Lock files should be stored within the
/var/lock directory structure.
Lock files for devices and other resources shared by multiple
applications, such as the serial device lock files that were
originally found in either
/usr/spool/uucp, must now be stored in
/var/lock. The naming convention which must be
used is "LCK.." followed by the base name of the device. For example,
to lock /dev/ttyS0 the file "LCK..ttyS0" would be created.
The format used for the contents of such lock files must be the HDB UUCP lock file format. The HDB format is to store the process identifier (PID) as a ten byte ASCII decimal number, with a trailing newline. For example, if process 1230 holds a lock file, it would contain the eleven characters: space, space, space, space, space, space, one, two, three, zero, and newline.
 Then, anything wishing to use
can read the lock file and act accordingly (all locks in
/var/lock should be world-readable).