diff --git a/client/lock.c b/client/lock.c
new file mode 100644
index 0000000..862048f
--- /dev/null
+++ b/client/lock.c
@@ -0,0 +1,255 @@
+    /*********************************************************************\
+    *  Copyright (c) 1991 by Wen-King Su (wen-king@vlsi.cs.caltech.edu)   *
+    *                                                                     *
+    *  You may copy or modify this file in any manner you wish, provided  *
+    *  that this notice is always included, and that you hold the author  *
+    *  harmless for any loss or damage resulting from the installation or *
+    *  use of this software.                                              *
+    \*********************************************************************/
+
+#include "tweak.h"
+#ifdef STDC_HEADERS
+#include <stdlib.h>
+#endif
+#include "client_def.h"
+#include "c_extern.h"
+#include "my-string.h"
+
+#ifndef NOLOCKING
+static char key_string[sizeof(KEY_PREFIX)+32];
+     
+static char code_str[] =
+       "0123456789:_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+     
+static void make_key_string PROTO2(unsigned long, server_addr,
+				   unsigned long, server_port)
+{
+  unsigned long v1, v2;
+  char *p;
+  
+  strcpy(key_string,KEY_PREFIX);
+  for(p = key_string; *p; p++);
+  v1 = server_addr;
+  v2 = server_port;
+  
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  v1 = v1 | (v2 << (32-3*6));
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p++ = code_str[v1 & 0x3f]; v1 >>= 6;
+  *p   = 0;
+}
+#endif
+
+/********************************************************************/
+/******* For those systems that has flock function call *************/
+/********************************************************************/
+#ifdef USE_FLOCK
+
+#include <sys/file.h>
+
+int key_persists = 1;
+static unsigned int lock_fd;
+static unsigned short okey;
+
+unsigned short client_get_key PROTO0((void))
+{
+  if(flock(lock_fd,LOCK_EX) == -1) {
+    perror("flock");
+    exit(1);
+  }
+  if(read(lock_fd,&okey,sizeof(okey)) == -1) {
+    perror("read"); exit(1);
+  }
+  if(lseek(lock_fd,0L,0) == -1) {
+    perror("seek");
+    exit(1);
+  }
+  return(okey);
+}
+
+void client_set_key PROTO1(unsigned short, key)
+{
+  if(write(lock_fd,&key,sizeof(key)) == -1) {
+    perror("write");
+    exit(1);
+  }
+  if(lseek(lock_fd,0L,0) == -1) {
+    perror("seek");
+    exit(1);
+  }
+  if(flock(lock_fd,LOCK_UN) == -1) {
+    perror("unflock");
+    exit(1);
+  }
+}
+
+void client_init_key PROTO3(unsigned long, server_addr,
+			    unsigned long, server_port,
+			    unsigned short, key)
+{
+  unsigned long omask;
+  okey = key;
+  
+  make_key_string(server_addr,server_port);
+  
+  omask = umask(0);
+  lock_fd = open(key_string,O_RDWR|O_CREAT,0666);
+  umask(omask);
+}
+
+#endif
+/********************************************************************/
+/******* For those systems that has lockf function call *************/
+/********************************************************************/
+#ifdef USE_LOCKF
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+int key_persists = 1;
+static unsigned int lock_fd;
+static unsigned short okey;
+
+unsigned short client_get_key PROTO0((void))
+{
+  if(lockf(lock_fd,F_LOCK,sizeof(okey)) == -1) {
+    perror("lockf");
+    exit(1);
+  }
+  if(read(lock_fd,&okey,sizeof(okey)) == -1) {
+    perror("read");
+    exit(1);
+  }
+  if(lseek(lock_fd,0L,0) == -1) {
+    perror("seek");
+    exit(1);
+  }
+  return(okey);
+}
+
+void client_set_key PROTO1(unsigned short, key)
+{
+  if(write(lock_fd,&key,sizeof(key)) == -1) {
+    perror("write");
+    exit(1);
+  }
+  if(lseek(lock_fd,0L,0) == -1) {
+    perror("seek");
+    exit(1);
+  }
+  if(lockf(lock_fd,F_ULOCK,sizeof(key)) == -1) {
+    perror("unlockf");
+    exit(1);
+  }
+}
+
+void client_init_key PROTO3(unsigned long, server_addr,
+			    unsigned long, server_port,
+			    unsigned short, key)
+{
+  unsigned long omask;
+  okey = key;
+  
+  make_key_string(server_addr,server_port);
+  
+  omask = umask(0);
+  lock_fd = open(key_string,O_RDWR|O_CREAT,0666);
+  umask(omask);
+}
+
+#endif
+/********************************************************************/
+/******* For those systems that has SysV shared memory + lockf ******/
+/********************************************************************/
+#ifdef USE_SHAREMEM_AND_LOCKF
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#include <sys/ipc.h>
+#include <sys/shm.h>
+
+int key_persists = 0;
+static unsigned short *share_key;
+static unsigned int lock_fd;
+
+unsigned short client_get_key PROTO0((void))
+{
+  if(lockf(lock_fd,F_LOCK,2) == -1) {
+    perror("lockf");
+    exit(1);
+  }
+  return(*share_key);
+}
+
+void client_set_key PROTO1(unsigned short, key)
+{
+  *share_key = key;
+  if(lockf(lock_fd,F_ULOCK,2) == -1) {
+    perror("unlockf");
+    exit(1);
+  }
+}
+
+void client_init_key PROTO3(unsigned long, server_addr,
+			    unsigned long, server_port,
+			    unsigned short, key)
+{
+  unsigned long omask;
+  key_t lock_key;
+  int   lock_shm;
+  
+  make_key_string(server_addr,server_port);
+  
+  omask = umask(0);
+  lock_fd = open(key_string,O_RDWR|O_CREAT,0666);
+  umask(omask);
+  
+  if((lock_key = ftok(key_string,238)) == -1) {
+    perror("ftok");
+    exit(1);
+  }
+  if((lock_shm = shmget(lock_key,sizeof(short),IPC_CREAT|0666)) == -1) {
+    perror("shmget");
+    exit(1);
+  }
+  if(!(share_key = (unsigned short *) shmat(lock_shm,(char*)0,0))) {
+    perror("shmat");
+    exit(1);
+  }
+  *share_key = key;
+}
+
+#endif
+/********************************************************************/
+/******* For those who does not want to use locking *****************/
+/********************************************************************/
+#ifdef NOLOCKING
+
+int key_persists = 0;
+static unsigned short okey;
+
+unsigned short client_get_key PROTO0((void))
+{
+  return(okey);
+}
+
+void client_set_key PROTO1(unsigned short, key)
+{
+  okey = key;
+}
+
+void client_init_key PROTO3(unsigned long, server_addr,
+			    unsigned long, server_port,
+			    unsigned short, key)
+{
+  okey = key;
+}
+
+#endif