SIGXFSZ
The file grew past its allowance; the bell rings at the write.
SIGXCPU's twin for disk: with ulimit -f, no file written by the process may pass the ceiling. The write that would cross the line doesn't write — it rings this bell.
If the process ignores it, the contract has a second clause: the write fails with EFBIG and life goes on. It was the classic fence against runaway logs before quotas and logrotate existed.
$ ulimit -f 1024
$ dd if=/dev/zero of=cheio.bin
File size limit exceeded (core dumped)
(1024 blocks of 512 bytes: 512 KiB and not one more)