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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>1996</year><year>2013</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
</legalnotice>
<title>slave</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
</header>
<module>slave</module>
<modulesummary>Functions to Starting and Controlling Slave Nodes</modulesummary>
<description>
<p>This module provides functions for starting Erlang slave nodes.
All slave nodes which are started by a master will terminate
automatically when the master terminates. All TTY output produced
at the slave will be sent back to the master node. File I/O is
done via the master.</p>
<p>Slave nodes on other hosts than the current one are started with
the program <c>rsh</c>. The user must be allowed to <c>rsh</c> to
the remote hosts without being prompted for a password. This can
be arranged in a number of ways (refer to the <c>rsh</c>
documentation for details). A slave node started on the same host
as the master inherits certain environment values from the master,
such as the current directory and the environment variables. For
what can be assumed about the environment when a slave is started
on another host, read the documentation for the <c>rsh</c>
program.</p>
<p>An alternative to the <c>rsh</c> program can be specified on
the command line to <c>erl</c> as follows: <c>-rsh Program</c>.</p>
<p>The slave node should use the same file system at the master. At
least, Erlang/OTP should be installed in the same place on both
computers and the same version of Erlang should be used.</p>
<p>Currently, a node running on Windows NT can only start slave
nodes on the host on which it is running.</p>
<p>The master node must be alive.</p>
</description>
<funcs>
<func>
<name name="start" arity="1"/>
<name name="start" arity="2"/>
<name name="start" arity="3"/>
<fsummary>Start a slave node on a host</fsummary>
<desc>
<p>Starts a slave node on the host <c><anno>Host</anno></c>. Host names need
not necessarily be specified as fully qualified names; short
names can also be used. This is the same condition that
applies to names of distributed Erlang nodes.</p>
<p>The name of the started node will be <c><anno>Name</anno>@<anno>Host</anno></c>. If no
name is provided, the name will be the same as the node which
executes the call (with the exception of the host name part of
the node name).</p>
<p>The slave node resets its <c>user</c> process so that all
terminal I/O which is produced at the slave is automatically
relayed to the master. Also, the file process will be relayed
to the master.</p>
<p>The <c><anno>Args</anno></c> argument is used to set <c>erl</c> command
line arguments. If provided, it is passed to the new node and
can be used for a variety of purposes. See
<seealso marker="erts:erl#erl">erl(1)</seealso></p>
<p>As an example, suppose that we want to start a slave node at
host <c>H</c> with the node name <c>Name@H</c>, and we also
want the slave node to have the following properties:</p>
<list type="bulleted">
<item>
<p>directory <c>Dir</c> should be added to the code path;</p>
</item>
<item>
<p>the Mnesia directory should be set to <c>M</c>;</p>
</item>
<item>
<p>the unix <c>DISPLAY</c> environment variable should be
set to the display of the master node.</p>
</item>
</list>
<p>The following code is executed to achieve this:</p>
<code type="none">
E = " -env DISPLAY " ++ net_adm:localhost() ++ ":0 ",
Arg = "-mnesia_dir " ++ M ++ " -pa " ++ Dir ++ E,
slave:start(H, Name, Arg).</code>
<p>If successful, the function returns <c>{ok, <anno>Node</anno>}</c>,
where <c><anno>Node</anno></c> is the name of the new node. Otherwise it
returns <c>{error, <anno>Reason</anno>}</c>, where <c><anno>Reason</anno></c> can be
one of:</p>
<taglist>
<tag><c>timeout</c></tag>
<item>
<p>The master node failed to get in contact with the slave
node. This can happen in a number of circumstances:</p>
<list type="bulleted">
<item>Erlang/OTP is not installed on the remote host</item>
<item>the file system on the other host has a different
structure to the the master</item>
<item>the Erlang nodes have different cookies.</item>
</list>
</item>
<tag><c>no_rsh</c></tag>
<item>
<p>There is no <c>rsh</c> program on the computer.</p>
</item>
<tag><c>{already_running, <anno>Node</anno>}</c></tag>
<item>
<p>A node with the name <c><anno>Name</anno>@<anno>Host</anno></c> already exists.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name name="start_link" arity="1"/>
<name name="start_link" arity="2"/>
<name name="start_link" arity="3"/>
<fsummary>Start and link to a slave node on a host</fsummary>
<desc>
<p>Starts a slave node in the same way as <c>start/1,2,3</c>,
except that the slave node is linked to the currently
executing process. If that process terminates, the slave node
also terminates.</p>
<p>See <c>start/1,2,3</c> for a description of arguments and
return values.</p>
</desc>
</func>
<func>
<name name="stop" arity="1"/>
<fsummary>Stop (kill) a node</fsummary>
<desc>
<p>Stops (kills) a node.</p>
</desc>
</func>
<func>
<name>pseudo([Master | ServerList]) -> ok</name>
<fsummary>Start a number of pseudo servers</fsummary>
<type>
<v>Master = node()</v>
<v>ServerList = [atom()]</v>
</type>
<desc>
<p>Calls <c>pseudo(Master, ServerList)</c>. If we want to start
a node from the command line and set up a number of pseudo
servers, an Erlang runtime system can be started as
follows:</p>
<pre>
% erl -name abc -s slave pseudo klacke@super x --</pre>
</desc>
</func>
<func>
<name name="pseudo" arity="2"/>
<fsummary>Start a number of pseudo servers</fsummary>
<desc>
<p>Starts a number of pseudo servers. A pseudo server is a
server with a registered name which does absolutely nothing
but pass on all message to the real server which executes at a
master node. A pseudo server is an intermediary which only has
the same registered name as the real server.</p>
<p>For example, if we have started a slave node <c>N</c> and
want to execute <c>pxw</c> graphics code on this node, we can
start the server <c>pxw_server</c> as a pseudo server at
the slave node. The following code illustrates:</p>
<code type="none">
rpc:call(N, slave, pseudo, [node(), [pxw_server]]).</code>
</desc>
</func>
<func>
<name name="relay" arity="1"/>
<fsummary>Run a pseudo server</fsummary>
<desc>
<p>Runs a pseudo server. This function never returns any value
and the process which executes the function will receive
messages. All messages received will simply be passed on to
<c><anno>Pid</anno></c>.</p>
</desc>
</func>
</funcs>
</erlref>
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