Para verificar as portas em uso utilize o NMAP

[root@oracle logs]# nmap -sV 192.168.21.50

Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2009-11-26 13:44 AMT
Interesting ports on oracle.com (192.168.21.50):
Not shown: 1673 closed ports
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 4.3 (protocol 2.0)
80/tcp open http Apache httpd 2.2.3 ((Oracle))
111/tcp open rpcbind 2 (rpc #100000)
682/tcp open status 1 (rpc #100024)
1158/tcp open http Oracle Application Server httpd 9.0.4.1.0
1521/tcp open oracle-tns Oracle TNS Listener 10.2.0.1.0 (for Linux)
5520/tcp open sdlog Oracle Enterprise Manager

[root@oracle logs]# nmap -sV 192.168.21.50 |wc -l
16

ou o LSOF

[root@oracle logs]# lsof -i
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
portmap 2161 rpc 3u IPv4 5460 UDP *:sunrpc
portmap 2161 rpc 4u IPv4 5461 TCP *:sunrpc (LISTEN)
rpc.statd 2196 root 3u IPv4 5587 UDP *:mrm
rpc.statd 2196 root 6u IPv4 5578 UDP *:vpps-via
rpc.statd 2196 root 7u IPv4 5597 TCP *:xfr (LISTEN)
hpiod 2808 root 0u IPv4 7852 TCP localhost.localdomain:2208 (LISTEN)
python 2813 root 4u IPv4 7870 TCP localhost.localdomain:2207 (LISTEN)
sshd 2826 root 3u IPv6 7906 TCP *:ssh (LISTEN)
cupsd 2835 root 4u IPv4 7941 TCP localhost.localdomain:ipp (LISTEN)
cupsd 2835 root 6u IPv4 7944 UDP *:ipp
sendmail 2868 root 4u IPv4 8064 TCP localhost.localdomain:smtp (LISTEN)
avahi-dae 3033 avahi 13u IPv4 8432 UDP *:mdns
avahi-dae 3033 avahi 14u IPv6 8433 UDP *:mdns
avahi-dae 3033 avahi 15u IPv4 8434 UDP *:61200
avahi-dae 3033 avahi 16u IPv6 8435 UDP *:53453
ocssd.bin 3983 oracle 7u IPv4 12009 UDP localhost.localdomain:32291
ocssd.bin 3983 oracle 9u IPv4 12012 UDP localhost.localdomain:41644
ocssd.bin 3983 oracle 10u IPv4 12013 TCP localhost.localdomain:50340 (LISTEN)
ocssd.bin 3983 oracle 11u IPv4 12014 UDP localhost.localdomain:47455
ocssd.bin 3983 oracle 14u IPv4 12019 UDP localhost.localdomain:7847
ocssd.bin 3983 oracle 15u IPv4 12020 TCP localhost.localdomain:19119 (LISTEN)
java 8892 oracle 7u IPv4 714077 TCP *:5520 (LISTEN)
java 8892 oracle 10u IPv4 714078 TCP *:dbcontrol-oms (LISTEN)
java 8892 oracle 25u IPv4 720399 TCP oracle.com:44781->oracle.com:ncube-lm (ESTABLISHED)

[root@oracle logs]# lsof -i:1521 |wc -l
20

[root@oracle logs]# dmesg
Linux version 2.6.18-164.el5PAE (mockbuild@x86-002.build.bos.redhat.com) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)) #1 SMP Tue Aug 18 15:59:11 EDT 2009
BIOS-provided physical RAM map:
BIOS-e820: 0000000000010000 – 000000000009f800 (usable)
BIOS-e820: 000000000009f800 – 00000000000a0000 (reserved)
BIOS-e820: 00000000000f0000 – 0000000000100000 (reserved)
BIOS-e820: 0000000000100000 – 00000000bfee0000 (usable)
BIOS-e820: 00000000bfee0000 – 00000000bfee3000 (ACPI NVS)
BIOS-e820: 00000000bfee3000 – 00000000bfef0000 (ACPI data)
BIOS-e820: 00000000bfef0000 – 00000000bff00000 (reserved)
BIOS-e820: 00000000c0000000 – 00000000d0000000 (reserved)
BIOS-e820: 00000000fec00000 – 0000000100000000 (reserved)
BIOS-e820: 0000000100000000 – 0000000140000000 (usable)
4224MB HIGHMEM available.
896MB LOWMEM available.
found SMP MP-table at 000f4f50
Memory for crash kernel (0x0 to 0x0) notwithin permissible range
disabling kdump