ServerAdmins.NET

Hey there!

Today I wanted to focus on something that’s helping me do my job in a more efficient fashion. At a former workplace, I was responsible for ~200 high capacity webhosting machines, and a host of supporting machines. Back then, I was a huge fan of a management system mostly comprised of SSH Keys and a ton of bash scripts. It worked, quite well for the time, but if I could do it again, I’d go with a slightly more refined approach, which is what we’ll discuss today.

So, let’s get started. The first thing you’ll need is a working perl installation, a few devel libs and a handful of perl modules.

yum install gmp-devel
perl -MCPAN -e 'install Crypt::DH , Math::GMP, Net::SSH::Perl'

This is going to install the GMP math development libraries necessary for Math::GMP to compile. Math::GMP and Crypt::DH are prereqs for Net::SSH::Perl.

So once this is done, we can proceed.


#!/usr/local/bin/perl -w

That’s a very basic/barebones SSH Connection script… If you have any questions or problems, please don’t hesitate to post in the comments.

Next up, we’ll go over a more complex variant of this script using subroutines and a few other nifty tricks.

Hey there!

I’m going to show you a few different ways to install Perl modules in a quick and easy way.

First up, the one liner.

perl -MCPAN -e 'install HTML::Template'
CPAN: CPAN::SQLite loaded ok (v0.199)
CPAN: LWP::UserAgent loaded ok (v5.834)
CPAN: Time::HiRes loaded ok (v1.9719)
Fetching with LWP:

Gathering information from index files ...
Obtaining current state of database ...
Populating database tables ...
.... snipped for brevity....
Running make install
Prepending /home/.cpan/build/HTML-Template-2.9-bALXdn/blib/arch /home/.cpan/build/HTML-Template-2.9-bALXdn/blib/lib to PERL5LIB for 'install'
Installing /usr/local/lib/perl5/site_perl/5.8.8/HTML/Template.pm
Appending installation info to /usr/local/lib/perl5/5.8.8/x86_64-linux/perllocal.pod
SAMTREGAR/HTML-Template-2.9.tar.gz
/usr/bin/make install UNINST=1 OTHERLDFLAGS=-L/usr/lib64 LDFLAGS=-L/usr/lib64 EXTRALIBDIR=/usr/lib64 -- OK
[root@vps ~]#


And there you go, quick and easy.

Now a lot of Perl modules are going to require other modules to be built, in which case, you’ll see something like this…

Writing Makefile for Net::SSH::Perl
---- Unsatisfied dependencies detected during ----
---- TURNSTEP/Net-SSH-Perl-1.34.tar.gz ----
Crypt::DSA [requires]
Convert::PEM [requires]
Crypt::RSA [requires]
Math::Pari [requires]
Crypt::IDEA [requires]
Digest::BubbleBabble [requires]
Crypt::DH [requires]
Math::GMP [requires]
Shall I follow them and prepend them to the queue
of modules we are processing right now? [yes]


Just go ahead and answer “yes” here, and let it continue… cpan *should* be smart enough to grab all of the required sources and build what you need, but sometimes, not so much. Perl modules are basically subroutines packaged into nice containers, ready to use. Now some of these require specific programs, libraries or even other perl modules to do what they do best. When a module has a large chain of dependencies and one of those fails, it can bring the whole show to a screeching halt.

For an example here, I’ll use Net::SSH::Perl, which happens to be what I use for a host of different things.

If you use the above listed one-liner to install it, i.e.,

perl -MCPAN -e 'install HTML::Template'

You’re going to end up seeing this…


Files=12, Tests=106, 1 wallclock secs ( 0.07 usr 0.04 sys + 0.40 cusr 0.14 csys = 0.65 CPU)
Result: PASS
TURNSTEP/Net-SSH-Perl-1.34.tar.gz
Tests succeeded but 2 dependencies missing (Crypt::DH,Math::GMP)
TURNSTEP/Net-SSH-Perl-1.34.tar.gz
[dependencies] -- NA
Running make install
make test had returned bad status, won't install without force


So, we have a dependency of Net::SSH::Perl that simply isn’t present. So let’s go ahead and get it installed…

On a RH Based system (CentOS/Trustix/RedHat Enterprise Linux), you can do the following…


yum install gmp-devel


On a Debian based distribution (Debian/Ubuntu, etc)

apt-get install libgmp-ocaml


On FreeBSD, I prefer prots builds personally, so let’s do the following…

cd /usr/ports/math/libgmp4
make && make install


So, now that you’ve got that taken care of, let’s proceed.


perl -MCPAN -e 'install Net::SSH::Perl'
...
...
Tests succeeded but one dependency not OK (Crypt::DH)
TURNSTEP/Net-SSH-Perl-1.34.tar.gz
[dependencies] -- NA
Running make install
make test had returned bad status, won't install without force


So, we need to build Crypt::DH… Apparently dependency handling isn’t too bright in this case. I’ll save you the trouble of the blow-by-blow here. We need to install Crypt::DH which depends on Math::BigInt::GMP. So, use your handy oneline skills, and get Math::BigInt::GMP installed, then do the same for Crypt::DH. You should now have a working Net::SSH::Perl installation.

You can specify multiple packages in the following way…


perl -MCPAN -e 'install Net::SSH, Term::ReadLine'


The other option, should cpan fail, is to just grab the module package yourself, which is typically a .tar.gz file, and perform the following.


wget http://search.cpan.org/CPAN/authors/id/T/TU/TURNSTEP/Net-SSH-Perl-1.34.tar.gz
tar -xzvf Net-SSH-Perl-1.34.tar.gz
cd ./Net-SSH-Perl-1.34
perl Makefile.PL
make && make install


That’s more or less what cpan is doing, except it will try to sort out requirements and dependencies for you (when it can).

So I hope you’ve learned a bit of something about getting Perl modules installed and running. If you have any questions, feel free to leave a comment.