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<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>1996</year><year>2018</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
</legalnotice>
<title>error_logger</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
</header>
<module>error_logger</module>
<modulesummary>Erlang error logger.</modulesummary>
<description>
<note>
<p>In Erlang/OTP 21.0, a new API for logging was added. The
old <c>error_logger</c> 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.</p>
<p><c>error_logger</c> is no longer started by default, but is
automatically started when an event handler is added
with <c>error_logger:add_report_handler/1,2</c>. The <c>error_logger</c>
module is then also added as a handler to the new logger.</p>
<p>See <seealso marker="logger"><c>logger(3)</c></seealso> and
the <seealso marker="logger_chapter">Logging</seealso> chapter
in the User's Guide for more information.</p>
</note>
<p>The Erlang <em>error logger</em> is an event manager (see
<seealso marker="doc/design_principles:des_princ">OTP Design Principles</seealso> and
<seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>),
registered as <c>error_logger</c>.</p>
<p>Error logger is no longer started by default, but is
automatically started when an event handler is added
with <seealso marker="#add_report_handler/1">
<c>add_report_handler/1,2</c></seealso>. The <c>error_logger</c>
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.</p>
<p>User-defined event handlers can be added to handle application-specific
events.</p>
<p>Existing event handlers provided by STDLIB and SASL are still
available, but are no longer used by OTP.</p>
<p>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 <c>errors</c> or <c>info</c> using command-line flag
<c><![CDATA[+W <e | i | w>]]></c>, thus showing up as
<c>ERROR REPORT</c> or <c>INFO REPORT</c> in the logs.</p>
</description>
<datatypes>
<datatype>
<name name="report"/>
</datatype>
</datatypes>
<funcs>
<func>
<name name="add_report_handler" arity="1"/>
<name name="add_report_handler" arity="2"/>
<fsummary>Add an event handler to the error logger.</fsummary>
<desc>
<p>Adds a new event handler to the error logger. The event
handler must be implemented as a <c>gen_event</c> callback
module, see
<seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>.</p>
<p><c><anno>Handler</anno></c> is typically the name of the callback module
and <c><anno>Args</anno></c> is an optional term (defaults to []) passed
to the initialization callback function <c><anno>Handler</anno>:init/1</c>.
The function returns <c>ok</c> if successful.</p>
<p>The event handler must be able to handle the events in this module, see
section <seealso marker="#events">Events</seealso>.</p>
<p>The first time this function is called,
<c>error_logger</c> is added as a Logger handler, and
the <c>error_logger</c> process is started.</p>
</desc>
</func>
<func>
<name name="delete_report_handler" arity="1"/>
<fsummary>Delete an event handler from the error logger.</fsummary>
<desc>
<p>Deletes an event handler from the error logger by calling
<c>gen_event:delete_handler(error_logger, <anno>Handler</anno>, [])</c>,
see <seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>.</p>
<p>If no more event handlers exist after the deletion,
<c>error_logger</c> is removed as a Logger handler, and
the <c>error_logger</c> process is stopped.</p>
</desc>
</func>
<func>
<name name="error_msg" arity="1"/>
<name name="error_msg" arity="2"/>
<name name="format" arity="2"/>
<fsummary>Log a standard error event.</fsummary>
<desc>
<p>Log a standard error event. The <c><anno>Format</anno></c>
and <c><anno>Data</anno></c> arguments are the same as the
arguments of
<seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
in STDLIB.</p>
<p>Error logger forwards the event to Logger, including
metadata that allows backwards compatibility with legacy
error logger event handlers.</p>
<p>The event is handled by the default Logger handler.</p>
<p>These functions are kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_ERROR</c></seealso> macro or
<seealso marker="logger#error-1"><c>logger:error/1,2,3</c></seealso>
instead.</p>
<p><em>Example:</em></p>
<pre>
1> <input>error_logger:error_msg("An error occurred in ~p", [a_module]).</input>
=ERROR REPORT==== 22-May-2018::11:18:43.376917 ===
An error occurred in a_module
ok</pre>
<warning>
<p>If the Unicode translation modifier (<c>t</c>) is used in
