这里举几个例子。
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在某地的双向系统中，两台服务器有一个httpd服务器，通过负载均衡承担4万多的机顶盒的首页面访问。因此，需要监测每台服务器的http连接数量。对并发量关注一段时期，如果并发量在设置的值之内，则不需要进行并发量的调整，而如果并发量比较大的话，则需要进行调整httpd参数。
http的连接数量可以通过ps -ef | grep httpd | wc -l来获取。Centos5版本默认的文件打开数量为1024。对/etc/httpd/conf/httpd.conf进行参数调整，使httpd可以承担1000个并发：
查询默认的服务方式：
# httpd -l
Compiled in modules:
core.c
prefork.c
http_core.c
mod_so.c
#
默认的服务方式为prefork，调整/etc/httpd/conf/httpd.conf参数（具体含义可到网上查找）：
StartServers 10
MinSpareServers 50
MaxSpareServers 100
ServerLimit 3000
MaxClients 3000
MaxRequestsPerChild 10000
重启httpd后，进行并发测试：
ab -n 10000 -c 1000 http://172.16.100.190/index.htm
这里共发送10000个请求，每次发送1000个，也就是每次并发1000个，共分10次发送。
如果是并发2000，则报错：
查询httpd的服务方式为：
ps -ef | grep httpd | wc -l
编写监测脚本：
#!/bin/bash
STATE_OK=0
STATE_WARNING=1
STATE_CRITICAL=2
STATE_UNKNOWN=3
count=`ps -ef | grep httpd | wc -l`
let "count =count-2"
if [ $count -gt 800 ]; then
echo "Critical ! httpd processes is $count!|HttpCounts=$count;600;800;0"
exit $STATE_CRITICAL
elif [ $count -gt 600 ]; then
echo "Warning ! httpd processes is $count!|HttpCounts=$count;600;800;0"
exit $STATE_WARNING
elif [ 600 -gt $count ]; then
echo "Ok ! httpd processes is $count!|HttpCounts=$count;600;800;0"
exit $STATE_OK
else
echo "Unknow"
exit $STATE_UNKNOWN
fi
脚本中echo一行最后添加的“|HttpCounts=$count;600;800;0”是pnp画图所需，否则不能画出图。其中600为预警，800为严重告警。
默认配置的httpd，在访问量比较大的话，使用命令：
# netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
TIME_WAIT=581
ESTABLISHED=1
SYN_RECV=1
就会有大量的time_wait。可以通过调整系统参数得到改善：
http://blog.csdn.net/sunvince/article/details/6622796
http://chembo.iteye.com/blog/1503770
这里，在/etc/sysctl.conf增加以下4个参数：
net.ipv4.tcp_syncookies = 1 //这个参数如果已经添加了的话，就不需要再次添加
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_fin_timeout = 30
然后执行 /sbin/sysctl -p 让参数生效。
继续使用netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'，观察到TIME_WAIT=3了。
可以根据下节中监测物理内存的check_mem脚本规范编写监测 TIME_WAIT的脚本：
#more /usr/local/nagios/libexec/check_timewait
#!/bin/bash
#netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
#TIME_WAIT 641
#ESTABLISHED 1
#SYN_RECV 1
if [ $# != 4 ];then
echo "Usage:$0 -w num1 -c num2"
exit
fi
time_wait=`netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'|grep TIME_WAIT|awk '{print $2}'`
established=`netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'|grep ESTABLISHED|awk '{print $2}'`
syn_recv=`netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'|grep SYN_RECV|awk '{print $2}'`
if [ $time_wait -gt $4 ];then
echo "Critical - TIME_WAIT=$time_wait ESTABLISHED=$established SYN_RECV=$syn_recv|TIME_WAIT=$time_wait;$2;$4;0 ESTABLISHED=$established;;; SYN_RECV=$syn_recv;;;"
exit 2
fi
if [ $time_wait -le $4 -a $time_wait -ge $2 ];then
echo "Warning - TIME_WAIT=$time_wait ESTABLISHED=$established SYN_RECV=$syn_recv |TIME_WAIT=$time_wait;$2;$4;0 ESTABLISHED=$established;;; SYN_RECV=$syn_recv;;;"
exit 1
fi
if [ $time_wait -lt $2 ];then
echo "OK - TIME_WAIT=$time_wait ESTABLISHED=$established SYN_RECV=$syn_recv |TIME_WAIT=$time_wait;$2;$4;0 ESTABLISHED=$established;;; SYN_RECV=$syn_recv;;;"
exit 0
fi
~
另外，由于这台机器不能丢失一个默认的路由，否则机顶盒无法获取首页面。默认的路由也可以编写脚本进行监测：
#!/bin/bash
STATE_OK=0
STATE_WARNING=1
STATE_CRITICAL=2
STATE_UNKNOWN=3
default_route=`route |grep default`
if [ "default 172.16.100.1 0.0.0.0 UG 0 0 0 bond0"x = "$default_route"x ]; then
echo "Ok! Default route is \"$default_route\"!|defaultRoute=1;0;0"
