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28 .\" @(#)syslog.3 8.1 (Berkeley) 6/4/93
40 .Nd control system log
46 .Fn syslog "int priority" "const char *message" "..."
48 .Fn openlog "const char *ident" "int logopt" "int facility"
52 .Fn setlogmask "int maskpri"
56 .Fn vsyslog "int priority" "const char *message" "va_list args"
63 to the system message logger.
64 The message is then written to the system console, log files,
65 logged-in users, or forwarded to other machines as appropriate.
69 The message is identical to a
71 format string, except that
73 is replaced by the current error
75 (As denoted by the global variable
79 A trailing newline is added if none is present.
84 is an alternate form in which the arguments have already been captured
85 using the variable-length argument facilities of
88 The message is tagged with
90 Priorities are encoded as a
94 The facility describes the part of the system
95 generating the message.
96 The level is selected from the following
99 .Bl -tag -width LOG_AUTHPRIV
102 This is normally broadcast to all users.
104 A condition that should be corrected immediately, such as a corrupted
107 Critical conditions, e.g., hard device errors.
113 Conditions that are not error conditions,
114 but should possibly be handled specially.
116 Informational messages.
118 Messages that contain information
119 normally of use only when debugging a program.
125 provides for more specialized processing of the messages sent
133 is a string that will be prepended to every message.
137 is a bit field specifying logging options, which is formed by
139 one or more of the following values:
140 .Bl -tag -width LOG_AUTHPRIV
144 cannot pass the message to
146 it will attempt to write the message to the console
147 .Pq Dq Pa /dev/console .
149 Open the connection to
152 Normally the open is delayed until the first message is logged.
153 Useful for programs that need to manage the order in which file
154 descriptors are allocated.
156 Write the message to standard error output as well to the system log.
158 Log the process id with each message: useful for identifying
159 instantiations of daemons.
162 this option is enabled by default.
167 argument encodes a default facility to be assigned to all messages
168 that do not have an explicit facility encoded:
169 .Bl -tag -width LOG_AUTHPRIV
171 The authorization system:
179 but logged to a file readable only by
180 selected individuals.
184 by the kernel console output driver.
189 System daemons, such as
191 that are not provided for explicitly by other facilities.
193 The file transfer protocol daemons:
197 Messages generated by the kernel.
198 These cannot be generated by any user processes.
200 The line printer spooling system:
208 The network news system.
210 The network time protocol system.
212 Security subsystems, such as
215 Messages generated internally by
218 Messages generated by random user processes.
219 This is the default facility identifier if none is specified.
223 Reserved for local use.
233 can be used to close the log file.
238 sets the log priority mask to
240 and returns the previous mask.
243 with a priority not set in
246 The mask for an individual priority
248 is calculated by the macro
250 the mask for all priorities up to and including
252 is given by the macro
253 .Fn LOG_UPTO toppri ; .
254 The default allows all priorities to be logged.
266 always returns the previous log mask level.
268 .Bd -literal -offset indent -compact
269 syslog(LOG_ALERT, "who: internal error 23");
271 openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
273 setlogmask(LOG_UPTO(LOG_ERR));
275 syslog(LOG_INFO, "Connection from host %d", CallingHost);
277 syslog(LOG_ERR|LOG_LOCAL2, "foobar error: %m");
284 functions appeared in
287 Never pass a string with user-supplied data as a format without using
289 An attacker can put format specifiers in the string to mangle your stack,
290 leading to a possible security hole.
291 This holds true even if the string was built using a function like
293 as the resulting string may still contain user-supplied conversion specifiers
294 for later interpolation by
297 Always use the proper secure idiom:
299 .Dl syslog(priority, \*q%s\*q, string);