the format string, all event handlers must ensure that the
formatted output is correctly encoded for the I/O
device.</p>
</warning>
</desc>
</func>
<func>
<name name="error_report" arity="1"/>
<fsummary>Log a standard error event.</fsummary>
<desc>
<p>Log a standard error event. Error logger forwards the event
to Logger, including metadata that allows backwards
compatibility with legacy error logger event handlers.</p>
<p>The event is handled by the default Logger handler.</p>
<p>This functions is kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_ERROR</c></seealso> macro or
<seealso marker="logger#error-1"><c>logger:error/1,2,3</c></seealso>
instead.</p>
<p><em>Example:</em></p>
<pre>
2> <input>error_logger:error_report([{tag1,data1},a_term,{tag2,data}]).</input>
=ERROR REPORT==== 22-May-2018::11:24:23.699306 ===
tag1: data1
a_term
tag2: data
ok
3> <input>error_logger:error_report("Serious error in my module").</input>
=ERROR REPORT==== 22-May-2018::11:24:45.972445 ===
Serious error in my module
ok</pre>
</desc>
</func>
<func>
<name name="error_report" arity="2"/>
<fsummary>Log a user-defined error event.</fsummary>
<desc>
<p>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.</p>
<p>Error logger also adds a <c>domain</c> field with
value <c>[<anno>Type</anno>]</c> 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.</p>
<p>It is recommended that <c><anno>Report</anno></c> follows the same
structure as for
<seealso marker="#error_report/1"><c>error_report/1</c></seealso>.</p>
<p>This functions is kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_ERROR</c></seealso> macro or
<seealso marker="logger#error-1"><c>logger:error/1,2,3</c></seealso>
instead.</p>
</desc>
</func>
<func>
<name name="get_format_depth" arity="0" since="OTP 20.0"/>
<fsummary>Get the value of the Kernel application variable
<c>error_logger_format_depth</c>.</fsummary>
<desc>
<p>Returns <c>max(10, Depth)</c>, where <c>Depth</c> is the
value of <c>error_logger_format_depth</c>
in the Kernel application, if Depth is an integer. Otherwise,
<c>unlimited</c> is returned.</p>
<note>
<p>The <c>error_logger_format_depth</c> variable
is <seealso marker="kernel_app#deprecated-configuration-parameters">
deprecated</seealso> since
the <seealso marker="logger">Logger API</seealso> 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.</p>
</note>
</desc>
</func>
<func>
<name name="info_msg" arity="1"/>
<name name="info_msg" arity="2"/>
<fsummary>Log a standard information event.</fsummary>
<desc>
<p>Log a standard information event. The <c><anno>Format</anno></c>
and <c><anno>Data</anno></c> arguments are the same as the
arguments of
<seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
in STDLIB.</p>
<p>Error logger forwards the event to Logger, including
metadata that allows backwards compatibility with legacy
error logger event handlers.</p>
<p>The event is handled by the default Logger handler.</p>
<p>These functions are kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_INFO</c></seealso> macro or
<seealso marker="logger#info-1"><c>logger:info/1,2,3</c></seealso>
instead.</p>
<p><em>Example:</em></p>
<pre>
1> <input>error_logger:info_msg("Something happened in ~p", [a_module]).</input>
=INFO REPORT==== 22-May-2018::12:03:32.612462 ===
Something happened in a_module
ok</pre>
<warning>
<p>If the Unicode translation modifier (<c>t</c>) is used in
the format string, all event handlers must ensure that the
formatted output is correctly encoded for the I/O
device.</p>
</warning>
</desc>
</func>
<func>
<name name="info_report" arity="1"/>
<fsummary>Log a standard information event.</fsummary>
<desc>
<p>Log a standard information event. Error logger forwards the
event to Logger, including metadata that allows backwards
compatibility with legacy error logger event handlers.</p>
<p>The event is handled by the default Logger handler.</p>
<p>This functions is kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_INFO</c></seealso> macro or
<seealso marker="logger#info-1"><c>logger:info/1,2,3</c></seealso>
instead.</p>
<p><em>Example:</em></p>
<pre>
2> <input>error_logger:info_report([{tag1,data1},a_term,{tag2,data}]).</input>
=INFO REPORT==== 22-May-2018::12:06:35.994440 ===
tag1: data1
a_term
tag2: data
ok
3> <input>error_logger:info_report("Something strange happened").</input>
=INFO REPORT==== 22-May-2018::12:06:49.066872 ===
Something strange happened
ok</pre>
</desc>
</func>
<func>
<name name="info_report" arity="2"/>
