from https://www.brendangregg.com/Articles/Netflix_Linux_Perf_Analysis_60s.pdf

uptime # Load averages to identify if load is increasing or  decreasing (compare 1-, 5-, and 15-minute averages).
dmesg -T | tail # Kernel errors including OOM events.
vmstat -SM 1 # System-wide statistics: run queue length, swapping, overall CPU usage.
mpstat -P ALL 1 # Per-CPU balance: a single busy CPU can indicate poor thread scaling.
pidstat 1 # Per-process CPU usage: identify unexpected CPU consumers, and user/system CPU time for each process.
iostat -sxz 1 # Disk I/O statistics: IOPS and throughput, average wait time, percent busy.
free -m # Memory usage including the file system cache.
sar -n DEV 1 # Network device I/O: packets and throughput.
sar -n TCP,ETCP 1 # TCP statistics: connection rates, retransmits.
top # Check overview.