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Old 12-19-2013, 03:17 AM   #1
sleepy_11
LQ Newbie
 
Registered: Apr 2008
Posts: 6

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Unhappy weird conflict with scp and "echo" in cshrc


Hi,

I'm working on a SUSE enterprise 10 ENV. Let's name this server as "servername".

My default login sh is tcsh. Recently, i add a new line to update the terminal title in the ~/.cshrc, like below:
echo -n "\033]0;${HOST}\007"

Then i found the remote "scp" command, launching the "scp" from another box to fetch data from it, won't work any more. Below is the output:
$ scp foo@servername:~/.cshrc ./
Password:
C0444 158 .cshrc

And if removing the new "echo" line, everything will be fine.

Could you please share your knowledge on this issue?

Thanks in adv.

Last edited by sleepy_11; 12-19-2013 at 03:20 AM.
 
Old 12-19-2013, 11:04 AM   #2
jpollard
Senior Member
 
Registered: Dec 2012
Location: Washington DC area
Distribution: Fedora, CentOS, Slackware
Posts: 4,654

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don't do that.

Test for a terminal before doing the echo. If no terminal is attached, don't do it.

What is happening is that the echo violates the file transfer protocol.

The way that works is that scp makes an initial connection, authenticates... and waits for a signal to start data transfer operation. I think that signal is a null byte sent by scp running as a child process of the sshd daemon. Setting up this client requires the sshd to fork a shell which initializes by processing the .cshrc and .login files... If those scripts cause an output, then the protocol is violated, and scp running locally terminates, which also terminates the sshd daemon and the remote scp client.

You can try something like:
Code:
if($?prompt) then               # Only interactive shells set $prompt
    echo -n "\033]0;${HOST}\007"
endif
You can also test terminal usage by a
Code:
if [ "`tty`" != "not a tty" ]; then

Last edited by jpollard; 12-19-2013 at 11:19 AM. Reason: error in my update. sorry about that.
 
1 members found this post helpful.
Old 12-19-2013, 07:49 PM   #3
sleepy_11
LQ Newbie
 
Registered: Apr 2008
Posts: 6

Original Poster
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Great thanks for your wisdom, jpollard.

The issue is gone with the second option. Also learned more with the explanation.

Regards,
Sleepy
 
  


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