<fsummary>Log a user-defined information event.</fsummary>
<desc>
<p>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.</p>
<p>Error logger also adds a <c>domain</c> field with
value <c>[<anno>Type</anno>]</c> 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.</p>
<p>It is recommended that <c><anno>Report</anno></c> follows the same
structure as for
<seealso marker="#info_report/1"><c>info_report/1</c></seealso>.</p>
<p>This functions is kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_INFO</c></seealso> macro or
<seealso marker="logger#info-1"><c>logger:info/1,2,3</c></seealso>
instead.</p>
</desc>
</func>
<func>
<name name="logfile" arity="1" clause_i="1"/>
<name name="logfile" arity="1" clause_i="2"/>
<name name="logfile" arity="1" clause_i="3"/>
<fsummary>Enable or disable error printouts to a file.</fsummary>
<type variable="Filename"/>
<type variable="OpenReason" name_i="1"/>
<type variable="CloseReason" name_i="2"/>
<type variable="FilenameReason" name_i="3"/>
<type name="open_error"/>
<desc>
<p>Enables or disables printout of standard events to a file.</p>
<p>This is done by adding or deleting
the <c>error_logger_file_h</c> event handler, and thus
indirectly adding <c>error_logger</c> as a Logger
handler.</p>
<p>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.</p>
<p>This function is useful as a shortcut during development
and testing, but must not be used in a production
system. See
section <seealso marker="logger_chapter">Logging</seealso>
in the Kernel User's Guide, and
the <seealso marker="logger"><c>logger(3)</c></seealso>
manual page for information about how to configure Logger
for live systems.</p>
<p><c>Request</c> is one of the following:</p>
<taglist>
<tag><c>{open, <anno>Filename</anno>}</c></tag>
<item>
<p>Opens log file <c><anno>Filename</anno></c>. Returns <c>ok</c> if
successful, or <c>{error, allready_have_logfile}</c> if
logging to file is already enabled, or an error tuple if
another error occurred (for example, if <c><anno>Filename</anno></c>
cannot be opened). The file is opened with encoding UTF-8.</p>
</item>
<tag><c>close</c></tag>
<item>
<p>Closes the current log file. Returns <c>ok</c>, or
<c>{error, module_not_found}</c>.</p>
</item>
<tag><c>filename</c></tag>
<item>
<p>Returns the name of the log file <c><anno>Filename</anno></c>, or
<c>{error, no_log_file}</c> if logging to file is not
enabled.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name name="tty" arity="1"/>
<fsummary>Enable or disable printouts to the terminal.</fsummary>
<desc>
<p>Enables (<c><anno>Flag</anno> == true</c>) or disables
(<c><anno>Flag</anno> == false</c>) printout of standard events
to the terminal.</p>
<p>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 <seealso marker="logger_chapter">Logging</seealso>
in the Kernel User's Guide, and
the <seealso marker="logger"><c>logger(3)</c></seealso>
manual page for information about how to configure Logger
for live systems.</p>
</desc>
</func>
<func>
<name name="warning_map" arity="0"/>
<fsummary>Return the current mapping for warning events.</fsummary>
<desc>
<p>Returns the current mapping for warning events. Events sent
using <c>warning_msg/1,2</c> or <c>warning_report/1,2</c>
are tagged as errors, warnings (default), or info, depending
on the value of command-line flag <c>+W</c>.</p>
<p><em>Example:</em></p>
<pre>
os$ <input>erl</input>
Erlang (BEAM) emulator version 5.4.8 [hipe] [threads:0] [kernel-poll]
Eshell V5.4.8 (abort with ^G)
1> <input>error_logger:warning_map().</input>
warning
2> <input>error_logger:warning_msg("Warnings tagged as: ~p~n", [warning]).</input>
=WARNING REPORT==== 11-Aug-2005::15:31:55 ===
Warnings tagged as: warning
ok
3>
User switch command
--> q
os$ <input>erl +W e</input>
Erlang (BEAM) emulator version 5.4.8 [hipe] [threads:0] [kernel-poll]
Eshell V5.4.8 (abort with ^G)
1> <input>error_logger:warning_map().</input>
error
2> <input>error_logger:warning_msg("Warnings tagged as: ~p~n", [error]).</input>
=ERROR REPORT==== 11-Aug-2005::15:31:23 ===
Warnings tagged as: error
ok</pre>
</desc>
</func>
<func>
<name name="warning_msg" arity="1"/>
<name name="warning_msg" arity="2"/>
<fsummary>Log a standard warning event.</fsummary>
<desc>
<p>Log a standard warning event. The <c><anno>Format</anno></c>
and <c><anno>Data</anno></c> arguments are the same as the
arguments of
<seealso marker="stdlib:io#format/2"><c>io:format/2</c></seealso>
in STDLIB.</p>
<p>Error logger forwards the event to Logger, including
