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1.1     ! harris41    1: <HTML>
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        !             3: <TITLE>LON-CAPA Network Processes Documentation</TITLE>
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        !             6: <H1>LON-CAPA Network Processes Documentation</H1>
        !             7: <P>
        !             8: Scott Harrison
        !             9: </P>
        !            10: <P>
        !            11: Last updated: 10/26/2000
        !            12: </P>
        !            13: <H3>Introduction</H3>
        !            14: <P>
        !            15: This file describes issues associated with the basic network
        !            16: layer of the LON-CAPA system.  When upgrading, installing, or reconfiguring a LON-CAPA system,
        !            17: it is often necessary to stop and start the network processes so that the code
        !            18: they are running with is up-to-date.
        !            19: </P>
        !            20: <P><I>
        !            21: There are also secondary network layers associated with the LON-CAPA system
        !            22: which are discussed elsewhere in the <A HREF="http://install.lon-capa.org/docs/index.html">
        !            23: documentation</A>.  These include NFS, Appleshare, and Samba (Windows Network Neighborhood).
        !            24: </I></P>
        !            25: <P>
        !            26: There are two basic levels of client-server processes associated with
        !            27: implementing the LON-CAPA network.
        !            28: <OL>
        !            29: <LI><B>Web level</B>: LON-CAPA users communicate with the system through their web browser
        !            30: <LI><B>Server-to-server level</B>: LON-CAPA machines communicate with other LON-CAPA machines
        !            31: </OL>
        !            32: </P>
        !            33: <H3>Description</H3>
        !            34: <P>
        !            35: The web level is implemented through a web server.  LON-CAPA uses the Apache web server.
        !            36: The apache web server forks off daemon children (<TT>httpd</TT>) which handle client requests
        !            37: (http requests from web browsers on the internet).  The more http requests, the more daemon children are
        !            38: made available.
        !            39: </P>
        !            40: <P>
        !            41: LON-CAPA functionality is enabled in the web level through the use of mod_perl.  mod_perl
        !            42: allows perl modules to be compiled once, and reside in memory in order to coordinate the
        !            43: interaction of http requests with services and resources provided by the LON-CAPA server machine.
        !            44: </P>
        !            45: <P>
        !            46: The server-to-server level is implemented through forked system processes which communicate with the
        !            47: TCP/IP protocol.  There are two types of children processes that LON-CAPA server machines maintain.
        !            48: <OL>
        !            49: <LI><TT>lonc</TT>- proxy server processes, these allow a LON-CAPA machine to act as a client toward another machine
        !            50: <LI><TT>lond</TT>- remote command interpreter, these respond to the proxy server processes to allow a LON-CAPA machine
        !            51: to act as a server toward another machine
        !            52: </OL>
        !            53: </P>
        !            54: <P>
        !            55: Of course, it becomes exciting when information passed through the web level requires the server to retrieve
        !            56: data through the server-to-server (TCP/IP) level.  This is handled by a perl module (loaded with mod_perl) that
        !            57: interfaces to <TT>lonc</TT>.  This perl module is <TT>lonnet.pm</TT>.
        !            58: </P>
        !            59: <H3>Managing Network Processes the Normal Way (/etc/rc.d/init.d)</H3>
        !            60: <P>
        !            61: <BR>Log in as <TT>root</TT>.  
        !            62: <BR>To stop the web level: <TT>/etc/rc.d/init.d/httpd stop</TT>
        !            63: <BR>To start the web level: <TT>/etc/rc.d/init.d/httpd start</TT>
        !            64: <BR>To restart the web level: <TT>/etc/rc.d/init.d/httpd restart</TT>
        !            65: <BR>To look at the status of the web level: <TT>/etc/rc.d/init.d/httpd status</TT>
        !            66: <BR>To stop the server-to-server and web level: <TT>/etc/rc.d/init.d/loncontrol stop</TT>
        !            67: <BR>To start the server-to-server and web level: <TT>/etc/rc.d/init.d/loncontrol start</TT>
        !            68: <BR>To restart the server-to-server and web level: <TT>/etc/rc.d/init.d/loncontrol restart</TT>
        !            69: <BR>To look at the status of the server-to-server and web level: <TT>/etc/rc.d/init.d/loncontrol status</TT>
        !            70: </P>
        !            71: <H3>Managing Network Processes the Dirty Way (killing pids directly)</H3>
        !            72: <P>
        !            73: <FONT SIZE=+3>Log in as <TT>www</TT></FONT>.  <B>Do not enter these commands as root</B>.
        !            74: <BR>To stop the server-to-server level: <TT>kill `cat /home/httpd/perl/logs/*.pid`</TT>
        !            75: <BR>To start the server-to-server level: <TT>/home/httpd/perl/loncron</TT>
        !            76: <BR>To restart the server-to-server level: <TT>kill `cat /home/httpd/perl/logs/*.pid`; /home/httpd/perl/loncron</TT>
        !            77: <BR>To look at the status of the server-to-server level: <TT>ps auxwww | grep lonc; ps auxwww | grep lond</TT>
        !            78: </P>
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