unit vsftpd.service could not be found

The error message "unit vsftpd.service could not be found" indicates that the system is unable to locate the vsftpd service unit file. This could be due to several reasons such as the service not being installed, the unit file being removed or renamed, or the system not having the necessary permissions to access the unit file.

To resolve this issue, you can try the following steps:

1. Check if the vsftpd service is installed on your system by running the command `sudo apt-get install vsftpd`.

2. If the service is already installed, try restarting the systemd daemon by running the command `sudo systemctl daemon-reload`.

3. Check if the unit file exists in the systemd directory by running the command `ls /lib/systemd/system/vsftpd.service`.

4. If the unit file is missing, you can create a new one by creating a file called vsftpd.service in the /etc/systemd/system directory with the following contents:

[Unit]
Description=vsftpd FTP server
After=network.target

[Service]
ExecStart=/usr/sbin/vsftpd /etc/vsftpd.conf
ExecReload=/bin/kill -HUP $MAINPID
Restart=always

[Install]
WantedBy=multi-user.target

5. After creating the unit file, run the command `sudo systemctl daemon-reload` to reload the systemd daemon, and then start the vsftpd service by running the command `sudo systemctl start vsftpd.service`.

6. You can also enable the vsftpd service to start automatically at boot time by running the command `sudo systemctl enable vsftpd.service`.

I hope this helps!