error_logger
Erlang Error Logger
The Erlang error logger is an event manager (see
OTP Design Principles and
gen_event(3)),
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(6).
Also the SASL application, if started, adds its own event handler, which by default writes supervisor, crash and progress reports to tty. See sasl(6).
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(3)
.
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.
Functions
error_msg(Format) -> ok
Format = string()
error_msg(Format, Data) -> ok
Format = string()
Data = list()
format(Format, Data) -> ok
Format = string()
Data = list()
Sends a standard error event to the error logger.
The
and
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
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
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
follows the same
structure as for error_report/1
.
warning_map() -> Tag
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
Format = string()
warning_msg(Format, Data) -> ok
Format = string()
Data = list()
Sends a standard warning event to the error logger.
The
and
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
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
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
Format = string()
info_msg(Format, Data) -> ok
Format = string()
Data = list()
Sends a standard information event to the error logger.
The
and
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
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
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
follows the same
structure as for info_report/1
.
add_report_handler(Handler) -> any()
Handler = module()
add_report_handler(Handler, Args) -> Result
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(3).
is typically the name of the callback module
and
is an optional term (defaults to []) passed
to the initialization callback function
.
The function returns ok
if successful.
The event handler must be able to handle the events described below.
delete_report_handler(Handler) -> Result
Handler = module()
Result = gen_event:del_handler_ret()
Deletes an event handler from the error logger by calling
gen_event:delete_handler(error_logger,
,
see gen_event(3).
tty(Flag) -> ok
Flag = boolean()
Enables (
) or disables
(
) 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}
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
. 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
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
, 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.
Note that also a number of system internal events may be
received, a catch-all clause last in the definition of
the event handler callback function Module:handle_event/2
is necessary. This also holds true for
Module:handle_info/2
, as there are a number of system
internal messages the event handler must take care of as well.
SEE ALSO
gen_event(3), log_mf_h(3), kernel(6), sasl(6)