nmap(1) - Network exploration tool and security / port scanner
nmap [Scan Type...] [Options] {target specification}
-iL inputfilename (Input from list) .
    Reads target specifications from inputfilename. Passing a huge list of hosts is often awkward on the
    command line, yet it is a common desire. For example, your DHCP server might export a list of 10,000
    current leases that you wish to scan. Or maybe you want to scan all IP addresses except for those to
    locate hosts using unauthorized static IP addresses. Simply generate the list of hosts to scan and
    pass that filename to Nmap as an argument to the -iL option. Entries can be in any of the formats
    accepted by Nmap on the command line (IP address, hostname, CIDR, IPv6, or octet ranges). Each entry
    must be separated by one or more spaces, tabs, or newlines. You can specify a hyphen (-) as the
    filename if you want Nmap to read hosts from standard input rather than an actual file.

    The input file may contain comments that start with # and extend to the end of the line.
-iR num hosts (Choose random targets) .
    For Internet-wide surveys and other research, you may want to choose targets at random. The num hosts
    argument tells Nmap how many IPs to generate. Undesirable IPs such as those in certain private,
    multicast, or unallocated address ranges are automatically skipped. The argument 0 can be specified
    for a never-ending scan. Keep in mind that some network administrators bristle at unauthorized scans
    of their networks and may complain. Use this option at your own risk! If you find yourself really
    bored one rainy afternoon, try the command nmap -sS -PS80 -iR 0 -p 80 to locate random web servers
    for browsing.
--exclude host1[,host2[,...]] (Exclude hosts/networks) .
    Specifies a comma-separated list of targets to be excluded from the scan even if they are part of the
    overall network range you specify. The list you pass in uses normal Nmap syntax, so it can include
    hostnames, CIDR netblocks, octet ranges, etc. This can be useful when the network you wish to scan
    includes untouchable mission-critical servers, systems that are known to react adversely to port
    scans, or subnets administered by other people.
--excludefile exclude_file (Exclude list from file) .
    This offers the same functionality as the --exclude option, except that the excluded targets are
    provided in a newline, space, or tab delimited exclude_file rather than on the command line.

    The exclude file may contain comments that start with # and extend to the end of the line.
-sL (List Scan) .
    The list scan is a degenerate form of host discovery that simply lists each host of the network(s)
    specified, without sending any packets to the target hosts. By default, Nmap still does reverse-DNS
    resolution on the hosts to learn their names. It is often surprising how much useful information
    simple hostnames give out. For example, fw.chi is the name of one company´s Chicago firewall.  Nmap
    also reports the total number of IP addresses at the end. The list scan is a good sanity check to
    ensure that you have proper IP addresses for your targets. If the hosts sport domain names you do not
    recognize, it is worth investigating further to prevent scanning the wrong company´s network.

    Since the idea is to simply print a list of target hosts, options for higher level functionality such
    as port scanning, OS detection, or ping scanning cannot be combined with this. If you wish to disable
    ping scanning while still performing such higher level functionality, read up on the -PN (skip ping)
-sP (Skip port scan) .
    This option tells Nmap not to do a port scan after host discovery, and only print out the available
    hosts that responded to the scan. This is often known as a “ping scan”, but you can also request that
    traceroute and NSE host scripts be run. This is by default one step more intrusive than the list
    scan, and can often be used for the same purposes. It allows light reconnaissance of a target network
    without attracting much attention. Knowing how many hosts are up is more valuable to attackers than
    the list provided by list scan of every single IP and host name.

    Systems administrators often find this option valuable as well. It can easily be used to count
    available machines on a network or monitor server availability. This is often called a ping sweep,
    and is more reliable than pinging the broadcast address because many hosts do not reply to broadcast

    The -sP option sends an ICMP echo request, TCP SYN to port 443, TCP ACK to port 80, and an ICMP
    timestamp request by default. When executed by an unprivileged user, only SYN packets are sent (using
    a connect call) to ports 80 and 443 on the target. When a privileged user tries to scan targets on a
    local ethernet network, ARP requests are used unless --send-ip was specified. The -sP option can be
    combined with any of the discovery probe types (the -P* options, excluding -PN) for greater
    flexibility. If any of those probe type and port number options are used, the default probes are
    overridden. When strict firewalls are in place between the source host running Nmap and the target
    network, using those advanced techniques is recommended. Otherwise hosts could be missed when the
    firewall drops probes or their responses.
-PN (No ping) .
    This option skips the Nmap discovery stage altogether. Normally, Nmap uses this stage to determine
    active machines for heavier scanning. By default, Nmap only performs heavy probing such as port
    scans, version detection, or OS detection against hosts that are found to be up. Disabling host
    discovery with -PN causes Nmap to attempt the requested scanning functions against every target IP
    address specified. So if a class B sized target address space (/16) is specified on the command line,
    all 65,536 IP addresses are scanned. Proper host discovery is skipped as with the list scan, but
    instead of stopping and printing the target list, Nmap continues to perform requested functions as if
    each target IP is active. To skip ping scan and port scan, while still allowing NSE to run, use the
    two options -PN -sP together.

    For machines on a local ethernet network, ARP scanning will still be performed (unless --send-ip is
    specified) because Nmap needs MAC addresses to further scan target hosts. This option flag used to be
    P0 (uses zero), but was renamed to avoid confusion with protocol ping´s PO (uses the letter O) flag.
-PS port list (TCP SYN Ping) .
    This option sends an empty TCP packet with the SYN flag set. The default destination port is 80
    (configurable at compile time by changing DEFAULT_TCP_PROBE_PORT_SPEC in nmap.h).  Alternate ports
    can be specified as a parameter. The syntax is the same as for the -p except that port type
    specifiers like T: are not allowed. Examples are -PS22 and -PS22-25,80,113,1050,35000. Note that
    there can be no space between -PS and the port list. If multiple probes are specified they will be
    sent in parallel.

    The SYN flag suggests to the remote system that you are attempting to establish a connection.
    Normally the destination port will be closed, and a RST (reset) packet sent back. If the port happens
    to be open, the target will take the second step of a TCP three-way-handshake.  by responding with a
    SYN/ACK TCP packet. The machine running Nmap then tears down the nascent connection by responding
    with a RST rather than sending an ACK packet which would complete the three-way-handshake and
    establish a full connection. The RST packet is sent by the kernel of the machine running Nmap in
    response to the unexpected SYN/ACK, not by Nmap itself.

    Nmap does not care whether the port is open or closed. Either the RST or SYN/ACK response discussed
    previously tell Nmap that the host is available and responsive.

    On Unix boxes, only the privileged user root.  is generally able to send and receive raw TCP
    packets..  For unprivileged users, a workaround is automatically employed.  whereby the connect
    system call is initiated against each target port. This has the effect of sending a SYN packet to the
    target host, in an attempt to establish a connection. If connect returns with a quick success or an
    ECONNREFUSED failure, the underlying TCP stack must have received a SYN/ACK or RST and the host is
    marked available. If the connection attempt is left hanging until a timeout is reached, the host is
    marked as down. This workaround is also used for IPv6 connections, as raw IPv6 packet building
    support is not yet available in Nmap..
-PA port list (TCP ACK Ping) .
    The TCP ACK ping is quite similar to the just-discussed SYN ping. The difference, as you could likely
    guess, is that the TCP ACK flag is set instead of the SYN flag. Such an ACK packet purports to be
    acknowledging data over an established TCP connection, but no such connection exists. So remote hosts
    should always respond with a RST packet, disclosing their existence in the process.

    The -PA option uses the same default port as the SYN probe (80) and can also take a list of
    destination ports in the same format. If an unprivileged user tries this, or an IPv6 target is
    specified, the connect workaround discussed previously is used. This workaround is imperfect because
    connect is actually sending a SYN packet rather than an ACK.

    The reason for offering both SYN and ACK ping probes is to maximize the chances of bypassing
    firewalls. Many administrators configure routers and other simple firewalls to block incoming SYN
    packets except for those destined for public services like the company web site or mail server. This
    prevents other incoming connections to the organization, while allowing users to make unobstructed
    outgoing connections to the Internet. This non-stateful approach takes up few resources on the
    firewall/router and is widely supported by hardware and software filters. The Linux
    Netfilter/iptables.  firewall software offers the --syn convenience option to implement this
    stateless approach. When stateless firewall rules such as this are in place, SYN ping probes (-PS)
    are likely to be blocked when sent to closed target ports. In such cases, the ACK probe shines as it
    cuts right through these rules.

    Another common type of firewall uses stateful rules that drop unexpected packets. This feature was
    initially found mostly on high-end firewalls, though it has become much more common over the years.
    The Linux Netfilter/iptables system supports this through the --state option, which categorizes
    packets based on connection state. A SYN probe is more likely to work against such a system, as
    unexpected ACK packets are generally recognized as bogus and dropped. A solution to this quandary is
    to send both SYN and ACK probes by specifying -PS and -PA.
-PU port list (UDP Ping) .
    Another host discovery option is the UDP ping, which sends a UDP packet to the given ports. For most
    ports, the packet will be empty, though for a few a protocol-specific payload will be sent that is
    more likely to get a response..  See the file payload.cc.  for exactly which ports have payloads. The
    --data-length.  option sends a fixed-length random payload for all ports.

    The port list takes the same format as with the previously discussed -PS and -PA options. If no ports
    are specified, the default is 40125. This default can be configured at compile-time by changing
    DEFAULT_UDP_PROBE_PORT_SPEC.  in nmap.h..  A highly uncommon port is used by default because sending
    to open ports is often undesirable for this particular scan type.

    Upon hitting a closed port on the target machine, the UDP probe should elicit an ICMP port
    unreachable packet in return. This signifies to Nmap that the machine is up and available. Many other
    types of ICMP errors, such as host/network unreachables or TTL exceeded are indicative of a down or
    unreachable host. A lack of response is also interpreted this way. If an open port is reached, most
    services simply ignore the empty packet and fail to return any response. This is why the default
    probe port is 40125, which is highly unlikely to be in use. A few services, such as the Character
    Generator (chargen) protocol, will respond to an empty UDP packet, and thus disclose to Nmap that the
    machine is available.

