) james_w: the "[ -d $dir]" checks that the directory exists before it is removed
(11:27:52 AM) dholbach: (that's the test(1) command)
(11:27:54 AM) james_w: the --ignore-fail-on-non-empty means that the command won't error if the directories are not empty
(11:28:28 AM) james_w: so, please go ahead and change the line in the original file to those few lines
(11:28:32 AM) dholbach: that looks good to me, so we just replace the original rmdir call and we're done?
(11:29:17 AM) james_w: for that file I think?
(11:29:27 AM) dholbach: yep, looks good
(11:29:56 AM) dholbach: so apart from test building the package and more importantly:
(11:29:58 AM) dholbach:  _____ _____ ____ _____ ___ _   _  ____ _
(11:29:58 AM) dholbach: |_   _| ____/ ___|_   _|_ _| \ | |/ ___| |
(11:29:58 AM) dholbach:   | | |  _| \___ \ | |  | ||  \| | |  _| |
(11:29:58 AM) dholbach:   | | | |___ ___) || |  | || |\  | |_| |_|
(11:29:58 AM) dholbach:   |_| |_____|____/ |_| |___|_| \_|\____(_)
(11:30:01 AM) dholbach:                                           
(11:30:08 AM) james_w: ok
(11:30:11 AM) dholbach: we need to document our changes properly so people know what we did and why :)
(11:30:16 AM) james_w: so, next step is to edit the changelog
(11:30:17 AM) james_w: yes!
(11:30:22 AM) james_w: want to take this bit?
(11:30:34 AM) dholbach: sure
(11:30:50 AM) dholbach: I use the    dch -i   command from the devscripts package
(11:30:59 AM) dholbach: this makes use of the DEBEMAIL variables we set before
(11:31:12 AM) dholbach: and will add a template changelog entry for us and increment the version number
(11:31:38 AM) dholbach: after some editing the first line for me now says
(11:31:39 AM) dholbach: xtux (0.2.030306-11ubuntu1) lucid; urgency=low
(11:31:44 AM) dholbach: let's go through it one by one
(11:31:53 AM) dholbach: first up is the name of the source package
(11:32:10 AM) dholbach: xtux-client (the binary ".deb" package) belongs to the xtux source package
(11:32:21 AM) dholbach: one source package can build multiple binary packages
(11:32:30 AM) dholbach: this is used to split things up for various reasons
(11:32:52 AM) dholbach: this example will show you a package that makes use of the idea extensively: apt-cache showsrc mono
(11:33:08 AM) dholbach: next up is the version number, which in our case now is: 0.2.030306-11ubuntu1
(11:33:44 AM) dholbach: it means that the software authors released 0.2.030306 at some stage which has gone through 11 revisions in Debian
(11:33:51 AM) dholbach: and we're just about to add the first change to it in Ubuntu
(11:34:10 AM) dholbach: next comes the distro release we want to upload it to later on
(11:34:24 AM) dholbach: this should always default to the current development release which since some days is lucid
(11:34:42 AM) dholbach: if you want to get something included in an older release, you might want to have a look at https://wiki.ubuntu.com/StableReleaseUpdates
(11:35:28 AM) dholbach: we can ignore "urgency=low" - that's a Debian'ism that Launchpad does not make use of as far as I know
(11:35:46 AM) dholbach:  -- Daniel Holbach <daniel.holbach@ubuntu.com>  Thu, 05 Nov 2009 17:30:38 +0100
(11:35:53 AM) dholbach: is the last line which isn't particularly interesting
(11:35:54 AM) dholbach: :-)
(11:36:01 AM) dholbach: so, let's document what we did
(11:37:03 AM) dholbach: james_w might have a better wording than I do, but I'd put something like this in there
(11:37:05 AM) dholbach:   * xtux-client.postrm: don't fail to remove directories which don't exist
(11:37:05 AM) dholbach:     or are not empty (LP: #454115)
(11:37:18 AM) dholbach: this does 3 things:
(11:37:26 AM) dholbach: it mentions which files we changed
(11:37:33 AM) dholbach: it mentions how we changed them
(11:37:48 AM) dholbach: and it references the bug report in Launchpad we attempt to fix
(11:38:01 AM) dholbach: (and it also closes the bug automatically when the package is uploaded)
(11:38:06 AM) dholbach: this is important for a few reasons
(11:38:19 AM) dholbach: we all work on Ubuntu packages togethere
(11:38:29 AM) dholbach: there is no strict "owner" of a package
(11:38:39 AM) dholbach: so you don't want others to have to second-guess what you actually changed
(11:38:41 AM) dholbach: AND
(11:38:50 AM) dholbach: YOU don't want to second-guess half a year later :-)
(11:39:06 AM) dholbach: once you've done that, please save the file
(11:39:23 AM) dholbach: james_w: anything I forgot before we crack on?
