Scroll to navigation



pcap_get_required_select_timeout - get a file descriptor on which a select() can be done for a live capture


#include <pcap/pcap.h>
struct timeval *pcap_get_required_select_timeout(pcap_t *p);


pcap_get_required_select_timeout() returns, on UNIX, a pointer to a struct timeval containing a value that must be used as the minimum timeout in select(2), poll(2), epoll_wait(2), and kevent() calls if pcap_get_selectable_fd(3PCAP) returns PCAP_ERROR.

The timeout that should be used in those calls must be no larger than the smallest of all timeouts returned by pcap_get_required_select_timeout() for devices from which packets will be captured.

The device for which pcap_get_selectable_fd() returned PCAP_ERROR must be put in non-blocking mode with pcap_setnonblock(3PCAP), and an attempt must always be made to read packets from the device when the select(), poll(), epoll_wait(), or kevent() call returns.

Note that a device on which a read can be done without blocking may, on some platforms, not have any packets to read if the packet buffer timeout has expired. A call to pcap_dispatch(3PCAP) or pcap_next_ex(3PCAP) will return 0 in this case, but will not block.

pcap_get_required_select_timeout() is not available on Windows.


A pointer to a struct timeval is returned if the timeout is required; otherwise NULL is returned.


This function became available in libpcap release 1.9.0. In previous releases, select(), poll(), epoll_wait(), and kevent() cannot be used on any capture source for which pcap_get_selectable_fd returns -1.


pcap(3PCAP), pcap_get_selectable_fd(3PCAP), select(2), poll(2), epoll_wait(2), kqueue(2)
25 July 2018