FSDB_UDFS(1M) Maintenance Commands FSDB_UDFS(1M)


fsdb_udfs - udfs file system debugger


fsdb [-F] udfs [generic_option] [-o specific_option] special


The fsdb_udfs command is an interactive tool that can be used to patch up
a damaged udfs file system. fsdb_udfs has conversions to translate block
and i-numbers into their corresponding disk addresses. Mnemonic offsets
to access different parts of an inode are also included. Mnemonic offsets
greatly simplify the process of correcting control block entries or
descending the file system tree.

fsdb contains several error-checking routines to verify inode and block
addresses. These can be disabled if necessary by invoking fsdb with the
-o option or by using the o command.

fsdb reads one block at a time, and therefore works with raw as well as
block I/O devices. 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. In order to modify any portion of the disk, fsdb
must be invoked with the -w option.

Wherever possible, adb-like syntax has been adopted to promote the use of
fsdb through familiarity.


The following options are supported:

-o specific_option
Specify udfs file system specific options in a
comma-separated list with no intervening spaces.
The following specific options are supported:

Override some error conditions.

Set prompt to string.

Open for write.

Display usage.


Numbers are considered hexadecimal by default. The user has control over
how data is to be displayed or accepted. The base command displays or
sets the input and output base. Once set, all input defaults to this base
and all output displays in this base. The base can be overridden
temporarily for input by preceding hexadecimal numbers by 0x, preceding
decimal numbers with a 0t, or octal numbers with a 0. Hexadecimal numbers
beginning with a-f or A-F must be preceded with a 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, and so
forth, to a byte address. After the address has been calculated, fsdb
records the result in the current address (dot).

Several global values are maintained by fsdb:

o Current base (referred to as base)

o Current address (referred to as dot)

o Current inode (referred to as inode)

o Current count (referred to as count)

o Current type (referred to as type)

Most commands use the preset value of dot in their execution. For

> 2:inode

first sets the value of dot (.) to 2, colon (:), signifies the start of a
command, and the inode command sets inode to 2. A count is specified
after a comma (,). Once set, count remains at this value until a new
command is encountered that resets the value back to 1 (the default).

So, if

> 2000,400/X

is entered, 400 hex longs are listed from 2000, and when completed, the
value of dot is 2000 + 400 * sizeof (long). If a RETURN is then entered,
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. An example showing several commands and the use of RETURN
would be:

> 2:ino; 0:dir?d


> 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, subsequently entering a
RETURN, plus (+), or minus (-) advances to subsequent entries. Notice

> 2:inode; :ls


> :ls /

is again synonymous.


The following symbols are recognized by fsdb:

Update the value of dot by the current value of type and
display using the current value of count.

Update the value of dot by specifying a numeric expression.
Specify numeric expressions using addition, subtraction,
multiplication, and division operators ( +, -, *, and %).
Numeric expressions are evaluated from left to right and can
use parentheses. After evaluation, the value of dot is

, count
Update the count indicator. The global value of count is
updated to count. The value of count remains until a new
command is run. A count specifier of * attempts to show a
blocks's worth of information. The default for count is 1.

? f
Display in structured style with format specifier f. See
Formatted Output.

/ f
Display in unstructured style with format specifier f. See
Formatted Output.

Display the value of dot.

Increment the value of dot by the expression 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 expression e.
Multiplication and division don't use type. In the above
calculation of dot, consider the sizeof (type) to be 1.

Divide the value of dot by the expression e. See *.

< name
Restore an address saved in register name. name must be a
single letter or digit.

> name
Save an address in register name. name must be a single
letter or digit.

= f
Display indicator. If f is a legitimate format specifier
(see Formatted Output), then the value of dot is displayed
using format specifier f. Otherwise, assignment is assumed.
See = [s] [e].

= [s] [e]
Change the value of dot using an assignment indicator. 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 can be useful for changing
directory names or ASCII file information.

=+ e
Change the value of dot using an incremental assignment. The
address pointed to by dot has its contents incremented by
expression e.

=- e
Change the value of dot using a decremental assignment.
Decrement the contents of the address pointed to by dot by
expression e.


A command must be prefixed by a colon (:). Only enough letters of the
command to uniquely distinguish it are needed. Multiple commands can be
entered on one line by separating them by a SPACE, TAB, or semicolon

To view a potentially unmounted disk in a reasonable manner, fsdb
supports the cd, pwd, ls, and find commands. The functionality of each of
these commands basically matches that of its UNIX counterpart. See cd(1),
pwd(1), ls(1), and find(1) for details. The *, ,, ?, and - wildcard
characters are also supported.

The following commands are supported:


Display or set the base. All input and output is governed by the
current base. Without the = b, displays the current base. Otherwise,
sets the current base to b. Base 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.

cd [dir]

Change the current directory to directory dir. The current values of
inode and dot are also updated. If dir is not specified, changes
directories to inode 2, root (/).


