telnet to another server

Shell Programming and Scripting
1

hi all,
i wanted to write a ksh script to telnet to another server on a particular port every 5 mins in order to send out an alert if that server went down.

how do i read the response that comes back when the server is down i.e "telnet: Unable to connect to remote host: Connection refused"

ta.

2

redirect the errors of the telnet to a file the grep for errors
If found display the appropriate error....

3

hey thanks for the reply, just came to mind that a telnet session if left open will get automatically shut/closed by the network. is there a better way of doing this rather than using telnet ??

ta.

4

you can use ping or an ftp session...

5

telnet and ftp uses different port, when telnetd is running, there is no guarantee that ftpd should be running or vice versa,
so ping on a telnet port is another alternative

6

Ex. ping is not service test. If you like to test some tcp/ip service, use that service = only correct method to check service.
And use ip and port/service number - test only service, not own dns, ...
Create socket ex. socket.sh 111.111.111.111 23

#!/usr/bin/ksh
host=$1
port=$2
exec 4<>/dev/tcp/$host/$port
exit $?

Using that nice ksh93 script, you can do something like (check.sh):

#!/usr/bin/ksh
ip=$1
port=$2
waittime=$3
while true 
do
        ./socket.sh  "$ip" "$port"  ||  ./not_ok.sh "$ip" "$port"
        sleep $waittime
done

chmod a+rx *.sh
# ex. port 23 = usually telnet, wait 300 s
./check.sh  xx.xxx.xxx.xx  23 300 >> telnet.log 2>&1     &

Now you can write your not_ok.sh script as you like.