badsect - create files to contain bad sectors
/sbin/badsect sector ...
Badsect makes a file to contain a bad sector. Normally, bad sectors are made inaccessible
by the standard formatter, which provides a forwarding table for bad sectors to the
driver; see bad144(8) for details. If a driver supports the bad blocking standard it is
much preferable to use that method to isolate bad blocks, since the bad block forwarding
makes the pack appear perfect, and such packs can then be copied with dd(1). The tech-
nique used by this program is also less general than bad block forwarding, as badsect
can't make amends for bad blocks in the i-list of file systems or in swap areas.
Adding a sector which is suddenly bad to the bad sector table currently requires the run-
ning of the standard DEC formatter, as UNIX does not supply formatters. Thus to deal with
a newly bad block or on disks where the drivers do not support the bad-blocking standard
badsect may be used to good effect.
Badsect is used on a quiet file system in the following way: First mount the file system,
and change to its root directory. Make a directory BAD there and change into it. Run
badsect giving as argument all the bad sectors you wish to add. (The sector numbers
should be given as physical disk sectors relative to the beginning of the file system,
exactly as the system reports the sector numbers in its console error messages.) Then
change back to the root directory, unmount the file system and run fsck(8) on the file
system. The bad sectors should show up in two files or in the bad sector files and the
free list. Have fsck remove files containing the offending bad sectors, but do not have
it remove the BAD/nnnnn files. This will leave the bad sectors in only the BAD files.
Badsect works by giving the specified sector numbers in a mknod(2) system call (after tak-
ing into account the filesystem's block size), creating a regular file whose first block
address is the block containing bad sector and whose name is the bad sector number. The
file has 0 length, but the check programs will still consider it to contain the block con-
taining the sector. This has the pleasant effect that the sector is completely inaccessi-
ble to the containing file system since it is not available by accessing the file.
mknod(2), bad144(8), fsck(8)
If both sectors which comprise a (1024 byte) disk block are bad, you should specify only
one of them to badsect, as the blocks in the bad sector files actually cover both (bad)
On the PDP-11, only sector number less than 131072 may be specified on 1024-byte block
filesystems, 65536 on 512-byte block filesystems. This is because only a short int is
passed to the system from mknod.
3rd Berkeley Distribution BADSECT(8)