    The primary advantage of this scan type is that it bypasses firewalls and filters that only screen
    TCP. For example, I once owned a Linksys BEFW11S4 wireless broadband router. The external interface
    of this device filtered all TCP ports by default, but UDP probes would still elicit port unreachable
    messages and thus give away the device.
-PY port list (SCTP INIT Ping) .
    This option sends an SCTP packet containing a minimal INIT chunk. The default destination port is 80
    (configurable at compile time by changing DEFAULT_SCTP_PROBE_PORT_SPEC in nmap.h).  Alternate ports
    can be specified as a parameter. The syntax is the same as for the -p except that port type
    specifiers like S: are not allowed. Examples are -PY22 and -PY22,80,179,5060. Note that there can be
    no space between -PY and the port list. If multiple probes are specified they will be sent in

    The INIT chunk suggests to the remote system that you are attempting to establish an association.
    Normally the destination port will be closed, and an ABORT chunk will be sent back. If the port
    happens to be open, the target will take the second step of an SCTP four-way-handshake.  by
    responding with an INIT-ACK chunk. If the machine running Nmap has a functional SCTP stack, then it
    tears down the nascent association by responding with an ABORT chunk rather than sending a
    COOKIE-ECHO chunk which would be the next step in the four-way-handshake. The ABORT packet is sent by
    the kernel of the machine running Nmap in response to the unexpected INIT-ACK, not by Nmap itself.

    Nmap does not care whether the port is open or closed. Either the ABORT or INIT-ACK response
    discussed previously tell Nmap that the host is available and responsive.

    On Unix boxes, only the privileged user root.  is generally able to send and receive raw SCTP
    packets..  Using SCTP INIT Pings is currently not possible for unprivileged users..  The same
    limitation applies to IPv6, which is currently not supported for SCTP INIT Ping..
-PE; -PP; -PM (ICMP Ping Types) .
    In addition to the unusual TCP, UDP and SCTP host discovery types discussed previously, Nmap can send
    the standard packets sent by the ubiquitous ping program. Nmap sends an ICMP type 8 (echo request)
    packet to the target IP addresses, expecting a type 0 (echo reply) in return from available hosts..
    Unfortunately for network explorers, many hosts and firewalls now block these packets, rather than
    responding as required by RFC 1122[2]. For this reason, ICMP-only scans are rarely reliable enough
    against unknown targets over the Internet. But for system administrators monitoring an internal
    network, they can be a practical and efficient approach. Use the -PE option to enable this echo
    request behavior.

    While echo request is the standard ICMP ping query, Nmap does not stop there. The ICMP standards (RFC
    792[3].  and RFC 950[4].  “a host SHOULD NOT implement these messages”. Timestamp and address mask
    queries can be sent with the -PP and -PM options, respectively. A timestamp reply (ICMP code 14) or
    address mask reply (code 18) discloses that the host is available. These two queries can be valuable
    when administrators specifically block echo request packets while forgetting that other ICMP queries
    can be used for the same purpose.
-PO protocol list (IP Protocol Ping) .
    The newest host discovery option is the IP protocol ping, which sends IP packets with the specified
    protocol number set in their IP header. The protocol list takes the same format as do port lists in
    the previously discussed TCP, UDP and SCTP host discovery options. If no protocols are specified, the
    default is to send multiple IP packets for ICMP (protocol 1), IGMP (protocol 2), and IP-in-IP
    (protocol 4). The default protocols can be configured at compile-time by changing
    DEFAULT_PROTO_PROBE_PORT_SPEC.  in nmap.h. Note that for the ICMP, IGMP, TCP (protocol 6), UDP
    (protocol 17) and SCTP (protocol 132), the packets are sent with the proper protocol headers.  while
    other protocols are sent with no additional data beyond the IP header (unless the --data-length.
    option is specified).

    This host discovery method looks for either responses using the same protocol as a probe, or ICMP
    protocol unreachable messages which signify that the given protocol isn´t supported on the
    destination host. Either type of response signifies that the target host is alive.
-PR (ARP Ping) .
    One of the most common Nmap usage scenarios is to scan an ethernet LAN. On most LANs, especially
    those using private address ranges specified by RFC 1918[5], the vast majority of IP addresses are
    unused at any given time. When Nmap tries to send a raw IP packet such as an ICMP echo request, the
    operating system must determine the destination hardware (ARP) address corresponding to the target IP
    so that it can properly address the ethernet frame. This is often slow and problematic, since
    operating systems weren´t written with the expectation that they would need to do millions of ARP
    requests against unavailable hosts in a short time period.

    ARP scan puts Nmap and its optimized algorithms in charge of ARP requests. And if it gets a response
    back, Nmap doesn´t even need to worry about the IP-based ping packets since it already knows the host
    is up. This makes ARP scan much faster and more reliable than IP-based scans. So it is done by
    default when scanning ethernet hosts that Nmap detects are on a local ethernet network. Even if
    different ping types (such as -PE or -PS) are specified, Nmap uses ARP instead for any of the targets
    which are on the same LAN. If you absolutely don´t want to do an ARP scan, specify --send-ip.
--traceroute (Trace path to host) .
    Traceroutes are performed post-scan using information from the scan results to determine the port and
    protocol most likely to reach the target. It works with all scan types except connect scans (-sT) and
    idle scans (-sI). All traces use Nmap´s dynamic timing model and are performed in parallel.

    Traceroute works by sending packets with a low TTL (time-to-live) in an attempt to elicit ICMP Time
    Exceeded messages from intermediate hops between the scanner and the target host. Standard traceroute
    implementations start with a TTL of 1 and increment the TTL until the destination host is reached.
    Nmap´s traceroute starts with a high TTL and then decrements the TTL until it reaches zero. Doing it
    backwards lets Nmap employ clever caching algorithms to speed up traces over multiple hosts. On
    average Nmap sends 5–10 fewer packets per host, depending on network conditions. If a single subnet
    is being scanned (i.e. Nmap may only have to send a single packet to most hosts.
-n (No DNS resolution) .
    Tells Nmap to never do reverse DNS resolution on the active IP addresses it finds. Since DNS can be
    slow even with Nmap´s built-in parallel stub resolver, this option can slash scanning times.
-R (DNS resolution for all targets) .
    Tells Nmap to always do reverse DNS resolution on the target IP addresses. Normally reverse DNS is
    only performed against responsive (online) hosts.
--system-dns (Use system DNS resolver) .
    By default, Nmap resolves IP addresses by sending queries directly to the name servers configured on
    your host and then listening for responses. Many requests (often dozens) are performed in parallel to
    improve performance. Specify this option to use your system resolver instead (one IP at a time via
    the getnameinfo call). This is slower and rarely useful unless you find a bug in the Nmap parallel
    resolver (please let us know if you do). The system resolver is always used for IPv6 scans.
--dns-servers server1[,server2[,...]]  (Servers to use for reverse DNS queries) .
    By default, Nmap determines your DNS servers (for rDNS resolution) from your resolv.conf file (Unix)
    or the Registry (Win32). Alternatively, you may use this option to specify alternate servers. This
    option is not honored if you are using --system-dns or an IPv6 scan. Using multiple DNS servers is
    often faster, especially if you choose authoritative servers for your target IP space. This option
    can also improve stealth, as your requests can be bounced off just about any recursive DNS server on
    the Internet.

    This option also comes in handy when scanning private networks. Sometimes only a few name servers
    provide proper rDNS information, and you may not even know where they are. You can scan the network
    for port 53 (perhaps with version detection), then try Nmap list scans (-sL) specifying each name
    server one at a time with --dns-servers until you find one which works.
-sS (TCP SYN scan) .
    SYN scan is the default and most popular scan option for good reasons. It can be performed quickly,
    scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. SYN
    scan is relatively unobtrusive and stealthy, since it never completes TCP connections. It also works
    against any compliant TCP stack rather than depending on idiosyncrasies of specific platforms as
    Nmap´s FIN/NULL/Xmas, Maimon and idle scans do. It also allows clear, reliable differentiation
    between the open, closed, and filtered states.

    This technique is often referred to as half-open scanning, because you don´t open a full TCP
    connection. You send a SYN packet, as if you are going to open a real connection and then wait for a
    response. A SYN/ACK indicates the port is listening (open), while a RST (reset) is indicative of a
    non-listener. If no response is received after several retransmissions, the port is marked as
    filtered. The port is also marked filtered if an ICMP unreachable error (type 3, code 1, 2, 3, 9, 10,
    or 13) is received.
-sT (TCP connect scan) .
    TCP connect scan is the default TCP scan type when SYN scan is not an option. This is the case when a
    user does not have raw packet privileges or is scanning IPv6 networks. Instead of writing raw packets
    as most other scan types do, Nmap asks the underlying operating system to establish a connection with
    the target machine and port by issuing the connect system call. This is the same high-level system
    call that web browsers, P2P clients, and most other network-enabled applications use to establish a
    connection. It is part of a programming interface known as the Berkeley Sockets API. Rather than read
    raw packet responses off the wire, Nmap uses this API to obtain status information on each connection

    When SYN scan is available, it is usually a better choice. Nmap has less control over the high level
    connect call than with raw packets, making it less efficient. The system call completes connections
    to open target ports rather than performing the half-open reset that SYN scan does. Not only does
    this take longer and require more packets to obtain the same information, but target machines are
    more likely to log the connection. A decent IDS will catch either, but most machines have no such
    alarm system. Many services on your average Unix system will add a note to syslog, and sometimes a
    cryptic error message, when Nmap connects and then closes the connection without sending data. Truly
    pathetic services crash when this happens, though that is uncommon. An administrator who sees a bunch
    of connection attempts in her logs from a single system should know that she has been connect
-sU (UDP scans) .
    While most popular services on the Internet run over the TCP protocol, UDP[6] services are widely
    deployed. DNS, SNMP, and DHCP (registered ports 53, 161/162, and 67/68) are three of the most common.
    Because UDP scanning is generally slower and more difficult than TCP, some security auditors ignore
    these ports. This is a mistake, as exploitable UDP services are quite common and attackers certainly
    don´t ignore the whole protocol. Fortunately, Nmap can help inventory UDP ports.

    UDP scan is activated with the -sU option. It can be combined with a TCP scan type such as SYN scan
    (-sS) to check both protocols during the same run.

