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error_logger(3erl) | Erlang Module Definition | error_logger(3erl) |
NAME¶
error_logger - Erlang Error LoggerDESCRIPTION¶
The Erlang error logger is an event manager (see OTP Design Principles and gen_event(3erl)), registered as error_logger. Error, warning and info events are sent to the error logger from the Erlang runtime system and the different Erlang/OTP applications. The events are, by default, logged to tty. Note that an event from a process P is logged at the node of the group leader of P. This means that log output is directed to the node from which a process was created, which not necessarily is the same node as where it is executing. Initially, error_logger only has a primitive event handler, which buffers and prints the raw event messages. During system startup, the application Kernel replaces this with a standard event handler, by default one which writes nicely formatted output to tty. Kernel can also be configured so that events are logged to file instead, or not logged at all, see kernel(7). Also the SASL application, if started, adds its own event handler, which by default writes supervisor, crash and progress reports to tty. See sasl(7). It is recommended that user defined applications should report errors through the error logger, in order to get uniform reports. User defined event handlers can be added to handle application specific events. ( add_report_handler/1,2). Also, there is a useful event handler in STDLIB for multi-file logging of events, see log_mf_h(3erl). Warning events was introduced in Erlang/OTP R9C. To retain backwards compatibility, these are by default tagged as errors, thus showing up as error reports in the logs. By using the command line flag +W <w | i>, they can instead be tagged as warnings or info. Tagging them as warnings may require rewriting existing user defined event handlers.DATA TYPES¶
report() = [{Tag :: term(), Data :: term()} | term()]| string()| term()
EXPORTS¶
error_msg(Format) -> ok
error_msg(Format, Data) -> ok
format(Format, Data) -> ok
Types:
Format = string()
Data = list()
Sends a standard error event to the error logger. The Format and
Data arguments are the same as the arguments of io:format/2. The
event is handled by the standard event handler.
1> error_logger:error_msg("An error occurred in ~p~n", [a_module]). =ERROR REPORT==== 11-Aug-2005::14:03:19 === An error occurred in a_module ok
Warning:
If called with bad arguments, this function can crash the standard event
handler, meaning no further events are logged. When in doubt, use
error_report/1 instead.
error_report(Report) -> ok
Types:
Report = report()
Sends a standard error report event to the error logger. The event is handled by
the standard event handler.
2> error_logger:error_report([{tag1,data1},a_term,{tag2,data}]). =ERROR REPORT==== 11-Aug-2005::13:45:41 === tag1: data1 a_term tag2: data ok 3> error_logger:error_report("Serious error in my module"). =ERROR REPORT==== 11-Aug-2005::13:45:49 === Serious error in my module ok
error_report(Type, Report) -> ok
Types:
Type = term()
Report = report()
Sends a user defined error report event to the error logger. An event handler to
handle the event is supposed to have been added. The event is ignored by the
standard event handler.
It is recommended that Report follows the same structure as for
error_report/1.
warning_map() -> Tag
Types:
Tag = error | warning | info
Returns the current mapping for warning events. Events sent using
warning_msg/1,2 or warning_report/1,2 are tagged as errors
(default), warnings or info, depending on the value of the command line flag
+W.
os$ erl Erlang (BEAM) emulator version 5.4.8 [hipe] [threads:0] [kernel-poll] Eshell V5.4.8 (abort with ^G) 1> error_logger:warning_map(). error 2> error_logger:warning_msg("Warnings tagged as: ~p~n", [error]). =ERROR REPORT==== 11-Aug-2005::15:31:23 === Warnings tagged as: error ok 3> User switch command --> q os$ erl +W w Erlang (BEAM) emulator version 5.4.8 [hipe] [threads:0] [kernel-poll] Eshell V5.4.8 (abort with ^G) 1> error_logger:warning_map(). warning 2> error_logger:warning_msg("Warnings tagged as: ~p~n", [warning]). =WARNING REPORT==== 11-Aug-2005::15:31:55 === Warnings tagged as: warning ok
warning_msg(Format) -> ok
warning_msg(Format, Data) -> ok
Types:
Format = string()
Data = list()
Sends a standard warning event to the error logger. The Format and
Data arguments are the same as the arguments of io:format/2. The
event is handled by the standard event handler. It is tagged either as an
error, warning or info, see warning_map/0.
Warning:
If called with bad arguments, this function can crash the standard event
handler, meaning no further events are logged. When in doubt, use
warning_report/1 instead.
warning_report(Report) -> ok
Types:
Report = report()
Sends a standard warning report event to the error logger. The event is handled
by the standard event handler. It is tagged either as an error, warning or
info, see warning_map/0.
warning_report(Type, Report) -> ok
Types:
Type = any()
Report = report()
Sends a user defined warning report event to the error logger. An event handler
to handle the event is supposed to have been added. The event is ignored by
the standard event handler. It is tagged either as an error, warning or info,
depending on the value of warning_map/0.
info_msg(Format) -> ok
info_msg(Format, Data) -> ok
Types:
Format = string()
Data = list()
Sends a standard information event to the error logger. The Format and
Data arguments are the same as the arguments of io:format/2. The
event is handled by the standard event handler.
