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NAME
error_logger - Erlang error logger.
DESCRIPTION
Note:
In Erlang/OTP 21.0, a new API for logging was added. The old error_logger module can still
be used by legacy code, but log events are redirected to the new Logger API. New code
should use the Logger API directly.
error_logger is no longer started by default, but is automatically started when an event
handler is added with error_logger:add_report_handler/1,2. The error_logger module is then
also added as a handler to the new logger.
See logger(3erl) and the Logging chapter in the User's Guide for more information.
The Erlang error logger is an event manager (see OTP Design Principles and
gen_event(3erl)), registered as error_logger.
Error logger is no longer started by default, but is automatically started when an event
handler is added with add_report_handler/1,2. The error_logger module is then also added
as a handler to the new logger, causing log events to be forwarded from logger to error
logger, and consequently to all installed error logger event handlers.
User-defined event handlers can be added to handle application-specific events.
Existing event handlers provided by STDLIB and SASL are still available, but are no longer
used by OTP.
Warning events were introduced in Erlang/OTP R9C and are enabled by default as from
Erlang/OTP 18.0. To retain backwards compatibility with existing user-defined event
handlers, the warning events can be tagged as errors or info using command-line flag +W <e
| i | w>, thus showing up as ERROR REPORT or INFO REPORT in the logs.
DATA TYPES
report() =
[{Tag :: term(), Data :: term()} | term()] | string() | term()
EXPORTS
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 in this module, see section
Events.
The first time this function is called, error_logger is added as a Logger handler,
and the error_logger process is started.
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).
If no more event handlers exist after the deletion, error_logger is removed as a
Logger handler, and the error_logger process is stopped.
error_msg(Format) -> ok
error_msg(Format, Data) -> ok
format(Format, Data) -> ok
Types:
Format = string()
Data = list()
Log a standard error event. The Format and Data arguments are the same as the
arguments of io:format/2 in STDLIB.
Error logger forwards the event to Logger, including metadata that allows backwards
compatibility with legacy error logger event handlers.
The event is handled by the default Logger handler.
These functions are kept for backwards compatibility and must not be used by new
code. Use the ?LOG_ERROR macro or logger:error/1,2,3 instead.
Example:
1> error_logger:error_msg("An error occurred in ~p", [a_module]).
=ERROR REPORT==== 22-May-2018::11:18:43.376917 ===
An error occurred in a_module
ok
Warning:
If the Unicode translation modifier (t) is used in the format string, all event
handlers must ensure that the formatted output is correctly encoded for the I/O
device.
error_report(Report) -> ok
Types:
Report = report()
Log a standard error event. Error logger forwards the event to Logger, including
metadata that allows backwards compatibility with legacy error logger event
handlers.
The event is handled by the default Logger handler.
This functions is kept for backwards compatibility and must not be used by new
code. Use the ?LOG_ERROR macro or logger:error/1,2,3 instead.
Example:
2> error_logger:error_report([{tag1,data1},a_term,{tag2,data}]).
=ERROR REPORT==== 22-May-2018::11:24:23.699306 ===
tag1: data1
a_term
tag2: data
ok
3> error_logger:error_report("Serious error in my module").
=ERROR REPORT==== 22-May-2018::11:24:45.972445 ===
Serious error in my module
ok
error_report(Type, Report) -> ok
Types:
Type = term()
Report = report()
Log a user-defined error event. Error logger forwards the event to Logger,
including metadata that allows backwards compatibility with legacy error logger
event handlers.
Error logger also adds a domain field with value [Type] to this event's metadata,
causing the filters of the default Logger handler to discard the event. A different
Logger handler, or an error logger event handler, must be added to handle this
event.
It is recommended that Report follows the same structure as for error_report/1.
This functions is kept for backwards compatibility and must not be used by new
code. Use the ?LOG_ERROR macro or logger:error/1,2,3 instead.
get_format_depth() -> unlimited | integer() >= 1
Returns max(10, Depth), where Depth is the value of error_logger_format_depth in
the Kernel application, if Depth is an integer. Otherwise, unlimited is returned.
Note:
The error_logger_format_depth variable is deprecated since the Logger API was
introduced in Erlang/OTP 21.0. The variable, and this function, are kept for
backwards compatibility since they still might be used by legacy report handlers.
info_msg(Format) -> ok
info_msg(Format, Data) -> ok
Types:
Format = string()
Data = list()
Log a standard information event. The Format and Data arguments are the same as the
arguments of io:format/2 in STDLIB.
Error logger forwards the event to Logger, including metadata that allows backwards
compatibility with legacy error logger event handlers.
The event is handled by the default Logger handler.
These functions are kept for backwards compatibility and must not be used by new
code. Use the ?LOG_INFO macro or logger:info/1,2,3 instead.
Example:
1> error_logger:info_msg("Something happened in ~p", [a_module]).
