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check_ntp.c

/*****************************************************************************
* 
* Nagios check_ntp plugin
* 
* License: GPL
* Copyright (c) 2006 Sean Finney <seanius@seanius.net>
* Copyright (c) 2006-2008 Nagios Plugins Development Team
* 
* Description:
* 
* This file contains the check_ntp plugin
* 
* This plugin to check ntp servers independant of any commandline
* programs or external libraries.
* 
* 
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
* 
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
* 
* You should have received a copy of the GNU General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>.
* 
* 
*****************************************************************************/

const char *progname = "check_ntp";
const char *copyright = "2006-2008";
const char *email = "nagiosplug-devel@lists.sourceforge.net";

#include "common.h"
#include "netutils.h"
#include "utils.h"

static char *server_address=NULL;
static int verbose=0;
static short do_offset=0;
static char *owarn="60";
static char *ocrit="120";
static short do_jitter=0;
static char *jwarn="5000";
static char *jcrit="10000";

int process_arguments (int, char **);
thresholds *offset_thresholds = NULL;
thresholds *jitter_thresholds = NULL;
void print_help (void);
void print_usage (void);

/* number of times to perform each request to get a good average. */
#define AVG_NUM 4

/* max size of control message data */
#define MAX_CM_SIZE 468

/* this structure holds everything in an ntp request/response as per rfc1305 */
typedef struct {
      uint8_t flags;       /* byte with leapindicator,vers,mode. see macros */
      uint8_t stratum;     /* clock stratum */
      int8_t poll;         /* polling interval */
      int8_t precision;    /* precision of the local clock */
      int32_t rtdelay;     /* total rt delay, as a fixed point num. see macros */
      uint32_t rtdisp;     /* like above, but for max err to primary src */
      uint32_t refid;      /* ref clock identifier */
      uint64_t refts;      /* reference timestamp.  local time local clock */
      uint64_t origts;     /* time at which request departed client */
      uint64_t rxts;       /* time at which request arrived at server */
      uint64_t txts;       /* time at which request departed server */
} ntp_message;

/* this structure holds data about results from querying offset from a peer */
typedef struct {
      time_t waiting;         /* ts set when we started waiting for a response */
      int num_responses;      /* number of successfully recieved responses */
      uint8_t stratum;        /* copied verbatim from the ntp_message */
      double rtdelay;         /* converted from the ntp_message */
      double rtdisp;          /* converted from the ntp_message */
      double offset[AVG_NUM]; /* offsets from each response */
      uint8_t flags;       /* byte with leapindicator,vers,mode. see macros */
} ntp_server_results;

/* this structure holds everything in an ntp control message as per rfc1305 */
typedef struct {
      uint8_t flags;       /* byte with leapindicator,vers,mode. see macros */
      uint8_t op;          /* R,E,M bits and Opcode */
      uint16_t seq;        /* Packet sequence */
      uint16_t status;     /* Clock status */
      uint16_t assoc;      /* Association */
      uint16_t offset;     /* Similar to TCP sequence # */
      uint16_t count;      /* # bytes of data */
      char data[MAX_CM_SIZE]; /* ASCII data of the request */
                              /* NB: not necessarily NULL terminated! */
} ntp_control_message;

/* this is an association/status-word pair found in control packet reponses */
typedef struct {
      uint16_t assoc;
      uint16_t status;
} ntp_assoc_status_pair;

/* bits 1,2 are the leap indicator */
#define LI_MASK 0xc0
#define LI(x) ((x&LI_MASK)>>6)
#define LI_SET(x,y) do{ x |= ((y<<6)&LI_MASK); }while(0)
/* and these are the values of the leap indicator */
#define LI_NOWARNING 0x00
#define LI_EXTRASEC 0x01
#define LI_MISSINGSEC 0x02
#define LI_ALARM 0x03
/* bits 3,4,5 are the ntp version */
#define VN_MASK 0x38
#define VN(x)     ((x&VN_MASK)>>3)
#define VN_SET(x,y)     do{ x |= ((y<<3)&VN_MASK); }while(0)
#define VN_RESERVED 0x02
/* bits 6,7,8 are the ntp mode */
#define MODE_MASK 0x07
#define MODE(x) (x&MODE_MASK)
#define MODE_SET(x,y)   do{ x |= (y&MODE_MASK); }while(0)
/* here are some values */
#define MODE_CLIENT 0x03
#define MODE_CONTROLMSG 0x06
/* In control message, bits 8-10 are R,E,M bits */
#define REM_MASK 0xe0
#define REM_RESP 0x80
#define REM_ERROR 0x40
#define REM_MORE 0x20
/* In control message, bits 11 - 15 are opcode */
#define OP_MASK 0x1f
#define OP_SET(x,y)   do{ x |= (y&OP_MASK); }while(0)
#define OP_READSTAT 0x01
#define OP_READVAR  0x02
/* In peer status bytes, bits 6,7,8 determine clock selection status */
#define PEER_SEL(x) ((ntohs(x)>>8)&0x07)
#define PEER_INCLUDED 0x04
#define PEER_SYNCSOURCE 0x06

