Why can't I scp to a specific machine?

Question

I have one machine that I can't seem to scp to but I can SSH into. I have tried scping from two separate machines. The basic output I get is:

scp /tmp/file dest@IP:/tmp

Password:
IP Address:

When I add some debug flags to scp, I can see that I get some fail messages but I am not sure what they mean:

Password:
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 0
debug1: Authentication succeeded (keyboard-interactive).
Authenticated to <IP> ([<IP>]:22).
debug2: fd 4 setting O_NONBLOCK
debug2: fd 5 setting O_NONBLOCK
debug1: channel 0: new [client-session]
debug2: channel 0: send open
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug2: callback start
debug2: fd 3 setting TCP_NODELAY
debug2: client_session2_setup: id 0
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
IP Address:
debug2: channel 0: read<=0 rfd 4 len 0
debug2: channel 0: read **failed**
debug2: channel 0: close_read
debug2: channel 0: input open -> drain
debug2: channel 0: ibuf empty
debug2: channel 0: send eof
debug2: channel 0: input drain -> **closed**
user:current_dir # debug2: channel 0: write **failed**
debug2: channel 0: close_write
debug2: channel 0: send eow
debug2: channel 0: output open -> **closed**
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug2: channel 0: rcvd eof
debug2: channel 0: rcvd 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
debug1: fd 0 clearing O_NONBLOCK
debug1: fd 1 clearing O_NONBLOCK
Transferred: sent 2660, received 2380 bytes, in 0.1 seconds
Bytes per second: sent 40626.2, received 36349.8
debug1: Exit status 0

Any info would be much appreciated!

Answer 1

It was because the .bashrc on the machine I was trying to scp to.bashrc was sourcing an alias shells script which had an echo var command. Removing the echo solved the problem.

Answer 2

Authenticated to <IP> ([<IP>]:22).
...
debug1: Entering interactive session.
...
debug2: exec request accepted on channel 0
IP Address:

These are all indications that you successfully authenticated to the remote system and started a session there. The "IP Address:" prompt must be coming from a program running on the remote system within your session.

In short, the remote system is launching a special-purpose program automatically when you log in. This would prevent scp and other programs launched through ssh from working, unless the program took special steps to permit them to work.

My guess is that the remote system is set up as a "jump server". It's prompting you for the IP address of another computer that you want to connect to. When you type in an IP address, it'll make an ssh connection to that system (or reboot it, or something).

Whatever the program's purpose, without knowing how this program is being launched, it's impossible to say how to work around it. If you have a legitimate need to copy files to or from the system, you should talk to the remote system's administrator.

Answer 3

scp does not use sftp protocol, but needs scp to be present and installed at the receiver aswell (It will spawn a scp command in a shell at the receiving host)