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Chapter 2. Resource Monitoring

File System Related Statistics

These statistics (such as number of files/directories, average file size, etc.) provide additional

detail over a single free space percentage. As such, these statistics make it possible for system

administrators to configure the system to give the best performance, as the I/O load imposed by

a file system full of many small files is not the same as that imposed by a file system filled with

one massive file.

Transfers per Second

This statistic is a good way of determining whether a particular device's bandwidth limitations

are being reached.

Reads/Writes per Second

A slightly more detailed breakdown of the transfers per second statistic, these allow the system

administrator to more fully understand the nature of the I/O loads a storage device is experi 

encing. This can be critical, as some storage technologies have widely different performance

characteristics for read versus write operations.

2.5. Red Hat Linux Specific Information

Red Hat Linux comes with a variety of resource monitoring tools. While there are more than those

listed here, these tools are representative in terms of functionality. The tools are:

  free

  top

(and GNOME System Monitor, a more graphically oriented version of

top

)

  vmstat

The Sysstat suite of resource monitoring tools

Let us look at each one in more detail.

2.5.1.

free

The

free

command displays system memory utilization. Here is an example of its output:

total

used

free

shared

buffers

cached

Mem:

255508

240268

15240

0

7592

86188

 /+ buffers/cache:

146488

109020

Swap:

530136

26268

503868

The

Mem:

row displays physical memory utilization, while the

Swap:

row displays the utilization of

the system swap space, and the

 /+ buffers/cache:

row displays the amount of physical memory

currently devoted to system buffers.

Since

free

by default only displays memory utilization information once, it is only useful for very

short term monitoring, or quickly determining if a memory related problem is currently in progress.

Although

free

has the ability to repetitively display memory utilization figures via its

 s

option, the

output scrolls, making it difficult to easily see changes in memory utilization.