Perhaps that example code would clearer if written:

(

   if ! flock -w 1 200 ; then

           echo >&2 "Another process is still running..."

           exit

   fi

   RunLocked

) 200> ${lockdir}/mirror.centos.lock

Or

exec 200> ${lockdir}/mirror.centos.lock

if ! flock -w 1 200 ; then

   echo >&2 "Another process is still running..."

   exit

fi

RunLocked

Or for a more succinct version:

( flock -w 1 200 && RunLocked ) 200> ${lockdir}/mirror.centos.lock

(Point is: referencing “$?” is almost never needed, and usually obfuscatory.)

Using "touch" and "test -e" as a lock test is not safe.  If the shell dies for any reason, the lock file will get stale.

If you sync station is linux, a safer option is to use the flock(1) program:


NAME
       flock - Manage locks from shell scripts

SYNOPSIS
       flock [-sxon] [-w timeout] lockfile [-c] command...

       flock [-sxon] [-w timeout] lockdir [-c] command...

       flock [-sxun] [-w timeout] fd


Here is the lock part of my mirror script:

RunLocked()
{
   ....
}

(
  flock -w 1 200
  if [ "$?" -ne 0 ] ; then
    echo "Error, lock is already taken..."
    exit
  else
    RunLocked
  fi
) 200> ${lockdir}/mirror.centos.lock

                                       Jonny

-- 

João Carlos Mendes Luís - Computer & Networking Engineer

jonny@jonny.eng.br

On 07/12/2011 11:56 AM, Adam wrote:

admin wrote:

Yes It would be great . I'm still rsync centos repo.
Could you provide me bash script to rsync with file locking ?

Attached is a bash locking rsync script.  This script is pretty informative and intelligent.  It verifies that the time stamp of the server you are syncing form is newer then yours before it syncs.  Hence it shouldn't ever delete files you have already downloaded if you hit an old mirror.

Adam

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