/**
 ** a note about the 32-bit "fixed point" numbers:
 **
 they are divided into halves, each being a 16-bit int in network byte order:
 - the first 16 bits are an int on the left side of a decimal point.
 - the second 16 bits represent a fraction n/(2^16)
 likewise for the 64-bit "fixed point" numbers with everything doubled :)
 **/

/* macros to access the left/right 16 bits of a 32-bit ntp "fixed point"
   number.  note that these can be used as lvalues too */
#define L16(x) (((uint16_t*)&x)[0])
#define R16(x) (((uint16_t*)&x)[1])
/* macros to access the left/right 32 bits of a 64-bit ntp "fixed point"
   number.  these too can be used as lvalues */
#define L32(x) (((uint32_t*)&x)[0])
#define R32(x) (((uint32_t*)&x)[1])

/* ntp wants seconds since 1/1/00, epoch is 1/1/70.  this is the difference */
#define EPOCHDIFF 0x83aa7e80UL

/* extract a 32-bit ntp fixed point number into a double */
#define NTP32asDOUBLE(x) (ntohs(L16(x)) + (double)ntohs(R16(x))/65536.0)

/* likewise for a 64-bit ntp fp number */
#define NTP64asDOUBLE(n) (double)(((uint64_t)n)?\
                         (ntohl(L32(n))-EPOCHDIFF) + \
                         (.00000001*(0.5+(double)(ntohl(R32(n))/42.94967296))):\
                         0)

/* convert a struct timeval to a double */
#define TVasDOUBLE(x) (double)(x.tv_sec+(0.000001*x.tv_usec))

/* convert an ntp 64-bit fp number to a struct timeval */
#define NTP64toTV(n,t) \
      do{ if(!n) t.tv_sec = t.tv_usec = 0; \
          else { \
                  t.tv_sec=ntohl(L32(n))-EPOCHDIFF; \
                  t.tv_usec=(int)(0.5+(double)(ntohl(R32(n))/4294.967296)); \
            } \
      }while(0)

/* convert a struct timeval to an ntp 64-bit fp number */
#define TVtoNTP64(t,n) \
      do{ if(!t.tv_usec && !t.tv_sec) n=0x0UL; \
            else { \
                  L32(n)=htonl(t.tv_sec + EPOCHDIFF); \
                  R32(n)=htonl((uint64_t)((4294.967296*t.tv_usec)+.5)); \
            } \
      } while(0)

/* NTP control message header is 12 bytes, plus any data in the data
 * field, plus null padding to the nearest 32-bit boundary per rfc.
 */
#define SIZEOF_NTPCM(m) (12+ntohs(m.count)+((ntohs(m.count)%4)?4-(ntohs(m.count)%4):0))

/* finally, a little helper or two for debugging: */
#define DBG(x) do{if(verbose>1){ x; }}while(0);
#define PRINTSOCKADDR(x) \
      do{ \
            printf("%u.%u.%u.%u", (x>>24)&0xff, (x>>16)&0xff, (x>>8)&0xff, x&0xff);\
      }while(0);

/* calculate the offset of the local clock */
static inline double calc_offset(const ntp_message *m, const struct timeval *t){
      double client_tx, peer_rx, peer_tx, client_rx;
      client_tx = NTP64asDOUBLE(m->origts);
      peer_rx = NTP64asDOUBLE(m->rxts);
      peer_tx = NTP64asDOUBLE(m->txts);
      client_rx=TVasDOUBLE((*t));
      return (.5*((peer_tx-client_rx)+(peer_rx-client_tx)));
}

/* print out a ntp packet in human readable/debuggable format */
void print_ntp_message(const ntp_message *p){
      struct timeval ref, orig, rx, tx;

