1CLOSELOG(3P) POSIX Programmer's Manual CLOSELOG(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 closelog, openlog, setlogmask, syslog — control system log
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16 #include <syslog.h>
17 void closelog(void);
19 void openlog(const char *ident, int logopt, int facility);
20 int setlogmask(int maskpri);
21 void syslog(int priority, const char *message, ... /* arguments */);
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24 The syslog() function shall send a message to an implementation-defined
25 logging facility, which may log it in an implementation-defined system
26 log, write it to the system console, forward it to a list of users, or
27 forward it to the logging facility on another host over the network.
28 The logged message shall include a message header and a message body.
29 The message header contains at least a timestamp and a tag string.
30 The message body is generated from the message and following arguments
32 in the same manner as if these were arguments to printf(), except that
33 the additional conversion specification %m shall be recognized; it
34 shall convert no arguments, shall cause the output of the error message
35 string associated with the value of errno on entry to syslog(), and may
36 be mixed with argument specifications of the "%n$" form. If a complete
37 conversion specification with the m conversion specifier character is
38 not just %m, the behavior is undefined. A trailing <newline> may be
39 added if needed.
40 Values of the priority argument are formed by OR'ing together a sever‐
42 ity-level value and an optional facility value. If no facility value is
43 specified, the current default facility value is used.
44 Possible values of severity level include:
46 LOG_EMERG A panic condition.
48 LOG_ALERT A condition that should be corrected immediately, such as a
50 corrupted system database.
51 LOG_CRIT Critical conditions, such as hard device errors.
53 LOG_ERR Errors.
55 LOG_WARNING
57 Warning messages.
58 LOG_NOTICE Conditions that are not error conditions, but that may
60 require special handling.
61 LOG_INFO Informational messages.
63 LOG_DEBUG Messages that contain information normally of use only when
65 debugging a program.
66 The facility indicates the application or system component generating
68 the message. Possible facility values include:
69 LOG_USER Messages generated by arbitrary processes. This is the
71 default facility identifier if none is specified.
72 LOG_LOCAL0 Reserved for local use.
74 LOG_LOCAL1 Reserved for local use.
76 LOG_LOCAL2 Reserved for local use.
78 LOG_LOCAL3 Reserved for local use.
80 LOG_LOCAL4 Reserved for local use.
82 LOG_LOCAL5 Reserved for local use.
84 LOG_LOCAL6 Reserved for local use.
86 LOG_LOCAL7 Reserved for local use.
88 The openlog() function shall set process attributes that affect subse‐
90 quent calls to syslog(). The ident argument is a string that is
91 prepended to every message. The logopt argument indicates logging
92 options. Values for logopt are constructed by a bitwise-inclusive OR of
93 zero or more of the following:
94 LOG_PID Log the process ID with each message. This is useful for
96 identifying specific processes.
97 LOG_CONS Write messages to the system console if they cannot be sent
99 to the logging facility. The syslog() function ensures that
100 the process does not acquire the console as a controlling
101 terminal in the process of writing the message.
102 LOG_NDELAY Open the connection to the logging facility immediately.
104 Normally the open is delayed until the first message is
105 logged. This is useful for programs that need to manage the
106 order in which file descriptors are allocated.
107 LOG_ODELAY Delay open until syslog() is called.
109 LOG_NOWAIT Do not wait for child processes that may have been created
111 during the course of logging the message. This option
112 should be used by processes that enable notification of
113 child termination using SIGCHLD, since syslog() may other‐
114 wise block waiting for a child whose exit status has
115 already been collected.
116 The facility argument encodes a default facility to be assigned to all
118 messages that do not have an explicit facility already encoded. The
119 initial default facility is LOG_USER.
120 The openlog() and syslog() functions may allocate a file descriptor. It
122 is not necessary to call openlog() prior to calling syslog().
123 The closelog() function shall close any open file descriptors allocated
125 by previous calls to openlog() or syslog().
126 The setlogmask() function shall set the log priority mask for the cur‐
128 rent process to maskpri and return the previous mask. If the maskpri
129 argument is 0, the current log mask is not modified. Calls by the cur‐
130 rent process to syslog() with a priority not set in maskpri shall be
131 rejected. The default log mask allows all priorities to be logged. A
132 call to openlog() is not required prior to calling setlogmask().
133 Symbolic constants for use as values of the logopt, facility, priority,
135 and maskpri arguments are defined in the <syslog.h> header.
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138 The setlogmask() function shall return the previous log priority mask.
139 The closelog(), openlog(), and syslog() functions shall not return a
140 value.
141
143 No errors are defined.
144 The following sections are informative.
146
148 Using openlog()
149 The following example causes subsequent calls to syslog() to log the
150 process ID with each message, and to write messages to the system con‐
151 sole if they cannot be sent to the logging facility.
152 #include <syslog.h>
154 char *ident = "Process demo";
156 int logopt = LOG_PID | LOG_CONS;
157 int facility = LOG_USER;
158 ...
159 openlog(ident, logopt, facility);
160 Using setlogmask()
162 The following example causes subsequent calls to syslog() to accept
163 error messages, and to reject all other messages.
164 #include <syslog.h>
166 int result;
168 int mask = LOG_MASK (LOG_ERR);
169 ...
170 result = setlogmask(mask);
171 Using syslog
173 The following example sends the message "Thisisamessage" to the default
174 logging facility, marking the message as an error message generated by
175 random processes.
176 #include <syslog.h>
178 char *message = "This is a message";
180 int priority = LOG_ERR | LOG_USER;
181 ...
182 syslog(priority, message);
183
185 None.
186
188 None.
189
191 None.
192
194 fprintf()
195 The Base Definitions volume of POSIX.1‐2008, <syslog.h>
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199 Portions of this text are reprinted and reproduced in electronic form
200 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
201 -- Portable Operating System Interface (POSIX), The Open Group Base
202 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
203 cal and Electronics Engineers, Inc and The Open Group. (This is
204 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
205 event of any discrepancy between this version and the original IEEE and
206 The Open Group Standard, the original IEEE and The Open Group Standard
207 is the referee document. The original Standard can be obtained online
208 at http://www.unix.org/online.html .
209 Any typographical or formatting errors that appear in this page are
211 most likely to have been introduced during the conversion of the source
212 files to man page format. To report such errors, see https://www.ker‐
213 nel.org/doc/man-pages/reporting_bugs.html .
214IEEE/The Open Group 2013 CLOSELOG(3P)