Hi guys,

I have a weird issue:

I have 3 PCs, they have the following IPs addresses and the related OS:

192.168.1.10 Ubuntu
192.168.1.11 Debian
192.168.1.12 Kubuntu

When I try to transfer a file from the .12 to the .11 no problem at all, but when I want to transfer a file from .10 to the .11 I get the following error message:

Connection closed by 192.168.1.11
lost connection

Here is the /etc/ssh/sshd_config file of the .11 machine:

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 10
PermitRootLogin no
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile %h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes


In my opinion everything looks fine as of the line ListenAddress 0.0.0.0 but why I get connection closed?? Why the .11 refuses the connection only from the .10 and not from the .12 machine??

I have tried to reinstall the ssh. There is no firewall and no iptables configured.

Thanks
fr2632

you need to look at the log files on the destination for information about this. That's why log files exist. check /var/log/secure and /var/log/messages

Thanks for your quick reply.

The file /var/log/secure does not exist, and the /var/log/messages says just this:

Jan 31 08:03:10 fr2632 rsyslogd: [origin software="rsyslogd" swVersion="4.6.4" x-pid="1044" x-info="http://www.rsyslog.com"] rsyslogd was HUPed, type 'lightweight'.

Not really helpful message I guess

There's nothing there??? how is that possible? there should always be something in there. Every single time you log in there should be a handful of entries in that logfile.

So why there's nothing logged is one thing you should investigate, but if you get the command line of the sshd process you're connecting to, from "ps -ef" etc, and run that command with a -D added to it (after stopping sshd first) and that'll run it in the foreground spitting out hopefully useful information.

There is something else logged into that file, but there is nothing to do with ssh as I see messages related to sdc1, usb, sdd1 and other things but nothing related to ssh. The message I have giving you was just after I tried connection again from the .10 to the .11 machine.

With the command ps -ef I dont see what is really wrong with ssh connection and why I get lost connection message. What do you mean with "run that command with a -D added to it" ?

However I tried to run the scp command with -vvv again from .10 to .11 and this is the results:

fr2632@fr2632:~$ scp -r -vvv textfile fr2632@192.168.1.11:"/home/fr2632/Documents"
Executing: program /usr/bin/ssh host 192.168.1.11, user fr2632, command scp -v -r -d -t -- /home/fr2632/Documents
OpenSSH_5.9p1 Debian-5ubuntu1, OpenSSL 1.0.1 14 Mar 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 192.168.1.11 [192.168.1.11] port 22.
debug1: Connection established.
debug1: identity file /home/fr2632/.ssh/id_rsa type -1
debug1: identity file /home/fr2632/.ssh/id_rsa-cert type -1
debug1: identity file /home/fr2632/.ssh/id_dsa type -1
debug1: identity file /home/fr2632/.ssh/id_dsa-cert type -1
debug1: identity file /home/fr2632/.ssh/id_ecdsa type -1
debug1: identity file /home/fr2632/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.5p1 Debian-6+squeeze2
debug1: match: OpenSSH_5.5p1 Debian-6+squeeze2 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9p1 Debian-5ubuntu1
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
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
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA e7:0f:9a:bc:e6:b7:6d:6d:70:ad:f5:71:e4:4c:b1:00
debug1: Host '192.168.1.11' is known and matches the RSA host key.
debug1: Found key in /home/fr2632/.ssh/known_hosts:2
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /home/fr2632/.ssh/id_rsa
debug1: Trying private key: /home/fr2632/.ssh/id_dsa
debug1: Trying private key: /home/fr2632/.ssh/id_ecdsa
debug1: Next authentication method: password
fr2632@192.168.1.11's password:
Connection closed by 192.168.1.11
lost connection
fr2632@fr2632:~$

Your SSH logs will be in /var/log/auth.log

Thanks! here is the /var/log/auth.log file:

