how do i reduce timeout on unix telnet on connection

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I have a unix shell script which test ftp ports of multiple hosts listed in a file.

for i in `cat ftp-hosts.txt`
        do
        echo "QUIT" | telnet $i 21
done

In general this scripts works, however if i encounter a host which does not connect, i.e telnet is "Trying...", how can I reduce this wait time so it can test the next host ?

Have you tried using netcat (nc) instead of telnet? It has more flexibility, including being able to set the timeout:

echo 'QUIT' | nc -w SECONDS YOUR_HOST PORT
# e.g.
echo "QUIT" | nc -w 5       localhost 21

The -w 5 option will timeout the connection after 5 seconds.

telnet command with custom timeout duration, 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? 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 / "; sleep 1; } | telnet hostname port & sleep 2 && kill %1 2>/dev/null && echo "timeout" This waits 2 seconds before killing the backgrounded telnet.

Try using timeout3 script is very robust and I used a lot without problems on different situations. Example to wait just 3 seconds trying to check if ssh port is open.

> echo QUIT > quit.txt
> ./timeout3 -t 3 telnet HOST 22 < quit.txt 

outputs: you can grep for "Connected" or "Terminated"

timeout3 file contents:

#
#!/bin/bash
#
# The Bash shell script executes a command with a time-out.
# Upon time-out expiration SIGTERM (15) is sent to the process. If the signal
# is blocked, then the subsequent SIGKILL (9) terminates it.
#
# Based on the Bash documentation example.
# If you find it suitable, feel free to include
# anywhere: the very same logic as in the original examples/scripts, a
# little more transparent implementation to my taste.
#
# Dmitry V Golovashkin <Dmitry.Golovashkin@sas.com>

scriptName="${0##*/}"
declare -i DEFAULT_TIMEOUT=9
declare -i DEFAULT_INTERVAL=1
declare -i DEFAULT_DELAY=1
# Timeout.
declare -i timeout=DEFAULT_TIMEOUT

# Interval between checks if the process is still alive.
declare -i interval=DEFAULT_INTERVAL

# Delay between posting the SIGTERM signal and destroying the process by SIGKILL.
declare -i delay=DEFAULT_DELAY

function printUsage() {
    cat <<EOF

Synopsis
    $scriptName [-t timeout] [-i interval] [-d delay] command
    Execute a command with a time-out.
    Upon time-out expiration SIGTERM (15) is sent to the process. If SIGTERM
    signal is blocked, then the subsequent SIGKILL (9) terminates it.

    -t timeout
        Number of seconds to wait for command completion.
        Default value: $DEFAULT_TIMEOUT seconds.

    -i interval
        Interval between checks if the process is still alive.
        Positive integer, default value: $DEFAULT_INTERVAL seconds.

    -d delay
        Delay between posting the SIGTERM signal and destroying the
        process by SIGKILL. Default value: $DEFAULT_DELAY seconds.

As of today, Bash does not support floating point arithmetic (sleep does),
therefore all delay/time values must be integers.
EOF
}

# Options.
while getopts ":t:i:d:" option; do  
    case "$option" in
        t) timeout=$OPTARG ;;
        i) interval=$OPTARG ;;
        d) delay=$OPTARG ;;
        *) printUsage; exit 1 ;;
    esac
done
shift $((OPTIND - 1))

# $# should be at least 1 (the command to execute), however it may be strictly
# greater than 1 if the command itself has options.

if (($# == 0 || interval <= 0)); then 
    printUsage
    exit 1
fi

# kill -0 pid   Exit code indicates if a signal may be sent to $pid process.
(
    ((t = timeout))

    while ((t > 0)); do
        sleep $interval
        kill -0 $$ || exit 0
        ((t -= interval))
    done
    # Be nice, post SIGTERM first.
    # The 'exit 0' below will be executed if any preceeding command fails.
    kill -s SIGTERM $$ && kill -0 $$ || exit 0
    sleep $delay
    kill -s SIGKILL $$
) 2> /dev/null &

exec "$@"
#

CentOS / RHEL : How to adjust the telnet timeout (and how to , To modify the telnet timeout you need to change the value of the parameter tcp_keepalive_time. Below is the details of the parameter from the man page of tcp. Hi, I have a Sun Ultra 5 desktop with Solaris 8. When I telnet/rlogin into any other host, the connection closes after few hours of inactivity. I also have another Windows box which I use rarely. But when I telnet/rlogin into the same hosts using putty, the connection stays for days without any (5 Replies)

Use start a process to sleep and kill the telnet process. Roughly:

echo QUIT >quit.txt
telnet $i 21 < quit.txt &
sleep 10 && kill -9 %1 &
ex=wait %1
kill %2
# Now check $ex for exit status of telnet.  Note: 127 inidicates success as the
# telnet process completed before we got to the wait.

