Standalone
----------
Use `fatrace` to record all file access during an `sbuild` run and find those
build dependencies which have their files never needed. You need superuser
privileges to run this script because of `fatrace` . You need to copy
`findunusedbd.sh` into `/home` so best run all of this inside a chroot to
prevent a mess (in case you use a chroot, don't forget to mount /proc and
install fatrace).
Run it like follows:
$ ./run.sh foo.dsc bar.dsc [...]
This will call sbuild like this for each `dsc` given:
$ sbuild \
--chroot-setup-commands='/home/findunusedbd.sh chroot-setup' \
--starting-build-commands='/home/findunusedbd.sh starting-build' \
--finished-build-commands='/home/findunusedbd.sh finished-build'
The first pass will use `fatrace` to find build dependencies on packages with
files that are never used during the whole build. Since many of these are gonna
be meta packages, a second pass replaces the candidate package with a fake
equivs package of same name and version but without dependencies and tries to
rebuild.
Both passes are done for `--arch-all` and `--no-arch-all` . Any unused
dependencies can then be found by investigating the `*.arch-all.unusedbd.real`
and `*.no-arch-all.unusedbd.real` . The result from the former can permanently
be dropped from the `Build-Depends` . The result from the latter can be moved to
`Build-Depends-Indep` .
Schroot setup
-------------
Create the schroot:
$ sudo sbuild-createchroot --make-sbuild-tarball=/var/lib/sbuild/sid-amd64.tar.gz sid `mktemp -d` http://127.0.0.1:3142/snapshot.debian.org/archive/debian/20140601T000000Z
Enter the schroot:
$ sbuild-shell source:sid-amd64-sbuild
Make apt ignore the `Valid-Until` header:
$ echo 'Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/80-nocheckvaliduntil
Install `equivs` and `dctrl-tools` :
$ apt-get install equivs dctrl-tools --no-install-recommends
The last action will also install file, gettext-base, gettext and debhelper so
these cannot be found as unused anymore.
Bugs
----
- maybe add list of packages whose files are never used but modify the build nevertheless (like `hardening-wrapper` )
- use reproducible builds to check that the output is the same
- when investigating which build dependencies are unused, virtual packages are not taken into account
- maybe the fake equivs package can be built outside the schroot to avoid the additional dependencies for installing equivs
- fatrace suffers from [bug#722901 ](https://bugs.debian.org/722901 ) which can be seen when trying to compile `lsof`
- if sbuild fails somehow (for example by the mirror becoming unavailable and sbuild failing with `E: apt-get update failed` ) then the finished-build-commands are not run and the started processes never quit
Feature Requests
----------------
- build with `DEB_BUILD_OPTIONS=nocheck` once it is possible to add `<!profile.nocheck>`
License
-------
Consider everything in this repository in the public domain. It is a gross hack
and I do not care what you do with it.
