I thought it would be a good idea in general to update all software on my computer regularly. Since CPAN modules are not managed by my package manager I figured I should do cpan -u every once in a while. It was only after executing this that I read the man page note on this:
-u Upgrade all installed modules. Blindly doing this can really break
things, so keep a backup.
Why should this break anything? And how should I keep my CPAN modules up to date otherwise; do I need to keep track of all manually installed modules (cpan doesn't seem to do this) and only update those regularly? How about the dependencies of my manually installed modules?
Why did cpan -u upgrade stuff for ~15min even though I haven't installed a single CPAN module?
Can I revert the cpan -u? Is it enough to delete ~/.cpan for this?
Why should this break anything?
It shouldn't, but complex systems are complex and sometimes things do break (e.g. if a module is updated with a non-backwards compatible change, or depends on a C library which has bugs which only show up in combination with specific dependencies).
And how should I keep my CPAN modules up to date otherwise;
Just keep backups in case things break.
Why did cpan -u upgrade stuff for ~15min even though I haven't installed a single CPAN module?
Perl is distributed with a large collection of modules, and other modules may have been installed by your distribution.
Can I revert the cpan -u?
You can overwrite it with the backup that the documentation recommended you take.
Is it enough to delete ~/.cpan for this?
No. That directory is used by the installer tool to cache data about available modules, to store source code, and to hold build artefacts. The installed files are written to your lib like any other library.
New or update code is new or updated bugs. I have the opposite view of Quentin: why would changing a bunch of stuff keep not break things? That's what I expect with most updates. However, the Perl 5 porters take great pains to test perl distributions against as much of CPAN as they can. That doesn't mean that your particular use of a module (and how you've worked around existing bugs) is stable.
Some modules that come with perl are also on CPAN. These are "dual-lived" modules and they might update from CPAN.
The cpan tool doesn't revert anything for you, but you can do what I do sometimes. Make your installation a git repo. Branch when you change it. Try the branch with your code. If anything goes wrong you can always switch back to master. You don't even need to commit the changes! Tools such as Pinto help you manage sets of Perl modules.
There are some other things to consider.
First, I recommend that you don't mess with the system perl. Let the system do that. If you want a fresher perl that you manage yourself, install a different one. You might like perlbrew for that (I don't, but that's no big deal).
You can screw up that one as much as you like and the system won't start doing weird things. Consider major changes like removing . from #INC and Deprecating unescaped left braces in regexes. Those were changes in perl but they broke some important things.
Second, you can configure cpan to install somewhere besides the system directories. The -I switch will use local::lib for you. Besides that, you can configure it manually.
Related
Is it possible to run multiple installs of Perl (in "containers") on one machine?
Reason is that I have different Perl-based server side web applications and wish to schedule updates to them independently.
For example, bugzilla upgrades seem to me to be very invasive, downloading all manner or module updates and lengthy, too (thereby increasing the chance of unpredictable behavior on other applications that depend on those modules, during the time that the upgrade is still partial).
I think it should be possible to run multiple independent server-side CGI Perl applications on one server, I'd rather not be told to separate them onto different machines - I think that's wasteful and I don't have that resource anyway.
Investigate PerlBrew and cpanm:
http://qa.celogeek.com/programming/perl/for/developer/overview
Edit, more info:
http://www.bryanesmith.com/documents/a2pm/perlbrew-june-14-2011.pdf
http://www.dagolden.com/index.php/1384/parallel-make-for-perlbrew/
http://www.perlbrew.pl/
It's easy to install and manage multiple perls. Simply install them in different places and use each perl's tools. I talk about this in The Effective Perler.
Some people suggest perlbrew without realizing that it doesn't really give you any benefit. It can download a perl, configure and install it, and switch around symbolic links to make one of those the default. It doesn't do anything magical, though.
