slave
Functions to Starting and Controlling Slave Nodes
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.
Slave nodes on other hosts than the current one are started with
the program rsh
. The user must be allowed to rsh
to
the remote hosts without being prompted for a password. This can
be arranged in a number of ways (refer to the rsh
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 rsh
program.
An alternative to the rsh
program can be specified on
the command line to erl
as follows: -rsh Program
.
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.
Currently, a node running on Windows NT can only start slave nodes on the host on which it is running.
The master node must be alive.
Functions
start(Host) ->
start(Host, Name) ->
start(Host, Name, Args) -> {ok, Node} | {error, Reason}
Host = Name = atom()
Args = string()
Node = node()
Reason = timeout | no_rsh | {already_running, Node}
Starts a slave node on the 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 will be Name@Host
. 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).
The slave node resets its user
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.
The Args
argument 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 we want to start a slave node at
host H
with the node name Name@H
, and we also
want the slave node to have the following properties:
-
directory
Dir
should be added to the code path; -
the Mnesia directory should be set to
M
; -
the unix
DISPLAY
environment variable should 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).
If successful, the function returns {ok, Node}
,
where Node
is the name of the new node. Otherwise it
returns {error, Reason}
, where Reason
can be
one of:
timeout
-
The master node failed to get in contact with the slave node. This can happen 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
There is no rsh
program on the computer.
{already_running, Node}
A node with the name Name@Host
already exists.
start_link(Host) ->
start_link(Host, Name) ->
start_link(Host, Name, Args) -> {ok, Node} | {error, Reason}
Host = Name = atom()
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.
See start/1,2,3
for a description of arguments and
return values.
stop(Node) -> ok
Node = node()
Stops (kills) a node.
pseudo([Master | ServerList]) -> ok
Master = node()
ServerList = [atom()]
Calls pseudo(Master, ServerList)
. 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:
% erl -name abc -s slave pseudo klacke@super x --
pseudo(Master, ServerList) -> ok
Master = node()
ServerList = [atom()]
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.
For example, if we have started a slave node N
and
want to execute pxw
graphics code on this node, we can
start the server pxw_server
as a pseudo server at
the slave node. The following code illustrates:
rpc:call(N, slave, pseudo, [node(), [pxw_server]]).
relay(Pid)
Pid = pid()
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
Pid
.