使用PyQt5创建一个FTP客户端应用程序。它连接到linux创建的FTP服务器，并提供了上传和下载文件的功能。

可以使用PyQt5和ftplib库创建一个FTP客户端应用程序。以下是一个示例代码，展示了如何连接到Linux上的FTP服务器，并提供上传和下载文件的功能。

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QPushButton, QFileDialog, QMessageBox
from ftplib import FTP

class FTPClient(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setWindowTitle("FTP Client")
        self.setGeometry(100, 100, 300, 200)

        self.btn_upload = QPushButton("Upload", self)
        self.btn_upload.setGeometry(50, 50, 200, 30)
        self.btn_upload.clicked.connect(self.uploadFile)

        self.btn_download = QPushButton("Download", self)
        self.btn_download.setGeometry(50, 100, 200, 30)
        self.btn_download.clicked.connect(self.downloadFile)

    def uploadFile(self):
        file_path, _ = QFileDialog.getOpenFileName(self, 'Select file to upload', '', 'All Files (*)')
        if file_path:
            ftp = FTP('ftp.example.com')  # Replace with your FTP server address
            ftp.login('username', 'password')  # Replace with your FTP credentials

            file_name = file_path.split('/')[-1]
            try:
                with open(file_path, 'rb') as file:
                    ftp.storbinary(f'STOR {file_name}', file)
                QMessageBox.information(self, 'Success', 'File uploaded successfully!')
            except Exception as e:
                QMessageBox.critical(self, 'Error', f'Failed to upload file: {str(e)}')

            ftp.quit()

    def downloadFile(self):
        file_name, _ = QFileDialog.getSaveFileName(self, 'Save file', '', 'All Files (*)')
        if file_name:
            ftp = FTP('ftp.example.com')  # Replace with your FTP server address
            ftp.login('username', 'password')  # Replace with your FTP credentials

            try:
                with open(file_name, 'wb') as file:
                    ftp.retrbinary(f'RETR {file_name}', file.write)
                QMessageBox.information(self, 'Success', 'File downloaded successfully!')
            except Exception as e:
                QMessageBox.critical(self, 'Error', f'Failed to download file: {str(e)}')

            ftp.quit()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = FTPClient()
    window.show()
    sys.exit(app.exec_())

请注意，上述代码中的服务器地址、用户名、密码等需要替换为您实际的FTP服务器信息。此外，代码中使用的是基本的FTP功能，如果需要更复杂的功能，可以根据ftplib库的文档进行扩展。