我们不仅可以通过相应工具识别目标主机上的服务指纹信息，还可以进行系统指纹信息识别。常见的系统指纹信息有操作系统类型、系统版本和内核版本等。本文介绍系统识别的 。
1. Nmap系统识别
在Nmap工具中，提供了一些选项可以用来实施系统识别。下面介绍具体的实现 。
（1）识别操作系统
在Nmap工具中提供了一个-O选项，可以用来识别操作系统。用于识别操作系统的语法格式如下：
nmap -O [host]
其中，-O选项用于识别操作系统类型。注意，这里的选项-O是大写字母O，不是0。
识别目标主机192.168.33.152的操作系统类型。执行命令如下：
root@daxueba:~# nmap -O 192.168.33.152
Starting Nmap 7.70 ( https://nmap.org ) at 2021-08-02 15:22 CST
Nmap scan report for 192.168.33.152 (192.168.33.152)
Host is up (0.00036s latency).
Not shown: 997 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
80/tcp open http
MAC Address: 00:0C:29:FD:58:4B (VMware) #MAC地址
Device type: general purpose #设备类型
Running: Linux 3.X|4.X #运行的系统
OS CPE: cpe:/o:linux:linux_kernel:3 cpe:/o:linux:linux_kernel:4 #操作系统中央处理单元
OS details: Linux 3.2 - 4.9 #操作系统详细信息
Network Distance: 1 hop # 距离，即从源到目标经过的 节点
OS detection performed. Please report any incorrect results at https://nmap.
org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1.86 seconds
从以上输出信息中可以看到，目标主机的操作系统类型为Linux，内核版本为3.2。如果Nmap不能够判断出目标操作系统的话，将会提供指纹信息给Nmap的系统数据库。例如，识别目标主机10.10.1.11的操作系统。执行命令如下：
root@daxueba:~# nmap -O 10.10.1.11
Starting Nmap 7.70 ( https://nmap.org ) at 2021-08-02 15:29 CST
……
No exact OS matches for host (If you know what OS is running on it, see http://nmap.org/submit/ ).
TCP/IP fingerprint:
OS:SCAN(V=5.00%D=12/16%OT=3001%CT=1%CU=32781%PV=Y%DS=1%G=Y%M=00204A%TM=4B29
OS:4048%P=i686-pc-windows-windows)SEQ(CI=I%II=I%TS=U)OPS(O1=M400%O2=%O3=%O4
OS:=%O5=%O6=)OPS(O1=M400%O2=M400%O3=%O4=%O5=%O6=)OPS(O1=%O2=M400%O3=M400%O4
OS:=%O5=%O6=)OPS(O1=%O2=%O3=M400%O4=%O5=%O6=)OPS(O1=M400%O2=%O3=M400%O4=%O5
OS:=%O6=)WIN(W1=7FF%W2=0%W3=0%W4=0%W5=0%W6=0)WIN(W1=7FF%W2=7FF%W3=0%W4=0%W5
OS:=0%W6=0)WIN(W1=0%W2=7FF%W3=7FF%W4=0%W5=0%W6=0)WIN(W1=0%W2=0%W3=7FF%W4=0%
OS:W5=0%W6=0)WIN(W1=7FF%W2=0%W3=7FF%W4=0%W5=0%W6=0)ECN(R=Y%DF=Y%T=40%W=0%O=
OS:%CC=N%Q=)T1(R=Y%DF=Y%T=40%S=O%A=S+%F=AS%RD=0%Q=)T1(R=Y%DF=Y%T=40%S=O%A=O
OS:%F=AS%RD=0%Q=)T1(R=Y%DF=Y%T=40%S=Z%A=S+%F=AR%RD=0%Q=)T2(R=Y%DF=Y%T=40%W=
OS:0%S=Z%A=S+%F=AR%O=%RD=0%Q=)T3(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=
OS:)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T5(R=Y%DF=Y%T=40%W=0%S=Z%A=
OS:S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0%Q=)T7(R=Y%DF
OS:=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R=Y%DF=Y%T=40%IPL=38%UN=0%RIPL=G
OS:%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=S%T=40%CD=S)
以上输出信息就是Nmap向数据库提交的指纹信息，这些指纹信息是自动生成的，并且标识了目标系统的操作系统。
（2）指定识别的操作系统
当扫描多个主机时，可以使用--osscan-limit选项来指定识别特定主机的操作系统类型。这样，使用该选项进行操作系统识别可以节约大量的时间。指定识别主机的操作系统类型语法格式如下：
nmap -O --osscan-limit [host]
其中，--osscan-limit选项表示针对指定的目标进行操作系统检测。如果发现一个打开和关闭的TCP端口时，操作系统检测会更有效。使用该选项，Nmap只对满足这个条件的主机进行操作系统检测。这样可以节约时间，特别是在使用-P0扫描多个主机时。该选项仅在使用-O或-A进行操作系统检测时起作用。
使用Nmap针对指定的目标进行操作系统检测。执行命令如下：
root@daxueba:~# nmap -P0 192.168.1.0/24 -O --osscan-limit
Starting Nmap 7.70 ( https://nmap.org ) at 2021-08-02 16:02 CST
Nmap scan report for 192.168.1.1 (192.168.1.1)
Host is up (0.00073s latency).
