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how do I close the port 37 ?

Posted on 2006-10-20
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Last Modified: 2013-12-05
Hi.
My linux (slackware)  is listening on TCP/UDP port 37. How can I stop this time service.
Is there some security problem or something depends on it?
Sorry my english.
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Question by:edgardvieira
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Expert Comment

by:Chatable
ID: 17777268
I found this website: http://www.auditmypc.com/port/udp-port-37.asp
This website states that port 37 is used for:
"Time. Provides remote timing stat's of internal processing events. Security Concerns: Gives remote attacker info on host's internal processing load. Can identify critical processing times, plus output can be looped to echo port (7) and create a DOS threat to the subnet. Disable this port on all hosts."
Well I don't agree that this is a major security concern however it still might be a good idea to close it.

Okay since I don't have slackware I will relate to the general task of closing an unneeded open port.
First you determine which application is bound to this port. Run this: netstat --inet -anp
This will dump a list of all open ports along with the PID of their associated process. Then, once you have the PID you can determine which program it is by running: ps -ef
Once you've found the program simply stop it and remove it from your /etc/rc#.d folder so it doesn't execute on startup.
An alternative approach is to simply use the linux built-in firewall (iptables) to block access to unneccessary ports.
You may check this page for an iptables guide: http://iptables-tutorial.frozentux.net/iptables-tutorial.html
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Duncan Roe earned 2000 total points
ID: 17778170
I find lsof easier to use than netstat:

10:36:02# lsof -i :time
COMMAND PID USER   FD   TYPE DEVICE SIZE NODE NAME
inetd   566 root    4u  IPv4    654       TCP *:time (LISTEN)
inetd   566 root    5u  IPv4    655       UDP *:time

On my (Slackware) system, inetd is accepting time calls (along with a lot of other ports, but I asked lsof to only show the time port ("man lsof" for an explanation)).

If you don't want the time service to be enabled, edit /etc/inetd.conf, to comment-out these 2 lines:

time    stream  tcp     nowait  root    internal
time    dgram   udp     wait    root    internal

These lines correspond exactly to the 2 entries that lsof showed earlier
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Expert Comment

by:Duncan Roe
ID: 17778180
After changing /etc/inetd.conf, send SIGHUP to the inetd process to have them take effect:

killall -HUP inetd
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by:Chatable
ID: 17779624
omg you're right, I forgot to relate to inetd... killing inetd isn't a good idea.
if inetd is indeed the process that listens on port 37 you should definitely do what duncan_roe has suggested.
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Author Comment

by:edgardvieira
ID: 17794827
Sorry my delay.
Thanks.
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