Jan 31 16:46:11 fr2632 sudo: fr2632 : TTY=pts/2 ; PWD=/home/fr2632 ; USER=root ; COMMAND=/usr/bin/nano /var/log/auth.log
Jan 31 16:46:40 fr2632 sshd[18993]: debug1: Forked child 22002.
Jan 31 16:46:40 fr2632 sshd[22002]: Set /proc/self/oom_adj to 0
Jan 31 16:46:40 fr2632 sshd[22002]: debug1: rexec start in 4 out 4 newsock 4 pipe 6 sock 7
Jan 31 16:46:40 fr2632 sshd[22002]: debug1: inetd sockets after dupping: 3, 3
Jan 31 16:46:40 fr2632 sshd[22002]: Connection from 192.168.1.10 port 51850
Jan 31 16:46:40 fr2632 sshd[22002]: debug1: Client protocol version 2.0; client software version OpenSSH_5.9p1 Debian-5ubuntu1
Jan 31 16:46:40 fr2632 sshd[22002]: debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1 pat OpenSSH*
Jan 31 16:46:40 fr2632 sshd[22002]: debug1: Enabling compatibility mode for protocol 2.0
Jan 31 16:46:40 fr2632 sshd[22002]: debug1: Local version string SSH-2.0-OpenSSH_5.5p1 Debian-6+squeeze2
Jan 31 16:46:41 fr2632 sshd[22002]: debug1: PAM: initializing for "fr2632"
Jan 31 16:46:41 fr2632 sshd[22002]: debug1: PAM: setting PAM_RHOST to "fr2632.local"
Jan 31 16:46:41 fr2632 sshd[22002]: debug1: PAM: setting PAM_TTY to "ssh"
Jan 31 16:46:41 fr2632 sshd[22002]: Failed none for fr2632 from 192.168.1.10 port 51850 ssh2
Jan 31 16:46:46 fr2632 sshd[22002]: debug1: PAM: password authentication accepted for fr2632
Jan 31 16:46:46 fr2632 sshd[22002]: debug1: do_pam_account: called
Jan 31 16:46:46 fr2632 sshd[22002]: Accepted password for fr2632 from 192.168.1.10 port 51850 ssh2
Jan 31 16:46:46 fr2632 sshd[22002]: debug1: monitor_child_preauth: fr2632 has been authenticated by privileged process
Jan 31 16:46:46 fr2632 sshd[22002]: debug1: PAM: establishing credentials
Jan 31 16:46:46 fr2632 sshd[22002]: pam_unix(sshd:session): session opened for user fr2632 by (uid=0)
Jan 31 16:46:47 fr2632 sshd[22002]: User child is on pid 22007
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: SELinux support disabled
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: PAM: establishing credentials
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: permanently_set_uid: 1000/1000
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: Entering interactive session for SSH2.
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: server_init_dispatch_20
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: server_input_channel_open: ctype session rchan 0 win 2097152 max 32768
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: input_session_request
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: channel 0: new [server-session]
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_new: session 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_open: channel 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_open: session 0: link with channel 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: server_input_channel_open: confirm session
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: server_input_global_request: rtype no-more-sessions@openssh.com want_reply 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: server_input_channel_req: channel 0 request env reply 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_by_channel: session 0 channel 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_input_channel_req: session 0 req env
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: server_input_channel_req: channel 0 request exec reply 1
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_by_channel: session 0 channel 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_input_channel_req: session 0 req exec
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: Received SIGCHLD.
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_by_pid: pid 22008
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_exit_message: session 0 channel 0 pid 22008
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_exit_message: release channel 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_by_channel: session 0 channel 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_close_by_channel: channel 0 child 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: session_close: session 0 pid 0
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: channel 0: free: server-session, nchannels 1
Jan 31 16:46:47 fr2632 sshd[22007]: Received disconnect from 192.168.1.10: 11: disconnected by user
Jan 31 16:46:47 fr2632 sshd[22007]: debug1: do_cleanup
Jan 31 16:46:47 fr2632 sshd[22002]: debug1: do_cleanup
Jan 31 16:46:47 fr2632 sshd[22002]: debug1: PAM: cleanup
Jan 31 16:46:47 fr2632 sshd[22002]: debug1: PAM: closing session
Jan 31 16:46:47 fr2632 sshd[22002]: pam_unix(sshd:session): session closed for user fr2632
Jan 31 16:46:47 fr2632 sshd[22002]: debug1: PAM: deleting credentials
Jan 31 16:47:13 fr2632 sudo: fr2632 : TTY=pts/2 ; PWD=/home/fr2632 ; USER=root ; COMMAND=/usr/bin/nano /var/log/auth.log

NOTE: line:"Jan 31 16:46:47 fr2632 sshd[22007]: Received disconnect from 192.168.1.10: 11: disconnected by user"
Obviously I didnt disconnect it...

Anyone ??

It's says it recieves a SIGCHLD, so it's the child process on the server stopping. This doesn't really figure when it is client specific. Are you able to run the sftp-server process as the correct destination user on the server itself? Are you using the same user account?

Thank you for your reply.

Yes, I am using the same user and I can sftp, ftp and ping the .10 machine without any problems ...

can you actually run sftp-server on the server directly?

Doesn't feel plausiblem, but there's nothing quirky in /etc/hosts.allow / hosts.deny?

Also there is, i blieve, deeper debugging you can still enable on the server side. some posts online show some potentially interesting debug3 statements, trey a -d 3 flag on the server process.

On the server .10 from .12:

sftp fr2632@192.168.1.10
fr2632@192.168.1.10's password:
Connected to 192.168.1.10.
sftp>

The other way around (from .10 to .12):

sftp fr2632v3@192.168.1.12
fr2632v3@192.168.1.12's password:
Connected to 192.168.1.12.
sftp>

There could be some blockage from PAM setup as well. Please check if PAM is configured (default) to block your operations.

A far as I can see in the /etc/ssh/sshd_config :

"UsePAM yes"

On both .10 and .11 machines. Is there a way how to check PAM for more details ?

Thanks

Change "UsePAM yes" to "UsePAM no" and try. If it works then we can tweak PAM config to allow your operations.

Make sure you have access to the consoles of the servers you are working on. If any thing goes wrong and if you cannot connect to the remote servers via ssh you revert back the changes via console.