FSDB_UFS(8) Maintenance Commands and Procedures FSDB_UFS(8)

NAME

fsdb_ufs - ufs file system debugger

SYNOPSIS

fsdb -F ufs [generic_options] [specific_options] special

DESCRIPTION

The fsdb_ufs command is an interactive tool that can be used to patch
up a damaged UFS file system. 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.


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 the use of the o command.


fsdb reads a block at a time and will therefore work 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. 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.

OPTIONS

The following option is supported:

-o
Specify UFS file system specific options. These options can be
any combination of the following separated by commas (with no
intervening spaces). The options available are:

?
Display usage


o
Override some error conditions


p='string'
set prompt to string


w
open for write

USAGE

Numbers are considered hexadecimal by default. However, the user has
control over how data is to be displayed or accepted. The base
command will display or set 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 numbers 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 and so forth to a byte address. Once the address has been
calculated, fsdb will record the result in dot (.).


Several global values are maintained by fsdb:

o the current base (referred to as base),

o the current address (referred to as dot),

o the current inode (referred to as inode),

o the current count (referred to as count),

o 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
specified 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 a RETURN is then
typed, the output routine will use the current values of dot, count,
and type and display 400 more hex longs. A '*' will cause the entire
block to be displayed.


End of fragment, block and file are maintained by fsdb. When
displaying data as fragments or blocks, an error message will be
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 would be:

> 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, any subsequent
RETURN (or +, -) will advance to subsequent entries. Note that

> 2:inode; :ls
or
> :ls /


is again synonymous.

Expressions

The symbols recognized by fsdb are:

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


#
numeric expressions may be composed of +, -, *, and %
operators (evaluated left to right) and may use
parentheses. Once evaluated, the value of dot is
updated.


, count
count indicator. The global value of count will be
updated to count. The value of count will remain until a
new command is run. A count specifier of '*' will
attempt 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.


.
the value of dot.


+e
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.


-e
decrement the value of dot by the expression e. See +.


*e
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.


%e
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, then the value of dot is displayed using the
format specifier f. See Formatted Output. Otherwise,
assignment is assumed. See =.


= [s] [e]
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 may be useful for changing directory names or ASCII
file information.


=+ e
incremental assignment. The address pointed to by dot
has its contents incremented by expression e.


=- 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.
See individual commands for details. The '*', '?', and '[-]' wild
card characters are available.

base=b

display or set base. As stated above, all input and output is
governed by the current base. If the =b is omitted, 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.


block

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 no dir is specified, then
change directories to inode 2 ("/").


cg

convert the value of dot to a cylinder group.


directory

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.


file

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 dir [ -name n] [-inum i]

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=p

fill an area of disk with pattern p. The area of disk is
delimited by dot and count.


fragment

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.


inode

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 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.


log_chk

run through the valid log entries without printing any
information and verify the layout.


log_delta

count the number of deltas into the log, using the value of dot
as an offset into the log. No checking is done to make sure that
offset is within the head/tail offsets.


log_head

display the header information about the file system logging.
This shows the block allocation for the log and the data
structures on the disk.


log_otodb

return the physical disk block number, using the value of dot as
an offset into the log.


log_show

display all deltas between the beginning of the log (BOL) and
the end of the log (EOL).


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 may be used (but, if used, must be specified before
the filename specifiers). Also, as stated above, wild card
characters are available and multiple arguments may be given. The
long listing shows only the i-number and the name; use the inode
command with '?i' to get more information.


override

toggle the value of override. Some error conditions may be
overridden if override is toggled on.


prompt p

change the fsdb prompt to p. p must be surrounded by (")s.


pwd

display the current working directory.


quit

quit fsdb.


sb

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.


shadow

if the current inode is a shadow inode, then the value of dot is
set to the beginning of the shadow inode data.


!

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 ':ib' 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.

at
access time.


bs
block size.


ct
creation time.


db
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.


gid
group id.


ib
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.


ln
link count.


mt
modification time.


md
mode.


maj
major device number.


min
minor device number.


nm
although listed here, this command 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 truncated to fit and a warning message to this
effect is displayed.


si
shadow inode.


sz
file size.


uid
user id.

Formatted Output

There are two styles and many format types. The two styles are
structured and unstructured. Structured output is used to display
inodes, directories, superblocks and the like. Unstructured displays
raw data. The following shows the different ways of displaying:

?

c
display as cylinder groups


i
display as inodes


d
display as directories


s
display as superblocks


S
display as shadow inode data


/

b
display as bytes


c
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

The format specifier immediately follows the '/' or '?'
character. The values displayed by '/b' and all '?' formats are
displayed in the current base. Also, type is appropriately
updated upon completion.

EXAMPLES

Example 1: Displaying in Decimal

The following command displays 2010 in decimal (use of fsdb as a
calculator for complex arithmetic):


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

Example 2: Displaying an i-number in Inode Format

The following command displays i-number 386 in an inode format. This
now becomes the current inode:


> 386:ino?i

Example 3: Changing the Link Count

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


> :ln=4

Example 4: Incrementing the Link Count

The following command increments the link count by 1:


> :ln=+1

Example 5: Displaying the Creation Time

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


> :ct=X

Example 6: Displaying the Modification Time

The following command displays the modification time in time format:


> :mt=t

Example 7: Displaying in ASCII

The following command displays in ASCII, block zero of the file
associated with the current inode:


> 0:file/c

Example 8: Displaying the First Block's Worth of Directorty Entries

The following command displays the first block's worth of directory
entries for the root inode of this file system. It will stop
prematurely if the EOF is reached:


> 2:ino,*?d

Example 9: Displaying Changes to the Current Inode

The following command displays 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:


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

Example 10: Displaying the Superblock

The following command displays the superblock of this file system:


> :sb

Example 11: Displaying the Cylinder Group

The following command displays cylinder group information and summary
for cylinder group 1:


> 1:cg?c

Example 12: Changing the i-number

The following command changes the i-number for the seventh directory
slot in the root directory to 3:


> 2:inode; 7:dir=3

Example 13: Displaying as Directory Entries

The following command displays the third block of the current inode
as directory entries:


> 2:db:block,*?d

Example 14: Changing the Name Field

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


> 7:dir:nm="name"

Example 15: Getting and Filling Elements

The following command gets fragment 3c3 and fill 20 type elements
with 0x20:


> 3c3:fragment,20:fill=0x20

Example 16: Setting the Contents of an Address

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


> 2050=0xffff

Example 17: Placing ASCII

The following command places the ASCII for the string at 1c92434:


> 1c92434="this is some text"

Example 18: Displaying Shadow Inode Data

The following command displays all of the shadow inode data in the
shadow inode associated with the root inode of this file system:


> 2:ino:si:ino;0:shadow,*?S

SEE ALSO

ufs(4FS), dir_ufs(5), attributes(7), clri(8), fsck_ufs(8)

WARNINGS

Since fsdb reads the disk raw, extreme caution is advised in
determining its availability of fsdb on the system. Suggested
permissions are 600 and owned by bin.

NOTES

The old command line syntax for clearing i-nodes using the ufs-
specific '-z i-number' option is still supported by the new debugger,
though it is obsolete and will be removed in a future release. Use of
this flag will result in correct operation, but an error message will
be printed warning of the impending obsolesence of this option to the
command. The equivalent functionality is available using the more
flexible clri(8) command.

April 14, 2003 FSDB_UFS(8)