Building the dependencies -- note that you might want to mark libfuse as external (spack external find --not-buildable pkg-config pkgconf libfuse) so that you can use the system setuid fusermount binary.
$ spack -e . install -v
If you build libfuse with spack, you'll have to do the system install by hand and make fusermount3 a setuid binary:
sudo chown root:root /path/to/fusermount3
sudo chmod u+s /path/to/bin/fusermount3
Now build the runtime:
$ export C_INCLUDE_PATH=.spack-env/view/include
$ export LIBRARY_PATH=.spack-env/view/lib
$ make
Size overhead from the runtime is small:
Now create an AppRun executable in a folder and squashfs it:
$ mkdir -p example
$ echo $'#!/usr/bin/bash'$'\n'$'echo "hello world"' > example/AppRun
$ chmod +x example/AppRun
$ mksquashfs example example.squashfs -comp zstd -quiet
And merge runtime and the squashfs file into an executable:
$ cat runtime example.squashfs > app
$ chmod +x app
$ ./app
hello world
Notes about licensing:
- zstd is dual BSD and GPLv2 licensed
- squashfuse is BSD licensed
- libfuse is LGPL licensed
- runtime.c is from AppImageKit and libappimage, which is licensed MIT
I still have to figure out whether or not statically linking to libfuse is a good idea in terms of licensing, as well as the implications of dual licensing of zstd.