doesn't flush by default, so the prompt is never printed

https://gitlab.alpinelinux.org/alpine/aports/-/blob/3.21-stable/main/tftp-hpa/fix-prompt-flush.patch

tftp/main.c

@@ -806,6 +806,7 @@ static void command(void)
             exit(0);            /* EOF */
 #else
         fputs(prompt, stdout);
+        fflush(stdout);
         if (fgets(line, LBUFLEN, stdin) == 0) {
             if (feof(stdin)) {
                 exit(0);