Under some OperatingSystems (especially Unix-like ones), you can mount(8) a single file onto your VirtualFileSystem. There are several reasons why you might want to do this:
This is what I did to make sure to test that my software failed gracefully when disk space ran out.
1) Create a file containing a filesystem
create a 2 MB file with an ext2 filesystem $ dd if=/dev/zero of=/tmp/loop.fs bs=1M count=2 $ mke2fs -F /tmp/loop.fs
2) mount it as a loop back device (must be done as root)
load the loop.ko kernel module if support is not compiled into the kernel # modprobe loop where I want it to be mounted # mount /tmp/loop.fs /mnt/directory -o loop
Now /mnt/directory will only allow around 2MB (minus filesystem overhead) of data to be written to it, and then the device will be out of space.
See also LoopbackMounting?
One page links to LoopDevice:
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