Returns a value indicating whether or not this socket has been marked to accept connections with listen(2). The value 0 indicates that this is not a listening socket, the value 1 indicates that this is a listening socket. This socket option is read-only.

Bind this socket to a particular device like “eth0”, as specified in the passed interface name. If the name is an empty string or the option length is zero, the socket device binding is removed. The passed option is a variable-length null-terminated interface name string with the maximum size of IFNAMSIZ. If a socket is bound to an interface, only packets received from that particular interface are processed by the socket. Note that this only works for some socket types, particularly AF_INET sockets. It is not supported for packet sockets (use normal bind(8) there).

Set or get the broadcast flag. When enabled, datagram sockets receive packets sent to a broadcast address and they are allowed to send packets to a broadcast address. This option has no effect on stream-oriented sockets.

Enable BSD bug-to-bug compatibility. This is used by the UDP protocol module in Linux 2.0 and 2.2. If enabled ICMP errors received for a UDP socket will not be passed to the user program. In later kernel versions, support for this option has been phased out: Linux 2.4 silently ignores it, and Linux 2.6 generates a kernel warning (printk()) if a program uses this option. Linux 2.0 also enabled BSD bug-to-bug compatibility options (random header changing, skipping of the broadcast flag) for raw sockets with this option, but that was removed in Linux 2.2.

Enable socket debugging. Only allowed for processes with the CAP_NET_ADMIN capability or an effective user ID of 0.

Retrieves the socket domain as an integer, returning a value such as AF_INET6. See socket(2) for details. This socket option is read-only.

Get and clear the pending socket error. This socket option is read-only. Expects an integer.

Don't send via a gateway, only send to directly connected hosts. The same effect can be achieved by setting the MSG_DONTROUTE flag on a socket send(2) operation. Expects an integer boolean flag.

Enable sending of keep-alive messages on connection-oriented sockets. Expects an integer boolean flag.

Sets or gets the SO_LINGER option. The argument is a linger structure.

When enabled, a close(2) or shutdown(2) will not return until all queued messages for the socket have been successfully sent or the linger timeout has been reached. Otherwise, the call returns immediately and the closing is done in the background. When the socket is closed as part of exit(2), it always lingers in the background.

If this option is enabled, out-of-band data is directly placed into the receive data stream. Otherwise out-of-band data is only passed when the MSG_OOB flag is set during receiving.

Enable or disable the receiving of the SCM_CREDENTIALS control message. For more information see unix(7).

Return the credentials of the foreign process connected to this socket. This is only possible for connected AF_UNIX stream sockets and AF_UNIX stream and datagram socket pairs created using socketpair(2); see unix(7). The returned credentials are those that were in effect at the time of the call to connect(2) or socketpair(2). Argument is a ucred structure. This socket option is read-only.

Set the protocol-defined priority for all packets to be sent on this socket. Linux uses this value to order the networking queues: packets with a higher priority may be processed first depending on the selected device queueing discipline. For ip(7), this also sets the IP type-of-service (TOS) field for outgoing packets. Setting a priority outside the range 0 to 6 requires the CAP_NET_ADMIN capability.

Retrieves the socket protocol as an integer, returning a value such as IPPROTO_SCTP. See socket(2) for details. This socket option is read-only.

Sets or gets the maximum socket receive buffer in bytes. The kernel doubles this value (to allow space for bookkeeping overhead) when it is set using setsockopt(2), and this doubled value is returned by getsockopt(2). The default value is set by the /proc/sys/net/core/rmem_default file, and the maximum allowed value is set by the /proc/sys/net/core/rmem_max file. The minimum (doubled) value for this option is 256.

Using this socket option, a privileged (CAP_NET_ADMIN) process can perform the same task as SO_RCVBUF, but the rmem_max limit can be overridden.

