$ dd if=/dev/zero    of=filename bs=1k count=5 # 5KB of zero content
$ dd if=/dev/urandom of=filename bs=1M count=7 # 7MB of random content
$ touch filename #  create 0B file (if file exists, updates mtime)

http://www.linuxtopia.org/online_books/linux_system_administration/debian_linux_guides/debian_linux_reference_guide/ch-tips.en_058.html

Create Dummy File In Linux

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