Start broad, then narrow
Begin with uptime, free, df, ss, and journalctl before drilling into a specific subsystem.
Monitoring
Linux Monitoring Toolkit
Generate Linux performance and diagnostic commands for CPU, memory, disk, network, processes and system logs.
Generated Output
Quick reference
Some tools require packages
Commands such as mpstat and iostat are commonly supplied by sysstat and may not be installed by default.
Correlate symptoms
A single high metric rarely tells the whole story. Compare CPU, memory, I/O, network, and logs over the same time period.