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Fedora Classroom - Package Taxonomy and Techniques - Ignacio Vazquez-Abrams - Saturday, November 7, 2008

IRC Log of the Class

 23:00 -!- nirik changed the topic of #fedora-classroom to: Fedora Classroom - Package Taxonomy and Techniques
 with your teacher: ivazquez  - See https://fedoraproject.org/wiki/Communicate/IRC/Classroom for more info
 23:00 < Ineluctable> thanks stickster
 23:00 < stickster> neverho0d: It is, but you could work with another person to edit your summaries
 23:00  * kdn *bell rings*
 23:00 < brunowolff> If it isn't, then translating it could be another area to help out.
 23:01 < neverho0d> stickster: thank you
 23:01 < stickster> brunowolff: +1, exactly
 23:01  * stickster really scoots now
 23:01 < ivazquez> Hello everyone, and thank you for coming.
 23:01 < mattia> hi ivazquez
 23:01 < Abd4llA> Helloo Mr ivazquez :P
 23:01 < neverho0d> brunowolff: I'll be glad to contribute as much as I can
 23:01 < thomasj> helloiva
 23:01 < thomasj> ops
 23:01 < ivazquez> You see them go by all the time in anaconda and PackageKit.
 23:01 < kiakli> hi
 23:02 < cga> ciao ivazquez, i'm here too ;)
 23:02 < thomasj> hello ivazquez
 23:02 < ivazquez> libfoo-3.2-5.fc9... barprogs-5.2.6-0.cvs20081016...
 23:02 < ivazquez> But just what is it that makes a package...
 23:02 < ivazquez> ... a package?
 23:02 < domg472> rpmbuil
 23:02 < domg472> nvm
 23:03 < brunowolff> A spec file.
 23:03 < ivazquez> At its simplest, a package is a set of files, and metadata about each file as well as
 about the entire bundle.
 23:03 < kdn> clean installs, clean uninstalls, clean upgrades?
 23:03 < ivazquez> Things like permissions, ownership, scripts executed during installation, etc.
 23:04 < ivazquez> So let's spend some time looking at these things.
 23:04 < ivazquez> The most important thing you need to know about a package is its NEVRA.
 23:04 < ivazquez> This stands for Name, Epoch, Version, Release, and Architecture.
 23:04 < ivazquez> It's what determines when a package can be installed or upgraded.
 23:05 < ivazquez> The name is the part we're most familiar with.
 23:05 < ivazquez> glibc, firefox, etc.
 23:05 < ivazquez> It is the smallest part of a package we can use and still talk about the package itself.
 23:06 < ivazquez> The epoch, version, and release determine the "order" of packages.
 23:06 < ivazquez> That is to say, which package is considered "newer" than others.
 23:07 < ivazquez> Normally we don't need to worry about the epoch, so we'll hold out on that one for just a
 moment.
 23:07 < ivazquez> Version is mostly self-explanatory.
 23:07 < ivazquez> 2.8, 3.0.2, etc.
 23:07 < ivazquez> When upstream releases software, they give it a version to keep it separate from all the
 other versions they release.
 23:08 < ivazquez> The first part of a package that we really get to handle as a distro is the release.
 23:08 < EvilBob> how should a packager deal with packaging a beta or prerelease version from upstream?
 23:09 < ivazquez> That is actually covered in Fedora's packaging guidelines.
 23:09 < ivazquez> I'll be happy to discuss packaging issues after.
 23:09 <@nirik> http://fedoraproject.org/wiki/Packaging/NamingGuidelines#Pre-Release_packages
 23:09 < ivazquez> The release is used to distinguish one package of a specific version from another.
 23:10 < ivazquez> So you package libfoo 3.2, and the first package gets a release of "1".
 23:10 < ivazquez> Then let's say someone notices a problem in your package, and you fix it.
 23:11 < ivazquez> When you go to fix it, you keep the version the same (since it's still the same code from
 upstream), but you bump the release up to "2".
 23:11 < ivazquez> That way people and tools realize that libfoo-3.2-2 is an update for libfoo-3.2-1.
 23:12 < ivazquez> And when upstream releases a new version, say, libfoo 3.3, you can drop the release back
 down to "1".
 23:12 < ivazquez> libfoo-3.3-1 is seen as an update to libfoo-3.2-2 since the version is higher.
 23:13 < brunowolff> The kernel seems to keep an increase release number even after minor releases?
 23:13 < ivazquez> It used to. They fixed that.
 23:13 < ivazquez> The exact details involve all sorts of ugliness regarding the "base" commit.