Specify the minimum number of bytes in the buffer until the socket layer will pass the data to the protocol (SO_SNDLOWAT) or the user on receiving (SO_RCVLOWAT). These two values are initialized to 1. SO_SNDLOWAT is not changeable on Linux (setsockopt(2) fails with the error ENOPROTOOPT). SO_RCVLOWAT is changeable only since Linux 2.4. The select(2) and poll(2) system calls currently do not respect the SO_RCVLOWAT setting on Linux, and mark a socket readable when even a single byte of data is available. A subsequent read from the socket will block until SO_RCVLOWAT bytes are available.

Specify the receiving or sending timeouts until reporting an error. The argument is a struct timeval. If an input or output function blocks for this period of time, and data has been sent or received, the return value of that function will be the amount of data transferred; if no data has been transferred and the timeout has been reached then −1 is returned with errno set to EAGAIN or EWOULDBLOCK just as if the socket was specified to be nonblocking. If the timeout is set to zero (the default) then the operation will never timeout. Timeouts only have effect for system calls that perform socket I/O (e.g., read(2), recvmsg(2), send(2), sendmsg(2)); timeouts have no effect for select(2), poll(2), epoll_wait(2), etc.

Indicates that the rules used in validating addresses supplied in a bind(2) call should allow reuse of local addresses. For AF_INET sockets this means that a socket may bind, except when there is an active listening socket bound to the address. When the listening socket is bound to INADDR_ANY with a specific port then it is not possible to bind to this port for any local address. Argument is an integer boolean flag.

Sets or gets the maximum socket send buffer in bytes. The kernel doubles this value (to allow space for bookkeeping overhead) when it is set using setsockopt(2), and this doubled value is returned by getsockopt(2). The default value is set by the /proc/sys/net/core/wmem_default file and the maximum allowed value is set by the /proc/sys/net/core/wmem_max file. The minimum (doubled) value for this option is 2048.

Using this socket option, a privileged (CAP_NET_ADMIN) process can perform the same task as SO_SNDBUF, but the wmem_max limit can be overridden.

Enable or disable the receiving of the SO_TIMESTAMP control message. The timestamp control message is sent with level SOL_SOCKET and the cmsg_data field is a struct timeval indicating the reception time of the last packet passed to the user in this call. See cmsg(3) for details on control messages.

Gets the socket type as an integer (e.g., SOCK_STREAM). This socket option is read-only.

contains the default setting in bytes of the socket receive buffer.

contains the maximum socket receive buffer size in bytes which a user may set by using the SO_RCVBUF socket option.

contains the default setting in bytes of the socket send buffer.

contains the maximum socket send buffer size in bytes which a user may set by using the SO_SNDBUF socket option.

configure the token bucket filter used to load limit warning messages caused by external network events.

Maximum number of packets in the global input queue.

Maximum length of ancillary data and user control data like the iovecs per socket.

Return a struct timeval with the receive timestamp of the last packet passed to the user. This is useful for accurate round trip time measurements. See setitimer(2) for a description of struct timeval. This ioctl should only be used if the socket option SO_TIMESTAMP is not set on the socket. Otherwise, it returns the timestamp of the last packet that was received while SO_TIMESTAMP was not set, or it fails if no such packet has been received, (i.e., ioctl(2) returns −1 with errno set to ENOENT).

Set the process or process group to send SIGIO or SIGURG signals to when an asynchronous I/O operation has finished or urgent data is available. The argument is a pointer to a pid_t. If the argument is positive, send the signals to that process. If the argument is negative, send the signals to the process group with the ID of the absolute value of the argument. The process may only choose itself or its own process group to receive signals unless it has the CAP_KILL capability or an effective UID of 0.

Change the O_ASYNC flag to enable or disable asynchronous I/O mode of the socket. Asynchronous I/O mode means that the SIGIO signal or the signal set with F_SETSIG is raised when a new I/O event occurs.

Argument is an integer boolean flag. (This operation is synonymous with the use of fcntl(2) to set the O_ASYNC flag.)

Get the current process or process group that receives SIGIO or SIGURG signals, or 0 when none is set.

The same as the SIOCGPGRP ioctl(2).

The same as the SIOCSPGRP ioctl(2).