UNDELETE

                            U. S. Geological Survey
                       National Strong Motion Data Center
                          Office of Earthquake Studies
                             Menlo Park, CA  94025

                                   22-JAN-80



 1.0  Operating Procedure


      UNDELETE attempts to resurrect  disk  files  that  have  been  accidently
 deleted.   Files  to be recovered are specified using a search pattern similar
 to the SRD Select Entry option:

      1.  A question mark or asterisk will match any single character;

      2.  Stem searches are performed for the file name and type fields;  and

      3.  Any unspecified fields default to a wild card search.

 The special version numbers, 0 and -1, are not supported.

      Whenever a matched file header is found, its file I.D.  is printed, along
 with  a  PIP-like  listing  of  the  file  owner, file specification, size and
 creation date.  This information will be helpful in returning the file to  the
 proper directory (usually the owner's UFD).

      The procedure to follow is:

      1.  Log on to  a  privileged  account,  if  necessary,  preferably  on  a
          hardcopy terminal.

      2.  Immediately halt all activity on the disk and DMOunt it.

      3.  ALLocate the disk to yourself  and  MOUnt  it  with  the  index  file
          unlocked (/UNL).

      4.  Run UNDELETE and provide the name of the disk and the search pattern.

      5.  Run the VFY /UP and /LO options with the listing  and  scratch  files
          directed  to  another disk.  (The listing file may get rather lengthy
          if lots of disk blocks were deleted, so you  may  want  to  send  the
          listing to a disk or NL:.)

      6.  Rename the recovered files from [1,3] to  their  proper  directories.
          (Warning:  recover all files before renaming, or copy them to another
          medium one directory at a time.  If you guess  wrong  at  the  proper
          UFD, it could be extended to accomodate the new directory entries and
          re-use a disk block from one of the files yet to be recovered.)









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      7.  If there are extra recovered files that you want to delete again,  be
          sure  to  rebuild  the  volume  bit  map again to take care of doubly
          allocated disk blocks before returning it to service (the /RE and /UP
          options in VFY).

      8.  Always VFY the disk one last time before putting it back on-line!

      9.  When you are satisfied everything is OK, return the disk back to  its
          original state (PUBLIC, /-UNL, etc.).




 2.0  Compilation and Task Building


      UNDELETE is a non-privileged program written in FORTRAN IV-PLUS (it needs
 32-bit  integer  arithmetic).   The command files supplied will re-compile and
 re-task build the program.  The requirements for a successful build are:

      1.  ASN the logical device SY:  to the source disk;

      2.  ASN the logical device MP:  to the map device;

      3.  Be sure USERLIB.OLB has been created first;

      4.  Invoke @UNDELETE to automatically compile and task build UNDELETE  in
          the current directory.


      UNDELETE does not use the MCR get command line feature  so  there  is  no
 reason to INStall UNDELETE permanently.  Since it is always risky messing with
 the on-disk structure on a live system, UNDELETE should be considered  a  last
 resort  to recover files that would be too costly or impossible to recover any
 other way.  It has, however, been  used  to  recover  an  entire  system  disk
 deleted  with  a  PIP  wild  card specification, and also to recover an entire
 directory on the system disk while the system was running.  IT WORKS!