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I am often on one computer in my house and I would like to SSH to another one, but often don't know the IP address of the one I want to connect to. Is there a way, from the command line, to scan the local network so I can find the computer I want to connect to?

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> but often don't know the IP address of the one I want to connect to Isn't this what DNS was invented for? – Chris McKeown Apr 5 '12 at 7:37
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If you don't know which computers are connected to your house's network, I think you might have a problem... – Massimo Apr 5 '12 at 8:31
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...and how do you know you're sshing into the right one? Time to sort out your ip addresses / name lookups. – symcbean Apr 5 '12 at 9:00
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In defense of Andrew: yes, it's desirable to set unchanging IPs in the DHCP lease, and to have local names. However, consider the real-world case where I just carried a headless Ubuntu PC into the office and hooked it up. For the first connection, I wanted to find the IP without carrying a keyboard and monitor over to it. To symcbean's question, it was easy to know the correct PC based on the MAC address decoding (automatically done by nmap/Zenmap) to the motherboard manufacturer, and the operating system used. Sometimes you don't know the IP and need to find it. – Phrogz Nov 12 '15 at 18:27
up vote 6 down vote accepted

Use "nmap" - this will tell you which hosts are up on a network, and indeed which have port 22 open. You could combine it with a few other tools (like grep) to produce more targetted output if need be.

Note: do this only on YOUR network. Running up nmap or its equivalents on someone else's network is considered bad form.

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bluebitter.de/portscn2.htm Use BluePortScan if you want a more simple thing than nmap – Gk. Apr 5 '12 at 7:16

From the command line you could use:

sudo nmap -sS -p 22 192.168.10.0/24

Substitute for the local address space on your network. I sometimes use this when I plug in a headless rasberry pi and want to find where to ssh to.

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Exactly one of the use-cases that lead me to ask this question. Thanks! – Andrew Nov 14 '15 at 20:27
    
+1 Also using for raspberry pi but: sudo nmap -sS -p 22 192.168.10.0/24 – Gtx Feb 14 at 18:21

You can manually telnet each ip at port 22.

If successful you should see the OpenSSH version string.

The process of checking each ip in the subnet can be done by means of the 'for' directive.

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