NUT UPS stopped working after upgrade from PVE 8 to 9

F

fcarneiro

New Member
Oct 1, 2026
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1
1
Hello,
I just upgraded a server running Proxmox version 8 (PVE 8.4.19, Debian 12.14, kernel 6.8.12-30-pve) to version 9 (PVE 9.2.21, Debian 13.7, kernel 7.0.14-20-pve) and the NUT UPS server/monitor stopped working. It doesn't connect to the UPS anymore and doesn't even detect it with nut-scanner.

Everything was working fine just before the upgrade. There were no physical changes or any change on the UPS, just the OS upgrade/reboot.

I've checked the nut group assignments and udev rules and everything seems to be right. The UPS is connected through a Serial-USB converter, which is shown on dmesg and lsusb.

I've seen some related threads about this same issue, but nothing worked for me so far.

Does anyone else have a clue on how to fix this?

PS: I've already tried rebooting, physically disconnecting/reconnecting the USB adapter and serial cable, completely powering off/on the server, reinstalling the nut packages, reconfiguring using the default configuration, restoring the old configuration files...


Here is my configuration (nothing has changed, I kept the old configuration files while upgrading):

/etc/nut/nut.conf
Code: 
MODE=standalone

/etc/nut/ups.conf
Code: 
maxretry = 3

[UPS-NAME]
    driver = nutdrv_qx
    port = /dev/ttyUSB0
    pollinterval = 2

MONITOR UPS-NAME@localhost 0 upsmonuser xxxxxxxxxxxxxxxxx primary


dmesg output:
Code: 
[   19.871354] usbserial: USB Serial support registered for FTDI USB Serial Device
[   19.872401] ftdi_sio 1-7:1.0: FTDI USB Serial Device converter detected
[   19.872918] usb 1-7: Detected FT2232C/D
[   19.873343] usb 1-7: FTDI USB Serial Device converter now attached to ttyUSB0
[   19.873630] ftdi_sio 1-7:1.1: FTDI USB Serial Device converter detected
[   19.873896] usb 1-7: Detected FT2232C/D
[   19.874260] usb 1-7: FTDI USB Serial Device converter now attached to ttyUSB1

lsusb:
Code: 
Bus 001 Device 002: ID 0403:6010 Future Technology Devices International, Ltd FT2232C/D/H Dual UART/FIFO IC

$ sudo service nut-server status
Code: 
× nut-server.service - Network UPS Tools - power devices information server
     Loaded: loaded (/usr/lib/systemd/system/nut-server.service; enabled; preset: enabled)
     Active: failed (Result: exit-code) since Thu 2026-10-01 08:12:01 UTC; 11min ago
   Duration: 6ms
 Invocation: fd841a0a19674524b103df6816ad2658
    Process: 1669 ExecStartPre=/usr/bin/systemd-tmpfiles --create /usr/lib/tmpfiles.d/nut-common-tmpfiles.conf (code=exited, status=0/SUCCESS)
    Process: 1672 ExecStart=/usr/sbin/upsd -F (code=exited, status=1/FAILURE)
   Main PID: 1672 (code=exited, status=1/FAILURE)

Oct 01 08:12:01 [hostname] systemd[1]: nut-server.service: Scheduled restart job, restart counter is at 5.
Oct 01 08:12:01 [hostname] systemd[1]: nut-server.service: Start request repeated too quickly.
Oct 01 08:12:01 [hostname] systemd[1]: nut-server.service: Failed with result 'exit-code'.
Oct 01 08:12:01 [hostname] systemd[1]: Failed to start nut-server.service - Network UPS Tools - power devices information server.

$ ls -l /dev/ttyUSB0
Code: 
crw-rw---- 1 root dialout 188, 0 Oct  1 08:24 /dev/ttyUSB0

$ sudo nut-scanner -U
Code: 
Cannot load IPMI library (libfreeipmi.so.17) : file not found. IPMI search disabled.
Scanning USB bus.