      NTP64toTV(p->refts,ref);
      NTP64toTV(p->origts,orig);
      NTP64toTV(p->rxts,rx);
      NTP64toTV(p->txts,tx);

      printf("packet contents:\n");
      printf("\tflags: 0x%.2x\n", p->flags);
      printf("\t  li=%d (0x%.2x)\n", LI(p->flags), p->flags&LI_MASK);
      printf("\t  vn=%d (0x%.2x)\n", VN(p->flags), p->flags&VN_MASK);
      printf("\t  mode=%d (0x%.2x)\n", MODE(p->flags), p->flags&MODE_MASK);
      printf("\tstratum = %d\n", p->stratum);
      printf("\tpoll = %g\n", pow(2, p->poll));
      printf("\tprecision = %g\n", pow(2, p->precision));
      printf("\trtdelay = %-.16g\n", NTP32asDOUBLE(p->rtdelay));
      printf("\trtdisp = %-.16g\n", NTP32asDOUBLE(p->rtdisp));
      printf("\trefid = %x\n", p->refid);
      printf("\trefts = %-.16g\n", NTP64asDOUBLE(p->refts));
      printf("\torigts = %-.16g\n", NTP64asDOUBLE(p->origts));
      printf("\trxts = %-.16g\n", NTP64asDOUBLE(p->rxts));
      printf("\ttxts = %-.16g\n", NTP64asDOUBLE(p->txts));
}

void print_ntp_control_message(const ntp_control_message *p){
      int i=0, numpeers=0;
      const ntp_assoc_status_pair *peer=NULL;

      printf("control packet contents:\n");
      printf("\tflags: 0x%.2x , 0x%.2x\n", p->flags, p->op);
      printf("\t  li=%d (0x%.2x)\n", LI(p->flags), p->flags&LI_MASK);
      printf("\t  vn=%d (0x%.2x)\n", VN(p->flags), p->flags&VN_MASK);
      printf("\t  mode=%d (0x%.2x)\n", MODE(p->flags), p->flags&MODE_MASK);
      printf("\t  response=%d (0x%.2x)\n", (p->op&REM_RESP)>0, p->op&REM_RESP);
      printf("\t  more=%d (0x%.2x)\n", (p->op&REM_MORE)>0, p->op&REM_MORE);
      printf("\t  error=%d (0x%.2x)\n", (p->op&REM_ERROR)>0, p->op&REM_ERROR);
      printf("\t  op=%d (0x%.2x)\n", p->op&OP_MASK, p->op&OP_MASK);
      printf("\tsequence: %d (0x%.2x)\n", ntohs(p->seq), ntohs(p->seq));
      printf("\tstatus: %d (0x%.2x)\n", ntohs(p->status), ntohs(p->status));
      printf("\tassoc: %d (0x%.2x)\n", ntohs(p->assoc), ntohs(p->assoc));
      printf("\toffset: %d (0x%.2x)\n", ntohs(p->offset), ntohs(p->offset));
      printf("\tcount: %d (0x%.2x)\n", ntohs(p->count), ntohs(p->count));
      numpeers=ntohs(p->count)/(sizeof(ntp_assoc_status_pair));
      if(p->op&REM_RESP && p->op&OP_READSTAT){
            peer=(ntp_assoc_status_pair*)p->data;
            for(i=0;i<numpeers;i++){
                  printf("\tpeer id %.2x status %.2x",
                         ntohs(peer[i].assoc), ntohs(peer[i].status));
                  if (PEER_SEL(peer[i].status) >= PEER_INCLUDED){
                        if(PEER_SEL(peer[i].status) >= PEER_SYNCSOURCE){
                              printf(" <-- current sync source");
                        } else {
                              printf(" <-- current sync candidate");
                        }
                  }
                  printf("\n");
            }
      }
}

void setup_request(ntp_message *p){
      struct timeval t;

      memset(p, 0, sizeof(ntp_message));
      LI_SET(p->flags, LI_ALARM);
      VN_SET(p->flags, 4);
      MODE_SET(p->flags, MODE_CLIENT);
      p->poll=4;
      p->precision=(int8_t)0xfa;
      L16(p->rtdelay)=htons(1);
      L16(p->rtdisp)=htons(1);

      gettimeofday(&t, NULL);
      TVtoNTP64(t,p->txts);
}

/* select the "best" server from a list of servers, and return its index.
 * this is done by filtering servers based on stratum, dispersion, and
 * finally round-trip delay. */
int best_offset_server(const ntp_server_results *slist, int nservers){
      int i=0, cserver=0, best_server=-1;

      /* for each server */
      for(cserver=0; cserver<nservers; cserver++){
            /* We don't want any servers that fails these tests */
            /* Sort out servers that didn't respond or responede with a 0 stratum;
             * stratum 0 is for reference clocks so no NTP server should ever report
             * a stratum 0 */
            if ( slist[cserver].stratum == 0){
                  if (verbose) printf("discarding peer %d: stratum=%d\n", cserver, slist[cserver].stratum);
                  continue;
            }
            /* Sort out servers with error flags */
            if ( LI(slist[cserver].flags) == LI_ALARM ){
                  if (verbose) printf("discarding peer %d: flags=%d\n", cserver, LI(slist[cserver].flags));
                  continue;
            }