Not shown: 994 closed ports
PORT STATE SERVICE
21/tcp open ftp
80/tcp open http
445/tcp open microsoft-ds
5678/tcp open rrac
8080/tcp open http-proxy
52869/tcp open unknown
MAC Address: 70:85:40:53:E0:35 (Unknown)
Device type: general purpose
Running: Linux 3.X|4.X
OS CPE: cpe:/o:linux:linux_kernel:3 cpe:/o:linux:Linux_kernel:4
OS details: Linux 3.2 - 4.9 #操作系统详细信息
Network Distance: 1 hop
Nmap scan report for kdkdahjd61y369j (192.168.1.3)
Host is up (0.000085s latency).
All 1000 scanned ports on kdkdahjd61y369j (192.168.1.3) are filtered
MAC Address: 1C:6F:65:C8:4C:89 (Giga-byte Technology)
Nmap scan report for test-pc (192.168.1.5)
Host is up (0.00047s latency).
Not shown: 982 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
80/tcp open http
135/tcp open msrpc
139/tcp open netbios-ssn
443/tcp open https
445/tcp open microsoft-ds
902/tcp open iss-realsecure
912/tcp open apex-mesh
1433/tcp open ms-sql-s
2383/tcp open ms-olap4
5357/tcp open wsdapi
49152/tcp open unknown
49153/tcp open unknown
49154/tcp open unknown
49155/tcp open unknown
49157/tcp open unknown
49158/tcp open unknown
MAC Address: 00:0C:29:21:8C:96 (VMware)
Device type: general purpose
Running: Microsoft Windows 7|2008|8.1
OS CPE: cpe:/o:microsoft:windows_7::- cpe:/o:microsoft:windows_7::sp1
cpe:/o:microsoft:windows_server_2008::sp1 cpe:/o:microsoft:windows_server_
2008:r2 cpe:/o:microsoft:windows_8 cpe:/o:microsoft:windows_8.1
OS details: Microsoft Windows 7 SP0 - SP1, Windows Server 2008 SP1, Windows
Server 2008 R2, Windows 8, or Windows 8.1 Update 1 #操作系统详细信息
Network Distance: 1 hop
Nmap scan report for 192.168.1.6 (192.168.1.6)
Host is up (0.00057s latency).
Not shown: 977 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
23/tcp open telnet
25/tcp open ***tp
53/tcp open domain
80/tcp open http
111/tcp open rpcbind
139/tcp open netbios-ssn
445/tcp open microsoft-ds
512/tcp open exec
513/tcp open login
514/tcp open shell
1099/tcp open rmiregistry
1524/tcp open ingreslock
2049/tcp open nfs
2121/tcp open ccproxy-ftp
3306/tcp open mysql
5432/tcp open postgresql
5900/tcp open vnc
6000/tcp open X11
6667/tcp open irc
8009/tcp open ajp13
8180/tcp open unknown
MAC Address: 00:0C:29:3E:84:91 (VMware)
Device type: general purpose
Running: Linux 2.6.X
OS CPE: cpe:/o:linux:linux_kernel:2.6
OS details: Linux 2.6.9 - 2.6.33 #操作系统详细信息
Network Distance: 1 hop
Nmap scan report for kali (192.168.1.9)
Host is up (0.00093s latency).
