CentOS 6自带postfix无法发信

通过CentOS 6系统自带的rpm包安装postfix之后，执行mail -s...测试发信无法成功。maillog如下：
 
May 29 10:44:04 cl101 postfix/pickup[31536]: BA5662A0AFC: uid=0 from=<root>
 May 29 10:44:04 cl101 postfix/cleanup[31559]: BA5662A0AFC: message-id=<20130529024404.BA5662A0AFC@cl101.dev.linuxidc.com>
 May 29 10:44:04 cl101 postfix/qmgr[31537]: BA5662A0AFC: from=<root@cl101.dev.linuxidc.com>, size=3431896, nrcpt=1 (queue active)
 May 29 10:44:04 cl101 postfix/smtp[31561]: fatal: unknown service: smtp/tcp
 May 29 10:44:05 cl101 postfix/qmgr[31537]: warning: private/smtp socket: malformed response
 May 29 10:44:05 cl101 postfix/qmgr[31537]: warning: transport smtp failure -- see a previous warning/fatal/panic logfile record for the problem description
 May 29 10:44:05 cl101 postfix/master[31534]: warning: process /usr/libexec/postfix/smtp pid 31561 exit status 1
 May 29 10:44:05 cl101 postfix/master[31534]: warning: /usr/libexec/postfix/smtp: bad command startup -- throttling
 May 29 10:44:05 cl101 postfix/error[31562]: BA5662A0AFC: to=<wmwu@linuxidc.net>, relay=none, delay=1.3, delays=0.23/1/0/0.02, dsn=4.3.0, status=deferred (unknown mail transport error)
 
这是由于postfix无法读取service文件所致。查看service的权限为640：
 
[root@cl101 etc]# ll|grep services
 -rw-r-----.  1 root root 641243 Nov  7  2012 services
 
于是将其改为644：
 [root@cl101 etc]# ll|grep services       
 -rw-r--r--.  1 root root 641243 Nov  7  2012 services
 
然后重试，即可解决此问题。