Dual WAN switching detection

[Igor]

How can I correctly detect Dual WAN switching from primary to secondary and back from the terminal?

Now I only see the fact of frequent switching:
# cat /tmp/syslog.log | grep 'PPP session'
Jul 14 11:30:52 pppd[4463]: PPP session is 24297 (0x5ee9)
Jul 14 11:33:48 pppd[6137]: PPP session is 24299 (0x5eeb)
Jul 14 11:34:55 pppd[7418]: PPP session is 24300 (0x5eec)
Jul 14 11:50:45 pppd[15870]: PPP session is 24305 (0x5ef1)
Jul 14 11:59:11 pppd[19108]: PPP session is 24308 (0x5ef4)
Jul 14 12:00:31 pppd[20925]: PPP session is 24309 (0x5ef5)
Jul 14 12:01:51 pppd[22113]: PPP session is 24310 (0x5ef6)
Jul 14 12:05:17 pppd[23828]: PPP session is 24313 (0x5ef9)

ASUS RT-AX68U, Firmware:3004.388.7

 

[Igor]

I think I found the command in the console.
# cat /tmp/syslog.log | grep restored