1、重新编译内核，加入watchdog

Device Drivers ->
Character Devices ->
Watchdog Cards ->

  [*] Watchdog Timer Support

  [ ]   Disable watchdog
shutdown on close
  ---   Watchdog Device
Drivers
  <*> Your Watchdog card or
chip

2、安装watchdog程序

apt-get install watchdog#

3、配置watchdog

可以参考的文档包括：

http://gentoo-wiki.com/HOWTO_Watchdog_Timer
man 8 watchdog
man 5 watchdog.conf
/usr/share/doc/watchdog/examples

我只是用它来保障sshd、apache和mysql运行稳定。

4、确保apache、ssh和mysql在watchdog之前起来

重起机器后，watchdog会查找这三个进程的pid，如果不存在，默认会重起机器（除非我们设置了repair binary），因此，一定要在启动脚本中改变启动顺序，让watchdog在这三者启动之后才启用。

5、设置repair脚本

我并不想这几个应用程序随便出点啥事就重启计算机，所以，写了个简单的脚本：

root@wlj:/var/run# cat /usr/sbin/repair.sh
#!/bin/sh
if [ -x /etc/init.d/networking ]; then
# Debian

/etc/init.d/networking restart
elif [ -x /etc/rc.d/init.d/network ]; then
# Redhat

/etc/rc.d/init.d/network restart
else
echo "Couldn't find network script to relaunch
networking. Please edit $0" | logger -i -t repair -p daemon.info
exit $1
fi
if [ -x /etc/rc.local ]; then
/etc/rc.local
else
echo "rc.local restart error" |logger -i -t
repair -p daemon.info
exit $1
fi
if [ -x /etc/init.d/apache2 ]; then
/etc/init.d/apache2 restart
else
echo "apache restart error" |logger -i -t repair
-p daemon.info
exit $1
fi
if [ -x /etc/init.d/ssh ]; then
/etc/init.d/ssh restart
else
echo "sshd restart error" |logger -i -t repair
-p daemon.info
exit $1
fi
if [ -x /etc/init.d/mysql ]; then
/etc/init.d/mysql restart
else
echo "mysql restart error" |logger -i -t repair
-p daemon.info
exit $1
fi
exit 0

6、测试watchdog是否成功启用

试着杀断ssh，然后看/var/log/syslog中的日志

Mar 20 11:34:26 SH600 watchdog[11662]: cannot open /var/run/sshd.pid (errno = 2 = ‘No such file or directory’)
Mar 20 11:34:28 SH600 mysqld[29396]: 070320 11:34:28 [Note] /usr/sbin/mysqld: Normal shutdown
Mar 20 11:34:28 SH600 mysqld[29396]:
Mar 20 11:34:28 SH600 mysqld[29396]: 070320 11:34:28 InnoDB: Starting shutdown…
Mar 20 11:34:30 SH600 mysqld[29396]: 070320 11:34:30 InnoDB: Shutdown completed; log sequence number 0 43655
Mar 20 11:34:30 SH600 mysqld[29396]: 070320 11:34:30 [Note] /usr/sbin/mysqld: Shutdown complete
Mar 20 11:34:30 SH600 mysqld[29396]:
Mar 20 11:34:30 SH600 mysqld_safe[883]: ended
Mar 20 11:34:31 SH600 mysqld_safe[988]: started
Mar 20 11:34:31 SH600 mysqld[991]: 070320 11:34:31 InnoDB: Started; log sequence number 0 43655
Mar 20 11:34:31 SH600 mysqld[991]: 070320 11:34:31 [Note] /usr/sbin/mysqld: ready for connections.
Mar 20 11:34:31 SH600 mysqld[991]: Version: ‘5.0.24a-Debian_9ubuntu1-log’ socket: ‘/var/run/mysqld/mysqld.sock’ port: 3306 Debian etch distribution
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1034]: Checking for crashed MySQL tables.
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1044]: Upgrading MySQL tables if necessary.
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]: This script updates all the mysql privilege tables to be usable by
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]: MySQL 4.0 and above.
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]:
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]: This is needed if you want to use the new GRANT functions,
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]: CREATE AGGREGATE FUNCTION, stored procedures, or
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]: more secure passwords in 4.1
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]:
Mar 20 11:34:32 SH600 /etc/mysql/debian-start[1048]: done

用watchdog保证服务器程序运行稳定

apt-get install watchdog#