Fix password setting by using passwd --stdin and sync

iridium_installer/backend/os_install.py

@@ -236,12 +236,15 @@ UUID={efi_uuid} /boot vfat defaults 0 2
             # Create user and add to wheel group (sudoer)
             run_command(["chroot", mount_root, "useradd", "-m", "-G", "wheel", user_info["username"]])
             
-            # Set password
+            # Ensure changes to /etc/passwd and /etc/shadow are flushed
+            run_command(["sync"])
+            
+            # Set password using passwd --stdin
             try:
                 logger.info("Setting user password...")
                 p = subprocess.run(
-                    ["chroot", mount_root, "chpasswd"],
-                    input=f"{user_info['username']}:{user_info['password']}\n",
+                    ["chroot", mount_root, "passwd", "--stdin", user_info["username"]],
+                    input=f"{user_info['password']}\n",
                     text=True,
                     check=True,
                     stdout=subprocess.PIPE,