Using "touch" command to create large files?? Is it possible??

[Angie_1]

Is it possible to use the touch comand to create large files? Like 50 GIG size files?

Thanks,
Angie

[Pete Randall]

No, touch, by definition, creates a 0 byte file. Try prealloc.


Pete

[Victor BERRIDGE]

Hi Angie,
No but you could use prealloc e.g
prealloc ./test 100000000 >> /tmp/testperf2

All the best
Victor

[Angie_1]

I have never heard of that command "prealloc"... does this below create a 50 GIG file? Looks like a 100 meg file?

prealloc ./test 100000000 >> /tmp/testperf2

Thanks!
Angie

[Fred Ruffet]

... or dd.

Regards,

Fred

[A. Clay Stephenson · Accepted solution]

No but you could use dd to create a large (though sparse) file very quickly.

dd if=/dev/zero bs=1k seek=52428799 count=1 of=mybigfile


If you do an ls -l mybigfile, it will display 50GB but a du -k will display only only 1 block because a sparse file has "holes". When a sparse file is read, the "holes" are filled in with NUL's so a copy of mybigfile will actually use 50GB of space.

[Angie_1]

So in order to get the actual 50 GIG of space to be used up, I would have to then copy that file after creating it with dd? Let me explain what I am doing. I am purposely filling up a disk with some files to control the amount of disk space for some users. Yes I could use a quota but this is easier.

Angie

[Pete Randall]

$ prealloc filler 100
$ ll filler
-rw-rw-r-- 1 plr support 100 May 18 12:20 filler
$


Pete

[john korterman]

Hi,
if you have all that space available, you could try something like this in the directory you want the file "big" to be put:
# prealloc big $((50*1024*1024*1024*1024))

regards,
John K.

[A. Clay Stephenson]

No, a modified dd command will do this nicely although it will take some time. I thought you wanted something quick like touch.

dd if=/dev/zero bs=256k count=204800 of=mybigfile


and unlike prealloc, dd is a standard UNIX/Linix command