On: Cluster SSH (OSX)

[ilikepi]

meh...

    for h in host1 host2 host3; do \
        echo -e "\n$h\n===========\n"; \
        ssh $h 'ln -s /some/path /path/to/link && ls -l /path/to/link'; \
    done

edit: woops, left out a couple semicolons...

[geocar → ilikepi]

> edit: woops

Exactly.

One-offs are easy to test interactively with cssh, and despite what anyone thinks, there are always one-offs in the real world.

[ilikepi → geocar]

True. Usually when creating a shell loop like this, I prepend 'echo' in front of 'ssh...' as a dry run first. I also wouldn't actually use something like this for commands that are destructive in nature. Usually it's for things like running informational commands ('rpm -q', 'uptime', etc). Of course anything can become destructive if you fat-finger it hard enough.

In short, use automation with care.

[fragsworth → ilikepi]

FUCKING SERIOUSLY?!

Thank you for this comment, I never knew you could pass commands to ssh.

[z2amiller → fragsworth]

Now combine that with dsh (http://www.netfort.gr.jp/~dancer/software/dsh.html.en) and authorized_keys, you can _really_ get in trouble. dsh is similar to this Cluster SSH, but is appropriate for use in scripts, cron jobs, etc.

Example:

dsh -Mg all-machines -F 20 'do something'

-M: Prepend any line of output with the machine that emitted it

-g: runs the group all-machines (just a text file in etc/dsh/group)

-F 20: forks at most 20 copies of ssh in the background so you don't overload the server you're running this from

[joh6nn → fragsworth]

i suggest perusing the ssh man, then, as it seems likely that it has other capabilities you don't know about.

[rbranson → joh6nn]

Like how SSH agent forwarding can allow you to hop from box to box with the SSH keys loaded onto your local machine's SSH agent? Found that one a few months ago, made me reflect on what I've been doing in life the past 10 years not thoroughly reading UNIX man pages.

[erikig → rbranson]

Thanks for this one. You just added a few days to my life and helped push out the onset of carpal tunnel/arthritis. ~ http://www.unixwiz.net/techtips/ssh-agent-forwarding.html

[_ezkx → joh6nn]

ssh is magic. checkout -X for X11 forwarding to run remote GUI apps, and -R which lets you set up a reverse SSH tunnel when you need to connect to a machine behind a firewall.

[Raphael_Amiard → joh6nn]

such a polite version of RTFM, i love you

[taylorbuley → fragsworth]

Based on a similar reaction a few months ago, this will definitely change the way you go about system work.

[veritgo → ilikepi]

You probably already know this, but if you have a significant number of hosts:

    for i in `seq 1 30`; do \
        echo -e "\nhost$i\n===========\n"; \
        ssh host$i 'ln -s /some/path /path/to/link && ls -l /path/to/link'; \
    done

Also, if you just start typing

  for i in `seq 1 30`
  do
     commands
     more commands
  done

On the command line itself, you don't need to worry about semicolons. Bash will take care of it.

[ilikepi → veritgo]

Ah, I was not aware of seq; good one. :)

Good point about not needing semicolons for multiple-line stuff (assuming the EOL's are not escaped, as you have it in your example). I blame the PHP I spent all week immersed in...bleh.

[jseban → veritgo]

    for i in {1..30}; do...