This is calling grub2-mkconfig at line 340
https://git.gnome.org/browse/ostree/tree/src/libostree/ostree-bootloader-...
And line 153 says this must have been called from a wrapper script.
I'm pretty much thinking grub2-mkconfig is not meant to be directly
called by the user either, and is envisioned to only get called by
e.g. ostree admin deploy/switch, or rpm-ostree rollback/upgrade, etc.
That's fine, it's just not obvious what user space tools belong to the
user.
Chris Murphy