How to reserve ports in /etc/services?

[UNIX System Admins]

I know that the /etc/services file can not be used for reserving ports, so how do you reserve ports for apps or DB that require certain ports? Ex.Our DBAs say that ports 7777, 4443, 7200 & 7001 need to be available for their apps to use. How can I keep something like MeasureWare from grabing one of those ports?

[A. Clay Stephenson]

The short answer is that you get there "firstest with the mostest". The first server to use the port gets it. You essentially make sure that none of the other services use it.

Check this listing: http://www.iana.org/assignments/port-numbers

The "proper" answer to your question is that you request an official registration of your service from IANA and then noone else is supposed to use it. Of course, you can guess how well that really works.

[Alex Lavrov.]

You can reserve ports .... Every program that has permissions to bind to some port, will do it (if it's free now).

You can write some script that will tell you that someone took these ports and it's not the program you want, it will send you a message. You can use lsof:

lsof -i:


If you don't have lsof:
http://ftp.cerias.purdue.edu/pub/tools/unix/sysutils/lsof/binaries/hpux/

Alex.

[A. Clay Stephenson]

The really neat thing is that your DBA's have already chosen IANA assigned ports so THEY are breaking the rules.

[Kent Ostby]

Un-assigned ports can be used via the /etc/services file.

HOWEVER, if you happen to use one without it being officially registered, you could be in trouble later when an officially registered product comes along and you want both products on the same system.

I recall this happening when ServiceGuard came out originally. Some application was using ports that it had not reserved and SG used those ports as well. It led to the application having to be fixed and recompiled.