    UDP scan works by sending a UDP packet to every targeted port. For some common ports such as 53 and
    161, a protocol-specific payload is sent, but for most ports the packet is empty..  The --data-length
    option can be used to send a fixed-length random payload to every port. If an ICMP port unreachable
    error (type 3, code 3) is returned, the port is closed. Other ICMP unreachable errors (type 3, codes
    1, 2, 9, 10, or 13) mark the port as filtered. Occasionally, a service will respond with a UDP
    packet, proving that it is open. If no response is received after retransmissions, the port is
    classified as open|filtered. This means that the port could be open, or perhaps packet filters are
    blocking the communication. Version detection (-sV) can be used to help differentiate the truly open
    ports from the filtered ones.

    A big challenge with UDP scanning is doing it quickly. Open and filtered ports rarely send any
    response, leaving Nmap to time out and then conduct retransmissions just in case the probe or
    response were lost. Closed ports are often an even bigger problem. They usually send back an ICMP
    port unreachable error. But unlike the RST packets sent by closed TCP ports in response to a SYN or
    connect scan, many hosts rate limit.  ICMP port unreachable messages by default. Linux and Solaris
    are particularly strict about this. For example, the Linux 2.4.20 kernel limits destination
    unreachable messages to one per second (in net/ipv4/icmp.c).

    Nmap detects rate limiting and slows down accordingly to avoid flooding the network with useless
    packets that the target machine will drop. Unfortunately, a Linux-style limit of one packet per
    second makes a 65,536-port scan take more than 18 hours. Ideas for speeding your UDP scans up include
    scanning more hosts in parallel, doing a quick scan of just the popular ports first, scanning from
    behind the firewall, and using --host-timeout to skip slow hosts.
-sY (SCTP INIT scan) .

    SCTP[7] is a relatively new alternative to the TCP and UDP protocols, combining most characteristics
    of TCP and UDP, and also adding new features like multi-homing and multi-streaming. It is mostly
    being used for SS7/SIGTRAN related services but has the potential to be used for other applications
    as well. SCTP INIT scan is the SCTP equivalent of a TCP SYN scan. It can be performed quickly,
    scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. Like
    SYN scan, INIT scan is relatively unobtrusive and stealthy, since it never completes SCTP
    associations. It also allows clear, reliable differentiation between the open, closed, and filtered

    This technique is often referred to as half-open scanning, because you don´t open a full SCTP
    association. You send an INIT chunk, as if you are going to open a real association and then wait for
    a response. An INIT-ACK chunk indicates the port is listening (open), while an ABORT chunk is
    indicative of a non-listener. If no response is received after several retransmissions, the port is
    marked as filtered. The port is also marked filtered if an ICMP unreachable error (type 3, code 1, 2,
    3, 9, 10, or 13) is received.
-sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) .
    These three scan types (even more are possible with the --scanflags option described in the next
    section) exploit a subtle loophole in the TCP RFC[8] to differentiate between open and closed ports.
    Page 65 of RFC 793 says that “if the [destination] port state is CLOSED .... an incoming segment not
    containing a RST causes a RST to be sent in response.”  Then the next page discusses packets sent to
    open ports without the SYN, RST, or ACK bits set, stating that: “you are unlikely to get here, but if
    you do, drop the segment, and return.”

    When scanning systems compliant with this RFC text, any packet not containing SYN, RST, or ACK bits
    will result in a returned RST if the port is closed and no response at all if the port is open. As
    long as none of those three bits are included, any combination of the other three (FIN, PSH, and URG)
    are OK. Nmap exploits this with three scan types:

    Null scan (-sN)
        Does not set any bits (TCP flag header is 0)

    FIN scan (-sF)
        Sets just the TCP FIN bit.

    Xmas scan (-sX)
        Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree.

    These three scan types are exactly the same in behavior except for the TCP flags set in probe
    packets. If a RST packet is received, the port is considered closed, while no response means it is
    open|filtered. The port is marked filtered if an ICMP unreachable error (type 3, code 1, 2, 3, 9, 10,
    or 13) is received.

    The key advantage to these scan types is that they can sneak through certain non-stateful firewalls
    and packet filtering routers. Another advantage is that these scan types are a little more stealthy
    than even a SYN scan. Don´t count on this though—most modern IDS products can be configured to detect
    them. The big downside is that not all systems follow RFC 793 to the letter. A number of systems send
    RST responses to the probes regardless of whether the port is open or not. This causes all of the
    ports to be labeled closed. Major operating systems that do this are Microsoft Windows, many Cisco
    devices, BSDI, and IBM OS/400. This scan does work against most Unix-based systems though. Another
    downside of these scans is that they can´t distinguish open ports from certain filtered ones, leaving
    you with the response open|filtered.
-sA (TCP ACK scan) .
    This scan is different than the others discussed so far in that it never determines open (or even
    open|filtered) ports. It is used to map out firewall rulesets, determining whether they are stateful
    or not and which ports are filtered.

    The ACK scan probe packet has only the ACK flag set (unless you use --scanflags). When scanning
    unfiltered systems, open and closed ports will both return a RST packet. Nmap then labels them as
    unfiltered, meaning that they are reachable by the ACK packet, but whether they are open or closed is
    undetermined. Ports that don´t respond, or send certain ICMP error messages back (type 3, code 1, 2,
    3, 9, 10, or 13), are labeled filtered.
-sW (TCP Window scan) .
    Window scan is exactly the same as ACK scan except that it exploits an implementation detail of
    certain systems to differentiate open ports from closed ones, rather than always printing unfiltered
    when a RST is returned. It does this by examining the TCP Window field of the RST packets returned.
    On some systems, open ports use a positive window size (even for RST packets) while closed ones have
    a zero window. So instead of always listing a port as unfiltered when it receives a RST back, Window
    scan lists the port as open or closed if the TCP Window value in that reset is positive or zero,

    This scan relies on an implementation detail of a minority of systems out on the Internet, so you
    can´t always trust it. Systems that don´t support it will usually return all ports closed. Of course,
    it is possible that the machine really has no open ports. If most scanned ports are closed but a few
    common port numbers (such as 22, 25, 53) are filtered, the system is most likely susceptible.
    Occasionally, systems will even show the exact opposite behavior. If your scan shows 1000 open ports
    and three closed or filtered ports, then those three may very well be the truly open ones.
-sM (TCP Maimon scan) .
    The Maimon scan is named after its discoverer, Uriel Maimon..  He described the technique in Phrack
    Magazine issue #49 (November 1996)..  Nmap, which included this technique, was released two issues
    later. This technique is exactly the same as NULL, FIN, and Xmas scans, except that the probe is
    FIN/ACK. According to RFC 793[8] (TCP), a RST packet should be generated in response to such a probe
    whether the port is open or closed. However, Uriel noticed that many BSD-derived systems simply drop
    the packet if the port is open.
--scanflags (Custom TCP scan) .
    Truly advanced Nmap users need not limit themselves to the canned scan types offered. The --scanflags
    option allows you to design your own scan by specifying arbitrary TCP flags..  Let your creative
    juices flow, while evading intrusion detection systems.  whose vendors simply paged through the Nmap
    man page adding specific rules!

           The --scanflags argument can be a numerical flag value such as 9 (PSH and FIN), but using symbolic
           names is easier. Just mash together any combination of URG, ACK, PSH, RST, SYN, and FIN. For example,
           --scanflags URGACKPSHRSTSYNFIN sets everything, though it´s not very useful for scanning. The order
           these are specified in is irrelevant.

           In addition to specifying the desired flags, you can specify a TCP scan type (such as -sA or -sF).
           That base type tells Nmap how to interpret responses. For example, a SYN scan considers no-response
           to indicate a filtered port, while a FIN scan treats the same as open|filtered. Nmap will behave the
           same way it does for the base scan type, except that it will use the TCP flags you specify instead.
           If you don´t specify a base type, SYN scan is used.
    SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes advantage of the fact that SCTP
    implementations should silently drop packets containing COOKIE ECHO chunks on open ports, but send an
    ABORT if the port is closed. The advantage of this scan type is that it is not as obvious a port scan
    than an INIT scan. Also, there may be non-stateful firewall rulesets blocking INIT chunks, but not
    COOKIE ECHO chunks. Don´t be fooled into thinking that this will make a port scan invisible; a good
    IDS will be able to detect SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO scans
    cannot differentiate between open and filtered ports, leaving you with the state open|filtered in
    both cases.
-sI zombie host[:probeport] (idle scan) .
    This advanced scan method allows for a truly blind TCP port scan of the target (meaning no packets
    are sent to the target from your real IP address). Instead, a unique side-channel attack exploits
    predictable IP fragmentation ID sequence generation on the zombie host to glean information about the
    open ports on the target. IDS systems will display the scan as coming from the zombie machine you
    specify (which must be up and meet certain criteria).  This fascinating scan type is too complex to
    fully describe in this reference guide, so I wrote and posted an informal paper with full details at

    Besides being extraordinarily stealthy (due to its blind nature), this scan type permits mapping out
    IP-based trust relationships between machines. The port listing shows open ports from the perspective
    of the zombie host.  So you can try scanning a target using various zombies that you think might be
    trusted.  (via router/packet filter rules).

    You can add a colon followed by a port number to the zombie host if you wish to probe a particular
    port on the zombie for IP ID changes. Otherwise Nmap will use the port it uses by default for TCP
    pings (80).
-sO (IP protocol scan) .
    IP protocol scan allows you to determine which IP protocols (TCP, ICMP, IGMP, etc.) are supported by
    target machines. This isn´t technically a port scan, since it cycles through IP protocol numbers
    rather than TCP or UDP port numbers. Yet it still uses the -p option to select scanned protocol
    numbers, reports its results within the normal port table format, and even uses the same underlying
    scan engine as the true port scanning methods. So it is close enough to a port scan that it belongs

    Besides being useful in its own right, protocol scan demonstrates the power of open-source software.
    While the fundamental idea is pretty simple, I had not thought to add it nor received any requests
    for such functionality. Then in the summer of 2000, Gerhard Rieger.  conceived the idea, wrote an
    excellent patch implementing it, and sent it to the nmap-hackers mailing list..  I incorporated that
    patch into the Nmap tree and released a new version the next day. Few pieces of commercial software
    have users enthusiastic enough to design and contribute their own improvements!