Downloading and installing aren't a problem though. You've never needed root or sudo to do that, and if you do, you'll still need it for perlbrew. You can always install into any directory where you have permission. perlbrew doesn't get around that at all. From the source directory, you have two simple commands to run:
$./Configure -des -Dprefix=/where/you/want/to/install
$ make install
For you, that might mean Bugzilla gets its own perl:
$./Configure -des -Dprefix=/where/you/want/to/install/bugzilla-perl
$ make install
From there, you have a completely self-contained perl installation. When it matters to me which perl I use, I give the program the full path to it:
#!/where/you/want/to/install/bugzilla-perl/bin/perl
It's much easier to make these per-applications installations without perlbrew, which wants to do as much as it can for you, including deciding the directory name, which it prefers you didn't know at all.
perlbrew's main advantage is not the compilation and installation, but it's switch feature to let you make one perl the default. You probably don't want that feature though because you want bugzilla, CGI programs, and so on using only the perl you want them to use, not whatever default perl you last specified.
When you want to update the bugzilla-perl, just use it's tools, which already have adjusted shebang lines to find the right perl:
$ /where/you/want/to/install/bugzilla-perl/bin/cpan ...
I don't like all of those long paths, though, which is why I make links to them all. Then I can just call them with whatever naming scheme I decide, which might be:
$ bugzilla-cpan ...
There's never a question about which tool or version I'm using.
I would like to ask my system administrator to install various Perl modules such as Moose and Data::Alias. The system is Red Hat Enterprise Linux 5, running Perl 5.8.8. The only problem that I can think of is that some already-installed modules might need to be upgraded and thus run the risk of breaking something. What else should I be concerned about?
I do not know your company's policy, but it would probably be a better idea not to mess with your system perl and install the additional libraries and their prerequisites (and even a dedicated perl) in a different location and use lib.
See also How do I keep my own module/library directory? in perlfaq.
Our systems administrators are the ones who are concerned with making sure requested Perl modules don't break anything else on their systems.
So we ask, then they can say "No, that will break X, please install that in user-space." or "We'll install that at non-standard location Y, for compatibility reasons." I don't know all of the things they take into consideration when making that decision. The only thing I am supposed to know is whether or not my applications will break when modules are installed/updated.
If your system administrators are passing this responsibility (i.e. knowing the impact on the system as a whole) to you as a developer, it's probably much safer to go along with Sinan's suggestion and install the modules you need in a non-standard location for yourself. Having to be a system administrator and a developer at the same time while being paid to be only one is no fun.
The trick is to not get rid of your old setup until you know your new setup works. The rub is that the CPAN toolchain doesn't care and will happily install new files over old ones without giving you a way to uninstall your damage.
If I'm working on a big project where I'm going to upgrade modules, I like to put the new modules in their own, new directory. I can test things by settingPERL5LIB to the new directories, and if it doesn't work out, I'm back to the old setup with a simple change of the environment.
Some people do something similar with source control. They put their modules directory in a versioning system. When they install new modules, they check in the source. When something breaks, they just roll back the changes. They can also tag versions so they can roll back to any working point.
This is an often asked question especially if you are using shared hosting or have a hosting provider that is leery of installing perl modules.
There is a fix, a way to work around this problem of mixing system modules and your own modules, and that fix is called local::lib. local::lib provides a way for you to install modules locally, in a library specified by you, which you have control over. You can use /home/you/perl5/ for example, or any path you think will work.
PS - Moose modules will most likely not interfere with other perl 5 modules since Moose has clean and separate namespace. It does require lots of modules from CPAN however, so warn your sysadmin in advance. :)
Also, ask your sysadmin to upgrade perl to 5.10, that brings lots of good new stuff into perl's core and allows you to use some shiny new perl technology.
This is a follow-up to my previous question about developing Perl applications. Let’s say I develop an application as a CPAN module using Module::Install. Now I upload the code to the production server, say using a git push, and I would like to install the application dependencies listed in Makefile.PL. If I simply run cpan ., the thing tries to install the application like a regular Perl module, ie. starts to copy the modules and documentation to standard Perl directories all over the system.
Is this the way it’s supposed to be? Do you install the application into the standard Perl directories? I am used to having my Perl applications in one directory with separate lib. Otherwise it seems I’d have to manage a lot of other things, like installing the resources somewhere on path etc. If I just want to install the deps declared in Makefile.PL and run the application tests to make sure everything works, what should I do?