$ sudo nut-scanner
Code: 
Cannot load IPMI library (libfreeipmi.so.17) : file not found. IPMI search disabled.
Scanning USB bus.
No start IP, skipping SNMP
Scanning XML/HTTP bus.
No start IP, skipping NUT bus (old connect method)
Scanning NUT bus (avahi method).
Failed to create Avahi client: Daemon not running


cat /etc/udev/rules.d/62-nut-usbups.rules
Code: 
# This file is generated and installed by the Network UPS Tools package.

ACTION=="remove", GOTO="nut-usbups_rules_end"
SUBSYSTEM=="usb_device", GOTO="nut-usbups_rules_real"
SUBSYSTEM=="usb", GOTO="nut-usbups_rules_real"
GOTO="nut-usbups_rules_end"

LABEL="nut-usbups_rules_real"
#  SNR-UPS-LID-XXXX UPSes  - nutdrv_qx
ATTR{idVendor}=="0001", ATTR{idProduct}=="0000", MODE="664", GROUP="nut"

[...]


# ID 0403:6010 Future Technology Devices International, Ltd FT2232C/D/H Dual UART/FIFO IC
# (added this line:)
ATTR{idVendor}=="0403", ATTR{idProduct}=="6010", MODE="664", GROUP="nut"

LABEL="nut-usbups_rules_end"