    Protocol scan works in a similar fashion to UDP scan. Instead of iterating through the port number
    field of a UDP packet, it sends IP packet headers and iterates through the eight-bit IP protocol
    field. The headers are usually empty, containing no data and not even the proper header for the
    claimed protocol. The exceptions are TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for
    those is included since some systems won´t send them otherwise and because Nmap already has functions
    to create them. Instead of watching for ICMP port unreachable messages, protocol scan is on the
    lookout for ICMP protocol unreachable messages. If Nmap receives any response in any protocol from
    the target host, Nmap marks that protocol as open. An ICMP protocol unreachable error (type 3, code
    2) causes the protocol to be marked as closed Other ICMP unreachable errors (type 3, code 1, 3, 9,
    10, or 13) cause the protocol to be marked filtered (though they prove that ICMP is open at the same
    time). If no response is received after retransmissions, the protocol is marked open|filtered
-b FTP relay host (FTP bounce scan) .
    An interesting feature of the FTP protocol (RFC 959[9]) is support for so-called proxy FTP
    connections. This allows a user to connect to one FTP server, then ask that files be sent to a
    third-party server. Such a feature is ripe for abuse on many levels, so most servers have ceased
    supporting it. One of the abuses this feature allows is causing the FTP server to port scan other
    hosts. Simply ask the FTP server to send a file to each interesting port of a target host in turn.
    The error message will describe whether the port is open or not. This is a good way to bypass
    firewalls because organizational FTP servers are often placed where they have more access to other
    internal hosts than any old Internet host would. Nmap supports FTP bounce scan with the -b option. It
    takes an argument of the form username:password@server:port.  Server is the name or IP address of a
    vulnerable FTP server. As with a normal URL, you may omit username:password, in which case anonymous
    login credentials (user: anonymous password:-wwwuser@) are used. The port number (and preceding
    colon) may be omitted as well, in which case the default FTP port (21) on server is used.

    This vulnerability was widespread in 1997 when Nmap was released, but has largely been fixed.
    Vulnerable servers are still around, so it is worth trying when all else fails. If bypassing a
    firewall is your goal, scan the target network for open port 21 (or even for any FTP services if you
    scan all ports with version detection), then try a bounce scan using each. Nmap will tell you whether
    the host is vulnerable or not. If you are just trying to cover your tracks, you don´t need to (and,
    in fact, shouldn´t) limit yourself to hosts on the target network. Before you go scanning random
    Internet addresses for vulnerable FTP servers, consider that sysadmins may not appreciate you abusing
    their servers in this way.
-p port ranges (Only scan specified ports) .
    This option specifies which ports you want to scan and overrides the default. Individual port numbers
    are OK, as are ranges separated by a hyphen (e.g.  1-1023). The beginning and/or end values of a
    range may be omitted, causing Nmap to use 1 and 65535, respectively. So you can specify -p- to scan
    ports from 1 through 65535. Scanning port zero.  is allowed if you specify it explicitly. For IP
    protocol scanning (-sO), this option specifies the protocol numbers you wish to scan for (0–255).

    When scanning both TCP and UDP ports, you can specify a particular protocol by preceding the port
    numbers by T: or U:. The qualifier lasts until you specify another qualifier. For example, the
    argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP ports 53, 111,and 137, as well as the
    listed TCP ports. Note that to scan both UDP and TCP, you have to specify -sU and at least one TCP
    scan type (such as -sS, -sF, or -sT). If no protocol qualifier is given, the port numbers are added
    to all protocol lists.  Ports can also be specified by name according to what the port is referred to
    in the nmap-services. You can even use the wildcards * and ? with the names. For example, to scan FTP
    and all ports whose names begin with “http”, use -p ftp,http*. Be careful about shell expansions and
    quote the argument to -p if unsure.

    Ranges of ports can be surrounded by square brackets to indicate ports inside that range that appear
    in nmap-services. For example, the following will scan all ports in nmap-services equal to or below
    1024: -p [-1024]. Be careful with shell expansions and quote the argument to -p if unsure.
-F (Fast (limited port) scan) .
    Specifies that you wish to scan fewer ports than the default. Normally Nmap scans the most common
    1,000 ports for each scanned protocol. With -F, this is reduced to 100.

    Nmap needs an nmap-services file with frequency information in order to know which ports are the most
    common. If port frequency information isn´t available, perhaps because of the use of a custom
    nmap-services file, -F means to scan only ports that are named in the services file (normally Nmap
    scans all named ports plus ports 1–1024).
-r (Don´t randomize ports) .
    By default, Nmap randomizes the scanned port order (except that certain commonly accessible ports are
    moved near the beginning for efficiency reasons). This randomization is normally desirable, but you
    can specify -r for sequential (sorted from lowest to highest) port scanning instead.
--port-ratio <decimal number between 0 and 1>
    Scans all ports in nmap-services file with a ratio greater than the number specified as the argument.
--top-ports <integer of 1 or greater>
    Scans the N highest-ratio ports found in nmap-services file.
-sV (Version detection) .
    Enables version detection, as discussed above. Alternatively, you can use -A, which enables version
    detection among other things.
--allports (Don´t exclude any ports from version detection) .
    By default, Nmap version detection skips TCP port 9100 because some printers simply print anything
    sent to that port, leading to dozens of pages of HTTP GET requests, binary SSL session requests, etc.
    This behavior can be changed by modifying or removing the Exclude directive in nmap-service-probes,
    or you can specify --allports to scan all ports regardless of any Exclude directive.
--version-intensity intensity (Set version scan intensity) .
    When performing a version scan (-sV), Nmap sends a series of probes, each of which is assigned a
    rarity value between one and nine. The lower-numbered probes are effective against a wide variety of
    common services, while the higher numbered ones are rarely useful. The intensity level specifies
    which probes should be applied. The higher the number, the more likely it is the service will be
    correctly identified. However, high intensity scans take longer. The intensity must be between 0 and
    9.  The default is 7.  When a probe is registered to the target port via the nmap-service-probes
    ports directive, that probe is tried regardless of intensity level. This ensures that the DNS probes
    will always be attempted against any open port 53, the SSL probe will be done against 443, etc.
--version-light (Enable light mode) .
    This is a convenience alias for --version-intensity 2. This light mode makes version scanning much
    faster, but it is slightly less likely to identify services.
--version-all (Try every single probe) .
    An alias for --version-intensity 9, ensuring that every single probe is attempted against each port.
--version-trace (Trace version scan activity) .
    This causes Nmap to print out extensive debugging info about what version scanning is doing. It is a
    subset of what you get with --packet-trace.
-sR (RPC scan) .
    This method works in conjunction with the various port scan methods of Nmap. It takes all the TCP/UDP
    ports found open and floods them with SunRPC program NULL commands in an attempt to determine whether
    they are RPC ports, and if so, what program and version number they serve up. Thus you can
    effectively obtain the same info as rpcinfo -p even if the target´s portmapper is behind a firewall
    (or protected by TCP wrappers). Decoys do not currently work with RPC scan..  This is automatically
    enabled as part of version scan (-sV) if you request that. As version detection includes this and is
    much more comprehensive, -sR is rarely needed.
-O (Enable OS detection) .
    Enables OS detection, as discussed above. Alternatively, you can use -A to enable OS detection along
    with other things.
--osscan-limit (Limit OS detection to promising targets) .
    OS detection is far more effective if at least one open and one closed TCP port are found. Set this
    option and Nmap will not even try OS detection against hosts that do not meet this criteria. This can
    save substantial time, particularly on -PN scans against many hosts. It only matters when OS
    detection is requested with -O or -A.
--osscan-guess; --fuzzy (Guess OS detection results) .
    When Nmap is unable to detect a perfect OS match, it sometimes offers up near-matches as
    possibilities. The match has to be very close for Nmap to do this by default. Either of these
    (equivalent) options make Nmap guess more aggressively. Nmap will still tell you when an imperfect
    match is printed and display its confidence level (percentage) for each guess.
--max-os-tries (Set the maximum number of OS detection tries against a target) .
    When Nmap performs OS detection against a target and fails to find a perfect match, it usually
    repeats the attempt. By default, Nmap tries five times if conditions are favorable for OS fingerprint
    submission, and twice when conditions aren´t so good. Specifying a lower --max-os-tries value (such
    as 1) speeds Nmap up, though you miss out on retries which could potentially identify the OS.
    Alternatively, a high value may be set to allow even more retries when conditions are favorable. This
    is rarely done, except to generate better fingerprints for submission and integration into the Nmap
    OS database.
-sC .
    Performs a script scan using the default set of scripts. It is equivalent to --script=default. Some
    of the scripts in this category are considered intrusive and should not be run against a target
    network without permission.
--script filename|category|directory|expression|all[,...] .
    Runs a script scan using the comma-separated list of filenames, script categories, and directories.
    Each element in the list may also be a Boolean expression describing a more complex set of scripts.
    Each element is interpreted first as an expression, then as a category, and finally as a file or
    directory name. The special argument all makes every script in Nmap´s script database eligible to
    run. The all argument should be used with caution as NSE may contain dangerous scripts including
    exploits, brute force authentication crackers, and denial of service attacks.

    File and directory names may be relative or absolute. Absolute names are used directly. Relative
    paths are looked for in the following places until found:
        ~/.nmap (not searched on Windows)
        the current directory
    A scripts subdirectory is also tried in each of these.

    When a directory name is given, Nmap loads every file in the directory whose name ends with .nse. All
    other files are ignored and directories are not searched recursively. When a filename is given, it
    does not have to have the .nse extension; it will be added automatically if necessary.  Nmap scripts
    are stored in a scripts subdirectory of the Nmap data directory by default (see

    For efficiency, scripts are indexed in a database stored in scripts/script.db,.  which lists the
    category or categories in which each script belongs.  When referring to scripts from script.db by
    name, you can use a shell-style ‘*’ wildcard.

    nmap --script "http-*"
        Loads all scripts whose name starts with http-, such as http-auth.nse and http-open-proxy.nse.
        The argument to --script had to be in quotes to protect the wildcard from the shell.