(Is this documented somewhere? I mean, is there something like best practice for deploying and updating non-trivial Perl applications? Or is everybody doing this his own way?)
I might be misunderstanding, but I think what you're looking for is
perl Makefile.PL
make installdeps
If you are using Module::Install, you're really using ExtUtils::MakeMaker behind the scenes. You can use all of the MakeMaker features and the targets it provides. Although the documentation doesn't show every feature, there are some valuable things to be found in the generated Makefile.
However, MakeMaker is old news and most everyone has asked Santa Claus for it to disappear. If you want better control, including creating your own targets and process, Module::Build is orders of magnitude easier to work with as well as cross-platform (even if that just means not using a different make, gmake, or whatever on the same OS on different boxes). If you deviate from the normal, consumer-grade installation process, you're life will be easier without MakeMaker.
Some people appreciate the brevity of the Module::Install build file, but once constructed, you don't spend a lot of time messing with your build file so it's not that much of a real benefit. When the little benefit you get locks you into MakeMaker, it's not a win at all.
A 2014 update: Module::Build has now fallen out of favor and needs a maintainer. It never quite got to the point where people could use it to build and distribute XS modules. It was deprecated in Perl v5.19 although you can still get it from CPAN.
You could look at Module::ScanDeps to generate a list of dependent modules for installing. Or Par::Packer for packaging up the whole thing as an "app".
It seems that most of the installers for Perl are centered around installing Perl modules, not applications. Things like ExtUtils::MakeMaker and Module::Build are very well suited for modules, but require some additional work for Web Apps.
Ideally it would be nice to be able to do the following after checking out the source from the repository:
Have missing dependencies detected
Download and install dependencies from CPAN
Run a command to "Build" the source into a final state (perform any source parsing or configuration necessary for the local environment).
Run a command to install the built files into the appropriate locations. Not only the perl modules, but also things like template (.tt) files, and CGI scripts, JS and image files that should be web-accessible.
Make sure proper permissions are set on installed files (and SELinux context if necessary).
Right now we have a system based on Module::Build that does most of this. The work was done by done by my co-worker who was learning to use Module::Build at the time, and we'd like some advice on generalizing our solution, since it's fairly app-specific right now. In particular, our system requires us to install dependencies by hand (although it does detect them).
Is there any particular system you've used that's been particularly successful? Do you have to write an installer based on Module::Build or ExtUtils::MakeMaker that's particular to your application, or is something more general available?
EDIT: To answer brian's questions below:
We can log into the machines
We do not have root access to the machines
The machines are all (ostensibly) identical builds of RHEL5 with SELinux enabled
Currently, the people installing the machines are only programmers from our group, and our source is not available to the general public. However, it's conceivable our source could eventually be installed on someone else's machines in our organization, to be installed by their programmers or systems people.
We install by checking out from the repository, though we'd like to have the option of using a distributed archive (see above).
The answer suggesting RPM is definitely a good one. Using your system's package manager can definitely make your life easier. However, it might mean you also need to package up a bunch of other Perl modules.
You might also take a look at Shipwright. This is a Perl-based tool for packaging up an app and all its Perl module dependencies. It's early days yet, but it looks promising.
As far as installing dependencies, it wouldn't be hard to simply package up a bunch of tarballs and then have you Module::Build-based solution install them. You should take a look at pip, which makes installing a module from a tarball quite trivial. You could package this with your code base and simply call it from your own installer to handle the deps.
I question whether relying on CPAN is a good idea. The CPAN shell always fetches the latest version of a distro, rather than a specific version. If you're interested in ensuring repeatable installs, it's not the right tool.
What are your limitations for installing web apps? Can you log into the machine? Are all of the machines running the same thing? Are the people installing the web apps co-workers or random people from the general public? Are the people installing this sysadmins, programmers, web managers, or something else? Do you install by distributed an archive or checking out from source control?
