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1990-07-24
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NAME
de(1) - minix disk editor
SYNOPSIS
de [-w] /dev/device
de -r lost_file_name
DESCRIPTION
De(1) allows a system administrator to examine and modify
a Minix file system device. Interactive observation of a
disk partition is initiated by a command line, for example:
de /dev/hd2
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 given,
de(1) will open the device for writing and words may be
modified.
Lost blocks and files can be recovered using a variety of
commands. The "-r" option supports automated recovery of
files removed by unlink(2).
POSITIONING
Disks are divided into blocks (also called "zones") of 1024
bytes. De(1) 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,
including a super block, bit maps, i-nodes and data blocks.
De(1) knows the type of the current block, but will allow
most positioning 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
address 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 indirectly jumps to that block.
The address may be set to the start of any i-node using
the 'i' 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 so that Minix can stat(2) it.
THE DISPLAY
The first line of the display contains the device name,
the name of the current output file (if one is open) and
the current search string. If de(1) 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. See section 5.6.2 of the text for
an explanation and a diagram. If the current address is
within a data block then the string "in use" is displayed
if the block corresponds to a set bit in the zone bit map.
The third line shows the offset in the current block. If
the current 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 display 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 current base is displayed
to the far right of the screen. It can be changed using the
'o' command followed by either an 'h' (hexadecimal), 'd'
(decimal), 'o' (octal) or 'b' (binary).
De(1) 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 executable
file or an ar(1) archive, then de(1) 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.
SEARCHING
A search for an ASCII string is initiated by the '/' command.
Control characters not used for other purposes may be
entered in the search string, for example ^J is an end-of-
line character. The search is from the current 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 ENTER is equivalent to an 'n').
Whenever a search is in progress de(1) will append one
'.' to the prompt line for every 500 blocks searched. If the
string is found between the end of the file system and the
actual end of the device, then the current address is set to
the end of the file system.
Some of the positioning commands 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 visual mode
from the stack. This stack is eight entries deep.
MODIFYING THE FILE SYSTEM
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.
RECOVERING FILES
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 '\0' or
'\177' are not copied. The 'W' command writes the current
block (1024 bytes) exactly to the output file.
When a file is deleted using unlink(2) the i-node number
in the directory is zeroed, but before its removal,