fsdb(8)fsdb(8)NAMEfsdb - File system debugger
SYNOPSIS
/usr/sbin/fsdb [options] path
OPTIONS
Display usage Override some error conditions Forces the path argument
to be processed only as a regular file. Set prompt to string Open for
write
DESCRIPTION
The fsdb utility operates on a device file or a file system image. The
utility first attempts to use the path argument as a device file. If
that fails, it attempts to use the path argument as a file system
image. To avoid conflict, you can specify the -f option to force the
path argument to be used as a file system image.
You must be root to use this command.
The fsdb command can be used to repair 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 inode. These greatly simplify the process
of correcting control block entries or descending the file system tree.
The fsdb command contains several error-checking routines to verify
inode and block addresses. These can be disabled if necessary by invok‐
ing fsdb with the -o option.
The fsdb command reads a block at a time and works 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 cor‐
responding block. Note that in order to modify any portion of the disk,
fsdb must be invoked with the -w option.
Wherever possible, adb-like syntax was adopted to promote the use of
fsdb through familiarity.
Numbers are considered hexadecimal by default. However, you have con‐
trol over how data is to be displayed or accepted. The base command
displays or sets the input/output base. Once set, all input will
default to this base and all output will be shown in this base. The
base can be overridden temporarily for input by preceding hexadecimal
numbers with '0x', preceding decimal numbers with '0t', or octal num‐
bers with '0'. Hexadecimal numbers beginning with a-f or A-F must be
preceded with '0x' to distinguish them from commands.
Disk addressing by fsdb is at the byte level. However, fsdb offers many
commands to convert a desired inode, directory entry, block, superblock
etc. to a byte address. Once the address has been calculated, fsdb will
record the result in dot.
Several global values are maintained by fsdb: The current base
(referred to as base); the current address (referred to as dot); the
current inode (referred to as inode); the current count (referred to as
count); and the current type (referred to as type). Most commands use
the preset value of dot in their execution. For example: > 2:inode
will first set the value of dot to 2, ':' will alert the start of a
command, and the inode command will set inode to 2. A count is speci‐
fied after a ','. Once set, count will remain at this value until a new
command is encountered which will then reset the value back to 1 (the
default). So, if >2000,400/X
is typed, 400 hex longs are listed from 2000, and when completed, the
value of dot will be 2000 + 400 * sizeof (long). If you press the
Return key, the output routine uses the current values of dot, count,
and type and displays 400 more hex longs. An asterisk (*) causes the
entire block to be displayed.
End of fragment, block and file are maintained by fsdb. When display‐
ing data as fragments or blocks, an error message is displayed when the
end of fragment or block is reached. When displaying data using the db,
ib, directory, or file commands, an error message is displayed if the
end of file is reached. This is mainly needed to avoid passing the end
of a directory or file and getting unknown and unwanted results.
An example showing several commands and the use of Return follows: >
2:ino; 0:dir?d
or > 2:ino; 0:db:block?d
The two examples are synonymous for getting to the first directory
entry of the root of the file system. Once there, subsequent use of
the Return key ( or +, -) advances to subsequent entries. The following
display is again synonymous: > 2:inode; :ls /
or > :ls /
EXAMPLES
displays 2010 in decimal (use of fsdb as a calculator for complex
arithmetic). displays i-number 386 in an inode format. This now
becomes the current inode. changes the link count for the current
inode to 4. increments the link count by 1. displays the creation
time as a hexadecimal long. displays the modification time in time
format. displays, in ASCII, block zero of the file associated with the
current inode. displays the first blocks worth of directory entries
for the root inode of this file system. It will stop prematurely if the
eof is reached. changes the current inode to that associated with the
5th directory entry (numbered from zero) of the current inode. The
first logical block of the file is then displayed in ASCII. displays
the superblock of this file system. displays cylinder group informa‐
tion and summary for cylinder group 1. changes the i-number for the
seventh directory slot in the root directory to 3. changes the name
field in the directory slot to name. displays the third block of the
current inode as directory entries. gets fragment 3c3 and fill 20 type
elements with 0x20. sets the contents of address 2050 to 0xffffffff.
0xffffffff may be truncated depending on the current type. places the
ASCII for the string at 1c92434.
Expressions
The symbols recognized by fsdb are: update the value of dot by the cur‐
rent value of type and display using the current value of count.
numeric expressions may be composed of +, -, *, and % operators (evalu‐
ated left to right) and may use parentheses. Once evaluated, the value
of dot is updated. count indicator. The global value of count will be
updated to count. The value of count remains until a new command is
run. A count specifier of '*' will attempt to show the information of a
block. The default for count is 1. display in structured style with
format specifier f. display in unstructured style with format speci‐
fier f. the value of dot. increment the value of dot by the expres‐
sion e. The amount actually incremented is dependent on the size of
type: dot = dot + e * sizeof (type)
The default for e is 1. decrement the value of dot by the
expression e (see +). multiply the value of dot by the expres‐
sion e. Multiplication and division do not use type. In the
above calculation of dot, consider the size of (type) to be 1.
divide the value of dot by the expression e (see *). restore an
address saved in register name. name must be a single letter or
digit. save an address in register name. name must be a single
letter or digit. display indicator. If f is a legitimate format
specifier, then the value of dot is displayed using format spec‐
ifier f. Otherwise, assignment is assumed. assignment indica‐
tor. The address pointed to by dot has its contents changed to
the value of the expression e or to the ASCII representation of
the quoted (" ") string s. This may be useful for changing
directory names or ASCII file information. incremental assign‐
ment. The address pointed to by dot has its contents incremented
by expression e. decremental assignment. The address pointed to
by dot has its contents decremented by expression e.
