I first looked at php.ini. post_max_size is set to 50M, and upload_max_filesize is 50M. My uploads are done in Perl, anyway, but I wanted to make sure.

perl has a similar global variable setting which you may want to explore - $CGI::POST_MAX

https://metacpan.org/pod/CGI#$CGI::POST_MAX

Any other suggestions on where I might be inadvertently limiting the file upload size?

have you checked the web server error log file for clues?

perl has a similar global variable setting which you may want to explore - $CGI::POST_MAX

Are you saying that this is a default setting somewhere, or just something that I may have added in the past? I looked but don't see it anywhere.

I also searched all of my scripts for "-s", knowing that I would normally use that to return the filesize. I didn't find anything that would have caused this problem, though.

have you checked the web server error log file for clues?

Yup, but no luck.

I've also tried uploading the exact same 4.4MB file on my end using the same script they would have used, but it worked just fine. So now I suspect that the issue isn't just the file size, but the time it takes them to get it to upload.

I found the "Timeout" setting in Apache, which I have set to 60 (assuming that's in seconds). I'll try bumping that up tonight, when I can rebuild Apache without disruption. Any other ideas of anything else that might cause a timeout?

What module are you using for your CGI variables? Or is the script hand processing them?

If you are using CGI that is what Phranque was referring too. Look for "use CGI" in the script.

If you are accidently "doing it by hand", there has be a limit to the number of bytes that can be uploaded, or you would be open to easy Ddos attacks from people flooding the script and causing buffer overflows.

What is the "upload" routine?

Oh, I see. The script is hand written, but I do use CGI for upload().

What's the default for $CGI::POST_MAX? The docs implied that there's no limit unless you explicitly set it.

[metacpan.org...]

Is that upload limit based on compressed files or uncompressed files? For example jpeg compression is about 10:1, and uncompressed files could easily take them over the 50mb limit.

Throw this in near the top of your script and then try to upload a large file. See if it throws an error:

use CGI::Carp qw (fatalsToBrowser);

also, I've not used CGI for uploads before, but the 16384 looks interesting. What does that mean?
read($old_pic,$data,16384)

just fyi - I have used CGI for uploads before...still do in fact.

# $SAVE_DIRECTORY = where to save file

sub GetUpload {
$| = 1;
use CGI qw(:standard);
$query = new CGI;

foreach $key (sort {$a <=> $b} $query->param()) {

#print "k: $key v: ". $query->param($key) . "<br>\n";
next if ($key =~ /^\s*$/);
next if ($query->param($key) =~ /^\s*$/);
next if ($key !~ /^file-to-upload-(\d+)$/);
$Number = $1;

if ($query->param($key) =~ /([^\/\\]+)$/) {
$Filename = $1;
$Filename =~ s/^\.+//;
$File_Handle = $query->param($key);
return(8);# if (!$ALLOW_INDEX && $Filename =~ /^index/i) {
} else {
$FILENAME_IN_QUESTION = $query->param($key);
return(7);# no filename
}

  if (!open(OUTFILE, ">$SAVE_DIRECTORY\/$Filename")) {
chmod(0777, "$SAVE_DIRECTORY\/$Filename") if $operatingsystem eq "unix";

  return(6); #print "There was an error opening the Output File\n";
  }

undef $BytesRead;
undef $Buffer;
  while ($Bytes = read($File_Handle,$Buffer,1024)) {
$BytesRead += $Bytes;
   print OUTFILE $Buffer;
  }
push(@Files_Written, "$SAVE_DIRECTORY\/$Filename");
$TOTAL_BYTES += $BytesRead;
$Confirmation{$File_Handle} = $BytesRead;
  close($File_Handle);
close(OUTFILE);
 }

$FILES_UPLOADED = scalar(keys(%Confirmation));

if ($TOTAL_BYTES > $MAXIMUM_UPLOAD && $MAXIMUM_UPLOAD > 0) {
foreach $File (@Files_Written) {
unlink $File;
}
return(5); #<TITLE>Error: Limit Reached</TITLE>
}
}