            /* If we don't have a server yet, use the first one */
            if (best_server == -1) {
                  best_server = cserver;
                  DBG(printf("using peer %d as our first candidate\n", best_server));
                  continue;
            }

            /* compare the server to the best one we've seen so far */
            /* does it have an equal or better stratum? */
            DBG(printf("comparing peer %d with peer %d\n", cserver, best_server));
            if(slist[cserver].stratum <= slist[best_server].stratum){
                  DBG(printf("stratum for peer %d <= peer %d\n", cserver, best_server));
                  /* does it have an equal or better dispersion? */
                  if(slist[cserver].rtdisp <= slist[best_server].rtdisp){
                        DBG(printf("dispersion for peer %d <= peer %d\n", cserver, best_server));
                        /* does it have a better rtdelay? */
                        if(slist[cserver].rtdelay < slist[best_server].rtdelay){
                              DBG(printf("rtdelay for peer %d < peer %d\n", cserver, best_server));
                              best_server = cserver;
                              DBG(printf("peer %d is now our best candidate\n", best_server));
                        }
                  }
            }
      }

      if(best_server >= 0) {
            DBG(printf("best server selected: peer %d\n", best_server));
            return best_server;
      } else {
            DBG(printf("no peers meeting synchronization criteria :(\n"));
            return -1;
      }
}

/* do everything we need to get the total average offset
 * - we use a certain amount of parallelization with poll() to ensure
 *   we don't waste time sitting around waiting for single packets.
 * - we also "manually" handle resolving host names and connecting, because
 *   we have to do it in a way that our lazy macros don't handle currently :( */
double offset_request(const char *host, int *status){
      int i=0, j=0, ga_result=0, num_hosts=0, *socklist=NULL, respnum=0;
      int servers_completed=0, one_written=0, one_read=0, servers_readable=0, best_index=-1;
      time_t now_time=0, start_ts=0;
      ntp_message *req=NULL;
      double avg_offset=0.;
      struct timeval recv_time;
      struct addrinfo *ai=NULL, *ai_tmp=NULL, hints;
      struct pollfd *ufds=NULL;
      ntp_server_results *servers=NULL;

      /* setup hints to only return results from getaddrinfo that we'd like */
      memset(&hints, 0, sizeof(struct addrinfo));
      hints.ai_family = address_family;
      hints.ai_protocol = IPPROTO_UDP;
      hints.ai_socktype = SOCK_DGRAM;

      /* fill in ai with the list of hosts resolved by the host name */
      ga_result = getaddrinfo(host, "123", &hints, &ai);
      if(ga_result!=0){
            die(STATE_UNKNOWN, "error getting address for %s: %s\n",
                host, gai_strerror(ga_result));
      }

      /* count the number of returned hosts, and allocate stuff accordingly */
      for(ai_tmp=ai; ai_tmp!=NULL; ai_tmp=ai_tmp->ai_next){ num_hosts++; }
      req=(ntp_message*)malloc(sizeof(ntp_message)*num_hosts);
      if(req==NULL) die(STATE_UNKNOWN, "can not allocate ntp message array");
      socklist=(int*)malloc(sizeof(int)*num_hosts);
      if(socklist==NULL) die(STATE_UNKNOWN, "can not allocate socket array");
      ufds=(struct pollfd*)malloc(sizeof(struct pollfd)*num_hosts);
      if(ufds==NULL) die(STATE_UNKNOWN, "can not allocate socket array");
      servers=(ntp_server_results*)malloc(sizeof(ntp_server_results)*num_hosts);
      if(servers==NULL) die(STATE_UNKNOWN, "can not allocate server array");
      memset(servers, 0, sizeof(ntp_server_results)*num_hosts);
      DBG(printf("Found %d peers to check\n", num_hosts));

      /* setup each socket for writing, and the corresponding struct pollfd */
      ai_tmp=ai;
      for(i=0;ai_tmp;i++){
            socklist[i]=socket(ai_tmp->ai_family, SOCK_DGRAM, IPPROTO_UDP);
            if(socklist[i] == -1) {
                  perror(NULL);
                  die(STATE_UNKNOWN, "can not create new socket");
            }
            if(connect(socklist[i], ai_tmp->ai_addr, ai_tmp->ai_addrlen)){
                  die(STATE_UNKNOWN, "can't create socket connection");
            } else {
                  ufds[i].fd=socklist[i];
                  ufds[i].events=POLLIN;
                  ufds[i].revents=0;
            }
            ai_tmp = ai_tmp->ai_next;
      }

