Proxmox is using watchdog-mux. It is using /dev/watchdog and exposes watchdog service to multiple daemons using socket:

root@pve4:~# lsof -n 2>&1 | grep watch
watchdog-    3923                               root  txt       REG               0,26     14728      75245 /usr/sbin/watchdog-mux
watchdog-    3923                               root    1u     unix 0x000000006ba3be2b       0t0      40514 type=STREAM
watchdog-    3923                               root    2u     unix 0x000000006ba3be2b       0t0      40514 type=STREAM
watchdog-    3923                               root    3w      CHR             10,130       0t0        853 /dev/watchdog
watchdog-    3923                               root    4u     unix 0x00000000ddb50a86       0t0      40529 /run/watchdog-mux.sock type=STREAM
watchdog-    3923                               root    5u  a_inode               0,14         0      12480 [eventpoll]
watchdog-    3923                               root    6u  a_inode               0,14         0      12480 [signalfd]
watchdog-    3923                               root    7u     unix 0x00000000bd6f8c4d       0t0      33495 /run/watchdog-mux.sock type=STREAM

maj 24 07:09:57 pve4 watchdog-mux[3923]: Watchdog driver 'Software Watchdog', version 0

 ls -l /dev/watchdog*
 
crw------- 1 root root  10, 130 maj 24 08:03 /dev/watchdog
crw------- 1 root root 245,   0 maj 24 08:03 /dev/watchdog0
 
 
cat /proc/devices
 10 misc
245 watchdog
 
cat /sys/dev/char/245:0/identity
Software Watchdog

What is /dev/watchdog ?

 10 char	Non-serial mice, misc features
		  1 = /dev/psaux	PS/2-style mouse port
                ...
		130 = /dev/watchdog	Watchdog timer port

Change watchdog

systemctl stop watchdog-mux
rmmod softdog
systemctl start watchdog-mux

journalctl -u watchdog-mux
 
watchdog-mux[3984]: Loading watchdog module 'sp5100_tco'
watchdog-mux[3984]: Watchdog driver 'SP5100 TCO timer', version 0