Provided by: erlang-manpages_25.3.2.12+dfsg-1ubuntu2_all 
NAME
logger - API module for Logger, the standard logging facility
in Erlang/OTP.
DESCRIPTION
This module implements the main API for logging in Erlang/OTP. To create a log event, use the API
functions or the log macros, for example:
?LOG_ERROR("error happened because: ~p", [Reason]). % With macro
logger:error("error happened because: ~p", [Reason]). % Without macro
To configure the Logger backend, use Kernel configuration parameters or configuration functions in the
Logger API.
By default, the Kernel application installs one log handler at system start. This handler is named
default. It receives and processes standard log events produced by the Erlang runtime system, standard
behaviours and different Erlang/OTP applications. The log events are by default printed to the terminal.
If you want your systems logs to be printed to a file instead, you must configure the default handler to
do so. The simplest way is to include the following in your sys.config:
[{kernel,
[{logger,
[{handler, default, logger_std_h,
#{config => #{file => "path/to/file.log"}}}]}]}].
For more information about:
* the Logger facility in general, see the User's Guide.
* how to configure Logger, see the Configuration section in the User's Guide.
* the built-in handlers, see logger_std_h and logger_disk_log_h.
* the built-in formatter, see logger_formatter.
* built-in filters, see logger_filters.
Note:
Since Logger is new in Erlang/OTP 21.0, we do reserve the right to introduce changes to the Logger API
and functionality in patches following this release. These changes might or might not be backwards
compatible with the initial version.
DATA TYPES
filter() =
{fun((log_event(), filter_arg()) -> filter_return()),
filter_arg()}
A filter which can be installed as a handler filter, or as a primary filter in Logger.
filter_arg() = term()
The second argument to the filter fun.
filter_id() = atom()
A unique identifier for a filter.
filter_return() = stop | ignore | log_event()
The return value from the filter fun.
formatter_config() = #{atom() => term()}
Configuration data for the formatter. See logger_formatter(3erl) for an example of a formatter
implementation.
handler_config() =
#{id => handler_id(),
config => term(),
level => level() | all | none,
module => module(),
filter_default => log | stop,
filters => [{filter_id(), filter()}],
formatter => {module(), formatter_config()}}
Handler configuration data for Logger. The following default values apply:
* level => all
* filter_default => log
* filters => []
* formatter => {logger_formatter, DefaultFormatterConfig}
In addition to these, the following fields are automatically inserted by Logger, values taken from
the two first parameters to add_handler/3:
* id => HandlerId
* module => Module
These are read-only and cannot be changed in runtime.
Handler specific configuration data is inserted by the handler callback itself, in a sub structure
associated with the field named config. See the logger_std_h(3erl) and logger_disk_log_h(3erl)
manual pages for information about the specific configuration for these handlers.
See the logger_formatter(3erl) manual page for information about the default configuration for
this formatter.
handler_id() = atom()
A unique identifier for a handler instance.
level() =
emergency | alert | critical | error | warning | notice |
info | debug
The severity level for the message to be logged.
log_event() =
#{level := level(),
msg :=
{io:format(), [term()]} |
{report, report()} |
{string, unicode:chardata()},
meta := metadata()}
metadata() =
#{pid => pid(),
gl => pid(),
time => timestamp(),
mfa => {module(), atom(), integer() >= 0},
file => file:filename(),
line => integer() >= 0,
domain => [atom()],
report_cb => report_cb(),
atom() => term()}
Metadata for the log event.
Logger adds the following metadata to each log event:
* pid => self()
* gl => group_leader()
* time => logger:timestamp()
When a log macro is used, Logger also inserts location information:
* mfa => {?MODULE, ?FUNCTION_NAME, ?FUNCTION_ARITY}
* file => ?FILE
* line => ?LINE
You can add custom metadata, either by:
* specifying a map as the last parameter to any of the log macros or the logger API functions.
* setting process metadata with set_process_metadata/1 or update_process_metadata/1.
* setting primary metadata with set_primary_config/1 or through the kernel configuration
parameter logger_metadata
Note:
When adding custom metadata, make sure not to use any of the keys mentioned above as that may
cause a lot of confusion about the log events.
Logger merges all the metadata maps before forwarding the log event to the handlers. If the same
keys occur, values from the log call overwrite process metadata, which overwrites the primary
metadata, which in turn overwrite values set by Logger.