    More complicated script selection can be done using the and, or, and not operators to build Boolean
    expressions. The operators have the same precedence[12] as in Lua: not is the highest, followed by
    and and then or. You can alter precedence by using parentheses. Because expressions contain space
    characters it is necessary to quote them.

    nmap --script "not intrusive"
        Loads every script except for those in the intrusive category.

    nmap --script "default or safe"
        This is functionally equivalent to nmap --script "default,safe". It loads all scripts that are in
        the default category or the safe category or both.

    nmap --script "default and safe"
        Loads those scripts that are in both the default and safe categories.

    nmap --script "(default or safe or intrusive) and not http-*"
        Loads scripts in the default, safe, or intrusive categories, except for those whose names start
        with http-.
--script-args name1=value1,name2={name3=value3},name4={value4,value5} .
    Lets you provide arguments to NSE scripts. Arguments are a comma-separated list of name=value pairs.
    Names and values may be strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’, or ‘,’. To
    include one of these characters in a string, enclose the string in single or double quotes. Within a
    quoted string, ‘\’ escapes a quote. A backslash is only used to escape quotation marks in this
    special case; in all other cases a backslash is interpreted literally. Values may also be tables
    enclosed in {}, just as in Lua. A table may contain simple string values or more name-value pairs,
    including nested tables. An example of script arguments: --script-args
    auth={user=foo,pass=´,{}=bar´},userdb=C:\Path\To\File. The online NSE Documentation Portal at
    http://nmap.org/nsedoc/ lists the arguments that each script accepts.
--script-trace .
    This option does what --packet-trace does, just one ISO layer higher. If this option is specified all
    incoming and outgoing communication performed by a script is printed. The displayed information
    includes the communication protocol, the source, the target and the transmitted data. If more than 5%
    of all transmitted data is not printable, then the trace output is in a hex dump format. Specifying
    --packet-trace enables script tracing too.
--script-updatedb .
    This option updates the script database found in scripts/script.db which is used by Nmap to determine
    the available default scripts and categories. It is only necessary to update the database if you have
    added or removed NSE scripts from the default scripts directory or if you have changed the categories
    of any script. This option is generally used by itself: nmap --script-updatedb.
--min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel scan group sizes) .
    Nmap has the ability to port scan or version scan multiple hosts in parallel. Nmap does this by
    dividing the target IP space into groups and then scanning one group at a time. In general, larger
    groups are more efficient. The downside is that host results can´t be provided until the whole group
    is finished. So if Nmap started out with a group size of 50, the user would not receive any reports
    (except for the updates offered in verbose mode) until the first 50 hosts are completed.

    By default, Nmap takes a compromise approach to this conflict. It starts out with a group size as low
    as five so the first results come quickly and then increases the groupsize to as high as 1024. The
    exact default numbers depend on the options given. For efficiency reasons, Nmap uses larger group
    sizes for UDP or few-port TCP scans.

    When a maximum group size is specified with --max-hostgroup, Nmap will never exceed that size.
    Specify a minimum size with --min-hostgroup and Nmap will try to keep group sizes above that level.
    Nmap may have to use smaller groups than you specify if there are not enough target hosts left on a
    given interface to fulfill the specified minimum. Both may be set to keep the group size within a
    specific range, though this is rarely desired.

    These options do not have an effect during the host discovery phase of a scan. This includes plain
    ping scans (-sP). Host discovery always works in large groups of hosts to improve speed and accuracy.

    The primary use of these options is to specify a large minimum group size so that the full scan runs
    more quickly. A common choice is 256 to scan a network in Class C sized chunks. For a scan with many
    ports, exceeding that number is unlikely to help much. For scans of just a few port numbers, host
    group sizes of 2048 or more may be helpful.
--min-parallelism numprobes; --max-parallelism numprobes (Adjust probe parallelization) .
    These options control the total number of probes that may be outstanding for a host group. They are
    used for port scanning and host discovery. By default, Nmap calculates an ever-changing ideal
    parallelism based on network performance. If packets are being dropped, Nmap slows down and allows
    fewer outstanding probes. The ideal probe number slowly rises as the network proves itself worthy.
    These options place minimum or maximum bounds on that variable. By default, the ideal parallelism can
    drop to one if the network proves unreliable and rise to several hundred in perfect conditions.

    The most common usage is to set --min-parallelism to a number higher than one to speed up scans of
    poorly performing hosts or networks. This is a risky option to play with, as setting it too high may
    affect accuracy. Setting this also reduces Nmap´s ability to control parallelism dynamically based on
    network conditions. A value of ten might be reasonable, though I only adjust this value as a last

    The --max-parallelism option is sometimes set to one to prevent Nmap from sending more than one probe
    at a time to hosts. The --scan-delay option, discussed later, is another way to do this.
--min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout time (Adjust probe timeouts) .
    Nmap maintains a running timeout value for determining how long it will wait for a probe response
    before giving up or retransmitting the probe. This is calculated based on the response times of
    previous probes.

    If the network latency shows itself to be significant and variable, this timeout can grow to several
    seconds. It also starts at a conservative (high) level and may stay that way for a while when Nmap
    scans unresponsive hosts.

    Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than the defaults can cut scan times
    significantly. This is particularly true for pingless (-PN) scans, and those against heavily filtered
    networks. Don´t get too aggressive though. The scan can end up taking longer if you specify such a
    low value that many probes are timing out and retransmitting while the response is in transit.

    If all the hosts are on a local network, 100 milliseconds is a reasonable aggressive
    --max-rtt-timeout value. If routing is involved, ping a host on the network first with the ICMP ping
    utility, or with a custom packet crafter such as hping2.  that is more likely to get through a
    firewall. Look at the maximum round trip time out of ten packets or so. You might want to double that
    for the --initial-rtt-timeout and triple or quadruple it for the --max-rtt-timeout. I generally do
    not set the maximum RTT below 100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.

    --min-rtt-timeout is a rarely used option that could be useful when a network is so unreliable that
    even Nmap´s default is too aggressive. Since Nmap only reduces the timeout down to the minimum when
    the network seems to be reliable, this need is unusual and should be reported as a bug to the
    nmap-dev mailing list..
--max-retries numtries (Specify the maximum number of port scan probe retransmissions) .
    When Nmap receives no response to a port scan probe, it could mean the port is filtered. Or maybe the
    probe or response was simply lost on the network. It is also possible that the target host has rate
    limiting enabled that temporarily blocked the response. So Nmap tries again by retransmitting the
    initial probe. If Nmap detects poor network reliability, it may try many more times before giving up
    on a port. While this benefits accuracy, it also lengthen scan times. When performance is critical,
    scans may be sped up by limiting the number of retransmissions allowed. You can even specify
    --max-retries 0 to prevent any retransmissions, though that is only recommended for situations such
    as informal surveys where occasional missed ports and hosts are acceptable.

    The default (with no -T template) is to allow ten retransmissions. If a network seems reliable and
    the target hosts aren´t rate limiting, Nmap usually only does one retransmission. So most target
    scans aren´t even affected by dropping --max-retries to a low value such as three. Such values can
    substantially speed scans of slow (rate limited) hosts. You usually lose some information when Nmap
    gives up on ports early, though that may be preferable to letting the --host-timeout expire and
    losing all information about the target.
--host-timeout time (Give up on slow target hosts) .
    Some hosts simply take a long time to scan. This may be due to poorly performing or unreliable
    networking hardware or software, packet rate limiting, or a restrictive firewall. The slowest few
    percent of the scanned hosts can eat up a majority of the scan time. Sometimes it is best to cut your
    losses and skip those hosts initially. Specify --host-timeout with the maximum amount of time you are
    willing to wait. For example, specify 30m to ensure that Nmap doesn´t waste more than half an hour on
    a single host. Note that Nmap may be scanning other hosts at the same time during that half an hour,
    so it isn´t a complete loss. A host that times out is skipped. No port table, OS detection, or
    version detection results are printed for that host.
--scan-delay time; --max-scan-delay time (Adjust delay between probes) .
    This option causes Nmap to wait at least the given amount of time between each probe it sends to a
    given host. This is particularly useful in the case of rate limiting..  Solaris machines (among many
    others) will usually respond to UDP scan probe packets with only one ICMP message per second. Any
    more than that sent by Nmap will be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate.
    Nmap tries to detect rate limiting and adjust the scan delay accordingly, but it doesn´t hurt to
    specify it explicitly if you already know what rate works best.

    When Nmap adjusts the scan delay upward to cope with rate limiting, the scan slows down dramatically.
    The --max-scan-delay option specifies the largest delay that Nmap will allow. A low --max-scan-delay
    can speed up Nmap, but it is risky. Setting this value too low can lead to wasteful packet
    retransmissions and possible missed ports when the target implements strict rate limiting.

    Another use of --scan-delay is to evade threshold based intrusion detection and prevention systems
--min-rate number; --max-rate number (Directly control the scanning rate) .
    Nmap´s dynamic timing does a good job of finding an appropriate speed at which to scan. Sometimes,
    however, you may happen to know an appropriate scanning rate for a network, or you may have to
    guarantee that a scan will be finished by a certain time. Or perhaps you must keep Nmap from scanning
    too quickly. The --min-rate and --max-rate options are designed for these situations.

    When the --min-rate option is given Nmap will do its best to send packets as fast as or faster than
    the given rate. The argument is a positive real number representing a packet rate in packets per
    second. For example, specifying --min-rate 300 means that Nmap will try to keep the sending rate at
    or above 300 packets per second. Specifying a minimum rate does not keep Nmap from going faster if
    conditions warrant.

    Likewise, --max-rate limits a scan´s sending rate to a given maximum. Use --max-rate 100, for
    example, to limit sending to 100 packets per second on a fast network. Use --max-rate 0.1 for a slow
    scan of one packet every ten seconds. Use --min-rate and --max-rate together to keep the rate inside
    a certain range.

    These two options are global, affecting an entire scan, not individual hosts. They only affect port
    scans and host discovery scans. Other features like OS detection implement their own timing.

