If you need to create a large test file on Linux, fallocate can help.

To create a 1GB file:

fallocate -l 1G test.img

If you need a different size, just change the -l option with the proper suffix.

  • -l 15k = 15KB
  • -l 15m = 15MB
  • -l 15g = 15GB
  • -l 15t = 15TB
  • -l 15p = 15PB

If your operating system does not support fallocate, you can always rely on the dd command.

To create a 1GB file:

dd if=/dev/zero of=/path/to/your/output/file bs=1024 count=1024000

Since dd is more complicated, here are what these inputs mean:

  • if= is your input, we’re using /dev/zero to generate junk data.
  • of= is your output.
  • bs= is the number of bytes read and written at a time.
  • count= is the number of input blocks we are copying, or how many times we want to run the bs= input.

Based on the above inputs, you just need to change the value of count= to increase/decrease the file size.

  • count=1024 = 1MB
  • count=10240 = 10MB
  • count=102400 = 100MB