Is `cp --no-clobber` vulnerable to race condition? The man page for `cp(1)` says > `--no-clobber` do not overwrite an existing file However, wouldn't the following scenario be possible? 1. `cp` checks the file existence, let's assume the file doesn't exist (yet) 2. Some other process writes to the same path, so now there is data written to the previously not existing file 3. Since `cp` isn't aware of the now existing file, it overwrites the data Is `cp --no-clobber` vulnerable to this race condition? And if not, how does `cp` avoid the situation above?

`cp` isn’t vulnerable to this race condition. When `--no-clobber` is set, it checks whether the destination already exists; if it determines it doesn’t, and it should therefore proceed with the copy, it remembers that it’s supposed to copy to a new file. When the time comes to open the destination file, it opens it with flags which enforce its creation, `O_CREAT` and `O_EXCL`; the operating system then checks that the file doesn’t exist _while opening it_ , and fails (`EEXIST`) if it does.