--- proftpd-1.3.8c/src/pidfile.c.~1~	2024-12-11 13:17:36.000000000 -0500
+++ proftpd-1.3.8c/src/pidfile.c	2025-01-06 01:04:36.506679884 -0500
@@ -49,6 +49,29 @@
   return 0;
 }
 
+// illumos does not have dprintf.  Use code from https://stackoverflow.com/questions/4246588/fprintf-like-function-for-file-descriptors-i-e-int-fd-instead-of-file-fp and hack dprintf into this routine.
+#ifdef __illumos__
+int
+fdprintf ( int d_fd, size_t d_bufmax, const char * d_fmt, ... )
+{
+  char * d_buffer;
+  int d_n;
+  va_list d_ap;
+
+  d_buffer = ( char * ) malloc ( d_bufmax );
+  if ( !d_buffer )
+    return 0;
+
+  va_start ( d_ap, d_fmt );
+  d_n = vsnprintf ( d_buffer, d_bufmax, d_fmt, d_ap );
+  va_end ( d_ap );
+
+  write ( d_fd, d_buffer, d_n );
+  free ( d_buffer );
+  return d_n;
+}
+#endif
+
 int pr_pidfile_write(void) {
   int fd, res, xerrno;
   mode_t mode = 0644;
@@ -74,7 +97,8 @@
       pidfile_path, strerror(xerrno));
   }
 
-  dprintf(fd, "%lu\n", (unsigned long) getpid());
+// assume pids (plus LF plus null) will never be greater than 22 characters long.
+  fdprintf(fd, 22, "%lu\n", (unsigned long) getpid());
   if (close(fd) < 0) {
     fprintf(stderr, "error writing PidFile '%s': %s\n", pidfile_path,
       strerror(errno));