metadata that allows backwards compatibility with legacy
error logger event handlers.</p>
<p>The event is handled by the default Logger handler. The log
level can be changed to error or info, see
<seealso marker="#warning_map/0"><c>warning_map/0</c></seealso>.</p>
<p>These functions are kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_WARNING</c></seealso> macro or
<seealso marker="logger#warning-1"><c>logger:warning/1,2,3</c></seealso>
instead.</p>
<warning>
<p>If the Unicode translation modifier (<c>t</c>) is used in
the format string, all event handlers must ensure that the
formatted output is correctly encoded for the I/O
device.</p>
</warning>
</desc>
</func>
<func>
<name name="warning_report" arity="1"/>
<fsummary>Log a standard warning event.</fsummary>
<desc>
<p>Log a standard warning event. Error logger forwards the event
to Logger, including metadata that allows backwards
compatibility with legacy error logger event handlers.</p>
<p>The event is handled by the default Logger handler. The log
level can be changed to error or info, see
<seealso marker="#warning_map/0"><c>warning_map/0</c></seealso>.</p>
<p>This functions is kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_WARNING</c></seealso> macro or
<seealso marker="logger#warning-1"><c>logger:warning/1,2,3</c></seealso>
instead.</p>
</desc>
</func>
<func>
<name name="warning_report" arity="2"/>
<fsummary>Log a user-defined warning event.</fsummary>
<desc>
<p>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.</p>
<p>Error logger also adds a <c>domain</c> field with
value <c>[<anno>Type</anno>]</c> 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.</p>
<p>The log level can be changed to error or info, see
<seealso marker="#warning_map/0"><c>warning_map/0</c></seealso>.</p>
<p>It is recommended that <c><anno>Report</anno></c> follows the same
structure as for
<seealso marker="#warning_report/1"><c>warning_report/1</c></seealso>.</p>
<p>This functions is kept for backwards compatibility and
must not be used by new code. Use the <seealso marker="logger#macros">
<c>?LOG_WARNING</c></seealso> macro or
<seealso marker="logger#warning-1"><c>logger:warning/1,2,3</c></seealso>
instead.</p>
</desc>
</func>
</funcs>
<section>
<marker id="events"></marker>
<title>Events</title>
<p>All event handlers added to the error logger must handle
the following events. <c>Gleader</c> is the group leader pid of
the process that sent the event, and <c>Pid</c> is the process
that sent the event.</p>
<taglist>
<tag><c>{error, Gleader, {Pid, Format, Data}}</c></tag>
<item>
<p>Generated when <c>error_msg/1,2</c> or <c>format</c> is
called.</p>
</item>
<tag><c>{error_report, Gleader, {Pid, std_error, Report}}</c></tag>
<item>
<p>Generated when <c>error_report/1</c> is called.</p>
</item>
<tag><c>{error_report, Gleader, {Pid, Type, Report}}</c></tag>
<item>
<p>Generated when <c>error_report/2</c> is called.</p>
</item>
<tag><c>{warning_msg, Gleader, {Pid, Format, Data}}</c></tag>
<item>
<p>Generated when <c>warning_msg/1,2</c> is called
if warnings are set to be tagged as warnings.</p>
</item>
<tag><c>{warning_report, Gleader, {Pid, std_warning, Report}}</c></tag>
<item>
<p>Generated when <c>warning_report/1</c> is called
if warnings are set to be tagged as warnings.</p>
</item>
<tag><c>{warning_report, Gleader, {Pid, Type, Report}}</c></tag>
<item>
<p>Generated when <c>warning_report/2</c> is called
if warnings are set to be tagged as warnings.</p>
</item>
<tag><c>{info_msg, Gleader, {Pid, Format, Data}}</c></tag>
<item>
<p>Generated when <c>info_msg/1,2</c> is called.</p>
</item>
<tag><c>{info_report, Gleader, {Pid, std_info, Report}}</c></tag>
<item>
<p>Generated when <c>info_report/1</c> is called.</p>
</item>
<tag><c>{info_report, Gleader, {Pid, Type, Report}}</c></tag>
<item>
<p>Generated when <c>info_report/2</c> is called.</p>
</item>
</taglist>
<p>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 <c>Module:handle_event/2</c>
is necessary. This also applies for
<c>Module:handle_info/2</c>, as the event handler must also take care of
some system-internal messages.</p>
</section>
<section>
<title>See Also</title>
<p><seealso marker="stdlib:gen_event"><c>gen_event(3)</c></seealso>,
<seealso marker="kernel:logger"><c>logger(3)</c></seealso>,
<seealso marker="stdlib:log_mf_h"><c>log_mf_h(3)</c></seealso>,
<seealso marker="kernel_app"><c>kernel(6)</c></seealso>,
<seealso marker="sasl:sasl_app"><c>sasl(6)</c></seealso></p>
</section>
</erlref>
