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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CLOSELOG(3P) POSIX Programmer's Manual CLOSELOG(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
closelog, openlog, setlogmask, syslog — control system log
#include <syslog.h>
void closelog(void);
void openlog(const char *ident, int logopt, int facility);
int setlogmask(int maskpri);
void syslog(int priority, const char *message, ... /* arguments */);
The syslog() function shall send a message to an implementation-
defined logging facility, which may log it in an implementation-
defined system log, write it to the system console, forward it to
a list of users, or forward it to the logging facility on another
host over the network. The logged message shall include a
message header and a message body. The message header contains
at least a timestamp and a tag string.
The message body is generated from the message and following
arguments in the same manner as if these were arguments to
printf(), except that the additional conversion specification %m
shall be recognized; it shall convert no arguments, shall cause
the output of the error message string associated with the value
of errno on entry to syslog(), and may be mixed with argument
specifications of the "%n$" form. If a complete conversion
specification with the m conversion specifier character is not
just %m, the behavior is undefined. A trailing <newline> may be
added if needed.
Values of the priority argument are formed by OR'ing together a
severity-level value and an optional facility value. If no
facility value is specified, the current default facility value
is used.
Possible values of severity level include:
LOG_EMERG A panic condition.
LOG_ALERT A condition that should be corrected immediately,
such as a corrupted system database.
LOG_CRIT Critical conditions, such as hard device errors.
LOG_ERR Errors.
LOG_WARNING
Warning messages.
LOG_NOTICE Conditions that are not error conditions, but that
may require special handling.
LOG_INFO Informational messages.
LOG_DEBUG Messages that contain information normally of use
only when debugging a program.
The facility indicates the application or system component
generating the message. Possible facility values include:
LOG_USER Messages generated by arbitrary processes. This is
the default facility identifier if none is specified.
LOG_LOCAL0 Reserved for local use.
LOG_LOCAL1 Reserved for local use.
LOG_LOCAL2 Reserved for local use.
LOG_LOCAL3 Reserved for local use.
LOG_LOCAL4 Reserved for local use.
LOG_LOCAL5 Reserved for local use.
LOG_LOCAL6 Reserved for local use.
LOG_LOCAL7 Reserved for local use.
The openlog() function shall set process attributes that affect
subsequent calls to syslog(). The ident argument is a string
that is prepended to every message. The logopt argument indicates
logging options. Values for logopt are constructed by a bitwise-
inclusive OR of zero or more of the following:
LOG_PID Log the process ID with each message. This is useful
for identifying specific processes.
LOG_CONS Write messages to the system console if they cannot
be sent to the logging facility. The syslog()
function ensures that the process does not acquire
the console as a controlling terminal in the process
of writing the message.
LOG_NDELAY Open the connection to the logging facility
immediately. Normally the open is delayed until the
first message is logged. This is useful for programs
that need to manage the order in which file
descriptors are allocated.
LOG_ODELAY Delay open until syslog() is called.
LOG_NOWAIT Do not wait for child processes that may have been
created during the course of logging the message.
This option should be used by processes that enable
notification of child termination using SIGCHLD,
since syslog() may otherwise block waiting for a
child whose exit status has already been collected.
The facility argument encodes a default facility to be assigned
to all messages that do not have an explicit facility already
encoded. The initial default facility is LOG_USER.
The openlog() and syslog() functions may allocate a file
descriptor. It is not necessary to call openlog() prior to
calling syslog().
The closelog() function shall close any open file descriptors
allocated by previous calls to openlog() or syslog().
The setlogmask() function shall set the log priority mask for the
current process to maskpri and return the previous mask. If the
maskpri argument is 0, the current log mask is not modified.
Calls by the current process to syslog() with a priority not set
in maskpri shall be rejected. The default log mask allows all
priorities to be logged. A call to openlog() is not required
prior to calling setlogmask().
Symbolic constants for use as values of the logopt, facility,
priority, and maskpri arguments are defined in the <syslog.h>
header.
The setlogmask() function shall return the previous log priority
mask. The closelog(), openlog(), and syslog() functions shall not
return a value.
No errors are defined.
The following sections are informative.
Using openlog()
The following example causes subsequent calls to syslog() to log
the process ID with each message, and to write messages to the
system console if they cannot be sent to the logging facility.
#include <syslog.h>
char *ident = "Process demo";
int logopt = LOG_PID | LOG_CONS;
int facility = LOG_USER;
...
openlog(ident, logopt, facility);
Using setlogmask()
The following example causes subsequent calls to syslog() to
accept error messages, and to reject all other messages.
#include <syslog.h>
int result;
int mask = LOG_MASK (LOG_ERR);
...
result = setlogmask(mask);
Using syslog
The following example sends the message "Thisisamessage" to the
default logging facility, marking the message as an error message
generated by random processes.
#include <syslog.h>
char *message = "This is a message";
int priority = LOG_ERR | LOG_USER;
...
syslog(priority, message);
None.
None.
None.
fprintf(3p)
The Base Definitions volume of POSIX.1‐2017, syslog.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 CLOSELOG(3P)
Pages that refer to this page: syslog.h(0p), openlog(3p), setlogmask(3p), syslog(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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