Monitor dmesg in real time with watch.

watch "dmesg | tail -20"

Analyze the boot process with the blame command ARCH linux

Install graphics tools in ARCH

pacman -S eog dot2tex

Script
#-------------------------------
#!/bin/bash

systemd-analyze
systemd-analyze blame
systemd-analyze plot > /tmp/graph.svg
systemd-analyze dot | dot -Tsvg > /tmp/dot-graph.svg
echo "Show graph
eog /tmp/graph.svg 
eog /tmp/dot-graph.svg
"
#------------------------------- 

Plot svg graph example

Plot svg dot-graph example