Ubuntu Manpage: zmq_setsockopt - set 0MQ socket options

Provided by: libzmq3-dev_4.2.5-1ubuntu0.2_amd64

NAME

       zmq_setsockopt - set 0MQ socket options

SYNOPSIS

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

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

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

DESCRIPTION

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

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

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

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

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

Option value type uint64_t

Option value unit N/A (bitmap)

Default value 0

Applicable socket types N/A

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

Option value type int

Option value unit connections

Default value 100

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

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

Note
requires setting CAP_NET_RAW on the compiled program. 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, when using TCP or UDP
transports.

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

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

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

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

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

Option value type binary data

Option value unit N/A

Default value NULL

Applicable socket types ZMQ_ROUTER, ZMQ_STREAM

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

Option value type int

Option value unit boolean

Default value 0 (false)

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

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

Option value type int

Option value unit milliseconds

Default value 0 (disabled)

Applicable socket types all, when using TCP transports.

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

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

Option value type binary data or Z85 text string

Option value size 32 or 41

Default value NULL

Applicable socket types all, when using TCP transport

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

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

Option value type binary data or Z85 text string

Option value size 32 or 41

Default value NULL

Applicable socket types all, when using TCP transport

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types all, when using TCP transport

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

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

Option value type binary data or Z85 text string

Option value size 32 or 41

Default value NULL

Applicable socket types all, when using TCP transport

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

Option value type int

Option value unit 0, 1

Default value 0 (false)

Applicable socket types all, when using TCP transport

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

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

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

Option value type int

Option value unit 0, 1

Default value 0 (false)

Applicable socket types all, when using TCP transport

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

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

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

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

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).

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

Option value type int

Option value unit 0, 1, 2

Default value 0 (ZMQ_GSSAPI_NT_HOSTBASED)

Applicable socket types all, when using TCP or IPC transport

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

Option value type int

Option value unit milliseconds

Default value 30000

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

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

Option value type int

Option value unit milliseconds

Default value 0

Applicable socket types all, when using connection-oriented
transports

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

Option value type int

Option value unit milliseconds

Default value 0

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

Applicable socket types all, when using connection-oriented
transports

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

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

Option value type int

Option value unit boolean

Default value 0 (false)

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

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

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

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

Option value type int

Option value unit 0,1

Default value 0

Applicable socket types ZMQ_PUB, ZMQ_XPUB, ZMQ_SUB

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

Option value type int

Option value unit boolean

Default value 0 (false)

Applicable socket types all, when using TCP transports.

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

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

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

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

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

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

Option value type int64_t

Option value unit bytes

Default value -1

Applicable socket types all

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

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

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all

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

Option value type int

Option value unit network hops

Default value 1

Applicable socket types all, when using multicast transports

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

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

Option value type int

Option value unit bytes

Default value 1500

Applicable socket types all, when using multicast transports

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

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types all, when using TCP transport

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

Option value type character string

Option value unit N/A

Default value not set

Applicable socket types all, when using TCP transport

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

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

Option value type int

Option value unit file descriptor

Default value -1

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

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

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER, ZMQ_DEALER, ZMQ_REQ

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

Option value type int

Option value unit kilobits per second

Default value 100

Applicable socket types all, when using multicast transports

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

Option value type int

Option value unit bytes

Default value -1

Applicable socket types all

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

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

Option value type int

Option value unit messages

Default value 1000

Applicable socket types all

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

Option value type int

Option value unit milliseconds

Default value -1 (infinite)

Applicable socket types all

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

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

Option value type int

Option value unit milliseconds

Default value 100

Applicable socket types all, only for connection-oriented
transports

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

Note
Values less than ZMQ_RECONNECT_IVL will be ignored.

Option value type int

Option value unit milliseconds

Default value 0 (only use ZMQ_RECONNECT_IVL)

Applicable socket types all, only for connection-oriented
transports

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

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

Option value type int

Option value unit milliseconds

Default value 10000

Applicable socket types all, when using multicast transports

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_REQ

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

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_REQ

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER

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

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER

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

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types ZMQ_ROUTER

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

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

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

Option value type binary data

Option value unit N/A

Default value NULL

Applicable socket types ZMQ_REQ, ZMQ_REP, ZMQ_ROUTER,
ZMQ_DEALER.

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

Option value type int

Option value unit bytes

Default value -1

Applicable socket types all

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

Note
0MQ does not guarantee that the socket will accept as many as ZMQ_SNDHWM messages, and the actual
limit may be as much as 90% lower depending on the flow of messages on the socket.

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). Does not
support SOCKS5 authentication. 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_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_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 lenght of zero to disable welcome message.

Option value type binary data

Option value unit N/A

Default value NULL

Applicable socket types ZMQ_XPUB

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

Option value type character string

Option value unit N/A

Default value empty

Applicable socket types all, when using TCP transport

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

Option value type int

Option value unit 0, 1

Default value 0

Applicable socket types all, when using ZAP

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

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

Option value type binary data

Option value unit N/A

Default value no filters (allow from all)

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

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

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

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

Option value type gid_t

Option value unit N/A

Default value no filters (allow from all)

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

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

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

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

Option value type pid_t

Option value unit N/A

Default value no filters (allow from all)

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

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

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

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

Option value type uid_t

Option value unit N/A

Default value no filters (allow from all)

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

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

Option value type int

Option value unit boolean

Default value 1 (true)

Applicable socket types all, when using TCP transports.

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

Option value type uint64_t

Option value unit bytes

Default value 65546

Applicable socket types all, when using VMCI transport

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

Option value type uint64_t

Option value unit bytes

Default value 128

Applicable socket types all, when using VMCI transport

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

Option value type uint64_t

Option value unit bytes

Default value 262144

Applicable socket types all, when using VMCI transport

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

Option value type int

Option value unit milliseconds

Default value -1

Applicable socket types all, when using VMCI transport

RETURN VALUE

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

ERRORS

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

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

       ENOTSOCK
           The provided socket was invalid.

       EINTR
           The operation was interrupted by delivery of a signal.

EXAMPLE

       Subscribing to messages on a ZMQ_SUB socket.

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

       Setting I/O thread affinity.

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

AUTHORS

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

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

EXAMPLE

SEE ALSO

AUTHORS