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)