Ubuntu – Detect internet connection

internetnetworking

On Windows, if there's no internet connectivity for whatever reason and the connection to the network is perfectly fine, a small icon shows on the network icon in the notification area. Is there any way to do the same on Ubuntu?

Even that is not necessary, I just want to know what ways are there to find if the internet connection is lost or not.

No ping to x website please, I've faced a few instances of DNS outage and ping failure can be due to DNS down time, not internet connectivity.

UPDATE

Thanks for all those interesting answers. My actual aim of this question was to know if there was a method to know the status of my connection at the local level (connection between the machine and AP), which is why I said no ping to x website please. The LAN private address that was mentioned by Alain is something that comes close. If I can diagnose that, I can rule out AP/network issues, then move onto diagnosing the actual connection to my ISP.

Best Answer

The command ip link show shows the status of available interfaces. At least one of the interfaces on needs be listed as UP in order for you to have any connectivity at all.

The command ip neigh show shows local link state, like this:

192.168.0.1 dev eth0 lladdr 00:15:e9:ec:cc:80 REACHABLE

You need at least one REACHABLE to have network access.

The command ip addr show shows all interfaces and their IP addresses.

Once you have a local IP address and a neighbor's IP address, you can then use ping or another tool to verify local IP connectivity.

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It's my understanding that /etc/resolv.conf is for public nameservers only. It appears that yours has been modified to use a private nameserver ostensibly over a VPN. If you wish your Ubuntu box to obtain Domain Name Service normally to allow internet access, I suggest that you revert back to the default /etc/resolv.conf file which contains:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1

You can revert back to the default /etc/resolv.conf file by either restoring the original from a recent backup from before it was modified, or opening the file the link points to with the command sudo gedit /etc/resolv.conf and pasting the code from the default file above into it overwriting it's current content. You may want to save a copy of the current content beforehand as a backup somewhere you will be able to locate it if you find you need it.

NOTE: /etc/resolv.conf is a symbolic link to the file /run/resolvconf/resolv.conf so file based operations such as editing on /etc/resolv.conf will actually be carried out on /run/resolvconf/resolv.conf

To confirm that the link hasn't been erroneously modified run the command ls -l /etc/resolv.conf which should result in the output below.

lrwxrwxrwx 1 root root 29 Feb 25 2016 /etc/resolv.conf -> ../run/resolvconf/resolv.conf

the arrow indicates it's a symlink.

For more information on resolvconf which modifies this file see the man page.

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