CGI.pm has been removed from the core Perl distribution. From 5.22, it is no longer included in a standard Perl installation.

There are good technical reasons for this. CGI is a dying technology. In 2015, there are far better ways to write web applications in Perl. We don’t want to be seen to encourage the use of a technology which no-one should be using.

This does lead to a small problem for us though. There are plenty of web hosting providers out there who don’t have particularly strong Perl support. They will advertise that they support Perl, but that’s just because they know that Perl comes as a standard part of the operating system that they run on their servers. They won’t do anything to change their installation in any way. Neither you nor I would use a hosting company that works like that – but plenty of people do.

The problem comes when these companies start to deploy an operating system that includes Perl 5.22. All of a sudden, those companies will stop including CGI.pm on their servers. And while we don’t want to encourage people to use CGI.pm (or, indeed, the CGI protocol itself) we need to accept that there are thousands of sites out there that have been happily using software based on CGI.pm for years and the owners of these sites will at some point change hosting providers or upgrade their service plan and end up on a server that has Perl 5.22 and doesn’t have CGI.pm. And their software will break.

I’ve always assumed that this problem is some time in the future. As far as I can see, the only mainstream Linux distribution that currently includes Perl 5.22 is Fedora 23. And you’d need to be pretty stupid to run a web hosting business on any version of Fedora. Fedora is a cutting edge distribution with no long term support. Versions of Fedora are only supported for about a year after their release.

So the problem is in the future, but it is coming. At some point Perl 5.22 or one of its successors will make it into Red Hat Enterprise Linux. And at that point we have a problem.

Or so I thought. But that’s not the case. The problem is here already. Not because of Perl 5.22 (that’s still a year or two in the future for most of these web hosting companies) but because of Red Hat.

Red Hat, like pretty much everyone, include Perl in their standard installation. If you install any Linux distribution based on Red Hat, then the out of the box installation includes an RPM called “perl”. But it’s not really what you would recognise as Perl. It’s a cut down version of Perl. They have stripped out many parts of Perl that they consider non-essential. And those parts include CGI.pm.

This change in the way they package Perl started with RHEL 6 – which comes with Perl 5.10. And remember it’s not just RHEL that is affected. There are plenty of other distributions that use RHEL as a base – Centos, Scientific Linux, Cloud Linux and many, many more.

So if someone uses a server running RHEL 6 or greater (or another OS that is based on RHEL 6 or greater) and the hosting company have not taken appropriate action, then that server will not have CGI.pm installed.

What is the “appropriate action” you ask. Well it’s pretty simple. Red Hat also make another RPM available that contains the whole Perl distribution. So bringing the Perl up to scratch on a RHEL host is as simple as running:

yum install perl-core

That will work on a server running RHEL 6 (which has Perl 5.10) and RHEL 7 (which has Perl 5.16). On a future version of RHEL which includes Perl 5.22 or later, that obviously won’t work as CGI.pm won’t be part of the standard Perl installation and therefore won’t be included in “perl-core”. At that point it will still be a good idea to install “perl-core” (to get the rest of the installation that you are missing) but to get CGI.pm, you’ll need to run:

yum install perl-CGI

So this is a plea to people who are running web hosting services using Red Hat style Linux distributions. Please ensure that your servers are running a complete Perl installation by running the “yum” command above.

All of which brings me to this blog post that Marc Lehmann wrote a couple of days ago. Marc found a web site which no longer worked because it had been moved to a new server which had a newer version of Perl – one that didn’t include CGI.pm. Marc thinks that the Perl 5 Porters have adopted a cavalier approach to backward compatibility and that the removal of CGI.pm is a good example of the problems they are causing. He therefore chose to interpret the problems this site was having as being caused by p5p’s approach to backward compatibility and the removal of CGI.pm.

This sounded unlikely to me. As I said above, it would be surprising if any web hosting company was using 5.22 at this point. So, I did a little digging. I found that the site was hosted by BlackNight solutions and that their web says that their servers run Perl 5.8. At the same time, Lee Johnson, the current maintainer of CGI.pm, got in touch with the web site’s owner who confirmed what I had worked out was correct.

Later yesterday I had a conversation with @BlackNight on Twitter. They told me that their hosts all ran Cloud Linux (which is based on RHEL) and that new servers were being provisioned using Cloud Linux 6 (which is based on RHEL 6).

So it seems clear what has happened here. The site was running on an older server which was running Cloud Linux 5. That includes Perl 5.8 and predates Red Hat removing CGI.pm from the “perl” RPM. It then moved to a new host running Cloud Linux 6 which is based on RHEL 6 and doesn’t include CGI.pm in the default installation. So what the site’s owner said is true, he moved to a new host with a newer version of Perl (that new version of Perl was 5.10!) but it wasn’t the new version of Perl that caused the problems, it was the new version of the operating system or, more specifically, the change in the way that Red Hat (and its derivatives) packaged Perl.

Marc is right that when Perl 5.22 hits the web hosting industry we’ll lose CGI.pm from a lot a web servers. You can make your own mind up on how important that is and whether or not you share Marc’s other opinions on how p5p is steering Perl. But he’s wrong to assume that, in this instance, the problem was caused by anything that p5p have done. In this instance, the problem was caused by Red Hat’s Perl packaging policy and was compounded by a hosting company who didn’t know that upgrading their servers to Cloud Linux 6 would remove CGI.pm.

RHEL 6 was released five years ago. I suspect it’s pretty mainstream in the web hosting industry by now. So CGI.pm will already have disappeared from a large number of web servers. I wonder why we haven’t seen a tsunami of complaints?

Update: More discussion on Reddit and Hacker News.