# zmq_setsockopt(3) Manual Page

## 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 ØMQ 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 ØMQ 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 ØMQ 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 ØMQ 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_DISCONNECT_MSG: set a disconnect message that the socket will generate when accepted peer disconnect

When set, the socket will generate a disconnect message when accepted peer has been disconnected. You may set this on ROUTER, SERVER and PEER sockets. The combination with ZMQ_HEARTBEAT_IVL is powerful and simplify protocols, when heartbeat recognize a connection drop it will generate a disconnect message that can match the protocol of the application.

Option value type | binary data
Option value unit | N/A
Default value | NULL
Applicable socket types | ZMQ_ROUTER, ZMQ_SERVER and ZMQ_PEER

### 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_HELLO_MSG: set an hello message that will be sent when a new peer connect

When set, the socket will automatically send an hello message when a new connection is made or accepted. You may set this on DEALER, ROUTER, CLIENT, SERVER and PEER sockets. The combination with ZMQ_HEARTBEAT_IVL is powerful and simplify protocols, as now heartbeat and sending the hello message can be left out of protocols and be handled by zeromq.

Option value type | binary data
Option value unit | N/A
Default value | NULL
Applicable socket types | ZMQ_ROUTER, ZMQ_DEALER, ZMQ_CLIENT, ZMQ_SERVER and ZMQ_PEER

### 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_PRIORITY: Set the Priority on socket

Sets the protocol-defined priority for all packets to be sent on this socket, where supported by the OS. In Linux, values greater than 6 require admin capability (CAP_NET_ADMIN)

Option value type | int
Option value unit | >0
Default value | 0
Applicable socket types | all, only for connection-oriented transports

### 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 ØMQ 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, ØMQ 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 | ØMQ 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 ØMQ 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 ØMQ 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 ØMQ 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_RECONNECT_STOP: Set condition where reconnection will stop

The ZMQ_RECONNECT_STOP option shall set the conditions under which automatic reconnection will stop. This can be useful when a process binds to a wild-card port, where the OS supplies an ephemeral port.

The ZMQ_RECONNECT_STOP_CONN_REFUSED option will stop reconnection when ØMQ receives the ECONNREFUSED return code from the connect. This indicates that there is no code bound to the specified endpoint.

The ZMQ_RECONNECT_STOP_HANDSHAKE_FAILED option will stop reconnection if the ØMQ handshake fails. This can be used to detect and/or prevent errant connection attempts to non-ØMQ sockets. Note that when specifying this option you may also want to set `ZMQ_HANDSHAKE_IVL`— the default handshake interval is 30000 (30 seconds), which is typically too large.

The ZMQ_RECONNECT_STOP_AFTER_DISCONNECT option will stop reconnection when zmq_disconnect() has been called. This can be useful when the user’s request failed (server not ready), as the socket does not need to continue to reconnect after user disconnect actively.

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

Option value type | int
Option value unit | 0, ZMQ_RECONNECT_STOP_CONN_REFUSED, ZMQ_RECONNECT_STOP_HANDSHAKE_FAILED, ZMQ_RECONNECT_STOP_CONN_REFUSED | ZMQ_RECONNECT_STOP_HANDSHAKE_FAILED
Default value | 0
Applicable socket types | all, only for connection-oriented transports (ZMQ_HANDSHAKE_IVL is not applicable for ZMQ_STREAM sockets)

### 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 ØMQ framing. This lets ØMQ applications talk to non-ØMQ 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 ØMQ 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 ØMQ 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, ØMQ 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 | ØMQ 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_ONLY_FIRST_SUBSCRIBE: Process only first subscribe/unsubscribe in a multipart message

If set, only the first part of the multipart message is processed as a subscribe/unsubscribe message. The rest are forwarded as user data regardless of message contents.

It not set (default), subscribe/unsubscribe messages in a multipart message are processed as such regardless of their number and order.

Option value type | int
Option value unit | boolean
Default value | 0 (false)
Applicable socket types | ZMQ_XSUB, 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 allowing / blocking.

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 allowing / blocking.

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 allowing / blocking.

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 allowing / blocking.

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 ØMQ 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);

## SEE ALSO

zmq_getsockopt(3) zmq_socket(3) zmq_plain(7) zmq_curve(7) zmq(7)

## AUTHORS

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