How to create a bash script to check the SSH connection?

user_154688 0
Viewed 200220

I am in the process of creating a bash script that would log into the remote machines and create private and public keys.

My problem is that the remote machines are not very reliable, and they are not always up. I need a bash script that would check if the SSH connection is up. Before actually creating the keys for future use.

ssh connection bash
14 Answers

Below ssh command should have an exit code of 0 on a successful connection and a non-zero value otherwise.

ssh -q -o BatchMode=yes user@remote.com exit

if [ $? != "0" ]; then
    echo "Connection failed"
fi
user_7608510

Following @user156676, to check a range of ips:

#!/bin/sh
IP='192.168.0.'
PWD='your_password'
USR='your_usr'

for i in $(seq 229 255);do
    sshpass -p $PWD ssh -q -o ConnectTimeout=3 ${USR}@${IP}${i} exit
    let ret=$?
    if [ $ret -eq 5 ]; then
        echo $IP$i "Refused!"  $ret
    elif [ $ret -eq 255 ] ; then
        echo $IP$i "Server Down!" $ret
    elif [ $ret -eq 0 ] ; then
        echo $IP$i "Connnected!" $ret
    else
        echo $IP$i "Unknown return code!" $ret
    fi  
done
user_2203160

To connect to a server with multiple interfaces

ssh -o ConnectTimeout=1 -q Necktwi@192.168.1.61;[ $? = 1 ] || ssh -o ConnectTimeout=1 -q Necktwi@192.168.1.51
user_11144980

If you would like to check a remote folder exists, or any other file-test really:

if [ -n "$(ssh "${user}@${server}" [ -d "$folder" ] && echo 1; exit)" ]; then
    # exists
else
    # doesn't exist
fi

Do not forget the quotes in "$(ssh ...)".

user_4726100

Example Using BASH 4+ script: 

# -- ip/host and res which is result of nmap (note must have nmap installed)
ip="192.168.0.1"
res=$(nmap ${ip} -PN -p ssh | grep open)

# -- if result contains open, we can reach ssh else assume failure) --
if [[ "${res}" =~ "open" ]] ;then
    echo "It's Open! Let's SSH to it.."
else
    echo "The host ${ip} is not accessible!"
fi
user_16186300
user_61793250

I wrote this script to check both netcat and SSH connectivity to all hosts in my servers /etc/hosts

reads /etc/hosts line by line and then tries netcat port 22, and then ssh as "sshuttle" user

quick way to check network sanity

script uses a "sshuttle" user, this is an account that has pub/priv keys on all my hosts and can ssh anywhere (non root account), we use this acct to spin up sshuttle VPN tunnels, but you can add any account that has SSH access to servers

https://gist.github.com/perfecto25/8687d563716ba4923c77162be724beda

output,

./conncheck.sh


netcat is installed, proceeding..
--------------------------------------
tm-us1 (127.0.0.1): ssh OK | nc OK
--------------------------------------
localhost (127.0.0.1): ssh OK | nc OK
--------------------------------------
atlas (192.168.142.21): ssh ERROR | nc OK
--------------------------------------
hydra (192.168.142.22): ssh OK | nc OK
--------------------------------------
nemesis (192.168.140.23): ssh OK | nc OK
--------------------------------------
vulcan (192.168.140.24): ssh OK | nc OK
--------------------------------------
athena (192.168.140.27): ssh OK | nc OK
--------------------------------------
nas1 (192.168.100.101): ssh ERROR | nc OK
--------------------------------------
tm-dev (192.10.23.71): ssh ERROR | nc ERROR
--------------------------------------
WARNING: Your password has expired.
Password change required but no TTY available.
infra01 (192.10.23.186): ssh ERROR | nc OK
--------------------------------------
ns-us1 (192.10.23.252): ssh ERROR | nc OK
--------------------------------------
ns-us2 (192.10.23.182): ssh ERROR | nc OK
--------------------------------------
proxy-us1 (192.10.23.120): ssh OK | nc OK
--------------------------------------
simtm-us1 (192.10.23.236): ssh OK | nc OK
--------------------------------------
tm-us1 (192.10.23.104): ssh OK | nc OK
--------------------------------------
tm-us2 (192.10.23.215): ssh OK | nc OK
--------------------------------------
tm-dev (192.10.23.77): ssh OK | nc OK
--------------------------------------
WARNING: Your password has expired.
Password change required but no TTY available.
tm-uat (192.10.23.225): ssh ERROR | nc OK
--------------------------------------
vpn-us1 (192.10.23.193): ssh OK | nc OK
--------------------------------------
user_73274760
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