Very Slow Shutdown when running 6.14.0-24-generic started within the past week

[TheSupremeVizier]

I am not a noob to Kubuntu, but this is my first post here and I don't know the ropes here yet, so call me a noob if you want. ;-) I had an older desktop which was running Kubuntu, but the motherboard died. I purchased components and built a new system. I downloaded kubuntu-24.04.2-desktop-LTS-amd64.iso (which I assumed from the ISO name has LTS support) on May 30 and built a bootable USB drive with unetbootin. I loaded kubuntu on June 6. The System.map, config and vmlinuz for 6.11.0-29-generic and 6.14.0-24-generic all have June 26 and July 7 timestamps, respectively, according to "ls -al /boot". The initrd.img files for 6.11.0-29-generic and 6.14.0-24-generic are dated July 15 and July 17, respectively.

I use connections on both LAN and WiFi. This may be pertinent to what follows.

While running 6.14.0-24-generic, my system experiences a very significant hang during shutdown coinciding with failure to shutdown NetworkManager and wpa_supplicant. This problem does NOT occur when running the 6.11.0-29-generic kernel. While performing a shutdown and viewing the logs concatenated to the monitor, it is easy to observe both NetworkManager and wpa_supplicant kill attempts repeatedly timing out failing to terminate until very late. Even after they finally terminate, the hardware does NOT actually power off, instead leaving the monitor hanging on while displaying:

systemd-shutdown[1]: Powering off.
sd 2:0:0:0 [sda] Synchronizing SCSI cache
sd 2:0:0:0 [sda] Stopping disk

...forever and ever and ever, so it fails to reboot if system restart was intended.

Kubuntu is installed to a SSD. I also have an HDD in the system (hence the /dev/sda), but /dev/sda is NOT mounted.

Again, this problem does NOT occur while running 6.11.0-29-generic and shutting down.

While running 6.11.0-29-generic, the output after executing

sudo apt -a list NetworkManager KNetworkManager networkmanager-qt libkf5networkmanagerqt-dev networkmanager-openvpn networkmanager-vpnc networkmanager-openconnect wpasupplicant
Listing... Done
libkf5networkmanagerqt-dev/noble 5.115.0-0ubuntu4 amd64
wpasupplicant/noble-updates,noble-security,now 2:2.10-21ubuntu0.2 amd64 [installed,automatic]
wpasupplicant/noble 2:2.10-21build4 amd64

As expected, the packages appear identical when both kernels are run. What is not understood is why the same configuration works to quickly shutdown the earlier kernel version operating system and fails to quickly shutdown the most recent kernel version operating system. I update this system on a daily basis.

I have manually killed both the NetworkManager and wpa_supplicant processes immediately prior to starting shutdown which results in apparently perfect shutdown and restart behavior, but this is an inelegant bandaid which I assume might have nasty side effects. Since this issue occurs with the newer kernel and does not occur with the older kernel, I suspect this is a kernel issue and likely not a configuration issue, but I am not a kernel expert, so I am asking for help and greatly appreciate your opinions.

If you need more information, please ask. Since this is my first post here, I could use a little advice regarding the information you need to investigate and how to present it...any links to how to provide you information would also be helpful.

Motherboard: MSI PRO B650-VC WIFI III
CPU: AMD Ryzen 9 9900X
GPU: NVIDIA GeForce RTX 5070
RAM: 32 GB DDR5
2 TB SSD (/dev/nvme0n1)
Wi-Fi 6E
Bluetooth 5.3
LinksTek 4-Ports PCIE 1394A Firewire 400 Card, TI TSB43AB23 chipset
2 TB unmounted HDD (/dev/sda)

Thank you very much in advance.

[TheSupremeVizier]

This is an update to my preceding post. The workaround described above has been shown to be inadequate when attempting to shutdown 6.14.0-24-generic. The processes that are reluctant to die during shutdown now include

avahi-daemon
NetworkManager
wpa_supplicant
cups-browsed
xdg-desktop-por
kded5
kdeconnectd
DiscoverNotifie
chrome
sudo
.plocate
postmulti

I wish to note that the processes

sudo kill <processID of NetworkManager>
sudo kill <processID of wpa_supplicant>

also hung and the process sadc was found running "full tilt boogie" full time at 100% on a single processor after these sudo processes were started. I was running the chrome browser when I attempted to shutdown. I have also noticed that the plasma desktop occasionally crashes.

I am now booting into the 6.11.0-29-generic kernel because it does not exhibit any of these problems. Please help. If you know of any other forum to which my request for assistance should be directed, please tell me.

[skyfishgoo]

i would suggest upgrading to 25.04 at your earliest .... plasma 6.1 had plenty of issues but i understand 6.3 is much more reliable.

[TheSupremeVizier]

Thank you very much, skyfishgoo. I will strongly consider your fix in the near future, but I am also looking for LTS support.
Please see https://www.kubuntuforums.net/forum/...ions-about-lts for the current state of this problem.
Again, thank you very much. I truly appreciate it.

[skyfishgoo]

you will not be able to back to LTS without reinstalling... but there is an upgrade path to go forward along the non-LTS until the next one becomes available in 26.04