---
name: "uml_mkcow"
section: "1"
platform: "linux"
package: "uml-utilities"
version: "20070815.4-2.1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/uml_mkcow"
---

# uml\_mkcow(1)

create a new COW file

## NAME

uml\_mkcow — create a new COW file

## SYNOPSIS

**uml\_mkcow** \[*-f*\]  \[COW\_file\]  \[backing\_file\]

## DESCRIPTION

This manual page documents briefly the  **uml\_mkcow** command.

This manual page was written for the **Debian GNU/Linux** distribution  because the original program does not have a manual page.  Instead, it has documentation in HTML format; see below.

**uml\_mkcow** is a small utility to create  COW (Copy-On-Write) files without the need to run the full UML kernel.

NOTE: you can save a lot of disk space using COW files.  When checking the size of the COW file in order to see the gobs  of space that you're saving, make sure you use 'ls -ls' to see the actual  disk consumption rather than the length of the file. The COW file is  sparse, so the length will be very different from the disk usage.

## OPTIONS

- **-f**

  Force overwrite of an exsiting COW file.

## EXAMPLES

Create a new COW file:

**uml\_mkcow** rootfs\_COW rootfs

Overwrite (destroying) an existing COW file:

**uml\_mkcow** -f rootfs\_COW rootfs

## SEE ALSO

The *UserModeLinux-HOWTO (link to URL http://user-mode-linux.sourceforge.net/UserModeLinux-HOWTO.html)*

## AUTHOR

uml\_mkcow was written by Steve Schnepp.

This manual page was written by Mattia Dongili malattia@debian.org for  the **Debian GNU/Linux** system, based on material in the  UserModeLinux-HOWTO by Rusty Russell.