ssh connection closes after successful login

Question

I am trying to run ssh on my computer so I can control it with my android phone. When I scan my local network with overlook fing at my phone I get that my computer is running ssh at port 22. So I try to connect with connectBot I get:

Linux linux 2.6.35-28-generic-pae #50-Ubuntu SMP Fri Mar 18 20:43:15 UTC 2011 i686 GNU/Linux
Ubuntu 10.10

Welcome to Ubuntu!
 * Documentation:  https://help.ubuntu.com/

0 packages can be updated.
0 updates are security updates.

Last login: Mon Apr 25 15:27:36 2011 from linux
Connection to localhost closed.

Then a message: "Host has disconnected. Close session?"

When I run ssh user@localhost at the computer I get the same thing. Seems that ssh is setup incorrectly, I get a password prompt and information about the computer, but then the connection instantly close. Why?

EDIT:

auth.log:

Apr 25 15:39:27 linux sshd[4932]: pam_sm_authenticate: Called
Apr 25 15:39:27 linux sshd[4932]: pam_sm_authenticate: username = [user]
Apr 25 15:39:27 linux sshd[4932]: pam_sm_authenticate: /home/user is already mounted
Apr 25 15:39:27 linux sshd[4932]: Accepted password for user from ::1 port 48442 ssh2
Apr 25 15:39:27 linux sshd[4932]: pam_unix(sshd:session): session opened for user user by (uid=0)
Apr 25 15:39:27 linux sshd[5079]: Received disconnect from ::1: 11: disconnected by user
Apr 25 15:39:27 linux sshd[4932]: pam_unix(sshd:session): session closed for user user

ssh -vvv user@localhost:

user@linux:~$ ssh -vvv user@localhost
OpenSSH_5.5p1 Debian-4ubuntu5, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to localhost [::1] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/id_rsa type -1
debug1: identity file /home/user/.ssh/id_rsa-cert type -1
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: identity file /home/user/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-4ubuntu5
debug1: match: OpenSSH_5.5p1 Debian-4ubuntu5 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-4ubuntu5
debug2: fd 3 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: [email protected],[email protected],ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-ctr hmac-md5 none
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug2: dh_gen_key: priv key bits set: 146/256
debug2: bits set: 513/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug3: check_host_in_hostfile: host localhost filename /home/user/.ssh/known_hosts
debug3: check_host_in_hostfile: host localhost filename /home/user/.ssh/known_hosts
debug3: check_host_in_hostfile: match line 1
debug1: Host 'localhost' is known and matches the RSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:1
debug2: bits set: 509/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/user/.ssh/id_rsa ((nil))
debug2: key: /home/user/.ssh/id_dsa ((nil))
debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Trying private key: /home/user/.ssh/id_rsa
debug3: no such identity: /home/user/.ssh/id_rsa
debug1: Trying private key: /home/user/.ssh/id_dsa
debug3: no such identity: /home/user/.ssh/id_dsa
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password
debug3: authmethod_is_enabled password
debug1: Next authentication method: password
user@localhost's password: 
debug3: packet_send2: adding 64 (len 57 padlen 7 extra_pad 64)
debug2: we sent a password packet, wait for reply
debug1: Authentication succeeded (password).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug2: callback start
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug1: Sending environment.
debug3: Ignored env ORBIT_SOCKETDIR
debug3: Ignored env SSH_AGENT_PID
debug3: Ignored env TERM
debug3: Ignored env SHELL
debug3: Ignored env XDG_SESSION_COOKIE
debug3: Ignored env WINDOWID
debug3: Ignored env GNOME_KEYRING_CONTROL
debug3: Ignored env GTK_MODULES
debug3: Ignored env USER
debug3: Ignored env LS_COLORS
debug3: Ignored env LIBGL_DRIVERS_PATH
debug3: Ignored env SSH_AUTH_SOCK
debug3: Ignored env DEFAULTS_PATH
debug3: Ignored env SESSION_MANAGER
debug3: Ignored env USERNAME
debug3: Ignored env XDG_CONFIG_DIRS
debug3: Ignored env DESKTOP_SESSION
debug3: Ignored env LIBGL_ALWAYS_INDIRECT
debug3: Ignored env PATH
debug3: Ignored env PWD
debug3: Ignored env GDM_KEYBOARD_LAYOUT
debug1: Sending env LANG = en_US.UTF-8
debug2: channel 0: request env confirm 0
debug3: Ignored env GNOME_KEYRING_PID
debug3: Ignored env MANDATORY_PATH
debug3: Ignored env GDM_LANG
debug3: Ignored env GDMSESSION
debug3: Ignored env SHLVL
debug3: Ignored env HOME
debug3: Ignored env GNOME_DESKTOP_SESSION_ID
debug3: Ignored env LOGNAME
debug3: Ignored env XDG_DATA_DIRS
debug3: Ignored env DBUS_SESSION_BUS_ADDRESS
debug3: Ignored env LESSOPEN
debug3: Ignored env WINDOWPATH
debug3: Ignored env DISPLAY
debug3: Ignored env LESSCLOSE
debug3: Ignored env XAUTHORITY
debug3: Ignored env COLORTERM
debug3: Ignored env _
debug2: channel 0: request shell confirm 1
debug2: fd 3 setting TCP_NODELAY
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
Linux linux 2.6.35-28-generic-pae #50-Ubuntu SMP Fri Mar 18 20:43:15 UTC 2011 i686 GNU/Linux
Ubuntu 10.10

