NAME

       shlock - Create lock files for use in shell scripts

SYNOPSIS

       shlock [-b|-c|-u] -f name -p pid

DESCRIPTION

       shlock tries to create a lock file named name and write the process ID pid into it.  If the file already
       exists, shlock will read the process ID from the file and test to see whether the process is currently
       running.  If the process exists, then the file will not be created.  shlock exits with a zero status if
       it could create the lock file, or non-zero if the file refers to a currently active process.

       A Perl wrapper around shlock can be used via the "INN::Utils::Shlock" module.

OPTIONS

       -b  Process  IDs  are  normally  read  and  written  in ASCII.  If the -b flag is used, then they will be
           written as a binary int.

       -c  If the -c flag is used, then shlock will not create a lock file, but will instead use the file to see
           if the lock is held by another program.  If the lock is valid, the program will exit with a  non-zero
           status;  if  the lock is not valid (i.e. invoking shlock without the flag would have succeeded), then
           the program will exit with a zero status.

       -f name
           name is the name of the lock file shlock attempts to create.  If the file  already  exists,  it  will
           read  the  process  ID  from  the  file  and exit with a non-zero status if this process is currently
           active.

       -p pid
           pid is the process ID to write into the file name.

       -u  For compatibility with other systems, the -u flag is accepted as a synonym for -b since binary  locks
           are used by many UUCP packages.

EXAMPLES

       The following example shows how shlock would be used within a shell script:

           LOCK=<pathrun in inn.conf>/LOCK.send
           trap 'rm -f ${LOCK} ; exit 1' 1 2 3 15
           if shlock -p $$ -f ${LOCK} ; then
               # Do appropriate work.
           else
               echo "Locked by `cat ${LOCK}`"
           fi

HISTORY

       Written  by Rich $alz <rsalz@uunet.uu.net> for InterNetNews after a description of HDB UUCP locking given
       by Peter Honeyman, and improved by Berend Reitsma to solve a race condition.  Converted to POD by  Julien
       Elie.

SEE ALSO

       INN::Utils::Shlock(3pm).

INN 2.7.2                                          2024-06-23                                          SHLOCK(1)