NETSNMP\_SESSION\_API(3) Net-SNMP NETSNMP\_SESSION\_API(3) # [NAME](#NAME) snmp\_sess\_init, snmp\_open, snmp\_send, snmp\_async\_send, snmp\_select\_info, snmp\_read, snmp\_timeout, snmp\_synch\_response, snmp\_close, snmp\_perror, snmp\_sess\_perror, snmp\_error, snmp\_api\_errstring - netsnmp\_session\_api functions # [SYNOPSIS](#SYNOPSIS) **#include <net-snmp/session\_api.h>** **void snmp\_sess\_init ( netsnmp\_session\*sess);** **netsnmp\_session* snmp\_open ( netsnmp\_session \*sess);** */* Input parameter not used in active sessions \*/* **int snmp\_send ( netsnmp\_session \*session,** **netsnmp\_pdu \*pdu);** **int snmp\_async\_send ( netsnmp\_session \*session,** **netsnmp\_pdu \*pdu,** **snmp\_callback callback,** **void \*callbackData);** **int snmp\_select\_info ( int * numfds,fd\_set \*fdset,** **struct timeval \*timeout,int \*block);** **void snmp\_read ( fd\_set \*fdset);** **void snmp\_timeout ( void );** **int snmp\_synch\_response ( netsnmp\_session \*session,** **netsnmp\_pdu \*pdu,** **netsnmp\_pdu \*\*response);** **int snmp\_close ( netsnmp\_session \*session);** **int snmp\_close\_sessions ( void );** ## [Error Reporting](#Error_Reporting) *(Move to [output\_api(3)](/man/os/net-snmp/output_api.3))* **void snmp\_error ( netsnmp\_session \*session,** **int \*pcliberr,int \*psnmperr,char \*\*pperrstring);** **char \*snmp\_api\_errstring ( intsnmperr);** **void snmp\_perror ( char \*msg);** */* for parsing errors only \*/* **void snmp\_sess\_perror (char \*msg,netsnmp\_session \*sess);** */* all other SNMP library errors \*/* # [DESCRIPTION](#DESCRIPTION) *Snmp\_sess\_init* prepares a netsnmp\_session that sources transport characteristics and common information that will be used for a set of SNMP transactions. After this structure is passed to *snmp\_open* to create an SNMP session, the structure is not used. *Snmp\_open* returns a pointer to a newly-formed *netsnmp\_session* object, which the application must use to reference the active SNMP session. *snmp\_send* and *snmp\_async\_send()* each take as input a pointer to a *netsnmp\_pdu* object. This structure contains information that describes a transaction that will be performed over an open session. Consult snmp\_api.h for the definitions of these structures. With the *snmp\_async\_send()* call, *snmp\_read* will invoke the specified callback when the response is received. *Snmp\_read, snmp\_select\_info,* and *snmp\_timeout* provide an interface for the use of the [*select(2)*](/man/os/net-snmp/select.2) system call so that SNMP transactions can occur asynchronously. *Snmp\_select\_info* is given the information that would have been passed to *select* in the absence of SNMP. For example, this might include window update information. This information is modified so that SNMP will get the service it requires from the call to *select.* In this case, *numfds, fdset,* and *timeout* correspond to the *nfds, readfds,* and *timeout* arguments to *select,* respectively. The only exception is that timeout must always point to an allocated (but perhaps uninitialized) *struct timeval.* If *timeout* would have been passed as NULL, *block* is set to true, and *timeout* is treated as undefined. This same rule applies upon return from *snmp\_select\_info.