0341-0344.html
来自「linux-unix130.linux.and.unix.ebooks130 l」· HTML 代码 · 共 440 行
HTML
440 行
<HTML>
<HEAD>
<TITLE>Developer.com - Online Reference Library - 0672311739:RED HAT LINUX 2ND EDITION:Advanced System Administration</TITLE>
<META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">
<SCRIPT>
<!--
function displayWindow(url, width, height) {
var Win = window.open(url,"displayWindow",'width=' + width +
',height=' + height + ',resizable=1,scrollbars=yes');
}
//-->
</SCRIPT>
</HEAD>
-->
<!-- ISBN=0672311739 //-->
<!-- TITLE=RED HAT LINUX 2ND EDITION //-->
<!-- AUTHOR=DAVID PITTS ET AL //-->
<!-- PUBLISHER=MACMILLAN //-->
<!-- IMPRINT=SAMS PUBLISHING //-->
<!-- PUBLICATION DATE=1998 //-->
<!-- CHAPTER=16 //-->
<!-- PAGES=0341-0350 //-->
<!-- UNASSIGNED1 //-->
<!-- UNASSIGNED2 //-->
<P><CENTER>
<a href="../ch15/0339-0340.html">Previous</A> | <a href="../ewtoc.html">Table of Contents</A> | <a href="0345-0347.html">Next</A>
</CENTER></P>
<A NAME="PAGENUM-341"><P>Page 341</P></A>
<H3><A NAME="ch16_ 1">
CHAPTER 16
</A></H3>
<H2>
Advanced System<BR>
Administration
</H2>
<P>
<B>by David Pitts</B>
</P>
<H3><A NAME="ch16_ 2">
IN THIS CHAPTER
</A></H3>
<UL>
<LI> Basic Performance Analysis
<LI> How Much Swap Is Enough?
<LI> Momma Always Said to Be Nice!
</UL>
<A NAME="PAGENUM-342"><P>Page 342</P></A>
<P>A large portion of this book is devoted to advanced system administration, including
script and automation development, configuring and building kernels, network management,
security, and many other tasks. One task not addressed thus far is performance analysis. This
chapter, then, looks at the initial steps of performance analysis, showing how to determine
CPU, memory, and paging space usage. Two tools are examined:
vmstat and top.
</P>
<H3><A NAME="ch16_ 3">
Basic Performance Analysis
</A></H3>
<P>Basic performance analysis is the process of identifying performance bottlenecks and
involves a number of steps. The first step is to look at the big picture: Is the problem CPU or I/O
related? If it is a CPU problem, what is the load average? You should probably check to see
what processes are running and who is causing the problem. If it is an I/O problem, then is it
paging or normal disk I/O? If it is paging, increasing memory might help. You can also try to
isolate the program or the user causing the problem. If it is a disk problem, then is the disk
activity balanced? If you have only one disk, perhaps you might want to install a second.
</P>
<P>The next section looks at several tools that can be used to determine the answers to the
preceding questions.
</P>
<H4><A NAME="ch16_ 4">
Determining CPU Usage
</A></H4>
<P>CPU usage is the first test on the list. There are many different ways to obtain a snapshot of
the current CPU usage. The one I am going to focus on here is
vmstat. The vmstat command gives you several pieces of data, including the CPU usage. The following is the syntax for the <BR>
command:</P>
<!-- CODE SNIP //-->
<PRE>
$ vmstat interval [count]
</PRE>
<!-- END CODE SNIP //-->
<P>interval is the number of seconds between reports, and
count is the total number of reports to give. If the count is not included,
vmstat will run continuously until you stop it with Ctrl+C or kill the process.
</P>
<P>Here is an example of the output from vmstat:</P>
<!-- CODE //-->
<PRE>
shell:/home/dpitts$ vmstat 5 5
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
0 0 0 1104 1412 10032 36228 0 0 10 8 31 15 7 4 24
0 0 0 1104 1736 10032 36228 0 0 0 3 111 18 1 1 99
0 0 0 1104 1816 10032 36228 0 0 0 1 115 23 2 2 96
0 1 0 1104 1148 10096 36268 8 0 7 4 191 141 4 6 91
0 0 0 1104 1868 9812 35676 6 0 2 10 148 39 25 4 70
</PRE>
<!-- END CODE //-->
<P>The first line of the report displays the average values for each statistic since boot time. It
should be ignored. For determining CPU used, you are
interested in the last three columns, as indicated by the
cpu heading. They are us, sy, and id and are explained in the following table.
</P>
<A NAME="PAGENUM-343"><P>Page 343</P></A>
<TABLE WIDTH="360">
<TR><TD>
<B>CPU</B>
</TD><TD>
<B>Description</B>
</TD></TR>
<TR><TD>
us
</TD><TD>
Percentage of CPU cycles spent on performing user tasks.
</TD></TR>
<TR><TD>
sy
</TD><TD>
Percentage of CPU cycles spent as system tasks. These
tasks include waiting on I/O, performing general operating
system functions, and so on.
</TD></TR>
<TR><TD>
id
</TD><TD>
Percentage of CPU cycles not used. This is the amount of
time the system was idle.
</TD></TR>
</TABLE>
<P>Just because the CPU time is high (or the idle time low) is not necessarily indicative of an
overall CPU problem. It could be that there are a number of batch jobs running that just need
to be rearranged. In order to determine that there is actually a CPU problem, it is important
to monitor the CPU percentages for a significant period of time. If the percentages are high
during this time, there is definitely a problem.
