I am trying to check that an SSH connection succeeds (while running a script).
I am trying to use the answer from here, but the unsuccessful connection returns an error code of 0.
$ ssh -q user#downhost exit
$ echo $?
0
I have tried a variety of invalid ssh commands but they all return a 0 return code; making it hard to check for failure.
I feel I must be doing something wrong, but can't work it out. Is there some setting that I have changed maybe?
I am running CentOS 7, with the following SSH version:
$ ssh -V
OpenSSH_6.6.1p1, OpenSSL 1.0.1e-fips 11 Feb 2013
I remain confused as to why the example is failing, but the following seems to be working for me.
can_connect_ssh()
{
HOST=$1
ssh -q -o BatchMode=yes -o ConnectTimeout=5 $HOST echo connection_success | \
grep connection_success &> /dev/null
}
Called as:
if can_connect_ssh <hostname>; then
echo "Successful Connection"
else
echo "Failed Connection"
fi
Related
I am passing command line arguments to a shell file i.e assignRole.sh which contains an SQL command which will use these arguments like below
ssh -o StrictHostKeyChecking=no -T $key < /oracle/oracle_user/makhshif/./assignRole.sh name open_mode >> /oracle/oracle_user/dftest.txt
This gives me error and does not accept arguments of name and open_mode and gives error, but if I execute the statement outside of ssh command like:
/oracle/oracle_user/makhshif/./assignRole.sh name open_mode
This runs fine
What is the problem with ssh command and how should I adjust these parameters so these can be accepted for the shell script assignRole.sh
< /oracle/oracle_user/makhshif/./assignRole.sh
This commands sends a content of that file to stdin. So obviously it can't process variables that you haven't send to remote machine. Just preprocess your script or create a script on remote machine and call it with arguments
Though it's even easier to pass variables like this:
ssh -o StrictHostKeyChecking=no -T $key "var1=$var1 var2=$var2" < /oracle/oracle_user/makhshif/./assignRole.sh name open_mode >> /oracle/oracle_user/dftest.txt
For example my function for executing update scripts on all cluster nodes:
# functions:
ssh_exec(){
local DESCR="$1"; shift
local SCRIPT="$1"; shift
local hosts=("$#")
echo =================================================
echo = $DESCR
echo = Going to execute $SCRIPT...
read -a res -p "Enter 'skip' to skip this step or press Enter to execute: "
if [[ $res = "skip" ]]
then
echo Skipping $SCRIPT...
else
echo Executing $SCRIPT...
for host in "${hosts[#]}"
do
local cur=${!host}
echo Executing $SCRIPT on $host - $cur...
sshpass -p "$rootpass" ssh -o "StrictHostKeyChecking no" root#${cur} \
"ns1=$ns1 ns2=$ns2 search=$search zoo1=$zoo1 zoo2=$zoo2 zoo3=$zoo3 node0=$node0 pass=$pass CURIP=$cur CURHOST=$host bash -s" \
<$SCRIPT >log-$SCRIPT-$cur.log 2>&1
echo Done.
done
echo =================================================
fi
}
Then I use it like this:
read -p "Please check that Solr started successfully and Press [Enter] key to continue..."
#Solr configset and collections:
ssh_exec "Solr configset and collections" script06.sh zoo1 zoo2 zoo3
This command executes script06.sh on 3 servers (zoo1,zoo2,zoo3)
As Sayan said, using < redirects the output of running the assignRole.sh script locally, but you want to execute that script on the remote host, with the arguments.
Pass the whole command as the final argument to ssh, in quotes:
ssh -o StrictHostKeyChecking=no -T $key "/oracle/oracle_user/makhshif/./assignRole.sh name open_mode" >> /oracle/oracle_user/dftest.txt
or split into multiple lines for readability:
ssh -o StrictHostKeyChecking=no -T $key \
"/oracle/oracle_user/makhshif/./assignRole.sh name open_mode" \
>> /oracle/oracle_user/dftest.txt
I use the kitty terminal emulator, so when I connect to a new server, I (usually) need to ad the terminfo (at least, this way it seems to work). To do this I wrote a script. While I was at it, I added a bit of code to add a public key if the user wants it to.
Not really relevant for the question, but here is the code:
#!/bin/bash
host=$1
ip=$(echo $host | cut -d# -f2 | cut -d: -f1)
# Check if it is a unknown host
if [[ -z $(ssh-keygen -F $ip) ]]; then
# Check if there are any ssh-keys
if [ $(ls $HOME/.ssh/*.pub > /dev/null | wc -l) -ne 0 ]; then
keys=$(echo $( (cd $HOME/.ssh/ && ls *.pub) | sed "s/.pub//g" ))
ssh -q -o PubkeyAuthentication=yes -o PasswordAuthentication=no $host "ls > /dev/null 2>&1"
# Check if the server has one of the public keys
if [ $? -ne 0 ]; then
echo "Do you want to add a SSh key to the server?"
while true; do
read -p " Choose [$keys] or leave empty to skip: " key
if [[ -z $key ]]; then
break
elif [[ -e $HOME/.ssh/$key ]]; then
# Give the server a public key
ssh $host "mkdir -p ~/.ssh && chmod 700 ~/.ssh && echo \"$(cat $HOME/.ssh/$key.pub)\" >> ~/.ssh/authorized_keys"
break
else
echo "No key with the name \"$key\" found."
fi
done
fi
fi
# Copy terminfo to server
ssh -t $host "echo \"$(infocmp -x)\" > \"\$TERM.info\" && tic -x \"\$TERM.info\" && rm \$TERM.info"
fi
It is not the best code, but it seems to work. Tips are ofcourse welcome.