The following custom metadata keys have special meaning:
domain:
The value associated with this key is used by filters for grouping log events originating
from, for example, specific functional areas. See logger_filters:domain/2 for a description of
how this field can be used.
report_cb:
If the log message is specified as a report(), the report_cb key can be associated with a fun
(report callback) that converts the report to a format string and arguments, or directly to a
string. See the type definition of report_cb(), and section Log Message in the User's Guide
for more information about report callbacks.
msg_fun() =
fun((term()) ->
msg_fun_return() | {msg_fun_return(), metadata()})
msg_fun_return() =
{io:format(), [term()]} |
report() |
unicode:chardata() |
ignore
olp_config() =
#{sync_mode_qlen => integer() >= 0,
drop_mode_qlen => integer() >= 1,
flush_qlen => integer() >= 1,
burst_limit_enable => boolean(),
burst_limit_max_count => integer() >= 1,
burst_limit_window_time => integer() >= 1,
overload_kill_enable => boolean(),
overload_kill_qlen => integer() >= 1,
overload_kill_mem_size => integer() >= 1,
overload_kill_restart_after => integer() >= 0 | infinity}
primary_config() =
#{level => level() | all | none,
metadata => metadata(),
filter_default => log | stop,
filters => [{filter_id(), filter()}]}
Primary configuration data for Logger. The following default values apply:
* level => info
* filter_default => log
* filters => []
report() = map() | [{atom(), term()}]
report_cb() =
fun((report()) -> {io:format(), [term()]}) |
fun((report(), report_cb_config()) -> unicode:chardata())
A fun which converts a report() to a format string and arguments, or directly to a string. See
section Log Message in the User's Guide for more information.
report_cb_config() =
#{depth := integer() >= 1 | unlimited,
chars_limit := integer() >= 1 | unlimited,
single_line := boolean()}
timestamp() = integer()
A timestamp produced with logger:timestamp().
MACROS
The following macros are defined in logger.hrl, which is included in a module with the directive
-include_lib("kernel/include/logger.hrl").
* ?LOG_EMERGENCY(StringOrReport[,Metadata])
* ?LOG_EMERGENCY(FunOrFormat,Args[,Metadata])
* ?LOG_ALERT(StringOrReport[,Metadata])
* ?LOG_ALERT(FunOrFormat,Args[,Metadata])
* ?LOG_CRITICAL(StringOrReport[,Metadata])
* ?LOG_CRITICAL(FunOrFormat,Args[,Metadata])
* ?LOG_ERROR(StringOrReport[,Metadata])
* ?LOG_ERROR(FunOrFormat,Args[,Metadata])
* ?LOG_WARNING(StringOrReport[,Metadata])
* ?LOG_WARNING(FunOrFormat,Args[,Metadata])
* ?LOG_NOTICE(StringOrReport[,Metadata])
* ?LOG_NOTICE(FunOrFormat,Args[,Metadata])
* ?LOG_INFO(StringOrReport[,Metadata])
* ?LOG_INFO(FunOrFormat,Args[,Metadata])
* ?LOG_DEBUG(StringOrReport[,Metadata])
* ?LOG_DEBUG(FunOrFormat,Args[,Metadata])
* ?LOG(Level,StringOrReport[,Metadata])
* ?LOG(Level,FunOrFormat,Args[,Metadata])
All macros expand to a call to Logger, where Level is taken from the macro name, or from the first
argument in the case of the ?LOG macro. Location data is added to the metadata as described under the
metadata() type definition.
The call is wrapped in a case statement and will be evaluated only if Level is equal to or below the
configured log level.
LOGGING API FUNCTIONS
EXPORTS
emergency(StringOrReport[,Metadata])
emergency(Format,Args[,Metadata])
emergency(Fun,FunArgs[,Metadata])
Equivalent to log(emergency,...).
alert(StringOrReport[,Metadata])
alert(Format,Args[,Metadata])
alert(Fun,FunArgs[,Metadata])
Equivalent to log(alert,...).
critical(StringOrReport[,Metadata])
critical(Format,Args[,Metadata])
critical(Fun,FunArgs[,Metadata])
Equivalent to log(critical,...).
error(StringOrReport[,Metadata])
error(Format,Args[,Metadata])
error(Fun,FunArgs[,Metadata])
Equivalent to log(error,...).
warning(StringOrReport[,Metadata])
warning(Format,Args[,Metadata])
warning(Fun,FunArgs[,Metadata])
Equivalent to log(warning,...).
