logger_std_h(3)



logger_std_h(3erl)         Erlang Module Definition         logger_std_h(3erl)

NAME
       logger_std_h - Standard handler for Logger.

DESCRIPTION
       This  is  the  standard  handler for Logger. Multiple instances of this
       handler can be added to Logger, and each instance prints logs to  stan-
       dard_io, standard_error, or to file.

       The handler has an overload protection mechanism that keeps the handler
       process and the Kernel application  alive  during  high  loads  of  log
       events.  How overload protection works, and how to configure it, is de-
       scribed in the User's Guide.

       To add a new instance of  the  standard  handler,  use  logger:add_han-
       dler/3.  The  handler configuration argument is a map which can contain
       general configuration parameters, as documented in  the  User's  Guide,
       and  handler  specific parameters. The specific data is stored in a sub
       map with the key config, and can contain the following parameters:

         type = standard_io | standard_error | file | {device, io:device()}:
           Specifies the log destination.

           The value is set when the  handler  is  added,  and  it  cannot  be
           changed in runtime.

           Defaults  to  standard_io, unless parameter file is given, in which
           case it defaults to file.

         file = file:filename():
           This specifies the name of the log file when the handler is of type
           file.

           The  value  is  set  when  the  handler  is added, and it cannot be
           changed in runtime.

           Defaults to the same name as the handler identity, in  the  current
           directory.

         modes = [file:mode()]:
           This specifies the file modes to use when opening the log file, see
           file:open/2. If modes are not specified, the default list  used  is
           [raw,append,delayed_write].  If  modes  are specified, the list re-
           places the default modes list with the following adjustments:

           *
              If raw is not found in the list, it is added.

           *
              If none of write, append or exclusive is found in the list,  ap-
             pend is added.

           * If  none  of delayed_write or {delayed_write,Size,Delay} is found
             in the list, delayed_write is added.

           Log files are always UTF-8 encoded. The encoding cannot be  changed
           by setting the mode {encoding,Encoding}.

           The  value  is  set  when  the  handler  is added, and it cannot be
           changed in runtime.

           Defaults to [raw,append,delayed_write].

         max_no_bytes = pos_integer() | infinity:
           This parameter specifies if the log file should be rotated or  not.
           The value infinity means the log file will grow indefinitely, while
           an integer value specifies at which file size (bytes) the  file  is
           rotated.

           Defaults to infinity.

         max_no_files = non_neg_integer():
           This parameter specifies the number of rotated log file archives to
           keep. This has meaning only if max_no_bytes is set  to  an  integer
           value.

           The  log archives are named FileName.0, FileName.1, ... FileName.N,
           where FileName is the name of the current log file.  FileName.0  is
           the newest of the archives. The maximum value for N is the value of
           max_no_files minus 1.

           Notice that setting this value to 0 does not turn of  rotation.  It
           only specifies that no archives are kept.

           Defaults to 0.

         compress_on_rotate = boolean():
           This  parameter specifies if the rotated log file archives shall be
           compressed or not. If set to true, all archives are compressed with
           gzip, and renamed to FileName.N.gz

           compress_on_rotate has no meaning if max_no_bytes has the value in-
           finity.

           Defaults to false.

         file_check = non_neg_integer():
           When logger_std_h logs to a file, it reads the file information  of
           the  log  file  prior to each write operation. This is to make sure
           the file still exists and has the same inode as when it was opened.
           This  implies some performance loss, but ensures that no log events
           are lost in the case when the file has been removed or  renamed  by
           an external actor.

           In  order  to allow minimizing the performance loss, the file_check
           parameter can be set to a positive integer value,  N.  The  handler
           will  then  skip  reading the file information prior to writing, as
           long as no more than N milliseconds have passed since it  was  last
           read.

           Notice  that  the  risk  of  loosing  log  events  grows  when  the
           file_check value grows.

           Defaults to 0.

         filesync_repeat_interval = pos_integer() | no_repeat:
           This value, in milliseconds, specifies how often the handler does a
           file sync operation to write buffered data to disk. The handler at-
           tempts the operation repeatedly, but only performs a  new  sync  if
           something has actually been logged.

           If  no_repeat  is set as value, the repeated file sync operation is
           disabled, and it is the operating system  settings  that  determine
           how  quickly  or  slowly data is written to disk. The user can also
           call the filesync/1 function to perform a file sync.

           Defaults to 5000 milliseconds.

       Other configuration parameters exist, to be used  for  customizing  the
       overload protection behaviour. The same parameters are used both in the
       standard handler and the disk_log handler, and are  documented  in  the
       User's Guide.

       Notice  that  if  changing the configuration of the handler in runtime,
       the type, file, or modes parameters must not be modified.

       Example of adding a standard handler:

       logger:add_handler(my_standard_h, logger_std_h,
                          #{config => #{file => "./system_info.log",
                                        filesync_repeat_interval => 1000}}).

       To set the default handler, that starts initially with the  Kernel  ap-
       plication, to log to file instead of standard_io, change the Kernel de-
       fault logger configuration. Example:

       erl -kernel logger '[{handler,default,logger_std_h,
                             #{config => #{file => "./log.log"}}}]'

       An example of how to replace the standard handler with a disk_log  han-
       dler at startup is found in the logger_disk_log_h manual.

EXPORTS
       filesync(Name) -> ok | {error, Reason}

              Types:

                 Name = atom()
                 Reason = handler_busy | {badarg, term()}

              Write buffered data to disk.

SEE ALSO
       logger(3erl), logger_disk_log_h(3erl)

Ericsson AB                       kernel 7.0                logger_std_h(3erl)

Man(1) output converted with man2html
list of all man pages