    There are two conditions when the actual scanning rate may fall below the requested minimum. The
    first is if the minimum is faster than the fastest rate at which Nmap can send, which is dependent on
    hardware. In this case Nmap will simply send packets as fast as possible, but be aware that such high
    rates are likely to cause a loss of accuracy. The second case is when Nmap has nothing to send, for
    example at the end of a scan when the last probes have been sent and Nmap is waiting for them to time
    out or be responded to. It´s normal to see the scanning rate drop at the end of a scan or in between
    hostgroups. The sending rate may temporarily exceed the maximum to make up for unpredictable delays,
    but on average the rate will stay at or below the maximum.

    Specifying a minimum rate should be done with care. Scanning faster than a network can support may
    lead to a loss of accuracy. In some cases, using a faster rate can make a scan take longer than it
    would with a slower rate. This is because Nmap´s

    adaptive retransmission algorithms will detect the network congestion caused by an excessive scanning
    rate and increase the number of retransmissions in order to improve accuracy. So even though packets
    are sent at a higher rate, more packets are sent overall. Cap the number of retransmissions with the
    --max-retries option if you need to set an upper limit on total scan time.
--defeat-rst-ratelimit .
    Many hosts have long used rate limiting.  to reduce the number of ICMP error messages (such as
    port-unreachable errors) they send. Some systems now apply similar rate limits to the RST (reset)
    packets they generate. This can slow Nmap down dramatically as it adjusts its timing to reflect those
    rate limits. You can tell Nmap to ignore those rate limits (for port scans such as SYN scan which
    don´t treat non-responsive ports as open) by specifying --defeat-rst-ratelimit.

           Using this option can reduce accuracy, as some ports will appear non-responsive because Nmap didn´t
           wait long enough for a rate-limited RST response. With a SYN scan, the non-response results in the
           port being labeled filtered rather than the closed state we see when RST packets are received. This
           option is useful when you only care about open ports, and distinguishing between closed and filtered
           ports isn´t worth the extra time.
-T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing template) .
    While the fine-grained timing controls discussed in the previous section are powerful and effective,
    some people find them confusing. Moreover, choosing the appropriate values can sometimes take more
    time than the scan you are trying to optimize. So Nmap offers a simpler approach, with six timing
    templates. You can specify them with the -T option and their number (0–5) or their name. The template
    names are paranoid (0), sneaky (1), polite (2), normal (3), aggressive (4), and insane (5). The first
    two are for IDS evasion. Polite mode slows down the scan to use less bandwidth and target machine
    resources. Normal mode is the default and so -T3 does nothing. Aggressive mode speeds scans up by
    making the assumption that you are on a reasonably fast and reliable network. Finally insane mode.
    assumes that you are on an extraordinarily fast network or are willing to sacrifice some accuracy for

    These templates allow the user to specify how aggressive they wish to be, while leaving Nmap to pick
    the exact timing values. The templates also make some minor speed adjustments for which fine-grained
    control options do not currently exist. For example, -T4.  prohibits the dynamic scan delay from
    exceeding 10 ms for TCP ports and -T5 caps that value at 5 ms. Templates can be used in combination
    with fine-grained controls, and the fine-grained controls will you specify will take precedence over
    the timing template default for that parameter. I recommend using -T4 when scanning reasonably modern
    and reliable networks. Keep that option even when you add fine-grained controls so that you benefit
    from those extra minor optimizations that it enables.

    If you are on a decent broadband or ethernet connection, I would recommend always using -T4. Some
    people love -T5 though it is too aggressive for my taste. People sometimes specify -T2 because they
    think it is less likely to crash hosts or because they consider themselves to be polite in general.
    They often don´t realize just how slow -T polite.  really is. Their scan may take ten times longer
    than a default scan. Machine crashes and bandwidth problems are rare with the default timing options
    (-T3) and so I normally recommend that for cautious scanners. Omitting version detection is far more
    effective than playing with timing values at reducing these problems.

    While -T0.  and -T1.  may be useful for avoiding IDS alerts, they will take an extraordinarily long
    time to scan thousands of machines or ports. For such a long scan, you may prefer to set the exact
    timing values you need rather than rely on the canned -T0 and -T1 values.

    The main effects of T0 are serializing the scan so only one port is scanned at a time, and waiting
    five minutes between sending each probe.  T1 and T2 are similar but they only wait 15 seconds and 0.4
    seconds, respectively, between probes.  T3 is Nmap´s default behavior, which includes
    parallelization..  -T4 does the equivalent of --max-rtt-timeout 1250 --initial-rtt-timeout 500
    --max-retries 6 and sets the maximum TCP scan delay to 10 milliseconds.  T5 does the equivalent of
    --max-rtt-timeout 300 --min-rtt-timeout 50 --initial-rtt-timeout 250 --max-retries 2 --host-timeout
    15m as well as setting the maximum TCP scan delay to 5 ms.
-f (fragment packets); --mtu (using the specified MTU) .
    The -f option causes the requested scan (including ping scans) to use tiny fragmented IP packets. The
    idea is to split up the TCP header over several packets to make it harder for packet filters,
    intrusion detection systems, and other annoyances to detect what you are doing. Be careful with this!
    Some programs have trouble handling these tiny packets. The old-school sniffer named Sniffit
    segmentation faulted immediately upon receiving the first fragment. Specify this option once, and
    Nmap splits the packets into eight bytes or less after the IP header. So a 20-byte TCP header would
    be split into three packets. Two with eight bytes of the TCP header, and one with the final four. Of
    course each fragment also has an IP header. Specify -f again to use 16 bytes per fragment (reducing
    the number of fragments)..  Or you can specify your own offset size with the --mtu option. Don´t also
    specify -f if you use --mtu. The offset must be a multiple of eight. While fragmented packets won´t
    get by packet filters and firewalls that queue all IP fragments, such as the CONFIG_IP_ALWAYS_DEFRAG
    option in the Linux kernel, some networks can´t afford the performance hit this causes and thus leave
    it disabled. Others can´t enable this because fragments may take different routes into their
    networks. Some source systems defragment outgoing packets in the kernel. Linux with the iptables.
    connection tracking module is one such example. Do a scan while a sniffer such as Wireshark.  is
    running to ensure that sent packets are fragmented. If your host OS is causing problems, try the
    --send-eth.  option to bypass the IP layer and send raw ethernet frames.

    Fragmentation is only supported for Nmap´s raw packet features, which includes TCP and UDP port scans
    (except connect scan and FTP bounce scan) and OS detection. Features such as version detection and
    the Nmap Scripting Engine generally don´t support fragmentation because they rely on your host´s TCP
    stack to communicate with target services.
-D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys) .
    Causes a decoy scan to be performed, which makes it appear to the remote host that the host(s) you
    specify as decoys are scanning the target network too. Thus their IDS might report 5–10 port scans
    from unique IP addresses, but they won´t know which IP was scanning them and which were innocent
    decoys. While this can be defeated through router path tracing, response-dropping, and other active
    mechanisms, it is generally an effective technique for hiding your IP address.

    Separate each decoy host with commas, and you can optionally use ME.  as one of the decoys to
    represent the position for your real IP address. If you put ME in the sixth position or later, some
    common port scan detectors (such as Solar Designer´s.  excellent Scanlogd).  are unlikely to show
    your IP address at all. If you don´t use ME, Nmap will put you in a random position. You can also use
    RND.  to generate a random, non-reserved IP address, or RND:number to generate number addresses.

    Note that the hosts you use as decoys should be up or you might accidentally SYN flood your targets.
    Also it will be pretty easy to determine which host is scanning if only one is actually up on the
    network. You might want to use IP addresses instead of names (so the decoy networks don´t see you in
    their nameserver logs).

    Decoys are used both in the initial ping scan (using ICMP, SYN, ACK, or whatever) and during the
    actual port scanning phase. Decoys are also used during remote OS detection (-O). Decoys do not work
    with version detection or TCP connect scan. When a scan delay is in effect, the delay is enforced
    between each batch of spoofed probes, not between each individual probe. Because decoys are sent as a
    batch all at once, they may temporarily violate congestion control limits.

    It is worth noting that using too many decoys may slow your scan and potentially even make it less
    accurate. Also, some ISPs will filter out your spoofed packets, but many do not restrict spoofed IP
    packets at all.
-S IP_Address (Spoof source address) .
    In some circumstances, Nmap may not be able to determine your source address (Nmap will tell you if
    this is the case). In this situation, use -S with the IP address of the interface you wish to send
    packets through.

    Another possible use of this flag is to spoof the scan to make the targets think that someone else is
    scanning them. Imagine a company being repeatedly port scanned by a competitor! The -e option and -PN
    are generally required for this sort of usage. Note that you usually won´t receive reply packets back
    (they will be addressed to the IP you are spoofing), so Nmap won´t produce useful reports.
-e interface (Use specified interface) .
    Tells Nmap what interface to send and receive packets on. Nmap should be able to detect this
    automatically, but it will tell you if it cannot.
--source-port portnumber; -g portnumber (Spoof source port number) .
    One surprisingly common misconfiguration is to trust traffic based only on the source port number. It
    is easy to understand how this comes about. An administrator will set up a shiny new firewall, only
    to be flooded with complains from ungrateful users whose applications stopped working. In particular,
    DNS may be broken because the UDP DNS replies from external servers can no longer enter the network.
    FTP is another common example. In active FTP transfers, the remote server tries to establish a
    connection back to the client to transfer the requested file.

    Secure solutions to these problems exist, often in the form of application-level proxies or
    protocol-parsing firewall modules. Unfortunately there are also easier, insecure solutions. Noting
    that DNS replies come from port 53 and active FTP from port 20, many administrators have fallen into
    the trap of simply allowing incoming traffic from those ports. They often assume that no attacker
    would notice and exploit such firewall holes. In other cases, administrators consider this a
    short-term stop-gap measure until they can implement a more secure solution. Then they forget the
    security upgrade.

    Overworked network administrators are not the only ones to fall into this trap. Numerous products
    have shipped with these insecure rules. Even Microsoft has been guilty. The IPsec filters that
    shipped with Windows 2000 and Windows XP contain an implicit rule that allows all TCP or UDP traffic
    from port 88 (Kerberos). In another well-known case, versions of the Zone Alarm personal firewall up
    to 2.1.25 allowed any incoming UDP packets with the source port 53 (DNS) or 67 (DHCP).

