Vim documentation: recover

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*recover.txt*   For Vim version 8.1.  Last change: 2019 May 07

		  VIM REFERENCE MANUAL    by Bram Moolenaar

Recovery after a crash					*crash-recovery*

You have spent several hours typing in that text that has to be finished
next morning, and then disaster strikes: Your computer crashes.


You can recover most of your changes from the files that Vim uses to store
the contents of the file.  Mostly you can recover your work with one command:
	vim -r filename

1. The swap file	|swap-file|
2. Recovery		|recovery|


1. The swap file					*swap-file*

Vim stores the things you changed in a swap file.  Using the original file
you started from plus the swap file you can mostly recover your work.

You can see the name of the current swap file being used with the command:

	:sw[apname]					*:sw* *:swapname*

Or you can use the |swapname()| function, which also allows for seeing the
swap file name of other buffers.

The name of the swap file is normally the same as the file you are editing,
with the extension ".swp".
- On Unix, a '.' is prepended to swap file names in the same directory as the
  edited file.  This avoids that the swap file shows up in a directory
- On MS-DOS machines and when the 'shortname' option is on, any '.' in the
  original file name is replaced with '_'.
- If this file already exists (e.g., when you are recovering from a crash) a
  warning is given and another extension is used, ".swo", ".swn", etc.
- An existing file will never be overwritten.
- The swap file is deleted as soon as Vim stops editing the file.

Technical: The replacement of '.' with '_' is done to avoid problems with
	   MS-DOS compatible filesystems (e.g., crossdos, multidos).  If Vim
	   is able to detect that the file is on an MS-DOS-like filesystem, a
	   flag is set that has the same effect as the 'shortname' option.
	   This flag is reset when you start editing another file.

	   If the ".swp" file name already exists, the last character is
	   decremented until there is no file with that name or ".saa" is
	   reached.  In the last case, no swap file is created.

By setting the 'directory' option you can place the swap file in another place
than where the edited file is.
- You will not pollute the directories with ".swp" files.
- When the 'directory' is on another partition, reduce the risk of damaging
  the file system where the file is (in a crash).
- You can get name collisions from files with the same name but in different
  directories (although Vim tries to avoid that by comparing the path name).
  This will result in bogus ATTENTION warning messages.
- When you use your home directory, and somebody else tries to edit the same
  file, he will not see your swap file and will not get the ATTENTION warning
On the Amiga you can also use a recoverable ram disk, but there is no 100%
guarantee that this works.  Putting swap files in a normal ram disk (like RAM:
on the Amiga) or in a place that is cleared when rebooting (like /tmp on Unix)
makes no sense, you will lose the swap file in a crash.

If you want to put swap files in a fixed place, put a command resembling the
following ones in your .vimrc:
	:set dir=dh2:tmp	(for Amiga)
	:set dir=~/tmp		(for Unix)
	:set dir=c:\\tmp	(for MS-DOS and Win32)
This is also very handy when editing files on floppy.  Of course you will have
to create that "tmp" directory for this to work!

For read-only files, a swap file is not used.  Unless the file is big, causing
the amount of memory used to be higher than given with 'maxmem' or
'maxmemtot'.  And when making a change to a read-only file, the swap file is
created anyway.

The 'swapfile' option can be reset to avoid creating a swapfile.  And the
|:noswapfile| modifier can be used to not create a swapfile for a new buffer.

:nos[wapfile]   {command}			*:nos* *:noswapfile*
		Execute {command}. If it contains a command that loads a new
		buffer, it will be loaded without creating a swapfile and the
		'swapfile' option will be reset.  If a buffer already had a
		swapfile it is not removed and 'swapfile' is not reset.

Detecting an existing swap file 

You can find this in the user manual, section |11.3|.

Updating the swapfile 

The swap file is updated after typing 200 characters or when you have not
typed anything for four seconds.  This only happens if the buffer was
changed, not when you only moved around.  The reason why it is not kept up to
date all the time is that this would slow down normal work too much.  You can
change the 200 character count with the 'updatecount' option.  You can set
the time with the 'updatetime' option.  The time is given in milliseconds.
After writing to the swap file Vim syncs the file to disk.  This takes some
time, especially on busy Unix systems.  If you don't want this you can set the
'swapsync' option to an empty string.  The risk of losing work becomes bigger
though.  On some non-Unix systems (MS-DOS, Amiga) the swap file won't be
written at all.

