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How to find out which application is using what port
Windows
By: Ted Heich, on 4.9.2009, filed underWindowsand tagged
asApache problem|find applications using port 80|port
80problem|Skype on port 80|Web server problem.
UPDATE (June 3, 2009): The original article describes the steps
to take on how to
findapplicationsthat are using your port in aWindowsmachine,
using only tools that came withyourWindowsinstallationno third
party apps. I am updating the article now to include a third
partytool; WinNetstat isa GUI tool for netstat,
itsatwinnetstat.zapto.org
Network-awareapplicationsare a pain in the __ when they are
acting up. They are particularlyannoyingand infuriating when they
dont want to start. If you have tried starting Apache or MySQLetc
either in stand-alone mode orservice mode (daemon mode in UNIX),
youd know what Im
saying.
The first thing to check when network-awareapplicationswont
start, is of course their log files, tryto see whats preventing
them fromstarting; Almost always, the log file isgoing to tell you
the reason
why the app wont start.
Lots of times, I encounter the problem of twoapplicationsusing
exactly the same portnumber justto be clear, thats bad What the
heck isa portnumber? Id point you to Wikipedia, but its toogeeky
and too academe-ish. Ill take ashot of defining what an
application
port
number
is instead; Ill
segue a bit, then Ill come back to the main point, which is how
to hunt an app thats hostaginga
portnumber.. (holdingmy breath now)What is an application port
number
Everyapplicationthat needs to talk to otherapplications, needs
to have a portnumber. Everycomputer can give out portnumbersranging
from 0 65535, and once a portnumberisgiven, itcannot be given to
anotherapplication(while it is runningat least) so,
oneapplicationis to oneportnumber. The reason whyapplicationhave
portnumbersisso that, when oneapplication(sayFirefox) wants to talk
to anotherapplication(in another computer, say Apache; a web
server), Firefoxneeds to know that when he sends out amessage, it
will be received by the intended recipient
(Apache), and this can only be done if Firefox knows exactly
where Apache is. There are 2
components that make up a unique address ofanapplication one is
the IP address of themachine where theapplicationis running, and
the other component is you guessed it, theportnumber; Collectively
these two (IP addressand portnumber) are known asasocket, but
thats
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anotherstory, letsstop here Whats important to know is that,
portnumbersare well,important; they determine the uniqueness
ofanapplicationwithin amachine.How to hunt down applications via
their port numbers
Imsure there could be amore neat albeit geekier way of finding
out which app is using which
port; but will do it verbosely; easier to follow too.
You will use a command line tool called netstat (networkstatus);
netstat isavailable onWindows,UNIX, and Linux, there are few
differences in the parameters though, so I will cover UNIX and
Linux
separately (in another post that is)
You will also use another command line utility
calledfindstr(short for find string), itsaWindowscommand line
utility which does well, find strings. It locates patterns
ofstrings within astream of otherstrings. So, itsa handy utility
when searching forvery specific words (or part of
words) within a large text file. If youve ever used the Find
function in a word processor, you get
thepicturealready. The UNIX folks have been enjoying this tool
fora long time, its called grep.Anyway, the basic idea is to use
the netstat command so that we can list all theapplicationsthat
areeitheraccepting orsending network traffic, and wed like to list
their portnumbersand their processIDs too. Then, when we find the
portnumberwe are looking for, we will list all the running
processesand make the match using the process ID then well know who
the culprit is.
Letssay that we are looking for port 80 IIS, Apache and other
web servers listen in port 80, so
when you are having problemsstarting Apache, this technique will
be useful. Here is the command.
C:\>netstat -aon | findstr 0.0:80
-ameans list all active connectionsand their ports. -o means
include their process IDs. -n means
display the portnumbersnumerically.The pipe symbol ( | ) means,
that instead of the result of netstat being displayed on the
screen, feed
its result to the findstr process we are lookingspecifically for
the line which has 0.0:80 you
actually dont need findstr, but I dont want to scroll down and
hunt down manually which app isusing port 80. You might see
something like this.
TCP 0.0.0.0:80 0.0.0.0:0 LISTENING 560
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Aha! now we know that process 560 is using port 80 (that last
column right there, is the process ID),
you could press CTRL-ALT-DEL now to show the process window, and
manually look up which app
has the process ID 560, or you could enter ..
C:\>tasklist | findstr 560
tasklist isanotherWindowscommand line utility which shows you a
list ofall active processes, againId feed it to the findstr utility
via the pipe operator, and voila Skype is the culprit.
Skype actually doesnt have to use port 80, it can use other
portnumbers but forsome reason, itjust does. This topic
deservesanother post (Imsuresomebodyelse has this covered). But for
now,this is what you do.
1. Shutdown skype, either via the GUI; or if youre feeling geeky
enough,you can try taskkill /F /PID 560 (this will be different on
your system)
2. Start Apache, or IIS or whatever it is that needs to use port
80
3. Then start skype again
if you repeat the procedure of netstat and tasklist, youll see
that skype now happily usesanother
portnumber.Ifyou want to show appreciation for my efforts dear
reader, you could buy me a tall hazel nut
Americano ($2) via PayPal. Thanks
