Syslog

`syslog' is a comprehensive logging system written by Eric Allman which is available on most Unix systems. It provides facilities for sorting messages by source or severity and mechanisms for sending messages off to files, terminals or other machines. See chapter 12 of the "Unix System Administration Handbook (2nd Edition)" by Nemeth, Snyder, Seebass and Hein for an excellent tutorial on `syslog'.

The rules used by `syslog' are normally defined in `/etc/syslog.conf'. Each line specifies the destination for messages with particular sources and priorities. For example:

# log mail messages at priority info to mailinfo
mail.info /var/log/mailinfo
# log all ftp information to syslog on a remote machine
ftp.* @remote-machine.cs.ntu.edu.au
# all critical errors to console
*.crit   /dev/console

To use `syslog' we merely redefine the default handlers and parameter values for `nana'. For example:

#include <syslog.h>
#define L_DEFAULT_HANDLER syslog /* replaces fprintf(3) by syslog(3) */
#define L_DEFAULT_PARAMS LOG_USER /* default priority for syslog info */
#include <nana.h>

int main() {
     openlog("nana", /* identifier for these log messages */
        LOG_PID, /* also log the process id */
        LOG_DAEMON /* facility */
     );

     L("temperature is falling to %d", 35); /* logged at LOG_USER priority */
     LP(LOG_CRIT, "the snow is falling in Darwin"); /* LOG_CRIT message */
        
     closelog();
     return 0;
}

This program results in the following addition to `/var/adm/messages':

Jun 12 16:04:46 chingiz nana[2671]: the temperature is falling to 35
Jun 12 16:04:46 chingiz nana[2671]: the snow is falling in Darwin

In addition the `LOG_CRIT' message about snow falling in Darwin is sent to the console for immediate action.

Note: `syslog' normally uses `UDP' for its network communications and that `UDP' does not guarantee delivery.

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