If the writing to the swap file is not wanted, it can be switched off by
setting the 'updatecount' option to 0.  The same is done when starting Vim
with the "-n" option.  Writing can be switched back on by setting the
'updatecount' option to non-zero.  Swap files will be created for all buffers
when doing this.  But when setting 'updatecount' to zero, the existing swap
files will not be removed, it will only affect files that will be opened
after this.

If you want to make sure that your changes are in the swap file use this

					*:pre* *:preserve* *E313* *E314*
:pre[serve]		Write all text for all buffers into swap file.  The
			original file is no longer needed for recovery.
			This sets a flag in the current buffer.  When the '&'
			flag is present in 'cpoptions' the swap file will not
			be deleted for this buffer when Vim exits and the
			buffer is still loaded |cpo-&|.

A Vim swap file can be recognized by the first six characters: "b0VIM ".
After that comes the version number, e.g., "3.0".

Links and symbolic links 

On Unix it is possible to have two names for the same file.  This can be done
with hard links and with symbolic links (symlinks).

For hard links Vim does not know the other name of the file.  Therefore, the
name of the swapfile will be based on the name you used to edit the file.
There is no check for editing the same file by the other name too, because Vim
cannot find the other swapfile (except for searching all of your harddisk,
which would be very slow).

For symbolic links Vim resolves the links to find the name of the actual file.
The swap file name is based on that name.  Thus it doesn't matter by what name
you edit the file, the swap file name will normally be the same.  However,
there are exceptions:
- When the directory of the actual file is not writable the swapfile is put

- When the symbolic links somehow create a loop you get an *E773* error
  message and the unmodified file name will be used.  You won't be able to
  save your file normally.


2. Recovery					*recovery* *E308* *E311*

Basic file recovery is explained in the user manual: |usr_11.txt|.

Another way to do recovery is to start Vim and use the ":recover" command.
This is easy when you start Vim to edit a file and you get the "ATTENTION:
Found a swap file ..." message.  In this case the single command ":recover"
will do the work.  You can also give the name of the file or the swap file to
the recover command:

					*:rec* *:recover* *E305* *E306* *E307*
:rec[over] [file]	Try to recover [file] from the swap file.  If [file]
			is not given use the file name for the current
			buffer.  The current contents of the buffer are lost.
			This command fails if the buffer was modified.

:rec[over]! [file]	Like ":recover", but any changes in the current
			buffer are lost.

							*E312* *E309* *E310*
Vim has some intelligence about what to do if the swap file is corrupt in
some way.  If Vim has doubt about what it found, it will give an error
message and insert lines with "???" in the text.  If you see an error message
while recovering, search in the file for "???" to see what is wrong.  You may
want to cut and paste to get the text you need.

The most common remark is "???LINES MISSING".  This means that Vim cannot read
the text from the original file.  This can happen if the system crashed and
parts of the original file were not written to disk.

Be sure that the recovery was successful before overwriting the original
file or deleting the swap file.  It is good practice to write the recovered
file elsewhere and run 'diff' to find out if the changes you want are in the
recovered file.  Or use |:DiffOrig|.

Once you are sure the recovery is ok delete the swap file.  Otherwise, you
will continue to get warning messages that the ".swp" file already exists.

ENCRYPTION AND THE SWAP FILE				*:recover-crypt*

When the text file is encrypted the swap file is encrypted as well.  This
makes recovery a bit more complicated.  When recovering from a swap file and
encryption has been used, you will be asked to enter one or two crypt keys.

If the text file does not exist you will only be asked to enter the crypt key
for the swap file.

If the text file does exist, it may be encrypted in a different way than the
swap file.  You will be asked for the crypt key twice:

	Need encryption key for "/tmp/tt" 
	Enter encryption key: ****** 
	"/tmp/tt" [crypted] 23200L, 522129C 
	Using swap file "/tmp/.tt.swp" 
	Original file "/tmp/tt" 
	Swap file is encrypted: "/tmp/.tt.swp" 
	If you entered a new crypt key but did not write the text file, 
	enter the new crypt key. 
	If you wrote the text file after changing the crypt key press enter 
	to use the same key for text file and swap file 
	Enter encryption key:  

You can be in one of these two situations:

1. The encryption key was not changed, or after changing the key the text file
   was written.  You will be prompted for the crypt key twice.  The second
   time you can simply press Enter.  That means the same key is used for the
   text file and the swap file.
2. You entered a new encryption key, but did not save the text file.  Vim will
   then use the new key for the swap file, and the text file will still be
   encrypted with the old key.  At the second prompt enter the new key.

Note that after recovery the key of the swap file will be used for the text
file.  Thus if you write the text file, you need to use that new key.

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