git-update-index

git-update-index - Register file contents in the working tree to the index

Modifies the index. Each file mentioned is updated into the index and any unmerged or needs updating state is cleared.

See also git-add[1] for a more user-friendly way to do some of the most common operations on the index.

The way git update-index handles files it is told about can be modified using the various options:

--refresh does not calculate a new sha1 file or bring the index up to date for mode/content changes. But what it does do is to "re-match" the stat information of a file with the index, so that you can refresh the index for a file that hasn’t been changed but where the stat entry is out of date.

For example, you’d want to do this after doing a git read-tree, to link up the stat index details with the proper files.

--cacheinfo is used to register a file that is not in the current working directory. This is useful for minimum-checkout merging.

To pretend you have a file at path with mode and sha1, say:

$ git update-index --add --cacheinfo <mode>,<sha1>,<path>

--info-only is used to register files without placing them in the object database. This is useful for status-only repositories.

Both --cacheinfo and --info-only behave similarly: the index is updated but the object database isn’t. --cacheinfo is useful when the object is in the database but the file isn’t available locally. --info-only is useful when the file is available, but you do not wish to update the object database.

--index-info is a more powerful mechanism that lets you feed multiple entry definitions from the standard input, and designed specifically for scripts. It can take inputs of three formats:

To place a higher stage entry to the index, the path should first be removed by feeding a mode=0 entry for the path, and then feeding necessary input lines in the third format.

For example, starting with this index:

$ git ls-files -s
100644 8a1218a1024a212bb3db30becd860315f9f3ac52 0       frotz

you can feed the following input to --index-info:

$ git update-index --index-info
0 0000000000000000000000000000000000000000        frotz
100644 8a1218a1024a212bb3db30becd860315f9f3ac52 1        frotz
100755 8a1218a1024a212bb3db30becd860315f9f3ac52 2        frotz

The first line of the input feeds 0 as the mode to remove the path; the SHA-1 does not matter as long as it is well formatted. Then the second and third line feeds stage 1 and stage 2 entries for that path. After the above, we would end up with this:

$ git ls-files -s
100644 8a1218a1024a212bb3db30becd860315f9f3ac52 1        frotz
100755 8a1218a1024a212bb3db30becd860315f9f3ac52 2        frotz

Many operations in Git depend on your filesystem to have an efficient lstat(2) implementation, so that st_mtime information for working tree files can be cheaply checked to see if the file contents have changed from the version recorded in the index file. Unfortunately, some filesystems have inefficient lstat(2). If your filesystem is one of them, you can set "assume unchanged" bit to paths you have not changed to cause Git not to do this check. Note that setting this bit on a path does not mean Git will check the contents of the file to see if it has changed — it makes Git to omit any checking and assume it has not changed. When you make changes to working tree files, you have to explicitly tell Git about it by dropping "assume unchanged" bit, either before or after you modify them.

In order to set "assume unchanged" bit, use --assume-unchanged option. To unset, use --no-assume-unchanged. To see which files have the "assume unchanged" bit set, use git ls-files -v (see git-ls-files[1]).

The command looks at core.ignorestat configuration variable. When this is true, paths updated with git update-index paths... and paths updated with other Git commands that update both index and working tree (e.g. git apply --index, git checkout-index -u, and git read-tree -u) are automatically marked as "assume unchanged". Note that "assume unchanged" bit is not set if git update-index --refresh finds the working tree file matches the index (use git update-index --really-refresh if you want to mark them as "assume unchanged").

To update and refresh only the files already checked out:

$ git checkout-index -n -f -a && git update-index --ignore-missing --refresh

Skip-worktree bit can be defined in one (long) sentence: When reading an entry, if it is marked as skip-worktree, then Git pretends its working directory version is up to date and read the index version instead.

To elaborate, "reading" means checking for file existence, reading file attributes or file content. The working directory version may be present or absent. If present, its content may match against the index version or not. Writing is not affected by this bit, content safety is still first priority. Note that Git can update working directory file, that is marked skip-worktree, if it is safe to do so (i.e. working directory version matches index version)

Although this bit looks similar to assume-unchanged bit, its goal is different from assume-unchanged bit’s. Skip-worktree also takes precedence over assume-unchanged bit when both are set.

This mode is designed for repositories with very large indexes, and aims at reducing the time it takes to repeatedly write these indexes.

In this mode, the index is split into two files, $GIT_DIR/index and $GIT_DIR/sharedindex.<SHA-1>. Changes are accumulated in $GIT_DIR/index, the split index, while the shared index file contains all index entries and stays unchanged.

