Also...
running it from inittab will ensure that even if the process crashes it will run again next time, unlike if you use a self created lockfile....
P.
Marko A. Jennings wrote:
On Tue, August 29, 2006 5:07 pm, Scott Silva wrote:
Johnny Hughes spake the following on 8/29/2006 1:02 PM:
On Tue, 2006-08-29 at 15:59 -0400, mike.redan@bell.ca wrote:
Maybe I am being dense here ... BUT ...
Doesn't the "echo $$" only happen AFTER the else process is finished ???
if you make the "else" process be the rsync script, then it will not create $pidfile until after the rsync is done ... which does not help you.
if you leave the else process as is and kick off the rsync after the echo $$ then it is not the same PID that you wrote to the $pidfile and you will start more than one rsync process ... as the PID that you wrote to $pidfile as the echo process ... that already finished ... or I am mistaken?
The idea of it is to place that bit of code at or near the beginning of your script, then have the rsync process start after the "echo $$". That will put the PID of your script into that file, the rsync process will be started in the script, and the script would not end until the rsync one does..so you are fairly safe that two instances of your script will run at thte same time..
OK ... I see.
The rsync process is a second PID ... but the first PID is also still open until after the script closes.
I tried the above, but was able to start multiple copies of the script. So I will have to see what is not catching the runs. The lockfile is there, but not stopping another execution of the script.
I use the lockfile utility. Take a look at its man page, it is well written. Here is how I use it (Bourne shell):
# try to create the lock and check the outcome lockfile -r 0 /var/run/myapp.lock 1>/dev/null 2>&1 status=$?
if [ ${status} -ne 0 ] ;then echo "Another instance already running. Aborting." exit 1 fi
# body of the script here
# remove the lock at the end of the script rm -f /var/run/myapp.lock
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