Ubuntu Manpage: zmq_setsockopt - set 0MQ socket options

Provided by: libzmq3-dev_4.3.2-2ubuntu1_amd64

NAME

       zmq_setsockopt - set 0MQ socket options

SYNOPSIS

       int zmq_setsockopt (void *socket, int option_name, const void *option_value, size_t
       option_len);

       Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE, ZMQ_LINGER,
       ZMQ_ROUTER_HANDOVER, ZMQ_ROUTER_MANDATORY, ZMQ_PROBE_ROUTER, ZMQ_XPUB_VERBOSE,
       ZMQ_XPUB_VERBOSER, ZMQ_REQ_CORRELATE, ZMQ_REQ_RELAXED, ZMQ_SNDHWM and ZMQ_RCVHWM, only
       take effect for subsequent socket bind/connects.

       Specifically, security options take effect for subsequent bind/connect calls, and can be
       changed at any time to affect subsequent binds and/or connects.

DESCRIPTION

The zmq_setsockopt() function shall set the option specified by the option_name argument
to the value pointed to by the option_value argument for the 0MQ socket pointed to by the
socket argument. The option_len argument is the size of the option value in bytes. For
options taking a value of type "character string", the provided byte data should either
contain no zero bytes, or end in a single zero byte (terminating ASCII NUL character).

The following socket options can be set with the zmq_setsockopt() function:

ZMQ_AFFINITY: Set I/O thread affinity
The ZMQ_AFFINITY option shall set the I/O thread affinity for newly created connections on
the specified socket.

Affinity determines which threads from the 0MQ I/O thread pool associated with the
socket’s context shall handle newly created connections. A value of zero specifies no
affinity, meaning that work shall be distributed fairly among all 0MQ I/O threads in the
thread pool. For non-zero values, the lowest bit corresponds to thread 1, second lowest
bit to thread 2 and so on. For example, a value of 3 specifies that subsequent connections
on socket shall be handled exclusively by I/O threads 1 and 2.

See also zmq_init(3) for details on allocating the number of I/O threads for a specific
context.

Option value type uint64_t

Option value unit N/A (bitmap)

Default value 0

Applicable socket types N/A

ZMQ_BACKLOG: Set maximum length of the queue of outstanding connections
The ZMQ_BACKLOG option shall set the maximum length of the queue of outstanding peer
connections for the specified socket; this only applies to connection-oriented transports.
For details refer to your operating system documentation for the listen function.

Option value type int

Option value unit connections

Default value 100

Applicable socket types all, only for
connection-oriented transports.

ZMQ_BINDTODEVICE: Set name of device to bind the socket to
The ZMQ_BINDTODEVICE option binds this socket to a particular device, eg. an interface or
VRF. If a socket is bound to an interface, only packets received from that particular
interface are processed by the socket. If device is a VRF device, then subsequent
binds/connects to that socket use addresses in the VRF routing table.

Note
requires setting CAP_NET_RAW on the compiled program.

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP or UDP
transports.

ZMQ_CONNECT_RID: Assign the next outbound connection id
This option name is now deprecated. Use ZMQ_CONNECT_ROUTING_ID instead. ZMQ_CONNECT_RID
remains as an alias for now.

ZMQ_CONNECT_ROUTING_ID: Assign the next outbound routing id
The ZMQ_CONNECT_ROUTING_ID option sets the peer id of the peer connected via the next
zmq_connect() call, such that that connection is immediately ready for data transfer with
the given routing id. This option applies only to the first subsequent call to
zmq_connect(), zmq_connect() calls thereafter use the default connection behaviour.

Typical use is to set this socket option ahead of each zmq_connect() call. Each connection
MUST be assigned a unique routing id. Assigning a routing id that is already in use is not
allowed.

Useful when connecting ROUTER to ROUTER, or STREAM to STREAM, as it allows for immediate
sending to peers. Outbound routing id framing requirements for ROUTER and STREAM sockets
apply.

The routing id must be from 1 to 255 bytes long and MAY NOT start with a zero byte (such
routing ids are reserved for internal use by the 0MQ infrastructure).

Option value type binary data

Option value unit N/A

Default value NULL

Applicable socket types ZMQ_ROUTER, ZMQ_STREAM

ZMQ_CONFLATE: Keep only last message
If set, a socket shall keep only one message in its inbound/outbound queue, this message
being the last message received/the last message to be sent. Ignores ZMQ_RCVHWM and
ZMQ_SNDHWM options. Does not support multi-part messages, in particular, only one part of
it is kept in the socket internal queue.

Note
If recv is not called on the inbound socket, the queue and memory will grow with each
message received. Use zmq_getsockopt(3) with ZMQ_EVENTS to trigger the conflation of
the messages.

Option value type int

Option value unit boolean

Default value 0 (false)

Applicable socket types ZMQ_PULL, ZMQ_PUSH, ZMQ_SUB,
ZMQ_PUB, ZMQ_DEALER

ZMQ_CONNECT_TIMEOUT: Set connect() timeout
Sets how long to wait before timing-out a connect() system call. The connect() system call
normally takes a long time before it returns a time out error. Setting this option allows
the library to time out the call at an earlier interval.

Option value type int

Option value unit milliseconds

Default value 0 (disabled)

Applicable socket types all, when using TCP transports.

ZMQ_CURVE_PUBLICKEY: Set CURVE public key
Sets the socket’s long term public key. You must set this on CURVE client sockets, see
zmq_curve(7). You can provide the key as 32 binary bytes, or as a 40-character string
encoded in the Z85 encoding format and terminated in a null byte. The public key must
always be used with the matching secret key. To generate a public/secret key pair, use
zmq_curve_keypair(3). To derive the public key from a secret key, use zmq_curve_public(3).