notice(StringOrReport[,Metadata])
notice(Format,Args[,Metadata])
notice(Fun,FunArgs[,Metadata])
Equivalent to log(notice,...).
info(StringOrReport[,Metadata])
info(Format,Args[,Metadata])
info(Fun,FunArgs[,Metadata])
Equivalent to log(info,...).
debug(StringOrReport[,Metadata])
debug(Format,Args[,Metadata])
debug(Fun,FunArgs[,Metadata])
Equivalent to log(debug,...).
log(Level, StringOrReport) -> ok
log(Level, StringOrReport, Metadata) -> ok
log(Level, Format, Args) -> ok
log(Level, Fun, FunArgs) -> ok
log(Level, Format, Args, Metadata) -> ok
log(Level, Fun, FunArgs, Metadata) -> ok
Types:
Level = level()
StringOrReport = unicode:chardata() | report()
Format = io:format()
Args = [term()]
Fun = msg_fun()
FunArgs = term()
Metadata = metadata()
Create a log event at the given log level, with the given message to be logged and metadata.
Examples:
%% A plain string
logger:log(info, "Hello World").
%% A plain string with metadata
logger:log(debug, "Hello World", #{ meta => data }).
%% A format string with arguments
logger:log(warning, "The roof is on ~ts",[Cause]).
%% A report
logger:log(warning, #{ what => roof, cause => Cause }).
The message and metadata can either be given directly in the arguments, or returned from a fun.
Passing a fun instead of the message/metadata directly is useful in scenarios when the
message/metadata is very expensive to compute. This is because the fun is only evaluated when the
message/metadata is actually needed, which may be not at all if the log event is not to be logged.
Examples:
%% A plain string with expensive metadata
logger:info(fun([]) -> {"Hello World", #{ meta => expensive() }} end,[]).
%% An expensive report
logger:debug(fun(What) -> #{ what => What, cause => expensive() } end,roof).
%% A plain string with expensive metadata and normal metadata
logger:debug(fun([]) -> {"Hello World", #{ meta => expensive() }} end,[],
#{ meta => data }).
When metadata is given both as an argument and returned from the fun they are merged. If equal
keys exists the values are taken from the metadata returned by the fun.
CONFIGURATION API FUNCTIONS
EXPORTS
add_handler(HandlerId, Module, Config) -> ok | {error, term()}
Types:
HandlerId = handler_id()
Module = module()
Config = handler_config()
Add a handler with the given configuration.
HandlerId is a unique identifier which must be used in all subsequent calls referring to this
handler.
add_handler_filter(HandlerId, FilterId, Filter) ->
ok | {error, term()}
Types:
HandlerId = handler_id()
FilterId = filter_id()
Filter = filter()
Add a filter to the specified handler.
The filter fun is called with the log event as the first parameter, and the specified
filter_args() as the second parameter.
The return value of the fun specifies if a log event is to be discarded or forwarded to the
handler callback:
log_event():
The filter passed. The next handler filter, if any, is applied. If no more filters exist for
this handler, the log event is forwarded to the handler callback.
stop:
The filter did not pass, and the log event is immediately discarded.
ignore:
The filter has no knowledge of the log event. The next handler filter, if any, is applied. If
no more filters exist for this handler, the value of the filter_default configuration
parameter for the handler specifies if the log event shall be discarded or forwarded to the
handler callback.
See section Filters in the User's Guide for more information about filters.
Some built-in filters exist. These are defined in logger_filters(3erl).
add_handlers(Application) -> ok | {error, term()}
Types:
Application = atom()
Reads the application configuration parameter logger and calls add_handlers/1 with its contents.
add_handlers(HandlerConfig) -> ok | {error, term()}
Types:
HandlerConfig = [config_handler()]
config_handler() =
{handler, handler_id(), module(), handler_config()}
This function should be used by custom Logger handlers to make configuration consistent no matter
which handler the system uses. Normal usage is to add a call to logger:add_handlers/1 just after
the processes that the handler needs are started, and pass the application's logger configuration
as the argument. For example:
-behaviour(application).
start(_, []) ->
case supervisor:start_link({local, my_sup}, my_sup, []) of
{ok, Pid} ->
ok = logger:add_handlers(my_app),
{ok, Pid, []};
Error -> Error
end.
This reads the logger configuration parameter from the my_app application and starts the
configured handlers. The contents of the configuration use the same rules as the logger handler
configuration.
