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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12 closelog, openlog, setlogmask, syslog — control system log
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15 #include <syslog.h>
16 void closelog(void);
18 void openlog(const char *ident, int logopt, int facility);
19 int setlogmask(int maskpri);
20 void syslog(int priority, const char *message, ... /* arguments */);
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23 The syslog() function shall send a message to an implementation-defined
24 logging facility, which may log it in an implementation-defined system
25 log, write it to the system console, forward it to a list of users, or
26 forward it to the logging facility on another host over the network.
27 The logged message shall include a message header and a message body.
28 The message header contains at least a timestamp and a tag string.
29 The message body is generated from the message and following arguments
31 in the same manner as if these were arguments to printf(), except that
32 the additional conversion specification %m shall be recognized; it
33 shall convert no arguments, shall cause the output of the error message
34 string associated with the value of errno on entry to syslog(), and may
35 be mixed with argument specifications of the "%n$" form. If a complete
36 conversion specification with the m conversion specifier character is
37 not just %m, the behavior is undefined. A trailing <newline> may be
38 added if needed.
39 Values of the priority argument are formed by OR'ing together a sever‐
41 ity-level value and an optional facility value. If no facility value is
42 specified, the current default facility value is used.
43 Possible values of severity level include:
45 LOG_EMERG A panic condition.
47 LOG_ALERT A condition that should be corrected immediately, such as a
49 corrupted system database.
50 LOG_CRIT Critical conditions, such as hard device errors.
52 LOG_ERR Errors.
54 LOG_WARNING
56 Warning messages.
57 LOG_NOTICE Conditions that are not error conditions, but that may
59 require special handling.
60 LOG_INFO Informational messages.
62 LOG_DEBUG Messages that contain information normally of use only when
64 debugging a program.
65 The facility indicates the application or system component generating
67 the message. Possible facility values include:
68 LOG_USER Messages generated by arbitrary processes. This is the
70 default facility identifier if none is specified.
71 LOG_LOCAL0 Reserved for local use.
73 LOG_LOCAL1 Reserved for local use.
75 LOG_LOCAL2 Reserved for local use.
77 LOG_LOCAL3 Reserved for local use.
79 LOG_LOCAL4 Reserved for local use.
81 LOG_LOCAL5 Reserved for local use.
83 LOG_LOCAL6 Reserved for local use.
85 LOG_LOCAL7 Reserved for local use.
87 The openlog() function shall set process attributes that affect subse‐
89 quent calls to syslog(). The ident argument is a string that is
90 prepended to every message. The logopt argument indicates logging
91 options. Values for logopt are constructed by a bitwise-inclusive OR of
92 zero or more of the following:
93 LOG_PID Log the process ID with each message. This is useful for
95 identifying specific processes.
96 LOG_CONS Write messages to the system console if they cannot be sent
98 to the logging facility. The syslog() function ensures that
99 the process does not acquire the console as a controlling
100 terminal in the process of writing the message.
101 LOG_NDELAY Open the connection to the logging facility immediately.
103 Normally the open is delayed until the first message is
104 logged. This is useful for programs that need to manage the
105 order in which file descriptors are allocated.
106 LOG_ODELAY Delay open until syslog() is called.
108 LOG_NOWAIT Do not wait for child processes that may have been created
110 during the course of logging the message. This option
111 should be used by processes that enable notification of
112 child termination using SIGCHLD, since syslog() may other‐
113 wise block waiting for a child whose exit status has
114 already been collected.
115 The facility argument encodes a default facility to be assigned to all
117 messages that do not have an explicit facility already encoded. The
118 initial default facility is LOG_USER.
119 The openlog() and syslog() functions may allocate a file descriptor. It
121 is not necessary to call openlog() prior to calling syslog().
122 The closelog() function shall close any open file descriptors allocated
124 by previous calls to openlog() or syslog().
125 The setlogmask() function shall set the log priority mask for the cur‐
127 rent process to maskpri and return the previous mask. If the maskpri
128 argument is 0, the current log mask is not modified. Calls by the cur‐
129 rent process to syslog() with a priority not set in maskpri shall be
130 rejected. The default log mask allows all priorities to be logged. A
131 call to openlog() is not required prior to calling setlogmask().
132 Symbolic constants for use as values of the logopt, facility, priority,
134 and maskpri arguments are defined in the <syslog.h> header.
135
137 The setlogmask() function shall return the previous log priority mask.
138 The closelog(), openlog(), and syslog() functions shall not return a
139 value.
140
142 No errors are defined.
143 The following sections are informative.
145
147 Using openlog()
148 The following example causes subsequent calls to syslog() to log the
149 process ID with each message, and to write messages to the system con‐
150 sole if they cannot be sent to the logging facility.
151 #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>
167 int result;
169 int mask = LOG_MASK (LOG_ERR);
170 ...
171 result = setlogmask(mask);
172 Using syslog
174 The following example sends the message "Thisisamessage" to the default
175 logging facility, marking the message as an error message generated by
176 random processes.
177 #include <syslog.h>
180 char *message = "This is a message";
182 int priority = LOG_ERR | LOG_USER;
183 ...
184 syslog(priority, message);
185
187 None.
188
190 None.
191
193 None.
194
196 fprintf()
197 The Base Definitions volume of POSIX.1‐2017, <syslog.h>
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201 Portions of this text are reprinted and reproduced in electronic form
202 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
203 table Operating System Interface (POSIX), The Open Group Base Specifi‐
204 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
205 Electrical and Electronics Engineers, Inc and The Open Group. In the
206 event of any discrepancy between this version and the original IEEE and
207 The Open Group Standard, the original IEEE and The Open Group Standard
208 is the referee document. The original Standard can be obtained online
209 at http://www.opengroup.org/unix/online.html .
210 Any typographical or formatting errors that appear in this page are
212 most likely to have been introduced during the conversion of the source
213 files to man page format. To report such errors, see https://www.ker‐
214 nel.org/doc/man-pages/reporting_bugs.html .
215IEEE/The Open Group 2017 CLOSELOG(3P)