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I am looking for a command to scan for any connected wireless device to my computer.

My computer has a problem that the wireless device getting disconnected if i put my hand on some part of it, so I have to restart the computer to find the wireless device again. Is thre any command in linux which scan for connected wireless devices that I can just and reconnect the wireless device?

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TR;DR: use nmcli dev status to get a list of which interfaces are connected to the network, and then use ping google.com -c 4 -I ifacex(where ifacex is actual interface name with number) to test if they are actually connected. To reconnect wireless interfaces nmcli nm wifi off; sleep 1; nmcli nm wifi on and let it automatically reconnect.

The simplest way to do so is through nmcli dev status. This command outputs the list of available interfaces on your system and tells you whether they are connected or not. Sample output from my system

DEVICE     TYPE              STATE        
eth0       802-3-ethernet    unavailable  
wlan0      802-11-wireless   connected 

If you'd wanna list only the devices which state is connected, then do nmcli dev status | awk '/connected/ {print $1}'. Here we match only lines that have 'connected' string in them, and print their name. In my case, it would give wlan0 only. If you'd have both eth0 and wlan0 connected, sample output would be

wlan0

eth0

Now , on my system network manager is kind of buggy. It may report device as connected, but in actuality it is disconnected. You could test wlan0 interface with ping google.com -c 4 -I wlan0. This sends 4 packets to google.com from interface wlan0. Now, I could also do nmcli dev status | awk '/connected/ {print $1}' | xargs ping google.com -c 4 -I , which will get the name of my wlan0 interface and stick it on the end of ping command as -I argument. Sample output

PING google.com (216.58.217.46) from 192.168.0.68 wlan0: 56(84) bytes of data.
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=1 ttl=57 time=44.0 ms
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=2 ttl=57 time=40.0 ms
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=3 ttl=57 time=48.0 ms
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=4 ttl=57 time=40.0 ms

--- google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3016ms
rtt min/avg/max/mdev = 40.000/43.000/48.000/3.316 ms

Often users might have dns issue, which means your machine cannot translate google.com to actual ip address (computers deal only in ip addresses, like phones only deal with phone numbers). In that case, you'd better run ping 8.8.8.8 -c 4 -I wlan0 && ping google.com -c 4 -I wlan0, where it will test if your machine has connection to the web AND resolves domain names.

Now, what if you have more than one connected interface ? Personally I'd test each interface with ping separately, without relying on that one-liner, but because I am having so much fun with scripting recently, here's another one-liner:

nmcli dev status | awk '/connected/ {print $1}' | xargs -n 1 ping google.com -c 4 -I

This one , basically finds names of connected interfaces, and executes ping command with each one. Since I don't have multiple devices connected, I'll just show you how it looks when I awk gets each item from first column, so note , the first output will be wrong, second is eth0, and third wlan0 nmcli dev status | awk '{print $1}' | xargs -n 1 ping google.com -c 4 -I

ping: SO_BINDTODEVICE: Invalid argument
ping: Warning: source address might be selected on device other than eth0.
PING google.com (216.58.217.46) from 192.168.0.68 eth0: 56(84) bytes of data.
From sergiy-Satellite-L455D.local (192.168.0.68) icmp_seq=1 Destination Host Unreachable
From sergiy-Satellite-L455D.local (192.168.0.68) icmp_seq=2 Destination Host Unreachable
From sergiy-Satellite-L455D.local (192.168.0.68) icmp_seq=3 Destination Host Unreachable
From sergiy-Satellite-L455D.local (192.168.0.68) icmp_seq=4 Destination Host Unreachable

--- google.com ping statistics ---
4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 3152ms
pipe 3
PING google.com (216.58.217.46) from 192.168.0.68 wlan0: 56(84) bytes of data.
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=1 ttl=57 time=44.0 ms
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=2 ttl=57 time=48.0 ms
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=3 ttl=57 time=40.0 ms
64 bytes from den03s10-in-f14.1e100.net (216.58.217.46): icmp_seq=4 ttl=57 time=40.0 ms

--- google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3016ms
rtt min/avg/max/mdev = 40.000/43.000/48.000/3.316 ms

And as it should, we see eth0 is disconnected, wlan0 is connected.

Another thing that you could use is nm-tool. This guy gives you long report about each one of your interfaces, with settings. We could cut that down to only the list of interfaces and their statuses with nm-tool | tr '-' ' ' | awk '/Device/,/State/ {print $1,$2}' . Here we substitute the annoying - character with space, and just get the text from Device to State strings.

Device: eth0
Type: Wired
Driver: r8169
State: unavailable
Device: wlan0
Type: 802.11
Driver: r8180
State: connected

What else ? whois,nslookup and dig are lookup utilities for domain names and ip addresses. If you can use them to find out info about a domain or ip address, you're connected. They won't tell you the interface, but nice to actually test the connectivity.

In conclusion: There's more than one way to skin a cat, as you know. The very first command nmcli dev status and ping is all you really need to test your connections, and ping is the "real MVP" on any system, so to speak. Now, if you wanna get fancy, learn some new command line tricks, by all means study the one-liners I've posted here ! The power of Ubuntu and Linux in general lies in command line

Additions:

Other's have appropriately noted that restarting network manager with sudo service network-manager restart will do the job most of the time. By default all connections are set to get autoconnected when network manager is in range. I use this method a lot !

What else can be done ? nmcli nm wifi off; sleep 1; nmcli nm wifi on. This will turn off wifi , pause for a second, and turn on wifi again; and your network should automatically reconnect.

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    a little more detail please – Panther Apr 12 '15 at 0:22
  • @bodhi.zazen I added some more details. I may have been having too much fun with this question :). Let me know how can I improve it, what else I could add – Sergiy Kolodyazhnyy Apr 12 '15 at 6:11
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I'm assuming you have a USB wifi device? I only ask this because it is odd to lose the device in the OS by physically touching it.

Anyway, have you tried to disable/enable networking with the GUI? That's the simplest first step to try. Click on the network signal icon in the upper-right corner near your clock, and uncheck Enable Networking. Give it a minute, then click on the network signal icon again and re-check the Enable Networking option, again give it a moment to catch up. See if you can then reconnect to your wireless network.

If that doesn't work, then open a terminal window and type the following command:

sudo service network-manager restart

That should force the NM to completely stop and restart, and your wifi adapter may pop back up.

If either of these does not help, then when you lose connection with your wifi adapter, pull up the terminal and run the following command and edit your question and post the results:

ifconfig

That should show you whether or not your device is being seen at all when you lose connection.

Assuming it is an USB adapter...can you use other USB devices in that same slot, or do they experience the same problem?

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