Commands
A command must be prefixed by a ':' character. Only enough letters of
the command to uniquely distinguish it are needed. Multiple commands
may be entered on one line by separating them by a space, tab or ';'.
In order to view a potentially unmounted disk in a reasonable manner,
fsdb offers the cd, pwd, ls, and find commands. The functionality of
these commands substantially matches those of its UNIX counterparts.
The '*', '?', and '[-]' wild card characters are available. display or
set base. As stated above, all input and output is governed by the
current base. If the '=b' is left off, the current base is displayed.
Otherwise, the current base is set to b. Note that this is interpreted
using the old value of base, so to ensure correctness use the '0',
'0t', or '0x' prefix when changing the base. The default for base is
hexadecimal. convert the value of dot to a block address. change the
current directory to directory dir. The current values of inode and
dot are also updated. If no dir is specified, then change directories
to inode 2 ("/"). convert the value of dot to a cylinder group. If
the current inode is a directory, then the value of dot is converted to
a directory slot offset in that directory and dot now points to this
entry. the value of dot is taken as a relative block count from the
beginning of the file. The value of dot is updated to the first byte of
this block. find files by name or i-number. find recursively searches
directory dir and below for filenames whose i-number matches i or whose
name matches pattern n. Note that only one of the two options (-name
or -inum) may be used at one time. Also, the -print is not needed or
accepted. fill an area of disk with pattern p. The area of disk is
delimited by dot and count. convert the value of dot to a fragment
address. The only difference between the fragment command and the block
command is the amount that is able to be displayed. convert the value
of dot to an inode address. If successful, the current value of inode
will be updated as well as the value of dot. As a convenient short‐
hand, if ':inode' appears at the beginning of the line, the value of
dot is set to the current inode and that inode is displayed in inode
format. list directories or files. If no file is specified, the cur‐
rent directory is assumed. Either or both of the options may be used
(but, if used, must be specified before the filename specifiers). Also,
as stated above, wild card characters are available and multiple argu‐
ments may be given. The long listing shows only the i-number and the
name; use the inode command with '?i' to get more information. toggle
the value of override. Some error conditions may be overridden if over‐
ride is toggled on. change the fsdb prompt to p. p must be surrounded
by (")s. display the current working directory. quit fsdb. the value
of dot is taken as a cylinder group number and then converted to the
address of the superblock in that cylinder group. As a shorthand, ':sb'
at the beginning of a line will set the value of dot to the superblock
and display it in superblock format. escape to shell
Inode Commands
In addition to the above commands, there are several commands that deal
with inode fields and operate directly on the current inode (they still
require the ':'). They may be used to more easily display or change the
particular fields.
The value of dot is only used by the ':db' and ':db' commands. Upon
completion of the command, the value of dot is changed to point to that
particular field. For example, >:ln=+1
would increment the link count of the current inode and set the value
of dot to the address of the link count field. access time. block
size. creation time. use the current value of dot as a direct block
index, where direct blocks number from 0 - 11. In order to display the
block itself, you need to 'pipe' this result into the block or fragment
command. For example, > 1:db:block,20/X
would get the contents of data block field 1 from the inode and
convert it to a block address. 20 longs are then displayed in
hexadecimal (see Formatted Output section). group id. use the
current value of dot as an indirect block index where indirect
blocks number from 0 - 2. This will only get the indirect block
itself (the block containing the pointers to the actual blocks).
Use the file command and start at block 12 to get to the actual
blocks. link count. modification time. mode. major device
number. minor device number. although listed here, this com‐
mand actually operates on the directory name field. Once poised
at the desired directory entry (using the directory command),
this command will allow you to change or display the directory
name. For example, > 7:dir:nm="foo"
will get the 7th directory entry of the current inode and change
its name to foo. Note that names cannot be made larger than the
field is set up for. If an attempt is made, the string is trun‐
cated to fit and a warning message to this effect is displayed.
file size. user id.
Formatted Output
There are two styles and many format types. The two styles are struc‐
tured and unstructured. Structured output is used to display inodes,
directories, superblocks and the like. Unstructured just displays raw
data. The following table shows the different ways of displaying: For‐
mat specifier, followed by one of: display as cylinder groups display
as inodes display as directories display as superblocks Format speci‐
fier, followed by one of: display as bytes display as characters dis‐
play as octal shorts or longs display as decimal shorts or longs dis‐
play as hexadecimal shorts or longs
The format specifier immediately follows the '/' or '?' character. The
values displayed by '/b' and all '?' formats are displayed in the cur‐
rent base. Also, type is appropriately updated upon completion.
FILES
Specifies the command path
SEE ALSO
Commands: fsck(8)fsdb(8)