sysop@hub:~/tools/linux-server-slow$

linux-server-slow

"The server is slow" is a symptom with eight usual causes. Work through them in order: each step gives you the commands, tells you how to read the output, and asks what you see. Your findings collect at the end. Nothing is sent anywhere, you run the commands yourself.

the first minute

If you only have a minute, run this block and read it top to bottom. It covers load, kernel errors, memory, CPU, disk and network in one go. iostat, mpstat and sar come with the package sysstat.

uptime
sudo dmesg -T | tail -n 15
vmstat 1 5
mpstat -P ALL 1 3
iostat -xz 1 3
free -h
df -hT
sar -n DEV 1 3
top -bn1 | head -n 20

what you found

The thresholds are rules of thumb, not limits: a database server at load 1.2 per core can be perfectly healthy, a desktop at 0.9 can feel sluggish. Commands follow Debian, Ubuntu and the RHEL family. Do not restart or kill anything on a production server before you know what it is and who depends on it.