WHAT?

perl-Systemd-Daemon is Perl interface (aka "binding") to the part of libsystemd
declared in <systemd/sd-daemon.h>. perl-Systemd-Daemon allows developers to
write systemd-aware daemons in Perl.

WHY?

I want to write systemd-aware daemons in Perl language.

systemd is a system and service manager. It is used in some modern GNU/Linux
distros. It have many nice features. In particular, writing daemons for systemd
is easier (compared to writing traditional Unix daemons), because systemd does
many routine tasks for daemons. For example, a systemd-style daemon does not
need to fork (twice), close and reopen standard streams, write pid file, etc,
see daemon for full details.

Actually, any program (including scripts written in Perl) can be easily run as
systemd-style daemon by preparing appropriate unit file.

However, to fully utilize systemd abilities (for example, socket- or
bus-activatable daemons), a daemon should be systemd-aware, i. e. use API
provided by systemd to receive file descriptors from systemd, notify systemd
about daemon state, etc.

systemd provides API in form of shared library (libsystemd) and C header file
(<systemd/sd-daemon.h>). Perl code cannot directly use shared libraries and C
header files, glue (aka "binding") is required. Systemd-Daemon is such a glue.

NAMING

perl-Systemd-Daemon is official software name.

However, in Perl world prefix "perl-" is redundant and not used. For example, on
meta::cpan <https://metacpan.org/> this software is named as Systemd-Daemon. In
the rest of the documentation shortened name Systemd-Daemon is used as synonym
for full name perl-Systemd-Daemon. We are in the Perl world, aren't we?

You may notice that name may be spelled with dashes (Systemd-Daemon) or with
double colons (Systemd::Daemon). Strictly speaking, there is difference: the
first one is software name, while the second is name of Perl package, but often
these names are interchangeable especially if software consists of single
package.

FORMS

You may face Systemd-Daemon in *source* or *distribution* forms.

If you are going to write systemd-aware daemons in Perl, you will likely be
interested in *using* Systemd-Daemon *distribution*. If you are going to
*develop* (or *hack*) the Systemd-Daemon itself, you will likely need the
*source*, not distribution.

Since Perl is an interpreting language, modules in the distribution *look* like
sources. Actually, they are Perl source files. But they are not *actual*
sources, because they are *built* (preprocessed or generated) by Dist-Zilla.

How to distinguish source and distribution:

*   Source may contain Mercurial files and directories .hgignore, .hgtags, .hg/,
    while distribution should not.

*   Source should contain dist.ini file, while distribution may not.

*   Source should *not* contain xt/ directory, while distribution should.

*   Name of source directory does *not* include version (e. g. Systemd-Daemon),
    while name of distribution does (e. g. Systemd-Daemon-v0.7.1).

SOURCE

Systemd-Daemon source is in Mercurial repository hosted on fedorapeople.org. To
clone the entire repository:

    $ hg clone https://vandebugger.fedorapeople.org/hg/perl-Systemd-Daemon

Source Files

Systemd-Daemon source files usually include a comment near the top of the file:

    This file is part of perl-Systemd-Daemon.

Not all source files are included into distribution. Some source files are used
at distribution build time only, and not required for installation.

DISTRIBUTION

Systemd-Daemon distributions are published on CPAN
<https://metacpan.org/release/Systemd-Daemon>.

Generated Files

Distribution may contain files preprocessed or generated by Dist-Zilla and its
plugins. Some generated files are made from Systemd-Daemon source, but some are
generated from third-party templates. Files generated from third-party templates
usually include a comment near the top of the file:

    This file was generated with NAME

(where *NAME* is a name of the plugin generated the file). Such files are *not*
part of Systemd-Daemon source, and Systemd-Daemon copyright and license are not
applicable to such files.

INSTALLING

With cpanm

cpanm tool is (probably) the easiest way to install distribution. It automates
downloading, building, testing, installing, and uninstalling.