 23:14 < ivazquez> We can come back to that later.
 23:14 < brunowolff> When 2.27.5 was released it had -88 for the release number?
 23:14 < ivazquez> Now, epoch.
 23:14 < brunowolff> OK
 23:14 < ivazquez> The epoch is the rarest-seen and the most troublesome part of a package.
 23:15 < ivazquez> By default it's not shown when you use rpm to query a package.
 23:15 < ivazquez> (and we'll come back to querying after)
 23:15 < zcat> if you have rpmdevtools installed you can play with the version/epoch comparisons.
 rpmdev-vercmp libfoo-3.2-2 libfoo-3.2-1
 23:16 < ivazquez> Additionally, when writing a spec file, you must include this invisible epoch in listing
 packages that you are dependent upon.
 23:16 < ivazquez> Many a packager has been bitten by omitting the epoch in this scenario.
 23:16 < ivazquez> Now, why would anyone use the epoch, given all this trouble?
 23:17 < ivazquez> The simple answer is that the version has had issues.
 23:18 < ivazquez> For instance, going from, say, "3.2preview" to "3.2final" will be a problem, since 3.2preview
 actually looks newer than 3.2final.
 23:19 < cga> how comes?
 23:19 < ivazquez> So what must be done is the epoch must be bumped to 1 (it is 0 by default), and everyone
 involved lets out a collective groan because of the issues mentioned earlier.
 23:19 < thomasj> cga, p - f
 23:19 < Sid> because 2.3preview comes later in an alphabetical listing than 2.3final
 23:19 < ivazquez> Strings in a VR are compared lexicographically.
 23:19 < Sid> 3.2 even
 23:19 < cga> i see thanks
 23:19 < EvilBob> cga: alphanumeric ordering
 23:19 < cga> fair enough
 23:20 < ivazquez> This brings us to the fifth part, the architecture.
 23:20 < ivazquez> You would think that this is a very small topic.
 23:20 < ivazquez> After all, i386 goes on i386 machines, x86_64 on x86_64, and so on.
 23:21 < ivazquez> Unfortunately this is not true.
 23:21 < ivazquez> And this is for 2 reasons.
 23:21 < ivazquez> The first is that there are architectures that are "equivalent" to each other.
 23:22 < ivazquez> E.g., i386, i486, i586, i686, etc.
 23:22 < ivazquez> You can only have a single package (with exceptions we'll cover later) with the same NA
 installed at a time.
 23:23 < ivazquez> So you can't have libfoo.i386 installed at the same time as libfoo.i686.
 23:23 < ivazquez> The second is a little feature called "multilib".
 23:24 < ivazquez> This allows packages from different equivalent architectures to be installed at the same time.
 23:24 < ivazquez> It's what lets you install glibc.x86_64 and glibc.i686 on the same system.
 23:25 < ivazquez> However, it also has its issues.
 23:25 < Discordian> Doesn't that increase the memory residency?
 23:26 < ivazquez> One of the issues is when the x86_64 package and the ix86 (i386, i686, etc.) package contain
 the same files.
 23:26 < ivazquez> Sorry, memory residency?
 23:26 < Discordian> Don't shared libs take up memory?
 23:27 < Discordian> Sorry ignore that please don't want to distract you
 23:27 < ivazquez> Only when they're loaded. Packages on the disk take up no memory until they're requested.
 23:27 < ivazquez> Alright, same files.
 23:28 < cga> Discordian: see differences between application and process (ie. installed versus running)
 23:28 < ivazquez> rpm does not have a problem with the x86_64 package and the ix86 package containing the same
 files, provided that the 
 files are *exactly* the same.
 23:28 < ivazquez> Timestamp, contents, permissions, etc.
 23:28 < Discordian> cga: thank you
 23:28 < ivazquez> But even this is not true.
 23:28 < ivazquez> And this is where we get into trouble.
 23:29 < ivazquez> If the x86_64 package and the ix86 package are installed in the same "transaction",
 rpm is perfectly willing to overlook differences in the files and will install both packages, with the x86_64
 files overwriting the ix86 files.
 23:29 < ivazquez> HOWEVER.
 23:30 < ivazquez> If either one of the packages is already installed, and we try to install the other package,
 rpm will complain about file conflicts since they don't match.
 23:31 < ivazquez> This sort of issue has spawned many more bug reports than are deserved.
 23:31 < ivazquez> So, something to keep in mind when you install or build packages.
 23:32 < ivazquez> So, now that we understand (I hope) these 5 elements, let's look at what else a package's
 metadata provides.
