Vitux published a tutorial about how to investigate and troubleshoot slow bootup.

How long does your Linux system take to boot?

When you boot up your system, it passes through a sequence of events before presenting you with the login screen. Have you ever checked how long your system takes to boot? Generally, it all occurs within seconds or a few minutes but we do not know the exact time. Sometimes due to some reasons, you might be required to find the exact time your system takes to boot. Regardless of the reason why you want to know it, there is a systemd-analyze utility that can let you know the exact time your Linux system takes to boot.

How long does your Linux system take to boot?