fallocate

Allocate 700 MiB file

$ fallocate -l 700M path/to/file

$ fallocate -c -l 200M path/to/file

$ fallocate -c -o 100M -l 20M path/to/file

fallocate [OPTIONS] filename

fallocate preallocates or deallocates space to a file. Unlike writing zeros, fallocate uses filesystem-specific operations to quickly allocate space without initializing the data, making it very fast for creating large files.

-l, --length size

Length of the range to allocate or deallocate

Offset of the range from the beginning of the file

Remove a range from the file without leaving a hole

Detect and convert zero blocks to holes

Deallocate space (create a hole) in the file

Zero a range but keep space allocated

Maintain apparent file size when extending allocation

Not all filesystems support all operations. The collapse operation requires filesystem support (ext4 4.2+, XFS 4.15+). Space allocation without zeroing means the file may contain previous disk data.

fallocate is a Linux-specific utility that uses the fallocate() system call introduced in kernel 2.6.23.

truncate(1), dd(1), fstrim(8)