fsdb(1M) DG/UX 5.4R3.00 fsdb(1M)
NAME
fsdb - file system debugger
SYNOPSIS
/etc/fsdb special [ - ]
where:
special The pathname of a special file referring to a device
containing a file system
DESCRIPTION
Fsdb views and alters information on the disk. This information
includes inodes, directory entries, and any other disk information.
The - or an O argument suppresses error-checking routines that verify
inode, directory, and block addresses. To do these checks, fsdb
reads the fsnodesperdar (inodes per disk allocation region) and
fssize (file system size) fields of of the file system's super-
block.
Fsdb is intended mainly for emergencies where fsck(1M) and clri(1M)
are ineffective in dealing with problems on the disk. To use fsdb
effectively, you must be familiar with the contents of inodes and
directory entries and how these structures are used.
Fsdb can display disk information in the following formats:
inode
directory entry
double word
word
byte
character
Fsdb supports decimal and octal numbers. A zero prefix indicates an
octal number. Decimal is the default.
Examining Inodes
To view an inode, type an integer followed by a lowercase i. fsdb
then lists the specified inode's number, mode, link count, user ID,
group ID, size, the fragment numbers stored in its direct and
indirect block arrays, and the creation, last-modification, and last-
access times. The default is the current inode. When you enter
fsdb, the current inode is number 2, indicating the root directory.
Otherwise the current inode is the last inode referenced.
To change the fields of the inode, use the mnemonics given for a
particular field followed by an equal sign and the desired contents
for that field. For example, sz=1024 sets the file size for the
current inode to 1024 bytes. The i-number of an inode cannot be
changed.
The following mnemonics are used to change inodes:
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md Mode
ln Link count
uid User ID number
gid Group ID number
sz File size in bytes
a # Data block numbers (0-12 for ordinary files, and 0-10
for non-ordinary files)
at Time of last access
mt Time of last modification
ct Time of creation
maj Major device number (special files only)
min Minor device number (special files only)
For control point directories only:
Max space usage Total amount of space allowed in this and
subordinate directories.
Cur space usage Current amount of space allowed in this directory
and subordinates.
Max file node Total number of inodes allowed in this and
subordinate directories.
Cur file node Current number of inodes allowed in this directory
and subordinate directories.
An inode's first 10 data blocks are direct blocks; the next 3 are
indirect. To print the contents of the data blocks, type an f. The
f can be followed by a logical block number and a print option or by
a print option alone. If you omit the number, block 0 is printed.
The data in the specified block are printed according to the mode
indicated by a print option. The print options are:
d Print as directories.
o Print as octal words.
e Print as decimal words.
c Print as characters.
b Print as octal bytes.
The f command does not work on a special file (device) or on empty
data blocks. (The pointer in the inode for an empty block in a file
is 0.)
The a field of the inode is examined and changed in a manner
different from other fields. To examine a data block entry, specify
a followed by a logical block number and then b. The address of the
array element within the inode for the logical block number is
printed, followed by A. Then the octal and the decimal disk block
number of the data block itself is printed.
Examining Directory Entries
To view a directory entry, type a d followed by an integer. A
directory entry consists of an inode number, the name length, entry
length, sequence number, and filename. Since directory entries are
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found in the data of a directory inode, fsdb displays the directory
entry specified relative to the current inode. If the current inode
is not a directory inode or there are fewer directory entries than
the one you indicate, fsdb prints this message:
nonexistent block
Cannot scan directory
All fields of the directory entry except the inode number can be
changed by giving the mnemonic for the field followed by an equal
sign and then a value. For the name field, the character string
following the equal sign should be enclosed in double quotation marks
if the first character is not alphabetic; otherwise, double quotation
marks are optional for this field. To alter the inode number for a
directory entry, omit the mnemonic. The mnemonics are as follows:
nl Name length in characters
el Entry length - total byte count used by the entry
nm Filename
sq Sequence number
Use extreme care in changing names, name lengths, and entry lengths,
because following entries can be corrupted or made unreachable.