Note
an option value size of 40 is supported for backwards compatibility, though is
deprecated.

Option value type binary data or Z85 text string

Option value size 32 or 41

Default value NULL

Applicable socket types all, when using TCP transport

ZMQ_CURVE_SECRETKEY: Set CURVE secret key
Sets the socket’s long term secret key. You must set this on both CURVE client and server
sockets, see zmq_curve(7). You can provide the key as 32 binary bytes, or as a
40-character string encoded in the Z85 encoding format and terminated in a null byte. To
generate a public/secret key pair, use zmq_curve_keypair(3). To derive the public key from
a secret key, use zmq_curve_public(3).

Note
an option value size of 40 is supported for backwards compatibility, though is
deprecated.

Option value type binary data or Z85 text string

Option value size 32 or 41

Default value NULL

Applicable socket types all, when using TCP transport

ZMQ_CURVE_SERVER: Set CURVE server role
Defines whether the socket will act as server for CURVE security, see zmq_curve(7). A
value of 1 means the socket will act as CURVE server. A value of 0 means the socket will
not act as CURVE server, and its security role then depends on other option settings.
Setting this to 0 shall reset the socket security to NULL. When you set this you must also
set the server’s secret key using the ZMQ_CURVE_SECRETKEY option. A server socket does not
need to know its own public key.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types all, when using TCP transport

ZMQ_CURVE_SERVERKEY: Set CURVE server key
Sets the socket’s long term server key. You must set this on CURVE client sockets, see
zmq_curve(7). You can provide the key as 32 binary bytes, or as a 40-character string
encoded in the Z85 encoding format and terminated in a null byte. This key must have been
generated together with the server’s secret key. To generate a public/secret key pair, use
zmq_curve_keypair(3).

Note
an option value size of 40 is supported for backwards compatibility, though is
deprecated.

Option value type binary data or Z85 text string

Option value size 32 or 41

Default value NULL

Applicable socket types all, when using TCP transport

ZMQ_GSSAPI_PLAINTEXT: Disable GSSAPI encryption
Defines whether communications on the socket will be encrypted, see zmq_gssapi(7). A value
of 1 means that communications will be plaintext. A value of 0 means communications will
be encrypted.

Option value type int

Option value unit 0, 1

Default value 0 (false)

Applicable socket types all, when using TCP transport

ZMQ_GSSAPI_PRINCIPAL: Set name of GSSAPI principal
Sets the name of the principal for whom GSSAPI credentials should be acquired.

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_GSSAPI_SERVER: Set GSSAPI server role
Defines whether the socket will act as server for GSSAPI security, see zmq_gssapi(7). A
value of 1 means the socket will act as GSSAPI server. A value of 0 means the socket will
act as GSSAPI client.

Option value type int

Option value unit 0, 1

Default value 0 (false)

Applicable socket types all, when using TCP transport

ZMQ_GSSAPI_SERVICE_PRINCIPAL: Set name of GSSAPI service principal
Sets the name of the principal of the GSSAPI server to which a GSSAPI client intends to
connect.

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE: Set name type of service principal
Sets the name type of the GSSAPI service principal. A value of ZMQ_GSSAPI_NT_HOSTBASED (0)
means the name specified with ZMQ_GSSAPI_SERVICE_PRINCIPAL is interpreted as a host based
name. A value of ZMQ_GSSAPI_NT_USER_NAME (1) means it is interpreted as a local user name.
A value of ZMQ_GSSAPI_NT_KRB5_PRINCIPAL (2) means it is interpreted as an unparsed
principal name string (valid only with the krb5 GSSAPI mechanism).

Option value type int

Option value unit 0, 1, 2

Default value 0 (ZMQ_GSSAPI_NT_HOSTBASED)

Applicable socket types all, when using TCP or IPC
transport

ZMQ_GSSAPI_PRINCIPAL_NAMETYPE: Set name type of principal
Sets the name type of the GSSAPI principal. A value of ZMQ_GSSAPI_NT_HOSTBASED (0) means
the name specified with ZMQ_GSSAPI_PRINCIPAL is interpreted as a host based name. A value
of ZMQ_GSSAPI_NT_USER_NAME (1) means it is interpreted as a local user name. A value of
ZMQ_GSSAPI_NT_KRB5_PRINCIPAL (2) means it is interpreted as an unparsed principal name
string (valid only with the krb5 GSSAPI mechanism).

Option value type int

Option value unit 0, 1, 2

Default value 0 (ZMQ_GSSAPI_NT_HOSTBASED)

Applicable socket types all, when using TCP or IPC
transport

ZMQ_HANDSHAKE_IVL: Set maximum handshake interval
The ZMQ_HANDSHAKE_IVL option shall set the maximum handshake interval for the specified
socket. Handshaking is the exchange of socket configuration information (socket type,
routing id, security) that occurs when a connection is first opened, only for
connection-oriented transports. If handshaking does not complete within the configured
time, the connection shall be closed. The value 0 means no handshake time limit.

Option value type int

Option value unit milliseconds

Default value 30000

Applicable socket types all but ZMQ_STREAM, only for
connection-oriented transports

ZMQ_HEARTBEAT_IVL: Set interval between sending ZMTP heartbeats
The ZMQ_HEARTBEAT_IVL option shall set the interval between sending ZMTP heartbeats for
the specified socket. If this option is set and is greater than 0, then a PING ZMTP
command will be sent every ZMQ_HEARTBEAT_IVL milliseconds.