exit $STATE_OK
else
echo "Critical! Default route is \"$default_route\"!|defaultRoute=0;0;0"
exit $STATE_CRITICAL
fi
默认的check_swap为监测虚拟内存，如果要监测物理内存，则可以编写以下脚本：
#cd /usr/local/nagios/libexec
#vi check_mem
#!/bin/bash
#memory
if [ $# != 4 ];then
echo "Usage:$0 -w num1 -c num2"
exit
fi
total_mem=`free -m |grep Mem|awk '{print $2}'`
free_mem=`free -m |grep Mem|awk '{print $4}'`
used_mem=`free -m |grep Mem|awk '{print $3}'`
if [ $free_mem -gt $2 ];then
echo "OK - total memory $total_mem MB used $used_mem MB free $free_mem MB|free_mem=$free_mem;$2;$4;0"
exit 0
fi
if [ $free_mem -ge $4 -a $free_mem -le $1 ];then
echo "Warning - total memory $total_mem MB used $used_mem MB free $free_mem MB|free_mem=$free_mem;$2;$4;0"
exit 1
fi
if [ $free_mem -lt $4 ];then
echo "Critical - total memory $total_mem MB used $used_mem MB free $free_mem MB|free_mem=$free_mem;$2;$4;0"
exit 2
fi
#chown -R nagios.nagios check_mem
#chmod a+x check_mem
#./check_mem -w 200 -c 100 //后面两个参数表示剩余内存容量，单位为兆。
网上还有另外一个监测脚本也可以参考 http://www.yunvn.com/thread-5136-1-5.html ：
#script to check real memory usage
# L.Gill 02/05/06 - V.1.0
# ------------------------------------------
# ######## Script Modifications ##########
# ------------------------------------------
# Who When What
# --- ---- ----
# LGill 17/05/06 "$percent" lt 1% fix - sed edits dc result beggining with "."
#
#
#!/bin/bash
USAGE="`basename $0` [-w|--warning]
THRESHOLD_USAGE="WARNING threshold must be greater than CRITICAL: `basename $0` $*"
calc=/tmp/memcalc
percent_free=/tmp/mempercent
critical=""
warning=""
STATE_OK=0
STATE_WARNING=1
STATE_CRITICAL=2
STATE_UNKNOWN=3
# print usage
if [[ $# -lt 4 ]]
then
echo ""
echo "Wrong Syntax: `basename $0` $*"
echo ""
echo "Usage: $USAGE"
echo ""
exit 0
fi
# read input
while [[ $# -gt 0 ]]
do
case "$1" in
-w|--warning)
shift
warning=$1
;;
-c|--critical)
shift
critical=$1
;;
esac
shift
done
# verify input
if [[ $warning -eq $critical || $warning -lt $critical ]]
then
echo ""
echo "$THRESHOLD_USAGE"
echo ""
echo "Usage: $USAGE"
echo ""
exit 0
fi
# Total memory available
total=`free -m | head -2 |tail -1 |gawk '{print $2}'`
# Total memory used
used=`free -m | head -2 |tail -1 |gawk '{print $3}'`
# Calc total minus used
free=`free -m | head -2 |tail -1 |gawk '{print $4+$7}'`
# normal values
#echo "$total"MB total
#echo "$used"MB used
#echo "$free"MB free
# make it into % percent free = ((free mem / total mem) * 100)
echo "5" > $calc # decimal accuracy
echo "k" >> $calc # commit
echo "100" >> $calc # multiply
echo "$free" >> $calc # division integer
echo "$total" >> $calc # division integer
echo "/" >> $calc # division sign
echo "*" >> $calc # multiplication sign
echo "p" >> $calc # print
percent=`/usr/bin/dc $calc|/bin/sed 's/^\./0./'|/usr/bin/tr "." " "|/usr/bin/gawk {'print $1'}`
#percent1=`/usr/bin/dc $calc`
#echo "$percent1"
if [[ "$percent" -le $critical ]]
then
echo "CRITICAL - $free MB ($percent%) Free Memory"
exit 2
fi
if [[ "$percent" -le $warning ]]
then
echo "WARNING - $free MB ($percent%) Free Memory"
exit 1
fi
if [[ "$percent" -gt $warning ]]
then
echo "OK - $free MB ($percent%) Free Memory"
exit 0
fi
用以下命令执行：
# ./check_memory -w 36 -c 10
OK - 185 MB (37%) Free Memory
# ./check_memory -w 37 -c 10
WARNING - 185 MB (37%) Free Memory
# ./check_memory -w 40 -c 37
CRITICAL - 184 MB (37%) Free Memory
#
-w表示低于多少百分比就预警，-c表示低于多少百分比就严重告警