 23:33 <@nirik> I have a question: where does rpm store the ix86 binaries? If the x86_64 package is removed
 it would have to place the ix86 ones back right?
 23:33 < ivazquez> It does not. It simply doesn't erase the files provided by the x86_64 package.
 23:33 < ivazquez> Yay multilib.
 23:34 <@nirik> yikes. ;(
 23:34 < Discordian> Does that mean you could rebuild both i386 and x64 rpms using rpmrebuild and they'd both
 be valid?
 23:35 < ivazquez> I don't know. I've never looked at how rpmrebuild works.
 23:35 < Discordian> My impression is it just uses the rpm db to reconstruct the rpm file
 23:36 < ivazquez> I'm glad you bring up the rpmdb.
 23:36 < ivazquez> A package in a file has a set of metadata.
 23:36 < ivazquez> When said package is installed, the metadata needs to be stored in order to retain
 information about the package.
 23:37 < ivazquez> The metadata is stored in what is called the rpmdb.
 23:37 < ivazquez> We can query the rpmdb via "rpm -q".
 23:38 < ivazquez> We pass it a name, and rpm will give us the metadata in a pre-programmed format.
 23:38 < ivazquez> Normally it looks like <name>-<version>-<release>.
 23:38 < ivazquez> I'm not sure if they've added .<arch> to that recently. I believe so though.
 23:39 < ivazquez> You can see an example by opening up a terminal and typing "rpm -q filesystem".
 23:39 < Discordian> That is the case on F9 yes
 23:39 < ivazquez> If someone could provide the output from theirs please?
 23:40 < Sid> filesystem-2.4.13-1.fc9.i386
 23:40 < ivazquez> Right, there we are.
 23:40 < ivazquez> The name is, of course, "filesystem".
 23:41 < ivazquez> The version is "2.4.13", the release is "1.fc9", and the arch is "i386".
 23:41 < EvilBob> [root@mediapc1 ~]# rpm -q filesystem
 23:41 < EvilBob> filesystem-2.4.13-1.fc9.i386
 23:41 < EvilBob> grrr
 23:41 < ivazquez> Sometimes we need more or less than is provided by the default format.
 23:41 < zcat> ah. so showing the arch is default now? i've been adding 
 "%_query_all_fmt  %%{name}-%%{version}-%%{release}.%%{arch}" to ~/.rpmmacros so i didn't notice
 23:41 < EvilBob> filesystem-2.4.11-1.fc8
 23:41 < Discordian> filesystem-2.4.13-1.fc9.i386 is what I have
 23:42 < ivazquez> Right, and we're get to query formats right now.
 23:42 < ivazquez> *getting
 23:42 < ivazquez> Let's say that you have a script that verifies the version of certain packages on
 your system.
 23:42 < ivazquez> You want to narrow down your focus to only the version.
 23:43 < ivazquez> Normally you'd do post-processing of the output of "rpm -q".
 23:43 < ivazquez> But the default output can be changed, as demonstrated by zcat just above.
 23:43 < Discordian> you mean using awk or perl?
 23:44 < ivazquez> Correct.
 23:44 < ivazquez> What you can do is you can pass rpm a parameter that tells it the format you want.
 23:44 < Discordian> cool I can see that would be useful
 23:44 < ivazquez> This argument is "--qf", and it takes the format in a special, err, format.
 23:45 < ivazquez> Let's deal with just the version for now.
 23:45 < ivazquez> To get the version of filesystem we run "rpm -q --qf '%{version}'".
 23:45 < ivazquez> This will return just the value, with no fancy formatting.
 23:46 < ivazquez> Naturally if the output will be consumed by a person we'll at least want to put it on its
 own line.
 23:46 < ivazquez> The query format string takes several C-style escapes, including \n for a newline.
 23:47 < nuonguy> you mean rpm -q filesystem --qf '%{version}' right?
 23:47 < ivazquez> "rpm -q --qf '%{version}\n'" will give us something that we can deal with easier.
 23:47 < ivazquez> Yes.
 23:47 < neverho0d> rpm -q --qf '%{version}\n' filesystem
 23:47 < ivazquez> Right.
 23:48 < ivazquez> There are a large number of these "query tags" built into rpm.
 23:48 < ivazquez> You can see a full list by running "rpm --querytags | less".
 23:48 < ivazquez> The query tags in the query format are not case-sensitive.
 23:48 < neverho0d> wow 163!
 23:49 < ivazquez> Most of them you'll never need though.
