[Koha] Error staging MARC records

[Mark Alexander]

I recently upgraded our Koha from 19.05 to 19.11.06, and upgraded the underlying
OS from Debian 8 to Debian 9.

I'm now getting an error when I try to stage MARC records for import.
The upload seems to work correctly, and I see the uploaded file in
/tmp/koha_rpl_upload/, but Koha says the file doesn't exist when I press the
"Stage for import" button.

Here are the last two lines in intranet-error.log; I've inserted
carriage returns for readability and anonymized the library name:

[Fri Jun 05 06:07:49.132250 2020] [cgi:error] [pid 2025] [client 104.219.99.61:42282] AH01215: [Fri Jun  5 06:07:49 2020]
  stage-marc-import.pl: Use of uninitialized value in subroutine entry at /usr/share/koha/lib/Koha/Plugins/Base.pm line 182.:
  /usr/share/koha/intranet/cgi-bin/tools/stage-marc-import.pl, referer: https://koha.OURLIBRARY.com:82/cgi-bin/koha/tools/manage-marc-import.pl
[Fri Jun 05 06:08:06.283046 2020] [cgi:error] [pid 2062] [client 104.219.99.61:42286] AH01215: [Fri Jun  5 06:08:06 2020]
  stage-marc-import.pl: /usr/share/koha/intranet/cgi-bin/tools/stage-marc-import.pl:
  cannot open input file /tmp/koha_rpl_upload/1371f85fdaf426b84bd9a782ce82bccf_set31.marc:
  No such file or directory: /usr/share/koha/intranet/cgi-bin/tools/stage-marc-import.pl,
  referer: https://koha.OURLIBRARY.com:82/cgi-bin/koha/tools/stage-marc-import.pl

When I log in with ssh, I can see the file mentioned in the error message:

% ls -laF /tmp/koha_rpl_upload/1371f85fdaf426b84bd9a782ce82bccf_set31.marc
-rw-r--r-- 1 rpl-koha rpl-koha 3953 Jun  5 06:07 /tmp/koha_rpl_upload/1371f85fdaf426b84bd9a782ce82bccf_set31.marc

I see that Elaine Bradtke reported this same error back on Aug 19, but said
that the problem was due to a configuration issue that she did not
describe.  I'd like to know what sort of configuration issues could
cause this error.

Just in case, I've disabled all plugins, and the problem persists.

For completeness, here is what the About page says:

Koha version: 	19.11.06.000
OS version ('uname -a'): 	Linux koha 5.6.1-x86_64-linode134 #1 SMP PREEMPT Wed Apr 1 22:25:48 UTC 2020 x86_64
Perl interpreter: 	/usr/bin/perl
Perl version: 	5.024001
Perl @INC: 	/usr/share/koha/lib
/usr/share/koha/installer
/usr/share/koha/lib/installer
/etc/perl
/usr/local/lib/x86_64-linux-gnu/perl/5.24.1
/usr/local/share/perl/5.24.1
/usr/lib/x86_64-linux-gnu/perl5/5.24
/usr/share/perl5
/usr/lib/x86_64-linux-gnu/perl/5.24
/usr/share/perl/5.24
/usr/local/lib/site_perl
/usr/lib/x86_64-linux-gnu/perl-base
/var/lib/koha/rpl/plugins
/var/lib/koha/rpl/plugins
MySQL version: 	mysql Ver 15.1 Distrib 10.1.44-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2
Apache version: 	Server version: Apache/2.4.25 (Debian)
PSGI: 	Plack (deployment)
Memcached: 	Servers: 127.0.0.1:11211 | Namespace: koha_rpl | Status: running. | Config read from: koha-conf.xml
Zebra version: 	Zebra 2.0.59 (C) 1994-2014, Index Data Zebra is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. SHA1 ID: c00bfddbf0f3608340d61298acc61dafb167f9b2 Using ICU
Date and time: 	06/05/2020 06:10
Time zone: 	Used: America/New_York | Config: Undefined | Environment (TZ): Undefined