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Recovery after a crash
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

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 listing.
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.
E326 Technical: 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. Advantages:
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). Disadvantages:
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, that user will not see your swap file and will not get the ATTENTION warning message.
If you want to put swap files in a fixed place, put a command resembling the following ones in your vimrc: :set dir=~/tmp (for Unix) :set dir=c:\\tmp (for 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 right away. The swap file is created only when making changes.
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.
W325 The default SwapExists handler (default-autocmds) skips the E325 prompt (and automatically chooses "(E)dit") if the swapfile owner process is still running and owned by the current user. This presumes that you normally don't want to be bothered with the ATTENTION message just because you happen to edit the same file from multiple Nvim instances. In the worst case (a system crash) there will be more than one swapfile for the file; use :recover to inspect all of its swapfiles.
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.
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 command:
:pre :preserve E313 E314 :pre[serve] Write all text for the current buffer into its swap file. The original file is no longer needed for recovery.
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 elsewhere.
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 E1364 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.
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