If the handler is meant to replace the default handler, the Kernel's default handler have to be
disabled before the new handler is added. A sys.config file that disables the Kernel handler and
adds a custom handler could look like this:
[{kernel,
[{logger,
%% Disable the default Kernel handler
[{handler, default, undefined}]}]},
{my_app,
[{logger,
%% Enable this handler as the default
[{handler, default, my_handler, #{}}]}]}].
add_primary_filter(FilterId, Filter) -> ok | {error, term()}
Types:
FilterId = filter_id()
Filter = filter()
Add a primary filter to Logger.
The filter fun is called with the log event as the first parameter, and the specified
filter_args() as the second parameter.
The return value of the fun specifies if a log event is to be discarded or forwarded to the
handlers:
log_event():
The filter passed. The next primary filter, if any, is applied. If no more primary filters
exist, the log event is forwarded to the handler part of Logger, where handler filters are
applied.
stop:
The filter did not pass, and the log event is immediately discarded.
ignore:
The filter has no knowledge of the log event. The next primary filter, if any, is applied. If
no more primary filters exist, the value of the primary filter_default configuration parameter
specifies if the log event shall be discarded or forwarded to the handler part.
See section Filters in the User's Guide for more information about filters.
Some built-in filters exist. These are defined in logger_filters(3erl).
get_config() ->
#{primary => primary_config(),
handlers => [handler_config()],
proxy => olp_config(),
module_levels =>
[{module(), level() | all | none}]}
Look up all current Logger configuration, including primary, handler, and proxy configuration, and
module level settings.
get_handler_config() -> [Config]
Types:
Config = handler_config()
Look up the current configuration for all handlers.
get_handler_config(HandlerId) -> {ok, Config} | {error, term()}
Types:
HandlerId = handler_id()
Config = handler_config()
Look up the current configuration for the given handler.
get_handler_ids() -> [HandlerId]
Types:
HandlerId = handler_id()
Look up the identities for all installed handlers.
get_primary_config() -> Config
Types:
Config = primary_config()
Look up the current primary configuration for Logger.
get_proxy_config() -> Config
Types:
Config = olp_config()
Look up the current configuration for the Logger proxy.
For more information about the proxy, see section Logger Proxy in the Kernel User's Guide.
get_module_level() -> [{Module, Level}]
Types:
Module = module()
Level = level() | all | none
Look up all current module levels. Returns a list containing one {Module,Level} element for each
module for which the module level was previously set with set_module_level/2.
get_module_level(Modules) -> [{Module, Level}]
Types:
Modules = [Module] | Module
Module = module()
Level = level() | all | none
Look up the current level for the given modules. Returns a list containing one {Module,Level}
element for each of the given modules for which the module level was previously set with
set_module_level/2.
get_process_metadata() -> Meta | undefined
Types:
Meta = metadata()
Retrieve data set with set_process_metadata/1 or update_process_metadata/1.
i() -> ok
i(What) -> ok
Types:
What = primary | handlers | proxy | modules | handler_id()
Pretty print the Logger configuration.
remove_handler(HandlerId) -> ok | {error, term()}
Types:
HandlerId = handler_id()
Remove the handler identified by HandlerId.
remove_handler_filter(HandlerId, FilterId) -> ok | {error, term()}
Types:
HandlerId = handler_id()
FilterId = filter_id()
Remove the filter identified by FilterId from the handler identified by HandlerId.
remove_primary_filter(FilterId) -> ok | {error, term()}
Types:
FilterId = filter_id()
Remove the primary filter identified by FilterId from Logger.
set_application_level(Application, Level) ->
ok | {error, not_loaded}
Types:
Application = atom()
Level = level() | all | none
Set the log level for all the modules of the specified application.
This function is a convenience function that calls logger:set_module_level/2 for each module
associated with an application.
set_handler_config(HandlerId, Config) -> ok | {error, term()}
Types:
HandlerId = handler_id()
Config = handler_config()
Set configuration data for the specified handler. This overwrites the current handler
configuration.
To modify the existing configuration, use update_handler_config/2, or, if a more complex merge is
needed, read the current configuration with get_handler_config/1, then do the merge before writing
the new configuration back with this function.
