Endless rss notifier errors leading to cups service collapse

[PeterDKC]

Hi,

We're running cups alongside PrintNode to do API printing. We're running a collection of Epson C6000 label printers in a fulfillment warehouse environment. cups versions is 2.4. There are other threads on this topic on the repo and stack overflow. We've been trying to follow those for weeks to no avail.

We're using PrintNode to grab PDFs off of our SaaS app and spool them to cups. Our current state is that the service runs fine "for a while". After several hundred print jobs, it starts to slow down, going from ~.5sec to handle a job to 60sec. Then 180sec. Eventually the service just stops working.

The logs are a never ending ream of the following error messages:

W [17/May/2023:13:58:06 -0500] Notifier for subscription 1 (rss://IMAGINATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 2 (rss://TRAIN) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 3 (rss://MEDITATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 4 (rss://SWEETSALVATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 5 (rss://WHATINTARNATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 6 (rss://FIRE) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 7 (rss://COLLEGERADIO) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 8 (rss://INSPIRATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 9 (rss://SPACE) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 10 (rss://PLAY) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 11 (rss://INFLATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 13 (rss://GRANDCENTRAL) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 14 (rss://CORPORATION) went away, retrying!
W [17/May/2023:13:58:06 -0500] Notifier for subscription 15 (rss://RADIATION) went away, retrying!
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to VACATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to TRAIN on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to IMAGINATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to MEDITATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to SWEETSALVATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to WHATINTARNATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to COLLEGERADIO on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to INSPIRATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to FIRE on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to SPACE on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to PLAY on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to INFLATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to CORPORATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to RADIATION on port 0: Resource temporarily unavailable
E [17/May/2023:13:58:06 -0500] [Notifier] Unable to connect to GRANDCENTRAL on port 0: Resource temporarily unavailable

To be very clear, we have absolutely no need of rss notifications. I also have absolutely no idea how to enable or disable them vis cups. I saw the comments that they are removed from the web ui, but that actually doesn't tell me anything about how to deal with them otherwise. I couldn't find anything in the docs.

In order to resolve this over the short terms I've cooked up the following script:

#!/bin/bash

sudo service PrintNode stop
sudo service cups stop
sleep 2
sudo rm /etc/cups/subscription*
sudo rm -rf /var/cache/cups/*
sudo service cups start
sudo service PrintNode start

echo "Print services unf@#$ed. Have a nice day."

This is inline w/ advice I've seen on issues in this repo. This does have the effect of temporarily getting the service back to responsiveness, but it does not stop the error messages or affect the overall issues.

Here's the notifier permissions, also adjusted per other issues:

$ ls -al /usr/lib/cups/notifier/
total 76
drwxr-xr-x  2 root root  4096 May  8 12:22 .
drwxr-xr-x 10 root root  4096 Feb 22 21:58 ..
-rwxr-xr-x  1 root root 18744 May 27  2022 dbus
-rwxr-xr-x  1 root root 22840 May 27  2022 mailto
-rwxr-xr-x  1 root root 22840 May  8 13:53 rss

The current box this is running on replaced another box suffering hardware issues. That box had identical issues and error messages. I thought I had this eliminated, I blew the cache away and rebooted a week ago or so and we had almost a full week of blissful silence out of it. However, the lead boxer added a new printer two days ago and it's been non-stop since then.

I'm not sure what the underlying issue is, but I am sure that this is a persistent drag on our business operations and my time and stress levels in particular. I would really love to find a permanent resolution to it.

Thanks much for your time.