问题
When I attempt to execute a command on a remote server with ssh, the ssh command hangs after the exec request accepted debug message, and eventually times out.
The failing command: ssh -v -v <username>@<server> uptime (also tried echo hello etc.)
debug1: Authentication succeeded (publickey).
Authenticated to <server> (<ip>:22).
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: client_session2_setup: id 0
debug2: fd 4 setting TCP_NODELAY
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug2: channel 0: request env confirm 0
debug1: Sending command: uptime
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
And there it hangs, indefinitely.
When I ssh without a command into my remote server, however, I get an interactive shell and all is good.
Successful Command: ssh -v -v <username>@<server>
Output:
debug1: Authentication succeeded (publickey).
Authenticated to <server> (<ip>:22).
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: client_session2_setup: id 0
debug2: fd 4 setting TCP_NODELAY
debug2: channel 0: request pty-req confirm 1
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug2: channel 0: request env confirm 0
debug2: channel 0: request shell confirm 1
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
Welcome!
<prompt>%
...
Has anyone an idea why an interactive session would be successful but a command execution not?
Has been haunting me for months now because I cannot use unison to sync my files any more (it used to work). Any help much appreciated.
回答1:
The problem was indeed my login script, although not to do with requiring a terminal (I'd suspected that and tested with the -t and -T options). The problem was that my .bashrc was running an exec (in this case to zsh - because our system doesn't allow chsh to zsh).
The offending line:
test -f /usr/bin/zsh && exec /usr/bin/zsh
Solved by first checking for interactive shell and exiting if so:
[ -z "$PS1" ] && return
test -f /usr/bin/zsh && exec /usr/bin/zsh
So, essentially, because the shell was execing into zsh, ssh was waiting for this to finish - which never happened.
I am a little confused why my .bashrc was being called at all - I thought this was only for interactive shells, but the exact purpose and order of the various init scripts is something I don't think I'll ever learn.
I hope this can be useful to others who have some kind of exec in their startup scripts.
BTW - the other two answers were on the right track so I was completely unsure if I should 'answer' or just comment their answers. If answering my own question is morally wrong on stackoverflow, let me know and I'll do penitence. Thank you to the other answerers.
回答2:
Your problem most likely lies in your shell startup or shell logout scripts. Without knowing what's in there, it's hard to guess the actual problem.
回答3:
Check for commands in your shell startup files (I would assume ~/.cshrc from your prompt; in a non-interactive session, ~/.login shouldn't matter) that require a terminal for some reason.
回答4:
I recently encountered a problem with the same symptoms, but determined that the issue was not a problem in my login scripts. Rather, my local .ssh/config file was configured with RequestTTY force for the host that I was trying to copy to.
回答5:
I had this problem on fedora server 22, after the resolution of other new problems.
ssh -t ziimp /bin/true was ok but not ssh ziimp /bin/true and all my git+ssh and scp were locked.
The solution i found was in the authorized_keys file. I had to remove the command="/usr/bin/bash" prefix from my trusted keys...
回答6:
We fixed this by adding adding -n (to redirect std in from /dev/null) and -t (force pseudo-tty allocation)
Example:
ssh -t -n user@host command
回答7:
I eventually found the "$-" var which works for me:
if [[ $- =~ i ]] ; then
[ -x /bin/tcsh ] && exec /bin/tcsh
# Bash startup stuff goes here...
fi
Got this from: https://www.gnu.org/software/bash/manual/html_node/Is-this-Shell-Interactive_003f.html
来源：https://stackoverflow.com/questions/5929552/ssh-command-execution-hangs-although-interactive-shell-functions-fine