nagios 监控无法发送mail邮件。发现是文件权限问题
You should first check the permissions on the following files:

# ls -l /usr/sbin/sendmail.sendmail
-r-xr-sr-x root smmsp /usr/sbin/sendmail.sendmail
# ls -l /var/spool
drwxrwx--- smmsp smmsp /var/spool/clientmqueue 
If your permissions are mis-matched, you can modify them by doing the following:

# chown root.smmsp /usr/sbin/sendmail.sendmail
# chmod g+s /usr/sbin/sendmail.sendmail
# chown smmsp.smmsp /var/spool/clientmqueue
After changing permissions, you need to restart the Sendmail service, type:

# service sendmail restart