(11:39:40 AM) james_w: don't think so
(11:40:07 AM) dholbach: I stand correct: maco points out that urgency DOES make a difference in Ubuntu too: https://help.launchpad.net/Packaging/BuildScores
(11:40:14 AM) dholbach: please use it wisely :)
(11:40:23 AM) dholbach: alright, we should be done now
(11:40:31 AM) dholbach: please run
(11:40:34 AM) dholbach:    debuild -S
(11:40:45 AM) dholbach: this will rebuild the source package for us
(11:41:20 AM) dholbach: (if you ran into an error saying something about Ubuntu maintainer, please run update-maintainer from ubuntu-dev-tools and debuild -S again)
(11:41:47 AM) dholbach: (it also uses quilt, so if you get an error about that, please install quilt too)
(11:42:45 AM) dholbach: once it completed I get the following files (below the xtux-0.2.0.030306 directory):
(11:42:46 AM) dholbach: xtux_0.2.030306-11.diff.gz         xtux_0.2.030306-11ubuntu1_source.build
(11:42:46 AM) dholbach: xtux_0.2.030306-11.dsc             xtux_0.2.030306-11ubuntu1_source.changes
(11:42:46 AM) dholbach: xtux_0.2.030306-11ubuntu1.diff.gz  xtux_0.2.030306.orig.tar.gz
(11:42:46 AM) dholbach: xtux_0.2.030306-11ubuntu1.dsc
(11:43:13 AM) dholbach: xtux_0.2.030306.orig.tar.gz contains the code that was actually released by the xtux authors
(11:43:40 AM) dholbach: xtux_0.2.030306-11.dsc and xtux_0.2.030306-11.diff.gz basically make up the packaging by the Debian maintainer (of the -11 version)
(11:43:54 AM) dholbach: xtux_0.2.030306-11ubuntu1.diff.gz and xtux_0.2.030306-11ubuntu1.dsc is -11 plus our good work
(11:44:14 AM) dholbach: the .diff.gz files contain the compressed set of changes we need to apply to make the package build the "Debian/Ubuntu way"
(11:44:20 AM) dholbach: the .dsc is metadata like md5sums
(11:44:49 AM) dholbach: there's a nifty tool called debdiff, which we'll use here to get us the patch for the changes we just did
(11:45:01 AM) dholbach: please run:
(11:45:03 AM) dholbach:   debdiff xtux_0.2.030306-11.dsc xtux_0.2.030306-11ubuntu1.dsc
(11:46:19 AM) dholbach: the output should be a bit like this one:
(11:46:20 AM) dholbach: http://paste.ubuntu.com/310719/
(11:46:43 AM) dholbach: if you got this far: you just created your first patch
(11:46:47 AM) dholbach: CONGRATULATIONS! :))))
(11:46:55 AM) dholbach: james_w: want to take us from here?
(11:48:04 AM) james_w: what's next?
(11:48:13 AM) dholbach: we could test-build it
(11:48:19 AM) dholbach: or try to squeeze in another bug :)
(11:48:21 AM) james_w: of course!