    Nmap offers the -g and --source-port options (they are equivalent) to exploit these weaknesses.
    Simply provide a port number and Nmap will send packets from that port where possible. Nmap must use
    different port numbers for certain OS detection tests to work properly, and DNS requests ignore the
    --source-port flag because Nmap relies on system libraries to handle those. Most TCP scans, including
    SYN scan, support the option completely, as does UDP scan.
--data-length number (Append random data to sent packets) .
    Normally Nmap sends minimalist packets containing only a header. So its TCP packets are generally 40
    bytes and ICMP echo requests are just 28. Some UDP ports.  and IP protocols.  get a custom payload by
    default. This option tells Nmap to append the given number of random bytes to most of the packets it
    sends, and not to use any protocol-specific payloads. (Use --data-length 0 for no random or
    protocol-specific payloads..  OS detection (-O) packets are not affected.  because accuracy there
    requires probe consistency, but most pinging and portscan packets support this. It slows things down
    a little, but can make a scan slightly less conspicuous.
--ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string (Send packets with specified ip
options) .
    The IP protocol[13] offers several options which may be placed in packet headers. Unlike the
    ubiquitous TCP options, IP options are rarely seen due to practicality and security concerns. In
    fact, many Internet routers block the most dangerous options such as source routing. Yet options can
    still be useful in some cases for determining and manipulating the network route to target machines.
    For example, you may be able to use the record route option to determine a path to a target even when
    more traditional traceroute-style approaches fail. Or if your packets are being dropped by a certain
    firewall, you may be able to specify a different route with the strict or loose source routing

    The most powerful way to specify IP options is to simply pass in values as the argument to
    --ip-options. Precede each hex number with \x then the two digits. You may repeat certain characters
    by following them with an asterisk and then the number of times you wish them to repeat. For example,
    \x01\x07\x04\x00*36\x01 is a hex string containing 36 NUL bytes.

    Nmap also offers a shortcut mechanism for specifying options. Simply pass the letter R, T, or U to
    request record-route,.  record-timestamp,.  or both options together, respectively. Loose or strict
    source routing.  may be specified with an L or S followed by a space and then a space-separated list
    of IP addresses.

    If you wish to see the options in packets sent and received, specify --packet-trace. For more
    information and examples of using IP options with Nmap, see
--ttl value (Set IP time-to-live field) .
    Sets the IPv4 time-to-live field in sent packets to the given value.
--randomize-hosts (Randomize target host order) .
    Tells Nmap to shuffle each group of up to 16384 hosts before it scans them. This can make the scans
    less obvious to various network monitoring systems, especially when you combine it with slow timing
    options. If you want to randomize over larger group sizes, increase PING_GROUP_SZ.  in nmap.h.  and
    recompile. An alternative solution is to generate the target IP list with a list scan (-sL -n -oN
    filename), randomize it with a Perl script, then provide the whole list to Nmap with -iL..
--spoof-mac MAC address, prefix, or vendor name (Spoof MAC address) .
    Asks Nmap to use the given MAC address for all of the raw ethernet frames it sends. This option
    implies --send-eth.  to ensure that Nmap actually sends ethernet-level packets. The MAC given can
    take several formats. If it is simply the number 0, Nmap chooses a completely random MAC address for
    the session. If the given string is an even number of hex digits (with the pairs optionally separated
    by a colon), Nmap will use those as the MAC. If fewer than 12 hex digits are provided, Nmap fills in
    the remainder of the six bytes with random values. If the argument isn´t a zero or hex string, Nmap
    looks through nmap-mac-prefixes to find a vendor name containing the given string (it is case
    insensitive). If a match is found, Nmap uses the vendor´s OUI (three-byte prefix).  and fills out the
    remaining three bytes randomly. Valid --spoof-mac argument examples are Apple, 0, 01:02:03:04:05:06,
    deadbeefcafe, 0020F2, and Cisco. This option only affects raw packet scans such as SYN scan or OS
    detection, not connection-oriented features such as version detection or the Nmap Scripting Engine.
--badsum (Send packets with bogus TCP/UDP checksums) .
    Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets sent to target hosts. Since
    virtually all host IP stacks properly drop these packets, any responses received are likely coming
    from a firewall or IDS that didn´t bother to verify the checksum. For more details on this technique,
    see http://nmap.org/p60-12.html
--adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums) .
    Asks Nmap to use the deprecated Adler32 algorithm for calculating the SCTP checksum. If --adler32 is
    not given, CRC-32C (Castagnoli) is used.  RFC 2960[14] originally defined Adler32 as checksum
    algorithm for SCTP; RFC 4960[7] later redefined the SCTP checksums to use CRC-32C. Current SCTP
    implementations should be using CRC-32C, but in order to elicit responses from old, legacy SCTP
    implementations, it may be preferrable to use Adler32.
-oN filespec (normal output) .
    Requests that normal output be directed to the given filename. As discussed above, this differs
    slightly from interactive output.
-oX filespec (XML output) .
    Requests that XML output be directed to the given filename. Nmap includes a document type definition
    (DTD) which allows XML parsers to validate Nmap XML output. While it is primarily intended for
    programmatic use, it can also help humans interpret Nmap XML output. The DTD defines the legal
    elements of the format, and often enumerates the attributes and values they can take on. The latest
    version is always available from http://nmap.org/data/nmap.dtd.

    XML offers a stable format that is easily parsed by software. Free XML parsers are available for all
    major computer languages, including C/C++, Perl, Python, and Java. People have even written bindings
    for most of these languages to handle Nmap output and execution specifically. Examples are
    Nmap::Scanner[15] and Nmap::Parser[16] in Perl CPAN. In almost all cases that a non-trivial
    application interfaces with Nmap, XML is the preferred format.

    The XML output references an XSL stylesheet which can be used to format the results as HTML. The
    easiest way to use this is simply to load the XML output in a web browser such as Firefox or IE. By
    default, this will only work on the machine you ran Nmap on (or a similarly configured one) due to
    the hard-coded nmap.xsl filesystem path. Use the --webxml or --stylesheet options to create portable
    XML files that render as HTML on any web-connected machine.
-oS filespec (ScRipT KIdd|3 oUTpuT) .
    Script kiddie output is like interactive output, except that it is post-processed to better suit the
    l33t HaXXorZ who previously looked down on Nmap due to its consistent capitalization and spelling.
    Humor impaired people should note that this option is making fun of the script kiddies before flaming
    me for supposedly “helping them”.
-oG filespec (grepable output) .
    This output format is covered last because it is deprecated. The XML output format is far more
    powerful, and is nearly as convenient for experienced users. XML is a standard for which dozens of
    excellent parsers are available, while grepable output is my own simple hack. XML is extensible to
    support new Nmap features as they are released, while I often must omit those features from grepable
    output for lack of a place to put them.

    Nevertheless, grepable output is still quite popular. It is a simple format that lists each host on
    one line and can be trivially searched and parsed with standard Unix tools such as grep, awk, cut,
    sed, diff, and Perl. Even I usually use it for one-off tests done at the command line. Finding all
    the hosts with the SSH port open or that are running Solaris takes only a simple grep to identify the
    hosts, piped to an awk or cut command to print the desired fields.

    Grepable output consists of comments (lines starting with a pound (#)).  and target lines. A target
    line includes a combination of six labeled fields, separated by tabs and followed with a colon. The
    fields are Host, Ports, Protocols, Ignored State, OS, Seq Index, IP ID, and Status.

    The most important of these fields is generally Ports, which gives details on each interesting port.
    It is a comma separated list of port entries. Each port entry represents one interesting port, and
    takes the form of seven slash (/) separated subfields. Those subfields are: Port number, State,
    Protocol, Owner, Service, SunRPC info, and Version info.

    As with XML output, this man page does not allow for documenting the entire format. A more detailed
    look at the Nmap grepable output format is available from
-oA basename (Output to all formats) .
    As a convenience, you may specify -oA basename to store scan results in normal, XML, and grepable
    formats at once. They are stored in basename.nmap, basename.xml, and basename.gnmap, respectively. As
    with most programs, you can prefix the filenames with a directory path, such as ~/nmaplogs/foocorp/
    on Unix or c:\hacking\sco on Windows.
-v (Increase verbosity level) .
    Increases the verbosity level, causing Nmap to print more information about the scan in progress.
    Open ports are shown as they are found and completion time estimates are provided when Nmap thinks a
    scan will take more than a few minutes. Use it twice or more for even greater verbosity.

    Most changes only affect interactive output, and some also affect normal and script kiddie output.
    The other output types are meant to be processed by machines, so Nmap can give substantial detail by
    default in those formats without fatiguing a human user. However, there are a few changes in other
    modes where output size can be reduced substantially by omitting some detail. For example, a comment
    line in the grepable output that provides a list of all ports scanned is only printed in verbose mode
    because it can be quite long.
-d [level] (Increase or set debugging level) .
    When even verbose mode doesn´t provide sufficient data for you, debugging is available to flood you
    with much more! As with the verbosity option (-v), debugging is enabled with a command-line flag (-d)
    and the debug level can be increased by specifying it multiple times..  Alternatively, you can set a
    debug level by giving an argument to -d. For example, -d9 sets level nine. That is the highest
    effective level and will produce thousands of lines unless you run a very simple scan with very few
    ports and targets.

