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Technical Reference: Base Operating System and Extensions, Volume 2
syslog_r, openlog_r, closelog_r, or setlogmask_r Subroutine
Purpose
Controls the system log.
Library
Standard C Library (libc.a)
Syntax
#include <syslog.h>
int syslog_r (Priority, SysLogData, Format, . . .)
int Priority;
struct syslog_data * SysLogData;
const char * Format;
int openlog_r (ID, LogOption, Facility, SysLogData)
const char * ID;
int LogOption;
int Facility;
struct syslog_data *SysLogData;
void closelog_r (SysLogData)
struct syslog_data *SysLogData;
int setlogmask_r ( MaskPriority, SysLogData)
int MaskPriority;
struct syslog_data *SysLogData;
Description
The syslog_r subroutine writes messages onto the
system log maintained by the syslogd daemon.
The messages are similar to the Format parameter
in the printf subroutine,
except that the %m field is replaced by the current error message obtained
from the errno global variable. A trailing new-line
character can be added to the message if needed.
Messages are read by the syslogd daemon and written
to the system console or log file, or forwarded to the syslogd daemon on the appropriate host.
If a program requires special processing, you can use the openlog_r subroutine to initialize the log file.
The syslog_r subroutine takes as a second parameter
a variable of the type struct syslog_data, which should
be provided by the caller. When that variable is declared, it should be set
to the SYSLOG_DATA_INIT value, which specifies an initialization
macro defined in the sys/syslog.h file. Without initialization,
the data structure used to support the thread safety is not set up and the syslog_r subroutine does not work properly.
Messages are tagged with codes indicating the type of Priority for each. A Priority is encoded as a Facility, which describes the part of the system generating
the message, and as a level, which indicates the severity of the message.
If the syslog_r subroutine cannot pass the message
to the syslogd daemon, it writes the message the /dev/console file, provided the LOG_CONS option is set.
The closelog_r subroutine closes the log file.
The setlogmask_r subroutine uses the bit mask in
the MaskPriority parameter to set the new log priority
mask and returns the previous mask.
The LOG_MASK and LOG_UPTO macros
in the sys/syslog.h file are used to create the priority
mask. Calls to the syslog_r subroutine with a priority
mask that does not allow logging of that particular level of message causes
the subroutine to return without logging the message.
Programs using this subroutine must link to the libpthreads.a library.
Parameters
Priority |
Specifies the part of the system generating the message and indicates
the level of severity of the message. The level of severity is selected from
the following list:
- A condition that should be corrected immediately, such as a corrupted
database.
- A critical condition, such as hard device errors.
- A message containing information useful to debug a program.
- A panic condition reported to all users, such as an unusable system.
- An error condition.
- A general information message.
- A condition requiring special handling, other than an error condition.
- A warning message.
|
SysLogData |
Specifies a structure that contains the following information:
- The file descriptor for the log file.
- The status bits for the log file.
- A string for tagging the log entry.
- The mask of priorities to be logged.
- The default facility code.
- The address of the local logger.
|
Format |
Specifies the format, given in the same format as for the printf subroutine. |
ID |
Contains a string attached to the beginning of every message. The Facility
parameter encodes a default facility from the previous list to be assigned
to messages that do not have an explicit facility encoded. |
LogOption |
Specifies a bit field that indicates logging options. The values of LogOption are:
- LOG_CONS
- Sends messages to the console if unable to send them to the syslogd command. This option is useful in daemon processes that have
no controlling terminal.
- LOG_NDELAY
- Opens the connection to the syslogd command
immediately, instead of when the first message is logged. This option is
useful for programs that need to manage the order in which file descriptors
are allocated.
- LOG_NOWAIT
- Logs messages to the console without waiting for forked children.
Use this option for processes that enable notification of child termination
through SIGCHLD; otherwise, the syslog subroutine may block, waiting for a child process whose exit status
has already been collected.
- LOG_ODELAY
- Delays opening until the syslog subroutine is
called.
- LOG_PID
- Logs the process ID with each message. This option is useful for identifying
daemons.
|
Facility |
Specifies which of the following values generated the message:
- LOG_AUTH
- Indicates the security authorization system: the login command, the su command, and so on.
- LOG_DAEMON
- Logs system daemons.
- LOG_KERN
- Logs messages generated by the kernel. Kernel processes should use
the bsdlog routine to generate syslog messages. The syntax of bsdlog is identical to syslog. The bsdlog messages can only
be created by kernel processes and must be of LOG_KERN priority.
- LOG_LPR
- Logs the line printer spooling system.
- LOG_LOCAL0 through LOG_LOCAL7
- Reserved for local use.
- LOG_MAIL
- Logs the mail system.
- LOG_NEWS
- Logs the news subsystem.
- LOG_UUCP
- Logs the UUCP subsystem.
- LOG_USER
- Logs messages generated by user processes. This is the default facility
when none is specified.
- Remote file systems, such as the Andrew File System (AFS).
- The UUCP subsystem.
- Messages generated by user processes. This is the default facility when
none is specified.
|
MaskPriority |
Enables logging for the levels indicated by the bits in the mask that
are set, and disables logging where the bits are not set. The default mask
allows all priorities to be logged. |
Return Values
0 |
Indicates that the subroutine was successful. |
-1 |
Indicates that the subroutine was not successful. |
Examples
- To log an error message concerning a possible security breach, enter:
syslog_r (LOG_ALERT, syslog_data_struct, "%s", "who:internal error 23");
- To initialize the log file, set the log priority mask, and log an error
message, enter:
openlog_r ("ftpd", LOG_PID, LOG_DAEMON, syslog_data_struct);
setlogmask_r (LOG_UPTO (LOG_ERR), syslog_data_struct);
syslog_r (LOG_INFO, syslog_data_struct, "");
- To log an error message from the system, enter:
syslog_r (LOG_INFO | LOG_LOCAL2, syslog_data_struct, "system error: %m");
Related Information
The prof command.
The syslogd
daemon.
The printf, fprintf, sprintf, wsprintf, vprintf, vfprintf, vsprintf, or vwsprintf subroutine.
Subroutines Overview and List of Multithread Subroutines in AIX 5L Version 5.2 General Programming Concepts: Writing and Debugging Programs.
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