svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
tcp(4)
The protocol provides reliable, flow-controlled, two-way trans‐
mission of data. It is a byte-stream protocol used to support
the abstraction. uses the standard Internet address format and,
in addition, provides a per-host collection of Thus, each address
is composed of an Internet address specifying the host and net‐
work, with a specific port on the host identifying the peer en‐
tity. Sockets utilizing the protocol are either or Active sock‐
ets initiate connections to passive sockets. By default, sockets
are created active; to create a passive socket, the system call
must be used after binding the socket with the system call. Only
passive sockets may use the call to accept incoming connections.
Only active sockets may use the call to initiate connections.
Passive sockets may their location to match incoming connection
requests from multiple networks. This technique, termed allows a
single server to provide service to clients on multiple networks.
To create a socket which listens on all networks, the Internet
address must be bound. The port may still be specified at this
time; if the port is not specified, the system will assign one.
Once a connection has been established, the socket's address is
fixed by the peer entity's location. The address assigned to the
socket is the address associated with the network interface
through which packets are being transmitted and received. Nor‐
mally, this address corresponds to the peer entity's network.
supports a number of socket options which can be set with and
tested with Information about a socket's underlying TCP session
may be retrieved by passing the read-only option to It accepts a
single argument: a pointer to an instance of This API is subject
to change; consult the source to determine which fields are cur‐
rently filled out by this option. specific additions include
send window size, receive window size, and bandwidth-controlled
window space. Set or query congestion control algorithm specific
parameters. See for details. Select or query the congestion
control algorithm that TCP will use for the connection. See for
details. Select or query the set of functions that TCP will use
for this connection. This allows a user to select an alternate
TCP stack. The alternate TCP stack must already be loaded in the
kernel. To list the available TCP stacks, see in the section
further down. To list the default TCP stack, see in the section.
This option accepts a per-socket timeout argument of in seconds,
for new, non-established connections. For the global default in
milliseconds see in the section further down. This option ac‐
cepts an argument of for the amount of time, in seconds, that the
connection must be idle before keepalive probes (if enabled) are
sent for the connection of this socket. If set on a listening
socket, the value is inherited by the newly created socket upon
For the global default in milliseconds see in the section further
down. This option accepts an argument of to set the per-socket
interval, in seconds, between keepalive probes sent to a peer.
If set on a listening socket, the value is inherited by the newly
created socket upon For the global default in milliseconds see in
the section further down. This option accepts an argument of and
allows a per-socket tuning of the number of probes sent, with no
response, before the connection will be dropped. If set on a
listening socket, the value is inherited by the newly created
socket upon For the global default see the in the section further
down. Under most circumstances, sends data when it is presented;
when outstanding data has not yet been acknowledged, it gathers
small amounts of output to be sent in a single packet once an ac‐
knowledgement is received. For a small number of clients, such
as window systems that send a stream of mouse events which re‐
ceive no replies, this packetization may cause significant de‐
lays. The boolean option defeats this algorithm. By default, a
sender- and will negotiate among themselves to determine the max‐
imum segment size to be used for each connection. The option al‐
lows the user to determine the result of this negotiation, and to
reduce it if desired. usually sends a number of options in each
packet, corresponding to various extensions which are provided in
this implementation. The boolean option is provided to disable
option use on a per-connection basis. By convention, the will
set the bit, and begin transmission immediately (if permitted) at
the end of every user call to or When this option is set to a
non-zero value, will delay sending any data at all until either
the socket is closed, or the internal send buffer is filled.