    Debugging output is useful when a bug is suspected in Nmap, or if you are simply confused as to what
    Nmap is doing and why. As this feature is mostly intended for developers, debug lines aren´t always
    self-explanatory. You may get something like: Timeout vals: srtt: -1 rttvar: -1 to: 1000000 delta
    14987 ==> srtt: 14987 rttvar: 14987 to: 100000. If you don´t understand a line, your only recourses
    are to ignore it, look it up in the source code, or request help from the development list
    (nmap-dev)..  Some lines are self explanatory, but the messages become more obscure as the debug
    level is increased.
--reason (Host and port state reasons) .
    Shows the reason each port is set to a specific state and the reason each host is up or down. This
    option displays the type of the packet that determined a port or hosts state. For example, A RST
    packet from a closed port or an echo reply from an alive host. The information Nmap can provide is
    determined by the type of scan or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed,
    but the TCP connect scan (-sT) is limited by the implementation of the connect system call. This
    feature is automatically enabled by the debug option (-d).  and the results are stored in XML log
    files even if this option is not specified.
--stats-every time (Print periodic timing stats) .
    Periodically prints a timing status message after each interval of time. The time is a specification
    of the kind described in the section called “TIMING AND PERFORMANCE”; so for example, use
    --stats-every 10s to get a status update every 10 seconds. Updates are printed to interactive output
    (the screen) and XML output.
--packet-trace (Trace packets and data sent and received) .
    Causes Nmap to print a summary of every packet sent or received. This is often used for debugging,
    but is also a valuable way for new users to understand exactly what Nmap is doing under the covers.
    To avoid printing thousands of lines, you may want to specify a limited number of ports to scan, such
    as -p20-30. If you only care about the goings on of the version detection subsystem, use
    --version-trace instead. If you only care about script tracing, specify --script-trace. With
    --packet-trace, you get all of the above.
--open (Show only open (or possibly open) ports) .
    Sometimes you only care about ports you can actually connect to (open ones), and don´t want results
    cluttered with closed, filtered, and closed|filtered ports. Output customization is normally done
    after the scan using tools such as grep, awk, and Perl, but this feature was added due to
    overwhelming requests. Specify --open to only see open, open|filtered, and unfiltered ports. These
    three ports are treated just as they normally are, which means that open|filtered and unfiltered may
    be condensed into counts if there are an overwhelming number of them.
--iflist (List interfaces and routes) .
    Prints the interface list and system routes as detected by Nmap. This is useful for debugging routing
    problems or device mischaracterization (such as Nmap treating a PPP connection as ethernet).
--log-errors (Log errors/warnings to normal mode output file) .
    Warnings and errors printed by Nmap usually go only to the screen (interactive output), leaving any
    normal-format output files (usually specified with -oN) uncluttered. When you do want to see those
    messages in the normal output file you specified, add this option. It is useful when you aren´t
    watching the interactive output or when you want to record errors while debugging a problem. The
    error and warning messages will still appear in interactive mode too. This won´t work for most errors
    related to bad command-line arguments because Nmap may not have initialized its output files yet. In
    addition, some Nmap error and warning messages use a different system which does not yet support this

    An alternative to --log-errors is redirecting interactive output (including the standard error
    stream) to a file. Most Unix shells make this approach easy, though it can be difficult on Windows.
--append-output (Append to rather than clobber output files) .
    When you specify a filename to an output format flag such as -oX or -oN, that file is overwritten by
    default. If you prefer to keep the existing content of the file and append the new results, specify
    the --append-output option. All output filenames specified in that Nmap execution will then be
    appended to rather than clobbered. This doesn´t work well for XML (-oX) scan data as the resultant
    file generally won´t parse properly until you fix it up by hand.
--resume filename (Resume aborted scan) .
    Some extensive Nmap runs take a very long time—on the order of days. Such scans don´t always run to
    completion. Restrictions may prevent Nmap from being run during working hours, the network could go
    down, the machine Nmap is running on might suffer a planned or unplanned reboot, or Nmap itself could
    crash. The administrator running Nmap could cancel it for any other reason as well, by pressing
    ctrl-C. Restarting the whole scan from the beginning may be undesirable. Fortunately, if normal (-oN)
    or grepable (-oG) logs were kept, the user can ask Nmap to resume scanning with the target it was
    working on when execution ceased. Simply specify the --resume option and pass the normal/grepable
    output file as its argument. No other arguments are permitted, as Nmap parses the output file to use
    the same ones specified previously. Simply call Nmap as nmap --resume logfilename. Nmap will append
    new results to the data files specified in the previous execution. Resumption does not support the
    XML output format because combining the two runs into one valid XML file would be difficult.
--stylesheet path or URL (Set XSL stylesheet to transform XML output) .
    Nmap ships with an XSL stylesheet named nmap.xsl for viewing or translating XML output to HTML.  The
    XML output includes an xml-stylesheet directive which points to nmap.xml where it was initially
    installed by Nmap (or in the current working directory on Windows). Simply load Nmap´s XML output in
    a modern web browser and it should retrieve nmap.xsl from the filesystem and use it to render
    results. If you wish to use a different stylesheet, specify it as the argument to --stylesheet. You
    must pass the full pathname or URL. One common invocation is --stylesheet
    http://nmap.org/data/nmap.xsl. This tells a browser to load the latest version of the stylesheet from
    Nmap.Org. The --webxml option does the same thing with less typing and memorization. Loading the XSL
    from Nmap.Org makes it easier to view results on a machine that doesn´t have Nmap (and thus nmap.xsl)
    installed. So the URL is often more useful, but the local filesystem location of nmap.xsl is used by
    default for privacy reasons.
--webxml (Load stylesheet from Nmap.Org) .
    This convenience option is simply an alias for --stylesheet http://nmap.org/data/nmap.xsl.
--no-stylesheet (Omit XSL stylesheet declaration from XML) .
    Specify this option to prevent Nmap from associating any XSL stylesheet with its XML output. The
    xml-stylesheet directive is omitted.
-6 (Enable IPv6 scanning) .
    Since 2002, Nmap has offered IPv6 support for its most popular features. In particular, ping scanning
    (TCP-only), connect scanning, and version detection all support IPv6. The command syntax is the same
    as usual except that you also add the -6 option. Of course, you must use IPv6 syntax if you specify
    an address rather than a hostname. An address might look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0,
    so hostnames are recommended. The output looks the same as usual, with the IPv6 address on the
    “interesting ports” line being the only IPv6 give away.

    While IPv6 hasn´t exactly taken the world by storm, it gets significant use in some (usually Asian)
    countries and most modern operating systems support it. To use Nmap with IPv6, both the source and
    target of your scan must be configured for IPv6. If your ISP (like most of them) does not allocate
    IPv6 addresses to you, free tunnel brokers are widely available and work fine with Nmap. I use the
    free IPv6 tunnel broker.  service at http://www.tunnelbroker.net. Other tunnel brokers are listed at
    Wikipedia[17]. 6to4 tunnels are another popular, free approach.
-A (Aggressive scan options) .
    This option enables additional advanced and aggressive options. I haven´t decided exactly which it
    stands for yet. Presently this enables OS detection (-O), version scanning (-sV), script scanning
    (-sC) and traceroute (--traceroute).  More features may be added in the future. The point is to
    enable a comprehensive set of scan options without people having to remember a large set of flags.
    However, because script scanning with the default set is considered intrusive, you should not use -A
    against target networks without permission. This option only enables features, and not timing options
    (such as -T4) or verbosity options (-v) that you might want as well.
--datadir directoryname (Specify custom Nmap data file location) .
    Nmap obtains some special data at runtime in files named nmap-service-probes, nmap-services,
    nmap-protocols, nmap-rpc, nmap-mac-prefixes, and nmap-os-db. If the location of any of these files
    has been specified (using the --servicedb or --versiondb options), that location is used for that
    file. After that, Nmap searches these files in the directory specified with the --datadir option (if
    any). Any files not found there, are searched for in the directory specified by the NMAPDIR
    environmental variable.  ~/.nmap.  for real and effective UIDs (POSIX systems only) or location of
    the Nmap executable (Win32 only), and then a compiled-in location such as /usr/local/share/nmap or
    /usr/share/nmap . As a last resort, Nmap will look in the current directory.
--servicedb services file (Specify custom services file) .
    Asks Nmap to use the specified services file rather than the nmap-services data file that comes with
    Nmap. Using this option also causes a fast scan (-F) to be used. See the description for --datadir
    for more information on Nmap´s data files.
--versiondb service probes file (Specify custom service probes file) .
    Asks Nmap to use the specified service probes file rather than the nmap-service-probes data file that
    comes with Nmap. See the description for --datadir for more information on Nmap´s data files.
--send-eth (Use raw ethernet sending) .
    Asks Nmap to send packets at the raw ethernet (data link) layer rather than the higher IP (network)
    layer. By default, Nmap chooses the one which is generally best for the platform it is running on.
    Raw sockets (IP layer).  are generally most efficient for Unix machines, while ethernet frames are
    required for Windows operation since Microsoft disabled raw socket support. Nmap still uses raw IP
    packets on Unix despite this option when there is no other choice (such as non-ethernet connections).
--send-ip (Send at raw IP level) .
    Asks Nmap to send packets via raw IP sockets rather than sending lower level ethernet frames. It is
    the complement to the --send-eth option discussed previously.
--privileged (Assume that the user is fully privileged) .
    Tells Nmap to simply assume that it is privileged enough to perform raw socket sends, packet
    sniffing, and similar operations that usually require root privileges.  on Unix systems. By default
    Nmap quits if such operations are requested but geteuid is not zero.  --privileged is useful with
    Linux kernel capabilities and similar systems that may be configured to allow unprivileged users to
    perform raw-packet scans. Be sure to provide this option flag before any flags for options that
    require privileges (SYN scan, OS detection, etc.). The NMAP_PRIVILEGED.  environmental variable may
    be set as an equivalent alternative to --privileged.
--unprivileged (Assume that the user lacks raw socket privileges) .
    This option is the opposite of --privileged. It tells Nmap to treat the user as lacking network raw
    socket and sniffing privileges. This is useful for testing, debugging, or when the raw network
    functionality of your operating system is somehow broken. The NMAP_UNPRIVILEGED.  environmental
    variable may be set as an equivalent alternative to --unprivileged.
--release-memory (Release memory before quitting) .
    This option is only useful for memory-leak debugging. It causes Nmap to release allocated memory just
    before it quits so that actual memory leaks are easier to spot. Normally Nmap skips this as the OS
    does this anyway upon process termination.
--interactive (Start in interactive mode) .
    Starts Nmap in interactive mode, which offers an interactive Nmap prompt allowing easy launching of
    multiple scans (either synchronously or in the background). This is useful for people who scan from
    multi-user systems as they often want to test their security without letting everyone else on the
    system know exactly which systems they are scanning. Use --interactive to activate this mode and then
    type h for help. This option is rarely used because proper shells are usually more familiar and
    feature-complete. This option includes a bang (!) operator for executing shell commands, which is one
    of many reasons not to install Nmap setuid root..
-V; --version (Print version number) .
    Prints the Nmap version number and exits.
-h; --help (Print help summary page) .
    Prints a short help screen with the most common command flags. Running Nmap without any arguments
    does the same thing.