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28 .\" @(#)syslog.3 8.1 (Berkeley) 6/4/93
40 .Nd control system log
47 .Fn syslog "int priority" "const char *message" "..."
49 .Fn vsyslog "int priority" "const char *message" "va_list args"
51 .Fn openlog "const char *ident" "int logopt" "int facility"
55 .Fn setlogmask "int maskpri"
62 to the system message logger.
63 The message is then written to the system console, log files,
64 logged-in users, or forwarded to other machines as appropriate.
68 The message is identical to a
70 format string, except that
72 is replaced by the current error
74 (As denoted by the global variable
78 A trailing newline is added if none is present.
83 is an alternate form in which the arguments have already been captured
84 using the variable-length argument facilities of
87 The message is tagged with
89 Priorities are encoded as a
93 The facility describes the part of the system
94 generating the message.
95 The level is selected from the following
98 .Bl -tag -width LOG_AUTHPRIV
101 This is normally broadcast to all users.
103 A condition that should be corrected immediately, such as a corrupted
106 Critical conditions, e.g., hard device errors.
112 Conditions that are not error conditions,
113 but should possibly be handled specially.
115 Informational messages.
117 Messages that contain information
118 normally of use only when debugging a program.
124 provides for more specialized processing of the messages sent
132 is a string that will be prepended to every message.
136 is a bit field specifying logging options, which is formed by
138 one or more of the following values:
139 .Bl -tag -width LOG_AUTHPRIV
143 cannot pass the message to
145 it will attempt to write the message to the console
146 .Pq Dq Pa /dev/console .
148 Open the connection to
151 Normally the open is delayed until the first message is logged.
152 Useful for programs that need to manage the order in which file
153 descriptors are allocated.
155 Write the message to standard error output as well to the system log.
157 Log the process id with each message: useful for identifying
158 instantiations of daemons.
163 argument encodes a default facility to be assigned to all messages
164 that do not have an explicit facility encoded:
165 .Bl -tag -width LOG_AUTHPRIV
167 The authorization system:
175 but logged to a file readable only by
176 selected individuals.
180 by the kernel console output driver.
185 System daemons, such as
187 that are not provided for explicitly by other facilities.
189 The file transfer protocol daemons:
193 Messages generated by the kernel.
194 These cannot be generated by any user processes.
196 The line printer spooling system:
204 The network news system.
206 The network time protocol system.
208 Security subsystems, such as
211 Messages generated internally by
214 Messages generated by random user processes.
215 This is the default facility identifier if none is specified.
219 Reserved for local use.
229 can be used to close the log file.
234 sets the log priority mask to
236 and returns the previous mask.
239 with a priority not set in
242 The mask for an individual priority
244 is calculated by the macro
246 the mask for all priorities up to and including
248 is given by the macro
249 .Fn LOG_UPTO toppri ; .
250 The default allows all priorities to be logged.
262 always returns the previous log mask level.
264 .Bd -literal -offset indent -compact
265 syslog(LOG_ALERT, "who: internal error 23");
267 openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
269 setlogmask(LOG_UPTO(LOG_ERR));
271 syslog(LOG_INFO, "Connection from host %d", CallingHost);
273 syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");
280 functions appeared in
283 Never pass a string with user-supplied data as a format without using
285 An attacker can put format specifiers in the string to mangle your stack,
286 leading to a possible security hole.
287 This holds true even if the string was built using a function like
289 as the resulting string may still contain user-supplied conversion specifiers
290 for later interpolation by
293 Always use the proper secure idiom:
295 .Dl syslog("%s", string);