Shell script to automatically login through ssh and create user

Sayan Acharjee · 10-20-2010, 03:51 AM

Hi everyone,

I was trying to create a shell script which will automatically login to the server 192.168.1.7 and checks if a user exists there or not, if it doesn't exist then it should create the user.

I have very little idea about shell scripts, please help me out here.
This is what I tried:

Quote:

#!/bin/bash
pass="sacharje"
ssh 192.168.1.7

Now, how to pass that password automatically to the ssh when it asks for the password? (I can't use public key authentication here)

ionrivera · 10-20-2010, 04:24 AM

Putting your password in a script is not a good practice. All you need is to do is to:
1.) set-up your ssh to login automatically without prompting for a password
2.) include ssh connection(which connects using key authentication instead of password)on your script
3.) add the necessary commands for checking/creating users.

sorry i didn't notice you mentioned (I can't use public key authentication here )

prayag_pjs · 10-20-2010, 04:27 AM

Install sshpass

sshpass is a tool for non-interactivly performing password authentication with SSH's so called "interactive keyboard password authentication". Most users should use SSH's more secure public key authentication instead.

Login to ssh server 192.168.1.10 with password called qaz123wsx:

Quote:

sshpass -p 'qaz123wsx' ssh john@192.168.1.10

Under shell script you may need to disable host key checking:

Quote:

sshpass -p 'qaz123wsx' ssh -o StrictHostKeyChecking=no john@192.168.1.10

Sayan Acharjee · 10-20-2010, 04:28 AM

Quote:

Originally Posted by ionrivera

All you need is to set-up your ssh to login automatically without prompting for a password.

First you’ll need to generate your local public key. This is the public end of a local public / private pair that you’ll share with the remote machine to identify you.

Code:

ssh-keygen -t dsa (on your local machine)

Second you’ll need to copy this key to the remote machine using a command such as:

Code:

scp ~/.ssh/id_dsa.pub user@yourserver.com:~

Lastly, log into the remote machine via ssh (using your password for the last time!) and use this command to add the newly generated key to the list of authenticated keys:

Code:

cat id_dsa.pub >> .ssh/authorized_keys

You’ll also probably want to delete the original key as well.

Code:

rm id_dsa.pub

At this point a copy of your key is now stored on the remote machine as an authorized keys and any ssh connection coming from the local machine will match that key and connect with the key authentication instead of a password.

Thanks,
but I know that procedure, I want the script to automatically pass the password. As I posted earlier, I can't use the PUBLIC KEY authentication.

Sayan Acharjee · 10-20-2010, 04:56 AM

Quote:

Originally Posted by prayag_pjs

Install sshpass

sshpass is a tool for non-interactivly performing password authentication with SSH's so called "interactive keyboard password authentication". Most users should use SSH's more secure public key authentication instead.

Login to ssh server 192.168.1.10 with password called qaz123wsx:

Under shell script you may need to disable host key checking:

Thanks Prayag, its working. I can log in to the server, but whatever command I'm running from the script after logging in is not executed in the server itself, those are getting executed only after logging out of the server, means they are not executed on the remote system.

Deviathan · 10-20-2010, 04:28 PM

You might want to look into using expect. It's a little awkward to get used to at first but I've written several utility scripts to make changes across hundreds of linux servers and workstations and it has worked pretty well.

prayag_pjs · 10-20-2010, 10:44 PM

Quote:

Originally Posted by sayan_acharjee

whatever command I'm running from the script after logging in is not executed in the server itself, those are getting executed only after logging out of the server, means they are not executed on the remote system.

Can you explain with example.Please elaborate

Sayan Acharjee · 10-20-2010, 10:48 PM

Quote:

Originally Posted by prayag_pjs

Can you explain with example.Please elaborate

This is the script:

Quote:

ssh 192.168.100.5

cat /etc/passwd|grep -i $1 > /dev/null
if [ $? -eq 0 ];
then
echo "User already exists";
else
{
useradd $1
echo $1|passwd --stdin $1 > /dev/null
}
fi

After running the script it is asking for ssh password, which is fine.
But the problem is, its not doing the rest of the work after logging in into the server, its checking and creating the user only when I'm logging out of the ssh connection, means the user is created locally only and not in the server.
How can I force this script to execute the rest of the commands in the server after logging in, not in the client?

prayag_pjs · 10-20-2010, 11:00 PM

Hi,

Hope this examples helps you:

List what ports are open on remote host

Quote:

ssh root@192.168.1.10 netstat -vatn

Following command displays memory in format of "available memory = used + free memory" :

Quote:

ssh root@192.168.1.10 free -m | grep "Mem:" | awk '{ print "Total memory (used+free): " $3 " + " $4 " = " $2 }'

Sayan Acharjee · 10-21-2010, 01:11 AM

Quote:

Originally Posted by prayag_pjs

Hi,

Hope this examples helps you:

List what ports are open on remote host

Following command displays memory in format of "available memory = used + free memory" :

These commands are working fine 'cos everytime you are executing them its executing after logging in to the server.
I can't use the ssh command everytime in the script.
How should I edit the script now? any idea?

prayag_pjs · 10-21-2010, 01:51 AM

Hi,

Try ssh again in script as show in example:

Quote:

ssh 192.168.100.5
cat /etc/passwd|grep -i $1 > /dev/null
if [ $? -eq 0 ];
then
echo "User already exists";
else
{
ssh 192.168.100.5 useradd $1
echo $1|passwd --stdin $1 > /dev/null
}
fi