Option value type int

Option value unit milliseconds

Default value 0

Applicable socket types all, when using
connection-oriented transports

ZMQ_HEARTBEAT_TIMEOUT: Set timeout for ZMTP heartbeats
The ZMQ_HEARTBEAT_TIMEOUT option shall set how long to wait before timing-out a connection
after sending a PING ZMTP command and not receiving any traffic. This option is only valid
if ZMQ_HEARTBEAT_IVL is also set, and is greater than 0. The connection will time out if
there is no traffic received after sending the PING command, but the received traffic does
not have to be a PONG command - any received traffic will cancel the timeout.

Option value type int

Option value unit milliseconds

Default value 0 normally, ZMQ_HEARTBEAT_IVL if
it is set

Applicable socket types all, when using
connection-oriented transports

ZMQ_HEARTBEAT_TTL: Set the TTL value for ZMTP heartbeats
The ZMQ_HEARTBEAT_TTL option shall set the timeout on the remote peer for ZMTP heartbeats.
If this option is greater than 0, the remote side shall time out the connection if it does
not receive any more traffic within the TTL period. This option does not have any effect
if ZMQ_HEARTBEAT_IVL is not set or is 0. Internally, this value is rounded down to the
nearest decisecond, any value less than 100 will have no effect.

Option value type int

Option value unit milliseconds

Default value 0

Maximum value 6553599 (which is 2^16-1
deciseconds)

Applicable socket types all, when using
connection-oriented transports

ZMQ_IDENTITY: Set socket identity
This option name is now deprecated. Use ZMQ_ROUTING_ID instead. ZMQ_IDENTITY remains as an
alias for now.

ZMQ_IMMEDIATE: Queue messages only to completed connections
By default queues will fill on outgoing connections even if the connection has not
completed. This can lead to "lost" messages on sockets with round-robin routing (REQ,
PUSH, DEALER). If this option is set to 1, messages shall be queued only to completed
connections. This will cause the socket to block if there are no other connections, but
will prevent queues from filling on pipes awaiting connection.

Option value type int

Option value unit boolean

Default value 0 (false)

Applicable socket types all, only for
connection-oriented transports.

ZMQ_INVERT_MATCHING: Invert message filtering
Reverses the filtering behavior of PUB-SUB sockets, when set to 1.

On PUB and XPUB sockets, this causes messages to be sent to all connected sockets except
those subscribed to a prefix that matches the message. On SUB sockets, this causes only
incoming messages that do not match any of the socket’s subscriptions to be received by
the user.

Whenever ZMQ_INVERT_MATCHING is set to 1 on a PUB socket, all SUB sockets connecting to it
must also have the option set to 1. Failure to do so will have the SUB sockets reject
everything the PUB socket sends them. XSUB sockets do not need to do this because they do
not filter incoming messages.

Option value type int

Option value unit 0,1

Default value 0

Applicable socket types ZMQ_PUB, ZMQ_XPUB, ZMQ_SUB

ZMQ_IPV6: Enable IPv6 on socket
Set the IPv6 option for the socket. A value of 1 means IPv6 is enabled on the socket,
while 0 means the socket will use only IPv4. When IPv6 is enabled the socket will connect
to, or accept connections from, both IPv4 and IPv6 hosts.

Option value type int

Option value unit boolean

Default value 0 (false)

Applicable socket types all, when using TCP transports.

ZMQ_LINGER: Set linger period for socket shutdown
The ZMQ_LINGER option shall set the linger period for the specified socket. The linger
period determines how long pending messages which have yet to be sent to a peer shall
linger in memory after a socket is disconnected with zmq_disconnect(3) or closed with
zmq_close(3), and further affects the termination of the socket’s context with
zmq_ctx_term(3). The following outlines the different behaviours:

• A value of -1 specifies an infinite linger period. Pending messages shall not be
discarded after a call to zmq_disconnect() or zmq_close(); attempting to terminate the
socket’s context with zmq_ctx_term() shall block until all pending messages have been
sent to a peer.

• The value of 0 specifies no linger period. Pending messages shall be discarded
immediately after a call to zmq_disconnect() or zmq_close().

• Positive values specify an upper bound for the linger period in milliseconds. Pending
messages shall not be discarded after a call to zmq_disconnect() or zmq_close();
attempting to terminate the socket’s context with zmq_ctx_term() shall block until
either all pending messages have been sent to a peer, or the linger period expires,
after which any pending messages shall be discarded.

Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all

ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size
Limits the size of the inbound message. If a peer sends a message larger than
ZMQ_MAXMSGSIZE it is disconnected. Value of -1 means no limit.

Option value type int64_t

Option value unit bytes

Default value -1

Applicable socket types all

ZMQ_METADATA: Add application metadata properties to a socket
The ZMQ_METADATA option shall add application metadata to the specified socket, the
metadata is exchanged with peers during connection setup. A metadata property is specfied
as a string, delimited by a colon, starting with the metadata property followed by the
metadata value, for example "X-key:value". Property names are restrited to maximum 255
characters and must be prefixed by "X-". Multiple application metadata properties can be
added to a socket by executing zmq_setsockopt() multiple times. As the argument is a
null-terminated string, binary data must be encoded before it is added e.g. using Z85
(zmq_z85_encode(3)).

Note
in DRAFT state, not yet available in stable releases.

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all

ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets
Sets the time-to-live field in every multicast packet sent from this socket. The default
is 1 which means that the multicast packets don’t leave the local network.

Option value type int

Option value unit network hops

Default value 1

Applicable socket types all, when using multicast
transports

ZMQ_MULTICAST_MAXTPDU: Maximum transport data unit size for multicast packets
Sets the maximum transport data unit size used for outbound multicast packets.

This must be set at or below the minimum Maximum Transmission Unit (MTU) for all network
paths over which multicast reception is required.

