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I have installed the ssh utility on an embedded system but I can't connect to it. I am able to ssh from the device to another computer on the network but not the other way around.

The only port opened in the device is the 21st:

userk@dopamine:~$ nmap 160.80.97.X

Starting Nmap 6.40 ( http://nmap.org ) at 2015-02-09 20:49 CET
Nmap scan report for 160.80.97.X
Host is up (0.0092s latency).
Not shown: 999 closed ports
PORT   STATE SERVICE
21/tcp open  ftp

When I try to connect to it I get a connection refused error. I have tried with another port but nothing has changed. The configuration file /etc/ssh/sshd_config is the following

#Port 22
Port 223
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

# The default requires explicit activation of protocol 1
Protocol 2

# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 1h
ServerKeyBits 1024

# Ciphers and keying
#RekeyLimit default none

# Logging
# obsoletes QuietMode and FascistLogging
SyslogFacility AUTH
LogLevel INFO

# Authentication:

LoginGraceTime 2m
PermitRootLogin yes
StrictModes yes
MaxAuthTries 6
#MaxSessions 10

RSAAuthentication yes
PubkeyAuthentication yes

# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
# but this is overridden so installations will only check .ssh/authorized_keys
AuthorizedKeysFile  .ssh/authorized_keys

I don't have iptables and I can't install it. How can I connect to the device using ssh?

Solution

There was a problem with the generated keys. Move them to the /tmp folder

mv /etc/ssh/ssh_host_* /tmp

And regenerate the keys with

/etc/init.d/S50sshd restart OR /etc/init.d/sshd restart

or

ssh-keygen -A

Thanks to Bratchley, Abrixas2 and 0xC0000022L.

10
  • 1
    Have you checked that sshd is actually running?
    – Abrixas2
    Feb 9, 2015 at 20:11
  • 1
    Joining the choir, I would check netstat -tlpn to see if sshd is both running and listening on the port you're expecting it to run on.
    – Bratchley
    Feb 9, 2015 at 20:18
  • 2
    @narutov6 then the problem is that something is wrong with the host keys. They may need to be re-generated. I would mv /etc/ssh/ssh_host_* /tmp and try to run /etc/init.d/sshd restart and see if it regenerates the keys for you that way.
    – Bratchley
    Feb 9, 2015 at 20:25
  • 1
    @narutov6 You can run ssh-keygen -A to generate host keys for all known key types, for which host keys do not exist. This should normally be done during the configuration of sshd or during the first start of sshd.
    – Abrixas2
    Feb 9, 2015 at 20:27
  • 1
    You're sure the device has that IP, though? What's the output of lsof -i TCP:22 -s TCP:LISTEN say? Did you try to reinstall (apt-get --reinstall openssh-server) sshd or set it to start by default (update-rc.d ssh defaults) and then start (with service)? All assuming Rasbian. Also, did you try to run the SSH server from the command line using $(which sshd) -Ddp 10222 (as superuser) and then connecting to port 10222 from a client? If sshd isn't running you can also leave out the -p 10222 altogether. What about dpkg-reconfigure openssh-server to regenerate all the host keys?
    – 0xC0000022L
    Feb 9, 2015 at 20:37

1 Answer 1

Reset to default
1 
#Port 22
Port 223

Is that not 22 being commented out and 223 being active? Have you tried 223 yet?

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  • 1
    Nice catch but tcp/223 probably would've came up in his nmap scan as well.
    – Bratchley
    Feb 9, 2015 at 20:16
  • 3
    Not at all. Maybe 223 is not a "common port" what will be scaned by the command nmap without parameters...
    – user34720
    Feb 9, 2015 at 20:59
  • @Bratchley: nwildner is right. The OP should use nmap -p 1-65535 160.80.97.X or similar.
    – 0xC0000022L
    Feb 9, 2015 at 21:05
  • I stand corrected, I just ran it on a local system and it doesn't scan 223 by default unless I do -p. The OP's problem is with the daemon not starting though.
    – Bratchley
    Feb 9, 2015 at 21:17
  • Yes, I've tried with ssh user@160.80.97.X -p 223. I deleted the keys and re-generated them. Now it works. Thank you anyway
    – UserK
    Feb 10, 2015 at 0:29

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