=INFO REPORT==== 22-May-2018::12:03:32.612462 ===
Something happened in a_module
ok
Warning:
If the Unicode translation modifier (t) is used in the format string, all event
handlers must ensure that the formatted output is correctly encoded for the I/O
device.
info_report(Report) -> ok
Types:
Report = report()
Log a standard information event. Error logger forwards the event to Logger,
including metadata that allows backwards compatibility with legacy error logger
event handlers.
The event is handled by the default Logger handler.
This functions is kept for backwards compatibility and must not be used by new
code. Use the ?LOG_INFO macro or logger:info/1,2,3 instead.
Example:
2> error_logger:info_report([{tag1,data1},a_term,{tag2,data}]).
=INFO REPORT==== 22-May-2018::12:06:35.994440 ===
tag1: data1
a_term
tag2: data
ok
3> error_logger:info_report("Something strange happened").
=INFO REPORT==== 22-May-2018::12:06:49.066872 ===
Something strange happened
ok
info_report(Type, Report) -> ok
Types:
Type = any()
Report = report()
Log a user-defined information event. Error logger forwards the event to Logger,
including metadata that allows backwards compatibility with legacy error logger
event handlers.
Error logger also adds a domain field with value [Type] to this event's metadata,
causing the filters of the default Logger handler to discard the event. A different
Logger handler, or an error logger event handler, must be added to handle this
event.
It is recommended that Report follows the same structure as for info_report/1.
This functions is kept for backwards compatibility and must not be used by new
code. Use the ?LOG_INFO macro or logger:info/1,2,3 instead.
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 error_logger_file_h event handler, and thus
indirectly adding error_logger as a Logger handler.
Notice that this function does not manipulate the Logger configuration directly,
meaning that if the default Logger handler is already logging to a file, this
function can potentially cause logging to a second file.
This function is useful as a shortcut during development and testing, but must not
be used in a production system. See section Logging in the Kernel User's Guide, and
the logger(3erl) manual page for information about how to configure Logger for live
systems.
Request is one of the following:
{open, Filename}:
Opens 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 cannot be opened). The file
is opened with encoding UTF-8.
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.
tty(Flag) -> ok
Types:
Flag = boolean()
Enables (Flag == true) or disables (Flag == false) printout of standard events to
the terminal.
This is done by manipulating the Logger configuration. The function is useful as a
shortcut during development and testing, but must not be used in a production
system. See section Logging in the Kernel User's Guide, and the logger(3erl) manual
page for information about how to configure Logger for live systems.
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, warnings (default), or info, depending
on the value of command-line flag +W.
Example:
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().
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
3>
User switch command
--> q
os$ erl +W e
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
warning_msg(Format) -> ok
warning_msg(Format, Data) -> ok
Types:
Format = string()
Data = list()
Log a standard warning event. The Format and Data arguments are the same as the
arguments of io:format/2 in STDLIB.
Error logger forwards the event to Logger, including metadata that allows backwards
compatibility with legacy error logger event handlers.
The event is handled by the default Logger handler. The log level can be changed to
error or info, see warning_map/0.
These functions are kept for backwards compatibility and must not be used by new
code. Use the ?LOG_WARNING macro or logger:warning/1,2,3 instead.
Warning:
If the Unicode translation modifier (t) is used in the format string, all event
handlers must ensure that the formatted output is correctly encoded for the I/O
device.
warning_report(Report) -> ok
Types:
Report = report()
Log a standard warning event. Error logger forwards the event to Logger, including
metadata that allows backwards compatibility with legacy error logger event
handlers.
The event is handled by the default Logger handler. The log level can be changed to
error or info, see warning_map/0.
This functions is kept for backwards compatibility and must not be used by new
code. Use the ?LOG_WARNING macro or logger:warning/1,2,3 instead.
warning_report(Type, Report) -> ok
Types:
Type = any()
Report = report()
Log a user-defined warning event. Error logger forwards the event to Logger,
including metadata that allows backwards compatibility with legacy error logger
event handlers.
Error logger also adds a domain field with value [Type] to this event's metadata,
causing the filters of the default Logger handler to discard the event. A different
Logger handler, or an error logger event handler, must be added to handle this
event.
The log level can be changed to error or info, see warning_map/0.
It is recommended that Report follows the same structure as for warning_report/1.
This functions is kept for backwards compatibility and must not be used by new
code. Use the ?LOG_WARNING macro or logger:warning/1,2,3 instead.
EVENTS
All event handlers added to the error logger must handle the following events. Gleader is
the group leader pid of the process that sent the event, and Pid is the process that 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 if warnings are set to be tagged as warnings.
{warning_report, Gleader, {Pid, std_warning, Report}}:
Generated when warning_report/1 is called if warnings are set to be tagged as
warnings.
{warning_report, Gleader, {Pid, Type, Report}}:
Generated when warning_report/2 is called if 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.
Notice that some system-internal events can also be received. Therefore a catch-all clause
last in the definition of the event handler callback function Module:handle_event/2 is
necessary. This also applies for Module:handle_info/2, as the event handler must also take
care of some system-internal messages.
SEE ALSO
gen_event(3erl), logger(3erl), log_mf_h(3erl), kernel(7), sasl(7)