linux上进程的开始时间 [英] start time of a process on linux

问题描述

如何使用c语言在ubuntu linux机器上查找进程启动时间.在 linux 中有提供信息的/proc/[pid]/stat 文件

How to find a process start time on ubuntu linux machine using c language. In linux there is /proc/[pid]/stat file which give information

starttime %lu/*系统启动后进程启动的jiffies时间*/
和文件/proc/stat 给出

starttime %lu /*The time in jiffies the process started after system boot*/
and file /proc/stat that gives

btime %lu /*measurement of system boot time since Epoch in seconds*/  

为了添加这两个值，我如何将前一个值转换为秒，因为它以 jiffies 为单位.

For adding both these values how can I convert former value into seconds because it is in jiffies unit.

推荐答案

当编译 Linux 内核时，每秒 Jiffies 是可配置的.

Jiffies per second is configurable when one compiles the Linux kernel.

以下程序使用您正在运行的内核上每秒的 jiffies 数.它需要一个可选的命令行参数，即进程号.默认是正在运行的程序本身的进程号.它每秒输出指定进程的开始时间，包括本地时间和 UTC.重复循环的唯一原因是为了证明该值不会改变.

The following program uses the number of jiffies per second on the kernel you're running. It takes an optional command line parameter, which is the process number. The default is the process number of the running program itself. Each second, it outputs the start time of the specified process, both as local time and UTC. The only reason for the repeat loop is to demonstrate that the value doesn't change.

#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>
int
find_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 spaces
");

  exit(1);

} /* find_nth_space() */

int
main(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() fail
");

      exit(1);
    }

    read_result=read(stat_fd,stat_buf,sizeof(stat_buf));

    if(read_result<0)
    {
      fprintf(stderr,"read() fail
");

      exit(1);
    }

    if(read_result>=sizeof(stat_buf))
    {
      fprintf(stderr,"stat_buf is too small
");

      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() fail
");

      exit(1);
    }

    read_result=read(stat_fd,stat_buf,sizeof(stat_buf));

    if(read_result<0)
    {
      fprintf(stderr,"read() fail
");

      exit(1);
    }

    if(read_result>=sizeof(stat_buf))
    {
      fprintf(stderr,"stat_buf is too small
");

      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:%02d
",
           local_buf.tm_hour,
           local_buf.tm_min,
           local_buf.tm_sec
          );

    printf("UTC:        %02d:%02d:%02d
",
           gm_buf.tm_hour,
           gm_buf.tm_min,
           gm_buf.tm_sec
          );

    sleep(1);
  }

  return 0;
} /* main() */

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