vnc-alive-check.sh

#!/bin/bash
if [[ "${1,,}" == "install" ]]; then
        # Call this script with argument 'install' to generate a systemd unit file.
        cat <<-EOF | sudo dd of=/etc/systemd/system/vnc-alive-check.service
                [Unit]
                Description=VNC-ALIVE-CHECK: Make sure VNC is connected and restart it if needed.
                After=network.target

                [Service]
                ExecStart=${PWD}/$0
                Restart=always

                [Install]
                WantedBy=multi-user.target
                EOF
        sudo systemctl enable vnc-alive-check.service
        sudo systemctl start vnc-alive-check.service
        exit 0
fi

function func_restartRemmina {
        killall remmina
        sleep 2
        #su --command='DISPLAY=:0 XAUTHORITY=/var/run/lightdm/root/:0 remmina --connect=/home/user/.remmina/1513445416363.remmina &' user
        su --command='DISPLAY=:0 remmina --connect=/home/user/.remmina/1513445416363.remmina &' user
}

####    MAIN   ####
function main {
        var_rchar=0 # initialize counter for later comparison
        while :; do
                sleep 10
                # no pid at all
                pidof remmina &>/dev/null || { echo Restarting due to no PID; func_restartRemmina; }

                # pid but no socket
                lsof -i -a -p $(pidof remmina) -n -P 2>/dev/null | grep -q ESTABLISHED || { echo Restarting due to no socket; func_restartRemmina; }

                # socket but no data
                var_lastRchar="$var_rchar"
                var_rchar="$(sed -n -r 's/rchar: ([0-9]+)$/\1/p' /proc/$(pidof remmina)/io)" 
                (( $var_rchar > $var_lastRchar )) || { echo Restarting due to not enough rchar: $var_rchar current / $var_lastRchar last; func_restartRemmina; }
        done
}


[[ -z "$1" ]] && main # main loop only runs when the script has no arguments.  this prevents main from running when script is actively run to perform a specific function.

For remmina VLC sessions that stay open (meaning process is running and socket is open), but no data comes back from the server, use an aggressive TCP timeout:

sysctl -w net.ipv4.tcp_keepalive_time=30
sysctl -w net.ipv4.tcp_keepalive_intvl=3
sysctl -w net.ipv4.tcp_keepalive_probes=5
sysctl -w net.ipv4.tcp_retries2=5 

May be able to change socket options to use "TCP_USER_TIMEOUT" to avoid setting system-wide configuration.
See https://patchwork.ozlabs.org/patch/62889/

"TCP_USER_TIMEOUT is a TCP level socket option that takes an unsigned int,
when > 0, to specify the maximum amount of time in ms that transmitted
data may remain unacknowledged before TCP will forcefully close the
corresponding connection and return ETIMEDOUT to the application. If
0 is given, TCP will continue to use the system default."