This option enables the use of MD5 digests (also known as TCP-
MD5) on writes to the specified socket. Outgoing traffic is di‐
gested; digests on incoming traffic are verified. When this op‐
tion is enabled on a socket, all inbound and outgoing TCP seg‐
ments must be signed with MD5 digests. One common use for this
in a router deployment is to enable based routers to interwork
with Cisco equipment at peering points. Support for this feature
conforms to RFC 2385. In order for this option to function cor‐
rectly, it is necessary for the administrator to add a tcp-md5
key entry to the system's security associations database (SADB)
using the utility. This entry can only be specified on a per-
host basis at this time. If an SADB entry cannot be found for
the destination, the system does not send any outgoing segments
and drops any inbound segments. Each dropped segment is taken
into account in the TCP protocol statistics. The option level
for the call is the protocol number for available from or All op‐
tions are declared in Options at the transport level may be used
with see Incoming connection requests that are source-routed are
noted, and the reverse source route is used in responding. The
default congestion control algorithm for is Other congestion con‐
trol algorithms can be made available using the framework. The
protocol implements a number of variables in the branch of the
MIB. Implement the window scaling and timestamp options of RFC
1323 (default is true). The default value used for the maximum
segment size when no advice to the contrary is received from MSS
negotiation. Maximum send window. Maximum receive window. Log
any connection attempts to ports where there is not a socket ac‐
cepting connections. The value of 1 limits the logging to (con‐
nection establishment) packets only. That of 2 results in any
packets to closed ports being logged. Any value unlisted above
disables the logging (default is 0, i.e., the logging is dis‐
abled). The Maximum Segment Lifetime, in milliseconds, for a
packet. Timeout, in milliseconds, for new, non-established con‐
nections. The default is 75000 msec. Amount of time, in mil‐
liseconds, that the connection must be idle before keepalive
probes (if enabled) are sent. The default is 7200000 msec (2
hours). The interval, in milliseconds, between keepalive probes
sent to remote machines, when no response is received on a probe.
The default is 75000 msec. Number of probes sent, with no re‐
sponse, before a connection is dropped. The default is 8 pack‐
ets. Assume that is set on all connections, the kernel will pe‐
riodically send a packet to the remote host to verify the connec‐
tion is still up. Certain unreachable messages may abort connec‐
tions in state. Flush packets in the reassembly queue if the
system is low on mbufs. If enabled, disable sending of RST when
a connection is attempted to a port where there is not a socket
accepting connections. See Delay ACK to try and piggyback it
onto a data packet. Maximum amount of time, in milliseconds, be‐
fore a delayed ACK is sent. Enable Path MTU Discovery. Size of
the control-block hash table (read-only). This may be tuned us‐
ing the kernel option or by setting in the Number of active
process control blocks (read-only). Determines whether or not
cookies should be generated for outbound packets. cookies are a
great help during flood attacks, and are enabled by default.
(See The interval (in seconds) specifying how often the secret
data used in RFC 1948 initial sequence number calculations should
be reseeded. By default, this variable is set to zero, indicat‐
ing that no reseeding will occur. Reseeding should not be neces‐
sary, and will break recycling for a few minutes. The current
total number of segments present in all reassembly queues. The
maximum limit on the total number of segments across all reassem‐
bly queues. The limit can be adjusted as a tunable. The maximum
number of segments allowed in each reassembly queue. By default,
the system chooses a limit based on each TCP connection's receive
buffer size and maximum segment size (MSS). The actual limit ap‐
plied to a session's reassembly queue will be the lower of the
system-calculated automatic limit and the user-specified limit.
Adjust the retransmit timer calculation for The slop is typically
added to the raw calculation to take into account occasional
variances that the (smoothed round-trip time) is unable to accom‐
modate, while the minimum specifies an absolute minimum. While a
number of RFCs suggest a 1 second minimum, these RFCs tend to fo‐
cus on streaming behavior, and fail to deal with the fact that a
1 second minimum has severe detrimental effects over lossy inter‐
active connections, such as a 802.11b wireless link, and over
very fast but lossy connections for those cases not covered by
the fast retransmit code. For this reason, we use 200ms of slop
and a near-0 minimum, which gives us an effective minimum of
200ms (similar to Enable the ability to specify initial conges‐
tion window in number of segments. The default value is 10 as
suggested by RFC 6928. Changing the value on fly would not af‐
fect connections using congestion window from the hostcache.
