关于unix linux daemon程序编写的文章 e文 Unix Daemon Server Programming

作者佚名技术来源操作系统浏览发布时间 2012-06-27

tant and should be logged. A programmer wants to see debug messages or a system operator wants to see error messages. There are several ways to handle those messages.

Redirecting all output to standard I/O : This is what ancient servers do, they use stdout and stderr so that messages are written to console, terminal, file or printed on paper. I/O is redirected when starting the server. (to change destination, server must be restarted) In fact this kind of a server is a program running in foreground (not a daemon).

# mydaemon 2> error.log

This example is a program that prints output (stdout) messages to console and error (stderr) messages to a file named "error.log". Note that this is not a daemon but a normal program.

Log file method : All messages are logged to files (to different files as needed). There is a sample logging function below.

void log_message(filename,message)
char *filename;
char *message;
{
FILE *logfile;
logfile=fopen(filename,"a");
if(!logfile) return;
fprintf(logfile,"%s\n",message);
fclose(logfile);
}

log_message("conn.log","connection accepted");
log_message("error.log","can not open file");

Log server method : A more flexible logging technique is using log servers. Unix distributions have system log daemon named "syslogd". This daemon groups messages into classes (known as facility) and these classes can be redirected to different places. Syslog uses a configuration file (/etc/syslog.conf) that those redirection rules reside in.

openlog("mydaemon",LOG_PID,LOG_DAEMON)
syslog(LOG_INFO, "Connection from host %d", callinghostname);
syslog(LOG_ALERT, "Database Error !");
closelog();

In openlog call "mydaemon" is a string that identifies our daemon, LOG_PID makes syslogd log the process id with each message and LOG_DAEMON is the message class. When calling syslog call first parameter is the priority and the rest works like printf/sprintf. There are several message classes (or facility names), log options and priority levels. Here are some examples :

Message classes : LOG_USER, LOG_DAEMON, LOG_LOCAL0 to LOG_LOCAL7
Log options : LOG_PID, LOG_CONS, LOG_PERROR
Priority levels : LOG_EMERG, LOG_ALERT, LOG_ERR, LOG_WARNING, LOG_INFO
About
This text is written by Levent Karakas . Several books, sources and manual pages are used. This text includes a sample daemon program (compiles on Linux 2.4.2, OpenBSD 2.7, SunOS 5.8, SCO-Unix 3.2 and probably on your flavor of Unix). You can also download plain source file : exampled.c. Hope you find this document useful. We do love Unix.

/*
UNIX Daemon Server Programming Sample Program
Levent Karakas May 2001

To compile: cc -o exampled examped.c
To run: ./exampled
To test daemon: ps -ef|grep exampled (or ps -aux on BSD systems)
To test log: tail -f /tmp/exampled.log
To test signal: kill -HUP `cat /tmp/exampled.lock`
To terminate: kill `cat /tmp/exampled.lock`
*/

#include
#include
#include
#include

#define RUNNING_DIR "/tmp"
#define LOCK_FILE "exampled.lock"

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