daemon.md

English | 中文版

Daemon Process

[TOC]

System Logging

Logging Messages

#include <syslog.h>
void syslog(int priority, const char *message, ...);

• priority priority level Composed of level and facility:

  level	Value	Description
  LOG_EMERG	0	System unusable (highest)
  LOG_ALERT	1	Action must be taken immediately
  LOG_CRIT	2	Critical conditions
  LOG_ERR	3	Error conditions
  LOG_WARNING	4	Warning conditions
  LOG_NOTICE	5	Normal but significant (default)
  LOG_INFO	6	Informational messages
  LOG_DEBUG	7	Debug-level messages (lowest)

  facility	Description
  LOG_AUTH	Security/authorization
  LOG_AUTHPRIV	Security/authorization (private)
  LOG_CRON	cron daemon
  LOG_DAEMON	System daemons
  LOG_FTP	FTP daemon
  LOG_KERN	Kernel messages
  LOG_LOCAL0	Local use
  LOG_LOCAL1	Local use
  LOG_LOCAL2	Local use
  LOG_LOCAL3	Local use
  LOG_LOCAL4	Local use
  LOG_LOCAL5	Local use
  LOG_LOCAL6	Local use
  LOG_LOCAL7	Local use
  LOG_LPR	Line printer subsystem
  LOG_MAIL	Mail system
  LOG_NEWS	Network news system
  LOG_SYSLOG	Messages generated by syslogd
  LOG_USER	User-level messages (default)
  LOG_UUCP	UUCP system

• message formatted string;

Log messages from daemon processes.

Open/Close Log

#include <syslog.h>
void openlog(const char *ident, int options, int facility);
void closelog(void);

• ident string prefixed to each log message by syslog (usually the program name);

• options options

  options	Description
  LOG_CONS	Log to console if unable to send to syslogd daemon.
  LOG_NDELAY	Open immediately, create socket right away.
  LOG_PERROR	Send to syslogd and also log to standard error.
  LOG_PID	Log process ID with each message.

• facility

Open/close log (by default, openlog does not immediately create a Unix domain socket; it is created on the first call to syslog. This can be changed by setting LOG_NDELAY).

References

[1] (US) W. Richard Stevens, (US) Bill Fenner, (US) Andrew M Rudoff. Unix Network Programming Volume 1: The Sockets Networking API. 3rd Edition