Originální popis anglicky:
closelog, openlog, setlogmask, syslog - control system log
Návod, kniha: POSIX Programmer's Manual
#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.
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);
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);
The following example sends the message
"This is a message" 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.
printf() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<syslog.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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
.
