FSDB(ADM) UNIX System V
Name
fsdb - filesystem debugger
Syntax
/etc/fsdb special [ - ]
Description
fsdb can be used to patch up a damaged filesystem after a
crash. It has conversions to translate block and i-numbers
into their corresponding disk addresses. Also included are
mnemonic offsets to access different parts of an i-node.
These greatly simplify the process of correcting control
block entries or descending the filesystem tree.
fsdb contains several error-checking routines to verify i-
node and block addresses. These can be disabled if
necessary by invoking fsdb with the optional - argument or
by the use of the O symbol. (fsdb reads the i-size and f-
size entries from the superblock of the filesystem as the
basis for these checks.)
Numbers are considered decimal by default. Octal numbers
must be prefixed with a zero. During any assignment
operation, numbers are checked for a possible truncation
error due to a size mismatch between source and destination.
fsdb reads a block at a time and will therefore work with
raw as well as block I/O. A buffer management routine is
used to retain commonly used blocks of data in order to
reduce the number of read system calls. All assignment
operations result in an immediate write-through of the
corresponding block.
The symbols recognized by fsdb are:
# absolute address
i convert from i-number to i-node address
b convert to block address
d directory slot offset
+,- address arithmetic
q quit
>,< save, restore an address
= numerical assignment
=+ incremental assignment
=- decremental assignment
=" character string assignment
O error checking flip flop
p general print facilities
f file print facility
B byte mode
W word mode
D double word mode
! escape to shell
The print facilities generate a formatted output in various
styles. The current address is normalized to an appropriate
boundary before printing begins. It advances with the
printing and is left at the address of the last item
printed. The output can be terminated at any time by typing
the delete character. If a number follows the p symbol,
that many entries are printed. A check is made to detect
block boundary overflows since logically sequential blocks
are generally not physically sequential. If a count of zero
is used, all entries to the end of the current block are
printed. The print options available are:
i print as i-nodes
d print as directories
o print as octal words
e print as decimal words
c print as characters
b print as octal bytes
The f symbol is used to print data blocks associated with
the current i-node. If followed by a number, that block of
the file is printed. (Blocks are numbered from zero.) The
desired print option letter follows the block number, if
present, or the f symbol. This print facility works for
small as well as large files. It checks for special devices
and that the block pointers used to find the data are not
zero.
Dots, tabs, and spaces may be used as function delimiters
but are not necessary. A line with just a new-line
character will increment the current address by the size of
the data type last printed. That is, the address is set to
the next byte, word, double word, directory entry or i-node,
allowing the user to step through a region of a filesystem.
Information is printed in a format appropriate to the data
type. Bytes, words and double words are displayed with the
octal address followed by the value in octal and decimal. A
.B or .D is appended to the address for byte and double word
values, respectively. Directories are printed as a
directory slot offset followed by the decimal i-number and
the character representation of the entry name. I-nodes are
printed with labeled fields describing each element.
The following mnemonics are used for i-node examination and
refer to the current working i-node:
md mode
ln link count
uid user ID number
gid group ID number
sz file size
a# data block numbers (0 - 12)
at access time
mt modification time
maj major device number
min minor device number
Examples
386i prints i-number 386 in an i-node format.
This now becomes the current working i-node.
ln=4 changes the link count for the working i-
node to 4.
ln=+1 increments the link count by 1.
fc prints, in ASCII, block zero of the file
associated with the working i-node.
2i.fd prints the first 32 directory entries for
the root i-node of this filesystem.
d5i.fc changes the current i-node to that
associated with the 5th directory entry
(numbered from zero) found from the above
command. The first logical block of the
file is then printed in ASCII.
512B.p0o prints the superblock of this filesystem in
octal.
2i.a0b.d7=3 changes the i-number for the seventh
directory slot in the root directory to 3.
This example also shows how several
operations can be combined on one command
line.
d7.nm="name" changes the name field in the directory slot
to the given string. Quotes are optional
when used with nm if the first character is
alphabetic.
a2b.p0d prints the third block of the current i-node
as directory entries.
Notes
The directory /etc/fscmd.d/TYPE contains programs for each
filesystem type; each of these programs applies some
appropriate heuristic to determine whether the supplied
special file is of the type for which it checks.
See Also
fsck(ADM), dir(F), filesystem(F), ``Patching a Filesystem
with fsdb'' in the ``Using Filesystems'' chapter of the
System Administrator's Guide
(printed 8/23/89) FSDB(ADM)