All 1000 scanned ports on kali (192.168.1.9) are closed
MAC Address: 00:0C:29:6C:C4:92 (VMware)
Nmap scan report for daxueba (192.168.1.4)
Host is up (0.000010s latency).
All 1000 scanned ports on daxueba (192.168.1.4) are closed
OS detection performed. Please report any incorrect results at
https://nmap.org/submit/ .
Nmap done: 256 IP addresses (6 hosts up) scanned in 7.64 seconds
从以上输出信息可以看到，如果探测到目标主机上存在开放的端口，则推测出了其操作系统类型；如果目标主机上不存在开放的端口，则无法推测其操作系统类型。
（3）推测操作系统
当Nmap无法确定所探测的操作系统时，会尽可能地提供最相近的匹配。为了对目标系统推测得更准确，可以使用--osscan-guess或--fuzzy选项来实现。语法格式如下：
nmap -O --osscan-guess;--fuzzy [host]
其中，--osscan-guess;--fuzzy选项用于推测操作系统检测结果，将以百分比的方式给出对操作系统信息的猜测。当Nmap无法确定所检测的操作系统时，会尽可能地提供最相近的匹配。Nmap默认进行这种匹配，使用任意一个选项将使得Nmap的推测更加有效。
推测目标主机www.163.com的操作系统类型。执行命令如下：
root@daxueba:~# nmap -O --osscan-guess www.163.com
Starting Nmap 7.70 ( https://nmap.org ) at 2021-08-02 16:08 CST
Nmap scan report for www.163.com (124.163.204.105)
Host is up (0.015s latency).
Other addresses for www.163.com (not scanned): 2408:8726:5100::4f
rDNS record for 124.163.204.105: 105.204.163.124.in-addr.arpa
Not shown: 955 closed ports
PORT STATE SERVICE
80/tcp open http
81/tcp open hosts2-ns
82/tcp open xfer
84/tcp open ctf
88/tcp open kerberos-sec
135/tcp filtered msrpc
139/tcp filtered netbios-ssn
443/tcp open https
445/tcp filtered microsoft-ds
……省略部分内容
Device type: general purpose|firewall|media device|phone|broadband router security-misc
Running (JUST GUESSING): Linux 3.X|2.6.X|4.X (92%), IPCop 2.X (91%), Tiandy
embedded (91%), Google Android 5.X (90%), D-Link embedded (90%), Draytek
embedded (89%)
OS CPE: cpe:/o:linux:linux_kernel:3.2 cpe:/o:linux:linux_kernel:2.6.32
cpe:/o:ipcop:ipcop:2.0 cpe:/o:linux:linux_kernel:4.9 cpe:/o:google:
android:5.0.1 cpe:/h:dlink:dsl-2890al cpe:/o:linux:linux_kernel:2.6.25.20
cpe:/h:draytek:vigor_2960
Aggressive OS guesses: Linux 3.2 (92%), IPCop 2.0 (Linux 2.6.32) (91%), Linux
2.6.32 (91%), Linux 4.9 (91%), Tiandy NVR (91%), Android 5.0.1 (90%), Linux
3.18 (90%), D-Link DSL-2890AL ADSL router (90%), OpenWrt Kamikaze 8.09 (Linux
2.6.25.20) (90%), Linux 2.6.18 - 2.6.22 (89%)
No exact OS matches for host (test conditions non-ideal).
Network Distance: 9 hops
OS detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 5.65 seconds
以上输出信息显示了目标主机可能使用的操作系统列表。这里列举可能的系统类型，并以百分比形式显示每种类型的概率。从输出结果显示的比例中可以看到，目标主机的操作系统类型可能是Linux 3.2。
2. Ping系统识别
Ping是Windows、UNIX和Linux系统下的一个命令，使用该命令可以检查 是否连通。如果目标主机正确响应的话，在响应包中将包括有对应的TTL值。TTL是Time To Live（生成时间）的缩写，该字段指定IP包被路由器丢弃之前允许通过的更大网段数量。其中，不同操作系统类型响应的TTL值不同。所以我们可以使用Ping命令进行系统识别。下面介绍使用Ping命令实施系统识别的 。
为了能够快速地确定一个目标系统的类型，下面给出了一个操作系统初始TTL值列表，如表1所示。
表1 各个操作系统的初始TTL值
使用Ping测试目标主机（192.168.33.152）的操作系统类型（该目标主机的操作系统类型为Linux）。执行命令如下：
root@daxueba:~# ping 192.168.33.152
PING 192.168.33.152 (192.168.33.152) 56(84) bytes of data.
