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Rayne
Asked: 2012-04-13 03:39:19 +0800 CST

Cannot connect to server via SSH

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I'm running RHEL 6.0, and I accidentally moved the /bin, /boot, /cgroup, console.txt, /data, /dev, /etc to another folder. I think I managed to move these folders back, but now I'm having trouble connecting to the server using SSH, but am able to access the server via VNC.

When I tried to connect to the server using a terminal from another server, I get the error

ssh_exchange_identification: Connection closed by remote host

I'm currently still connected via SSH to the server (haven't closed the window yet), and am still able to access it normally. But if I try to open a new SSH terminal from my current session, I see 

/bin/bash: Permission denied

If I try to open a new SSH File Transfer window from my current session, I get the error

File transfer server could not be started or it exited unexpectedly. 
Exit value 0 was returned. Most likely the sftp-server is not in the path of the user on the server-side

I checked and I have 

Subsystem  sftp  /usr/libexec/openssh/sftp-server

which is the same path as the output of 

locate sftp-server

Also, when I tried to restart sshd, I get the error

Couldn't open /dev/null: Permission denied

But my /dev/null has the permissions

crw-rw-rw-

for root,root.

How can I resolve this?

ETA: Thanks for all your help! I was able to start ssh by running the application directly

/usr/sbin/sshd

Even though the status of the openssh-daemon is still "stopped".

login ssh centos6

3 Answers

  1. As things are clearly not working as they should be and you aren't really certain that you have fully undone any damage caused by moving things around I suggest that the only sensible course of action at this point is to restore the system from backup. Anything else is liable to leave your system in an unpredictable state.

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  2. Unfortunately, your best course of action here is to reinstall your OS. It may theoretically be possible to fix this specific permissions error, but then you still have hundreds of other files and folders in an unknown state, any of which could cause malfunctions in the future.

    This is your only path back to a stable, reliable system.

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  3. As others have remarked the only safe way to restore the system fully is to restore from backup.

    If you are unable to do so you could check the RPM DB (rpm -Va) to see what files are still missing and/or have the wrong permissions.

    See e.g. this post and this on how to restore permissions using rpm.

    Good luck.

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