Sometimes it makes sense to ship a program to linux users in ready-to-run form that will work no matter what distribution they are using. This is hard.
Often a commerical linux game will bundle up a few of the more problimatic libraries, and ship a dynamic executable that still depends on other system libaries. These days they're building and shipping entire Debian derivatives instead, to avoid needing to deal with that.
There have been a few efforts to provide so-called one click install package systems that AFAIK, have not been widely used. I don't know if they generally solved the problem.
More modern appoaches seem to be things like docker, which move the application bundle into a containerized environment. I have not looked at these, but so far it does not seem to have spread widely enough to be a practical choice if you're wanting to provide something that will work for a majority of linux users.
So, I'm surprised that I seem to have managed to solve this problem using nothing more than some ugly shell scripts.
My standalone tarballs of git-annex now seem fairly good at running on a very wide variety of systems.
For example, I unpacked the tarball into the Debian-Installer initramfs and
git-annex could run there. I can delete all of /usr and it keeps working!
All it needs is a basic
sh, which even busybox provides.
Looks likely that the new armel standalone tarball of git-annex will soon be working on embedded systems as odd as the Synology NAS, and it's already been verified to work on Raspbian. (I'm curious if it would work on Android, but that might be a stretch.)
Currently these tarballs are built for a specific architecture, but there's no particular reason a single one couldn't combine binaries built for each supported architecture.
The main trick is to ship a copy of ld-linux.so, as well as all the glibc libraries and associated files, and of course every other library and file the application needs.
Shipping ld-linux.so lets a shell script wrapper be made around each binary, that runs ld-linux.so and passes it the library directories to search. This way the binary can be run, bypassing the system's own dynamic linker (which might not like it) and using the included glibc.
For example a shell script that runs the git binary from the bundle:
exec "$GIT_ANNEX_LINKER" --library-path "$GIT_ANNEX_LD_LIBRARY_PATH" "$GIT_ANNEX_SHIMMED/git/git" "$@"
I have to set quite a lot of environment variables, to avoid using any
files from the system and instead use ones from my tarball. One important
GCONV_PATH. Note that
LD_LIBRARY_PATH does not have to be set,
and this is nice because it allows running a few programs from the host
system, such as its web browser.
worse is better
Of course I'll take a proper distribution package anytime over this.
Still, it seems to work quite well, in all the horrible cases that require it.