A Crude Personal Package Manager

For the past couple of months I’ve been using a custom package manager to manage a handful of software packages within various unix-like environments. Packages are installed in my home directory under ~/.local/bin, and the package manager itself is just a 110 line Bourne shell script. It’s is not intended to replace the system’s package manager but, instead, compliment it in some cases where I need more flexibility. I use it to run custom versions of specific pieces of software — newer or older than the system-installed versions, or with my own patches and modifications — without interfering with the rest of system, and without a need for root access. It’s worked out really well so far and I expect to continue making heavy use of it in the future.

It’s so simple that I haven’t even bothered putting the script in its own repository. It sits unadorned within my dotfiles repository with the name qpkg (“quick package”):

Sitting alongside my dotfiles means it’s always there when I need it, just as if it was a built-in command.

I say it’s crude because its “install” (-I) procedure is little more than a wrapper around tar. It doesn’t invoke libtool after installing a library, and there’s no post-install script — or postinst as Debian calls it. It doesn’t check for conflicts between packages, though there’s a command for doing so manually ahead of time. It doesn’t manage dependencies, nor even have them as a concept. That’s all on the user to screw up.

In other words, it doesn’t attempt solve most of the hard problems tackled by package managers… except for three important issues:

  1. It provides a clean, guaranteed-to-work uninstall procedure. Some Makefiles do have a token “uninstall” target, but it’s often unreliable.

  2. Unlike blindly using a Makefile “install” target, I can check for conflicts before installing the software. I’ll know if and how a package clobbers an already-installed package, and I can manage, or ignore, that conflict manually as needed.

  3. It produces a compact, reusable package file that I can reinstall later, even on a different machine (with a couple of caveats). I don’t need to keep around the original source and build directories should I want to install or uninstall later. I can also rapidly switch back and forth between different builds of the same software.

The first caveat is that the package will be configured for exactly my own home directory, so I usually can’t share it with other users, or install it on machines where I have a different home directory. Though I could still create packages for different installation prefixes.

The second caveat is that some builds tailor themselves by default to the host (e.g. -march=native). If care isn’t taken, those packages may not be very portable. This is more common than I had expected and has mildly annoyed me.

Birth of a package manager

While the package manager is new, I’ve been building and installing software in my home directory for years. I’d follow the normal process of setting the install prefix to $HOME/.local, running the build, and then letting the “install” target do its thing.

$ tar xzf name-version.tar.gz
$ cd name-version/
$ ./configure --prefix=$HOME/.local
$ make -j$(nproc)
$ make install

This worked well enough for years. However, I’ve come to rely a lot on this technique, and I’m using it for increasingly sophisticated purposes, such as building custom cross-compiler toolchains.

A common difficulty has been handling the release of new versions of software. I’d like to upgrade to the new version, but lack a way to cleanly uninstall the previous version. Simply clobbering the old version by installing it on top usually works. Occasionally it wouldn’t, and I’d have to blow away ~/.local and start all over again. With more and more software installed in my home directory, restarting has become more and more of a chore that I’d like to avoid.

What I needed was a way to track exactly which files were installed so that I could remove them later when I needed to uninstall. Fortunately there’s a widely-used convention for exactly this purpose: DESTDIR.

It’s expected that when a Makefile provides an “install” target, it prefixes the installation path with the DESTDIR macro, which is assigned to the empty string by default. This allows the user to install the software to a temporary location for the purposes of packaging. Unlike the installation prefix (--prefix) configured before the build began, the software is not expected to function properly when run in the DESTDIR location.

$ DESTDIR=_destdir
$ mkdir $DESTDIR
$ make DESTDIR=destdir install

A different tool will used to copy these files into place and actually install it. This tool can track what files were installed, allowing them to be removed later when uninstalling. My package manager uses the tar program for both purposes. First it creates a package by packing up the DESTDIR (at the root of the actual install prefix):

$ tar czf package.tgz -C $DESTDIR$HOME/.local .

So a package is nothing more than a gzipped tarball. To install, it unpacks the tarball in ~/.local.

$ cd $HOME/.local
$ tar xzf ~/package.tgz

But how does it uninstall a package? It didn’t keep track of what was installed. Easy! The tarball itself contains the package list, and it’s printed with tar’s t mode.

cd $HOME/.local
for file in $(tar tzf package.tgz | grep -v '/$'); do
    rm -f "$file"
done

I’m using grep to skip directories, which are conveniently listed with a trailing slash. Note that in the example above, there are a couple of issues with file names containing whitespace. If the file contains a space character, it will word split incorrectly in the for loop. A Makefile couldn’t handle such a file in the first place, but, in case it’s still necessary, my package manager sets IFS to just a newline.

If the file name contains a newline, then my package manager relies on a cosmic ray striking just the right bit at just the right instant to make it all work out, because no version of tar can unambiguously print such file names. Crossing your fingers during this process may help.

Commands

There are five commands, each assigned to a capital letter: -B, -C, -I, -V, and -U. It’s an interface pattern inspired by Ted Unangst’s signify (see signify(1)). I also used this pattern with Blowpipe and, in retrospect, wish I had also used with Enchive.

