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These days, I’m managing many, many servers. The servers are ordered in few groups. Each of the servers in the server groups contains identical hardware, identical Linux distribution as well as identical configuration.
Since managing multiple servers normally, takes a lot of time, applying changes to every single host loosing time in looking for the password is not a a good idea.
Thus I was forced to start managing the servers in a cluster like fashion, by executing commands on a server group using a simple for bash loop etc.
To be able to use this mass execution of course I needed away either to pass on the server group password just once and issue a command on the whole server group or use a passwordless authentication ssh key pair.
Before I switched to using SSH keys to authenticate passwordless, I first tried to use a bit of tools which were claimed to be helpful in the task of executing the same commands to a group of servers. I have tested the tools pssh, sudossh and dsh but none of them was capable of logging in and executing a bunch of commands to the group of remote servers.
I gave my best to make pssh work on Debian and CentOS distributions, but even though all my experiemnts and efforts to make the so much talked about pssh to work were bad!
I’ve seen also another tool called Cluster SSH which was said to be capable of issuing commands simultaneously on a number of hosts.
Cluster SSH looked promising, however the only problem was it’s supposed to run under xterm or some kind of X graphics based terminal and therefore it did not matched my desired.
Finally I got pissed of trying these mostly useless mass command linux server administration tools and decided to come COME BACK TO THE PRIMITIVE 😉 and use the good all known, well established method of Passwordless SSH server login with ssh public/private DSA key auth.
Therefore here the problem come to this to generate one single DSA ssh authenticatoin key and replicate/copy it to the whole group of 50 servers.
These task initially seemed quite complex, but with the help of a one liner bash shell script, it seemed to be a piece of cake 😉
To achieve this task, all I had to do is:
a. Generate an SSH key with ssh-keygen command
b. Use a one liner shell script to copy the generated id_rsa.pub file, to each server.
c. Create a file containig all server IP addresses to pass to the shell script.
Here are the two lines of code you will have to use to achieve these tasks:
1. Generate a DSA ssh key
linux:~# ssh-keygen -t dsa
Generating public/private dsa key pair.
Enter file in which to save the key (/home/hipo/.ssh/id_dsa): y
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in y.
Your public key has been saved in y.pub.
The key fingerprint is:
Here press enter few times and be sure not to fill in any passphrase when asked ’bout it.
2. Create a file containing all server IPs
Just create a file let’s say server-list.txt and make sure you include all the server IPs, one per line.
3. Use the following little script to upload the newly generated id_dsa.pub to the server list
linux:~# while read line; do ssh-copy-id -i ~/.ssh/id_dsa.pub root@"$line"; done < server-list.txt
Now you will have to paste the server password for about 50 times (if you have a file with 50 servers), however the good news is it will be just a wait and paste 50 times, if the servers are all configured to have the same root administrator pass (which was the case with me).
So until you do the boring pasting part, you can start up a nice music and enjoy 😉