I'm trying to execute telnet command and getting the out put on shell script. But when the port not open or the ip not exist. The command take too much time to give the response. Will it be possible to limit the maximum try time on telnet?

telnet host port
  • What OS/distribution and which version of telnet (there are many variants in the world) are you using? Are you allowed to use other programs than telnet, for example netcat?
    – yaegashi
    Aug 21, 2015 at 10:04
  • Oracle enterprise linux. And this is for some big company. They won't easily allow to install new tools. Need to use some thing in the server already.
    – sugunan
    Aug 21, 2015 at 10:06
  • Related and maybe useful: stackoverflow.com/q/1128011/4937930
    – yaegashi
    Aug 21, 2015 at 10:24
  • nc not available in the server and they wont allow to install it also.
    – sugunan
    Aug 21, 2015 at 10:29
  • 1
    nmap available on server ? Or just write a simple perl script, e.g. perlmonks.org/?node_id=571066
    – steve
    Aug 21, 2015 at 10:37

5 Answers 5


This will run for no more than 2 secounds:

[]# echo quit | timeout --signal=9 2 telnet [SERVER] [PORT]

You can consider the neater command netcat aka nc as discussed here

echo 'QUIT' | nc -w SECONDS YOUR_HOST PORT; echo $?
  • This is a great one, thanks for this. I hate when can't quit telnet with even a Ctrl + ] nor Ctrl + 5...
    – antivirtel
    Jan 19, 2022 at 18:06

Do you necessary have to run telnet? I think timeout(1) will help you.

Alternative #1: Use timeout, which is part of GNU coreutils. This won't confirm if you were able to establish a connection or not.

TIMEOUT=10 timeout $TIMEOUT telnet <host> <port>

Alternative #2: Use Bash/Perl/Python to solve the same problem, with more or less granularity.

A few examples:

Bash: TIMEOUT=10; telnet <host> <port> 2>&1 >/dev/null & WPID=$!; sleep $TIMEOUT && kill $! & KPID=$!; wait $WPID

Perl: perl -e "alarm 10; exec @ARGV" "telnet my.server.com 23"

Python: python -c 'import telnetlib;HOST="my.server.com"; PORT=23; TIMEOUT=10; PATTERN="Login: "; t = telnetlib.Telnet (HOST, PORT); t_read = t.read_until(PATTERN, TIMEOUT); print(repr(t_read))'

  • as always the Perl based cmd is the shortest one ;o) Thanks ! Mar 2, 2022 at 9:51
  • You have some extra stuff in the BASH that I don't see the use for, for example KPID is not used
    – Mike Q
    Jan 31 at 17:36

If scripting, you can run the telnet in background, and then if it's still running after a delay you can kill it. Example:

{ printf "HEAD /\n\n"; sleep 1; } | telnet hostname port & sleep 2 && kill %1 2>/dev/null && echo "timeout"

This waits 2 seconds before killing the backgrounded telnet.


Check if Host is reachable or port is reachable/refused or host is up

NOTE: this script is just providing visual feedback.

Example using BASH v4+ where we read the hosts from a list and use the port from that list. In this example I am just testing the port, and if it can reach the host etc.

declare -a remote_hosts=("" "")
for each in ${remote_hosts[@]} ;do

        ip=$(echo $each | cut -d ':' -f1)
        port=$(echo $each | cut -d ':' -f2)
        echo "Connecting ${ip}:${port} .."
        telnet $ip $port & WPID=$!
        sleep 3

        if ps -p $WPID > /dev/null ;then
            echo "FAILED TO REACH ($WPID is running)"
            kill $! 2>&1 >/dev/null
            wait $WPID 2>&1 >/dev/null

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