</P>
<P>Next, look at a different section of the vmstat output. If the problem is not CPU related,
look to see whether it is a problem with paging or normal disk I/O. To determine whether it is
a memory problem, look at the headings memory and
swap:
</P>
<!-- CODE //-->
<PRE>
shell:/home/dpitts$ vmstat 5 5
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
1 0 0 1096 1848 4580 37524 0 0 9 8 8 17 7 3 29
1 0 0 1096 1424 4580 37980 0 0 92 10 125 24 94 4 3
2 0 0 1096 864 4536 38408 0 0 112 31 146 42 93 2 5
2 0 0 1096 732 4360 38480 10 0 98 7 146 48 97 3 1
</PRE>
<!-- END CODE //-->
<TABLE WIDTH"360">
<TR><TD>
<B>Memory</B>
</TD><TD>
<B>Description</B>
</TD></TR>
<TR><TD>
swpd
</TD><TD>
The amount of virtual memory used (KB)
</TD></TR>
<TR><TD>
free
</TD><TD>
The amount of idle memory (KB)
</TD></TR>
<TR><TD>
buff
</TD><TD>
The amount of memory used as buffers (KB)
</TD></TR>
<TR><TD>
cache
</TD><TD>
The amount of memory left in the cache (KB)
</TD></TR>
</TABLE>
<BR>
<TABLE WIDTH="360">
<TR><TD>
<B>Swap</B>
</TD><TD>
<B>Description</B>
</TD></TR>
<TR><TD>
si
</TD><TD>
The amount of memory swapped in from disk (KB/s)
</TD></TR>
<TR><TD>
so
</TD><TD>
The amount of memory swapped to disk (KB/s)
</TD></TR>
</TABLE>
<P>The most important of these fields is the swap
in column. This column shows paging that has previously been swapped out, even if it was done before the
vmstat command was issued.
</P>
<A NAME="PAGENUM-344"><P>Page 344</P></A>
<P>The io section is used to determine if the problem is with blocks sent in or out of the
device:
</P>
<!-- CODE //-->
<PRE>
shell:/home/dpitts$ vmstat 5 5
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
1 0 0 1096 1848 4580 37524 0 0 9 8 8 17 7 3 29
1 0 0 1096 1424 4580 37980 0 0 92 10 125 24 94 4 3
2 0 0 1096 864 4536 38408 0 0 112 31 146 42 93 2 5
2 0 0 1096 732 4360 38480 10 0 98 7 146 48 97 3 1
</PRE>
<!-- END CODE //-->
<P>The io section is described in the following table.</P>
<TABLE WIDTH="360">
<TR><TD>
<B>IO</B>
</TD><TD>
<B>Description</B>
</TD></TR>
<TR><TD>
bi
</TD><TD>
The blocks sent to a block device (blocks/s)
</TD></TR>
<TR><TD>
bo
</TD><TD>
The blocks received from a block device (blocks/s)
</TD></TR>
<TR><TD>
cs
</TD><TD>
The number of context switches per second
</TD></TR>
</TABLE>
<P>These fields run from several to several hundred (maybe even several thousands). If you
are having a lot of in and out block transfers, the problem is probably here.
Keep in mind, though, that a single reading is not indicative of the system as a whole, just a snapshot of the system
at that time. There are three states in which the processes can exist. They are runtime,
uninterrupted sleep, and swapped out. These are defined in the following table.
</P>
<TABLE WIDTH="360">
<TR><TD>
<B>Procs</B>
</TD><TD>
<B>Description</B>
</TD></TR>
<TR><TD>
r
</TD><TD>
The number of processes waiting for runtime
</TD></TR>
<TR><TD>
b
</TD><TD>
The number of processes in uninterrupted sleep
</TD></TR>
<TR><TD>
w
</TD><TD>
The number of processes swapped out but otherwise able to run
</TD></TR>
</TABLE>
<P>The number of processes waiting for runtime is a good indication that there is a problem.
The more processes waiting, the slower the system. More than likely, you won't be looking at
vmstat unless you already know there is a bottleneck somewhere, so the
r field doesn't give you much vital information.
</P>
<H5><A NAME="ch16_ 5">
top
</A></H5>
<P>The top command provides another tool for identifying problems with a Linux system.
The top command displays the top CPU processes. More specifically,
top provides an ongoing look at processor activity in real time. It displays a listing of the most CPU-intensive tasks on
the system and can provide an interactive interface for manipulating processes. The default is
to update every five seconds. The following is an example of the output from
top:
</P>
<!-- CODE //-->
<PRE>
1:36am up 16 days, 7:50, 3 users, load average: 1.41, 1.44, 1.21
60 processes: 58 sleeping, 2 running, 0 zombie, 0 stopped
CPU states: 89.0% user, 8.5% system, 92.4% nice, 3.9% idle
Mem: 63420K av, 62892K used, 528K free, 32756K shrd, 6828K buff
Swap: 33228K av, 1096K used, 32132K free 38052K cached
PID USER PRI NI SIZE RSS SHARE STATE LIB %CPU %MEM TIME COMMAND
</PRE>
<!-- END CODE //-->
<P><CENTER>
<a href="../ch15/0339-0340.html">Previous</A> | <a href="../ewtoc.html">Table of Contents</A> | <a href="0345-0347.html">Next</A>
</CENTER></P>
</td>
</tr>
</table>
<!-- begin footer information -->
</body></html>⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?