Option value type int

Option value unit bytes

Default value 1500

Applicable socket types all, when using multicast
transports

ZMQ_PLAIN_PASSWORD: Set PLAIN security password
Sets the password for outgoing connections over TCP or IPC. If you set this to a non-null
value, the security mechanism used for connections shall be PLAIN, see zmq_plain(7). If
you set this to a null value, the security mechanism used for connections shall be NULL,
see zmq_null(3).

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_PLAIN_SERVER: Set PLAIN server role
Defines whether the socket will act as server for PLAIN security, see zmq_plain(7). A
value of 1 means the socket will act as PLAIN server. A value of 0 means the socket will
not act as PLAIN server, and its security role then depends on other option settings.
Setting this to 0 shall reset the socket security to NULL.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types all, when using TCP transport

ZMQ_PLAIN_USERNAME: Set PLAIN security username
Sets the username for outgoing connections over TCP or IPC. If you set this to a non-null
value, the security mechanism used for connections shall be PLAIN, see zmq_plain(7). If
you set this to a null value, the security mechanism used for connections shall be NULL,
see zmq_null(3).

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_USE_FD: Set the pre-allocated socket file descriptor
When set to a positive integer value before zmq_bind is called on the socket, the socket
shall use the corresponding file descriptor for connections over TCP or IPC instead of
allocating a new file descriptor. Useful for writing systemd socket activated services. If
set to -1 (default), a new file descriptor will be allocated instead (default behaviour).

Note
if set after calling zmq_bind, this option shall have no effect. NOTE: the file
descriptor passed through MUST have been ran through the "bind" and "listen" system
calls beforehand. Also, socket option that would normally be passed through
zmq_setsockopt like TCP buffers length, IP_TOS or SO_REUSEADDR MUST be set beforehand
by the caller, as they must be set before the socket is bound.

Option value type int

Option value unit file descriptor

Default value -1

Applicable socket types all bound sockets, when using
IPC or TCP transport

ZMQ_PROBE_ROUTER: bootstrap connections to ROUTER sockets
When set to 1, the socket will automatically send an empty message when a new connection
is made or accepted. You may set this on REQ, DEALER, or ROUTER sockets connected to a
ROUTER socket. The application must filter such empty messages. The ZMQ_PROBE_ROUTER
option in effect provides the ROUTER application with an event signaling the arrival of a
new peer.

Note
do not set this option on a socket that talks to any other socket types: the results
are undefined.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER, ZMQ_DEALER, ZMQ_REQ

ZMQ_RATE: Set multicast data rate
The ZMQ_RATE option shall set the maximum send or receive data rate for multicast
transports such as zmq_pgm(7) using the specified socket.

Option value type int

Option value unit kilobits per second

Default value 100

Applicable socket types all, when using multicast
transports

ZMQ_RCVBUF: Set kernel receive buffer size
The ZMQ_RCVBUF option shall set the underlying kernel receive buffer size for the socket
to the specified size in bytes. A value of -1 means leave the OS default unchanged. For
details refer to your operating system documentation for the SO_RCVBUF socket option.

Option value type int

Option value unit bytes

Default value -1

Applicable socket types all

ZMQ_RCVHWM: Set high water mark for inbound messages
The ZMQ_RCVHWM option shall set the high water mark for inbound messages on the specified
socket. The high water mark is a hard limit on the maximum number of outstanding messages
0MQ shall queue in memory for any single peer that the specified socket is communicating
with. A value of zero means no limit.

If this limit has been reached the socket shall enter an exceptional state and depending
on the socket type, 0MQ shall take appropriate action such as blocking or dropping sent
messages. Refer to the individual socket descriptions in zmq_socket(3) for details on the
exact action taken for each socket type.

Note
0MQ does not guarantee that the socket will be able to queue as many as ZMQ_RCVHWM
messages, and the actual limit may be lower or higher, depending on socket transport.
A notable example is for sockets using TCP transport; see zmq_tcp(7).

Option value type int

Option value unit messages

Default value 1000

Applicable socket types all

ZMQ_RCVTIMEO: Maximum time before a recv operation returns with EAGAIN
Sets the timeout for receive operation on the socket. If the value is 0, zmq_recv(3) will
return immediately, with a EAGAIN error if there is no message to receive. If the value is
-1, it will block until a message is available. For all other values, it will wait for a
message for that amount of time before returning with an EAGAIN error.

Option value type int

Option value unit milliseconds

Default value -1 (infinite)

Applicable socket types all

ZMQ_RECONNECT_IVL: Set reconnection interval
The ZMQ_RECONNECT_IVL option shall set the initial reconnection interval for the specified
socket. The reconnection interval is the period 0MQ shall wait between attempts to
reconnect disconnected peers when using connection-oriented transports. The value -1 means
no reconnection.

Note
The reconnection interval may be randomized by 0MQ to prevent reconnection storms in
topologies with a large number of peers per socket.

Option value type int

Option value unit milliseconds

Default value 100

Applicable socket types all, only for
connection-oriented transports

ZMQ_RECONNECT_IVL_MAX: Set maximum reconnection interval
The ZMQ_RECONNECT_IVL_MAX option shall set the maximum reconnection interval for the
specified socket. This is the maximum period 0MQ shall wait between attempts to reconnect.
On each reconnect attempt, the previous interval shall be doubled untill
ZMQ_RECONNECT_IVL_MAX is reached. This allows for exponential backoff strategy. Default
value means no exponential backoff is performed and reconnect interval calculations are
only based on ZMQ_RECONNECT_IVL.

Note
Values less than ZMQ_RECONNECT_IVL will be ignored.

Option value type int

Option value unit milliseconds

Default value 0 (only use ZMQ_RECONNECT_IVL)

Applicable socket types all, only for
connection-oriented transports

ZMQ_RECOVERY_IVL: Set multicast recovery interval
The ZMQ_RECOVERY_IVL option shall set the recovery interval for multicast transports using
the specified socket. The recovery interval determines the maximum time in milliseconds
that a receiver can be absent from a multicast group before unrecoverable data loss will
occur.

