zmq_getsockopt - Man Page

The ZMQ_AFFINITY option shall retrieve 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.

The ZMQ_BACKLOG option shall retrieve 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.

The ZMQ_BINDTODEVICE option retrieves the name of the device this socket is bound to, eg. an interface or VRF. If a socket is bound to an interface, only packets received from that 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.

Retrieves 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.

Retrieves the current long term public key for the socket. You can provide either a 32 byte buffer, to retrieve the binary key value, or a 41 byte buffer, to retrieve the key in a printable Z85 format. NOTE: to fetch a printable key, the buffer must be 41 bytes large to hold the 40-char key value and one null byte.

Retrieves the current long term secret key for the socket. You can provide either a 32 byte buffer, to retrieve the binary key value, or a 41 byte buffer, to retrieve the key in a printable Z85 format. NOTE: to fetch a printable key, the buffer must be 41 bytes large to hold the 40-char key value and one null byte.

Retrieves the current server key for the client socket. You can provide either a 32 byte buffer, to retrieve the binary key value, or a 41-byte buffer, to retrieve the key in a printable Z85 format. NOTE: to fetch a printable key, the buffer must be 41 bytes large to hold the 40-char key value and one null byte.

The ZMQ_EVENTS option shall retrieve the event state for the specified socket. The returned value is a bit mask constructed by OR’ing a combination of the following event flags:

ZMQ_POLLIN

Indicates that at least one message may be received from the specified socket without blocking.

ZMQ_POLLOUT

Indicates that at least one message may be sent to the specified socket without blocking.

The combination of a file descriptor returned by the ZMQ_FD option being ready for reading but no actual events returned by a subsequent retrieval of the ZMQ_EVENTS option is valid; applications should simply ignore this case and restart their polling operation/event loop.

The ZMQ_FD option shall retrieve the file descriptor associated with the specified socket. The returned file descriptor can be used to integrate the socket into an existing event loop; the 0MQ library shall signal any pending events on the socket in an edge-triggered fashion by making the file descriptor become ready for reading.

Returns the ZMQ_GSSAPI_PLAINTEXT option, if any, previously set on the socket. A value of 1 means that communications will be plaintext. A value of 0 means communications will be encrypted.

The ZMQ_GSSAPI_PRINCIPAL option shall retrieve the principal name set for the GSSAPI security mechanism. The returned value shall be a NULL-terminated string and MAY be empty. The returned size SHALL include the terminating null byte.

Returns the ZMQ_GSSAPI_SERVER option, if any, previously set on the socket.

The ZMQ_GSSAPI_SERVICE_PRINCIPAL option shall retrieve the principal name of the GSSAPI server to which a GSSAPI client socket intends to connect. The returned value shall be a NULL-terminated string and MAY be empty. The returned size SHALL include the terminating null byte.

Returns the ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE option, if any, previously set on the socket. 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).

Returns the ZMQ_GSSAPI_PRINCIPAL_NAMETYPE option, if any, previously set on the socket. 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).

The ZMQ_HANDSHAKE_IVL option shall retrieve 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.

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

Retrieve the state of the attach on connect value. If set to 1, will delay the attachment of a pipe on connect until the underlying connection has completed. This will cause the socket to block if there are no other connections, but will prevent queues from filling on pipes awaiting connection.

Returns the value of the ZMQ_INVERT_MATCHING option. A value of 1 means the socket uses inverted prefix matching.

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.

Retrieve the IPv4-only option for the socket. This option is deprecated. Please use the ZMQ_IPV6 option.

Retrieve 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.

The ZMQ_LAST_ENDPOINT option shall retrieve the last endpoint bound for TCP and IPC transports. The returned value will be a string in the form of a ZMQ DSN. Note that if the TCP host is INADDR_ANY, indicated by a *, then the returned address will be 0.0.0.0 (for IPv4). Note: not supported on GNU/Hurd with IPC due to non-working getsockname().

The ZMQ_LINGER option shall retrieve 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 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:

• The default value of -1 specifies an infinite linger period. Pending messages shall not be discarded after a call to 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 when the socket is closed with 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_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

The option shall retrieve limit for the inbound messages. If a peer sends a message larger than ZMQ_MAXMSGSIZE it is disconnected. Value of -1 means no limit.