Caution: This regulates the burst of packets allowed to be sent
in the first RTT. The value should be relative to the link ca‐
pacity. Start with small values for lower-capacity links. Large
bursts can cause buffer overruns and packet drops if routers have
small buffers or the link is experiencing congestion. Enable the
Limited Transmit algorithm as described in RFC 3042. It helps
avoid timeouts on lossy links and also when the congestion window
is small, as happens on short transfers. Enable support for RFC
3390, which allows for a variable-sized starting congestion win‐
dow on new connections, depending on the maximum segment size.
This helps throughput in general, but particularly affects short
transfers and high-bandwidth large propagation-delay connections.
Enable support for RFC 2018, TCP Selective Acknowledgment option,
which allows the receiver to inform the sender about all success‐
fully arrived segments, allowing the sender to retransmit the
missing segments only. Maximum number of SACK holes per connec‐
tion. Defaults to 128. Maximum number of SACK holes per system,
across all connections. Defaults to 65536. When a TCP connec‐
tion enters the state, its associated socket structure is freed,
since it is of negligible size and use, and a new structure is
allocated to contain a minimal amount of information necessary
for sustaining a connection in this state, called the compressed
TCP TIME_WAIT state. Since this structure is smaller than a
socket structure, it can save a significant amount of system mem‐
ory. The MIB variable controls the maximum number of these
structures allocated. By default, it is initialized to / 5.
Suppress creating of compressed TCP TIME_WAIT states for connec‐
tions in which both endpoints are local. Recycle connections
faster when the socket is marked as (no user process has the
socket open, data received on the socket cannot be read). The
timeout used here is Timeout to use for fast recycling of connec‐
tions. Defaults to 60 seconds. Enable support for TCP Explicit
Congestion Notification (ECN). ECN allows a TCP sender to reduce
the transmission rate in order to avoid packet drops. Settings:
Disable ECN. Allow incoming connections to request ECN. Outgo‐
ing connections will request ECN. Allow incoming connections to
request ECN. Outgoing connections will not request ECN. Number
of retries (SYN or SYN/ACK retransmits) before disabling ECN on a
specific connection. This is needed to help with connection es‐
tablishment when a broken firewall is in the network path. Turn
on automatic path MTU blackhole detection. In case of retrans‐
mits OS will lower the MSS to check if it's MTU problem. If cur‐
rent MSS is greater than configured value to try, it will be set
to configured value, otherwise, MSS will be set to default values
and MSS to try for IPv4 if PMTU blackhole detection is turned on.
MSS to try for IPv6 if PMTU blackhole detection is turned on.
Number of times configured values were used in an attempt to
downshift. Number of times default MSS was used in an attempt to
downshift. Number of connections for which retransmits continued
even after MSS downshift. List of available TCP function blocks
(TCP stacks). The default TCP function block (TCP stack). De‐
termines whether to inherit listen socket's tcp stack or use the
current system default tcp stack, as defined by Default is true.
Use criteria defined in RFC793 instead of RFC5961 for accepting
RST segments. Default is false. Use criteria defined in RFC793
instead of RFC5961 for accepting SYN segments. Default is false.
A socket operation may fail with one of the following errors re‐
turned: when trying to establish a connection on a socket which
already has one; when the system runs out of memory for an inter‐
nal data structure; when a connection was dropped due to exces‐
sive retransmissions; when the remote peer forces the connection
to be closed; when the remote peer actively refuses connection
establishment (usually because no process is listening to the
port); when an attempt is made to create a socket with a port
which has already been allocated; when an attempt is made to cre‐
ate a socket with a network address for which no network inter‐
face exists; when an attempt is made to bind or connect a socket
to a multicast address. when trying to change TCP function
blocks at an invalid point in the session; when trying to use a
TCP function block that is not available; The protocol appeared
in The RFC 1323 extensions for window scaling and timestamps were
added in The option was introduced in and is