Redémarrage gracieux du process master de gunicorn

`pc -C gunicorn` only lists the processes with `gunicorn` command, i.e., workers and master process. Workers are children of master as can be seen using `ps -C gunicorn fc -o ppid,pid,cmd`. We only need the pid of the master, therefore h flag is used to remove the first line which is PID text. Note that, f flag assures that master is printed above workers.

The correct procedure is to send `HUP` signal only to the master. In this way `gunicorn` is gracefully restarted, only the workers, not master, are recreated.

source/part-2-deployment/debian.adoc

@@ -357,8 +357,9 @@ git checkout vX.Y.Z
 pip install -U requirements/prod.txt
 python manage.py migrate
 python manage.py collectstatic
-gunicorn reload -HUP
+kill -HUP `ps -C gunicorn fch -o pid | head -n 1` <1>
 ----
+<1> https://stackoverflow.com/questions/26902930/how-do-i-restart-gunicorn-hup-i-dont-know-masterpid-or-location-of-pid-file
 
 ==== Configuration des sauvegardes