kernel

APPLICATION

kernel

APPLICATION SUMMARY

The Kernel Application

DESCRIPTION

The Kernel application is the first application started, and it is one of two mandatory applications. The Kernel application contains the following services:

• application_controller
  


• auth
  


• code
  


• disk_log
  


• erl_boot_server
  


• erl_ddll
  


• error_logger
  


• file
  


• global_group
  


• global_name_server
  


• net_kernel
  


• os
  


• rpc
  


• pg2
  


• timer
  


• user
  



It is possible to synchronize a set of Erlang nodes. One can specify for a node to wait a specified amount of time for other nodes to become alive.

Error Logger Event Handlers

Two error logger event handlers are defined in the Kernel application. These are described in error_logger(3).

Configuration

The following configuration parameters are defined for the Kernel application. See application(3) for more information about configuration parameters.

distributed = [Distrib] <optional>

Specifies which applications are distributed and on which nodes they may execute. In this parameter:


• Distrib = {ApplName, Nodes} | {ApplName, Time, Nodes}
  


• ApplName = atom()
  


• Time = integer() > 0
  


• Nodes = [node() | {node(), ..., node()}]
  



These parameters are described in application(3).


dist_auto_connect = Value <optional>

Specifies when nodes will be automatically connected. If this parameter is not specified, a node is always automatically connected, e.g when a message is to be sent to that node. Value is one of:


never

Connections are never automatically connected, they must be explicitly connected. See net_kernel(3).


once

Connections will be established automatically, but only once per node. If a node goes down, it must thereafter be explicitly connected. See net_kernel(3).


permissions = [Perm] <optional>

Specifies the default permission for applications when they are started. In this parameter:


• Perm = {ApplName, Bool}
  


• ApplName = atom()
  


• Bool = boolean()
  



error_logger = Value <optional>

Value is one of:


tty

All standard error reports are written to stdio. This is the default option.


{file, FileName}

All standard error reports are written to the file FileName, where FileName is a string.


false

No error logger handler is installed.


global_groups = [GroupTuple] <optional>

Specifies the groups of nodes which will have their own global name space. In this parameter:


• GroupTuple = {GroupName, [Node]} | {GroupName, PublishType, [Node]}
  


• GroupName = atom()
  


• PublishType = atom()
  


• Node = atom()
  



These parameters are described in global_group(3).


inet_parse_error_log = LogMode <optional>

LogMode is one of:


silent

No error_logger messages are generated when erroneous lines are found and skipped in the various configuration files. The default if the variable is not set is that erroneous lines are reported via the error_logger.





net_ticktime = TickTime <optional>

Specifies the net_kernel tick time. TickTime is given in seconds. Once every TickTime / 4 second, all connected nodes are ticked (if anything else has been written to a node) and if nothing has been received from another node within the last four (4) tick times that node is considered to be down. This ensures that nodes which are not responding, for reasons such as hardware errors, are considered to be down.
The time T, in which a node that is not responding is detected, is calculated as: MinT < T < MaxT where


MinT = TickTime - TickTime / 4
MaxT = TickTime + TickTime / 4
        

TickTime is by default 60 (seconds). Thus, 45 < T < 75 seconds.
Note:All communicating nodes should have the same TickTime value specified.
Note: Normally, a terminating node is detected immediately.


sync_nodes_mandatory = [NodeName] <optional>

Specifies which other nodes must be alive in order for this node to start properly. If some node in this list does not start within the specified time, this node will not start either. If this parameter is undefined, it defaults to the empty list.



sync_nodes_optional = [NodeName] <optional>

Specifies which other nodes can be alive in order for this node to start properly. If some node in this list does not start within the specified time, this node starts anyway. If this parameter is undefined, it defaults to the empty list.



sync_nodes_timeout = integer() | infinity <optional>

Specifies the amount of time (in milliseconds) this node will wait for the mandatory and optional nodes to start. If this parameter is undefined, no node synchronization is performed. This option also makes sure that global is synchronized.


start_ddll = true | false <optional>

Starts the ddll_server if the parameter is true (see erl_ddll(3)). This parameter should be set to true in an embedded system which uses this service.
The default value is false.


start_dist_ac = true | false <optional>

Starts the dist_ac server if the parameter is true (see application(3)). This parameter should be set to true for systems that use distributed applications.
The default value is false. If this parameter is undefined, the server is started if the parameter distributed is set.


start_boot_server = true | false <optional>

Starts the boot_server if the parameter is true (see erl_boot_server(3)). This parameter should be set to true in an embedded system which uses this service.
The default value is false.


boot_server_slaves = [SlaveIP] <optional>

If the start_boot_server configuration parameter is true, this parameter can be used to initialize boot_server with a list of slave IP addresses. SlaveIP = string() | atom | { integer(),integer(),integer(),integer()}
where 0 <= integer() <=255.
Examples of SlaveIP in atom, string and tuple form are:
'150.236.16.70', "150,236,16,70", {150,236,16,70}.
The default value is [].


start_disk_log = true | false <optional>

Starts the disk_log_server if the parameter is true (see disk_log(3)). This parameter should be set to true in an embedded system which uses this service.
The default value is false.


start_pg2 = true | false <optional>

Starts the pg2 server (see pg2(3)) if the parameter is true. This parameter should be set to true in an embedded system which uses this service.
The default value is false.


start_timer = true | false <optional>

Starts the timer_server if the parameter is true (see timer(3)). This parameter should be set to true in an embedded system which uses this service.
The default value is false.


keep_zombies = integer() <optional>

Sets the value of the system flag keep_zombies.
The default value is 0.


shutdown_func = {Mod,Func} <optional>

Where:


• Mod = atom()
  


• Func = atom()
  



Sets a function that application_controller calls when it starts to terminate. The function is called as: Mod:Func(Reason), where Reason is the terminate reason for application_controller, and it must return as soon as possible for application_controller to terminate properly.

See Also

application(3), auth(3), code(3), disk_log(3), erl_ddll(3), erl_boot_server(3), error_logger(3), file(3), global(3), global_group(3), net_kernel(3), pg2(3), rpc(3), timer(3), user(3)

AUTHORS

Martin Björklund - support@erlang.ericsson.se
Magnus Fröberg - support@erlang.ericsson.se