Is there an easy way for  a non root user to find if a port is open ?

Posted on 2011-03-10
Last Modified: 2012-05-11
As I non root user ( nmap is not installed) I want to find out if I can ssh to a box.  

I tried telnet  x.y.z.a  22 and if it is open, it show on the screen and then does not terminate process so my script can do something.  If it is not open, I still have a process that stays open for too long.

what I am looking for is
$ line of code
$ if $? then xxxx

I am in a large network and some systems are available from some ip's and in other environments they are not .

Question by:TIMFOX123
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LVL 31

Expert Comment

ID: 35094322
It is installed but non-root account doesn't have the priviledge.

So, for example, the following should do it:
sudo nmap -sS  localhost

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LVL 31

Expert Comment

ID: 35094358
You have to setup sudo privileges for this user.  You can also set it up without password.

Second, if you want to do with remotely using ssh, the command would be
ssh sudo "nmap -v -sS localhost"

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LVL 68

Accepted Solution

woolmilkporc earned 500 total points
ID: 35094363
If you don't have sudo permission, try this script I once wrote here at EE:


rm $CHECKFILE 2>/dev/null
( telnet $HOST $PORT 2>&1 ) > $CHECKFILE &
   sleep $SLEEPTIME
   kill $JOB 2>/dev/null

if grep -q "Connected to" $CHECKFILE ; then
   echo SSH Server on $HOST is UP
   echo SSH Server on $HOST is DOWN
rm $CHECKFILE 2>/dev/null


Expert Comment

ID: 35094439
I guess you can use netstat to see if a port is open or not. Here is the syntax

netstat -ntlp |grep port number

You can omit the p option if you want, it will show you the program that is holding the port you are looking for. For example in your case

netstat -ntlp | grep 22

Will show no output if port 22 is not open, but if it is open it ll show you the output giving you details like program holding the port, whether port is at Listen status or connection is Established also to what IP addresses the port is listening to.


Author Closing Comment

ID: 35095606
What a great solution !!!



did the impossable


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