In Unix if you have to delete a large file because you need the space, but it might be owned by a running service, then you should proceed your delete command with a "cat /dev/null"
/bin/cat /dev/null > filename.txt
This will ensure that the file, is truncated to 0 bytes and the space is returned to the filesystem.
You can then delete it with the usual tools (with or without success) afterwards.
I appreciate that this is a little late, and most admins know to do this, but it's something we often overlook and then regret.
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