Caution
Exercise care when setting large recovery intervals as the data needed for recovery
will be held in memory. For example, a 1 minute recovery interval at a data rate of
1Gbps requires a 7GB in-memory buffer.

Option value type int

Option value unit milliseconds

Default value 10000

Applicable socket types all, when using multicast
transports

ZMQ_REQ_CORRELATE: match replies with requests
The default behaviour of REQ sockets is to rely on the ordering of messages to match
requests and responses and that is usually sufficient. When this option is set to 1, the
REQ socket will prefix outgoing messages with an extra frame containing a request id. That
means the full message is (request id, 0, user frames...). The REQ socket will discard all
incoming messages that don’t begin with these two frames.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_REQ

ZMQ_REQ_RELAXED: relax strict alternation between request and reply
By default, a REQ socket does not allow initiating a new request with zmq_send(3) until
the reply to the previous one has been received. When set to 1, sending another message is
allowed and previous replies will be discarded if any. The request-reply state machine is
reset and a new request is sent to the next available peer.

If set to 1, also enable ZMQ_REQ_CORRELATE to ensure correct matching of requests and
replies. Otherwise a late reply to an aborted request can be reported as the reply to the
superseding request.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_REQ

ZMQ_ROUTER_HANDOVER: handle duplicate client routing ids on ROUTER sockets
If two clients use the same routing id when connecting to a ROUTER, the results shall
depend on the ZMQ_ROUTER_HANDOVER option setting. If that is not set (or set to the
default of zero), the ROUTER socket shall reject clients trying to connect with an
already-used routing id. If that option is set to 1, the ROUTER socket shall hand-over the
connection to the new client and disconnect the existing one.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER

ZMQ_ROUTER_MANDATORY: accept only routable messages on ROUTER sockets
Sets the ROUTER socket behaviour when an unroutable message is encountered. A value of 0
is the default and discards the message silently when it cannot be routed or the peers
SNDHWM is reached. A value of 1 returns an EHOSTUNREACH error code if the message cannot
be routed or EAGAIN error code if the SNDHWM is reached and ZMQ_DONTWAIT was used. Without
ZMQ_DONTWAIT it will block until the SNDTIMEO is reached or a spot in the send queue opens
up.

When ZMQ_ROUTER_MANDATORY is set to 1, ZMQ_POLLOUT events will be generated if one or more
messages can be sent to at least one of the peers. If ZMQ_ROUTER_MANDATORY is set to 0,
the socket will generate a ZMQ_POLLOUT event on every call to zmq_poll resp.
zmq_poller_wait_all.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER

ZMQ_ROUTER_RAW: switch ROUTER socket to raw mode
Sets the raw mode on the ROUTER, when set to 1. When the ROUTER socket is in raw mode, and
when using the tcp:// transport, it will read and write TCP data without 0MQ framing. This
lets 0MQ applications talk to non-0MQ applications. When using raw mode, you cannot set
explicit identities, and the ZMQ_SNDMORE flag is ignored when sending data messages. In
raw mode you can close a specific connection by sending it a zero-length message
(following the routing id frame).

Note
This option is deprecated, please use ZMQ_STREAM sockets instead.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER

ZMQ_ROUTING_ID: Set socket routing id
The ZMQ_ROUTING_ID option shall set the routing id of the specified socket when connecting
to a ROUTER socket.

A routing id must be at least one byte and at most 255 bytes long. Identities starting
with a zero byte are reserved for use by the 0MQ infrastructure.

If two clients use the same routing id when connecting to a ROUTER, the results shall
depend on the ZMQ_ROUTER_HANDOVER option setting. If that is not set (or set to the
default of zero), the ROUTER socket shall reject clients trying to connect with an
already-used routing id. If that option is set to 1, the ROUTER socket shall hand-over the
connection to the new client and disconnect the existing one.

Option value type binary data

Option value unit N/A

Default value NULL

Applicable socket types ZMQ_REQ, ZMQ_REP, ZMQ_ROUTER,
ZMQ_DEALER.

ZMQ_SNDBUF: Set kernel transmit buffer size
The ZMQ_SNDBUF option shall set the underlying kernel transmit buffer size for the socket
to the specified size in bytes. A value of -1 means leave the OS default unchanged. For
details please refer to your operating system documentation for the SO_SNDBUF socket
option.

Option value type int

Option value unit bytes

Default value -1

Applicable socket types all

ZMQ_SNDHWM: Set high water mark for outbound messages
The ZMQ_SNDHWM option shall set the high water mark for outbound messages on the specified
socket. The high water mark is a hard limit on the maximum number of outstanding messages
0MQ shall queue in memory for any single peer that the specified socket is communicating
with. A value of zero means no limit.

Note
0MQ does not guarantee that the socket will accept as many as ZMQ_SNDHWM messages, and
the actual limit may be as much as 90% lower depending on the flow of messages on the
socket. The socket may even be able to accept more messages than the ZMQ_SNDHWM
threshold; a notable example is for sockets using TCP transport; see zmq_tcp(7).

Option value type int

Option value unit messages

Default value 1000

Applicable socket types all

ZMQ_SNDTIMEO: Maximum time before a send operation returns with EAGAIN
Sets the timeout for send operation on the socket. If the value is 0, zmq_send(3) will
return immediately, with a EAGAIN error if the message cannot be sent. If the value is -1,
it will block until the message is sent. For all other values, it will try to send the
message for that amount of time before returning with an EAGAIN error.

