1.\" $NetBSD: syslog.3,v 1.18 2003/05/06 08:28:38 wiz Exp $ 2.\" 3.\" Copyright (c) 1985, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)syslog.3 8.1 (Berkeley) 6/4/93 35.\" 36.Dd March 14, 2001 37.Dt SYSLOG 3 38.Os 39.Sh NAME 40.Nm syslog , 41.Nm vsyslog , 42.Nm openlog , 43.Nm closelog , 44.Nm setlogmask 45.Nd control system log 46.Sh LIBRARY 47.Lb libc 48.Sh SYNOPSIS 49.In syslog.h 50.Ft void 51.Fn syslog "int priority" "const char *message" "..." 52.Ft void 53.Fn openlog "const char *ident" "int logopt" "int facility" 54.Ft void 55.Fn closelog void 56.Ft int 57.Fn setlogmask "int maskpri" 58.In stdarg.h 59.Ft void 60.Fn vsyslog "int priority" "const char *message" "va_list args" 61.Sh DESCRIPTION 62The 63.Fn syslog 64function 65writes 66.Fa message 67to the system message logger. 68The message is then written to the system console, log files, 69logged-in users, or forwarded to other machines as appropriate (See 70.Xr syslogd 8 ) . 71.Pp 72The message is identical to a 73.Xr printf 3 74format string, except that 75.Ql %m 76is replaced by the current error 77message. 78(As denoted by the global variable 79.Va errno ; 80see 81.Xr strerror 3 . ) 82A trailing newline is added if none is present. 83.Pp 84The 85.Fn vsyslog 86function 87is an alternative form in which the arguments have already been captured 88using the variable-length argument facilities of 89.Xr varargs 3 . 90.Pp 91The message is tagged with 92.Fa priority . 93Priorities are encoded as a 94.Fa facility 95and a 96.Em level . 97The facility describes the part of the system 98generating the message. 99The level is selected from the following 100.Em ordered 101(high to low) list: 102.Bl -tag -width LOG_AUTHPRIV 103.It Dv LOG_EMERG 104A panic condition. 105This is normally broadcast to all users. 106.It Dv LOG_ALERT 107A condition that should be corrected immediately, such as a corrupted 108system database. 109.It Dv LOG_CRIT 110Critical conditions, e.g., hard device errors. 111.It Dv LOG_ERR 112Errors. 113.It Dv LOG_WARNING 114Warning messages. 115.It Dv LOG_NOTICE 116Conditions that are not error conditions, 117but should possibly be handled specially. 118.It Dv LOG_INFO 119Informational messages. 120.It Dv LOG_DEBUG 121Messages that contain information 122normally of use only when debugging a program. 123.El 124.Pp 125The 126.Fn openlog 127function 128provides for more specialized processing of the messages sent 129by 130.Fn syslog 131and 132.Fn vsyslog . 133The parameter 134.Fa ident 135is a string that will be prepended to every message. 136The 137.Fa logopt 138argument 139is a bit field specifying logging options, which is formed by 140.Tn OR Ns 'ing 141one or more of the following values: 142.Bl -tag -width LOG_AUTHPRIV 143.It Dv LOG_CONS 144If 145.Fn syslog 146cannot pass the message to 147.Xr syslogd 8 148it will attempt to write the message to the console 149.Pq Dq Pa /dev/console . 150.It Dv LOG_NDELAY 151Open the connection to 152.Xr syslogd 8 153immediately. 154Normally the open is delayed until the first message is logged. 155Useful for programs that need to manage the order in which file 156descriptors are allocated. 157.It Dv LOG_PERROR 158Write the message to standard error output as well to the system log. 159.It Dv LOG_PID 160Log the process id with each message: useful for identifying 161instantiations of daemons. 162(This PID is placed within brackets 163between the ident and the message.) 164.El 165.Pp 166The 167.Fa facility 168parameter encodes a default facility to be assigned to all messages 169that do not have an explicit facility encoded: 170.Bl -tag -width LOG_AUTHPRIV 171.It Dv LOG_AUTH 172The authorization system: 173.Xr login 1 , 174.Xr su 1 , 175.Xr getty 8 , 176etc. 177.It Dv LOG_AUTHPRIV 178The same as 179.Dv LOG_AUTH , 180but logged to a file readable only by 181selected individuals. 182.It Dv LOG_CRON 183The cron daemon: 184.Xr cron 8 . 185.It Dv LOG_DAEMON 186System daemons, such as 187.Xr routed 8 , 188that are not provided for explicitly by other facilities. 189.It Dv LOG_FTP 190The file transfer protocol daemon: 191.Xr ftpd 8 . 192.It Dv LOG_KERN 193Messages generated by the kernel. 194These cannot be generated by any user processes. 195.It Dv LOG_LPR 196The line printer spooling system: 197.Xr lpr 1 , 198.Xr lpc 8 , 199.Xr lpd 8 , 200etc. 201.It Dv LOG_MAIL 202The mail system. 203.It Dv LOG_NEWS 204The network news system. 205.It Dv LOG_SYSLOG 206Messages generated internally by 207.Xr syslogd 8 . 208.It Dv LOG_USER 209Messages generated by random user processes. 210This is the default facility identifier if none is specified. 211.It Dv LOG_UUCP 212The uucp system. 213.It Dv LOG_LOCAL0 214Reserved for local use. 215Similarly for 216.Dv LOG_LOCAL1 217through 218.Dv LOG_LOCAL7 . 219.El 220.Pp 221The 222.Fn closelog 223function 224can be used to close the log file. 225.Pp 226The 227.Fn setlogmask 228function 229sets the log priority mask to 230.Fa maskpri 231and returns the previous mask. 232Calls to 233.Fn syslog 234with a priority not set in 235.Fa maskpri 236are rejected. 237The mask for an individual priority 238.Fa pri 239is calculated by the macro 240.Fn LOG_MASK pri ; 241the mask for all priorities up to and including 242.Fa toppri 243is given by the macro 244.Fn LOG_UPTO toppri . 245The default allows all priorities to be logged. 246.Sh RETURN VALUES 247The routines 248.Fn closelog , 249.Fn openlog , 250.Fn syslog 251and 252.Fn vsyslog 253return no value. 254.Pp 255The routine 256.Fn setlogmask 257always returns the previous log mask level. 258.Sh EXAMPLES 259.Bd -literal -offset indent -compact 260syslog(LOG_ALERT, "who: internal error 23"); 261 262openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP); 263 264setlogmask(LOG_UPTO(LOG_ERR)); 265 266syslog(LOG_INFO, "Connection from host %d", CallingHost); 267 268syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m"); 269.Ed 270.Sh SEE ALSO 271.Xr logger 1 , 272.Xr syslogd 8 273.Sh HISTORY 274These 275functions appeared in 276.Bx 4.2 . 277.Sh CAVEATS 278It is important never to pass a string with user-supplied data as a 279format without using 280.Ql %s . 281An attacker can put format specifiers in the string to mangle your stack, 282leading to a possible security hole. 283This holds true even if you have built the string 284.Dq by hand 285using a function like 286.Fn snprintf , 287as the resulting string may still contain user-supplied conversion specifiers 288for later interpolation by 289.Fn syslog . 290.Pp 291Always be sure to use the proper secure idiom: 292.Bd -literal -offset indent 293syslog(priority, "%s", string); 294.Ed 295