The ZMQ_MECHANISM option shall retrieve the current security mechanism for the socket.

The option shall retrieve time-to-live used for outbound multicast packets. The default of 1 means that the multicast packets don’t leave the local network.

The ZMQ_MULTICAST_MAXTPDU option shall retrieve 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.

The ZMQ_PLAIN_PASSWORD option shall retrieve the last password set for the PLAIN security mechanism. The returned value shall be a NULL-terminated string and MAY be empty. The returned size SHALL include the terminating null byte.

Returns the ZMQ_PLAIN_SERVER option, if any, previously set on the socket.

The ZMQ_PLAIN_USERNAME option shall retrieve the last username set for the PLAIN security mechanism. The returned value shall be a NULL-terminated string and MAY be empty. The returned size SHALL include the terminating null byte.

The ZMQ_USE_FD option shall retrieve the pre-allocated file descriptor that has been assigned to a ZMQ socket, if any. -1 shall be returned if a pre-allocated file descriptor was not set for the socket.

ZMQ_PRIORITY: Retrieve the Priority on socket

Gets the protocol-defined priority for all packets to be sent on this
socket, where supported by the OS.

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


ZMQ_RATE: Retrieve multicast data rate

The ZMQ_RATE option shall retrieve the maximum send or receive data rate for multicast transports using the specified socket.

The ZMQ_RCVBUF option shall retrieve the underlying kernel receive buffer size for the specified socket. For details refer to your operating system documentation for the SO_RCVBUF socket option.

The ZMQ_RCVHWM option shall return 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.

The ZMQ_RCVMORE option shall return True (1) if the message part last received from the socket was a data part with more parts to follow. If there are no data parts to follow, this option shall return False (0).

Refer to zmq_send(3) and zmq_recv(3) for a detailed description of multi-part messages.

Retrieve the timeout for recv 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.

The ZMQ_RECONNECT_IVL option shall retrieve 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.

The ZMQ_RECONNECT_IVL_MAX option shall retrieve the max reconnection interval for the specified socket. 0MQ shall wait at most the configured interval between reconnection attempts. The interval grows exponentionally (i.e.: it is doubled) with each attempt until it reaches ZMQ_RECONNECT_IVL_MAX. Default value means that the reconnect interval is based exclusively on ZMQ_RECONNECT_IVL and no exponential backoff is performed.

The ZMQ_RECONNECT_STOP option shall retrieve the conditions under which automatic reconnection will stop.

The ZMQ_RECONNECT_STOP_CONN_REFUSED option will stop reconnection when 0MQ receives the ECONNREFUSED return code from the connect. This indicates that there is no code bound to the specified endpoint.

The ZMQ_RECOVERY_IVL option shall retrieve 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.

The ZMQ_ROUTING_ID option shall retrieve the routing id of the specified socket. Routing ids are used only by the request/reply pattern. Specifically, it can be used in tandem with ROUTER socket to route messages to the peer with a specific routing id.

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.

The ZMQ_SNDBUF option shall retrieve the underlying kernel transmit buffer size for the specified socket. For details refer to your operating system documentation for the SO_SNDBUF socket option.

The ZMQ_SNDHWM option shall return 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.

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.

Retrieve 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.

The ZMQ_SOCKS_PROXY option shall retrieve the SOCKS5 proxy address in string format. The returned value shall be a NULL-terminated string and MAY be empty. The returned size SHALL include the terminating null byte.

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.

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.

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.

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.

On OSes where it is supported, retrieves 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.

The ZMQ_THREAD_SAFE option shall retrieve a boolean value indicating whether or not the socket is threadsafe. See zmq_socket(3) for which sockets are thread-safe.

Retrieve the IP_TOS option for the socket.

The ZMQ_TYPE option shall retrieve the socket type for the specified socket. The socket type is specified at socket creation time and cannot be modified afterwards.

The ZMQ_ZAP_DOMAIN option shall retrieve the last ZAP domain set for the socket. The returned value shall be a NULL-terminated string and MAY be empty. An empty string means that ZAP authentication is disabled. The returned size SHALL include the terminating null byte.

