Creating a startup daemon for a shell script in FreeBSD

Question

I am trying to create a file in rc.d/ that will start up a /bin/sh script that I have written. I am following some examples found here:

http://www.freebsd.org/doc/en/articles/rc-scripting/article.html#rc-flags

#!/bin/sh -x

# PROVIDE: copyfiles

. /etc/rc.subr

name=copyfiles
rcvar=copyfiles_enable
pidfile="/var/run/${name}.pid"

command="/var/etc/copy_dat_files.sh -f /var/etc/copydatafiles.conf"
command_args="&"


load_rc_config $name
run_rc_command "$1"

It seems like I am having a problem with the pidfile. Does my script need to be the one that creates the pid file, or does it automatically get created? I have tried both ways, and whether or not i make my script create a pid file, I get an error that the pid file is not readable.

If my script is supposed to make it, what is the proper way to make the pid file?

Thanks

Answer 1

Look at the existing daemons for example (such as /etc/rc.d/mountd). Then look at the subroutines in /etc/rc.subr -- there is code in there to check the PID-file, but nothing creates it.

In other words, you can declare in the daemon-starting script, what the PID-file is, but creating it is up to the daemon. Speaking of the daemons, you may wish to use the daemon(8) utility, if your daemon is, in fact, a shell script. The utility will take care of the PID-file creation for you. (If the daemon is written in C, you can/should use daemon(3) function.)

BTW, in my own opinion, daemons, when opening up the PID-files for creation, should also lock them (with flock(3) or fcntl(2) or lockf(3)). This way, if an instance crashes (or is killed) without removing the PID-file, the next instance will have no problem determining, the file is stale.

Answer 2

In general, a daemon is supposed to create and clean up its own PID file.

From a shell-script you can give the following command to create it;

echo $$ >/var/run/${name}.pid

Do not forget to remove the file before exiting the script. Write a cleanup() function that does that and let trap call that function when certain signals occur. Also call cleanup just before exiting the script.