1CLOSELOG(3P) POSIX Programmer's Manual CLOSELOG(3P)
2
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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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
48 A panic condition.
49 LOG_ALERT
51 A condition that should be corrected immediately, such as a cor‐
52 rupted system database.
53 LOG_CRIT
55 Critical conditions, such as hard device errors.
56 LOG_ERR
58 Errors.
59 LOG_WARNING
61 Warning messages.
63 LOG_NOTICE
65 Conditions that are not error conditions, but that may require
66 special handling.
67 LOG_INFO
69 Informational messages.
70 LOG_DEBUG
72 Messages that contain information normally of use only when
73 debugging a program.
74 The facility indicates the application or system component generating
77 the message. Possible facility values include:
78 LOG_USER
80 Messages generated by arbitrary processes. This is the default
81 facility identifier if none is specified.
82 LOG_LOCAL0
84 Reserved for local use.
85 LOG_LOCAL1
87 Reserved for local use.
88 LOG_LOCAL2
90 Reserved for local use.
91 LOG_LOCAL3
93 Reserved for local use.
94 LOG_LOCAL4
96 Reserved for local use.
97 LOG_LOCAL5
99 Reserved for local use.
100 LOG_LOCAL6
102 Reserved for local use.
103 LOG_LOCAL7
105 Reserved for local use.
106 The openlog() function shall set process attributes that affect subse‐
109 quent calls to syslog(). The ident argument is a string that is
110 prepended to every message. The logopt argument indicates logging
111 options. Values for logopt are constructed by a bitwise-inclusive OR of
112 zero or more of the following:
113 LOG_PID
115 Log the process ID with each message. This is useful for identi‐
116 fying specific processes.
117 LOG_CONS
119 Write messages to the system console if they cannot be sent to
120 the logging facility. The syslog() function ensures that the
121 process does not acquire the console as a controlling terminal
122 in the process of writing the message.
123 LOG_NDELAY
125 Open the connection to the logging facility immediately. Nor‐
126 mally the open is delayed until the first message is logged.
127 This is useful for programs that need to manage the order in
128 which file descriptors are allocated.
129 LOG_ODELAY
131 Delay open until syslog() is called.
132 LOG_NOWAIT
134 Do not wait for child processes that may have been created dur‐
135 ing the course of logging the message. This option should be
136 used by processes that enable notification of child termination
137 using SIGCHLD, since syslog() may otherwise block waiting for a
138 child whose exit status has already been collected.
139 The facility argument encodes a default facility to be assigned to all
142 messages that do not have an explicit facility already encoded. The
143 initial default facility is LOG_USER.
144 The openlog() and syslog() functions may allocate a file descriptor. It
146 is not necessary to call openlog() prior to calling syslog().
147 The closelog() function shall close any open file descriptors allocated
149 by previous calls to openlog() or syslog().
150 The setlogmask() function shall set the log priority mask for the cur‐
152 rent process to maskpri and return the previous mask. If the maskpri
153 argument is 0, the current log mask is not modified. Calls by the cur‐
154 rent process to syslog() with a priority not set in maskpri shall be
155 rejected. The default log mask allows all priorities to be logged. A
156 call to openlog() is not required prior to calling setlogmask().
157 Symbolic constants for use as values of the logopt, facility, priority,
159 and maskpri arguments are defined in the <syslog.h> header.
160
162 The setlogmask() function shall return the previous log priority mask.
163 The closelog(), openlog(), and syslog() functions shall not return a
164 value.
165
167 No errors are defined.
168 The following sections are informative.
170
172 Using openlog()
173 The following example causes subsequent calls to syslog() to log the
174 process ID with each message, and to write messages to the system con‐
175 sole if they cannot be sent to the logging facility.
176 #include <syslog.h>
179 char *ident = "Process demo";
182 int logopt = LOG_PID | LOG_CONS;
183 int facility = LOG_USER;
184 ...
185 openlog(ident, logopt, facility);
186 Using setlogmask()
188 The following example causes subsequent calls to syslog() to accept
189 error messages, and to reject all other messages.
190 #include <syslog.h>
193 int result;
196 int mask = LOG_MASK (LOG_ERR);
197 ...
198 result = setlogmask(mask);
199 Using syslog
201 The following example sends the message "This is a message" to the
202 default logging facility, marking the message as an error message gen‐
203 erated by random processes.
204 #include <syslog.h>
207 char *message = "This is a message";
210 int priority = LOG_ERR | LOG_USER;
211 ...
212 syslog(priority, message);
213
215 None.
216
218 None.
219
221 None.
222
224 printf(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys‐
225 log.h>
226
228 Portions of this text are reprinted and reproduced in electronic form
229 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
230 -- Portable Operating System Interface (POSIX), The Open Group Base
231 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
232 Electrical and Electronics Engineers, Inc and The Open Group. In the
233 event of any discrepancy between this version and the original IEEE and
234 The Open Group Standard, the original IEEE and The Open Group Standard
235 is the referee document. The original Standard can be obtained online
236 at http://www.opengroup.org/unix/online.html .
237IEEE/The Open Group 2003 CLOSELOG(3P)