ZMQ_GETSOCKOPT(3)

NAME
zmq_getsockopt - get 0MQ socket options

SYNOPSIS

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

DESCRIPTION

The zmq_getsockopt() function shall retrieve the value for the option specified by the option_name argument for the 0MQ socket pointed to by the socket argument, and store it in the buffer pointed to by the option_value argument. The option_len argument is the size in bytes of the buffer pointed to by option_value; upon successful completion zmq_getsockopt() shall modify the option_len argument to indicate the actual size of the option value stored in the buffer.

The following options can be retrieved with the zmq_getsockopt() function:

  ZMQ_AFFINITY: Retrieve I/O thread affinity

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.
Option value type | uint64_t
Option value unit | N/A (bitmap)
Default value | 0
Applicable socket types | N/A

  ZMQ_BACKLOG: Retrieve maximum length of the queue of outstanding connections

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.
Option value type | int
Option value unit | connections
Default value | 100
Applicable socket types | all, only for connection-oriented transports

  ZMQ_BINDTODEVICE: Retrieve name of device the socket is bound to

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.
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_TIMEOUT: Retrieve connect() timeout

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.
Option value type | int
Option value unit | milliseconds
Default value | 0 (disabled)
Applicable socket types | all, when using TCP transports.

  ZMQ_CURVE_PUBLICKEY: Retrieve current CURVE public key

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.
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: Retrieve current CURVE secret key

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.
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_SERVERKEY: Retrieve current CURVE server key

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.
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_EVENTS: Retrieve socket event state

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.
Option value type | int
Option value unit | N/A (flags)
Default value | N/A
Applicable socket types | all

  ZMQ_FD: Retrieve file descriptor associated with the socket

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.

    Note

    The ability to read from the returned file descriptor does not necessarily indicate that messages are available to be read from, or can be written to, the underlying socket; applications must retrieve the actual event state with a subsequent retrieval of the ZMQ_EVENTS option.

    Note

    The returned file descriptor is also used internally by the zmq_send and zmq_recv functions. As the descriptor is edge triggered, applications must update the state of ZMQ_EVENTS after each invocation of zmq_send or zmq_recv.To be more explicit: after calling zmq_send the socket may become readable (and vice versa) without triggering a read event on the file descriptor.

    Caution

    The returned file descriptor is intended for use with a poll or similar system call only. Applications must never attempt to read or write data to it directly, neither should they try to close it.

Option value type | int on POSIX systems, SOCKET on Windows
Option value unit | N/A
Default value | N/A
Applicable socket types | all

  ZMQ_GSSAPI_PLAINTEXT: Retrieve GSSAPI plaintext or encrypted status

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.
Option value type | int
Option value unit | 0, 1
Default value | 0 (false)
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_GSSAPI_PRINCIPAL: Retrieve the name of the GSSAPI principal

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.
Option value type | NULL-terminated character string
Option value unit | N/A
Default value | null string
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_GSSAPI_SERVER: Retrieve current GSSAPI server role

Returns the ZMQ_GSSAPI_SERVER option, if any, previously set on the socket.
Option value type | int
Option value unit | 0, 1
Default value | 0 (false)
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_GSSAPI_SERVICE_PRINCIPAL: Retrieve the name of the GSSAPI service principal

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.
Option value type | NULL-terminated character string
Option value unit | N/A
Default value | null string
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE: Retrieve nametype for service principal

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).
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 transports

  ZMQ_GSSAPI_PRINCIPAL_NAMETYPE: Retrieve nametype for service principal

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).
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 transports

  ZMQ_HANDSHAKE_IVL: Retrieve maximum handshake interval

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.
Option value type | int
Option value unit | milliseconds
Default value | 30000
Applicable socket types | all but ZMQ_STREAM, only for connection-oriented transports

  ZMQ_IDENTITY: Retrieve socket identity

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

  ZMQ_IMMEDIATE: Retrieve attach-on-connect value

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.
Option value type | int
Option value unit | boolean
Default value | 0 (false)
Applicable socket types | all, primarily when using TCP/IPC transports.

