NAME

fsdb − file system debugger

SYNOPSIS

/etc/fsdb special [ − ]

DESCRIPTION

fsdb can be used to patch up a damaged file system 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 file system tree. 

fsdb automatically determines the type of file system you are trying to repair and invokes the appropriate module:

fsdb.s54k
to repair System V file systems

fsdb.affs
to repair Ardent Fast File Systems

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 file system 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

e extent slot offset (only available for the Ardent Fast File System)

+,− 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

x print as hexadecimal 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 file system.  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 file system. 

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 file system 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. 

e0b.p0x prints the first block of the current extent (for an Ardent Fast File System) in hexadecimal format

SEE ALSO

dir(4), fs(4), fsck(1M)

September 02, 1992