Option value type int

Option value unit milliseconds

Default value -1 (infinite)

Applicable socket types all

ZMQ_SOCKS_PROXY: Set SOCKS5 proxy address
Sets the SOCKS5 proxy address that shall be used by the socket for the TCP connection(s).
Supported authentication methods are: no authentication or basic authentication when setup
with ZMQ_SOCKS_USERNAME. If the endpoints are domain names instead of addresses they shall
not be resolved and they shall be forwarded unchanged to the SOCKS proxy service in the
client connection request message (address type 0x03 domain name).

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_SOCKS_USERNAME: Set SOCKS username and select basic authentication
Sets the username for authenticated connection to the SOCKS5 proxy. If you set this to a
non-null and non-empty value, the authentication method used for the SOCKS5 connection
shall be basic authentication. In this case, use ZMQ_SOCKS_PASSWORD option in order to set
the password. If you set this to a null value or empty value, the authentication method
shall be no authentication, the default.

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_SOCKS_PASSWORD: Set SOCKS basic authentication password
Sets the password for authenticating to the SOCKS5 proxy server. This is used only when
the SOCKS5 authentication method has been set to basic authentication through the
ZMQ_SOCKS_USERNAME option. Setting this to a null value (the default) is equivalent to an
empty password string.

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

ZMQ_STREAM_NOTIFY: send connect and disconnect notifications
Enables connect and disconnect notifications on a STREAM socket, when set to 1. When
notifications are enabled, the socket delivers a zero-length message when a peer connects
or disconnects.

Option value type int

Option value unit 0, 1

Default value 1

Applicable socket types ZMQ_STREAM

ZMQ_SUBSCRIBE: Establish message filter
The ZMQ_SUBSCRIBE option shall establish a new message filter on a ZMQ_SUB socket. Newly
created ZMQ_SUB sockets shall filter out all incoming messages, therefore you should call
this option to establish an initial message filter.

An empty option_value of length zero shall subscribe to all incoming messages. A non-empty
option_value shall subscribe to all messages beginning with the specified prefix. Multiple
filters may be attached to a single ZMQ_SUB socket, in which case a message shall be
accepted if it matches at least one filter.

Option value type binary data

Option value unit N/A

Default value N/A

Applicable socket types ZMQ_SUB

ZMQ_TCP_KEEPALIVE: Override SO_KEEPALIVE socket option
Override SO_KEEPALIVE socket option (where supported by OS). The default value of -1 means
to skip any overrides and leave it to OS default.

Option value type int

Option value unit -1,0,1

Default value -1 (leave to OS default)

Applicable socket types all, when using TCP transports.

ZMQ_TCP_KEEPALIVE_CNT: Override TCP_KEEPCNT socket option
Override TCP_KEEPCNT socket option (where supported by OS). The default value of -1 means
to skip any overrides and leave it to OS default.

Option value type int

Option value unit -1,>0

Default value -1 (leave to OS default)

Applicable socket types all, when using TCP transports.

ZMQ_TCP_KEEPALIVE_IDLE: Override TCP_KEEPIDLE (or TCP_KEEPALIVE on some OS)
Override TCP_KEEPIDLE (or TCP_KEEPALIVE on some OS) socket option (where supported by OS).
The default value of -1 means to skip any overrides and leave it to OS default.

Option value type int

Option value unit -1,>0

Default value -1 (leave to OS default)

Applicable socket types all, when using TCP transports.

ZMQ_TCP_KEEPALIVE_INTVL: Override TCP_KEEPINTVL socket option
Override TCP_KEEPINTVL socket option(where supported by OS). The default value of -1 means
to skip any overrides and leave it to OS default.

Option value type int

Option value unit -1,>0

Default value -1 (leave to OS default)

Applicable socket types all, when using TCP transports.

ZMQ_TCP_MAXRT: Set TCP Maximum Retransmit Timeout
On OSes where it is supported, sets how long before an unacknowledged TCP retransmit times
out. The system normally attempts many TCP retransmits following an exponential backoff
strategy. This means that after a network outage, it may take a long time before the
session can be re-established. Setting this option allows the timeout to happen at a
shorter interval.

Option value type int

Option value unit milliseconds

Default value 0 (leave to OS default)

Applicable socket types all, when using TCP transports.

ZMQ_TOS: Set the Type-of-Service on socket
Sets the ToS fields (Differentiated services (DS) and Explicit Congestion Notification
(ECN) field of the IP header. The ToS field is typically used to specify a packets
priority. The availability of this option is dependent on intermediate network equipment
that inspect the ToS field and provide a path for low-delay, high-throughput,
highly-reliable service, etc.

Option value type int

Option value unit >0

Default value 0

Applicable socket types all, only for
connection-oriented transports

ZMQ_UNSUBSCRIBE: Remove message filter
The ZMQ_UNSUBSCRIBE option shall remove an existing message filter on a ZMQ_SUB socket.
The filter specified must match an existing filter previously established with the
ZMQ_SUBSCRIBE option. If the socket has several instances of the same filter attached the
ZMQ_UNSUBSCRIBE option shall remove only one instance, leaving the rest in place and
functional.

Option value type binary data

Option value unit N/A

Default value N/A

Applicable socket types ZMQ_SUB

ZMQ_XPUB_VERBOSE: pass duplicate subscribe messages on XPUB socket
Sets the XPUB socket behaviour on new duplicated subscriptions. If enabled, the socket
passes all subscribe messages to the caller. If disabled, only the first subscription to
each filter will be passed. The default is 0 (disabled).

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_XPUB

ZMQ_XPUB_VERBOSER: pass duplicate subscribe and unsubscribe messages on XPUB socket
Sets the XPUB socket behaviour on new duplicated subscriptions and unsubscriptions. If
enabled, the socket passes all subscribe and unsubscribe messages to the caller. If
disabled, only the first subscription to each filter and the last unsubscription from each
filter will be passed. The default is 0 (disabled).

