2FA Stopped Working

It is usually a time synchronization issue.

Diagnosis

• Check your server's time with date - if the time is off, you need to synchronize it.
• Check your NTP configuration with cat /etc/ntp.conf.
• Check with systemctl status systemd-timesyncd.service if your operating system is using systemd to synchronize time.
• Check your firewall (ufw, iptables) rules to see if you have any rules that block time synchronization ports (123/udp, 123/tcp).

Solution

• If your operating system is using systemd, you can synchronize the time with sudo timedatectl set-ntp true.
• If your operating system is not using systemd, you can synchronize the time with sudo ntpdate ntp.ubuntu.com.