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:
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.
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:
Current base (referred to as base)
Current address (referred to as dot)
Current inode (referred to as inode)
Current count (referred to as count)
Current type (referred to as type)
Most commands use the preset value of dot in their execution. For example,
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).
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 that
> 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 updated.
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.
Display in structured style with format specifier f. See Formatted Output.
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 *.
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 (see Formatted Output), then the value of dot is displayed using format specifier f. Otherwise, assignment is assumed. See = [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.
Change the value of dot using an incremental assignment. The address pointed to by dot has its contents incremented by expression 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.
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 entry.
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 block.
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.
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.
Change the fsdb prompt to p. p must be enclosed in quotes.
Display the current working directory.
Convert the value of dot and if this is a valid tag, print the volume structure according to the tag.
Escape to the shell.
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,
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:
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,
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.
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.
Display as octal shorts or longs.
Display as decimal shorts or longs.
Display as hexadecimal shorts or longs.
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)=DExample 2 Using fsdb to display an i-number in inode format
The following command displays the i-number 386 in inode format.386 becomes the current inode.
> 386:ino?iExample 3 Using fsdb to change the link count
The following command changes the link count for the current inode to 4.
> :ln=4Example 4 Using fsdb to increment the link count
The following command increments the link count by 1.
> :ln=+1Example 5 Using fsdb to display the creation time as a hexadecimal long
The following command displays the creation time as a hexadecimal long.
> :ct=XExample 6 Using fsdb to display the modification time in time format
The following command displays the modification time in time format.
> :mt=tExample 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/cExample 8 Using fsdb to display the directory entries 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,*?dExample 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,*/cExample 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=3Example 11 Using fsdb to change the name field
The following command changes the name field in the directory slot to name.
> 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=0xffffExample 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"
See attributes(7) for descriptions of the following attributes: