1 files changed, 6 insertions, 1 deletions
diff --git a/src/os_unix.c b/src/os_unix.c
index 4228aaaf0..f20763e5b 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4435,7 +4435,12 @@ static int unixLockSharedMemory(unixFile *pDbFd, unixShmNode *pShmNode){
       rc = SQLITE_READONLY_CANTINIT;
     }else{
       rc = unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1);
-      if( rc==SQLITE_OK && robust_ftruncate(pShmNode->hShm, 0) ){
+      /* The first connection to attach must truncate the -shm file.  We
+      ** truncate to 3 bytes (an arbitrary small number, less than the
+      ** -shm header size) rather than 0 as a system debugging aid, to
+      ** help detect if a -shm file truncation is legitimate or is the work
+      ** or a rogue process. */
+      if( rc==SQLITE_OK && robust_ftruncate(pShmNode->hShm, 3) ){
         rc = unixLogError(SQLITE_IOERR_SHMOPEN,"ftruncate",pShmNode->zFilename);
       }
     }