  ZMQ_INVERT_MATCHING: Retrieve inverted filtering status

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.
Option value type | int
Option value unit | 0,1
Default value | 0
Applicable socket types | ZMQ_PUB, ZMQ_XPUB, ZMQ_SUB

  ZMQ_IPV4ONLY: Retrieve IPv4-only socket override status

Retrieve 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_IPV6: Retrieve IPv6 socket status

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.
Option value type | int
Option value unit | boolean
Default value | 0 (false)
Applicable socket types | all, when using TCP transports.

  ZMQ_LAST_ENDPOINT: Retrieve the last endpoint set

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().
Option value type | NULL-terminated character string
Option value unit | N/A
Default value | NULL
Applicable socket types | all, when binding TCP or IPC transports

  ZMQ_LINGER: Retrieve linger period for socket shutdown

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

  ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size

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.
Option value type | int64_t
Option value unit | bytes
Default value | -1
Applicable socket types | all

  ZMQ_MECHANISM: Retrieve current security mechanism

The ZMQ_MECHANISM option shall retrieve the current security mechanism for the socket.
Option value type | int
Option value unit | ZMQ_NULL, ZMQ_PLAIN, ZMQ_CURVE, or ZMQ_GSSAPI
Default value | ZMQ_NULL
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets

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.
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

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.
Option value type | int
Option value unit | bytes
Default value | 1500
Applicable socket types | all, when using multicast transports

  ZMQ_PLAIN_PASSWORD: Retrieve current password

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.
Option value type | NULL-terminated character string
Option value unit | N/A
Default value | null string
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_PLAIN_SERVER: Retrieve current PLAIN server role

Returns the ZMQ_PLAIN_SERVER option, if any, previously set on the socket.
Option value type | int
Option value unit | 0, 1
Default value | int
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_PLAIN_USERNAME: Retrieve current PLAIN username

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.
Option value type | NULL-terminated character string
Option value unit | N/A
Default value | null string
Applicable socket types | all, when using TCP or IPC transports

  ZMQ_USE_FD: Retrieve the pre-allocated socket file descriptor

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.
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: Retrieve the Priority on socket

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

    [horizontal]
    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.
Option value type | int
Option value unit | kilobits per second
Default value | 100
Applicable socket types | all, when using multicast transports

  ZMQ_RCVBUF: Retrieve kernel receive buffer size

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.
Option value type | int
Option value unit | bytes
Default value | 8192
Applicable socket types | all

  ZMQ_RCVHWM: Retrieve high water mark for inbound messages

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.
Option value type | int
Option value unit | messages
Default value | 1000
Applicable socket types | all

  ZMQ_RCVMORE: More message data parts to follow

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.
Option value type | int
Option value unit | boolean
Default value | N/A
Applicable socket types | all

  ZMQ_RCVTIMEO: Maximum time before a socket operation returns with EAGAIN

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

  ZMQ_RECONNECT_IVL: Retrieve reconnection interval

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.

    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: Retrieve max reconnection interval

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.

    Note

    Value has to be greater or equal than ZMQ_RECONNECT_IVL, or else it will be ignored.

Option value type | int
Option value unit | milliseconds
Default value | 0 (ZMQ_RECONNECT_IVL will be used)
Applicable socket types | all, only for connection-oriented transport

  ZMQ_RECONNECT_STOP: Retrieve condition where reconnection will stop

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

  ZMQ_RECOVERY_IVL: Get multicast recovery interval

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.
Option value type | int
Option value unit | milliseconds
Default value | 10000
Applicable socket types | all, when using multicast transports

  ZMQ_ROUTING_ID: Retrieve socket routing id

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.
Option value type | binary data
Option value unit | N/A
Default value | NULL
Applicable socket types | ZMQ_REP, ZMQ_REQ, ZMQ_ROUTER, ZMQ_DEALER.