      /* now do AVG_NUM checks to each host.  we stop before timeout/2 seconds
       * have passed in order to ensure post-processing and jitter time. */
      now_time=start_ts=time(NULL);
      while(servers_completed<num_hosts && now_time-start_ts <= socket_timeout/2){
            /* loop through each server and find each one which hasn't
             * been touched in the past second or so and is still lacking
             * some responses.  for each of these servers, send a new request,
             * and update the "waiting" timestamp with the current time. */
            one_written=0;
            now_time=time(NULL);

            for(i=0; i<num_hosts; i++){
                  if(servers[i].waiting<now_time && servers[i].num_responses<AVG_NUM){
                        if(verbose && servers[i].waiting != 0) printf("re-");
                        if(verbose) printf("sending request to peer %d\n", i);
                        setup_request(&req[i]);
                        write(socklist[i], &req[i], sizeof(ntp_message));
                        servers[i].waiting=now_time;
                        one_written=1;
                        break;
                  }
            }

            /* quickly poll for any sockets with pending data */
            servers_readable=poll(ufds, num_hosts, 100);
            if(servers_readable==-1){
                  perror("polling ntp sockets");
                  die(STATE_UNKNOWN, "communication errors");
            }

            /* read from any sockets with pending data */
            for(i=0; servers_readable && i<num_hosts; i++){
                  if(ufds[i].revents&POLLIN && servers[i].num_responses < AVG_NUM){
                        if(verbose) {
                              printf("response from peer %d: ", i);
                        }

                        read(ufds[i].fd, &req[i], sizeof(ntp_message));
                        gettimeofday(&recv_time, NULL);
                        DBG(print_ntp_message(&req[i]));
                        respnum=servers[i].num_responses++;
                        servers[i].offset[respnum]=calc_offset(&req[i], &recv_time);
                        if(verbose) {
                              printf("offset %.10g\n", servers[i].offset[respnum]);
                        }
                        servers[i].stratum=req[i].stratum;
                        servers[i].rtdisp=NTP32asDOUBLE(req[i].rtdisp);
                        servers[i].rtdelay=NTP32asDOUBLE(req[i].rtdelay);
                        servers[i].waiting=0;
                        servers[i].flags=req[i].flags;
                        servers_readable--;
                        one_read = 1;
                        if(servers[i].num_responses==AVG_NUM) servers_completed++;
                  }
            }
            /* lather, rinse, repeat. */
      }

      if (one_read == 0) {
            die(STATE_CRITICAL, "NTP CRITICAL: No response from NTP server\n");
      }

      /* now, pick the best server from the list */
      best_index=best_offset_server(servers, num_hosts);
      if(best_index < 0){
            *status=STATE_UNKNOWN;
      } else {
            /* finally, calculate the average offset */
            for(i=0; i<servers[best_index].num_responses;i++){
                  avg_offset+=servers[best_index].offset[j];
            }
            avg_offset/=servers[best_index].num_responses;
      }

      /* cleanup */
      /* FIXME: Not closing the socket to avoid re-use of the local port
       * which can cause old NTP packets to be read instead of NTP control
       * pactets in jitter_request(). THERE MUST BE ANOTHER WAY...
       * for(j=0; j<num_hosts; j++){ close(socklist[j]); } */
      free(socklist);
      free(ufds);
      free(servers);
      free(req);
      freeaddrinfo(ai);

      if(verbose) printf("overall average offset: %.10g\n", avg_offset);
      return avg_offset;
}

void
setup_control_request(ntp_control_message *p, uint8_t opcode, uint16_t seq){
      memset(p, 0, sizeof(ntp_control_message));
      LI_SET(p->flags, LI_NOWARNING);
      VN_SET(p->flags, VN_RESERVED);
      MODE_SET(p->flags, MODE_CONTROLMSG);
      OP_SET(p->op, opcode);
      p->seq = htons(seq);
      /* Remaining fields are zero for requests */
}

/* XXX handle responses with the error bit set */
double jitter_request(const char *host, int *status){
      int conn=-1, i, npeers=0, num_candidates=0, syncsource_found=0;
      int run=0, min_peer_sel=PEER_INCLUDED, num_selected=0, num_valid=0;
      int peers_size=0, peer_offset=0;
      ntp_assoc_status_pair *peers=NULL;
      ntp_control_message req;
      const char *getvar = "jitter";
      double rval = 0.0, jitter = -1.0;
      char *startofvalue=NULL, *nptr=NULL;
      void *tmp;

