How can i check that a remote computer is online for ssh / script acess?

Question

i'm writting a script that will backup data from my laptop to an ubuntu server. to do so, i'm looking for a (ba)sh command to test if the server is available before starting the backup. something like "ping" on port 22 that returns a boolean

how can i do this ? thanks for helping

Answer 1

Like this:

nc -z hostname 22 > /dev/null
echo $?

If it's 0 then it's available. If it's 1 then it's not.

Answer 2

Use netcat:

nc -z localhost 22

From the manpage

 -z      Specifies that nc should just scan for listening daemons,
         without sending any data to them.

Answer 3

What about

MACHINE=192.168.0.8
exec 3>/dev/tcp/${MACHINE}/22
if [ $? -eq 0 ]
then
    echo "SSH up"
else
    echo "SSH down"
fi