For most of my stuff, which involves sysadmins familiar with Perl installing in control environments, I just use MakeMaker. It's easy to get it to do all the things you listed if you know a little about MakeMaker. If you want to know more about that, ask a another question. ;) Module::Build is just as easy, though, and the way to go if you don't already like using MakeMaker.
Module::Build would be a good way to go to handle lots of different situations if the people are moderately clueful about the command line and installing software. You'll have a lot of flexibility with Module::Build, but also a bit more work. And, the cpan tool (which comes with Perl), can install from the current directory and handle dependencies for you. Just tell it to install the current directory:
$ cpan .
If you only have to install on a single platorm, you'll probably have an easier time making a package in the native format. You could even have Module::Build make that package for you so the developers have the flexibility of Module::Build, but the installers have the ease of the native process. Sticking with Module::Build also means that you could create different packages for different platforms from a single build tool.
If the people installing the web application really have no idea about command lines, CPAN, and other things, you'll probably want to use a packager and installer that doesn't scare them or make them think about what is going on, and can accurately report problems to you automatically.
As Dave points out, using a real CPAN mirror always gets you the latest version of a module, but you can also make your own "fake" CPAN mirror with exactly the distributions you want and have the normal CPAN tools install from that. For our customers, we make "CPAN on a CD" (although thumb drives are good now too). With a simple "run me" script everything gets installed in exactly the versions they need. See, for instance, my Making my own CPAN talk if you're interested in that. Again, consider the audience when you think about that. It's not something you'd hand to the general public.
Good luck, :)
I'd recommend seriously considering a package system such as RPM to do this. Even if you're running on Windows I'd consider RPM and cygwin to do the installation. You could even set up a yum or apt repository to deliver the packages to remote systems.
If you're looking for a general installer for customers running any number of OSes and distros, then the problem becomes much harder.
Take a look at PAR.
Jonathan Rockway as a small section on using this with Catalyst in his book.
I want to use Apple's or RedHat's built-in Apache but I want to use Perl 5.10 and mod_perl. What's the least intrusive way to accomplish this? I want the advantage of free security patching for the vendor's Apache, dav, php, etc., but I care a lot about which version of Perl I use and what's in my #INC path. I don't mind compiling my own mod_perl.
Build your version of Perl 5.10 following any special instructions from the mod_perl documentation. Tell Perl configurator to install in some non-standard place, like /usr/local/perl/5.10.0
Use the instructions to build a shared library (or dynamic, or .so) mod_perl against your distribution's Apache, but make sure you run the Makefile.PL using your version of perl:
/usr/local/perl/5.10.0/bin/perl Makefile.PL APXS=/usr/bin/apxs
Install and configure mod_perl like normal.
It may be helpful, after step one, to change your path so you don't accidentially get confused about which version of Perl you're using:
export PATH=/usr/local/perl/5.10.0/bin:$PATH
You'll want to look into mod_so
I've done this before. It wasn't pretty, but it worked, especially since vendor perl's are usually 2-3 years old.
I started with making my own perl RPM that installed perl into a different location, like /opt/. This was pretty straight forward. I mostly started with this because I didn't want the system utilities that used perl to break when I upgraded/installed new modules. I had to modify all my scripts to specify #!/opt/bin/perl at the top and sometimes I even played with the path to make sure my perl came first.
Next, I grabbed a mod_perl source RPM and modified it to use my /opt/bin/perl instead of /usr/bin/perl. I don't have access to the changes I made, since it was at a different gig. It took me a bit of playing around to get it.
It did work, but I'm not an RPM wizard, so dependency checking didn't work out so well. For example, I could uninstall my custom RPM and break everything. It wasn't a big deal for me, so I moved on.
I was also mixing RPM's with CPAN installs of modules (did I mention we built our own custom CPAN mirror with our own code?). This was a bit fragile too. Again, I didn't have the resources (ie, time) to figure out how to bend cpan2rpm to use my perl and not cause RPM conflicts.
If I had it all to do again, I would make a custom 5.10 perl RPM and just replace the system perl. Then I would use cpan2rpm to create the RPM packages I needed for my software and compile my own mod_perl RPM.