Definition of Load Average in Linux

note: see also for Unix.

Question:

What is the relation between I/O wait and load average?

Answer: (by Jeff Layton)

Linux follows the standard of traditional UNIX and computes its load average as the average number of runnable or running processes (R state), and the number of processes in un-interruptible sleep (D state) over the specified interval.

Some other operating systems calculate their load averages simply by looking at processes in R state. On those systems, load average is synonymous with the run queue -- high load averages mean that the box is CPU bound.

This is not the case with Linux. On Linux the load average is a measurement of the amount of "work" being done by the machine (without being specific as to what that work is). This "work" could reflect a CPU intensive application (compiling a program or encrypting a file), or something I/O intensive (copying a file from disk to disk, or doing a database full table scan), or a combination of the two.