64 bytes from 192.168.33.152: ICMP_seq=1 ttl=64 time=0.242 ms
64 bytes from 192.168.33.152: icmp_seq=2 ttl=64 time=0.431 ms
64 bytes from 192.168.33.152: icmp_seq=3 ttl=64 time=0.431 ms
64 bytes from 192.168.33.152: icmp_seq=4 ttl=64 time=0.440 ms
从输出的信息可以看到，响应包中的TTL值为64。根据前面列出的表格6.1，可以看到这是Linux操作系统。
使用Ping测试目标主机（192.168.33.229）的操作系统类型（该目标主机的操作系统类型为Windows 7）。执行命令如下：
root@daxueba:~# ping 192.168.33.229
PING 192.168.33.229 (192.168.33.229) 56(84) bytes of data.
64 bytes from 192.168.33.229: icmp_seq=1 ttl=128 time=1.57 ms
64 bytes from 192.168.33.229: icmp_seq=2 ttl=128 time=1.01 ms
64 bytes from 192.168.33.229: icmp_seq=3 ttl=128 time=0.276 ms
64 bytes from 192.168.33.229: icmp_seq=4 ttl=128 time=1.52 ms
从输出的信息可以看到，该响应包中的TTL值为128。由此可以说明，这是一个Windows操作系统。
3. xProbe2系统识别
xProbe2是一款远程主机操作系统探查工具，该工具通过icmp协议来获得指纹。xProbe2通过模糊矩阵统计分析主动探测数据报文对应的ICMP数据报特征，进而探测得到远端操作系统的类型。下面介绍使用xProbe2工具实施操作系统指纹识别的 。使用xProbe2工具实施系统识别的语法格式如下：
xProbe2 [host]
使用xProbe2工具对目标主机www.163.com实施系统识别。执行命令如下：
root@Kali:~# xprobe2 www.163.com
Xprobe2 v.0.3 Copyright (c) 2002-2005 fyodor@o0o.nu, ofir@sys-security.com,meder@o0o.nu
[+] Target is www.163.com #目标地址
[+] Loading modules. #正在加载模块
[+] Following modules are loaded: #被加载的模块
[x] [1] ping:icmp_ping - ICMP echo discovery module
[x] [2] ping:tcp_ping - TCP-based ping discovery module
[x] [3] ping:udp_ping - UDP-based ping discovery module
[x] [4] infogather:ttl_calc - TCP and UDP based TTL distance calculation
[x] [5] infogather:portscan - TCP and UDP PortScanner
[x] [6] fingerprint:icmp_echo - ICMP Echo request fingerprinting module
[x] [7] fingerprint:icmp_tstamp - ICMP Timestamp request fingerprinting module
[x] [8] fingerprint:icmp_amask - ICMP Address mask request fingerprinting module
[x] [9] fingerprint:icmp_port_unreach - ICMP port unreachable fingerprinting module
[x] [10] fingerprint:tcp_hshake - TCP Handshake fingerprinting module
[x] [11] fingerprint:tcp_rst - TCP RST fingerprinting module
[x] [12] fingerprint:***b - ***B fingerprinting module
[x] [13] fingerprint:snmp - SNMPv2c fingerprinting module
[+] 13 modules registered
[+] Initializing scan engine #初始化扫描引擎
[+] Running scan engine #正在实施扫描
[-] ping:tcp_ping module: no closed/open TCP ports known on 124.163.204.105.
Module test failed
[-] ping:udp_ping module: no closed/open UDP ports known on 124.163.204.105.
