NAME

       dgit-user - making and sharing changes to Debian packages, with git

INTRODUCTION

       dgit lets you fetch the source code to every package on your system as if your distro used git to
       maintain all of it.

       You can then edit it, build updated binary packages (.debs) and install and run them.  You can also share
       your work with others.

       This tutorial gives some recipes and hints for this.  It assumes you have basic familiarity with git.  It
       does not assume any initial familiarity with Debian's packaging processes.

       If you are a package maintainer within Debian; a DM or DD; and/or a sponsee: this tutorial is not for
       you.  Try dgit-nmu-simple(7), dgit-maint-*(7), or dgit(1) and dgit(7).

SUMMARY

       (These runes will be discussed later.)

           % dgit clone glibc jessie,-security
           % cd glibc
           % curl 'https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=28250;mbox=yes;msg=89' | patch -p1 -u
           % git commit -a -m 'Fix libc lost output bug'
           % gbp dch -S --since=dgit/dgit/sid --ignore-branch --commit
           % mk-build-deps --root-cmd=sudo --install
           % dpkg-buildpackage -uc -b
           % sudo dpkg -i ../libc6_*.deb

       Occasionally:

           % git clean -xdf
           % git reset --hard

       Later:

           % cd glibc
           % dgit pull jessie,-security
           % gbp dch -S --since=dgit/dgit/sid --ignore-branch --commit
           % dpkg-buildpackage -uc -b
           % sudo dpkg -i ../libc6_*.deb

FINDING THE RIGHT SOURCE CODE - DGIT CLONE

           % dgit clone glibc jessie,-security
           % cd glibc

       dgit clone needs to be told the source package name (which might be different to the binary package name,
       which was the name you passed to "apt-get install") and the codename or alias of the Debian release (this
       is called the "suite").

   Finding the source package name
       For many packages, the source package name is obvious.  Otherwise, if you know a file that's in the
       package, you can look it up with dpkg:

           % dpkg -S /lib/i386-linux-gnu/libc.so.6
           libc6:i386: /lib/i386-linux-gnu/libc.so.6
           % dpkg -s libc6:i386
           Package: libc6
           Status: install ok installed
           ...
           Source: glibc

       (In this example, libc6 is a "multi-arch: allowed" package, which means that it exists in several
       different builds for different architectures.  That's where ":i386" comes from.)

   Finding the Debian release (the "suite")
       Internally, Debian (and derived) distros normally refer to their releases by codenames.  Debian also has
       aliases which refer to the current stable release etc.  So for example, at the time of writing Debian
       "jessie" (Debian 8) is Debian "stable"; and the current version of Ubuntu is "yakkety" (Yakkety Yak,
       16.10).  You can specify either the codename "jessie" or the alias "stable".  If you don't say, you get
       "sid", which is Debian "unstable" - the main work-in progress branch.

       If you don't know what you're running, try this:

           % grep '^deb' /etc/apt/sources.list
           deb http://the.earth.li/debian/ jessie main non-free contrib
           ...
           %

       For Debian, you should add ",-security" to the end of the suite name, unless you're on unstable or
       testing.  Hence, in our example "jessie" becomes "jessie,-security".  (Yes, with a comma.)

WHAT DGIT CLONE PRODUCES

   What branches are there
       dgit clone will give you a new working tree, and arrange for you to be on a branch named like
       "dgit/jessie,-security" (yes, with a comma in the branch name).

       For each release (like "jessie") there is a tracking branch for the contents of the archive, called
       "remotes/dgit/dgit/jessie" (and similarly for other suites).  This can be updated with "dgit fetch
       jessie".  This, the remote suite branch, is synthesized by your local copy of dgit.  It is fast
       forwarding.

       Debian separates out the security updates, into "*-security".  Telling dgit "jessie,-security" means that
       it should include any updates available in "jessie-security".  The comma notation is a request to dgit to
       track jessie, or jessie-security if there is an update for the package there.

       (You can also dgit fetch in a tree that wasn't made by dgit clone.  If there's no "debian/changelog"
       you'll have to supply a "-p"package option to dgit fetch.)

   What kind of source tree do you get
       If the Debian package is based on some upstream release, the code layout should be like the upstream
       version.  You should find "git grep" helpful to find where to edit.

       The package's Debian metadata and the scripts for building binary packages are under "debian/".
       "debian/control", "debian/changelog" and "debian/rules" are the starting points.  The Debian Policy
       Manual has most of the in-depth technical details.

       For many Debian packages, there will also be some things in "debian/patches/".  It is best to ignore
       these.  Insofar as they are relevant the changes there will have been applied to the actual files,
       probably by means of actual comments in the git history.  The contents of debian/patches are ignored when
       building binaries from dgitish git branches.

       (For Debian afficionados: the git trees that come out of dgit are "patches-applied packaging branches
       without a .pc directory".)

   What kind of history you get
       If you're lucky, the history will be a version of, or based on, the Debian maintainer's own git history,
       or upstream's git history.

       But for many packages the real git history does not exist, or has not been published in a dgitish form.
       So you may find that the history is a rather short history invented by dgit.

       dgit histories often contain automatically-generated commits, including commits which make no changes but
       just serve to make a rebasing branch fast-forward.  This is particularly true of combining branches like
       "jessie,-security".

       If the package maintainer is using git then after dgit clone you may find that there is a useful
       "vcs-git" remote referring to the Debian package maintainer's repository for the package.  You can see
       what's there with "git fetch vcs-git".  But use what you find there with care: Debian maintainers' git
       repositories often have contents which are very confusing and idiosyncratic.  In particular, you may need
       to manually apply the patches that are in debian/patches before you do anything else!

