Tag Archives: ssh

Backup with rsync using SSH Tunneling

For those of you that read my blog often, you know that I admin the cluster that our research group uses here at CU Boulder.  Because of this, I get a lot of questions from users who don’t want to take the time to solve their own problems.  Fairly recently, our RAID-6 crashed (we had a 4th drive die and had to rebuild the array).  Normally this wouldn’t be very much of a problem as most of the files saved on our storage drive are just input files that we can re-download from a separate server, or so I thought.  Personally, all my source code is in my home folder, backed up on our data server, and backed up onto my personal laptop.  For researchers in our group who are developing code, not having a backup of source code can lead to many many months of lost work.  Well, as it turns out, many of the people in our group had their source code on our data server (the one that crashed), without a backup anywhere.  So months of work had been lost.  Well, after the rebuild I have gotten many questions on how to set up an ssh tunnel so that they can backup from our cluster, through the front end, to their home computer.

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How to: Passwordless SSH

As some of you know, I prefer to set up passwordless logins to all of my accounts on remote machines. I recently made a post describing how to enable passwordless SSH to compute nodes, however what if you are attempting to enable passwordless logins to remote machines?

If you are on a Linux machine, or have a copy of the “ssh-copy-id” script on your system then the process is fairly simple.  You must first create the private/public key pairing.  For passwordless SSH, just accept the defaults for each option.

ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/cmaqadj/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/cmaqadj/.ssh/id_rsa.
Your public key has been saved in /home/cmaqadj/.ssh/id_rsa.pub.

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Enable Passwordless SSH to Compute Nodes (Rocks Linux)

A few of the users on our server have run into issues where, when running MPI jobs, they get an error message from mpdboot.  The message states that the connection is refused.

mpdboot_compute-0-12.local (handle_mpd_output 905): from mpd on
compute-0-11, invalid port info:
connect to address port 544: Connection refused
connect to address port 544: Connection refused

The problem was that Rock Linux was prompting for a password when the user tried to log into the compute nodes.  There is a simple solution to this problem; setup passwordless ssh to the nodes.

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