Download an older version of the lib, and the INSTALL file contains a
section:
T.  How can I use Lock Files with rxtx?

Redhat users.  Note that Redhat changed group uucp to group lock with
Redhat 7.2.

Mandrake users.  Note that /var/lock needs to be group uucp for this to
work.

Mac OS X users.  Note that you may need to create the lock directory
with group uucp ownership.

RXTX uses lock files by default.  configure --disable-lockfiles to
generate rxtx libraries without lock files.  Its strongly recommended
that you do use lock files to prevent rxtx from stomping on other
programs using serial ports.

Lock files are used to prevent more than one program accessing a port at
a time.  Lock files require a bit of sysadmin to work properly..

Rxtx has support for lock files on Linux only.  It may work on other
platforms but read the source before blindly trying it.

Before you use lock files you need to do one of two things:

1.  Be the root or uucp user on your machine whenever you use rxtx
2.  add the specific user that needs to use rxtx to the group uucp.
    (preferred)

To add a user to the uucp group edit /etc/group as root and change the
following:
    uucp::14:uucp
to something like:
    uucp::14:uucp,jarvi
In this case jarvi is the login name for the user that needs to use lock
files.
Do not change the number (14).  Whatever is in your group file is correct.

User jarvi in this case can now use rxtx with lock files.

The lock file code does not support kermit style lock files or lock files in
/var/spool.  Its sure to fail if you're using subdirectories in /dev or
do not have /dev.

Still cant get things to run under a root account?

Vadim Tkachenko writes:
   
"Maybe you remember - couple of months back I've run into inability to
run the JDK 1.3+ from under root account. Today, absolutely suddenly,
something clicked in my head and the cause was found: libsafe. To make
JDK work, it is enough to disable libsafe (unset LD_PRELOAD)."

As another option it is possible to use a Lock File Server.  In this
case, a server runs in group uucp or lock and rxtx then connects to
localhost to lock and unlock the port.  The server and install
instructions can be found in src/lfd.  RXTX will need to be configured
to use the server:
  configure --enable-lockfile_server

Any user can then lock the ports if they are not already locked.

Good luck

---
JSC