Here's the timer vsftpd-restart.timer
[Unit]
Description=Restart vsftpd daily at 6 AM
After=network.target
[Timer]
Unit=vsftpd-restart.service
OnCalendar=*-*-* 06:00:00
Persistent=true
[Install]
WantedBy=timers.target
This is the script vsftpd-restart.service
[Unit]
Description=Restart vsftpd daily at 6 AM
After=network.target
[Service]
Type=oneshot
ExecStart=/bin/bash -c 'systemctl stop vsftpd; systemctl start vsftpd'
[Install]
WantedBy=vsftpd-restart.timer
And here's the vsftpd systemctl log
Oct 07 06:00:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:00:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:00:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:00:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:00:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:01:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:01:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:01:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:01:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:01:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:02:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:02:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:02:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:02:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:02:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:03:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:03:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:03:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:03:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:03:02 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:04:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:04:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:04:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:04:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:04:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:05:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:05:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:05:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:05:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:05:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:06:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:06:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:06:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:06:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:06:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:07:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:07:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:07:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:07:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:07:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:08:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:08:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:08:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:08:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:08:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:09:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:09:01 test systemd[1]: vsftpd.service: Deactivated successfully.
Oct 07 06:09:01 test systemd[1]: Stopped vsftpd.service - vsftpd FTP server.
Oct 07 06:09:01 test systemd[1]: Starting vsftpd.service - vsftpd FTP server...
Oct 07 06:09:01 test systemd[1]: Started vsftpd.service - vsftpd FTP server.
Oct 07 06:10:01 test systemd[1]: Stopping vsftpd.service - vsftpd FTP server...
Oct 07 06:10:01 test systemd[1]: vsftpd.service: Deactivated successfully.
The reason your current setup is causing the vsftpd service to restart every minute from 6:00 to 7:00 AM is due to the OnCalendar=--* 06:00:00 timer being persistent (Persistent=true). This means the timer attempts to "catch up" on missed events during the time the system was off, so if the system was off at 6 AM, it can lead to multiple triggers when the system comes back online. This should do it:
vsftpd-restart.timer
And don't forget to reload with the new timer script: