Comment 0 for bug 1934147

On a system that is monitored via telegraf I found many abandoned systemd session which I believe are created by a potential race where systemd is reloading unit files and at the same time a user is connecting to the system via ssh or is executing the su command.

The simple reproducer

for i in {1..100}; do ssh localhost sudo systemctl daemon-reload & ssh localhost sleep 1 & done
jobs -p | xargs --verbose --no-run-if-empty kill -KILL
systemctl status --all 2> /dev/null | grep --before-context 3 abandoned

will produce something similar to

           │ ├─ 175 su - ubuntu
           │ ├─ 178 -su
           │ ├─62375 systemctl status --all
           │ └─62376 grep --color=auto --before-context 3 abandoned
--
● session-273.scope - Session 273 of user ubuntu
   Loaded: loaded (/run/systemd/transient/session-273.scope; transient)
Transient: yes
   Active: active (abandoned) since Wed 2021-06-30 13:32:03 UTC; 4min 7s ago
--
● session-274.scope - Session 274 of user ubuntu
   Loaded: loaded (/run/systemd/transient/session-274.scope; transient)
Transient: yes
   Active: active (abandoned) since Wed 2021-06-30 13:32:03 UTC; 4min 7s ago
--
● session-30.scope - Session 30 of user ubuntu
   Loaded: loaded (/run/systemd/transient/session-30.scope; transient)
Transient: yes
   Active: active (abandoned) since Wed 2021-06-30 10:05:56 UTC; 3h 30min ago
--
● session-302.scope - Session 302 of user ubuntu
   Loaded: loaded (/run/systemd/transient/session-302.scope; transient)
Transient: yes
   Active: active (abandoned) since Wed 2021-06-30 13:32:04 UTC; 4min 6s ago
--
           │ ├─ 175 su - ubuntu
           │ ├─ 178 -su
           │ ├─62375 systemctl status --all
           │ └─62376 grep --color=auto --before-context 3 abandoned

The system in question is running Bionic, systemd-237-3ubuntu10.48