Ubuntu – Wired Connection shared with other computers connects then disconnects in the nm-applet

The following script, put in /etc/NetworkManager/dispatcher.d/99-disable-wireless-when-wired, mostly works—it disables wireless even when I want to share wired with wireless or vice-versa.

To do this, run the following command in terminal:

sudo nano /etc/NetworkManager/dispatcher.d/99-disable-wireless-when-wired

And paste the following code into the text editor.

#!/bin/sh
myname=${0##*/}
log() { logger -p user.info -t "${myname}[$$]" "$*"; }
IFACE=$1
ACTION=$2

release=$(lsb_release -s -c)
case ${release} in
    trusty|utopic) nmobj=nm;;
    *) nmobj=radio;;
esac

case ${IFACE} in
    eth*|usb*|en*)
        case ${ACTION} in
            up)
                log "disabling wifi radio"
                nmcli "${nmobj}" wifi off
                ;;
            down)
                log "enabling wifi radio"
                nmcli "${nmobj}" wifi on
                ;;
        esac
        ;;
esac

Then save and exit.

Note the following conditions on the script, as documented in the NetworkManager manual page:

Each script should be:

• a regular file,
• owned by root,
• not writable by group or other,
• not set-uid,
• and executable by the owner.

Instead of nmcli radio wifi off (or nmcli nm wifi off for older versions of NetworkManager), there is also rfkill block wifi. However, if rfkill is used instead of nmcli, newer versions of NetworkManager will turn wifi back on during boot.

you can try one of the below solution:

Open terminal and type in: sudo service network-manager restart.
OR
Go to System Setting -> Network -> Forget your wifi and reconnect to it.
OR
Restart or Log off and Log into your laptop.