System information
12 System Analysis and Tuning Guide
in
Interrupts per second. A high value indicates a high I/O level (network and/or
disk).
cs
Number of context switches per second. Simplified this means that the kernel has
to replace executable code of one program in memory with that of another pro-
gram.
us
Percentage of CPU usage from user processes.
sy
Percentage of CPU usage from system processes.
id
Percentage of CPU time spent idling. If this value is zero over a longer period of
time, your CPU(s) are working to full capacity. This is not necessarily a bad sign
—rather refer to the values in columns r and b to determine if your machine is
equipped with sufficient CPU power.
wa
If "wa" time is non-zero, it indicates throughput lost due to waiting for I/O. This
may be inevitable, for example, if a file is being read for the first time, back-
ground writeback cannot keep up, and so on. It can also be an indicator for a
hardware bottleneck (network or hard disk). Lastly, it can indicate a potential
for tuning the virtual memory manager (refer to Chapter15, Tuning the Memory
Management Subsystem (page179)).
st
Percentage of CPU time used by virtual machines.
See vmstat --help for more options.
2.1.2 System Activity Information: sar and
sadc
sar can generate extensive reports on almost all important system activities, among
them CPU, memory, IRQ usage, IO, or networking. It can either generate reports on