[root@csit yang]# service httpd start
Starting httpd:                                            [FAILED]
[root@csit httpd]# tail error_log -F   #查看错误日志
[Mon May 27 13:02:48 2013] [error] NSSEngine on; no certificate nickname provided by NSSNickname.
[Mon May 27 13:05:56 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Mon May 27 13:05:56 2013] [error] NSSEngine on; no certificate nickname provided by NSSNickname.
[Mon May 27 13:06:52 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Mon May 27 13:06:52 2013] [error] NSSEngine on; no certificate nickname provided by NSSNickname.
[Mon May 27 13:13:29 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Mon May 27 13:13:29 2013] [error] NSSEngine on; no certificate nickname provided by NSSNickname.
[Mon May 27 13:13:35 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Mon May 27 13:13:35 2013] [error] NSSEngine on; no certificate nickname provided by NSSNickname.

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[root@csit httpd]# cd /etc/httpd/conf.d/    #进入配置文件目录
[root@csit conf.d]$ grep NSSEngine *    #查找配置选项，并且知道在 nss.conf 这个文件中
nss.conf:NSSEngine on
[root@csit conf.d]$ vi  nss.conf    #注释NSSEngine
#   SSL Engine Switch:
#   Enable/Disable SSL for this virtual host.
#NSSEngine on

[root@csit httpd]# service httpd restart
Stopping httpd:                                            [  OK  ]
Starting httpd:
                                                                    [  OK  ]


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总结下： httpd启动不起来，不要慌了神。
               首先擦看错误日志，分析错误原因。
               配置文件在修改前一定要先备份。