Arch Linux

This is because /etc/profile merely appends to your PATH now, instead of hardcoding a PATH. Which means that whatever the PATH used to be before /etc/profile is loaded, is still lingering around... The default Arch install does not add those at all. At least mine does not.

Also why do you have the /etc/profile.d/perlbin.sh paths appearing three times?

Though I do note that before /etc/profile is loaded, my PATH=/usr/bin which produces unexpected results of a different nature.
My new PATH is "/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl".

These results are from a devtools build chroot. So these are unmodified defaults.

uhh... I get that in devtools too, apparently.

And apparently for my logged in system this is derived from /etc/login.defs:
ENV_PATH PATH=/usr/bin

Our bash PKGBUILD has the following CFLAGS: -DDEFAULT_PATH_VALUE='"/usr/local/sbin:/usr/local/bin:/usr/bin"'

Does systemd-nspawn *also* try to set this somehow?

My guess is that values (and orders) are defined in the systemd variable DEFAULT_PATH_SPLIT_USR in src/basic/path-util.h and added by systemd-nspawn, called by arch-nspawn, called by makechrootpkg.
The PATH is not the same between a «booted» system (.service units) and a «spawned» system.

Side discovery, all our daemons PATH environment are also defined by a value in this file, which make our default PATH to be /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin.
I added an environment generator to define our arch default path in systemd in 2017.09-1.

With the previous version of filesystem, the PATH variable was reset when the shell loads /etc/profile. See  FS#47884 .
Our build system is several bash scripts, and the PATH in the chrooted environment was defined by /etc/profile.

We have a several options:
- We restore the previous behaviour in filesystem;
- We fix systemd-nspawn to use DEFAULT_PATH instead of DEFAULT_PATH_SPLIT_USR;
- We fix arch-nspawn to set the arch default path

I sent a patch to arch-project which define the Arch default PATH when calling systemd-nspawn.

I pushed a new version of devtools in testing with a patched arch default environment. Looks good so far.