Examining Other Data
Information can also be printed as double words, words, bytes, or
characters. To view data in these forms, one can use D, W, or B for
double words, words, or bytes, respectively. Used alone, these
options print the current address in octal, followed by an indicator
of the mode requested (D., W., or B.). The contents of the current
location follow in octal and then in decimal. If the mode desired is
preceded by a number, that number is taken as the address and becomes
the current address.
To alter the contents of a double word, word, or byte, follow the
address and mode indicator (B, W, or D) by an equal sign and a value.
For example, 01006W=0177777 sets the contents of word 01006 to
0177777.
Current Address
The contents of the current address can also be viewed by following
the letter p with an i for inodes or one of the print options
described above for use with the f command. If the p is followed by
a number, that many elements (inodes, words, etc., depending on the
print option used) are printed.
The current address is normalized to an appropriate boundary before
printing begins. The current address advances with the printing and
is left at the address of the last item printed.
The current address can be saved by using the < symbol. The symbol >
restores the saved address. Only one address can be saved at any one
time; a subsequent use of < replaces a previously saved address with
the current address.
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Commands and Symbols
Following is a summary of fsdb commands:
[n]i Print inode n; current is the default.
dn Print directory entry number n.
p[n]o|i Print the next n inodes according to option o or in inode
format.
f[n]o Print logical data block n according to option o; block 0
is the default.
[a]B Enter byte mode at address a; default is the current
address.
[a]W Enter word mode at address a; default is the current
address.
[a]D Enter double-word mode at address a; default is the
current address.
+,- Print next item, last item.
>,< Save current address, restore saved address.
O Set or unset error-checking toggle.
! Escape to the shell.
q Quit; terminate the program.
<NL> Print next item of the previously specified type.
The following symbols are used for assignment to inode and directory
fields and also to locations directly:
=n Assignment
=+n Incremental assignment
=-n Decremental assignment
You can use dots, tabs, and spaces as delimiters within commands to
fsdb, but they are not necessary. A line with just a new-line
character increases 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 inode, letting you step through a
region of the file system. A line with just a + or - takes you to
the next or previous item, respectively.
Miscellaneous
Fsdb cannot print more than a block's worth of data at once because
only one block of data is kept in memory at any one time. If a count
of 0 is used with the p command, all entries to the end of the
current block are printed. Because fsdb deals with only a block at a
time, raw devices and block devices can be debugged.
All assignment operations result in immediate write-through of the
current block. During any assignment operation, numbers are checked
for a possible truncation error due to the size of the destination
address. The message "alignment" is printed if such a truncation
would have taken place if the assignment had been made.
To terminate output at any time, type the delete character.
EXAMPLES
2i Prints the root inode of the current file system.
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386i Prints inode number 386 in inode format; this becomes
the current inode.
ln=4 Changes the link count for the current inode to 4.
ln=+1 Increases the current inode's link count by 1.
fc Prints, in ASCII, block zero of the file associated
with the current inode.
f2c Prints the third data block of the current inode as
characters.
2i.fd Prints the root inode's first data block in the form of
directory entries. This example combines several
operations on one command line; the same effect would
occur if the `2i' were followed by `fd' as a separate
command.
d2 Prints the third directory entry in the current inode.
d0=32 Sets the inode number of the first directory entry of
the current inode to 32.
d5i.fc Changes the current inode to that associated with the
sixth directory entry of the current inode; the first
logical block of the file is then printed in ASCII.
0B.p0o Prints the super-block of a DG/UX file system in octal.
2i.a0b.d7=3 Changes the i-number for the eighth directory slot in
the root directory to 3.
d7.nm="name" Changes the name field in the directory slot to "name."
a2b.p0d Prints the third block of the current inode as
directory entries.
0140B Produces the output
0140B.: 14 (12)
if location 0140 happens to contain 014.
SEE ALSO
clri(1M), fsck(1M).
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