05. Remote Access - some exercises for ssh and parallel-ssh

heiko_s

Chapter 5 gives some examples for ssh and parallel-ssh (pssh...). As a note, in Debian/Ubuntu etc. pssh etc. has been renamed to:
parallel-ssh
parallel-scp
parallel-slurp
etc.

I have 5 VMs running on my PC - master, worker1...worker4. The workers are Ubuntu 18.04 servers, so they use the /etc/netplan/...yaml file for network configuration. I had already manually configured all of them, except for the ~/.ssh/config file.

I created a ~/.ssh/config file on the host with the following content:

Host master
    HostName 192.168.0.130
    User student
 
Host worker1
    HostName 192.168.0.131
    User student
 
Host worker2
    HostName 192.168.0.132
    User student
 
Host worker3
    HostName 192.168.0.133
    User student
 
Host worker4
    HostName 192.168.0.134
    User student
 

I then ran the following script as an exercise:

#!/bin/bash
# Exercise using parallel-scp and parallel-ssh
#
# ips.txt contains the IP addresses of the hosts, one per line
# -h hostfile -- provides list of hosts (IP addresses)
# -i inline -- print output inline on localhost
#
# This script does the following:
# 1. Copies the ~.ssh/config file on LOCALHOST to the remote hosts
#    specified in ips.txt.
# 2. Shows the remote config files using cat.
# 3. Deletes the remote config files.
# 4. Shows the remote config files using cat - this gives an error.
# 5. Copies again the ~.ssh/config file on LOCALHOST to the remote hosts.
# 6. Shows the remote config files using cat.
 
parallel-scp -h ips.txt ~/.ssh/config /home/heiko/.ssh/
parallel-ssh -ih ips.txt cat ~/.ssh/config
parallel-ssh -ih ips.txt rm ~/.ssh/config
parallel-ssh -ih ips.txt cat ~/.ssh/config
parallel-scp -h ips.txt ~/.ssh/config /home/heiko/.ssh/
parallel-ssh -ih ips.txt cat ~/.ssh/config
 

Since I already defined aliases for all my VMs, I could also use the aliases inside ips.txt:

worker1
worker2
worker3
worker4
 

The following is an exercise using parallel-slurp to copy remote files to the local host under ~/outdir:

#!/bin/bash
#
# Copy /etc/netplan/0....yaml files on remote hosts to local host:
parallel-slurp -L ~/outdir -h remhosts.txt /etc/netplan/0* .
# Copy the /etc/hosts and /etc/hostname files to local host:
parallel-slurp -L ~/outdir -h remhosts.txt /etc/hosts .
parallel-slurp -L ~/outdir -h remhosts.txt /etc/hostname .
 

Using the aliases, these files are then neatly stored in folders worker1...worker4.

I wonder if I could use pscp / parallel-scp to copy configuration stanzas to remote hosts and then manually change e.g. the IP. I'm talking specifically about the /etc/netplan/...yaml config file where I would have to change just the IP.

If I understand correctly, the IP would only change with the "netplan apply" command?

lee42x

Thank you for the suggestion !

coop

Just as a footnote, the text already says names may be different, and I just checked on RHEL-8:

c8:/home/coop/Desktop>rpm -qil pssh | grep bin
/usr/bin/pnuke
/usr/bin/prsync
/usr/bin/pscp.pssh
/usr/bin/pslurp
/usr/bin/pssh
c8:/home/coop/Desktop>
 

heiko_s

Thanks for the response. I was trying to find out if pssh etc. were actually used for sysadmin tasks and tried to figure out a practical use case. As my experience = inexperience, I probably come up with all kinds of strange ideas on how to use commands.

My post was by no means a critique, just my way of thinking and the hope that someone sets me straight, or confirms the possible use case.