Build (-B)

Unlike the other three commands, the “build” command isn’t essential, and is just for convenience. It assumes the build uses an Autoconfg-like configure script and runs it automatically, followed by make with the appropriate -j (jobs) option. It automatically sets the --prefix argument when running the configure script.

If the build uses something other and an Autoconf-like configure script, such as CMake, then you can’t use the “build” command and must perform the build yourself. For example, I must do this when building LLVM and Clang.

Before using the “build” command, the package must first be unpacked and patched if necessary. Then the package manager can take over to run the build.

$ tar xzf name-version.tar.gz
$ cd name-version/
$ patch -p1 < ../0001.patch
$ patch -p1 < ../0002.patch
$ patch -p1 < ../0003.patch
$ cd ..
$ mkdir build
$ cd build/
$ qpkg -B ../name-version/

In this example I’m doing an out-of-source build by invoking the configure script from a different directory. Did you know Autoconf scripts support this? I didn’t know until recently! Unfortunately some hand-written Autoconf-like scripts don’t, though this will be immediately obvious.

Once qpkg returns, the program will be fully built — or stuck on a build error if you’re unlucky. If you need to pass custom configure options, just tack them on the qpkg command:

$ qpkg -B ../name-version/ --without-libxml2 --with-ncurses

Since the second and third steps — creating the build directory and moving into it — is so common, there’s an optional switch for it: -d. This option’s argument is the build directory. qpkg creates that directory and runs the build inside it. In practice I just use “x” for the build directory since it’s so quick to add “dx” to the command.

$ tar xzf name-version.tar.gz
$ qpkg -Bdx ../name-version/

With the software compiled, the next step is creating the package.

Create (-C)

The “create” command creates the DESTDIR (_destdir in the working directory) and runs the “install” Makefile target to fill it with files. Continuing with the example above and its x/ build directory:

$ qpkg -Cdx name

Where “name” is the name of the package, without any file name extension. Like with “build”, extra arguments after the package name are passed to make in case there needs to be any additional tweaking.

When the “create” command finishes, there will be new package named name.tgz in the working directory. At this point the source and build directories are no longer needed, assuming everything went fine.

$ rm -rf name-version/
$ rm -rf x/

This package is ready to install, though you may want to verify it first.

Verify (-V)

The “verify” command checks for collisions against installed packages. It works like uninstallation, but rather than deleting files, it checks if any of the files already exist. If they do, it means there’s a conflict with an existing package. These file names are printed.

$ qpkg -V name.tgz

The most common conflict I’ve seen is in the info index (info/dir) file, which is safe to ignore since I don’t care about it.

If the package has already been installed, there will of course be tons of conflicts. This is the easiest way to check if a package has been installed.

Install (-I)

The “install” command is just the dumb tar xzf explained above. It will clobber anything in its way without warning, which is why, if that matters, “verify” should be used first.

$ qpkg -I name.tgz

When qpkg returns, the package has been installed and is probably ready to go. A lot of packages complain that you need to run libtool to finalize an installation, but I’ve never had a problem skipping it. This dumb unpacking generally works fine.

Uninstall (-U)

Obviously the last command is “uninstall”. As explained above, this needs the original package that was given to the “install” command.

$ qpkg -U name.tgz

Just as “install” is dumb, so is “uninstall,” blindly deleting anything listed in the tarball. One thing I like about dumb tools is that there are no surprises.

I typically suffix the package name with the version number to help keep the packages organized. When upgrading to a new version of a piece of software, I build the new package, which, thanks to the version suffix, will have a distinct name. Then I uninstall the old package, and, finally, install the new one in its place. So far I’ve been keeping the old package around in case I still need it, though I could always rebuild it in a pinch.

Package by accumulation

Building a GCC cross-compiler toolchain is a tricky case that doesn’t fit so well with the build, create, and install process illustrated above. It would be nice for the cross-compiler to be a single, big package, but due to the way it’s built, it would need to be five or so packages, a couple of which will conflict (one being a subset of another):

  1. binutils
  2. C headers
  3. core GCC
  4. C runtime
  5. rest of GCC

Each step needs to be installed before the next step will work. (I don’t even want to think about cross-compiling a cross-compiler.)

To deal with this, I added a “keep” (-k) option that leaves the DESTDIR around after creating the package. To keep things tidy, the intermediate packages exist and are installed, but the final, big cross-compiler package accumulates into the DESTDIR. The final package at the end is actually the whole cross compiler in one package, a superset of them all.

Complicated situations like these are where I can really understand the value of Debian’s fakeroot tool.

My use case, and an alternative

The role filled by my package manager is actually pretty well suited for pkgsrc, which is NetBSD’s ports system made available to other unix-like systems. However, I just need something really lightweight that gives me absolute control — even more than I get with pkgsrc — in the dozen or so cases where I really need it.

All I need is a standard C toolchain in a unix-like environment (even a really old one), the source tarballs for the software I need, my 110 line shell script package manager, and one to two cans of elbow grease. From there I can bootstrap everything I might need without root access, even in a disaster. If the software I need isn’t written in C, it can ultimately get bootstrapped from some crusty old C compiler, which might even involve building some newer C compilers in between. After a certain point it’s C all the way down.

Load Comments

null program

Chris Wellons