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 = standard_io | standard_error | file | {device, io:device()}:
25 Specifies the log destination.
26 The value is set when the handler is added, and it cannot be
28 changed in runtime.
29 Defaults to standard_io, unless parameter file is given, in which
31 case it defaults to file.
32 file = file:filename():
34 This specifies the name of the log file when the handler is of type
35 file.
36 The value is set when the handler is added, and it cannot be
38 changed in runtime.
39 Defaults to the same name as the handler identity, in the current
41 directory.
42 modes = [file:mode()]:
44 This specifies the file modes to use when opening the log file, see
45 file:open/2. If modes are not specified, the default list used is
46 [raw,append,delayed_write]. If modes are specified, the list re‐
47 places the default modes list with the following adjustments:
48 *
50 If raw is not found in the list, it is added.
51 *
53 If none of write, append or exclusive is found in the list, ap‐
54 pend is added.
55 * If none of delayed_write or {delayed_write,Size,Delay} is found
57 in the list, delayed_write is added.
58 Log files are always UTF-8 encoded. The encoding cannot be changed
60 by setting the mode {encoding,Encoding}.
61 The value is set when the handler is added, and it cannot be
63 changed in runtime.
64 Defaults to [raw,append,delayed_write].
66 max_no_bytes = pos_integer() | infinity:
68 This parameter specifies if the log file should be rotated or not.
69 The value infinity means the log file will grow indefinitely, while
70 an integer value specifies at which file size (bytes) the file is
71 rotated.
72 Defaults to infinity.
74 max_no_files = non_neg_integer():
76 This parameter specifies the number of rotated log file archives to
77 keep. This has meaning only if max_no_bytes is set to an integer
78 value.
79 The log archives are named FileName.0, FileName.1, ... FileName.N,
81 where FileName is the name of the current log file. FileName.0 is
82 the newest of the archives. The maximum value for N is the value of
83 max_no_files minus 1.
84 Notice that setting this value to 0 does not turn off rotation. It
86 only specifies that no archives are kept.
87 Defaults to 0.
89 compress_on_rotate = boolean():
91 This parameter specifies if the rotated log file archives shall be
92 compressed or not. If set to true, all archives are compressed with
93 gzip, and renamed to FileName.N.gz
94 compress_on_rotate has no meaning if max_no_bytes has the value in‐
96 finity.
97 Defaults to false.
99 file_check = non_neg_integer():
101 When logger_std_h logs to a file, it reads the file information of
102 the log file prior to each write operation. This is to make sure
103 the file still exists and has the same inode as when it was opened.
104 This implies some performance loss, but ensures that no log events
105 are lost in the case when the file has been removed or renamed by
106 an external actor.
107 In order to allow minimizing the performance loss, the file_check
109 parameter can be set to a positive integer value, N. The handler
110 will then skip reading the file information prior to writing, as
111 long as no more than N milliseconds have passed since it was last
112 read.
113 Notice that the risk of loosing log events grows when the
115 file_check value grows.
116 Defaults to 0.
118 filesync_repeat_interval = pos_integer() | no_repeat:
120 This value, in milliseconds, specifies how often the handler does a
121 file sync operation to write buffered data to disk. The handler at‐
122 tempts the operation repeatedly, but only performs a new sync if
123 something has actually been logged.
124 If no_repeat is set as value, the repeated file sync operation is
126 disabled, and it is the operating system settings that determine
127 how quickly or slowly data is written to disk. The user can also
128 call the filesync/1 function to perform a file sync.
129 Defaults to 5000 milliseconds.
131 Other configuration parameters exist, to be used for customizing the
133 overload protection behaviour. The same parameters are used both in the
134 standard handler and the disk_log handler, and are documented in the
135 User's Guide.
136 Notice that if changing the configuration of the handler in runtime,
138 the type, file, or modes parameters must not be modified.
139 Example of adding a standard handler:
141 logger:add_handler(my_standard_h, logger_std_h,
143 #{config => #{file => "./system_info.log",
144 filesync_repeat_interval => 1000}}).
145 To set the default handler, that starts initially with the Kernel ap‐
148 plication, to log to file instead of standard_io, change the Kernel de‐
149 fault logger configuration. Example:
150 erl -kernel logger '[{handler,default,logger_std_h,
152 #{config => #{file => "./log.log"}}}]'
153 An example of how to replace the standard handler with a disk_log han‐
156 dler at startup is found in the logger_disk_log_h manual.
157
159 filesync(Name) -> ok | {error, Reason}
160 Types:
162 Name = atom()
164 Reason = handler_busy | {badarg, term()}
165 Write buffered data to disk.
167
169 logger(3), logger_disk_log_h(3)
170Ericsson AB kernel 8.1.3 logger_std_h(3)