Comment 12 for bug 1828496

Going over the details from comment #7

This is the state before the reload:
ubuntu@foo:~$ ps auxfwww | grep haproxy
root 1346 0.0 0.0 4356 684 ? Ss May22 0:00 /usr/sbin/haproxy-systemd-wrapper -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
haproxy 2210 0.0 0.2 42644 10520 ? S May22 0:00 \_ /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 1378
haproxy 2215 2.7 0.8 68576 36308 ? Ss May22 84:46 \_ /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 1378

-sf means to send the finish signal (which is SIGTTOU and SIGUSR1 according to haproxy(1)) to the pids listed after startup, which is pid 1378 in this case. There is no haproxy 1378 in this list, so I wonder if the "before" state was already a bit borked and what haproxy does if the pids listed after -sf do not exist.

After reload, we have:
ubuntu@foo:~$ ps auxfwww | grep haproxy
root 1346 0.0 0.0 4356 724 ? Ss May22 0:00 /usr/sbin/haproxy-systemd-wrapper -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
haproxy 2210 0.0 0.2 42644 10520 ? S May22 0:00 \_ /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 1378
haproxy 2215 2.7 0.8 68496 36228 ? Ss May22 84:47 | \_ /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 1378
haproxy 8151 0.0 0.2 42644 10456 ? S 07:36 0:00 \_ /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 2215
haproxy 8152 2.0 0.2 43048 10568 ? Ss 07:36 0:00 \_ /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds -sf 2215
ubuntu@foo:~$

Here we can see new haproxy processes with -sf pointing at the previous 2215 one. The ones with -sf 1378 are still there, and will remain there until a full restart probably.