SYSLOG(3)                  Linux Programmer's Manual                 SYSLOG(3)

       closelog, openlog, syslog, vsyslog - send messages to the system logger

       #include <syslog.h>

       void openlog(const char *ident, int option, int facility);
       void syslog(int priority, const char *format, ...);
       void closelog(void);

       void vsyslog(int priority, const char *format, va_list ap);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       vsyslog(): _BSD_SOURCE

       closelog() closes the descriptor being used to write to the system log-
       ger.  The use of closelog() is optional.

       openlog() opens a connection to the system logger for a  program.   The
       string  pointed to by ident is prepended to every message, and is typi-
       cally set to the program name.  If ident is NULL, the program  name  is
       used.  (POSIX.1-2008 does not specify the behavior when ident is NULL.)

       The  option  argument  specifies  flags  which control the operation of
       openlog() and subsequent calls  to  syslog().   The  facility  argument
       establishes  a  default  to  be used if none is specified in subsequent
       calls to syslog().  Values for option and  facility  are  given  below.
       The  use  of  openlog() is optional; it will automatically be called by
       syslog() if necessary, in which case ident will default to NULL.

       syslog() generates a log message, which will  be  distributed  by  sys-
       logd(8).  The priority argument is formed by ORing the facility and the
       level values (explained below).  The remaining arguments are a  format,
       as  in  printf(3) and any arguments required by the format, except that
       the two character sequence %m will be replaced  by  the  error  message
       string strerror(errno).  A trailing newline may be added if needed.

       The function vsyslog() performs the same task as syslog() with the dif-
       ference that it takes a set of arguments which have been obtained using
       the stdarg(3) variable argument list macros.

       The  subsections  below  list  the parameters used to set the values of
       option, facility, and priority.

       The option argument to openlog() is an OR of any of these:

       LOG_CONS       Write directly to system console if there  is  an  error
                      while sending to system logger.

       LOG_NDELAY     Open  the  connection immediately (normally, the connec-
                      tion is opened when the first message is logged).

       LOG_NOWAIT     Don't wait for child processes that may have  been  cre-
                      ated while logging the message.  (The GNU C library does
                      not create a child process, so this option has no effect
                      on Linux.)

       LOG_ODELAY     The converse of LOG_NDELAY; opening of the connection is
                      delayed until syslog() is called.  (This is the default,
                      and need not be specified.)

       LOG_PERROR     (Not  in POSIX.1-2001 or POSIX.1-2008.)  Print to stderr
                      as well.

       LOG_PID        Include PID with each message.

       The facility argument is used to specify what type of program  is  log-
       ging  the  message.  This lets the configuration file specify that mes-
       sages from different facilities will be handled differently.

       LOG_AUTH       security/authorization messages

       LOG_AUTHPRIV   security/authorization messages (private)

       LOG_CRON       clock daemon (cron and at)

       LOG_DAEMON     system daemons without separate facility value

       LOG_FTP        ftp daemon

       LOG_KERN       kernel messages (these can't be generated from user pro-

       LOG_LOCAL0 through LOG_LOCAL7
                      reserved for local use

       LOG_LPR        line printer subsystem

       LOG_MAIL       mail subsystem

       LOG_NEWS       USENET news subsystem

       LOG_SYSLOG     messages generated internally by syslogd(8)

       LOG_USER (default)
                      generic user-level messages

       LOG_UUCP       UUCP subsystem

       This  determines  the  importance  of  the message.  The levels are, in
       order of decreasing importance:

       LOG_EMERG      system is unusable

       LOG_ALERT      action must be taken immediately

       LOG_CRIT       critical conditions

       LOG_ERR        error conditions

       LOG_WARNING    warning conditions

       LOG_NOTICE     normal, but significant, condition

       LOG_INFO       informational message

       LOG_DEBUG      debug-level message

       The function setlogmask(3) can be used to restrict logging to specified
       levels only.

       For   an   explanation   of   the  terms  used  in  this  section,  see

       |Interface             | Attribute     | Value              |
       |openlog(), closelog() | Thread safety | MT-Safe            |
       |syslog(), vsyslog()   | Thread safety | MT-Safe env locale |
       The functions openlog(), closelog(), and syslog() (but  not  vsyslog())
       are  specified  in SUSv2, POSIX.1-2001, and POSIX.1-2008.  POSIX.1-2001
       specifies only the LOG_USER and LOG_LOCAL* values for  facility.   How-
       ever,  with the exception of LOG_AUTHPRIV and LOG_FTP, the other facil-
       ity values appear on most  UNIX  systems.   The  LOG_PERROR  value  for
       option  is not specified by POSIX.1-2001 or POSIX.1-2008, but is avail-
       able in most versions of UNIX.

       The argument ident in the call of openlog() is probably  stored  as-is.
       Thus,  if  the  string  it  points  to  is  changed, syslog() may start
       prepending the changed string, and if the string it points to ceases to
       exist,  the  results  are  undefined.  Most portable is to use a string

       Never pass a string with user-supplied data as a format, use  the  fol-
       lowing instead:

           syslog(priority, "%s", string);

       logger(1), setlogmask(3), syslog.conf(5), syslogd(8)

       This  page  is  part of release 4.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at

Linux                             2015-02-21                         SYSLOG(3)
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