Lockfile

A lockfile is a file created in the filesystem to establish that a given file is locked for reading and writing by other processes. If .git/index needs to be written, for example, a .git/index.lock file will be created. Any modifications needed to the index will be written to the lockfile, then the changes are committed by renaming index.lock to index. While the lockfile exists, no other process may read or write to the locked file.