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_XPUB

ZMQ_XPUB_MANUAL: change the subscription handling to manual
Sets the XPUB socket subscription handling mode manual/automatic. A value of 0 is the
default and subscription requests will be handled automatically. A value of 1 will change
the subscription requests handling to manual, with manual mode subscription requests are
not added to the subscription list. To add subscription the user need to call setsockopt
with ZMQ_SUBSCRIBE on XPUB socket.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_XPUB

ZMQ_XPUB_MANUAL_LAST_VALUE: change the subscription handling to manual
This option is similar to ZMQ_XPUB_MANUAL. The difference is that
ZMQ_XPUB_MANUAL_LAST_VALUE changes the XPUB socket behaviour to send the first message to
the last subscriber after the socket receives a subscription and call setsockopt with
ZMQ_SUBSCRIBE on XPUB socket. This prevents duplicated messages when using last value
caching(LVC).

Note
in DRAFT state, not yet available in stable releases.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_XPUB

ZMQ_XPUB_NODROP: do not silently drop messages if SENDHWM is reached
Sets the XPUB socket behaviour to return error EAGAIN if SENDHWM is reached and the
message could not be send.

A value of 0 is the default and drops the message silently when the peers SNDHWM is
reached. A value of 1 returns an EAGAIN error code if the SNDHWM is reached and
ZMQ_DONTWAIT was used.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_XPUB, ZMQ_PUB

ZMQ_XPUB_WELCOME_MSG: set welcome message that will be received by subscriber when connecting
Sets a welcome message the will be recieved by subscriber when connecting. Subscriber must
subscribe to the Welcome message before connecting. Welcome message will also be sent on
reconnecting. For welcome message to work well user must poll on incoming subscription
messages on the XPUB socket and handle them.

Use NULL and length of zero to disable welcome message.

Option value type binary data

Option value unit N/A

Default value NULL

Applicable socket types ZMQ_XPUB

ZMQ_ZAP_DOMAIN: Set RFC 27 authentication domain
Sets the domain for ZAP (ZMQ RFC 27) authentication. A ZAP domain must be specified to
enable authentication. When the ZAP domain is empty, which is the default, ZAP
authentication is disabled. This is not compatible with previous versions of libzmq, so it
can be controlled by ZMQ_ZAP_ENFORCE_DOMAIN which for now is disabled by default. See
http://rfc.zeromq.org/spec:27 for more details.

Option value type character string

Option value unit N/A

Default value empty

Applicable socket types all, when using TCP transport

ZMQ_ZAP_ENFORCE_DOMAIN: Set ZAP domain handling to strictly adhere the RFC
The ZAP (ZMQ RFC 27) authentication protocol specifies that a domain must always be set.
Older versions of libzmq did not follow the spec and allowed an empty domain to be set.
This option can be used to enabled or disable the stricter, backward incompatible
behaviour. For now it is disabled by default, but in a future version it will be enabled
by default.

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types all, when using ZAP

ZMQ_TCP_ACCEPT_FILTER: Assign filters to allow new TCP connections
Assign an arbitrary number of filters that will be applied for each new TCP transport
connection on a listening socket. If no filters are applied, then the TCP transport allows
connections from any IP address. If at least one filter is applied then new connection
source ip should be matched. To clear all filters call zmq_setsockopt(socket,
ZMQ_TCP_ACCEPT_FILTER, NULL, 0). Filter is a null-terminated string with ipv6 or ipv4
CIDR.

Note
This option is deprecated, please use authentication via the ZAP API and IP address
whitelisting / blacklisting.

Option value type binary data

Option value unit N/A

Default value no filters (allow from all)

Applicable socket types all listening sockets, when
using TCP transports.

ZMQ_IPC_FILTER_GID: Assign group ID filters to allow new IPC connections
Assign an arbitrary number of filters that will be applied for each new IPC transport
connection on a listening socket. If no IPC filters are applied, then the IPC transport
allows connections from any process. If at least one UID, GID, or PID filter is applied
then new connection credentials should be matched. To clear all GID filters call
zmq_setsockopt(socket, ZMQ_IPC_FILTER_GID, NULL, 0).

Note
GID filters are only available on platforms supporting SO_PEERCRED or LOCAL_PEERCRED
socket options (currently only Linux and later versions of OS X).

Note
This option is deprecated, please use authentication via the ZAP API and IPC
whitelisting / blacklisting.

Option value type gid_t

Option value unit N/A

Default value no filters (allow from all)

Applicable socket types all listening sockets, when
using IPC transports.

ZMQ_IPC_FILTER_PID: Assign process ID filters to allow new IPC connections
Assign an arbitrary number of filters that will be applied for each new IPC transport
connection on a listening socket. If no IPC filters are applied, then the IPC transport
allows connections from any process. If at least one UID, GID, or PID filter is applied
then new connection credentials should be matched. To clear all PID filters call
zmq_setsockopt(socket, ZMQ_IPC_FILTER_PID, NULL, 0).

Note
PID filters are only available on platforms supporting the SO_PEERCRED socket option
(currently only Linux).

Note
This option is deprecated, please use authentication via the ZAP API and IPC
whitelisting / blacklisting.

Option value type pid_t

Option value unit N/A

Default value no filters (allow from all)

Applicable socket types all listening sockets, when
using IPC transports.

ZMQ_IPC_FILTER_UID: Assign user ID filters to allow new IPC connections
Assign an arbitrary number of filters that will be applied for each new IPC transport
connection on a listening socket. If no IPC filters are applied, then the IPC transport
allows connections from any process. If at least one UID, GID, or PID filter is applied
then new connection credentials should be matched. To clear all UID filters call
zmq_setsockopt(socket, ZMQ_IPC_FILTER_UID, NULL, 0).

