The syslog system import defines the interface:
extern void syslog (int __pri, __const char *__fmt, ...)
which allows for variable-lengthed argument lists, much like printf. The interface is pretty simple, the first argument specifies a priority or type of log statement; the second, a formatted string in the same form that printf takes.
A simple C
#include <stdio.h>
#include <syslog.h>
int main(int argc, char *argv[]) {
syslog(LOG_NOTICE,"%s process started", argv[0]);
sleep(3);
syslog(LOG_NOTICE,"%s process terminating", argv[0]);
}Compile and running this example will result in two log entries in the system logs. Determining what log will contain the log statements can be determined by:
1) the log type, and
2) the /etc/syslog.conf file.
Note, that the log type is defined as LOG_NOTICE, and the entry in the syslog.conf file entry;
*.=info;*.=notice;*.=warn;\
auth,authpriv.none;\
cron,daemon.none;\
mail,news.none -/var/log/messages
shows that the notice log entries will be evident in /var/log/messages.Since the files are only accessible to superusers, logging in as root and tailing the log file should show the messages in the same manner as:
# cat /var/log/syslog
.
.
.
Jul 5 20:30:18 riffraff syslogd 1.4.1#18: restart.
Jul 5 20:42:07 riffraff app: ./app process started
Jul 5 20:42:10 riffraff app: ./app process terminating
You can interface with the syslog service using scripts as well.
$ logger -p user.notice "hello again"
# cat /var/log/syslog
.
.
.
Jul 5 20:42:07 riffraff app: ./app process started
Jul 5 20:42:10 riffraff app: ./app process terminating
Jul 5 21:04:06 riffraff lipeltgm: hello again
Pretty slick, huh?
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