 23:49 < daMaestro> and shortcuts for those that don't want to type ;-)
 23:49 < ivazquez> Among the important ones are the 5 parts that we started with here:
 23:50 < ivazquez> name, epoch, version, release, arch.
 23:50 < ivazquez> Also important is sourcerpm, which gives you the name of the component in Bugzilla to file
 bugs against.
 23:51 < ivazquez> installtime is also useful.
 23:51 < ivazquez> But there are 2 things to know about it.
 23:51 < ivazquez> 1) It only makes sense in the rpmdb. Querying it from a package in a file makes no sense.
 23:51 < ivazquez> And we'll get to querying a package in a file in a moment.
 23:52 < ivazquez> 2) It gives its result as a *nix timestamp. Not exactly human-friendly.
 23:53 < ivazquez> So "rpm -q --qf '%{name}: %{installtime}\n' filesystem", while technically correct, isn't
 all that useful.
 23:53 < ivazquez> Fortunately query tags support a suffix that you can add to modify them.
 23:54 < ivazquez> The suffix ":date" will convert a timestamp into a human-readable date and time.
 23:54 < ivazquez> So with a small change we get "rpm -q --qf '%{name}: %{installtime:date}\n' filesystem",
 and we can see more clearly when our system was installed or upgraded.
 23:56 < ivazquez> Another query tag of interest is dsaheader.
 23:56 < ivazquez> This tag tells us how, when, and who signed a package.
 23:56 < ivazquez> We'll get into signing packages a bit later.
 23:57 < Discordian> Cool, this is good stuff
 23:57 < cga> night all, this is interesting but i'm falling asleep. i'll read the logs tomorrow.
 i find the classroom idea very interesting. kudos.
 23:57 < ivazquez> Take care.
 23:57 < ivazquez> Again, it spews a long hex string that will make our brains asplode if we try to consume it.
 23:57  * nirik didn't know the :date stuff. very cool. 
 23:58 < ivazquez> Suffixing it with ":pgpsig" processes it and gives us a result we can use.
 23:58 < daMaestro> yes, i just wasted a few moments trying to pipe the unix timestamp to data -d via xargs
 23:58 < daMaestro> thanks.
 23:58 < kdn> Thanks to all.  This was a Good Thing(tm).
 23:58  * delhage agrees
 23:58 < ivazquez> rpm -q --qf '%{name}: %{dsaheader:pgpsig}\n' filesystem
 23:58 < daMaestro> it's not over
 23:58 < Discordian> I'm not going
 23:58 < ivazquez> I'll leave it as an exercise for the reader as to whose key that is ;)
 23:59 < Discordian> heh
 23:59 < brunowolff> How well do you have to know the code to package something from upstream?
 23:59  * nirik notes that this is the last class scheduled today... more classess tomorrow. 
 23:59 < ivazquez> Almost not at all.
 23:59 < domg472> why --qf and not -qf, would that conflict?
 00:00 < brunowolff> So a good working relationship with upstream would be good enough?
 00:00 < ivazquez> -qf is seen as a combination of 2 flags, -q and -f.
 00:00 < domg472> i see
 00:00 < Discordian> -qf is which package does this file come from
 00:00 < ivazquez> brunowolff: Not even. There are a number of instances where upstream is not even aware
 of it.
 00:00 < ivazquez> Okay, packages on disk.
 00:00 < Sid> is it possible to query packages that aren't installed?
 00:01 < ivazquez> Yes it is.
 00:01 < ivazquez> There isn't much to say about packages on disk, other than you need to add -p to rpm.
 00:01 < ivazquez> And of course, some tags such as installtime don't make sense.
 00:01 < brunowolff> Is there a good place to get info on how to package java apps? I have one I build from
 ant locally, but I don't know where fedora wants
 00:02 < ivazquez> After all, a package on disk isn't considered to be installed.
 00:02 < brunowolff> java apps placed or if there are any particular build practices to use.
 00:02 < neverho0d> ivazquez: it would be helpful to explain a package breaking on docs, devel and other things....
 00:02 < Sid> ok, what if the package isn't on disk but simply in the yum repo, can I then query it?
 00:02 < ivazquez> brunowolff: Fedora has an extensive set of packaging guidelines in the wiki.
 00:02 < Sid> or do I at least need to download the .rpm?
 00:02 < ivazquez> Another excellent question.
 00:02 < ivazquez> neverho0d: We'll handle that in a bit.
 00:03 < ivazquez> Packages in a repo.
 00:03 < neverho0d> ivazquez: ok. thnks
 00:03 < ivazquez> yum-utils has a script, repoquery, which can be used to query packages in a repo.
