Apache Error [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)

One fine morning I have discovered that my Apache (httpd) service is down and can't be started :)

Step 1: Checking httpd Service Status:
#/etc/init.d/httpd status
httpd dead but pid file exists

Step 2: Search httpd processes and kill those
#ps -ef | grep httpd

# killall -9 httpd

Step 3: Remove httpd lock file if exist
# rm -f /var/lock/subsys/httpd

Step4: Restart Apache/httpd Service
# service httpd restart
Stop httpd    [FAILED]
Start httpd   [FAILED]

Need to dig down more.

Step 5: Check httpd error log file

# grep suexec /var/log/httpd/error_log
[Sun Sep 22 10:32:06 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Sun Sep 22 10:33:51 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Sun Sep 22 10:38:03 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[Sun Sep 22 10:45:53 2013] [notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)

Step 6: Check httpd nss error log file

#tail -300 /var/log/httpd/nss_error_log

[Sun Sep 22 04:03:27 2013] [error] Certificate not verified: 'Server-Cert'

[Sun Sep 22 04:03:27 2013] [error] SSL Library Error: -8181 Certificate has expired

[Sun Sep 22 04:03:27 2013] [error] Unable to verify certificate 'Server-Cert'. Add "NSSEnforceValidCerts off" to nss.conf so the server can start until the problem can be resolved.

[Sun Sep 22 10:38:03 2013] [error] Certificate not verified: 'Server-Cert'

[Sun Sep 22 10:38:03 2013] [error] SSL Library Error: -8181 Certificate has expired

[Sun Sep 22 10:38:03 2013] [error] Unable to verify certificate 'Server-Cert'. Add "NSSEnforceValidCerts off" to nss.conf so the server can start until the problem can be resolved.

[Sun Sep 22 10:45:53 2013] [error] Certificate not verified: 'Server-Cert'

[Sun Sep 22 10:45:53 2013] [error] SSL Library Error: -8181 Certificate has expired

[Sun Sep 22 10:45:53 2013] [error] Unable to verify certificate 'Server-Cert'. Add "NSSEnforceValidCerts off" to nss.conf so the server can start until the problem can be resolved.

root cause of this issue is in a module called nss. mod_nss is an alternative to mod_ssl; it does a few things that mod_ssl doesn't do, and can run along side mod_ssl. For more information's, please go through the links [What is mod_nss , On Setting up Mod_NSS ,More detail ] 

Step 7: Remove nss.conf file from httpd conf.d directory

#cd /etc/httpd/conf.d

#mv nss.conf nss.conf.orig

#/etc/init.d/httpd start

Start httpd   [OK]