If a key is removed compared to the current configuration, and the key is known by Logger, the
default value is used. If it is a custom key, then it is up to the handler implementation if the
value is removed or a default value is inserted.
set_handler_config(HandlerId, Key :: level, Level) -> Return
set_handler_config(HandlerId,
Key :: filter_default,
FilterDefault) ->
Return
set_handler_config(HandlerId, Key :: filters, Filters) -> Return
set_handler_config(HandlerId, Key :: formatter, Formatter) ->
Return
set_handler_config(HandlerId, Key :: config, Config) -> Return
Types:
HandlerId = handler_id()
Level = level() | all | none
FilterDefault = log | stop
Filters = [{filter_id(), filter()}]
Formatter = {module(), formatter_config()}
Config = term()
Return = ok | {error, term()}
Add or update configuration data for the specified handler. If the given Key already exists, its
associated value will be changed to the given value. If it does not exist, it will be added.
If the value is incomplete, which for example can be the case for the config key, it is up to the
handler implementation how the unspecified parts are set. For all handlers in the Kernel
application, unspecified data for the config key is set to default values. To update only
specified data, and keep the existing configuration for the rest, use update_handler_config/3.
See the definition of the handler_config() type for more information about the different
parameters.
set_primary_config(Config) -> ok | {error, term()}
Types:
Config = primary_config()
Set primary configuration data for Logger. This overwrites the current configuration.
To modify the existing configuration, use update_primary_config/1, or, if a more complex merge is
needed, read the current configuration with get_primary_config/0, then do the merge before writing
the new configuration back with this function.
If a key is removed compared to the current configuration, the default value is used.
set_primary_config(Key :: level, Level) -> ok | {error, term()}
set_primary_config(Key :: filter_default, FilterDefault) ->
ok | {error, term()}
set_primary_config(Key :: filters, Filters) ->
ok | {error, term()}
set_primary_config(Key :: metadata, Meta) -> ok | {error, term()}
Types:
Level = level() | all | none
FilterDefault = log | stop
Filters = [{filter_id(), filter()}]
Meta = metadata()
Add or update primary configuration data for Logger. If the given Key already exists, its
associated value will be changed to the given value. If it does not exist, it will be added.
set_proxy_config(Config) -> ok | {error, term()}
Types:
Config = olp_config()
Set configuration data for the Logger proxy. This overwrites the current proxy configuration. Keys
that are not specified in the Config map gets default values.
To modify the existing configuration, use update_proxy_config/1, or, if a more complex merge is
needed, read the current configuration with get_proxy_config/0, then do the merge before writing
the new configuration back with this function.
For more information about the proxy, see section Logger Proxy in the Kernel User's Guide.
set_module_level(Modules, Level) -> ok | {error, term()}
Types:
Modules = [module()] | module()
Level = level() | all | none
Set the log level for the specified modules.
The log level for a module overrides the primary log level of Logger for log events originating
from the module in question. Notice, however, that it does not override the level configuration
for any handler.
For example: Assume that the primary log level for Logger is info, and there is one handler, h1,
with level info and one handler, h2, with level debug.
With this configuration, no debug messages will be logged, since they are all stopped by the
primary log level.
If the level for mymodule is now set to debug, then debug events from this module will be logged
by the handler h2, but not by handler h1.
Debug events from other modules are still not logged.
To change the primary log level for Logger, use set_primary_config(level, Level).
To change the log level for a handler, use set_handler_config(HandlerId, level, Level).
Note:
The originating module for a log event is only detected if the key mfa exists in the metadata, and
is associated with {Module, Function, Arity}. When log macros are used, this association is
automatically added to all log events. If an API function is called directly, without using a
macro, the logging client must explicitly add this information if module levels shall have any
effect.
set_process_metadata(Meta) -> ok
Types:
Meta = metadata()
Set metadata which Logger shall automatically insert in all log events produced on the current
process.
Location data produced by the log macros, and/or metadata given as argument to the log call (API
function or macro), are merged with the process metadata. If the same keys occur, values from the
metadata argument to the log call overwrite values from the process metadata, which in turn
overwrite values from the location data.
Subsequent calls to this function overwrites previous data set. To update existing data instead of
overwriting it, see update_process_metadata/1.
unset_application_level(Application) ->
ok | {error, {not_loaded, Application}}
Types:
Application = atom()
Unset the log level for all the modules of the specified application.