Module test failed
[-] No distance calculation. 124.163.204.105 appears to be dead or no ports known
[+] Host: 124.163.204.105 is up (Guess probability: 50%)#主机是活动的
[+] Target: 124.163.204.105 is alive. Round-Trip Time: 0.01503 sec
[+] Selected safe Round-Trip Time value is: 0.03007 sec
[-] fingerprint:tcp_hshake Module execution aborted (no open TCP ports known)
[-] fingerprint:***b need either TCP port 139 or 445 to run
[-] fingerprint:snmp: need UDP port 161 open
[+] Primary guess: #主要猜测
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.19" (Guess
probability: 100%)
[+] Other guesses: #其他猜测
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.20" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.21" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.22" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.23" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.24" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.25" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.26" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.27" (Guess
probability: 100%)
[+] Host 124.163.204.105 Running OS: "Linux Kernel 2.4.28" (Guess
probability: 100%)
[+] Cleaning up scan engine
[+] Modules deinitialized
[+] Execution completed.
从输出的信息中可以看到，通过xProbe2工具成功解析出了目标主机的IP地址，并且识别出了其操作系统类型。其中，目标主机的IP地址为124.163.204.105，操作系统类型为Linux，内核版本在2.4.19～2.4.28之间。
xProbe2工具在NAT模式下存在Bug，扫描后会出现HP的位置或者直接报错，具体如下：
root@Kali:~# xprobe2 www.163.com
Xprobe2 v.0.3 Copyright (c) 2002-2005 fyodor@o0o.nu, ofir@sys-security.com,meder@o0o.nu
[+] Target is www.163.com
[+] Loading modules.
[+] Following modules are loaded:
[x] [1] ping:icmp_ping - ICMP echo discovery module
[x] [2] ping:tcp_ping - TCP-based ping discovery module
[x] [3] ping:udp_ping - UDP-based ping discovery module
[x] [4] infogather:ttl_calc - TCP and UDP based TTL distance calculation
[x] [5] infogather:portscan - TCP and UDP PortScanner
[x] [6] fingerprint:icmp_echo - ICMP Echo request fingerprinting module
[x] [7] fingerprint:icmp_tstamp - ICMP Timestamp request fingerprinting module
[x] [8] fingerprint:icmp_amask - ICMP Address mask request fingerprinting module
[x] [9] fingerprint:icmp_port_unreach - ICMP port unreachable
fingerprinting module
[x] [10] fingerprint:tcp_hshake - TCP Handshake fingerprinting module
[x] [11] fingerprint:tcp_rst - TCP RST fingerprinting module
[x] [12] fingerprint:***b - ***B fingerprinting module
[x] [13] fingerprint:snmp - SNMPv2c fingerprinting module
[+] 13 modules registered
[+] Initializing scan engine
[+] Running scan engine
[-] ping:tcp_ping module: no closed/open TCP ports known on 124.163.204.105.
Module test failed
[-] ping:udp_ping module: no closed/open UDP ports known on 124.163.204.105.
Module test failed
[-] No distance calculation. 124.163.204.105 appears to be dead or no ports known
[+] Host: 124.163.204.105 is up (Guess probability: 50%)
[+] Target: 124.163.204.105 is alive. Round-Trip Time: 0.01528 sec
[+] Selected safe Round-Trip Time value is: 0.03056 sec
[-] fingerprint:tcp_hshake Module execution aborted (no open TCP ports known)
[-] fingerprint:***b need either TCP port 139 or 445 to run
[-] fingerprint:snmp: need UDP port 161 open
[+] Primary guess:
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.07.02 EEPROM G.07.17" (Guess probability: 83%)
[+] Other guesses:
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.07.02 EEPROM G.07.20" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.07.02 EEPROM G.08.04" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.07.19 EEPROM G.07.20" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.07.19 EEPROM G.08.03" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.07.19 EEPROM G.08.04" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.08.08 EEPROM G.08.04" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.08.21 EEPROM G.08.21" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM H.07.15 EEPROM H.08.20" (Guess probability: 83%)
[+] Host 124.163.204.105 Running OS: "HP JetDirect ROM G.06.00 EEPROM G.06.00" (Guess probability: 83%)
[+] Cleaning up scan engine
[+] Modules deinitialized
[+] Execution completed.