      /* Long-winded explanation:
       * Getting the jitter requires a number of steps:
       * 1) Send a READSTAT request.
       * 2) Interpret the READSTAT reply
       *  a) The data section contains a list of peer identifiers (16 bits)
       *     and associated status words (16 bits)
       *  b) We want the value of 0x06 in the SEL (peer selection) value,
       *     which means "current synchronizatin source".  If that's missing,
       *     we take anything better than 0x04 (see the rfc for details) but
       *     set a minimum of warning.
       * 3) Send a READVAR request for information on each peer identified
       *    in 2b greater than the minimum selection value.
       * 4) Extract the jitter value from the data[] (it's ASCII)
       */
      my_udp_connect(server_address, 123, &conn);

      /* keep sending requests until the server stops setting the
       * REM_MORE bit, though usually this is only 1 packet. */
      do{
            setup_control_request(&req, OP_READSTAT, 1);
            DBG(printf("sending READSTAT request"));
            write(conn, &req, SIZEOF_NTPCM(req));
            DBG(print_ntp_control_message(&req));
            /* Attempt to read the largest size packet possible */
            req.count=htons(MAX_CM_SIZE);
            DBG(printf("recieving READSTAT response"))
            read(conn, &req, SIZEOF_NTPCM(req));
            DBG(print_ntp_control_message(&req));
            /* Each peer identifier is 4 bytes in the data section, which
             * we represent as a ntp_assoc_status_pair datatype.
             */
            peers_size+=ntohs(req.count);
            if((tmp=realloc(peers, peers_size)) == NULL)
                  free(peers), die(STATE_UNKNOWN, "can not (re)allocate 'peers' buffer\n");
            peers=tmp;
            memcpy((void*)((ptrdiff_t)peers+peer_offset), (void*)req.data, ntohs(req.count));
            npeers=peers_size/sizeof(ntp_assoc_status_pair);
            peer_offset+=ntohs(req.count);
      } while(req.op&REM_MORE);

      /* first, let's find out if we have a sync source, or if there are
       * at least some candidates.  in the case of the latter we'll issue
       * a warning but go ahead with the check on them. */
      for (i = 0; i < npeers; i++){
            if (PEER_SEL(peers[i].status) >= PEER_INCLUDED){
                  num_candidates++;
                  if(PEER_SEL(peers[i].status) >= PEER_SYNCSOURCE){
                        syncsource_found=1;
                        min_peer_sel=PEER_SYNCSOURCE;
                  }
            }
      }
      if(verbose) printf("%d candiate peers available\n", num_candidates);
      if(verbose && syncsource_found) printf("synchronization source found\n");
      if(! syncsource_found){
            *status = STATE_UNKNOWN;
            if(verbose) printf("warning: no synchronization source found\n");
      }


      for (run=0; run<AVG_NUM; run++){
            if(verbose) printf("jitter run %d of %d\n", run+1, AVG_NUM);
            for (i = 0; i < npeers; i++){
                  /* Only query this server if it is the current sync source */
                  if (PEER_SEL(peers[i].status) >= min_peer_sel){
                        num_selected++;
                        setup_control_request(&req, OP_READVAR, 2);
                        req.assoc = peers[i].assoc;
                        /* By spec, putting the variable name "jitter"  in the request
                         * should cause the server to provide _only_ the jitter value.
                         * thus reducing net traffic, guaranteeing us only a single
                         * datagram in reply, and making intepretation much simpler
                         */
                        /* Older servers doesn't know what jitter is, so if we get an
                         * error on the first pass we redo it with "dispersion" */
                        strncpy(req.data, getvar, MAX_CM_SIZE-1);
                        req.count = htons(strlen(getvar));
                        DBG(printf("sending READVAR request...\n"));
                        write(conn, &req, SIZEOF_NTPCM(req));
                        DBG(print_ntp_control_message(&req));

                        req.count = htons(MAX_CM_SIZE);
                        DBG(printf("recieving READVAR response...\n"));
                        read(conn, &req, SIZEOF_NTPCM(req));
                        DBG(print_ntp_control_message(&req));

                        if(req.op&REM_ERROR && strstr(getvar, "jitter")) {
                              if(verbose) printf("The 'jitter' command failed (old ntp server?)\nRestarting with 'dispersion'...\n");
                              getvar = "dispersion";
                              num_selected--;
                              i--;
                              continue;
                        }

