I just happened to see some posts here about weird things happening on a Pi5 when the monitor was switched off. This rang some very loud bells for me. My Pi5 runs as a server for my smart-home system, using my own software. One of the components that runs continuously listens for incoming network connections, then accepts requests for data from the system's database and returns that data to the remote caller. I want to leave the Pi's monitor switched off most of the time, to minimise power usage.
Just recently, I noted that sometimes the remote clients (I have clients for Android and Windows) would have inexplicable difficulty establishing a connection to the Pi. Just in the last few days - by pure chance - I observed that the problem was worse when the Pi's monitor was switched off. I could hardly believe that, so I did some tests - switched it on and off many times, doing attempted connections along the way. I was astounded to see that the correlation was almost 100% - when the monitor was on all was well: when it was off, it hardly ever worked. I still found it hard to believe that switching off a monitor could somehow interfere with network operation, but that was what my eyes were telling me. The short-term workaround was simply to leave the monitor on.
I found the other posts because I had turned on screen blanking, but it was not working. While following that thread I saw the parameters that could be added to the cmdline.txt configuration file, to tell the kernel to ignore the spurious messages that a monitor can apparently send when it is switched off. That appears to have fixed my problem, which is good. But it is NOT good that this sort of system interference should be able to be caused by simply switching off a monitor.
I can't be 100% sure, but my feeling is that this problem has only arisen relatively recently (for me) - maybe after a system update?? I only upgraded my system to the Pi5 (from a Pi400) about last December. It is a stock Bookworm 64-bit install. Most of the time it has been running quite happily with the monitor switched off, but I needed to make some minor mods to my software in the last month or so. I do recall doing at least one Pi OS update in the last few weeks, and it has been since that timeframe that this problem has become evident.
Anyway, I thought I would post this because it might ring bells for others as it did for me. It appears that the glitches that can be caused by innocently switching off a monitor can affect a lot of things! The post that describes the config changes is here:
viewtopic.php?p=2146832&hilit=waggle+hotplug#p2146832
Scroll down to the post from user JumpZero
Just recently, I noted that sometimes the remote clients (I have clients for Android and Windows) would have inexplicable difficulty establishing a connection to the Pi. Just in the last few days - by pure chance - I observed that the problem was worse when the Pi's monitor was switched off. I could hardly believe that, so I did some tests - switched it on and off many times, doing attempted connections along the way. I was astounded to see that the correlation was almost 100% - when the monitor was on all was well: when it was off, it hardly ever worked. I still found it hard to believe that switching off a monitor could somehow interfere with network operation, but that was what my eyes were telling me. The short-term workaround was simply to leave the monitor on.
I found the other posts because I had turned on screen blanking, but it was not working. While following that thread I saw the parameters that could be added to the cmdline.txt configuration file, to tell the kernel to ignore the spurious messages that a monitor can apparently send when it is switched off. That appears to have fixed my problem, which is good. But it is NOT good that this sort of system interference should be able to be caused by simply switching off a monitor.
I can't be 100% sure, but my feeling is that this problem has only arisen relatively recently (for me) - maybe after a system update?? I only upgraded my system to the Pi5 (from a Pi400) about last December. It is a stock Bookworm 64-bit install. Most of the time it has been running quite happily with the monitor switched off, but I needed to make some minor mods to my software in the last month or so. I do recall doing at least one Pi OS update in the last few weeks, and it has been since that timeframe that this problem has become evident.
Anyway, I thought I would post this because it might ring bells for others as it did for me. It appears that the glitches that can be caused by innocently switching off a monitor can affect a lot of things! The post that describes the config changes is here:
viewtopic.php?p=2146832&hilit=waggle+hotplug#p2146832
Scroll down to the post from user JumpZero
Statistics: Posted by marshallarts — Fri Jun 27, 2025 5:48 am