1
<?xml version="1.0" encoding="latin1" ?>
2
<!DOCTYPE chapter SYSTEM "chapter.dtd">
7
<year>2002</year><year>2011</year>
8
<holder>Ericsson AB. All Rights Reserved.</holder>
11
The contents of this file are subject to the Erlang Public License,
12
Version 1.1, (the "License"); you may not use this file except in
13
compliance with the License. You should have received a copy of the
14
Erlang Public License along with this software. If not, it can be
15
retrieved online at http://www.erlang.org/.
17
Software distributed under the License is distributed on an "AS IS"
18
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
19
the License for the specific language governing rights and limitations
24
<title>Creating a First Target System</title>
25
<prepared>Peter Högfeldt</prepared>
26
<responsible></responsible>
30
<date>2002-09-17</date>
32
<file>create_target.xml</file>
36
<title>Introduction</title>
37
<p>When creating a system using Erlang/OTP, the most simple way is
38
to install Erlang/OTP somewhere, install the application specific
39
code somewhere else, and then start the Erlang runtime system,
40
making sure the code path includes the application specific code.</p>
41
<p>Often it is not desirable to use an Erlang/OTP system as is. A
42
developer may create new Erlang/OTP compliant applications for a
43
particular purpose, and several original Erlang/OTP applications
44
may be irrelevant for the purpose in question. Thus, there is a
45
need to be able to create a new system based on a given
46
Erlang/OTP system, where dispensable applications are removed,
47
and a set of new applications are included. Documentation and
48
source code is irrelevant and is therefore not included in the
50
<p>This chapter is about creating such a system, which we call a
51
<em>target system</em>.</p>
52
<p>In the following sections we consider creating target systems with
53
different requirements of functionality:</p>
54
<list type="bulleted">
55
<item>a <em>basic target system</em> that can be started by
56
calling the ordinary <c>erl</c> script, </item>
57
<item>a <em>simple target system</em> where also code
58
replacement in run-time can be performed, and</item>
59
<item>an <em>embedded target system</em> where there is also
60
support for logging output from the system to file for later
61
inspection, and where the system can be started automatically
64
<p>We only consider the case when Erlang/OTP is running on a UNIX
66
<p>In the <c>sasl</c> application there is an example Erlang
67
module <c>target_system.erl</c> that contains functions for
68
creating and installing a target system. This module is used in
69
the examples below, and the source code of the module is listed
70
at the end of this chapter.</p>
74
<title>Creating a Target System</title>
75
<p>It is assumed that you have a working Erlang/OTP system structured
76
according to the OTP Design Principles.</p>
77
<p><em>Step 1.</em> First create a <c>.rel</c> file (see
78
<c>rel(4)</c>) that specifies the <c>erts</c> version
79
and lists all applications that should be included in the new
80
basic target system. An example is the following
81
<c>mysystem.rel</c> file:</p>
85
{"MYSYSTEM", "FIRST"},
90
{pea, "1.0"}]}. </code>
91
<p>The listed applications are not only original Erlang/OTP
92
applications but possibly also new applications that you have
93
written yourself (here examplified by the application
95
<p><em>Step 2.</em> From the directory where the <c>mysystem.rel</c>
96
file reside, start the Erlang/OTP system:</p>
98
os> <input>erl -pa /home/user/target_system/myapps/pea-1.0/ebin</input></pre>
99
<p>where also the path to the <c>pea-1.0</c> ebin directory is
101
<p><em>Step 3.</em> Now create the target system: </p>
103
1> <input>target_system:create("mysystem").</input></pre>
104
<p>The <c>target_system:create/1</c> function does the following:</p>
105
<list type="ordered">
106
<item>Reads the <c>mysystem.rel</c> file, and creates a new file
107
<c>plain.rel</c> which is identical to former, except that it
108
only lists the <c>kernel</c> and <c>stdlib</c> applications. </item>
109
<item>From the <c>mysystem.rel</c> and <c>plain.rel</c> files
110
creates the files <c>mysystem.script</c>,
111
<c>mysystem.boot</c>, <c>plain.script</c>, and
112
<c>plain.boot</c> through a call to
113
<c>systools:make_script/2</c>.</item>
115
<p>Creates the file <c>mysystem.tar.gz</c> by a call to
116
<c>systools:make_tar/2</c>. That file has the following
120
releases/FIRST/start.boot
121
releases/FIRST/mysystem.rel
122
releases/mysystem.rel
127
<p>The file <c>releases/FIRST/start.boot</c> is a copy of our
128
<c>mysystem.boot</c></p>
129
<p>The release resource file <c>mysystem.rel</c> is duplicated
130
in the tar file. Originally, this file was only stored in
131
the <c>releases</c> directory in order to make it possible
132
for the <c>release_handler</c> to extract this file
133
separately. After unpacking the tar
134
file, <c>release_handler</c> would automatically copy the
135
file to <c>releases/FIRST</c>. However, sometimes the tar
136
file is unpacked without involving
137
the <c>release_handler</c> (e.g. when unpacking the first
138
target system) and therefore the file is now instead
139
duplicated in the tar file so no manual copying is
142
<item>Creates the temporary directory <c>tmp</c> and extracts the tar file
143
<c>mysystem.tar.gz</c> into that directory. </item>
144
<item>Deletes the <c>erl</c> and <c>start</c> files from
145
<c>tmp/erts-5.1/bin</c>. These files will be created again from
146
source when installing the release.</item>
147
<item>Creates the directory <c>tmp/bin</c>.</item>
148
<item>Copies the previously created file <c>plain.boot</c> to
149
<c>tmp/bin/start.boot</c>.</item>
150
<item>Copies the files <c>epmd</c>, <c>run_erl</c>, and
151
<c>to_erl</c> from the directory <c>tmp/erts-5.1/bin</c> to
152
the directory <c>tmp/bin</c>.</item>
153
<item>Creates the file <c>tmp/releases/start_erl.data</c> with
154
the contents "5.1 FIRST". This file is to be passed as data
155
file to the <c>start_erl</c> script.