The problem is that I need to run this script every time I connect te a new remote server (or I need to keep track of which server is new, but that is even worse). Is there a way to run this script every time I connect to a server (the script checks if the ip is a known host).
Or is there an other way to do this? Adding the public keys is nice to have, but not very important.
I hope somone can help,
Thanks!
There is a trick to identify that you are using ssh to login on the target machine:
pgrep -af "sshd.*"$USER |wc -l
The above command will count the user's processes using sshd
You can add the above command in the target machine, to test if you are connected via ssh. Add the above command to your .profile or .bash_profile script in the target machine.
So that only if you login via ssh your script will run initiation script on the target machine when you login/connect.
Sample .bash_profile on target machine
#!/bin/bash
# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
# User specific environment and startup programs
if [[ $(pgrep -af "sshd.*"$USER |wc -l) -gt 0 ]]; then
your_init_script
fi
Setup:
Local *nix machine with a SQL script script.sql (Postgres).
Remote machine remote (Debian 7) with Postgres.
I can SSH in as some_user, who is a sudoer.
Anything with Postgres needs to be done as postgres user.
The server only listens on localhost:5432.
How do I execute script.sql on remote without copying it there first?
This works well:
ssh -t some_user#remote 'sudo -u postgres psql -c "COMMANDS FOO BAR"'
The -t flag means that sudo will ask for some_user's password correctly on the local terminal.
One thing remains, to be able to pipe script.sql to psql. This does not work:
ssh -t some_user#remote 'sudo -u postgres psql' < script.sql
It fails with the message:
Pseudo-terminal will not be allocated because stdin is not a terminal.
sudo: no tty present and no askpass program specified
Edit: simplified example
Postgres and psql don't seem to figure much in the problem. The following code has the same issues:
ssh some_user#remote xargs sudo ls < input_file
The problem seems to be: we need to send 2 inputs to sudo, both the password using a tty, and the stdin to pass to ls.
Edit: even simpler
ssh localhost xargs sudo ls < input_file
sudo: no tty present and no askpass program specified
Adding -t does not work:
$ ssh -t localhost xargs sudo ls < input_file
Pseudo-terminal will not be allocated because stdin is not a terminal.
sudo: no tty present and no askpass program specified
Adding another -t does not work either:
$ ssh -t -t localhost xargs sudo ls < input_file
<content of input_file>
<waiting on a prompt>
ssh -T some_user#remote "sudo -u postgres psql -f-" < script.sql
"-f-" will read the script from STDIN. Just redirect the file in there, and there you go.
Don't bother with -t option to ssh, you don't need a full terminal for this.
ssh -T ${user}#${ip} sudo DEBIAN_FRONTEND=noninteractive postgres psql -f- < test.sql
Use DEBIAN_FRONTEND=noninteractive for resolve no tty present or equivalent of your distribution.
Is there a way to execute a command before accessing a remote terminal
When I enter this command:
bash
$> ssh user#server.com 'ls'
The ls command is executed on the remote computer but ssh quits and I cannot continue in my remote session.
Is there a way of keeping the connection? The reason that I am asking this is that I want to create a setup for ssh session without having to modify the remote .bashrc file.
I would force the allocation of a pseudo tty and then run bash after the ls command:
syzdek#host1$ ssh -t host2.example.com 'ls -l /dev/null; bash'
-rwxrwxrwx 1 root other 27 Apr 1 2005 /dev/null
bash-4.1$
You can try using process subsitution on the init file of bash. In the example below, I define a function myfunc:
myfunc () {
echo "Running myfunc"
}
which I transform to a properly-escaped one-liner echoed in the <(...) construct for process subsitution for the --init-file argument of bash:
$ ssh -t localhost 'bash --init-file <( echo "myfunc() { echo \"Running myfunc\" ; }" ) '
Password:
bash-3.2$ myfunc
Running myfunc
bash-3.2$ exit
Note that once connected, my .bashrc is not sourced but myfunc is defined and properly usable in an interactive session.
It might prove a little difficult for more complex bash functions, but it works.
The command
ssh -q -o "BatchMode=yes" user#host "echo 2>&1" && echo "OK" || echo "NOK"
will help in checking whether the SSH connection to peer IP is a success or not.
But I am having only Peer IP so
ssh -q -o "BatchMode=yes" peerIP 2>&1" && echo "OK" || echo "NOK"
doesnt work.
Anyone knows how can i solve it? A One-liner command is required and it should work on AIX, HP, Linux... any help or suggestion is very much appreciated.
Why do you mention awk ?
Whatever, here a solution that works for me:
ssh USER#HOST 'env |grep SSH_CLIENT && echo "OK" || echo "NOK"'
When SSH is connected to the host, some environment variable will be set.
Also, when your connection to a remote host without using a User in the SSH URL, your current should be set by default. You can change that behavior in your */etc/ssh/ssh_config* .
Maybe that will fix it.
Good luck