从以上输出的信息中可以看到，执行结果出错了（HP JetDirect ROM G.07.02 EEPROM G.07.17）。
在Kali Linux的新版本中，xProbe2工具运行后，测试的结果中操作系统类型显示为乱码。具体如下：
[+] Primary guess:
[+] Host 192.168.1.8 Running OS: ????U (Guess probability: 100%)
[+] Other guesses:
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Host 192.168.1.8 Running OS: ?????U (Guess probability: 100%)
[+] Cleaning up scan engine
[+] Modules deinitialized
[+] Execution completed.
4. p0f系统识别
p0f是一款用于识别远程操作系统的工具，该工具与前面介绍的其他工具不同，它是一个完全被动地识别操作系统指纹信息的工具，不会直接作用于目标系统。当启动该工具后，即可监听 中的所有数据包。通过分析监听到的数据包，即可找出与系统相关的信息。下面介绍使用p0f工具来实施操作系统指纹识别的 。
使用p0f工具对目标主机实施系统识别。执行命令如下：
1）启动p0f工具。执行命令如下：
root@daxueba:~# p0f
--- p0f 3.09b by Michal Zalewski <lcamtuf@coredump.cx> ---
[+] Closed 1 file descriptor.
[+] Loaded 322 signatures from '/etc/p0f/p0f.fp'.
[+] Intercepting traffic on default interface 'eth0'.
[+] Default packet filtering configured [+VLAN].
[+] Entered main event loop.
从以上输出信息中可以看到，p0f工具仅显示了几行信息，无法捕获到其他信息。但是，p0f会一直处于监听状态。
2）此时，当有其他主机在 中产生数据流量的话，将会被p0f工具监听到。例如，在另一台主机上通过浏览器访问一个站点，然后返回到p0f所在的终端，将看到如下信息：
.-[ 192.168.1.4/38934 -> 65.200.22.161/80 (http request) ]- #HTTP请求
| client = 192.168.1.4/38934 #客户端
| app = Safari 5.1-6 #应用
| lang = English #语言
| params = dishonest #程序
| raw_sig = 1:Host,User-Agent,Accept=[*/*],Accept-Language=[en-US,en;q=0.5],Accept-Encoding=[gzip, deflate],?Cache-Control,Pragma=[no-cache],Connection=[keep-alive]:Accept-Charset,Keep-Alive:Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0 #数据内容
----
.-[ 192.168.1.4/38934 -> 65.200.22.161/80 (uptime) ]-
| server = 65.200.22.161/80 #服务器
| uptime = 30 days 0 hrs 22 min (modulo 45 days) #时间
| raw_freq = 1048.46 Hz #频率
----
.-[ 192.168.1.4/38934 -> 65.200.22.161/80 (http response) ]-
| server = 65.200.22.161/80
| app = ???
| lang = none
| params = none
| raw_sig = 1:Content-Type,?Content-Length,?Last-Modified,?ETag,Accept-Ranges=[bytes],Server,X-Amz-Cf-Id=[X7nIiIIBBeQOTeLSHRH3U4***6xDHfgwK1EaKf8bdyemtuUoR8JK9Xg==],?Cache-Control,Date,Connection=[keep-alive]:Keep-Alive:AmazonS3
----
.-[ 192.168.1.4/32854 -> 52.27.184.151/443 (syn) ]-
| client = 192.168.1.4/32854
| os = Linux 3.11 and newer
| dist = 0
| params = none
| raw_sig = 4:64+0:0:1460:mss*20,7:mss,sok,ts,nop,ws:df,id+:0
----
.-[ 192.168.1.4/32854 -> 52.27.184.151/443 (host change) ]-
| client = 192.168.1.4/32854
| reason = tstamp port
| raw_hits = 0,1,1,1
----
.-[ 192.168.1.4/32854 -> 52.27.184.151/443 (mtu) ]-
| client = 192.168.1.4/32854
| link = Ethernet or modem
| raw_mtu = 1500
----
.-[ 192.168.1.4/32856 -> 52.27.184.151/443 (syn) ]-
| client = 192.168.1.4/32856
| os = Linux 3.11 and newer
| dist = 0
| params = none
| raw_sig = 4:64+0:0:1460:mss*20,7:mss,sok,ts,nop,ws:df,id+:0
----
以上输出的信息，就是执行监听到客户端访问的数据信息。从以上输出的信息可以看到，探测到客户端的操作系统类型为Linux 3.11或更新的内核版本。