grep nut /var/log/syslog:
Code: 
2026-10-01T08:24:59.681711+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:04.681913+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:09.682172+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:14.682362+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:19.682551+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:24.682715+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:29.682921+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:34.683164+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:39.683317+00:00 hostname nut-monitor[1556]: UPS [UPS-NAME@localhost]: connect failed: Connection failure: Connection refused
2026-10-01T08:25:42.185841+00:00 hostname nut-monitor[1556]: Signal 15: exiting
2026-10-01T08:25:42.186035+00:00 hostname systemd[1]: Stopping nut-monitor.service - Network UPS Tools - power device monitor and shutdown controller...
2026-10-01T08:25:42.186817+00:00 hostname nut-monitor[1556]: Network UPS Tools upsmon 2.8.1
2026-10-01T08:25:42.187583+00:00 hostname systemd[1]: nut-monitor.service: Deactivated successfully.
2026-10-01T08:25:42.187788+00:00 hostname systemd[1]: Stopped nut-monitor.service - Network UPS Tools - power device monitor and shutdown controller.
2026-10-01T08:25:45.643526+00:00 hostname systemd[1]: Starting nut-server.service - Network UPS Tools - power devices information server...
2026-10-01T08:25:45.663522+00:00 hostname systemd[1]: Started nut-server.service - Network UPS Tools - power devices information server.
2026-10-01T08:25:45.669906+00:00 hostname nut-server[8515]: fopen /run/nut/upsd.pid: No such file or directory
2026-10-01T08:25:45.669961+00:00 hostname nut-server[8515]: Could not find PID file '/run/nut/upsd.pid' to see if previous upsd instance is already running!
2026-10-01T08:25:45.670011+00:00 hostname nut-server[8515]: not listening on ::1 port 3493
2026-10-01T08:25:45.670116+00:00 hostname nut-server[8515]: listening on 127.0.0.1 port 3493
2026-10-01T08:25:45.670136+00:00 hostname nut-server[8515]: no listening interface available
2026-10-01T08:25:45.670153+00:00 hostname nut-server[8515]: Network UPS Tools upsd 2.8.1
2026-10-01T08:25:45.670608+00:00 hostname systemd[1]: nut-server.service: Main process exited, code=exited, status=1/FAILURE
2026-10-01T08:25:45.670726+00:00 hostname systemd[1]: nut-server.service: Failed with result 'exit-code'.
2026-10-01T08:25:45.814848+00:00 hostname systemd[1]: nut-server.service: Scheduled restart job, restart counter is at 1.
2026-10-01T08:25:45.815972+00:00 hostname systemd[1]: Starting nut-server.service - Network UPS Tools - power devices information server...
2026-10-01T08:25:45.832549+00:00 hostname systemd[1]: Started nut-server.service - Network UPS Tools - power devices information server.
2026-10-01T08:25:45.838421+00:00 hostname nut-server[8548]: fopen /run/nut/upsd.pid: No such file or directory
2026-10-01T08:25:45.838480+00:00 hostname nut-server[8548]: Could not find PID file '/run/nut/upsd.pid' to see if previous upsd instance is already running!
2026-10-01T08:25:45.838508+00:00 hostname nut-server[8548]: not listening on ::1 port 3493
2026-10-01T08:25:45.838523+00:00 hostname nut-server[8548]: listening on 127.0.0.1 port 3493
2026-10-01T08:25:45.838537+00:00 hostname nut-server[8548]: no listening interface available
2026-10-01T08:25:45.838553+00:00 hostname nut-server[8548]: Network UPS Tools upsd 2.8.1
2026-10-01T08:25:45.838936+00:00 hostname systemd[1]: nut-server.service: Main process exited, code=exited, status=1/FAILURE
2026-10-01T08:25:45.839063+00:00 hostname systemd[1]: nut-server.service: Failed with result 'exit-code'.
2026-10-01T08:25:46.064806+00:00 hostname systemd[1]: nut-server.service: Scheduled restart job, restart counter is at 2.
2026-10-01T08:25:46.065972+00:00 hostname systemd[1]: Starting nut-server.service - Network UPS Tools - power devices information server...
2026-10-01T08:25:46.079871+00:00 hostname systemd[1]: Started nut-server.service - Network UPS Tools - power devices information server.
2026-10-01T08:25:46.086103+00:00 hostname nut-server[8553]: fopen /run/nut/upsd.pid: No such file or directory
2026-10-01T08:25:46.086164+00:00 hostname nut-server[8553]: Could not find PID file '/run/nut/upsd.pid' to see if previous upsd instance is already running!
2026-10-01T08:25:46.086213+00:00 hostname nut-server[8553]: not listening on ::1 port 3493
2026-10-01T08:25:46.086227+00:00 hostname nut-server[8553]: listening on 127.0.0.1 port 3493
2026-10-01T08:25:46.086241+00:00 hostname nut-server[8553]: no listening interface available
2026-10-01T08:25:46.086331+00:00 hostname nut-server[8553]: Network UPS Tools upsd 2.8.1
2026-10-01T08:25:46.086806+00:00 hostname systemd[1]: nut-server.service: Main process exited, code=exited, status=1/FAILURE
2026-10-01T08:25:46.086921+00:00 hostname systemd[1]: nut-server.service: Failed with result 'exit-code'.
2026-10-01T08:25:46.314805+00:00 hostname systemd[1]: nut-server.service: Scheduled restart job, restart counter is at 3.
2026-10-01T08:25:46.315996+00:00 hostname systemd[1]: Starting nut-server.service - Network UPS Tools - power devices information server...
2026-10-01T08:25:46.329607+00:00 hostname systemd[1]: Started nut-server.service - Network UPS Tools - power devices information server.
2026-10-01T08:25:46.335818+00:00 hostname nut-server[8560]: fopen /run/nut/upsd.pid: No such file or directory
2026-10-01T08:25:46.335881+00:00 hostname nut-server[8560]: Could not find PID file '/run/nut/upsd.pid' to see if previous upsd instance is already running!
2026-10-01T08:25:46.335907+00:00 hostname nut-server[8560]: not listening on ::1 port 3493
2026-10-01T08:25:46.335923+00:00 hostname nut-server[8560]: listening on 127.0.0.1 port 3493
2026-10-01T08:25:46.335935+00:00 hostname nut-server[8560]: no listening interface available
2026-10-01T08:25:46.336019+00:00 hostname nut-server[8560]: Network UPS Tools upsd 2.8.1
2026-10-01T08:25:46.336194+00:00 hostname systemd[1]: nut-server.service: Main process exited, code=exited, status=1/FAILURE
2026-10-01T08:25:46.336302+00:00 hostname systemd[1]: nut-server.service: Failed with result 'exit-code'.
2026-10-01T08:25:46.564829+00:00 hostname systemd[1]: nut-server.service: Scheduled restart job, restart counter is at 4.
2026-10-01T08:25:46.566078+00:00 hostname systemd[1]: Starting nut-server.service - Network UPS Tools - power devices information server...
2026-10-01T08:25:46.579784+00:00 hostname systemd[1]: Started nut-server.service - Network UPS Tools - power devices information server.
2026-10-01T08:25:46.585788+00:00 hostname nut-server[8565]: fopen /run/nut/upsd.pid: No such file or directory
2026-10-01T08:25:46.585831+00:00 hostname nut-server[8565]: Could not find PID file '/run/nut/upsd.pid' to see if previous upsd instance is already running!
2026-10-01T08:25:46.585873+00:00 hostname nut-server[8565]: not listening on ::1 port 3493
2026-10-01T08:25:46.585889+00:00 hostname nut-server[8565]: listening on 127.0.0.1 port 3493
2026-10-01T08:25:46.585944+00:00 hostname nut-server[8565]: no listening interface available
2026-10-01T08:25:46.585963+00:00 hostname nut-server[8565]: Network UPS Tools upsd 2.8.1
2026-10-01T08:25:46.586208+00:00 hostname systemd[1]: nut-server.service: Main process exited, code=exited, status=1/FAILURE
2026-10-01T08:25:46.586317+00:00 hostname systemd[1]: nut-server.service: Failed with result 'exit-code'.
2026-10-01T08:25:46.814934+00:00 hostname systemd[1]: nut-server.service: Scheduled restart job, restart counter is at 5.
2026-10-01T08:25:46.815036+00:00 hostname systemd[1]: nut-server.service: Start request repeated too quickly.
2026-10-01T08:25:46.815074+00:00 hostname systemd[1]: nut-server.service: Failed with result 'exit-code'.
2026-10-01T08:25:46.815107+00:00 hostname systemd[1]: Failed to start nut-server.service - Network UPS Tools - power devices information server.


