usr.bin/netstat/netstat.1

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.\"	from: @(#)netstat.1	8.8 (Berkeley) 4/18/94
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.Dd $Mdocdate: January 2 2021 $
.Dt NETSTAT 1
.Os
.Sh NAME
.Nm netstat
.Nd show network status
.Sh SYNOPSIS
.Nm
.Op Fl AaBln
.Op Fl M Ar core
.Op Fl N Ar system
.Op Fl p Ar protocol
.Op Fl T Ar rtable
.Nm
.Fl W Ar interface
.Nm
.Fl m
.Nm
.Fl I Ar interface | Fl i
.Op Fl bdehnqt
.Nm
.Fl w Ar wait
.Op Fl bdehnqt
.Op Fl c Ar count
.Op Fl I Ar interface
.Nm
.Fl s
.Op Fl gru
.Op Fl f Ar address_family
.Op Fl p Ar protocol
.Nm
.Fl g
.Op Fl lnu
.Op Fl f Ar address_family
.Nm
.Fl R
.Nm
.Fl r
.Op Fl AFu
.Op Fl f Ar address_family
.Op Fl M Ar core
.Op Fl N Ar system
.Op Fl p Ar protocol
.Op Fl T Ar rtable
.Nm
.Fl P Ar pcbaddr
.Op Fl v
.Op Fl M Ar core
.Op Fl N Ar system
.Sh DESCRIPTION
The
.Nm
command shows various aspects of network status.
The default display shows information about
all active network connections and sockets.
.Pp
The first form of the command displays a list of active sockets for
each protocol.
The second form displays per-interface statistics for
the specified wireless (802.11) device.
The third form displays statistics related to memory use.
The fourth form displays per-interface statistics.
The fifth form continuously displays the information regarding packet
traffic on the configured network interfaces.
The sixth form displays per-protocol statistics.
The seventh form shows information related to multicast routing.
The eighth form displays information about routing domains.
The ninth form displays information about routing tables.
The final form displays internals of the protocol control block (PCB)
and the socket structure.
The forms are shown in order of precedence:
for example, if
.Fl rg
is specified,
then
.Fl r
is ignored in favour of
.Fl g .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl A
Show the address of any protocol control blocks associated with sockets;
useful for debugging e.g. with the
.Fl P
flag.
When used with the
.Fl r
flag it shows the internal addresses of the routing table.
Only the super-user can see these addresses;
unprivileged users will see them as 0x0.
.It Fl a
With the default display,
show the state of all sockets; normally sockets used by
server processes are not shown.
.It Fl B
With the default display,
show buffer sizes for TCP sockets.
This includes the send window size, receive window size and congestion
window size.
.It Fl b
With the interface display (options
.Fl I
or
.Fl i ) ,
show bytes in and out, instead of packet statistics.
.It Fl c Ar count
Display
.Ar count
updates, then exit.
This option has no effect unless
.Fl w
is specified as well.
.It Fl d
With either the interface display (options
.Fl I
or
.Fl i )
or an interval (option
.Fl w ) ,
show only the number of dropped packets.
.It Fl e
With either the interface display (options
.Fl I
or
.Fl i )
or an interval (option
.Fl w ) ,
show only the number of errors on the interface.
.It Fl F
When showing routes, only show routes whose gateway are in the
same address family as the destination.
.It Fl f Ar address_family
Limit statistics or address control block reports to those
of the specified
.Ar address_family .
.Pp
The following address families are recognized:
.Bl -column "Address Family" AF_INET6 Description -offset indent
.It Sy Address Family Ta Sy Constant Ta Sy Description
.It Cm inet  Ta Dv AF_INET  Ta IP Version 4
.It Cm inet6 Ta Dv AF_INET6 Ta IP Version 6
.It Cm local Ta Dv AF_UNIX  Ta Alias for Cm unix
.It Cm mpls  Ta Dv AF_MPLS  Ta MPLS
.It Cm unix  Ta Dv AF_UNIX  Ta Local to Host (i.e., pipes)
.El
.It Fl h
Use unit suffixes to reduce the number of digits shown with the
.Fl b
and
.Fl w
options.
.It Fl g
Show information related to multicast (group address) routing.
