[systemd-devel] Cannot set PATH environment variable from environment.d

[Yeongjin Kwon]

Hi, I've been trying to set the PATH environment variable in systemd
user daemon with environment.d but it's not working. I'm using Arch
Linux, and my systemd version is below:
> systemd 252 (252.2-2-arch)
> +PAM +AUDIT -SELINUX -APPARMOR -IMA +SMACK +SECCOMP +GCRYPT +GNUTLS +OPENSSL +ACL +BLKID +CURL +ELFUTILS +FIDO2 +IDN2 -IDN +IPTC +KMOD +LIBCRYPTSETUP +LIBFDISK +PCRE2 -PWQUALITY +P11KIT -QRENCODE +TPM2 +BZIP2 +LZ4 +XZ +ZLIB +ZSTD -BPF_FRAMEWORK +XKBCOMMON +UTMP -SYSVINIT default-hierarchy=unified

I created a file at the path ~/.config/environment.d/50-my-vars.conf
with the following content:
> PATH=custom_path
> ANOTHER_VAR=foo
and then ran `systemctl --user daemon-reload` and then `systemctl
--user show-environment`. The latter command showed that ANOTHER_VAR
had been set to foo, but PATH had not changed. I replaced the content
of the file with:
> PATH=bar
> ANOTHER_VAR=baz
and daemon-reloaded again, but only ANOTHER_VAR had changed to baz and
PATH remained the same again.

To see if the issue was with my environment.d config, I ran
`/usr/lib/systemd/user-environment-generators/30-systemd-environment-d-generator`.
It showed the same output as my environment.d config.
I also made a script with the following content:
> #!/bin/bash
>
> echo "$PATH" > /tmp/log.txt
and placed it at
/run/systemd/user-environment-generators/99_test_generator. When I
daemon reloaded and checked the value of /tmp/log.txt, it showed the
value of PATH that I set in my environment.d config. I then moved the
script to /run/systemd/user-generators/99_test_generator and daemon
reloaded again, and it also showed the same value.
What I gathered from this is that the problem is not with the
generators. The environment.d generator is working and it's setting
PATH to what I expect, but this change is either undone by something
else later in the daemon reload, or is not being propagated to the
actual systemd environment.

After that, I checked if I could adjust the PATH myself manually. I
ran `systemctl --user set-environment PATH=my_path_value`, and checked
the systemd environment. It showed that PATH had been updated to
my_path_value. This new value of PATH persisted after I daemon
reloaded multiple times.

And so I honestly can't figure out what is going on at this point. I'm
guessing something is preventing a change to PATH from environment
generators from propagating to systemd's actual environment, but I
have no clues as to what that may be. Could someone help me understand
why my environment.d configuration is not setting PATH to what I want?
Thank you.