Note
UID filters are only available on platforms supporting SO_PEERCRED or LOCAL_PEERCRED
socket options (currently only Linux and later versions of OS X).

Note
This option is deprecated, please use authentication via the ZAP API and IPC
whitelisting / blacklisting.

Option value type uid_t

Option value unit N/A

Default value no filters (allow from all)

Applicable socket types all listening sockets, when
using IPC transports.

ZMQ_IPV4ONLY: Use IPv4-only on socket
Set the IPv4-only option for the socket. This option is deprecated. Please use the
ZMQ_IPV6 option.

Option value type int

Option value unit boolean

Default value 1 (true)

Applicable socket types all, when using TCP transports.

ZMQ_VMCI_BUFFER_SIZE: Set buffer size of the VMCI socket
The ZMQ_VMCI_BUFFER_SIZE option shall set the size of the underlying buffer for the
socket. Used during negotiation before the connection is established.

Option value type uint64_t

Option value unit bytes

Default value 65546

Applicable socket types all, when using VMCI transport

ZMQ_VMCI_BUFFER_MIN_SIZE: Set min buffer size of the VMCI socket
The ZMQ_VMCI_BUFFER_MIN_SIZE option shall set the min size of the underlying buffer for
the socket. Used during negotiation before the connection is established.

Option value type uint64_t

Option value unit bytes

Default value 128

Applicable socket types all, when using VMCI transport

ZMQ_VMCI_BUFFER_MAX_SIZE: Set max buffer size of the VMCI socket
The ZMQ_VMCI_BUFFER_MAX_SIZE option shall set the max size of the underlying buffer for
the socket. Used during negotiation before the connection is established.

Option value type uint64_t

Option value unit bytes

Default value 262144

Applicable socket types all, when using VMCI transport

ZMQ_VMCI_CONNECT_TIMEOUT: Set connection timeout of the VMCI socket
The ZMQ_VMCI_CONNECT_TIMEOUT option shall set connection timeout for the socket.

Option value type int

Option value unit milliseconds

Default value -1

Applicable socket types all, when using VMCI transport

ZMQ_MULTICAST_LOOP: Control multicast local loopback
For multicast UDP sender sockets this option sets whether the data sent should be looped
back on local listening sockets.

Option value type int

Option value unit 0, 1

Default value 1

Applicable socket types ZMQ_RADIO, when using UDP
multicast transport

ZMQ_ROUTER_NOTIFY: Send connect and disconnect notifications
Enable connect and disconnect notifications on a ROUTER socket. When enabled, the socket
delivers a zero-length message (with routing-id as first frame) when a peer connects or
disconnects. It’s possible to notify both events for a peer by OR-ing the flag values.
This option only applies to stream oriented (tcp, ipc) transports.

Note
in DRAFT state, not yet available in stable releases.

Option value type int

Option value unit 0, ZMQ_NOTIFY_CONNECT,
ZMQ_NOTIFY_DISCONNECT,
ZMQ_NOTIFY_CONNECT |
ZMQ_NOTIFY_DISCONNECT

Default value 0

Applicable socket types ZMQ_ROUTER

ZMQ_IN_BATCH_SIZE: Maximal receive batch size
Sets the maximal amount of messages that can be received in a single recv system call.
WARNING: this option should almost never be changed. The default has been chosen to offer
the best compromise between latency and throughtput. In the vast majority of cases,
changing this option will result in worst result if not outright breakages.

Cannot be zero.

Note
in DRAFT state, not yet available in stable releases.

Option value type int

Option value unit messages

Default value 8192

Applicable socket types All, when using TCP, IPC, PGM or
NORM transport.

ZMQ_OUT_BATCH_SIZE: Maximal send batch size
Sets the maximal amount of messages that can be sent in a single send system call.
WARNING: this option should almost never be changed. The default has been chosen to offer
the best compromise between latency and throughtput. In the vast majority of cases,
changing this option will result in worst result if not outright breakages.

Cannot be zero.

Note
in DRAFT state, not yet available in stable releases.

Option value type int

Option value unit messages

Default value 8192

Applicable socket types All, when using TCP, IPC, PGM or
NORM transport.

RETURN VALUE

       The zmq_setsockopt() function shall return zero if successful. Otherwise it shall return
       -1 and set errno to one of the values defined below.

ERRORS

       EINVAL
           The requested option option_name is unknown, or the requested option_len or
           option_value is invalid.

       ETERM
           The 0MQ context associated with the specified socket was terminated.

       ENOTSOCK
           The provided socket was invalid.

       EINTR
           The operation was interrupted by delivery of a signal.

EXAMPLE

       Subscribing to messages on a ZMQ_SUB socket.

           /* Subscribe to all messages */
           rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "", 0);
           assert (rc == 0);
           /* Subscribe to messages prefixed with "ANIMALS.CATS" */
           rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "ANIMALS.CATS", 12);

       Setting I/O thread affinity.

           int64_t affinity;
           /* Incoming connections on TCP port 5555 shall be handled by I/O thread 1 */
           affinity = 1;
           rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &affinity, sizeof (affinity));
           assert (rc);
           rc = zmq_bind (socket, "tcp://lo:5555");
           assert (rc);
           /* Incoming connections on TCP port 5556 shall be handled by I/O thread 2 */
           affinity = 2;
           rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &affinity, sizeof (affinity));
           assert (rc);
           rc = zmq_bind (socket, "tcp://lo:5556");
           assert (rc);

AUTHORS

       This page was written by the 0MQ community. To make a change please read the 0MQ
       Contribution Policy at http://www.zeromq.org/docs:contributing.

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

EXAMPLE

SEE ALSO

AUTHORS