Dirty Bash hack to run the ssh connections in the Parallel mode

Question

A Few years back I used to opt the below method to run the shell program in a Parallel way to open multiple ssh session at a time to get a quick result.

I know there are various other good utilities available, however due to some pressing needs I've to use this way, this dirty piece of code works well however I would like to know if there are some suggestion to improve it further considering the fact I have to use it for some compelling reasons over other better tools.

#!/bin/bash
echo "$(date) Starting the SSH Connection Check...."
#set -x
read -rsp $'Please Enter password below: ' SSHPASS
export SSHPASS
SSH_Connection () {
 hostTarget=${1}
 sshpass -e ssh -q "${hostTarget}" "true" -o StrictHostKeyChecking=no -o ConnectTimeout=60 2>>/dev/null
 if [[ $? -eq 0 ]]
 then
 echo "$CurrntTime $MachineName : SSH connection is Up"
 elif [[ $? -eq 255 ]]
 then
 echo "$CurrntTime $MachineName : SSH Authentication Failed"
 elif [[ $? -eq 2 ]]
 then
 echo "$CurrntTime $MachineName : SSH connection is Down"
 elif [[ $? -eq 1 ]]
 then
 echo "$CurrntTime $MachineName : SSH Authentication Failed"
 else
 echo "$CurrntTime $MachineName : SSH connection is Down"
 fi
}
HostList=$(<~/host2)
CurrntTime=$(date +'%m/%d/%Y %T')
for MachineName in ${HostList}
do
 SSH_Connection "${MachineName}" &
done
# wait for all outstanding background jobs to complete before continuing
wait
# at last clear the exported variable containing the password
unset SSHPASS

• chicks: Do you have compelling reasons for not using ssh keys? digitalocean.com/community/tutorials/…
• Karn Kumar: Yes.. I can not supply keys even. I know about ssh keys and another methods as well even about pssh but as i mentioned, its not always where we have liberty to choose our freedom over companies policies for any reasons.

Answer 1

The only part I would change are the chained if statements. Use case:

CurrntTime="some_timestamp"
MachineName="some_host"
for retval in 0 255 2 1 8; do
 echo "Testing exitcode ${retval}"
 case ${retval} in
 0)
 echo "$CurrntTime $MachineName : SSH connection is Up";;
 255)
 echo "$CurrntTime $MachineName : SSH Authentication Failed";;
 2)
 echo "$CurrntTime $MachineName : SSH connection is Down";;
 1)
 echo "$CurrntTime $MachineName : SSH Authentication Failed";;
 *)
 echo "$CurrntTime $MachineName : SSH connection is Down";;
 esac
done

More optimisation is not needed. The alternative beneath is slightly shorter but makes the code harder to read (more fun, though):

CurrntTime="some_timestamp"
MachineName="some_host"
ssh_err_0="connection is Up"
ssh_err_1="Authentication Failed"
ssh_err_2="connection is Down"
ssh_err_255="Authentication Failed"
ssh_err_other="connection is Down"
for retval in 0 255 2 1 8; do
 echo "Testing exitcode ${retval}"
 printf "%s" "$CurrntTime $MachineName : SSH "
 case ${retval} in
 0|1|2|255)
 message="ssh_err_${retval}"
 echo "${!message}";;
 *)
 echo "${ssh_err_other}";;
 esac
done

When you use the first case in the total script, and move the SSH_Connection() function to the start of the script, it would be

#!/bin/bash
SSH_Connection () {
 hostTarget=${1}
 sshpass -e ssh -q "${hostTarget}" "true" -o StrictHostKeyChecking=no \
 -o ConnectTimeout=60 2>/dev/null
 case $? in
 0)
 echo "$CurrntTime $hostTarget: SSH connection is Up";;
 255)
 echo "$CurrntTime $hostTarget: SSH Authentication Failed";;
 2)
 echo "$CurrntTime $hostTarget: SSH connection is Down";;
 1)
 echo "$CurrntTime $hostTarget: SSH Authentication Failed";;
 *)
 echo "$CurrntTime $hostTarget: SSH connection is Down";;
 esac
}
echo "$(date) Starting the SSH Connection Check...."
read -rsp $'Please Enter password below: ' SSHPASS
export SSHPASS
HostList=$(<~/host2)
CurrntTime=$(date +'%m/%d/%Y %T')
for MachineName in ${HostList}; do
 SSH_Connection "${MachineName}" &
done
# wait for all outstanding background jobs to complete before continuing
wait
# at last clear the exported variable containing the password
unset SSHPASS

I did not move the CurrentTime=$(..) inside the function. When you want to see the date/time after the ssh is finished, then you will need to store the exit code in a variable:

...
sshpass -e ssh ...
retval=$?
CurrentTime=$(date +'%m/%d/%Y %T')
case ${retval} in ...

• Karn Kumar: Thanks Walter, How the complete code would look like then, can your formulate the code with you adjustment.
• Walter A: Is the code clear for you?