If the current inode is a directory, converts the value of dot to a
directory slot offset in that directory, and dot now points to this


Set the value of dot as a relative block count from the beginning of
the file. The value of dot is updated to the first byte of this

find dir [-name n] | [-inum i]

Find files by name or i-number. Recursively searches directory dir
and below for file names whose i-number matches i or whose name
matches pattern n. Only one of the two options (-name or -inum) can
be used at one time. The find -print is not necessary 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 an inode address. If successful, the
current value of inode is updated as well as the value of dot. As a
convenient shorthand, 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.

ls [ -R ] [-l ] pat1 pat2...

List directories or files. If no file is specified, the current
directory is assumed. Either or both of the options can be used (but,
if used, must be specified before the filename specifiers). Wild card
characters are available and multiple arguments are acceptable. 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 might be
overridden if override is toggled to on.

prompt "p"

Change the fsdb prompt to p. p must be enclosed in quotes.


Display the current working directory.


Quit fsdb.


Convert the value of dot and if this is a valid tag, print the volume
structure according to the tag.


Escape to the shell.

Inode Commands

In addition to the above commands, several other commands deal with inode
fields and operate directly on the current inode (they still require the
colon (:). They can be used to more easily display or change the
particular fields. The value of dot is only used by the :db and :ib
commands. Upon completion of the command, the value of dot is changed so
that it points to that particular field. For example,

> :ln=+1

increments the link count of the current inode and sets the value of dot
to the address of the link count field.

The following inode commands are supported:

Access time

Block size

Creation time

Group id

Link number

Modification time


Major device number

Minor device number

This command actually operates on the directory name field. Once
poised at the desired directory entry (using the directory
command), this command allows you to change or display the
directory name. For example,

> 7:dir:nm="foo"

gets the 7th directory entry of the current inode and changes its
name to foo. Directory names cannot be made larger than the field
allows. If an attempt is made to make a directory name larger
than the field allows,, the string is truncated to fit and a
warning message is displayed.

File size

User ID

Unique ID

Formatted Output

Formatted output comes in two styles and many format types. The two
styles of formatted output are: structured and unstructured. Structured
output is used to display inodes, directories, and so forth. Unstructured
output displays raw data.

Format specifiers are preceded by the slash (/) or question mark (?)
character. type is updated as necessary upon completion.

The following format specifiers are preceded by the ? character:

Display as inodes in the current base.

Display as directories in the current base.

The following format specifiers are preceded by the / character:

Display as bytes in the current base.

Display as characters.

o | O
Display as octal shorts or longs.

d | D
Display as decimal shorts or longs.

x | X
Display as hexadecimal shorts or longs.


Example 1: Using fsdb as a calculator for complex arithmetic

The following command displays 2010 in decimal format, and is an example
of using fsdb as a calculator for complex arithmetic.

> 2000+400%(20+20)=D

Example 2: Using fsdb to display an i-number in inode fomat

The following command displays the i-number 386 in inode format.386
becomes the current inode.

> 386:ino?i

Example 3: Using fsdb to change the link count

The following command changes the link count for the current inode to 4.

> :ln=4

Example 4: Using fsdb to increment the link count

The following command increments the link count by 1.

> :ln=+1

Example 5: Using fsdb to display the creation time as a hexadecimal long

The following command displays the creation time as a hexadecimal long.

> :ct=X

Example 6: Using fsdb to display the modification time in time format

The following command displays the modification time in time format.

> :mt=t

Example 7: Using fsdb to display in ASCII

The following command displays, in ASCII, block 0 of the file associated
with the current inode.

> 0:file/c

Example 8: Using fsdb to display the directory enteries for the root inode

The following command displays the first block's directory entries for
the root inode of this file system. This command stops prematurely if the
EOF is reached.

> 2:ino,*?d

Example 9: Using fsdb to change the current inode

The following command changes the current inode to that associated with
the 5th directory entry (numbered from 0) of the current inode. The first
logical block of the file is then displayed in ASCII.

> 5:dir:inode; 0:file,*/c

Example 10: Using fsdb to change the i-number

The following command changes the i-number for the 7th directory slot in
the root directory to 3.

> 2:inode; 7:dir=3

Example 11: Using fsdb to change the name field

The following command changes the name field in the directory slot to

> 7:dir:nm="name"

Example 12: Using fsdb to display the a block

The following command displays the 3rd block of the current inode as
directory entries.

Example 13: Using fsdb to set the contents of address

The following command sets the contents of address 2050 to 0xffffffff.
0xffffffff can be truncated, depending on the current type.

> 2050=0xffff

Example 14: Using fsdb to place an ASCII string at an address

The following command places the ASCII string this is some text at
address 1c92434.

> 1c92434="this is some text"


clri(1M), fsck_udfs(1M), dir(4), attributes(5)

November 26, 2017 FSDB_UDFS(1M)