Linux的所有開放Ports的列表

TCP 與 UDP 等 Protocol 用於 communication sessions 的port號。

一個IP位置，port 和 Protocol 結合被稱作 Socket 每個服務都必須有一個 Socket。

以下是不同類別的 Port:

• 0-1023 – 平常知道 Ports，被稱作System Ports. 
• 1024-49151 –註冊 Ports, 被稱作User Ports. 
• 49152-65535 – 動態 Ports, 被稱作Private Ports. 

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接著在Linux使用

$ cat /etc/services 
OR
$ cat /etc/services | less

Network Service and Ports

# /etc/services:
# $Id: services,v 1.48 2009/11/11 14:32:31 ovasik Exp $
#
# Network services, Internet style
# IANA services version: last updated 2009-11-10
#
# Note that it is presently the policy of IANA to assign a single well-known
# port number for both TCP and UDP; hence, most entries here have two entries
# even if the protocol doesn't support UDP operations.
# Updated from RFC 1700, ``Assigned Numbers'' (October 1994).  Not all ports
# are included, only the more common ones.
#
# The latest IANA port assignments can be gotten from
#       http://www.iana.org/assignments/port-numbers
# The Well Known Ports are those from 0 through 1023.
# The Registered Ports are those from 1024 through 49151
# The Dynamic and/or Private Ports are those from 49152 through 65535
#
# Each line describes one service, and is of the form:
#
# service-name  port/protocol  [aliases ...]   [# comment]

tcpmux          1/tcp                           # TCP port service multiplexer
tcpmux          1/udp                           # TCP port service multiplexer
rje             5/tcp                           # Remote Job Entry
rje             5/udp                           # Remote Job Entry
echo            7/tcp
echo            7/udp
discard         9/tcp           sink null
discard         9/udp           sink null
systat          11/tcp          users
systat          11/udp          users
daytime         13/tcp
daytime         13/udp
qotd            17/tcp          quote
qotd            17/udp          quote
msp             18/tcp                          # message send protocol
msp             18/udp                          # message send protocol
chargen         19/tcp          ttytst source
chargen         19/udp          ttytst source
ftp-data        20/tcp
ftp-data        20/udp
# 21 is registered to ftp, but also used by fsp
ftp             21/tcp
ftp             21/udp          fsp fspd
ssh             22/tcp                          # The Secure Shell (SSH) Protocol
ssh             22/udp                          # The Secure Shell (SSH) Protocol
telnet          23/tcp

要列出在 Linux 中所有打開的 Port 或正在運行的 Port，可以使用 netstat 他是用於監控網路連接和統計信息的工具。

所有 Network Ports Using Netstat Command

[root@www ~]# netstat -lntu
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State
tcp        0      0 127.0.0.1:25                0.0.0.0:*                   LISTEN
tcp        0      0 0.0.0.0:3306                0.0.0.0:*                   LISTEN
tcp        0      0 0.0.0.0:21                  0.0.0.0:*                   LISTEN
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN
tcp        0      0 ::1:25                      :::*                        LISTEN
tcp        0      0 :::80                       :::*                        LISTEN
tcp        0      0 :::22                       :::*                        LISTEN
udp        0      0 0.0.0.0:68                  0.0.0.0:*

• -l – 只有打印 listening sockets
• -n – 顯示 port number
• -t – 啟用 listing of tcp ports
• -u – 啟用 listing of udp ports

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參考資料
http://www.tecmint.com/find-open-ports-in-linux/