Hello,

ExecStopPost does not execute when a forking service fails to start.
On the other hand, ExecStopPost appropriately executes when a non-forking service fails to start.

Version: systemd 212
+PAM -AUDIT -SELINUX -IMA -SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ +SECCOMP -APPARMOR
(Arch Linux)

Steps to reproduce:
1- Create a .service file such as below:
------
[Unit]
Description=testExecStopPost
[Service]
Type=forking
PIDFile=/var/run/testExecStopPost.pid
ExecStart=/bin/bash -c 'false& echo $! > /var/run/testExecStopPost.pid'
ExecStopPost=/usr/bin/echo ExecStopPost ran
[Install]
WantedBy=multi-user.target
------

2- Execute the below commands:
systemctl daemon-reload
systemctl start testExecStopPost
systemctl status testExecStopPost

3- Notice that the ExecStopPost command does not execute (no 'echo' in the log):
<date> htpc systemd[1]: Starting testExecStopPost...
<date> htpc systemd[1]: PID 20110 read from file /var/run/testExecStopPost.pid does not exist or is a zombie.
<date> htpc systemd[1]: Failed to start testExecStopPost.
<date> htpc systemd[1]: Unit testExecStopPost.service entered failed state.

4- The issue is not reproducible with non-forking services. With non-forking services, ExecStopPost is correctly executed even if the service fails to start (notice the 'echo' in the logs)
------
[Service]
ExecStart=/usr/bin/false
ExecStopPost=/usr/bin/echo ExecStopPost ran
------
<date> htpc systemd[1]: Started testExecStopPost.
<date> htpc systemd[1]: testExecStopPost.service: main process exited, code=exited, status=1/FAILURE
<date> htpc echo[20242]: ExecStopPost ran
<date> htpc systemd[1]: Unit testExecStopPost.service entered failed state.

5- Indirectly related: it would be useful to have a directive to force execute ExecStopPost if ExecStartPre fails.
Rationale: ExecStopPost is typically used for cleanup, but if ExecStartPre fails, there is today no way to perform this cleanup. Systematically executing ExecStopPost is probably debatable (e.g. C++ destructors do not run if contructors fail) so having a directive, or at worst a command to force execute ExecStopPost would be useful.