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While any command executed by ssh is executed "on the other side of the pond" at remote server, the output is channeled to the host on which ssh command is entered. That creates very interesting opportunities
First a very simple example
ssh [email protected] 'tail -100 /var/log/messages' | egrep 'Terminal|Serious|Aborted'
ssh [email protected] "cat /var/log/messages" | grep 'su\['
Even more interesting possibilities exist if you analyze proxy logs or logs of the Apache webserver.
Of course all those examples require to provide password for the server. To avoid it you can use password-less SSH login
If we put this command in a loop so that it executed for each server we manage we will get a simple monitoring system that can help us to detect abnormal situation.
But the most interesting trick with using ssh in pipes is so called "ssh tar pipe". Like r-tools ssh supports cross computer pipes:
tar cvzf - . | rsh xxx.xxx.xxx.xxx "( cd $dir; tar xzf - )"or
tar cvzf - . | ssh xxx.xxx.xxx.xxx "( cd $dir; tar xzf - )"
This is also possible to do the same in the reverse direction
ssh xxx.xxx.xxx.xxx "( cd $dir; tar cvzf - )" | tar xzf -The same idea can be implemented using cpio instead of pipe. In this case you can transfer hard links, which is a problem for tar.
June 15, 2007 | Spikelab
Command Compression Fileset Time scp No Small 0:01:53 scp No Large 0:10:10 scp Yes Small 0:02:46 scp Yes Large 0:14:11 tar | ssh No Small 0:00:24 tar | ssh No Large 0:03:18 tar | ssh Yes ssh Small 0:01:09 tar | ssh Yes ssh Large 0:11:33 tar | ssh Yes tar gz Small 0:00:18 tar | ssh Yes tar gz Large 0:01:57 tar | nc No Small 0:00:21 tar | nc No Large 0:03:24 tar | nc Yes tar gz Small 0:00:20 tar | nc Yes tar gz Large 0:01:16
Copying files (keeping permissions with tar)
ssh remote_host "tar -cf - -C srcdir ." | tar xpf - -C destdir
Backing up/compressing mysql db.
mysqldump | bzip2 | ssh remotehost backup.sh -
Or how about this one from freesbsd handbook, remote backups using dump.
/sbin/dump -0uan -f - /usr | gzip -2 | ssh \
targetu[email protected] dd of=/mybigfiles/dump-usr-l0.gz
You could also copy/restore a partition this way through ssh.
ssh -NLf localport:remotehost:remoteport remotehost
ssh is an indispensable unix tool: remote cvs, rsync, remote X forwarding,
scp, sftp just to name a few, can't live without ssh :)
On Fri, Jul 19, 2002 at 11:40:48AM -0700, tedu wrote:
> Generically, here's my question. I'd like to know how to set up some pipe between two networked computers sent via ssh channel. Such that
> host1$ echo hi > ssh_pipe_file
> host2$ cat ssh_pipe_file
> would happen.
> Specifically, I'm trying to transfer audio data from a host with a player
> to a host with a sound card. Maybe there's a simpler way to do just this?
I have used nc(1) (netcat) to do that exact job. It would be easy to
set up ssh to forward a port and then use netcat to pipe the data over
the encrypted pipe.
> Hi, > > I am relatively new to ssh and I'd like to know if it is possible to do > the following: > > I want to force the VNC server to only accept connection thru an ssh > secure pipe. [chop] > The right-hand side of the drawing I have sorted out. The server side is > still a mystery. How do I convince VNC to only use and ssh pipe and > refuse connection from any other tcp port? I think you can say "vnc -localhost" so that it only accepts connection from the local host, if the ssh pipe ends at the same machine as the one where the ssh pipe ends. Of course, VNC will still accept unenctypted connections from the localhost, but not from remote hosts. Incompetence disclaimer: I haven't tried, and I don't know much about the gearworks of TCP and tunneling. So I don't know whether my logic is sound, and whether it'll actuelly work.
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