slave(3erl) Erlang Module Definition slave(3erl)
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 with-
out 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 vari-
ables. 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 "$RSH" "$RE-
MOTE_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 exe-
cute pxw graphics code on this node, you can start server
pxw_server as a pseudo server at the slave node. This is illus-
trated 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 necessar-
ily 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 pro-
vided, it is passed to the new node and can be used for a vari-
ety 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 struc-
ture 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.
Ericsson AB stdlib 3.13 slave(3erl)