To install the latest version from CPAN:

    $ cpanm Systemd::Daemon

To install a specific version (e. g. *v0.7.1*) from CPAN:

    $ cpanm Systemd::Daemon@v0.7.1

To install locally available distribution (e. g. previously downloaded from CPAN
or built from sources):

    $ cpanm ./Systemd-Daemon-v0.7.1.tar.gz

To uninstall the distribution:

    $ cpanm -U Systemd::Daemon

Manually

To install distribution tarball manually (let us assume you have version
*v0.7.1* of the distribution):

    $ tar xaf Systemd-Daemon-v0.7.1.tar.gz
    $ cd Systemd-Daemon-v0.7.1
    $ perl Build.PL
    $ ./Build build
    $ ./Build test
    $ ./Build install

See Also

How to install CPAN modules <http://www.cpan.org/modules/INSTALL.html>

HACKING

For hacking, you will need Mercurial, Perl interpreter and Dist-Zilla (with some
plugins), and likely cpanm to install missed parts.

Clone the repository first:

    $ hg clone https://vandebugger.fedorapeople.org/hg/perl-Systemd-Daemon
    $ cd perl-Systemd-Daemon

To build a distribution from the source, run:

    $ dzil build

If required Dist-Zilla plugins are missed, dzil tool will warn you and show the
command to install all the required plugins, e. g.:

    Required plugin Dist::Zilla::Plugin::Test::EOL isn't installed.

    Run 'dzil authordeps' to see a list of all required plugins.
    You can pipe the list to your CPAN client to install or update them:

        dzil authordeps --missing | cpanm

To run the tests:

    $ dzil test

To run all the tests, including release tests:

    $ dzil test --release

To install the distribution:

    $ dzil install

or

    $ cpanm ./Systemd-Daemon-VERSION.tar.gz

where *VERSION* is a version of built distribution.

To clean the directory:

    $ dzil clean

DOCUMENTATION

Online

The easiest way is browsing the documentation online at meta::cpan
<https://metacpan.org/release/Systemd-Daemon>.

Locally Installed

If you have the distribution installed, use perldoc tool to browse locally
installed documentation:

    $ perldoc Systemd::Daemon::Manual
    $ perldoc Systemd::Daemon

Built from Source

Build Systemd-Daemon first (see "HACKING"), then:

    $ cd Systemd-Daemon-VERSION
    $ perldoc Systemd::Daemon::Manual
    $ perldoc Systemd::Daemon

where *VERSION* is a version of built distribution.

FEEDBACK

CPAN Request Tracker

The quickest way to report a bug in Systemd-Daemon is by sending email to
bug-Systemd-Daemon [at] rt.cpan.org.

CPAN request tracker can be used via web interface also:

Browse bugs <https://rt.cpan.org/Public/Dist/Display.html?Name=Systemd-Daemon>
    Browsing bugs does not require authentication.

Report bugs <https://rt.cpan.org/Public/Bug/Report.html?Queue=Systemd-Daemon>
    You need to be a CPAN author, have a BitCard <https://www.bitcard.org/>
    account, or OpenID in order to report bugs via the web interface.

    (On 2015-04-27 I have logged in successfully with my LiveJournal OpenID, but
    my Google OpenID did not work for CPAN. I did not check other OpenID
    providers.)

Send Email to Author

As a last resort, send email to author: Van de Bugger <van.de.bugger@gmail.com>.
Please start message subject with "perl-Systemd-Daemon:".

GLOSSARY

CPAN
    Comprehensive Perl Archive Network, a large collection of Perl software and
    documentation. See cpan.org <http://www.cpan.org>, What is CPAN?
    <http://www.cpan.org/misc/cpan-faq.html#What_is_CPAN>.

Distribution
    Tarball, containing Perl modules and accompanying files (documentation,
    metainfo, tests). Usually distributions are uploaded to CPAN, and can be
    installed with dedicated tools (cpan, cpanm, and others).

Module
    Perl library file, usually with .pm suffix. Usually contains one package.
    See perlmod <http://perldoc.perl.org/perlmod.html#Perl-Modules>.

Package
    Perl language construct. See package
    <http://perldoc.perl.org/functions/package.html> and perlmod
    <http://perldoc.perl.org/perlmod.html#Packages>.