If you experience lengthy boots on your Linux PC then all what you need to do one simple command to know why.
This command does not require root to execute and may be run using normal users.
There is even more beautiful command that can make a nice graph with even more details:
systemd-analyze plot > some_out_file.svg
The last command generates an SVG image with all data you may need to know what behind your Linux long time boot.
These command assumes your Linux used systemd including Fedora, CentOS/RHEL 7+, Arch Linux, Debian, Ubuntu, openSUSE, and Slackware