--- a/common/linuxlockfile.c	Wed Oct 15 13:24:59 2014 +0200
+++ b/common/linuxlockfile.c	Wed Oct 15 14:19:46 2014 +0200
@@ -12,8 +12,11 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <string.h>
 
 #include "logging.h"
+#include "util.h"
+#include "strhelp.h"
 
 int
 open_lockfile(char *path)
@@ -30,23 +33,55 @@
       lk.l_whence = SEEK_SET;
       lk.l_start = 0;
       lk.l_len = 0;
+      fcntl(fd, F_SETLK, &lk);
       if (fcntl(fd, F_SETLK, &lk) != -1)
-        {
-          /* FIXME (issue139): For extra security we should check if there is
-             already a pid in the file.  If so we should check in
-             /proc/$PID if there is still a process of the same name
-             as ours running... */
-          ftruncate(fd, 0);
-          pidstrlen = (size_t)snprintf(pidstr, sizeof(pidstr), "%d", getpid());
-          write(fd, pidstr, pidstrlen);
-        }
-      else
-        {
-          /* Lock can not be acquired.  Bail out... */
-          close(fd);
-          DEBUGPRINTF("Could not get an exclusive lock on %s.\n", path);
-          return -1;
-        }
+         {
+           char oldpid[20];
+           FILE *f = fopen(path, "r");
+           size_t bytes_read;
+           if (f)
+             {
+               bytes_read = fread(oldpid, 1, sizeof(oldpid), f);
+               if (bytes_read)
+                 {
+                   char *oldPath,
+                        *newPath;
+                   if (bytes_read == sizeof(oldpid))
+                     {
+                       ERRORPRINTF ("Bad information in pidfile\n");
+                     }
+                   else
+                     {
+                       oldpid[bytes_read] = '\0';
+                       oldPath = get_proc_install_dir(oldpid);
+                       newPath = get_install_dir();
+                       if (oldPath && newPath && strcmp(oldPath, newPath) == 0)
+                         {
+                           DEBUGPRINTF("Got lock but process from %s is still"
+                                       "running.\n", oldPath);
+                           xfree(oldPath);
+                           xfree(newPath);
+                           return -1;
+                         }
+                       xfree(oldPath);
+                       xfree(newPath);
+                     }
+                 }
+               fclose(f);
+             }
+
+           ftruncate(fd, 0);
+           pidstrlen = (size_t)snprintf(pidstr, sizeof(pidstr), "%d",
+                                        getpid());
+           write(fd, pidstr, pidstrlen);
+         }
+       else
+         {
+           /* Lock can not be acquired.  Bail out... */
+           close(fd);
+           DEBUGPRINTF("Could not get an exclusive lock on %s.\n", path);
+           return -1;
+         }
     }
   else
     {