some questions about unix processes https://questions.wizardzines.com/unix-processes.html …
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2 processes _can_ write to the same file at the same time, but the writes aren't guaranteed to be atomic; bytes from one write can interleave between bytes from another! It's important to use some sort of locking mechanism when this isn't acceptable (pipes have _some_ guarantees)
There are some atomicity guarantees, though relying on that for anything other than the "multiple loggers to the same logfile" use case is a recipe for trouble. E.g. CephFS does not always guarantee it (and that's one of the very few ways it's not strictly POSIX compliant).
