1logger_std_h(3) Erlang Module Definition logger_std_h(3)
2
6 logger_std_h - Standard handler for Logger.
7
9 This is the standard handler for Logger. Multiple instances of this
10 handler can be added to Logger, and each instance prints logs to stan‐
11 dard_io, standard_error, or to file.
12 The handler has an overload protection mechanism that keeps the handler
14 process and the Kernel application alive during high loads of log
15 events. How overload protection works, and how to configure it, is de‐
16 scribed in the User's Guide.
17 To add a new instance of the standard handler, use logger:add_han‐
19 dler/3. The handler configuration argument is a map which can contain
20 general configuration parameters, as documented in the User's Guide,
21 and handler specific parameters. The specific data is stored in a sub
22 map with the key config, and can contain the following parameters:
23 type = io:standard_io() | io:standard_error() | file | {device,
25 io:device()}:
26 Specifies the log destination.
27 The value is set when the handler is added, and it cannot be
29 changed in runtime.
30 Defaults to standard_io, unless parameter file is given, in which
32 case it defaults to file.
33 file = file:filename():
35 This specifies the name of the log file when the handler is of type
36 file.
37 The value is set when the handler is added, and it cannot be
39 changed in runtime.
40 Defaults to the same name as the handler identity, in the current
42 directory.
43 modes = [file:mode()]:
45 This specifies the file modes to use when opening the log file, see
46 file:open/2. If modes are not specified, the default list used is
47 [raw,append,delayed_write]. If modes are specified, the list re‐
48 places the default modes list with the following adjustments:
49 *
51 If raw is not found in the list, it is added.
52 *
54 If none of write, append or exclusive is found in the list, ap‐
55 pend is added.
56 * If none of delayed_write or {delayed_write,Size,Delay} is found
58 in the list, delayed_write is added.
59 Log files are always UTF-8 encoded. The encoding cannot be changed
61 by setting the mode {encoding,Encoding}.
62 The value is set when the handler is added, and it cannot be
64 changed in runtime.
65 Defaults to [raw,append,delayed_write].
67 max_no_bytes = pos_integer() | infinity:
69 This parameter specifies if the log file should be rotated or not.
70 The value infinity means the log file will grow indefinitely, while
71 an integer value specifies at which file size (bytes) the file is
72 rotated.
73 Defaults to infinity.
75 max_no_files = non_neg_integer():
77 This parameter specifies the number of rotated log file archives to
78 keep. This has meaning only if max_no_bytes is set to an integer
79 value.
80 The log archives are named FileName.0, FileName.1, ... FileName.N,
82 where FileName is the name of the current log file. FileName.0 is
83 the newest of the archives. The maximum value for N is the value of
84 max_no_files minus 1.
85 Notice that setting this value to 0 does not turn off rotation. It
87 only specifies that no archives are kept.
88 Defaults to 0.
90 compress_on_rotate = boolean():
92 This parameter specifies if the rotated log file archives shall be
93 compressed or not. If set to true, all archives are compressed with
94 gzip, and renamed to FileName.N.gz
95 compress_on_rotate has no meaning if max_no_bytes has the value in‐
97 finity.
98 Defaults to false.
100 file_check = non_neg_integer():
102 When logger_std_h logs to a file, it reads the file information of
103 the log file prior to each write operation. This is to make sure
104 the file still exists and has the same inode as when it was opened.
105 This implies some performance loss, but ensures that no log events
106 are lost in the case when the file has been removed or renamed by
107 an external actor.
108 In order to allow minimizing the performance loss, the file_check
110 parameter can be set to a positive integer value, N. The handler
111 will then skip reading the file information prior to writing, as
112 long as no more than N milliseconds have passed since it was last
113 read.
114 Notice that the risk of losing log events grows when the file_check
116 value grows.
117 Defaults to 0.
119 filesync_repeat_interval = pos_integer() | no_repeat:
121 This value, in milliseconds, specifies how often the handler does a
122 file sync operation to write buffered data to disk. The handler at‐
123 tempts the operation repeatedly, but only performs a new sync if
124 something has actually been logged.
125 If no_repeat is set as value, the repeated file sync operation is
127 disabled, and it is the operating system settings that determine
128 how quickly or slowly data is written to disk. The user can also
129 call the filesync/1 function to perform a file sync.
130 Defaults to 5000 milliseconds.
132 Other configuration parameters exist, to be used for customizing the
134 overload protection behaviour. The same parameters are used both in the
135 standard handler and the disk_log handler, and are documented in the
136 User's Guide.
137 Notice that if changing the configuration of the handler in runtime,
139 the type, file, or modes parameters must not be modified.
140 Example of adding a standard handler:
142 logger:add_handler(my_standard_h, logger_std_h,
144 #{config => #{file => "./system_info.log",
145 filesync_repeat_interval => 1000}}).
146 To set the default handler, that starts initially with the Kernel ap‐
149 plication, to log to file instead of standard_io, change the Kernel de‐
150 fault logger configuration. Example:
151 erl -kernel logger '[{handler,default,logger_std_h,
153 #{config => #{file => "./log.log"}}}]'
154 An example of how to replace the standard handler with a disk_log han‐
157 dler at startup is found in the logger_disk_log_h manual.
158
160 filesync(Name) -> ok | {error, Reason}
161 Types:
163 Name = atom()
165 Reason = handler_busy | {badarg, term()}
166 Write buffered data to disk.
168
170 logger(3), logger_disk_log_h(3)
171Ericsson AB kernel 9.1 logger_std_h(3)