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NAME
slave - Functions for starting and controlling slave nodes.
DESCRIPTION
This module provides functions for starting Erlang slave nodes. All slave nodes that are
started by a master terminate automatically when the master terminates. All terminal
output produced at the slave is sent back to the master node. File I/O is done through the
master.
Slave nodes on other hosts than the current one are started with the ssh program. The user
must be allowed to ssh to the remote hosts without being prompted for a password. This can
be arranged in a number of ways (for details, see the ssh documentation). 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, see the
documentation for the ssh program.
An alternative to the ssh program can be specified on the command line to erl(1) as
follows:
-rsh Program
Note that the command specified with the -rsh flag is treated as a file name which may
contain spaces. It is thus not possible to include any command line options. The remote
node will be launched as "$RSH" "$REMOTE_HOSTNAME" erl -detached -noinput ..., so the erl
command must be found in the path on the remote host.
The slave node is to use the same file system at the master. At least, Erlang/OTP is to be
installed in the same place on both computers and the same version of Erlang is to be
used.
A node running on Windows can only start slave nodes on the host on which it is running.
The master node must be alive.
EXPORTS
pseudo([Master | ServerList]) -> ok
Types:
Master = node()
ServerList = [atom()]
Calls pseudo(Master, ServerList). If you 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:
% erl -name abc -s slave pseudo klacke@super x --
pseudo(Master, ServerList) -> ok
Types:
Master = node()
ServerList = [atom()]
Starts a number of pseudo servers. A pseudo server is a server with a registered
name that does nothing but pass on all message to the real server that executes at
a master node. A pseudo server is an intermediary that only has the same registered
name as the real server.
For example, if you have started a slave node N and want to execute pxw graphics
code on this node, you can start server pxw_server as a pseudo server at the slave
node. This is illustrated as follows:
rpc:call(N, slave, pseudo, [node(), [pxw_server]]).
relay(Pid) -> no_return()
Types:
Pid = pid()
Runs a pseudo server. This function never returns any value and the process that
executes the function receives messages. All messages received are simply passed on
to Pid.
start(Host) -> {ok, Node} | {error, Reason}
start(Host, Name) -> {ok, Node} | {error, Reason}
start(Host, Name, Args) -> {ok, Node} | {error, Reason}
Types:
Host = inet:hostname()
Name = atom() | string()
Args = string()
Node = node()
Reason = timeout | no_rsh | {already_running, Node}
Starts a slave node on host Host. 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.
The name of the started node becomes Name@Host. If no name is provided, the name
becomes the same as the node that executes the call (except the host name part of
the node name).
The slave node resets its user process so that all terminal I/O that is produced at
the slave is automatically relayed to the master. Also, the file process is relayed
to the master.
Argument Args is used to set erl command-line arguments. If provided, it is passed
to the new node and can be used for a variety of purposes; see erl(1).
As an example, suppose that you want to start a slave node at host H with node name
Name@H and want the slave node to have the following properties:
* Directory Dir is to be added to the code path.
* The Mnesia directory is to be set to M.
* The Unix DISPLAY environment variable is to be set to the display of the master
node.
The following code is executed to achieve this:
E = " -env DISPLAY " ++ net_adm:localhost() ++ ":0 ",
Arg = "-mnesia_dir " ++ M ++ " -pa " ++ Dir ++ E,
slave:start(H, Name, Arg).
The function returns {ok, Node}, where Node is the name of the new node, otherwise
{error, Reason}, where Reason can be one of:
timeout:
The master node failed to get in contact with the slave node. This can occur in
a number of circumstances:
* Erlang/OTP is not installed on the remote host.
* The file system on the other host has a different structure to the the
master.
* The Erlang nodes have different cookies.
no_rsh:
No remote shell program was found on the computer. Note that ssh is used by
default, but this can be overridden with the -rsh flag.
{already_running, Node}:
A node with name Name@Host already exists.
start_link(Host) -> {ok, Node} | {error, Reason}
start_link(Host, Name) -> {ok, Node} | {error, Reason}
start_link(Host, Name, Args) -> {ok, Node} | {error, Reason}
Types:
Host = inet:hostname()
Name = atom() | string()
Args = string()
Node = node()
Reason = timeout | no_rsh | {already_running, Node}
Starts a slave node in the same way as start/1,2,3, except that the slave node is
linked to the currently executing process. If that process terminates, the slave
node also terminates.
For a description of arguments and return values, see start/1,2,3.
stop(Node) -> ok
Types:
Node = node()
Stops (kills) a node.