Linux · Systems fluency
What does load average mean, and how do you interpret it?
Short answer
Load average counts processes that are runnable or in uninterruptible sleep, averaged over 1, 5, and 15 minutes. Compare it with the number of CPUs, and check whether the cause is CPU, I/O, or memory pressure.
On Linux, load includes both processes waiting for CPU and processes blocked in uninterruptible sleep, often on disk or network I/O. A load of 4 on an 8-CPU host is not necessarily saturation, while a load of 2 on a single-CPU host with high iowait can be severe.
uptime
nproc
cat /proc/loadavg
vmstat 1 5Reading the trend
- Divide load by CPU count for a rough utilization ratio
- A rising 1-minute value with a stable 15-minute value means a new spike
- A high 15-minute value means sustained pressure
- Runnable count appears in /proc/loadavg after the three averages
- High load with idle CPU points to I/O or memory stalls
Load average alone cannot tell you the bottleneck. Correlate it with vmstat, iostat, memory pressure, and per-process CPU. In containers, load may reflect the host unless you are reading a namespaced view.
Follow-ups you should expect
Interviewers use these to check whether the first answer was understanding or memorisation.
- 1Why can load average be high while CPU usage is low?
- 2How do you normalize load by CPU count?
- 3What is the difference between the 1, 5, and 15 minute averages?
- 4Why can load inside a container be misleading?
Say it in the interview
Load average counts runnable and uninterruptible processes over 1, 5, and 15 minutes. I normalize by CPU count and look at the trend. High load with low CPU usually means I/O or memory stalls. I confirm the bottleneck with vmstat and iostat rather than treating the load number alone as a diagnosis.
Use this as a model, not a script. Saying it in your own words is what makes it survive follow-up pressure.
Related questions
Reading is step one
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