pcap_activate.3pcap man page
pcap_activate — activate a capture handle
#include <pcap/pcap.h> int pcap_activate(pcap_t *p);
pcap_activate() is used to activate a packet capture handle to look at packets on the network, with the options that were set on the handle being in effect.
pcap_activate() returns 0 on success without warnings, a non-zero positive value on success with warnings, and a negative value on error. A non-zero return value indicates what warning or error condition occurred.
The possible warning values are:
Promiscuous mode was requested, but the capture source doesn't support promiscuous mode.
The time stamp type specified in a previous pcap_set_tstamp_type() call isn't supported by the capture source (the time stamp type is left as the default),
Another warning condition occurred; pcap_geterr() or pcap_perror() may be called with p as an argument to fetch or display a message describing the warning condition.
The possible error values are:
The handle has already been activated.
The capture source specified when the handle was created doesn't exist.
The process doesn't have permission to open the capture source.
The process has permission to open the capture source but doesn't have permission to put it into promiscuous mode.
Monitor mode was specified but the capture source doesn't support monitor mode.
The capture source device is not up.
Another error occurred. pcap_geterr() or pcap_perror() may be called with p as an argument to fetch or display a message describing the error.
If PCAP_WARNING_PROMISC_NOTSUP, PCAP_ERROR_NO_SUCH_DEVICE, or PCAP_ERROR_PERM_DENIED is returned, pcap_geterr() or pcap_perror() may be called with p as an argument to fetch or display an message giving additional details about the problem that might be useful for debugging the problem if it's unexpected.
Additional warning and error codes may be added in the future; a program should check for positive, negative, and zero return codes, and treat all positive return codes as warnings and all negative return codes as errors. pcap_statustostr() can be called, with a warning or error code as an argument, to fetch a message describing the warning or error code.