* After calling *snmp\_select\_info, select* is called with the returned data. When select returns, *snmp\_read* should be called with the *fd\_set* returned from *select* to read each SNMP socket that has input. If *select* times out, *snmp\_timeout* should be called to see if the timeout was intended for SNMP. *snmp\_synch\_response* is a convenience routine that will send the request, wait for the response and process it before returning. See the descriptions of *snmp\_send , snmp\_read* etc for details. # [DIAGNOSTICS](#DIAGNOSTICS) Previous versions of the library used *snmp\_get\_errno* to read the global variable *snmp\_errno* which may have held the error status within the SNMP library. The existing method *snmp\_perror* should be used to log ASN.1 coding errors only. The new method *snmp\_sess\_perror* is provided to capture errors that occur during the processing of a particular SNMP session. *Snmp\_sess\_perror* calls *snmp\_error* function to obtain the "C" library error *errno* , the SNMP library error *snmperr* , and the SNMP library detailed error message that is associated with an error that occurred during a given session. Note that in all cases except one, *snmp\_sess\_perror* should be handed the *netsnmp\_session \** pointer returned from *snmp\_open.* If *snmp\_open* returns a null pointer, pass the INPUT *netsnmp\_session \** pointer used to call *snmp\_open.* Error return status from *snmp\_close* and *snmp\_send* is indicated by return of 0. A successful status will return a 1 for *snmp\_close* and the request id of the packet for *snmp\_send.* Upon successful return from *snmp\_send* the pdu will be freed by the library. Consult snmp\_api.h for the complete set of SNMP library error values. The SNMP library error value *snmperr* can be one of the following values: [SNMPERR\_GENERR](#SNMPERR_GENERR) A generic error occurred. [SNMPERR\_BAD\_LOCPORT](#SNMPERR_BAD_LOCPORT) The local port was bad because it had already been allocated or permission was denied. [SNMPERR\_BAD\_ADDRESS](#SNMPERR_BAD_ADDRESS) The host name or address given was not useable. [SNMPERR\_BAD\_SESSION](#SNMPERR_BAD_SESSION) The specified session was not open. [SNMPERR\_TOO\_LONG](#SNMPERR_TOO_LONG) [SNMPERR\_NO\_SOCKET](#SNMPERR_NO_SOCKET) [SNMPERR\_V2\_IN\_V1](#SNMPERR_V2_IN_V1) [SNMPERR\_V1\_IN\_V2](#SNMPERR_V1_IN_V2) [SNMPERR\_BAD\_REPEATERS](#SNMPERR_BAD_REPEATERS) [SNMPERR\_BAD\_REPETITIONS](#SNMPERR_BAD_REPETITIONS) [SNMPERR\_BAD\_ASN1\_BUILD](#SNMPERR_BAD_ASN1_BUILD) [SNMPERR\_BAD\_SENDTO](#SNMPERR_BAD_SENDTO) [SNMPERR\_BAD\_PARSE](#SNMPERR_BAD_PARSE) [SNMPERR\_BAD\_VERSION](#SNMPERR_BAD_VERSION) [SNMPERR\_NOAUTH\_DESPRIV](#SNMPERR_NOAUTH_DESPRIV) [SNMPERR\_ABORT](#SNMPERR_ABORT) [SNMPERR\_UNKNOWN\_PDU](#SNMPERR_UNKNOWN_PDU) [SNMPERR\_TIMEOUT](#SNMPERR_TIMEOUT) A string representation of the error code can be obtained with *snmp\_api\_errstring*, and a standard error message may be printed using *snmp\_perror* that functions like the *perror* standard routine. # [SEE ALSO](#SEE_ALSO) [select(2)](/man/os/net-snmp/select.2), [netsnmp\_sess\_api(3)](/man/os/net-snmp/netsnmp_sess_api.3), [netsnmp\_mib\_api(3)](/man/os/net-snmp/netsnmp_mib_api.3), [netsnmp\_pdu\_api(3)](/man/os/net-snmp/netsnmp_pdu_api.3), [netsnmp\_varbind\_api(3)](/man/os/net-snmp/netsnmp_varbind_api.3), snmp\_api.h 19 May 2011 V5.9.5.2 --- Document: netsnmp_session_api(3) from net-snmp 5.9.5.2-r10 (Chainguard OS) Source: https://github.com/net-snmp/net-snmp.git