Hello!
You can use lxsplit.
lxsplit -s file_name.ext 20M --> split the big file into 20MB files
lsxplit -j file_name.ext.001 --> join the splited files.
Here you have a tutorial about installing and using lxsplit for split and join files.
http://www.gazduiretm.eu/blog/2009/07/21/split-si-join-fisiere-un-ubuntu-cu-lxsplit/
Hope that helps you!
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