  ZMQ_SNDBUF: Retrieve kernel transmit buffer size

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.
Option value type | int
Option value unit | bytes
Default value | 8192
Applicable socket types | all

  ZMQ_SNDHWM: Retrieves high water mark for outbound messages

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.
Option value type | int
Option value unit | messages
Default value | 1000
Applicable socket types | all

  ZMQ_SNDTIMEO: Maximum time before a socket operation returns with EAGAIN

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

  ZMQ_SOCKS_PROXY: Retrieve SOCKS5 proxy address

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.
Option value type | NULL-terminated character string
Option value unit | N/A
Default value | null string
Applicable socket types | all, when using TCP transports

  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: Retrieve Max TCP Retransmit Timeout

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.
Option value type | int
Option value unit | milliseconds
Default value | 0 (leave to OS default)
Applicable socket types | all, when using TCP transports.

  ZMQ_THREAD_SAFE: Retrieve socket thread safety

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.
Option value type | int
Option value unit | boolean
Applicable socket types | all

  ZMQ_TOS: Retrieve the Type-of-Service socket override status

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

  ZMQ_TYPE: Retrieve socket type

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.
Option value type | int
Option value unit | N/A
Default value | N/A
Applicable socket types | all

  ZMQ_ZAP_DOMAIN: Retrieve RFC 27 authentication domain

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.
Option value type | character string
Option value unit | N/A
Default value | not set
Applicable socket types | all, when using TCP transport

  ZMQ_ZAP_ENFORCE_DOMAIN: Retrieve ZAP domain handling mode

The ZMQ_ZAP_ENFORCE_DOMAIN option shall retrieve the flag that determines whether a ZAP domain is strictly required or not.
Option value type | int
Option value unit | 0, 1
Default value | 0
Applicable socket types | all, when using ZAP

  ZMQ_VMCI_BUFFER_SIZE: Retrieve buffer size of the VMCI socket

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.
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: Retrieve min buffer size of the VMCI socket

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.
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: Retrieve max buffer size of the VMCI socket

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.
Option value type | uint64_t
Option value unit | bytes
Default value | 262144
Applicable socket types | all, when using VMCI transport

  ZMQ_VMCI_CONNECT_TIMEOUT: Retrieve connection timeout of the VMCI socket

The ZMQ_VMCI_CONNECT_TIMEOUT option shall retrieve 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: Retrieve multicast local loopback configuration

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.
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: Retrieve router socket notification settings

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.

    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

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

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

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

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_TOPICS_COUNT: Number of topic subscriptions received

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

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | N/A
Default value | 0
Applicable socket types | ZMQ_PUB, ZMQ_XPUB, ZMQ_SUB, ZMQ_XSUB

  ZMQ_NORM_MODE: Retrieve NORM Sender Mode

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.

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | 0, 1, 2, 3, 4
Default value | 1 (ZMQ_NORM_CC)
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_UNICAST_NACK: Retrieve NORM Unicast NACK mode

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).

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | boolean
Default value | 0 (false)
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_BUFFER_SIZE: Retrieve NORM buffer size

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

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | kilobytes
Default value | 2048
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_SEGMENT_SIZE: Retrieve NORM segment size

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).

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | bytes
Default value | 1400
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_BLOCK_SIZE: Retrieve NORM block size

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.

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | >0, ⟨255
Default value | 16
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_NUM_PARITY: Retrieve NORM parity segment setting

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.

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | >0, <255
Default value | 4
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_NUM_AUTOPARITY: Retrieve proactive NORM parity segment setting

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.

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | >=0, <255
Default value | 0
Applicable socket types | All, when using NORM transport.

  ZMQ_NORM_PUSH: Retrieve NORM push mode

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.

    Note

    in DRAFT state, not yet available in stable releases.

Option value type | int
Option value unit | boolean
Default value | 0 (false)
Applicable socket types | All, when using NORM transport.

RETURN VALUE

The zmq_getsockopt() 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, or the size of the buffer pointed to by option_value, as specified by option_len, is insufficient for storing the option value.

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

Retrieving the high water mark for outgoing messages.

    /* Retrieve high water mark into sndhwm */
    int sndhwm;
    size_t sndhwm_size = sizeof (sndhwm);
    rc = zmq_getsockopt (socket, ZMQ_SNDHWM, &sndhwm, &sndhwm_size);
    assert (rc == 0);

SEE ALSO

zmq_setsockopt(3) zmq_socket(3) zmq(7)

AUTHORS

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