The ZMQ_ZAP_ENFORCE_DOMAIN option shall retrieve the flag that determines whether a ZAP domain is strictly required or not.

The ZMQ_VMCI_BUFFER_SIZE option shall retrieve the size of the underlying buffer for the socket. Used during negotiation before the connection is established.

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

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

The ZMQ_VMCI_CONNECT_TIMEOUT option shall retrieve connection timeout for the socket.

Retrieve the current multicast loopback configuration. A value of 1 means that the multicast packets sent on this socket will be looped back to local listening interface.

Retrieve the current notification settings of a router socket. The returned value is a bitmask composed of ZMQ_NOTIFY_CONNECT and ZMQ_NOTIFY_DISCONNECT flags, meaning connect and disconnect notifications are enabled, respectively. A value of 0 means the notifications are off.

Gets the maximal amount of messages that can be received in a single recv system call.

Cannot be zero.

Gets the maximal amount of messages that can be sent in a single send system call.

Cannot be zero.

Gets the number of topic (prefix) subscriptions either * received on a (X)PUB socket from all the connected (X)SUB sockets or * acknowledged on an (X)SUB socket from all the connected (X)PUB sockets

Gets the NORM sender mode to control the operation of the NORM transport. NORM supports fixed rate operation (0=ZMQ_NORM_FIXED), congestion control mode (1=ZMQ_NORM_CC), loss-tolerant congestion control (2=ZMQ_NORM_CCL), explicit congestion notification (ECN)-enabled congestion control (3=ZMQ_NORM_CCE), and ECN-only congestion control (4=ZMQ_NORM_CCE_ECNONLY). The default value is TCP-friendly congestion control mode. Fixed rate mode (using datarate set by ZMQ_RATE) offers better performance, but care must be taken to prevent data loss.

Retrieves status of NORM unicast NACK mode setting for multicast receivers. If set, NORM receiver will send Negative ACKnowledgements (NACKs) back to the sender using unicast instead of multicast. NORM transport endpoints specifying a unicast address will use unicast NACKs by default (without setting ZMQ_NORM_UNICAST_NACK).

Gets NORM buffer size for NORM transport sender, receiver, and stream.

Gets NORM sender segment size, which is the maximum message payload size of individual NORM messages (ZMQ messages may be split over multiple NORM messages). Ideally, this value should fit within the system/network maximum transmission unit (MTU) after accounting for additional NORM message headers (up to 48 bytes).

Gets NORM sender block size, which is the number of segments in a NORM FEC coding block. NORM repair operations take place at block boundaries. Maximum value is 255, but parity packets (ZMQ_NORM_NUM_PARITY) are limited to a value of (255 - ZMQ_NORM_BLOCK_SIZE). Minimum value is (ZMQ_NORM_NUM_PARITY + 1). Effective value may be different based on the settings of ZMQ_NORM_NUM_PARITY and ZMQ_NORM_NUM_AUTOPARITY if invalid settings are provided.

Gets the maximum number of NORM parity symbol segments that the sender is willing to calculate per FEC coding block for the purpose of reparing lost data. Maximum value is 255, but is further limited to a value of (255 - ZMQ_NORM_BLOCK_SIZE). Minimum value is ZMQ_NORM_NUM_AUTOPARITY. Effective value may be different based on the setting of ZMQ_NORM_NUM_AUTOPARITY if invalid settings are provided.

Gets the number of NORM parity symbol segments that the sender will proactively send at the end of each FEC coding block. By default, no proactive parity segments will be sent; instead, parity segments will only be sent in response to repair requests (NACKs). Maximum value is 255, but is further limited to a maximum value of ZMQ_NORM_NUM_PARITY.

Gets status of NORM stream push mode, which alters the behavior of the sender when enqueueing new data. By default, NORM will stop accepting new messages while waiting for old data to be transmitted and/or repaired. Enabling push mode discards the oldest data (which may be pending repair or may never have been transmitted) in favor of accepting new data. This may be useful in cases where it is more important to quickly deliver new data instead of reliably delivering older data.