runaway grep - (nf)

[Dave Martindale]

A runaway process that slowly eats space and suddenly releases it when
it is killed does this because its output file has already been rm'ed.
When a file is unlinked in UNIX, the directory entry vanishes immediately
but the file still exists in its entirety, and can even continue to grow,
as long as some process still has it open.  Once the last process which
has it open exits or otherwise closes it, the inode is deallocated and
all its disk blocks freed, thus instantly releasing all that space.