Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

A server I can ssh into fine has begun refusing to scp.

$ scp ~/tmp/foo
lost connection

With scp -v -v I can see the connection succeeds and the transfer appears to succeed, but no file appears on the other side.

OpenSSH_5.9p1, OpenSSL 0.9.8r 8 Feb 2011
debug1: Reading configuration data /Users/schwern/.ssh/config
debug1: /Users/schwern/.ssh/config line 1: Applying options for *
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to [] port 22.
debug1: Connection established.
debug1: identity file /Users/schwern/.ssh/id_rsa type -1
debug1: identity file /Users/schwern/.ssh/id_rsa-cert type -1
debug1: identity file /Users/schwern/.ssh/id_dsa type -1
debug1: identity file /Users/schwern/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3
debug1: match: OpenSSH_4.3 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9
debug2: fd 3 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
...lots of authentication details...
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (publickey).
Authenticated to ([]:22).
debug2: fd 5 setting O_NONBLOCK
debug2: fd 6 setting O_NONBLOCK
debug1: channel 0: new [client-session]
debug2: channel 0: send open
debug1: Entering interactive session.
debug2: callback start
debug2: client_session2_setup: id 0
debug2: fd 3 setting TCP_NODELAY
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug2: channel 0: request env confirm 0
debug1: Sending command: scp -v -t -- ~/tmp/
debug2: channel 0: request exec confirm 1
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel 0: rcvd adjust 2097152
debug2: channel_input_status_confirm: type 99 id 0
debug2: exec request accepted on channel 0
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
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug2: channel 0: rcvd close
debug2: channel 0: close_read
debug2: channel 0: input open -> closed
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
debug1: fd 0 clearing O_NONBLOCK
debug1: fd 1 clearing O_NONBLOCK
Transferred: sent 4576, received 2520 bytes, in 0.0 seconds
Bytes per second: sent 167737.0, received 92372.6
debug1: Exit status 0
debug1: compress outgoing: raw data 135, compressed 121, factor 0.90
debug1: compress incoming: raw data 66, compressed 52, factor 0.79
lost connection

It is a CentOS 5.9 machine.

Things I've checked...

  • I have permission to write to that directory.
  • The user has a sensible shell (/bin/bash).
  • I tried moving my ~/.ssh/config out of the way.
  • scp'ing to that machine from others with entirely different operating systems also fail.
  • The disk is not full.
  • Restarting sshd.

/var/log/secure contains...

Apr  4 14:23:22 some sshd[12576]: Postponed publickey for user from port 33581 ssh2
Apr  4 14:23:22 some sshd[12575]: Accepted publickey for user from port 33581 ssh2
Apr  4 14:23:22 some sshd[12575]: pam_unix(sshd:session): session opened for user user by (uid=0)
Apr  4 14:23:22 some sshd[12575]: pam_unix(sshd:session): session closed for user user

What might I check next?

share|improve this question
Not the error I would expect, but just in case, do your ~/.bashrc or ~/.profile or /etc/bash.bashrc or /etc/profile print anything to STDOUT? And I assume you are using Linux? – terdon Apr 4 '13 at 14:16
Nope. I just get the usual Last login: Thu Apr 4 10:15:28 2013 from – Schwern Apr 4 '13 at 14:18
Anything in any of the system logs on the target host? – Flup Apr 4 '13 at 14:21
@Flup Looks normal. I posted what shows up in the logs when I connect. – Schwern Apr 4 '13 at 18:25
Could you start strace -f -o /tmp/sshd.strace -p [pid of sshd] on the server, try again, then post anything from that file that looks relevant? – Flup Apr 5 '13 at 7:06
up vote 1 down vote accepted

Had the same issue.

If you did a minimal install of Centos, it only install the openssh and openssh-server packages but not the openssh-clients. sudo yum install openssh-clients will fix your issue.

share|improve this answer
I don't have access to that machine anymore, but that seems a likely answer. – Schwern Nov 13 '14 at 21:26

scp works by making an ssh connection to the remote host, then launching another copy of the scp program on that host. The two scp instances communicate through the ssh connection to perform the file transfer.

"lost connection" is printed by the local scp program when the ssh connection drops prematurely. The usual reason for that is the scp program on the remote host either failed to start or else it exited prematurely. This could have happened because the scp program doesn't exist on the remote host, or it's not in your command PATH, or it's not marked executable, or it crashed after starting, or something along those lines.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.