The names for reject files (files containing patches that
patch could not find a place to apply) are normally the name
of the output file with ‘.rej’ appended (or ‘#’ if using
‘.rej’ would make the backup file name too long).
Alternatively, you can tell
patch to place all of the rejected
patches in a single file. The -r reject-file or
--reject-file=reject-file option uses reject-file as
the reject file name.