This function is a utility function that calls logger:unset_module_level/2 for each module
associated with an application.
unset_module_level() -> ok
Remove module specific log settings. After this, the primary log level is used for all modules.
unset_module_level(Modules) -> ok
Types:
Modules = [module()] | module()
Remove module specific log settings. After this, the primary log level is used for the specified
modules.
unset_process_metadata() -> ok
Delete data set with set_process_metadata/1 or update_process_metadata/1.
update_formatter_config(HandlerId, FormatterConfig) ->
ok | {error, term()}
Types:
HandlerId = handler_id()
FormatterConfig = formatter_config()
Update the formatter configuration for the specified handler.
The new configuration is merged with the existing formatter configuration.
To overwrite the existing configuration without any merge, use
set_handler_config(HandlerId, formatter, {FormatterModule, FormatterConfig}).
update_formatter_config(HandlerId, Key, Value) ->
ok | {error, term()}
Types:
HandlerId = handler_id()
Key = atom()
Value = term()
Update the formatter configuration for the specified handler.
This is equivalent to
update_formatter_config(HandlerId, #{Key => Value})
update_handler_config(HandlerId, Config) -> ok | {error, term()}
Types:
HandlerId = handler_id()
Config = handler_config()
Update configuration data for the specified handler. This function behaves as if it was
implemented as follows:
{ok, {_, Old}} = logger:get_handler_config(HandlerId),
logger:set_handler_config(HandlerId, maps:merge(Old, Config)).
To overwrite the existing configuration without any merge, use set_handler_config/2.
update_handler_config(HandlerId, Key :: level, Level) -> Return
update_handler_config(HandlerId,
Key :: filter_default,
FilterDefault) ->
Return
update_handler_config(HandlerId, Key :: filters, Filters) ->
Return
update_handler_config(HandlerId, Key :: formatter, Formatter) ->
Return
update_handler_config(HandlerId, Key :: config, Config) -> Return
Types:
HandlerId = handler_id()
Level = level() | all | none
FilterDefault = log | stop
Filters = [{filter_id(), filter()}]
Formatter = {module(), formatter_config()}
Config = term()
Return = ok | {error, term()}
Add or update configuration data for the specified handler. If the given Key already exists, its
associated value will be changed to the given value. If it does not exist, it will be added.
If the value is incomplete, which for example can be the case for the config key, it is up to the
handler implementation how the unspecified parts are set. For all handlers in the Kernel
application, unspecified data for the config key is not changed. To reset unspecified data to
default values, use set_handler_config/3.
See the definition of the handler_config() type for more information about the different
parameters.
update_primary_config(Config) -> ok | {error, term()}
Types:
Config = primary_config()
Update primary configuration data for Logger. This function behaves as if it was implemented as
follows:
Old = logger:get_primary_config(),
logger:set_primary_config(maps:merge(Old, Config)).
To overwrite the existing configuration without any merge, use set_primary_config/1.
update_process_metadata(Meta) -> ok
Types:
Meta = metadata()
Set or update metadata to use when logging from current process
If process metadata exists for the current process, this function behaves as if it was implemented
as follows:
logger:set_process_metadata(maps:merge(logger:get_process_metadata(), Meta)).
If no process metadata exists, the function behaves as set_process_metadata/1.
update_proxy_config(Config) -> ok | {error, term()}
Types:
Config = olp_config()
Update configuration data for the Logger proxy. This function behaves as if it was implemented as
follows:
Old = logger:get_proxy_config(),
logger:set_proxy_config(maps:merge(Old, Config)).
To overwrite the existing configuration without any merge, use set_proxy_config/1.
For more information about the proxy, see section Logger Proxy in the Kernel User's Guide.
MISCELLANEOUS API FUNCTIONS
EXPORTS
compare_levels(Level1, Level2) -> eq | gt | lt
Types:
Level1 = Level2 = level() | all | none
Compare the severity of two log levels. Returns gt if Level1 is more severe than Level2, lt if
Level1 is less severe, and eq if the levels are equal.
format_report(Report) -> FormatArgs
Types:
Report = report()
FormatArgs = {io:format(), [term()]}
Convert a log message on report form to {Format, Args}. This is the default report callback used
by logger_formatter(3erl) when no custom report callback is found. See section Log Message in the
Kernel User's Guide for information about report callbacks and valid forms of log messages.
The function produces lines of Key: Value from key-value lists. Strings are printed with ~ts and
other terms with ~tp.
If Report is a map, it is converted to a key-value list before formatting as such.
timestamp() -> timestamp()
Return a timestamp that can be inserted as the time field in the meta data for a log event. It is
produced with os:system_time(microsecond).