By default, show the IP multicast virtual-interface and routing tables.
If the
.Fl s
option is also present, show multicast routing statistics.
.It Fl I Ar interface
Show information about the specified
.Ar interface ;
used with a
.Ar wait
interval as described below.
.It Fl i
Show the state of interfaces which have been auto-configured
(interfaces statically configured into a system but not
located at boot-time are not shown).
.It Fl l
With the default display,
show only listening sockets.
With the
.Fl g
option, display wider fields for the IPv6 multicast routing table
.Qq Origin
and
.Qq Group
columns.
.It Fl M Ar core
Extract values associated with the name list from the specified core
instead of the running kernel.
.It Fl m
Show statistics recorded by the memory management routines
(the network manages a private pool of memory buffers).
.It Fl N Ar system
Extract the name list from the specified system instead of the running kernel.
.It Fl n
Show network addresses as numbers (normally
.Nm
interprets addresses and attempts to display them
symbolically).
This option may be used with any of the display formats.
.It Fl P Ar pcbaddr
Display the contents of the protocol control block (PCB)
located at the kernel virtual address
.Ar pcbaddr .
PCB addresses can be obtained using the
.Fl A
flag.
When used with the
.Fl v
option, also print socket, domain and protocol specific structures.
Only the super-user can use the
.Fl P
option.
.Pp
The
.Fl P
option requires the ability to open
.Pa /dev/kmem
which may be restricted based upon the value of the
.Ar kern.allowkmem
.Xr sysctl 8 .
.It Fl p Ar protocol
Restrict the output to
.Ar protocol ,
which is either a well-known name for a protocol or an alias for it.
Some protocol names and aliases are listed in the file
.Pa /etc/protocols .
The program will complain if
.Ar protocol
is unknown.
If the
.Fl s
option is specified, the per-protocol statistics are displayed.
Otherwise the states of the matching sockets are shown.
.It Fl q
Only show interfaces that have seen packets (or bytes if
.Fl b
is specified).
.It Fl R
List all rdomains with associated interfaces and routing tables.
.It Fl r
Show the routing tables.
The output is explained in more detail below.
If the
.Fl s
option is also specified, show routing statistics instead.
When used with the
.Fl v
option, also print routing labels.
.It Fl s
Show per-protocol statistics.
If this option is repeated, counters with a value of zero are suppressed.
.It Fl T Ar rtable
Select an alternate routing table to query.
The default is to use the current routing table.
.It Fl t
With the
.Fl i
option, display the current value of the watchdog timer function.
.It Fl u
Limit statistics or address control block reports to the
.Dv AF_UNIX
address family.
.It Fl v
Show extra (verbose) detail for the routing tables
.Pq Fl r ,
or avoid truncation of long addresses.
When used with the
.Fl P
option, also print socket, domain and protocol specific structures.
.It Fl W Ar interface
(IEEE 802.11 devices only)
Show per-interface IEEE 802.11 wireless statistics.
.It Fl w Ar wait
Show network interface statistics at intervals of
.Ar wait
seconds.
.El
.Pp
Address formats are of the form
.Dq host.port
or
.Dq network.port
if a socket's address specifies a network but no specific host address.
When known, the host addresses are displayed symbolically
according to the
.Xr hosts 5
database.
If a symbolic name for an address is unknown, or if the
.Fl n
option is specified, the address is printed numerically, according
to the address family.
.Pp
For more information regarding the Internet
.Dq dot format ,
refer to
.Xr inet_ntop 3 .
Unspecified or
.Dq wildcard
addresses and ports appear as a single
.Sq * .
If a local port number is registered as being in use for RPC by
.Xr portmap 8 ,
its RPC service name or RPC service number will be printed in
.Dq []
immediately after the port number.
.Pp
The interface display provides a table of cumulative
statistics regarding packets transferred, errors, and collisions.
The network addresses of the interface
and the maximum transmission unit (MTU) are also displayed.
.Pp
The routing table display indicates the available routes and their status.
Each route consists of a destination host or network and
a gateway to use in forwarding packets.
If the destination is a
network in numeric format, the netmask (in /24 style format) is appended.
The flags field shows a collection of information about
the route stored as binary choices.
