当人们编译Linux内核时，每秒Jiffies是可配置的。
以下程序使用您正在运行的内核上每秒的跳动次数。它带有一个可选的命令行参数，即进程号。默认值为正在运行的程序本身的进程号。每秒，它输出指定过程的开始时间，既是本地时间又是UTC。重复循环的唯一原因是证明该值没有改变。
#include <sys/stat.h>#include <sys/types.h>#include <fcntl.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <time.h>#include <unistd.h>intfind_nth_space(char *search_buffer, int space_ordinality ){ int jndex; int space_count; space_count=0; for(jndex=0; search_buffer[jndex]; jndex++ ) { if(search_buffer[jndex]==' ') { space_count++; if(space_count>=space_ordinality) { return jndex; } } } fprintf(stderr,"looking for too many spacesn"); exit(1);} intmain(int argc, char **argv ){ int field_begin; int stat_fd; char proc_buf[80]; char stat_buf[2048]; long jiffies_per_second; long long boot_time_since_epoch; long long process_start_time_since_boot; time_t process_start_time_since_epoch; ssize_t read_result; struct tm gm_buf; struct tm local_buf; jiffies_per_second=sysconf(_SC_CLK_TCK); if(argc<2) { strcpy(proc_buf,"/proc/self/stat"); } else { sprintf(proc_buf,"/proc/%ld/stat",strtol(argv[1],NULL,0)); } for(;;) { stat_fd=open(proc_buf,O_RDONLY); if(stat_fd<0) { fprintf(stderr,"open() failn"); exit(1); } read_result=read(stat_fd,stat_buf,sizeof(stat_buf)); if(read_result<0) { fprintf(stderr,"read() failn"); exit(1); } if(read_result>=sizeof(stat_buf)) { fprintf(stderr,"stat_buf is too smalln"); exit(1); } field_begin=find_nth_space(stat_buf,21)+1; stat_buf[find_nth_space(stat_buf,22)]=0; sscanf(stat_buf+field_begin,"%llu",&process_start_time_since_boot); close(stat_fd); stat_fd=open("/proc/stat",O_RDONLY); if(stat_fd<0) { fprintf(stderr,"open() failn"); exit(1); } read_result=read(stat_fd,stat_buf,sizeof(stat_buf)); if(read_result<0) { fprintf(stderr,"read() failn"); exit(1); } if(read_result>=sizeof(stat_buf)) { fprintf(stderr,"stat_buf is too smalln"); exit(1); } close(stat_fd); field_begin=strstr(stat_buf,"btime ")-stat_buf+6; sscanf(stat_buf+field_begin,"%llu",&boot_time_since_epoch); process_start_time_since_epoch = boot_time_since_epoch+process_start_time_since_boot/jiffies_per_second; localtime_r(&process_start_time_since_epoch,&local_buf); gmtime_r (&process_start_time_since_epoch,&gm_buf ); printf("local time: %02d:%02d:%02dn",local_buf.tm_hour,local_buf.tm_min,local_buf.tm_sec ); printf("UTC: %02d:%02d:%02dn",gm_buf.tm_hour,gm_buf.tm_min,gm_buf.tm_sec ); sleep(1); } return 0;} 