Notice that Logger automatically inserts a timestamp in the meta data unless it already exists.
This function is exported for the rare case when the timestamp must be taken at a different point
in time than when the log event is issued.
reconfigure() -> ok | {error, term()}
Reconfigure Logger using updated kernel configuration that was set after kernel application was
loaded.
Beware, that this is meant to be run only by the build tools, not manually during application
lifetime, as this may cause missing log entries.
HANDLER CALLBACK FUNCTIONS
The following functions are to be exported from a handler callback module.
EXPORTS
HModule:adding_handler(Config1) -> {ok, Config2} | {error, Reason}
Types:
Config1 = Config2 = handler_config()
Reason = term()
This callback function is optional.
The function is called on a temporary process when a new handler is about to be added. The purpose
is to verify the configuration and initiate all resources needed by the handler.
The handler identity is associated with the id key in Config1.
If everything succeeds, the callback function can add possible default values or internal state
values to the configuration, and return the adjusted map in {ok,Config2}.
If the configuration is faulty, or if the initiation fails, the callback function must return
{error,Reason}.
HModule:changing_config(SetOrUpdate, OldConfig, NewConfig) -> {ok, Config} | {error, Reason}
Types:
SetOrUpdate = set | update
OldConfig = NewConfig = Config = handler_config()
Reason = term()
This callback function is optional.
The function is called on a temporary process when the configuration for a handler is about to
change. The purpose is to verify and act on the new configuration.
OldConfig is the existing configuration and NewConfig is the new configuration.
The handler identity is associated with the id key in OldConfig.
SetOrUpdate has the value set if the configuration change originates from a call to
set_handler_config/2,3, and update if it originates from update_handler_config/2,3. The handler
can use this parameter to decide how to update the value of the config field, that is, the handler
specific configuration data. Typically, if SetOrUpdate equals set, values that are not specified
must be given their default values. If SetOrUpdate equals update, the values found in OldConfig
must be used instead.
If everything succeeds, the callback function must return a possibly adjusted configuration in
{ok,Config}.
If the configuration is faulty, the callback function must return {error,Reason}.
HModule:filter_config(Config) -> FilteredConfig
Types:
Config = FilteredConfig = handler_config()
This callback function is optional.
The function is called when one of the Logger API functions for fetching the handler configuration
is called, for example logger:get_handler_config/1.
It allows the handler to remove internal data fields from its configuration data before it is
returned to the caller.
HModule:log(LogEvent, Config) -> void()
Types:
LogEvent = log_event()
Config = handler_config()
This callback function is mandatory.
The function is called when all primary filters and all handler filters for the handler in
question have passed for the given log event. It is called on the client process, that is, the
process that issued the log event.
The handler identity is associated with the id key in Config.
The handler must log the event.
The return value from this function is ignored by Logger.
HModule:removing_handler(Config) -> ok
Types:
Config = handler_config()
This callback function is optional.
The function is called on a temporary process when a handler is about to be removed. The purpose
is to release all resources used by the handler.
The handler identity is associated with the id key in Config.
The return value is ignored by Logger.
FORMATTER CALLBACK FUNCTIONS
The following functions are to be exported from a formatter callback module.
EXPORTS
FModule:check_config(FConfig) -> ok | {error, Reason}
Types:
FConfig = formatter_config()
Reason = term()
This callback function is optional.
The function is called by a Logger when formatter configuration is set or modified. The formatter
must validate the given configuration and return ok if it is correct, and {error,Reason} if it is
faulty.
The following Logger API functions can trigger this callback:
* logger:add_handler/3
* logger:set_handler_config/2,3
* logger:update_handler_config/2,3
* logger:update_formatter_config/2
See logger_formatter(3erl) for an example implementation. logger_formatter is the default
formatter used by Logger.
FModule:format(LogEvent, FConfig) -> FormattedLogEntry
Types:
LogEvent = log_event()
FConfig = formatter_config()
FormattedLogEntry = unicode:chardata()
This callback function is mandatory.
The function can be called by a log handler to convert a log event term to a printable string. The
returned value can, for example, be printed as a log entry to the console or a file using
io:put_chars/1,2.
See logger_formatter(3erl) for an example implementation. logger_formatter is the default
formatter used by Logger.
SEE ALSO
config(5), erlang(3erl), io(3erl), logger_disk_log_h(3erl), logger_filters(3erl), logger_formatter(3erl), logger_std_h(3erl), unicode(3erl)