syslog rotation

Question

I wrote a small c app that uses the syslog c interface to write messages (from man 3 syslog):

void openlog(const char *ident, int logopt, int facility);
void syslog(int priority, const char *message, ...);
void closelog(void);

My question: I'm writing messages to LOCAL0 in /var/log/local0.log. I also have cron calling logrotate on /var/log/local0.log. I've noticed that after the rotation, my app continues writing to the file that was rotated out instead of the new /var/log/local0.log.

What is the best way to fix this with a postrotate script?

1. Easy, but not ideal: completely restart the rsyslog daemon.

2. Send and handle SIGHUP in my app. This seems like the most appropriate solution. But I'm not sure what I need to do when I get the HUP. Do I just need to call closelog() then openlog()?

Answer 1

Send the SIGHUP to syslogd, not your program.

Answer 2

Another decent workaround, which doesn't quite fit your situation but can be used "in a pinch" is the copytruncate option in logrotate. It means whatever is writing to the logfile does not need to be notified.