Normally, git-annex stores annexed files in the repository, locked down, which prevents the content of the file from being modified. That's a good thing, because it might be the only copy, you wouldn't want to lose it in a fumblefingered mistake.
# git annex add some_file add some_file # echo oops > some_file bash: some_file: Permission denied
Sometimes though you want to modify a file. Maybe once, or maybe
repeatedly. To modify a locked file, you have to first unlock it,
git annex unlock.
# git annex unlock some_file # echo "new content" > some_file
Back before git-annex version 6, and its v6 repository mode, unlocking a file
like this was a transient thing. You'd modify it and then
git annex add the
modified version to the annex, and finally
git commit. The new version of
the file was then back to being locked.
# git annex add some_file add some_file # git commit
But, that had some problems. The main one is that some users want to be able to edit files repeatedly, without manually having to unlock them every time. The direct mode made all files be unlocked all the time, but it had many problems of its own.
enter v6 mode
This is an new feature; see its todo list for known issues.
This led to the v6 repository mode, which makes unlocked files remain unlocked after they're committed, so you can keep changing them and committing the changes whenever you'd like. It also lets you use more normal git commands (or even interfaces on top of git) for handling annexed files.
# git annex upgrade
Or, you can init a new repository in v6 mode.
# git init # git annex init --version=6
Using a v6 repository is easy! Simply use regular git commands to add and commit files. In a git-annex repository, git will use git-annex to store the file contents, and the files will be left unlocked.
git add to add some file contents to the annex, but store the contents of
smaller files in git itself? Configure annex.largefiles to match the former.
# cp ~/my_cool_big_file . # git add my_cool_big_file # git commit -m "added my_cool_big_file to the annex" [master (root-commit) 92f2725] added my_cool_big_file to the annex 1 file changed, 1 insertion(+) create mode 100644 my_cool_big_file # git annex find my_cool_big_file
You can make whatever modifications you want to unlocked files, and commit your changes.
# echo more stuff >> my_cool_big_file # git mv my_cool_big_file my_cool_bigger_file # git commit -a -m "some changes" [master 196c0e2] some changes 2 files changed, 1 insertion(+), 1 deletion(-) delete mode 100644 my_cool_big_file create mode 100644 my_cool_bigger_file
Under the hood, this uses git's smudge filter interface, and git-annex converts between the content of the big file and a pointer file, which is what gets committed to git. All the regular git-annex commands (get, drop, etc) can be used on unlocked files too.
By default, git-annex commands will add files in locked mode,
unless used on a filesystem that does not support symlinks, when unlocked
mode is used. To make them always use unlocked mode, run:
git config annex.addunlocked true
mixing locked and unlocked files
A v6 repository can contain both locked and unlocked files. You can switch
a file back and forth using the
git annex lock and
git annex unlock
commands. This changes what's stored in git between a git-annex symlink
(locked) and a git-annex pointer file (unlocked). To add a file to
the repository in locked mode, use
git annex add; to add a file in
unlocked mode, use
If you want to mostly keep files locked, but be able to locally switch
to having them all unlocked, you can do so using
git annex adjust
--unlock. See git-annex-adjust for details. This is particularly
useful when using filesystems like FAT, and OS's like Windows that don't
using less disk space
Unlocked files are handy, but they have one significant disadvantage compared with locked files: They use more disk space.
While only one copy of a locked file has to be stored, often
two copies of an unlocked file are stored on disk. One copy is in
the git work tree, where you can use and modify it,
and the other is stashed away in
.git/annex/objects (see internals).
The reason for that second copy is to preserve the old version of the file, when you modify the unlocked file in the work tree. Being able to access old versions of files is an important part of git after all!
That's a good safe default. But there are ways to use git-annex that make the second copy not be worth keeping:
- When you're using git-annex to sync the current version of files across devices, and don't care much about previous versions.
- When you have set up a backup repository, and use git-annex to copy your files to the backup.
In situations like these, you may want to avoid the overhead of the second local copy of unlocked files. There's a config setting for that.
Note that setting annex.thin only has any effect on systems that support hard links. It is supported on Windows, but not on FAT filesystems.
git config annex.thin true
After changing annex.thin, you'll want to fix up the work tree to match the new setting:
git annex fix
Unfortunately, git's smudge interface does not let git-annex honor
the annex.thin configuration when git is checking out a file.
git checkout to check out a different branch, or even
git merge can result in some non-thin files making their way into the
working tree, and using more disk space. A warning will be printed out in
this situation. You can always run
git annex fix to re-thin such files.
When a direct mode repository is upgraded, annex.thin is automatically set, because direct mode made the same single-copy tradeoff.
Setting annex.thin can save a lot of disk space, but it's a tradeoff between disk usage and safety.
Keeping files locked is safer and also avoids using unnecessary disk space, but trades off easy modification of files.
Pick the tradeoff that's right for you.