I avoided the echo QUIT | telnet pipeline to leave no ambiguity when it comes to the exit code of the first job.

This code has not been tested.

Telnet Timeout - UNIX and Linux Forums, is there a way to add a timeout parameter to telnet when connecting to any IP #!/usr/bin/expect -- set timeout [lindex $argv 0] set machine [lindex $argv 1]� To modify the telnet timeout you need to change the value of the parameter tcp_keepalive_time. You can also adjust timeout by using 'TMOUT=' environment variable. If you don't want to use auto logging out, please put the below in ~/.bashrc file of the respective user.

if you have nmap

 nmap -iL hostfile -p21  | awk '/Interesting/{ip=$NF}/ftp/&&/open/{print "ftp port opened for: "ip}'

Knowledge: TELNET connection times out after 15 minutes, Windows clients using Telnet to connect to a Linux server, where the ABL application is Is there any setting in OpenEdge that would deactivate Telnet timeouts on systems that 000001269, FAQ on TCP Keepalive for UNIX� Hello, I need help, I have the following which save in the result file ping and telnet:port test. Basically the script works but I should implement a check on ping and telnet command so that ping has 5 seconds threshold and telnet (more important) 10 seconds. Over that threshold ping and telnet should be interrupted giving a negative answer.

Use timeout in order to quit in x seconds whether the operation succeed or fails:

timeout runs a command with a time limit , Start COMMAND, and kill it if still running after DURATION.

Formula:

timeout <seconds> <operation>

example:

timeout 5 ping google.com

your example:

for i in `cat ftp-hosts.txt`
do
    timeout 5 telnet $i 21
done

Troubleshooting a Telnet Connection, TCP is the network protocol and telnet the IP protocol used by Anzio Lite and AnzioWin to Use this document to troubleshoot telnet connections. time, it may be an indication that a telnet client will also have problems (possibly timeout issues). This is another utility that normally exists on the UNIX host and on Windows. telnet runs in the background as does a command sequence that will kill it in 10 seconds. The 'ex=wait %1' gets the exit code of the telnet. If the telnet finishes before the timeout, the kill %2 gets rid of it. But if the timeout happens the kill %2 does nothing.

Linux nc command help and examples, On Unix-like operating systems, the nc command runs Netcat, a utility for This makes it possible to use nc to script telnet sessions. -w timeout, Connections which cannot be established or are idle timeout after timeout seconds. After the connection was set up, nc does not really care which side is� Protocol. Once a connection is opened, telnet will attempt to enable the TELNET LINEMODE option. If this fails, then telnet will revert to one of two input modes: either "character at a time" or "old line by line" depending on what the remote system supports.

5 simple methods to test ssh connection in Linux & Unix , Multiple commands to test ssh connection in Linux and Unix. How to Method 1: Use timeout with bash utility to test SSH connection Here we have defined a connection timeout period of 5 second which you can change based on your echo quit | telnet <server> <port> 2>/dev/null | egrep -qi Connected. For example, telnet textmmode.com 23 is the same as running the command telnet textmmode.com, but not the same as telnet textmmode.com 95, which connects to the same server but on port 95. Microsoft keeps this list of telnet commands if you'd like to learn more about how to do things like open and close a Telnet connection, display the Telnet

netcat, nc -- netcat, Unlike bsdtelnet, netcat scripts nicely, and separates error messages onto standard Change IPv4 TOS value. toskeyword may be one of critical, inetcontrol, For UNIX-domain sockets, use a datagram socket instead of a stream socket. Connections which cannot be established or are idle timeout after timeout seconds. Telnet is easiest remote management protocol used in Computer networks. It remains popular even today because of its simplicity. Telnet is a client server protocol where clients uses telnet tool which to connect remote telnet server. This telnet server may be switch, router, windows operating system, linux server or a printer.

Comments
  • this idea works.. i will need to use it in this way "nc -z -w 3 ip port". However for hosts which do not connect it does not generate an exit code.
  • strange. when i try -w 1 it just sits there hanging for a lot more than 1 second...
  • @Michael There's also -G option for specifying TCP connection timeout
  • Beautiful! This make me swtich from telnet tonc in postgres-check solution here stackoverflow.com/a/59657648/248616
  • telnet runs in the background as does a command sequence that will kill it in 10 seconds. The 'ex=wait %1' gets the exit code of the telnet. If the telnet finishes before the timeout, the kill %2 gets rid of it. But if the timeout happens the kill %2 does nothing.
  • My version of this: nmap -PS -p "$port" --host-timeout 1501ms "$host" 2>/dev/null | grep '/tcp *open '. $? will be 0 for success, 1 for closed / timeout. 1501ms is the minimum timeout.