 00:03 <@nirik> brunowolff: https://fedoraproject.org/wiki/Packaging/Java
 00:04 < ivazquez> It takes a subset of the query tags that rpm does, due to the fact that the repo metadata has
 only a small fraction of the package metadata.
 00:04 < ivazquez> Other than that it takes -q and --qf just like rpm.
 00:05 < ivazquez> Alright, I think I've chewed up enough time on my bit. Which topics did I say I'd defer?
 00:05 < brunowolff> nirik: Thanks that looks pretty readable. I'll see if I can make it work locally. There are
 other issues with packaging the app (Colossus) that I am interested in.
 00:05  * nirik is sad that it doesn't provide sourcerpm. ;( 
 00:05 < domg472> thanks
 00:05 < domg472> very informative day
 00:06 < ivazquez> Package breakup.
 00:06 < Discordian> Thank you very much
 00:06 < erinlea80> Thanks ivazquez :) Its been informative.
 00:06 < Discordian> I learned a lot
 00:06 < ivazquez> Not quite done yet, but I understand if you have other things to do.
 00:06 < mattia> thanks ivazquez
 00:06 < Discordian> No no I'll stay
 00:06 < Bugz> thanks ivazquez
 00:06 < ivazquez> Part of the metadata in a package is what "type" a file is.
 00:07 < ivazquez> That is to say, whether it's a normal file, a configuration file, or documentation.
 00:08 < Discordian> or a script?
 00:08 < ivazquez> rpm allows you to query only these specific files by passing -c or -d, but most of the query
 tags are at the package level and so don't apply.
 00:08 < ivazquez> Package scripts are actually stored separately.
 00:08 < ivazquez> They're in the metadata, not the files.
 00:08 < Discordian> Okay I've wondered about that
 00:09 < ivazquez> They're viewable as either any of the *prog query tags, or by passing --scripts when querying
 a package.
 00:09 < domg472> rpm -q --scripts
 00:09 < Discordian> Thank you
 00:09 < ivazquez> No, I lie. Not the *prog tags.
 00:10 < ivazquez> Those are what is used to actually run the scripts.
 00:10 < ivazquez> The scripts themselves are in the prein, postin, preun, postun, and other related tags.
 00:11 < ivazquez> Okay, I can't seem to find what other audience topics I decided to defer.
 00:11 < ivazquez> Does anyone have any questions?]
 00:12 < domg472> it was all clear except the x86 x86_64 bit but that must be my fault
 00:12 < nuonguy> is there a virtual file system like /selinux or /proc to browse the rpm database?
 00:12 < domg472> ill digginto that myself
 00:12 < Discordian> since this is Fedora : what impact will the new version of rpm have?
 00:12 < nuonguy> domg472: +1
 00:12 < Discordian> or is that unfair?
 00:12 < ivazquez> No. The rpmdb is stored as a set of bdb or sqlite databases in /var/lib/rpm.
 00:13 < erinlea80> My questions were answered up above.
 00:13 < ivazquez> Which one, rpm5?
 00:13  * nirik muses that someone could make a fuse-rpmdb someday... 
 00:13 < Discordian> Yeah
 00:13 < domg472> by the way nuonguy id like to hear what is your reason to contribute to fedora or oss
 in general?
 00:14 < ivazquez> rpm5 is an independent project. I cannot speak for Red Hat, but it has little or no
 impact in Fedora as far as I can see.
 00:14 < ivazquez> the rpm maintainers in RH could probably give you a more complete answer on that one.
 00:15 < Discordian> Okay I noted that F10 had flagged up a new version of rpm
 00:15 < Discordian> I think perhaps it's 4.x
 00:15 < ivazquez> That would be further development in the 4.x branch.
 00:15 < Discordian> Yes
 00:15 <@nirik> yes, 4.6.0
 00:15 < sdodson> F10 will use 4.6.
 00:15 < sdodson> Though, I believe it's been requested that newer features of 4.6 not actually be used until
 a later date.
 00:16 < Discordian> Ahhh cool
 00:16 < ivazquez> Anyone else?
 00:16 <@nirik> thanks ivazquez. Great session!
 00:16 < ivazquez> In that case, thank you for coming, and thank you for listening.
 00:17 < Discordian> yes thank you very much ivazquez
 00:17 < nuonguy> domg472: when I interview candidates, I ask them if they contribute to any open source projects
 00:17  * erinlea80 applauds
 00:17 < neverho0d> ivazquez: may be one another class om spec-file building? ;)