                        /* get to the float value */
                        if(verbose) {
                              printf("parsing jitter from peer %.2x: ", ntohs(peers[i].assoc));
                        }
                        startofvalue = strchr(req.data, '=');
                        if(startofvalue != NULL) {
                              startofvalue++;
                              jitter = strtod(startofvalue, &nptr);
                        }
                        if(startofvalue == NULL || startofvalue==nptr){
                              printf("warning: unable to read server jitter response.\n");
                              *status = STATE_UNKNOWN;
                        } else {
                              if(verbose) printf("%g\n", jitter);
                              num_valid++;
                              rval += jitter;
                        }
                  }
            }
            if(verbose){
                  printf("jitter parsed from %d/%d peers\n", num_valid, num_selected);
            }
      }

      rval = num_valid ? rval / num_valid : -1.0;

      close(conn);
      if(peers!=NULL) free(peers);
      /* If we return -1.0, it means no synchronization source was found */
      return rval;
}

int process_arguments(int argc, char **argv){
      int c;
      int option=0;
      static struct option longopts[] = {
            {"version", no_argument, 0, 'V'},
            {"help", no_argument, 0, 'h'},
            {"verbose", no_argument, 0, 'v'},
            {"use-ipv4", no_argument, 0, '4'},
            {"use-ipv6", no_argument, 0, '6'},
            {"warning", required_argument, 0, 'w'},
            {"critical", required_argument, 0, 'c'},
            {"jwarn", required_argument, 0, 'j'},
            {"jcrit", required_argument, 0, 'k'},
            {"timeout", required_argument, 0, 't'},
            {"hostname", required_argument, 0, 'H'},
            {0, 0, 0, 0}
      };


      if (argc < 2)
            usage ("\n");

      while (1) {
            c = getopt_long (argc, argv, "Vhv46w:c:j:k:t:H:", longopts, &option);
            if (c == -1 || c == EOF || c == 1)
                  break;

            switch (c) {
            case 'h':
                  print_help();
                  exit(STATE_OK);
                  break;
            case 'V':
                  print_revision(progname, NP_VERSION);
                  exit(STATE_OK);
                  break;
            case 'v':
                  verbose++;
                  break;
            case 'w':
                  do_offset=1;
                  owarn = optarg;
                  break;
            case 'c':
                  do_offset=1;
                  ocrit = optarg;
                  break;
            case 'j':
                  do_jitter=1;
                  jwarn = optarg;
                  break;
            case 'k':
                  do_jitter=1;
                  jcrit = optarg;
                  break;
            case 'H':
                  if(is_host(optarg) == FALSE)
                        usage2(_("Invalid hostname/address"), optarg);
                  server_address = strdup(optarg);
                  break;
            case 't':
                  socket_timeout=atoi(optarg);
                  break;
            case '4':
                  address_family = AF_INET;
                  break;
            case '6':
#ifdef USE_IPV6
                  address_family = AF_INET6;
#else
                  usage4 (_("IPv6 support not available"));
#endif
                  break;
            case '?':
                  /* print short usage statement if args not parsable */
                  usage5 ();
                  break;
            }
      }

      if(server_address == NULL){
            usage4(_("Hostname was not supplied"));
      }

      return 0;
}

char *perfd_offset (double offset)
{
      return fperfdata ("offset", offset, "s",
            TRUE, offset_thresholds->warning->end,
            TRUE, offset_thresholds->critical->end,
            FALSE, 0, FALSE, 0);
}

char *perfd_jitter (double jitter)
{
      return fperfdata ("jitter", jitter, "s",
            do_jitter, jitter_thresholds->warning->end,
            do_jitter, jitter_thresholds->critical->end,
            TRUE, 0, FALSE, 0);
}

int main(int argc, char *argv[]){
      int result, offset_result, jitter_result;
      double offset=0, jitter=0;
      char *result_line, *perfdata_line;

      setlocale (LC_ALL, "");
      bindtextdomain (PACKAGE, LOCALEDIR);
      textdomain (PACKAGE);

      result = offset_result = jitter_result = STATE_OK;

      /* Parse extra opts if any */
      argv=np_extra_opts (&argc, argv, progname);

      if (process_arguments (argc, argv) == ERROR)
            usage4 (_("Could not parse arguments"));

      set_thresholds(&offset_thresholds, owarn, ocrit);
      set_thresholds(&jitter_thresholds, jwarn, jcrit);

      /* initialize alarm signal handling */
      signal (SIGALRM, socket_timeout_alarm_handler);

