plesk 9.5 httpd service getting down after every 2 to 3 hours
It is a shared hosting server.

I suspect that questions about this would best be directed to Plesk, as it's a commercial product. http://www.parallels.com/products/plesk/

If you want more assistance from us, you would need to provide lots more information about what's going on.

I have installed Plesk 9.5 on centos , but from last few days
I need to restart httpd service more than 10 times in a single day. It is a VPS hosted only
28 domains.

Here are the httpd error_log file content at the time it shows httpd is down.

[Fri Jul 13 15:52:35 2012] [notice] mod_bw : Memory Allocated 0 bytes (each conf takes 28 bytes)
[Fri Jul 13 15:52:35 2012] [notice] mod_bw : Version 0.8 - Initialized [0 Confs]
[Fri Jul 13 15:52:35 2012] [warn] No JkShmFile defined in httpd.conf. Using default /etc/httpd/logs/jk-runtime-status
PHP Warning: Directive 'safe_mode' is deprecated in PHP 5.3 and greater in Unknown on line 0
[Fri Jul 13 15:52:35 2012] [notice] mod_python: Creating 4 session mutexes based on 10 max processes and 0 max threads.
[Fri Jul 13 15:52:35 2012] [notice] Apache configured -- resuming normal operations
[Fri Jul 13 15:53:51 2012] [error] server reached MaxClients setting, consider raising the MaxClients setting

Is any one can help me to resolve this .

Thanks

Did you read what you posted??? Specifically, pay attention to the line bolded above. It's telling you it reached the MaxClients setting, and even told you to raise it. Did you??

And again, Plesk is a commercial product that you're paying for...contact Plesk tech support.

Thanks for your reply.
Here are the httpd.conf file content. Please tell me to which no. I raise it.

<IfModule prefork.c>
StartServers 8
MinSpareServers 5
MaxSpareServers 20
ServerLimit 300
MaxClients 300
MaxRequestsPerChild 4000
</IfModule>


<IfModule worker.c>
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 0
</IfModule>

Again, Plesk is commercial, pay-for software. You should contact them for support, since you are paying for it. And again, the error is clear, you raise the MaxClients line. You don't say where what you posted came from, but if you tried to look up this error (or contacted support), you'd see the likely place to change it is /etc/httpd/conf.d/swtune.conf.

I increased MaxClient value in swtune.conf

and it's solved the issue.

Thank you