Ports and Services

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To check which port is currently used in your Linux Server you can run the netstat command, root, to also list the ID and name of the process watching that port:

# netstat -tulpen

You can turn services on and off by the update-inetd command. For example, to turn telnet off:

# update-inetd --disable telnet

You can also manually turn services off by directly editing /etc/inetd.conf. For example, if you have telnetd installed (not recommended) and wish to turn it off (rather than uninstalling it) then comment out the line in /etc/inetd.conf that starts with telnet and restart inetd:

# /etc/init.d/inetd restart

7		echo
9		discard	This is like /dev/null but for networks. This port is generally not needed, especially if you are worried about attacks.
13		daytime	Prints the current date as a string (e.g., Mon May 23 07:14:21 2001). Not generally not needed. Can be turned off to avoid possible denial of service attacks where an attacker may link it to the echo port using spoofing. Also, the returned format could be used to guess the operating system type.
17		quotd
20		ftp-data
21		ftp
22		ssh
23		telnet
25		smtp
37		time	prints the current time as seconds sine the epoch in machine readable form. This can be useful if network clients expect the service for crude time synchronisation (some windows clients can use this service). Otherwise it is not generally needed.
53		domain
70		gopher
79		finger
80		http
110		pop3
111		sunrpc
113		auth	The IDENT protocol. It is not useful but most IRC servers require this port to be open and returning information. Apparently some FTP servers and postgresql require this service as well.
119		nntp	is the Network News Transport Service if you are running a news server (e.g., inn or cnews). Otherwise it is not needed.
123		ntp
143		imap2
161	udp	snmp	Simple Net Management Protocol
194	tcp	irc	Internet Relay Chat
194	udp	irc
220		imap3
389	tcp	ldap	Lightweight Directory Access Protocol
443	tcp	https	Secure HTTP
873	tcp	rsync	Efficient protocol for copying and syncing files.
2049	tcp	nfs	This port will advertise the export list for NFS.
2049	udp	nfs	Older versions of nfsd have bugs so make sure your nfs is up to date.
3306	tcp	mysql
6000		X Window System
6667	udp	ircd	Internet Relay Chat
8080	tcp	webcache	WWW caching service
32860	udp	nlockmgr	Not known to be a security problem but could be turned off.

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