minix man page for de

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.