BUILDING

   Always commit before building
           % wget 'https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=28250;mbox=yes;msg=89' | patch -p1 -u
           % git commit -a -m 'Fix libc lost output bug'

       Debian package builds are often quite messy: they may modify files which are also committed to git, or
       leave outputs and temporary files not covered by ".gitignore".

       If you always commit, you can use

           % git clean -xdf
           % git reset --hard

       to tidy up after a build.  (If you forgot to commit, don't use those commands; instead, you may find that
       you can use "git add -p" to help commit what you actually wanted to keep.)

       These are destructive commands which delete all new files (so you must remember to say "git add") and
       throw away edits to every file (so you must remember to commit).

   Update the changelog (at least once) before building
           % gbp dch -S --since=dgit/dgit/sid --ignore-branch --commit

       The binaries you build will have a version number which ultimately comes from the "debian/changelog".
       You want to be able to tell your binaries apart from your distro's.

       So you should update "debian/changelog" to add a new stanza at the top, for your build.

       This rune provides an easy way to do this.  It adds a new changelog entry with an uninformative message
       and a plausible version number (containing a bit of your git commit id).

       If you want to be more sophisticated, the package "dpkg-dev-el" has a good Emacs mode for editing
       changelogs.  Alternatively, you could edit the changelog with another text editor, or run "dch" or "gbp
       dch" with different options.  Choosing a good version number is slightly tricky and a complete treatment
       is beyond the scope of this tutorial.

   Actually building
           % mk-build-deps --root-cmd=sudo --install
           % dpkg-buildpackage -uc -b

       dpkg-buildpackage is the primary tool for building a Debian source package.  "-uc" means not to pgp-sign
       the results.  "-b" means build all binary packages, but not to build a source package.

   Using sbuild
       You can build in an schroot chroot, with sbuild, instead of in your main environment.  (sbuild is used by
       the Debian build daemons.)

           % git clean -xdf
           % sbuild -c jessie -A --no-clean-source \
                    --dpkg-source-opts='-Zgzip -z1 --format=1.0 -sn'

       Note that this will seem to leave a "source package" (.dsc and .tar.gz) in the parent directory, but that
       source package should not be used.  It is likely to be broken.  For more information see Debian bug
       #868527.

INSTALLING

   Debian Stretch or newer
           % sudo apt install ../libc6_*.deb

   Debian Jessie or older
           % sudo dpkg -i ../libc6_*.deb

       You can use "dpkg -i" to install the .debs that came out of your package.

       If the dependencies aren't installed, you will get an error, which can usually be fixed with "apt-get -f
       install".

Multiarch

       If you're working on a library package and your system has multiple architectures enabled, you may see
       something like this:

           dpkg: error processing package libpcre3-dev:amd64 (--configure):
            package libpcre3-dev:amd64 2:8.39-3~3.gbp8f25f5 cannot be configured because libpcre3-dev:i386 is at a different version (2:8.39-2)

       The multiarch system used by Debian requires each package which is present for multiple architectures to
       be exactly the same across all the architectures for which it is installed.

       The proper solution is to build the package for all the architectures you have enabled.  You'll need a
       chroot for each of the secondary architectures.  This is somewhat tiresome, even though Debian has
       excellent tools for managing chroots.  "sbuild-debian-developer-setup" from the package of the same name
       and "sbuild-createchroot" from the "sbuild" package are good starting points.

       Otherwise you could deinstall the packages of interest for those other architectures with something like
       "dpkg --remove libpcre3:i386".

       If neither of those are an option, your desperate last resort is to try using the same version number as
       the official package for your own package.  (The version is controlled by "debian/changelog" - see
       above.)  This is not ideal because it makes it hard to tell what is installed, and because it will
       mislead and confuse apt.

       With the "same number" approach you may still get errors like

           trying to overwrite shared '/usr/include/pcreposix.h', which is different from other instances of
           package libpcre3-dev

       but passing "--force-overwrite" to dpkg will help - assuming you know what you're doing.

SHARING YOUR WORK

       The "dgit/jessie,-security" branch (or whatever) is a normal git branch.  You can use "git push" to
       publish it on any suitable git server.

       Anyone who gets that git branch from you will be able to build binary packages (.deb) just as you did.

       If you want to contribute your changes back to Debian, you should probably send them as attachments to an
       email to the Debian Bug System <https://bugs.debian.org/> (either a followup to an existing bug, or a new
       bug).  Patches in "git-format-patch" format are usually very welcome.

   Source packages
       The git branch is not sufficient to build a source package the way Debian does.  Source packages are
       somewhat awkward to work with.  Indeed many plausible git histories or git trees cannot be converted into
       a suitable source package.  So I recommend you share your git branch instead.

       If a git branch is not enough, and you need to provide a source package but don't care about its
       format/layout (for example because some software you have consumes source packages, not git histories)
       you can use this recipe to generate a "3.0 (native)" source package, which is just a tarball with
       accompanying .dsc metadata file:

           % echo '3.0 (native)' >debian/source/format
           % git commit -m 'switch to native source format' debian/source/format
           % dgit -wgf build-source

       If you need to provide a good-looking source package, be prepared for a lot more work.  You will need to
       read much more, perhaps starting with dgit-nmu-simple(7), dgit-sponsorship(7) or dgit-maint-*(7)

SEE ALSO

       dgit(1), dgit(7)