探测本身是 nslookup 命令的无限 while 循环。while 循环之前,将设置一个临时文件以放置 nslookup 回复。probefail 和 retries 变量均初始化为 0。
# Set up a temporary file for the nslookup replies. DNSPROBEFILE=/tmp/.$RESOURCE_NAME.probe probefail=0 retries=0
while 循环执行以下任务:
设置探测程序的休眠间隔
使用 hatimerun 启动 nslookup,传递 Probe_timeout 值并标识目标主机
根据 nslookup 返回码成功与否设置 probefail 变量
如果 probefail 设置为 1(失败),验证对 nslookup 的回复来自于数据服务样例,而不是某一其他 DNS 服务器
下面是 while 循环代码。
while : do # The interval at which the probe needs to run is specified in the # property THOROUGH_PROBE_INTERVAL. Therefore, set the probe to sleep # for a duration of THOROUGH_PROBE_INTERVAL. sleep $PROBE_INTERVAL # Run an nslookup command of the IP address on which DNS is serving. hatimerun -t $PROBE_TIMEOUT /usr/sbin/nslookup $DNS_HOST $DNS_HOST \ > $DNSPROBEFILE 2>&1 retcode=$? if [ $retcode -ne 0 ]; then probefail=1 fi # Make sure that the reply to nslookup comes from the HA-DNS # server and not from another nameserver mentioned in the # /etc/resolv.conf file. if [ $probefail -eq 0 ]; then # Get the name of the server that replied to the nslookup query. SERVER=` awk ' $1=="Server:" { print $2 }' \ $DNSPROBEFILE | awk -F. ' { print $1 } ' ` if [ -z "$SERVER" ]; then probefail=1 else if [ $SERVER != $DNS_HOST ]; then probefail=1 fi fi fi