Welcome to Ubuntu!
 * Documentation:  https://help.ubuntu.com/

Last login: Mon Apr 25 15:39:27 2011 from linux
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype [email protected] reply 0
debug2: channel 0: rcvd eow
debug2: channel 0: close_read
debug2: channel 0: input open -> closed
debug2: channel 0: rcvd eof
debug2: channel 0: output open -> drain
debug2: channel 0: obuf empty
debug2: channel 0: close_write
debug2: channel 0: output drain -> closed
debug2: channel 0: rcvd close
debug3: channel 0: will not send data after close
debug2: channel 0: almost dead
debug2: channel 0: gc: notify user
debug2: channel 0: gc: user detached
debug2: channel 0: send close
debug2: channel 0: is dead
debug2: channel 0: garbage collecting
debug1: channel 0: free: client-session, nchannels 1
debug3: channel 0: status: The following connections are open:
  #0 client-session (t4 r0 i3/0 o3/0 fd -1/-1 cc -1)

debug3: channel 0: close_fds r -1 w -1 e 6
Connection to localhost closed.
Transferred: sent 1800, received 2232 bytes, in 0.4 seconds
Bytes per second: sent 4972.2, received 6165.5
debug1: Exit status 0
user@linux:~$ 

Answer 1

Because you get the same problem when connecting from localhost, it's probably a fault at the servers-side.

With the information given currently, it is quite hard to figure out what went wrong. Take a look at the server-side logs : grep 'sshd' /var/log/auth.log

You could try using ssh -v or ssh -vv to get a more detailed output on the client side, but I suppose the auth.log is more promising.

Once that information is gathered, you could edit your question to describe the problem more properly!

Edit:

Another option might be setting "LogLevel INFO" to "LogLevel DEBUG" in /etc/sshd_config and gathering more output from the server. Please go through your logs before posting them, the man page warns that a high LogLevel might impair privacy.

Answer 2

Here's another possiblity, in case anyone finds this while searching like I did: same symptoms, SSH session closes after entering password. My variation was that SSH from the server to itself worked, but would fail after authentication from any external source.

I'd looked at most of the above suggestions already. When I finally ran sshd with DEBUG3 I noticed it was doing a reverse DNS look up on the source IP.

What I finally found was that the DNS resolvers had been set up originally while we were in the middle of upgrading the DNS servers, so the first resolver IP was still one of the temporary transition IPs that was now gone. Seems the extra delay with all the DNS timeouts was enough for the SSHD login process to time out. I set the correct DNS resolver IPs and SSH started working flawlessly.

Answer 3

I had a similar problem

With one user I could connect so I checked /etc/passwd. I saw this user could connect with bash, the other (not working) with fish

So I changed to bash and both worked.

Then I put it back to fish, and analysed my fish config and removed a line at the end that was added with byobu-enable. Then it worked. Then I reran byobu-enable and it works.

No idea what happened and it's a VERY specific case but I think I had the config file open while I ran byobu-enable and it messed things up