There is a race upon reload, where it can happen that:
1. systemd forks off /bin/kill -HUP $MAINPID
2. Current instance forks off new one and notifies systemd with the
new MAINPID.
3. systemd sets new MAINPID.
4. systemd receives SIGCHLD for the kill process (which is the current
control process for the service) and reads the PID of the old
instance from the PID file, resetting MAINPID to the PID of the old
instance.
5. Old instance exits.
6. systemd receives SIGCHLD for the old instance, reads the PID of the
old instance from the PID file once more. systemd sees that the
MAINPID matches the child PID and considers the service exited.
7. systemd receivese notification from the new PID and is confused.
The service won't get active, because the notification wasn't
handled.
To fix it, update the PID file before sending the MAINPID
notification, similar to what a comment in systemd's
src/core/service.c suggests:
> /* Forking services may occasionally move to a new PID.
> * As long as they update the PID file before exiting the old
> * PID, they're fine. */
but for our Type=notify "before sending the notification" rather than
"before exiting", because otherwise, the mix-up in 4. could still
happen (although it might not actually be problematic without the
mix-up in 6., it still seems better to avoid).
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
until now, we manually polled the systemd service state during a reload
so that the sd_notify messages get processed in the correct order
(RELOAD(old) -> MAINPID(old) -> READY(new))
with systemd >= 246 there is now 'sd_notify_barrier' which
blocks until systemd processed all prior messages
with that change, the daemon does not need to know the service name anymore
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
show how to generally start a daemon that serves a rest api + index page
api calls are (prefixed with either /api2/json or /api2/extjs):
/ GET listing
/ping GET returns "pong"
/items GET lists existing items
POST lets user create new items
/items/{id} GET returns the content of a single item
PUT updates an item
DELETE deletes an item
Contains a small dummy user/authinfo
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