      /* set socket timeout */
      alarm (socket_timeout);

      offset = offset_request(server_address, &offset_result);
      /* check_ntp used to always return CRITICAL if offset_result == STATE_UNKNOWN.
       * Now we'll only do that is the offset thresholds were set */
      if (do_offset && offset_result == STATE_UNKNOWN) {
            result = STATE_CRITICAL;
      } else {
            result = get_status(fabs(offset), offset_thresholds);
      }

      /* If not told to check the jitter, we don't even send packets.
       * jitter is checked using NTP control packets, which not all
       * servers recognize.  Trying to check the jitter on OpenNTPD
       * (for example) will result in an error
       */
      if(do_jitter){
            jitter=jitter_request(server_address, &jitter_result);
            result = max_state_alt(result, get_status(jitter, jitter_thresholds));
            /* -1 indicates that we couldn't calculate the jitter
             * Only overrides STATE_OK from the offset */
            if(jitter == -1.0 && result == STATE_OK)
                  result = STATE_UNKNOWN;
      }
      result = max_state_alt(result, jitter_result);

      switch (result) {
            case STATE_CRITICAL :
                  asprintf(&result_line, _("NTP CRITICAL:"));
                  break;
            case STATE_WARNING :
                  asprintf(&result_line, _("NTP WARNING:"));
                  break;
            case STATE_OK :
                  asprintf(&result_line, _("NTP OK:"));
                  break;
            default :
                  asprintf(&result_line, _("NTP UNKNOWN:"));
                  break;
      }
      if(offset_result == STATE_UNKNOWN){
            asprintf(&result_line, "%s %s", result_line, _("Offset unknown"));
            asprintf(&perfdata_line, "");
      } else {
            asprintf(&result_line, "%s %s %.10g secs", result_line, _("Offset"), offset);
            asprintf(&perfdata_line, "%s", perfd_offset(offset));
      }
      if (do_jitter) {
            asprintf(&result_line, "%s, jitter=%f", result_line, jitter);
            asprintf(&perfdata_line, "%s %s", perfdata_line,  perfd_jitter(jitter));
      }
      printf("%s|%s\n", result_line, perfdata_line);

      if(server_address!=NULL) free(server_address);
      return result;
}



void print_help(void){
      print_revision(progname, NP_VERSION);

      printf ("Copyright (c) 2006 Sean Finney\n");
      printf (COPYRIGHT, copyright, email);

      printf ("%s\n", _("This plugin checks the selected ntp server"));

      printf ("\n\n");

      print_usage();
      printf (_(UT_HELP_VRSN));
      printf (_(UT_EXTRA_OPTS));
      printf (_(UT_HOST_PORT), 'p', "123");
      printf (" %s\n", "-w, --warning=THRESHOLD");
      printf ("    %s\n", _("Offset to result in warning status (seconds)"));
      printf (" %s\n", "-c, --critical=THRESHOLD");
      printf ("    %s\n", _("Offset to result in critical status (seconds)"));
      printf (" %s\n", "-j, --jwarn=THRESHOLD");
      printf ("    %s\n", _("Warning threshold for jitter"));
      printf (" %s\n", "-k, --jcrit=THRESHOLD");
      printf ("    %s\n", _("Critical threshold for jitter"));
      printf (_(UT_TIMEOUT), DEFAULT_SOCKET_TIMEOUT);
      printf (_(UT_VERBOSE));

      printf("\n");
      printf("%s\n", _("Notes:"));
      printf(_(UT_THRESHOLDS_NOTES));
#ifdef NP_EXTRA_OPTS
      printf("\n");
      printf(_(UT_EXTRA_OPTS_NOTES));
#endif

      printf("\n");
      printf("%s\n", _("Examples:"));
      printf(" %s\n", _("Normal offset check:"));
      printf("  %s\n", ("./check_ntp -H ntpserv -w 0.5 -c 1"));
      printf("\n");
      printf(" %s\n", _("Check jitter too, avoiding critical notifications if jitter isn't available"));
      printf(" %s\n", _("(See Notes above for more details on thresholds formats):"));
      printf("  %s\n", ("./check_ntp -H ntpserv -w 0.5 -c 1 -j -1:100 -k -1:200"));

      printf (_(UT_SUPPORT));

      printf ("%s\n", _("WARNING: check_ntp is deprecated. Please use check_ntp_peer or"));
      printf ("%s\n\n", _("check_ntp_time istead."));
}

void
print_usage(void)
{
      printf ("%s\n", _("WARNING: check_ntp is deprecated. Please use check_ntp_peer or"));
      printf ("%s\n\n", _("check_ntp_time istead."));
      printf (_("Usage:"));
      printf(" %s -H <host> [-w <warn>] [-c <crit>] [-j <warn>] [-k <crit>] [-v verbose]\n", progname);
}

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