All changes in the split index are pushed back to the shared index file when the number of entries in the split index reaches a level specified by the splitIndex.maxPercentChange config variable (see git-config[1]).

Each time a new shared index file is created, the old shared index files are deleted if their modification time is older than what is specified by the splitIndex.sharedIndexExpire config variable (see git-config[1]).

To avoid deleting a shared index file that is still used, its modification time is updated to the current time every time a new split index based on the shared index file is either created or read from.

This cache is meant to speed up commands that involve determining untracked files such as git status.

This feature works by recording the mtime of the working tree directories and then omitting reading directories and stat calls against files in those directories whose mtime hasn’t changed. For this to work the underlying operating system and file system must change the st_mtime field of directories if files in the directory are added, modified or deleted.

You can test whether the filesystem supports that with the --test-untracked-cache option. The --untracked-cache option used to implicitly perform that test in older versions of Git, but that’s no longer the case.

If you want to enable (or disable) this feature, it is easier to use the core.untrackedCache configuration variable (see git-config[1]) than using the --untracked-cache option to git update-index in each repository, especially if you want to do so across all repositories you use, because you can set the configuration variable to true (or false) in your $HOME/.gitconfig just once and have it affect all repositories you touch.

When the core.untrackedCache configuration variable is changed, the untracked cache is added to or removed from the index the next time a command reads the index; while when --[no-|force-]untracked-cache are used, the untracked cache is immediately added to or removed from the index.

Before 2.17, the untracked cache had a bug where replacing a directory with a symlink to another directory could cause it to incorrectly show files tracked by git as untracked. See the "status: add a failing test showing a core.untrackedCache bug" commit to git.git. A workaround for that is (and this might work for other undiscovered bugs in the future):

$ git -c core.untrackedCache=false status

This bug has also been shown to affect non-symlink cases of replacing a directory with a file when it comes to the internal structures of the untracked cache, but no case has been reported where this resulted in wrong "git status" output.

There are also cases where existing indexes written by git versions before 2.17 will reference directories that don’t exist anymore, potentially causing many "could not open directory" warnings to be printed on "git status". These are new warnings for existing issues that were previously silently discarded.

As with the bug described above the solution is to one-off do a "git status" run with core.untrackedCache=false to flush out the leftover bad data.

This feature is intended to speed up git operations for repos that have large working directories.

It enables git to work together with a file system monitor (see the "fsmonitor-watchman" section of githooks[5]) that can inform it as to what files have been modified. This enables git to avoid having to lstat() every file to find modified files.

When used in conjunction with the untracked cache, it can further improve performance by avoiding the cost of scanning the entire working directory looking for new files.

If you want to enable (or disable) this feature, it is easier to use the core.fsmonitor configuration variable (see git-config[1]) than using the --fsmonitor option to git update-index in each repository, especially if you want to do so across all repositories you use, because you can set the configuration variable in your $HOME/.gitconfig just once and have it affect all repositories you touch.

When the core.fsmonitor configuration variable is changed, the file system monitor is added to or removed from the index the next time a command reads the index. When --[no-]fsmonitor are used, the file system monitor is immediately added to or removed from the index.

The command honors core.filemode configuration variable. If your repository is on a filesystem whose executable bits are unreliable, this should be set to false (see git-config[1]). This causes the command to ignore differences in file modes recorded in the index and the file mode on the filesystem if they differ only on executable bit. On such an unfortunate filesystem, you may need to use git update-index --chmod=.

Quite similarly, if core.symlinks configuration variable is set to false (see git-config[1]), symbolic links are checked out as plain files, and this command does not modify a recorded file mode from symbolic link to regular file.

The command looks at core.ignorestat configuration variable. See Using "assume unchanged" bit section above.

The command also looks at core.trustctime configuration variable. It can be useful when the inode change time is regularly modified by something outside Git (file system crawlers and backup systems use ctime for marking files processed) (see git-config[1]).

The untracked cache extension can be enabled by the core.untrackedCache configuration variable (see git-config[1]).

Users often try to use the assume-unchanged and skip-worktree bits to tell Git to ignore changes to files that are tracked. This does not work as expected, since Git may still check working tree files against the index when performing certain operations. In general, Git does not provide a way to ignore changes to tracked files, so alternate solutions are recommended.

For example, if the file you want to change is some sort of config file, the repository can include a sample config file that can then be copied into the ignored name and modified. The repository can even include a script to treat the sample file as a template, modifying and copying it automatically.

git-config[1], git-add[1], git-ls-files[1]