问题:

I have two users in Fedora:

Wani
root (quite obvious!)

My contents of .bashrc of user Wani are:

# .bashrc echo "Hello" # Source global definitions if [ -f /etc/bashrc ]; then     . /etc/bashrc fi  # User specific aliases and functions

Now after logging into root, I type the following commands:

[root@Dell Wani]# touch try.txt [root@Dell Wani]# service sshd start [root@Dell Wani]# scp try.txt Wani@localhost:~/ Wani@localhost's password:  Hello [root@Dell Wani]#

Now I log into Wani, and type:

[Wani@Dell ~]$ cat try.txt cat: try.txt: No such file or directory [Wani@Dell ~]$

Now I again log into root and type the same command with -v:

[root@Dell Wani]# scp -v morph.log Wani@localhost: Executing: program /usr/bin/ssh host localhost, user Wani, command scp -v -t -- . OpenSSH_5.6p1, OpenSSL 1.0.0j-fips 10 May 2012 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug1: Connecting to localhost [127.0.0.1] port 22. debug1: Connection established. debug1: permanently_set_uid: 0/0 debug1: identity file /root/.ssh/id_rsa type -1 debug1: identity file /root/.ssh/id_rsa-cert type -1 debug1: identity file /root/.ssh/id_dsa type -1 debug1: identity file /root/.ssh/id_dsa-cert type -1 debug1: Remote protocol version 2.0, remote software version OpenSSH_5.6 debug1: match: OpenSSH_5.6 pat OpenSSH* debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_5.6 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

(And after I press Enter)

[root@Dell Wani]#

Can anyone please shed some light as to what exactly happened here? Why did the file not get copied to Wani from root?

回答1:

Using echo in a .bashrc will break scp, as scp expects to see its protocol data over the stdin/stdout channels. See https://bugzilla.redhat.com/show_bug.cgi?id=20527 for more discussion on this issue.

There's a few workarounds available:

Condition on the 'interactive' flag (e.g. case $- in *i* as suggested by tripleee)
Use the tty utility to detect an interactive shell (e.g. if tty > /dev/null or if [ -t 0 ])
Check the value of $SSH_TTY

I suppose you should use whichever one works for you. I don't know what the best (most portable/most reliable) option is, unfortunately.

回答2:

To add to nneonneo's options, you can also condition with the interactive flag with

if [[ $- =~ "i" ]]

which I think is possibly the clearest way in bash.

回答3:

This works for me,
In .bashrc add first line as:

if [ -z "$PS1" ]; then     return fi

https://superuser.com/questions/690735/can-i-tell-if-im-in-an-scp-session-in-my-bashrc

回答4:

The default Ubuntu .bashrc contains the following snippet which already takes care of the problem:

# If not running interactively, don't do anything case $- in     *i*) ;;     *) return;; esac

回答5:

In .bashrc, use STDERR as output instead:

echo "# Important Notice" >&2

Update: do not use it! We had an issue recently that a (closed source) tool failed due to an echo to STDERR in .bashrc. The tool (using rcp) expected no output at all, neither on STDOUT nor STDERR. And it stuck when it got the echo. Lesson learned: make separate accounts for humans and for machines (scripts), or just stop tattling via .bashrc.

回答6:

nneonneo's solution worked for me as well. But since my default shell is TCSH, I had to slightly edit the fix as follows (in .tcshrc):

if ( $?SSH_TTY ) then     exec /bin/bash endif

Just thought I would share for everyone's benefit.

回答7:

if [ 0 -eq $(shopt -q login_shell; echo $?) ]; then   echo "do something?" fi

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