Thanks!
 
ghusson said:
Is nut on the dialout group ?
cat /etc/group | grep nut

if not (result = nut:x:119:), try to add it : adduser nut dialout
It is just an idea.
Click to expand...

Hi, thanks.
Yes, it is. I’ve even tried removing and adding it to the group again (usermod -a -G dialout nut), with no luck.

Also, I replicated this exact same configuration to another server running the same old version of PVE 8 and it worked. Just can get it working on PVE9/Debian 13.
 
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Since you've already tried adding the nut user to the dialout group and it didn't work, you might be running into a classic Debian upgrade trap: interference from the brltty service.

I checked my own Proxmox 9 lab environment (which was a fresh install) and verified that brltty isn't included by default. However, since you performed an in-place upgrade from PVE 8 to 9 (Debian 12 to 13), it's very common for this package to get pulled in automatically during the upgrade process.

brltty is a background driver for Braille displays, and it is notorious for aggressively claiming USB-to-Serial converter chips (like the FTDI one you are using). When it runs in the background, it exclusively locks the serial port. As a result, even if your NUT user and udev permissions are perfectly configured, your nutdrv_qx driver will be denied access to /dev/ttyUSB0 and fail to start.

You can easily check if this package is installed by running:
Code: 
dpkg -l | grep brltty
If it shows up in the output, you can completely remove it with:
Code: 
apt-get remove --purge brltty
apt-get autoremove
After uninstalling, simply unplug and reconnect your USB-to-Serial adapter, then try starting the NUT service again.

Hope this helps!
 
Last edited:
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