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Fri Oct 27 02:28:11 2000 UTC (23 years, 10 months ago) by
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howto's and descriptions of system services associated with LON-CAPA -Scott
1: <HTML>
2: <HEAD>
3: <TITLE>LON-CAPA Network Processes Documentation</TITLE>
4: </HEAD>
5: <BODY>
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>
79: </BODY>
80: </HTML>
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