Red Hat Enterprise Linux-Specific Information; Free Top Vmstat - Red Hat ENTERPRISE LINUX 3 - INTRODUCTION TO SYSTEM ADMINISTRATION Administration Manual

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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 transfers per second, these statistics allow the system ad-
ministrator to more fully understand the nature of the I/O loads a storage device is experiencing.
This can be critical, as some storage technologies have widely different performance character-
istics for read versus write operations.
2.5. Red Hat Enterprise Linux-Specific Information
Red Hat Enterprise 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
(and GNOME System Monitor, a more graphically oriented version of
• top
• vmstat
The Sysstat suite of resource monitoring tools
•
The OProfile system-wide profiler
•
Let us examine each one in more detail.
2.5.1.
free
The command displays system memory utilization. Here is an example of its output:
free
total
Mem: 255508
-/+ buffers/cache:
Swap: 530136
The row displays physical memory utilization, while the
Mem:
the system swap space, and the
currently devoted to system buffers.
Since by default only displays memory utilization information once, it is only useful for very
free
short-term monitoring, or quickly determining if a memory-related problem is currently in progress.
Although has the ability to repetitively display memory utilization figures via its
free
output scrolls, making it difficult to easily detect changes in memory utilization.
Tip
A better solution than using
to display memory utilization every two seconds (the default display interval for
command:
watch free
The command issues the
watch
This makes it much easier to determine how memory utilization changes over time, as it is not nec-
essary to scan continually scrolling output. You can control the delay between updates by using the
used free
240268 15240
146488 109020
26268 503868
-/+ buffers/cache:
would be to run
free -s
command every two seconds, after first clearing the screen.
free
Chapter 2. Resource Monitoring
shared buffers
0 7592
row displays the utilization of
Swap:
row displays the amount of physical memory
using the
free watch
)
top
cached
86188
option, the
-s
command. For example,
), use this
watch