topic Re: /etc/services in Operating System - HP-UX

/etc/services

j773303 — Tue, 08 Apr 2003 00:56:46 GMT

Any command should be run after modified /etc/services?

Re: /etc/services

Michael Tully — Tue, 08 Apr 2003 01:02:59 GMT

Simple answer is no. The /etc/services file is used as a reference for the port numbers and their aliases.

# man services

Re: /etc/services

j773303 — Tue, 08 Apr 2003 01:06:58 GMT

But if I disable
#TCP 25 SMTP

Does this disable port 25 immediately?

Re: /etc/services

Michael Steele_2 — Tue, 08 Apr 2003 01:09:14 GMT

As long as there is no conflict with other applications and its not own by root, (* < 1024 *) then you shouldn't have a problem. Order your /etc/services file with sort a check for duplicates:

cat /etc/services | sort -n | more

Don't confuse this with starting the network utility like oracle's listener or one of the inetd utilities. When you make a port you reserve buffer space and allow the system to create a system file for parsing. That's why ports are analyzed with lsof, the list open files command.

lsof -i tcp:23
lsof -i udp:123, etc.

Re: /etc/services

Michael Steele_2 — Tue, 08 Apr 2003 01:13:25 GMT

Regarding: "...But if I disable #TCP 25 SMTP Does this disable port 25 immediately? ..."

Probably not. You've got to stop the application. Run:

lsof -i smtp:25

Is there a sendmail daemon perhaps?

killsm

Re: /etc/services

Bill Hassell — Tue, 08 Apr 2003 01:25:29 GMT

Think of /etc/services as a documentation file. A port may be used even though it is not defined in /etc/services. The file /etc/inetd.conf is used to associate a service with a daemon and route appropriate packets to the listed daemons. However, sendmail is not managed by inetd. To stop sendmail (the typical program that handles port 25), use the command:

/sbin/init.d/sendmail stop

Sendmail will no longer run and port 25 will be unused and will not respond to probes. To keep sendmail from running upon a reboot, edit the config file:

/etc/rc.config.d/mailservs

and change this line to read:

export SENDMAIL_SERVER=0

That will keep sendmail from running.

Re: /etc/services

Michael Steele_2 — Tue, 08 Apr 2003 03:52:20 GMT

Now j773303, don't you think that 'killsm' is a lot easier to use than '/sbin/init.d/sendmail stop?'

Re: /etc/services

Michael Tully — Tue, 08 Apr 2003 04:06:39 GMT

The man pages (killsm) also states

"HP recommends that system administrators use ``/sbin/init.d/sendmail start'' and ``/sbin/init.d/sendmail stop'' to start and stop sendmail;"

Re: /etc/services

Steven E. Protter — Tue, 08 Apr 2003 12:16:01 GMT

I think of /etc/services as a documentation or reservation file.

If you comment out the port 25 reference you have no functional effect.

You can control stmp traffic by making changes to the sendmail.mc file, generating a new sendmail.cf file and block incoming mail traffic on any port or IP address.

If you want to block traffic further, you need to have some kind of firewall between your box and your users. HP has a free one, or you can have an external pc based firewall.

I refer to /etc/services as a reservation file because when you install oracle on a system it takes up several ports. Oracle doesn't bother adding entries to the /etc/services file and everything works great.

SEP