[LON-CAPA-admin] Only One Access Server Serving Maps?

Stuart Raeburn raeburn at msu.edu
Mon Aug 17 23:08:52 EDT 2009


I'm seeing the same thing when I log-into a LON-CAPA session on ndsua1  
and select an old course of mine, for which the home server is msul1,  
so I don't think this issue is related to cloning or recent creation  
of courses.  This seems more of a general issue to do with file  
replication on ndsua1.

I suspect there may be a network issue of some sort which prevents the  
response to outgoing web requests from ndsua1 being received  again by  
the server.  It seems that it's not a disk space, as these files are  
very small, or a permissions issue as you tested that.

As nsdua1 allows me to start a session on nsdua1 (which will  
authenticate my log-in against the msu library server), connectivity  
via the LON-CAPA port (5663) is evidently available.  Furthermore,  
nmap run against port 5663 reports that it is open.

The missing file issue seems to be related to inbound traffic from  
remote web servers, as what nsdua1 will do in the case of a  
default.sequence file (which is an "uploaded" file) is to make an LWP  
request for the file to the course's home server (the msu library  
server), which it will then store locally.

I see the request from ndsua1 for the file in my MSU course in the  
server logs on the MSU library server: - - [17/Aug/2009:21:59:01 -0400] "GET  
/raw/uploaded/msu/33803011027874598msul1/default.sequence HTTP/1.1"  
200 4781 "-" "libwww-perl

and the logs suggest that the file was served successfully.

The question is then:

1. Were the requested data ever received on ndsua1?
2. If so, what did ndsua1 do with the data?

You may find some clues in /home/httpd/perl/logs/lonnet.log

The fact that you found that the problem persisted after copying the  
missing file via the command line suggests that the LWP request for  
the HEAD to check if the file exists also resulted in an error.

This is the relevant code from lonnet.pm for that check.  I'm assuming  
that the file you copied was not deleted, but that instead, $lwpresp  
was not "ok" but the return code was something other than a 404.

my $lwpresp = &getuploaded('HEAD',$uri,$cdom,$cnum,\$info,\$rtncode);
if ($lwpresp ne 'ok') {
# there is no such file anymore, even though we had a local copy
if ($rtncode eq '404') {
return -1;

In the case where the file has yet to be replicated, this is the  
relevant chunk of code (from lonnet.pm which fetches the file

my $transferfile=$file.'.in.transfer';

my $response=$ua->request($request,$transferfile);
# did it work?
if ($response->is_error()) {
     &logthis("Userfile repcopy failed for $uri");
     return -1;
# worked, rename the transfer file

You could put some debugging lines in there to print out the status of  
the LWP request, and also the result of the rename()   unfortunately  
LON-CAPA doesn't check this presently.

For example add this before the line:  unlink($transferfile);

print STDERR "repcopy_userfile LWP result: ".$response->status_line."\n";

and maybe change the rename to do:

if (!rename($transferfile,$file)) {
     print STDERR "repcopy_userfile rename failed: ".$!."\n";

Then reload Apache and look in /etc/httpd/logs/error_log after  
attempting to select a course, and retrieve the default.sequence file.

Stuart Raeburn

Quoting Paul Omernik <paul.omernik at ndsu.edu>:

> Of our two access servers, only one appears to be allowing mapping to the
> library server.  The one with issues (ndsua1) returns:
> The following problems occurred:
> Map not loaded: The file
> /home/httpd/html/userfiles/ndsu/1H214826f5d894a41ndsul1/default.sequencedoes
> not exist.
> Much like Lars, I clone the courses from the previous semester, and I can
> find the previous hash on ndsua2, in fact, it's listed in the Course
> Environment:
> /ndsu/2B66911d60f49493bndsul1
> and
> drwxr-x---  6 www  www  4096 Jun 24 09:32 2B66911d60f49493bndsul1
> (on ndsua2).
> The hash that ndsua1 can't find is located on ndsua2, so I attempted scp'ing
> the information over to ndsua1, matched the www:www ownership, and still
> nothing.
> This 'inaccessibility' exists for all courses I've created recently.
> Courses were created by logging in to the library server and cloning a
> previous course.
> Thank you,
> Paul

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