[simcop2387]

It's a bit non-obvious from that description but Syd does in fact use kernel facilities to do the sandboxing. A sibling comment links to some better documentation (the syd man page) that explains what it uses https://man.exherbolinux.org/syd.1.html

1) Seccomp, a BPF based kernel filter for syscalls

2) Bind mounts inside a filesystem namespace to control what files are visible

3) Landlock - more path restriction type stuff and permission changes to paths that are local to the application being wrapped

4) seccomp-notify (used with ptrace to inspect types of arguments to syscalls that bpf isn't allowed to access for security reasons, i.e. pointers)