I there any possibility to recover file contents after
echo "" > file.txt?
I'm using Ubuntu 10.04 and my filesystem is vzfs
If another had access to the original file, your edit creates a local version of the shared file, that's how vzfs works.
So they would have the original file and could let you have a copy back.
However, if you've edited it and then truncated, you are stuffed unless you also have a backup or version control.