The individual flags are discussed in more detail in the
.Xr route 8
and
.Xr route 4
manual pages.
.Pp
The mapping between letters and flags is:
.Bl -column "1" "RTF_BLACKHOLE" "Protocol specific routing flag #1."
.It 1 Ta Dv RTF_PROTO1 Ta "Protocol specific routing flag #1."
.It 2 Ta Dv RTF_PROTO2 Ta "Protocol specific routing flag #2."
.It 3 Ta Dv RTF_PROTO3 Ta "Protocol specific routing flag #3."
.It B Ta Dv RTF_BLACKHOLE Ta "Just discard pkts (during updates)."
.It b Ta Dv RTF_BROADCAST Ta "Correspond to a local broadcast address."
.It C Ta Dv RTF_CLONING Ta "Generate new routes on use."
.It c Ta Dv RTF_CLONED Ta "Cloned routes (generated from RTF_CLONING)."
.It D Ta Dv RTF_DYNAMIC Ta "Created dynamically (by redirect)."
.It d Ta Dv RTF_DONE Ta "Completed (for routing messages only)."
.It G Ta Dv RTF_GATEWAY Ta "Destination requires forwarding by intermediary."
.It H Ta Dv RTF_HOST Ta "Host entry (net otherwise)."
.It h Ta Dv RTF_CACHED Ta "Referenced by gateway route."
.It L Ta Dv RTF_LLINFO Ta "Valid protocol to link address translation."
.It l Ta Dv RTF_LOCAL Ta "Correspond to a local address."
.It M Ta Dv RTF_MODIFIED Ta "Modified dynamically (by redirect)."
.It m Ta Dv RTF_MULTICAST Ta "Correspond to a multicast address."
.It n Ta Dv RTF_CONNECTED Ta "Interface route."
.It P Ta Dv RTF_MPATH Ta "Multipath route."
.It R Ta Dv RTF_REJECT Ta "Host or net unreachable."
.It S Ta Dv RTF_STATIC Ta "Manually added."
.It T Ta Dv RTF_MPLS Ta "MPLS route."
.It U Ta Dv RTF_UP Ta "Route usable."
.El
.Pp
Direct routes are created for each interface attached to the local host;
the gateway field for such entries shows the address of the outgoing interface.
The refcnt field gives the current number of active uses of the route.
Connection oriented protocols normally hold on to a single route for the
duration of a connection while connectionless protocols obtain a route while
sending to the same destination.
The use field provides a count of the number of packets sent using that route.
The MTU entry shows the MTU associated with that route.
This MTU value is used as the basis for the TCP maximum segment size (MSS).
The
.Sq L
flag appended to the MTU value indicates that the value is
locked, and that path MTU discovery is turned off for that route.
A
.Sq -
indicates that the MTU for this route has not been set, and a default
TCP maximum segment size will be used.
The interface entry indicates the network interface utilized for the route.
.Pp
When
.Nm
is invoked with the
.Fl w
option and a
.Ar wait
interval argument, it displays a running count of statistics related to
network interfaces.
An obsolescent version of this option used a numeric parameter
with no option, and is currently supported for backward compatibility.
This display consists of a column for the primary interface (the first
interface found during autoconfiguration) and a column summarizing
information for all interfaces.
The primary interface may be replaced with another interface with the
.Fl I
option.
The first line of each screen of information contains a summary since the
system was last rebooted.
Subsequent lines of output show values accumulated over the preceding interval.
.Sh SEE ALSO
.Xr fstat 1 ,
.Xr nfsstat 1 ,
.Xr ps 1 ,
.Xr systat 1 ,
.Xr tcpbench 1 ,
.Xr top 1 ,
.Xr inet_ntop 3 ,
.Xr netintro 4 ,
.Xr route 4 ,
.Xr hosts 5 ,
.Xr protocols 5 ,
.Xr services 5 ,
.Xr iostat 8 ,
.Xr portmap 8 ,
.Xr pstat 8 ,
.Xr route 8 ,
.Xr tcpdrop 8 ,
.Xr trpt 8 ,
.Xr vmstat 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
IPv6 support was added by the WIDE/KAME project.
.Sh BUGS
The notion of errors is ill-defined.