(11:48:33 AM) james_w: pbuilder build xtux_0.2.030306-11ubuntu1.dsc
(11:48:42 AM) james_w: that will build your new package inside pbuilder
(11:48:57 AM) dholbach: you might want to add a    sudo     in front :)
(11:49:29 AM) dholbach: ok, let's hear some more questions
(11:49:44 AM) dholbach: for those of you who want more bugs and more bug fixing action, you could try having a look at these bugs:
(11:49:45 AM) dholbach: http://bugs.launchpad.net/ubuntu/+source/fet/+bug/368017
(11:49:45 AM) dholbach: https://bugs.launchpad.net/ubuntu/+source/ibus/+bug/429986
(11:49:45 AM) dholbach: https://bugs.launchpad.net/ubuntu/+source/ibus/+bug/429988
(11:49:45 AM) dholbach: https://bugs.launchpad.net/ubuntu/+source/usermode/+bug/461365
(11:50:13 AM) dholbach: and check out https://wiki.ubuntu.com/MOTU/TODO which lists a lot of good stuff to get started with
(11:50:35 AM) dholbach: do we have more questions?
(11:51:16 AM) dholbach: did pbuilder succeed for anybody already? :)
(11:51:43 AM) dholbach: <jsgruber> QUESTION: Is it reasonable to use your ppa rather than using pbuilder to test build a package?
(11:51:48 AM) dholbach: jsgruber: good one
(11:52:26 AM) dholbach: so jsgruber is referring to PPAs (personal package archives), a service by Launchpad to build your package for you: https://help.launchpad.net/PPA has more details about that
(11:52:45 AM) dholbach: I usually prefer to build them locally - it's mostly quicker because you don't have a queue :)
(11:53:05 AM) dholbach: I just use PPAs to distribute packages for testing
(11:53:13 AM) dholbach: <openweek7> QUESTION: What if the bug fix you create fixes the bug you intended to fix, but creates other bugs in the source? How would you test for this?
(11:53:37 AM) dholbach: openweek7: in our case, I'd test-install the package and see if I can remove it safely again
(11:53:59 AM) dholbach: it's really important that you install the packages you just built and play around with them to make sure the fix indeed does what you promised
(11:54:07 AM) dholbach: <Jesi-Idle> Question: what are the differences from building the "Debian/Ubuntu way" or the "Fedora" or "Suse" way since you mentioned it, just little things or is there a significant difference?
(11:54:31 AM) dholbach: I won't go into much speculation about how it works for Fedora or SuSE because I don't really know
(11:54:48 AM) dholbach: I know that in the .rpm world a .spec file is involved which is a condensed ./debian directory
(11:55:05 AM) mode (+v mneptok ) by jcastro
(11:55:34 AM) dholbach: what I can say is that the debian/ubuntu way of building software basically means that you wrap a well-defined build system around that that comes from the upstream software
(11:55:40 AM) dholbach: I know that's a bit "meta" :)
(11:56:03 AM) mode (+v jussi01 ) by jcastro
(11:56:06 AM) dholbach: a lot of C programs usually take you a  ./configure && make && sudo make install  route
(11:56:20 AM) dholbach: python projects might require a   python ./setup.py build <something>
(11:56:31 AM) dholbach: and there's lots of other software that does it in different ways
(11:56:46 AM) dholbach: we have clever tools for all the "regular" cases
(11:56:59 AM) dholbach: so you merely run      fakeroot debian/rules clean
(11:57:05 AM) dholbach: or fakeroot debian/rules binary
(11:57:08 AM) dholbach: or whatever
(11:57:32 AM) dholbach: basically a build system with build targets around the one you're required to follow by that software
(11:57:42 AM) dholbach: <ia> QUESTION: is it reasonable updating system (using for testing devel releases and ubuntu devel purposes) to lucid (before alpha1 release) today? or should better to wait for alpha1?
(11:57:56 AM) dholbach: I'd encourage you to read https://wiki.ubuntu.com/UbuntuDevelopment/UsingDevelopmentReleases
(11:58:13 AM) dholbach: because it explains how to set up lucid in a chroot or a vm or a separate partition or something
(11:58:22 AM) dholbach: and you don't have to deal with the daily pain :-)
(11:58:37 AM) dholbach: alrightie
(11:58:46 AM) dholbach: please bookmark:
(11:58:46 AM) dholbach: ¡¡¡ https://wiki.ubuntu.com/MOTU/GettingStarted !!!
(11:58:51 AM) dholbach: see you in #ubuntu-motu
(11:58:57 AM) dholbach: and make james_w and me proud!
(11:59:00 AM) dholbach: thanks a lot james_w
(11:59:06 AM) dholbach: and thanks a lot everybody for attending the session!