The de program allows a system administrator to examine and modi-
fy a MINIX file system device. Commands are available to move to
any address on the disk and display the disk block contents. This
information may be presented in one of three visual modes: as
two-byte words, as ASCII characters or as a bit map. The disk may
be searched for a string of characters. If the -w option is giv-
en, de will open the device for writing and words may be modi-
fied. Without this flag, writing is prohibited. Lost blocks and
files can be recovered using a variety of commands. The -r option
supports automated recovery of files removed by unlink. Disks
are divided into blocks (also called zones) of 1024 bytes. De
keeps a current address on the disk as a block number and a byte
offset within the block. In some visual modes the offset is
rounded off, for example, in word mode the offset must be even.
There are different types of blocks on a file system device, in-
cluding a super block, bit maps, i-nodes and data blocks. De
knows the type of the current block, but will allow most posi-
tioning commands and visual modes to function anywhere on the
disk. The f command (or PGDN on the keypad) moves forward to the
next block, similarly b (PGUP) moves backwards one block. F
(END) moves to the last block and B (HOME) moves to the first
block. The arrow keys (or u, d, l, and r) change the current ad-
dress by small increments. The size of the increment depends on
the current display mode, as shown below. The various sizes suit
each display and pointers move on the screen to follow each press
of an arrow key.
Mode Up Down Left Right
Word -2 +2 -32 +32
Block -64 +64 -1 +1
Map -256 +256 -4 +4
The g command allows movement to any specified block. Like all
commands that take arguments, a prompt and subsequent input are
written to the bottom line of the screen. Numerical entry may be
decimal, octal or hexadecimal, for example 234, -1, 070, 0xf3,
-X3C. While checking an i-node one may want to move to a block
listed as a zone of the file. The G command takes the contents at
the current address in the device as a block number and indirect-
ly jumps to that block. The address may be set to the start of
any i-node using the command and supplying an i-node number. The
I command maps a given file name into an i-node address. The
file must exist on the current device and this device must be
mounted. The first line of the display contains the device name,
the name of the current output file (if one is open) and the cur-
rent search string. If de is being run with the -w option then
the device name is flagged with (w). If a string is too long to
fit on the line it is marked with .... The second line contains
the current block number, the total number of blocks, and the
type of the current block. The types are: boot, super, i-node
bit map, zone bit map, i-nodes and data block. If the current
address is within a data block then the string in use is dis-
played if the block corresponds to a set in the zone bit map.
The third line shows the offset in the current block. If the cur-
rent address is within either the i-node or zone bit maps then
the i-node or block number corresponding to the current bit is
shown. If the current address is within an i-node then the i-node
number and in use status is displayed. If the address is within
a bit map or i-node block, but past the last usable entry, then
the string padding is shown. The rest of the screen is used to
display data from the current block. There are three visual dis-
play modes: word, block, and map. The v command followed by w,
b, or m sets the current display mode. In word mode 16 words, of
two bytes each, are shown in either base 2, 8, 10 or 16. The cur-
rent base is displayed to the far right of the screen. It can be
changed using the o command followed by either an h (hexadeci-
mal), d (decimal), o (octal) or b (binary). De knows where i-
nodes are, and will display the contents in a readable format,
including the rwx bits, the user name and the time field. If the
current page is at the beginning of the super block, or an exe-
cutable file or an ar archive, then de will also inform the user.
In all other cases the contents of the 16 words are shown to the
right as equivalent ASCII characters. In block mode a whole
block of 1024 bytes is displayed as ASCII characters, 64 columns
by 16 lines. Control codes are shown as highlighted characters.
If the high order bit is set in any of the 1024 bytes then an MSB
flag is shown on the far right of the screen, but these bytes are
not individually marked. In map mode 2048 bits (256 bytes) are
displayed from the top to the bottom (32 bits) and from the left
to the right of the screen. Bit zero of a byte is towards the top
of the screen. This visual mode is generally used to observe the
bit map blocks. The number of set bits displayed is written on
the far right of the screen. A search for an ASCII string is
initiated by the / command. Control characters not used for oth-
er purposes may be entered in the search string, for example
CTRL-J is an end-of-line character. The search is from the cur-
rent position to the end of the current device. Once a search
string has been defined by a use of /, the next search may be
initiated with the n command, (a / followed immediately by an EN-
TER is equivalent to an n). Whenever a search is in progress de
will append one . to the prompt line for every 500 blocks
searched. If the string is found between the end of the file sys-
tem and the actual end of the device, then the current address is
set to the end of the file system. Some of the positioning com-
mands push the current address and visual mode in a stack before
going to a new address. These commands are B, F, g, G, i, I, n,
x and /. The p (previous) command pops the last address and vis-
ual mode from the stack. This stack is eight entries deep. The s
command will prompt for a data word and store it at the current
address on the disk. This is used to change information that can
not be easily changed by any other means. The data word is 16
bits wide, it may be entered in decimal, octal or hexadecimal.