1> error_logger:info_msg("Something happened in ~p~n", [a_module]). =INFO REPORT==== 11-Aug-2005::14:06:15 === Something happened in a_module ok
Warning:
If called with bad arguments, this function can crash the standard event
handler, meaning no further events are logged. When in doubt, use
info_report/1 instead.
info_report(Report) -> ok
Types:
Report = report()
Sends a standard information report event to the error logger. The event is
handled by the standard event handler.
2> error_logger:info_report([{tag1,data1},a_term,{tag2,data}]). =INFO REPORT==== 11-Aug-2005::13:55:09 === tag1: data1 a_term tag2: data ok 3> error_logger:info_report("Something strange happened"). =INFO REPORT==== 11-Aug-2005::13:55:36 === Something strange happened ok
info_report(Type, Report) -> ok
Types:
Type = any()
Report = report()
Sends a user defined information report event to the error logger. An event
handler to handle the event is supposed to have been added. The event is
ignored by the standard event handler.
It is recommended that Report follows the same structure as for
info_report/1.
add_report_handler(Handler) -> any()
add_report_handler(Handler, Args) -> Result
Types:
Handler = module()
Args = gen_event:handler_args()
Result = gen_event:add_handler_ret()
Adds a new event handler to the error logger. The event handler must be
implemented as a gen_event callback module, see gen_event(3erl).
Handler is typically the name of the callback module and Args is
an optional term (defaults to []) passed to the initialization callback
function Handler:init/1. The function returns ok if successful.
The event handler must be able to handle the events described
below.
delete_report_handler(Handler) -> Result
Types:
Handler = module()
Result = gen_event:del_handler_ret()
Deletes an event handler from the error logger by calling
gen_event:delete_handler(error_logger, Handler, []), see
gen_event(3erl).
tty(Flag) -> ok
Types:
Flag = boolean()
Enables ( Flag == true) or disables (Flag == false) printout of
standard events to the tty.
This is done by adding or deleting the standard event handler for output to tty,
thus calling this function overrides the value of the Kernel
error_logger configuration parameter.
logfile(Request :: {open, Filename}) -> ok | {error, OpenReason}
logfile(Request :: close) -> ok | {error, CloseReason}
logfile(Request :: filename) -> Filename | {error, FilenameReason}
Types:
Filename = file:name()
OpenReason = allready_have_logfile | open_error()
CloseReason = module_not_found
FilenameReason = no_log_file
open_error() = file:posix() | badarg | system_limit
Enables or disables printout of standard events to a file.
This is done by adding or deleting the standard event handler for output to
file, thus calling this function overrides the value of the Kernel
error_logger configuration parameter.
Enabling file logging can be used in combination with calling tty(false),
in order to have a silent system, where all standard events are logged to a
file only. There can only be one active log file at a time.
Request is one of:
- {open, Filename}:
- Opens the log file Filename. Returns ok if successful, or {error, allready_have_logfile} if logging to file is already enabled, or an error tuple if another error occurred. For example, if Filename could not be opened.
- close:
- Closes the current log file. Returns ok, or {error, module_not_found}.
- filename:
- Returns the name of the log file Filename, or {error, no_log_file} if logging to file is not enabled.
EVENTS¶
All event handlers added to the error logger must handle the following events. Gleader is the group leader pid of the process which sent the event, and Pid is the process which sent the event.- {error, Gleader, {Pid, Format, Data}}:
- Generated when error_msg/1,2 or format is called.
- {error_report, Gleader, {Pid, std_error, Report}}:
- Generated when error_report/1 is called.
- {error_report, Gleader, {Pid, Type, Report}}:
- Generated when error_report/2 is called.
- {warning_msg, Gleader, {Pid, Format, Data}}:
- Generated when warning_msg/1,2 is called, provided that warnings are set to be tagged as warnings.
- {warning_report, Gleader, {Pid, std_warning, Report}}:
- Generated when warning_report/1 is called, provided that warnings are set to be tagged as warnings.
- {warning_report, Gleader, {Pid, Type, Report}}:
- Generated when warning_report/2 is called, provided that warnings are set to be tagged as warnings.
- {info_msg, Gleader, {Pid, Format, Data}}:
- Generated when info_msg/1,2 is called.
- {info_report, Gleader, {Pid, std_info, Report}}:
- Generated when info_report/1 is called.
- {info_report, Gleader, {Pid, Type, Report}}:
- Generated when info_report/2 is called.
SEE ALSO¶
gen_event(3erl), log_mf_h(3erl), kernel(7), sasl(7)kernel 3.0.3 | Ericsson AB |