[erlang-questions] Meaning of the 'local' option atom in systools:make_script/2

[Siri Hansen]

Hi Ivan!

First, be aware that systools:make_script/[1,2] does not fetch any erlang
applications or create any kind of a release package, it only creates
<relname>.script and <relname>.boot from the given <relname>.rel file.
<relname>.script is a text file and <relname>.boot is a binary version of
the same. The .boot file is used when starting an erlang node to give the
initial information about which applications to start and where to find
them.

>From the same .rel file, I have run make_script, once with 'local' and once
without it. Running diff on the two generated .script files does only give
results like this:

14c12
<      {path,["/ldisk/siri/git/otp/lib/kernel/ebin"]},
---
>      {path,["$ROOT/lib/kernel-3.0/ebin"]},

So, what does it mean? It means that if I use 'local', then I can start my
erlang node with the created <relname>.boot and it will pick all
applications from the exact same place as the erlang node from which I
executed systools:make_script. This is mostly intended for testing!

A .boot file created without 'local' is intended to use in a "real"
release, which could e.g. be created with systools:make_tar etc. The point
beeing that you can create your .script/.boot at build time, without the
knowledge about the installation destination. It is assumed that the
installation is structured in a standard OTP way with all applications
under a $ROOT/lib (this can, however, be omitted by using the 'variables'
option to make_script - see documentation). When starting the erlang node
with this .boot file, $ROOT will be replaced with the real root dir of the
installation.

Regards
/siri



2014-02-04 Ivan Uemlianin <ivan@REDACTED>:

> Dear All
>
> What is the meaning of the 'local' option atom in systools:make_script/2?
>
> My understanding of the erlang documentation [1] is that, if 'local' is
> given, make_script will find paths to the application directories on the
> current file system, and it will use those paths in the release script.
>  Nothing is copied into the release directory structure.  A release built
> with 'local' will only be portable to another system if that system has
> exactly the same applications at exactly the same paths.  If I would like
> the release to be portable, I should omit 'local' and make sure all
> required applications are in a lib/ directory in the release directory
> structure.
>
> This seems to be more-or-less what "Erlang and OTP in Action" says [2],
> but "Learn You Some Erlang" seems to say the exact opposite [3].
>
> So my questions are:
>
> 1.  Do I understand the documentation correctly?
>
> 2.  If I omit 'local' will make_scripts/2 fetch the required erlang
> applications and put them in lib/, or must I do that myself?
>
> With thanks and best wishes
>
> Ivan
>
>
> ** [1] erlang documentation
>
> http://www.erlang.org/doc/man/systools.html#make_script-2
>
>     In the generated boot script all application directories are
>     structured as App-Vsn/ebin and assumed to be located in $ROOT/lib,
>     where $ROOT is the root directory of the installed release. If the
>     local option is supplied, the actual directories where the
>     applications were found are used instead. This is a useful way to
>     test a generated boot script locally.
>
>
> ** [2] Erlang and OTP in Action (2011)
>
> Ch 10. Packaging, services and deployment, p. 250
>
>     1> systools:make_script("simple_cache", [local]).
>     ok
>
>     The local option ... stipulates that absolute paths to all
>     applications are written in the script and boot files --- meaning
>     that if you try to start a system using this boot file, all
>     application code must reside in exactly the same place it did when
>     the boot file was created.  The local option is good for testing,
>     but it isn't very portable and may not be suitable for production.
>
>     Without the local option, the generated script and boot files
>     expect that all applications are located in a directory called lib,
>     pointed out by a system variable $ROOT.  This is suitable for a
>     release that you want to be able to install on different host
>     machines that don't necessarily have the same paths.
>
>
> ** [3] Learn You Some Erlang (2013)
>
> Ch 21. Release is the Word, p. 340
>
>     1> systools:make_script("erlcount-1.0", [local]).
>     ok
>
>     Here, the local option means that we want the release to be
>     possible to run from anywhere, and not just the current install.
>
>
>
> --
> ============================================================
> Ivan A. Uemlianin PhD
> Llaisdy
> Speech Technology Research and Development
>
>                     ivan@REDACTED
>                      www.llaisdy.com
>                          llaisdy.wordpress.com
>               github.com/llaisdy
>                      www.linkedin.com/in/ivanuemlianin
>
>                         festina lente
> ============================================================
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> erlang-questions mailing list
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