Remember that the -w option must be specified for the s command
to operate. Be careful when modifying a mounted file system. Any
block on the disk may be written to an output file. This is used
to recover blocks marked as free on the disk. A write command
will request a file name the first time it is used, on subsequent
writes the data is appended to the current output file. The name
of the current output file is changed using the c command. This
file should be on a different file system, to avoid overwriting
an i-node or block before it is recovered. An ASCII block is
usually recovered using the w command. All bytes will have their
most significant bit cleared before being written to the output
file. Bytes containing ' ' or '177' are not copied. The W com-
mand writes the current block (1024 bytes exactly) to the output
file. When a file is deleted using unlink the i-node number in
the directory is zeroed, but before its removal, it is copied in-
to the end of the file name field. This allows the i-node of a
deleted file to be found by searching through a directory. The x
command asks for the path name of a lost file, extracts the old
i-node number and changes the current disk address to the start
of the i-node. Once an i-node is found, all of the freed blocks
may be recovered by checking the i-node zone fields, using 'G' to
go to a block, writing it back out using 'w', going back to the
i-node with p and advancing to the next block. This file extrac-
tion process is automated by using the X command, which goes
through the i-node, indirect and double indirect blocks finding
all the block pointers and recovering all the blocks of the file.
The X command closes the current output file and asks for the
name of a new output file. All of the disk blocks must be marked
as free, if they are not the command stops and the file must be
recovered manually. When extracting lost blocks de will maintain
holes in the file. Thus, a recovered sparse file does not allo-
cate unused blocks and will keep its efficient storage scheme.
This property of the X command may be used to move a sparse file
from one device to another. Automatic recovery may be initiated
by the -r option on the command line. Also specified is the path
name of a file just removed by unlink. De determines which mount-
ed file system device held the file and opens it for reading. The
lost i-node is found and the file extracted by automatically per-
forming an x and an X command. The recovered file will be writ-
ten to /tmp. De will refuse to automatically recover a file on
the same file system as /tmp. The lost file must have belonged to
the user. If automatic recovery will not complete, then manual
recovery may be performed. The user can terminate a session with
de by typing q, CTRL-D, or the key associated with SIGQUIT. The
m command invokes the MINIX sh shell as a subprocess. For help
while using de use h.
PGUP b Back one block
PGDN f Forward one block
HOME B Goto first block
END F Goto last block
UP u Move back 2/64/256 bytes
DOWN d Move forward 2/64/256 bytes
LEFT l Move back 32/1/4 bytes
RIGHT r Move forward 32/1/4 bytes
g Goto specified block
G Goto block indirectly
i Goto specified i-node
I Filename to i-node
/ Search
n Next occurrence
p Previous address
h Help
EOF q Quit
m MINIX shell
v Visual mode (w b m)
o Output base (h d o b)
c Change file name
w Write ASCII block
W Write block exactly
x Extract lost directory entry
X Extract lost file blocks
s Store word
NOTES
: When entering a line in response to a prompt from de there
are a couple of editing characters available. The previous char-
acter may be erased by typing CTRL-H and the whole line may be
erased by typing CTRL-U. ENTER terminates the input. If DELETE or
a non-ASCII character is typed then the command requesting the
input is aborted. The commands G, s and X will only function if
the current visual display mode is word. The commands i, I and x
change the mode to word on completion. The commands G and /
change the mode to block. These restrictions and automatic mode
conversions are intended to aid the user. The map mode uses spe-
cial graphic characters, and only functions if the user is at the
console. De generates warnings for illegal user input or if er-
roneous data is found on the disk, for example a corrupted magic
number. Warnings appear in the middle of the screen for two sec-
onds, then the current page is redrawn. Some minor errors, for
example, setting an unknown visual mode, simply ring the bell.
Major errors, for example I/O problems on the file system device
cause an immediate exit from de. The i-node and zone bit maps
are read from the device when de starts up. These determine
whether in use or not in use is displayed in the status field at
the top of the screen. The bit maps are not re-read while using
de and will become out-of-date if observing a mounted file sys-
tem. De requires termcap definitions for cm and cl. Further-
more, so and se will also be used if available. The ANSI strings
generated by the keypad arrows are recognized, as well as any
single character codes defined by ku, kd, kl and kr. The de pro-
gram was written by Terrence Holm.