157
<item>Recreates the file <c>mysystem.tar.gz</c> from the directories
158
in the directory <c>tmp</c>, and removes <c>tmp</c>.</item>
163
<title>Installing a Target System</title>
164
<p><em>Step 4.</em> Install the created target system in a
165
suitable directory. </p>
167
2> <input>target_system:install("mysystem", "/usr/local/erl-target").</input></pre>
168
<p>The function <c>target_system:install/2</c> does the following:
170
<list type="ordered">
171
<item>Extracts the tar file <c>mysystem.tar.gz</c> into the target
172
directory <c>/usr/local/erl-target</c>.</item>
173
<item>In the target directory reads the file <c>releases/start_erl.data</c>
174
in order to find the Erlang runtime system version ("5.1").</item>
175
<item>Substitutes <c>%FINAL_ROOTDIR%</c> and <c>%EMU%</c> for
176
<c>/usr/local/erl-target</c> and <c>beam</c>, respectively, in
177
the files <c>erl.src</c>, <c>start.src</c>, and
178
<c>start_erl.src</c> of the target <c>erts-5.1/bin</c>
179
directory, and puts the resulting files <c>erl</c>,
180
<c>start</c>, and <c>run_erl</c> in the target <c>bin</c>
182
<item>Finally the target <c>releases/RELEASES</c> file is created
183
from data in the <c>releases/mysystem.rel</c> file.</item>
188
<title>Starting a Target System</title>
189
<p>Now we have a target system that can be started in various ways.</p>
190
<p>We start it as a <em>basic target system</em> by invoking</p>
192
os> <input>/usr/local/erl-target/bin/erl</input></pre>
193
<p>where only the <c>kernel</c> and <c>stdlib</c> applications are
194
started, i.e. the system is started as an ordinary development
195
system. There are only two files needed for all this to work:
196
<c>bin/erl</c> file (obtained from <c>erts-5.1/bin/erl.src</c>)
197
and the <c>bin/start.boot</c> file (a copy of <c>plain.boot</c>).</p>
198
<p>We can also start a distributed system (requires <c>bin/epmd</c>).</p>
199
<p>To start all applications specified in the original
200
<c>mysystem.rel</c> file, use the <c>-boot</c> flag as follows:</p>
202
os> <input>/usr/local/erl-target/bin/erl -boot /usr/local/erl-target/releases/FIRST/start</input></pre>
203
<p>We start a <em>simple target system</em> as above. The only difference
204
is that also the file <c>releases/RELEASES</c> is present for
205
code replacement in run-time to work.</p>
206
<p>To start an <em>embedded target system</em> the shell script
207
<c>bin/start</c> is used. That shell script calls
208
<c>bin/run_erl</c>, which in turn calls <c>bin/start_erl</c>
209
(roughly, <c>start_erl</c> is an embedded variant of
211
<p>The shell script <c>start</c> is only an example. You should
212
edit it to suite your needs. Typically it is executed when the
213
UNIX system boots.</p>
214
<p><c>run_erl</c> is a wrapper that provides logging of output from
215
the run-time system to file. It also provides a simple mechanism
216
for attaching to the Erlang shell (<c>to_erl</c>).</p>
217
<p><c>start_erl</c> requires the root directory
218
(<c>"/usr/local/erl-target"</c>), the releases directory
219
(<c>"/usr/local/erl-target/releases"</c>), and the location of
220
the <c>start_erl.data</c> file. It reads the run-time system
221
version (<c>"5.1"</c>) and release version (<c>"FIRST"</c>) from
222
the <c>start_erl.data</c> file, starts the run-time system of the
223
version found, and provides <c>-boot</c> flag specifying the boot
224
file of the release version found
225
(<c>"releases/FIRST/start.boot"</c>).</p>
226
<p><c>start_erl</c> also assumes that there is <c>sys.config</c> in
227
release version directory (<c>"releases/FIRST/sys.config"</c>). That
228
is the topic of the next section (see below).</p>
229
<p>The <c>start_erl</c> shell script should normally not be
230
altered by the user.</p>
234
<title>System Configuration Parameters</title>
235
<p>As was pointed out above <c>start_erl</c> requires a
236
<c>sys.config</c> in the release version directory
237
(<c>"releases/FIRST/sys.config"</c>). If there is no such a
238
file, the system start will fail. Hence such a file has to
239
be added as well.</p>
241
<p>If you have system configuration data that are neither file
242
location dependent nor site dependent, it may be convenient to
243
create the <c>sys.config</c> early, so that it becomes a part of
244
the target system tar file created by
245
<c>target_system:create/1</c>. In fact, if you create, in the
246
current directory, not only the <c>mysystem.rel</c> file, but
247
also a <c>sys.config</c> file, that latter file will be tacitly
248
put in the apropriate directory.</p>
252
<title>Differences from the Install Script</title>
253
<p>The above <c>install/2</c> procedure differs somewhat from that
254
of the ordinary <c>Install</c> shell script. In fact, <c>create/1</c>
255
makes the release package as complete as possible, and leave to the
256
<c>install/2</c> procedure to finish by only considering location
261
<title>Listing of target_system.erl</title>
262
<p>This module can also be found in the <c>examples</c> directory
263
of the <c>sasl</c> application.</p>
264
<codeinclude file="../../../lib/sasl/examples/src/target_system.erl" tag="%module" type="erl"></codeinclude>