我如何从PROC获取有关子进程的信息

时间:2018-10-21 17:49:14

标签: c linux process child-process

我正在尝试编写一个以几个进程作为参数的程序。然后,父进程执行每个子进程并打印出有关该子进程的一些统计信息。

示例:/ generate ls -l //将导致打印程序的结果列出有关ls -l的一些统计信息(具体是它的系统时间,用户时间和上下文切换次数)。

我不想使用getrusage()函数,而是希望从中获取必要的信息。 Proc文件系统。现在,我的理解是,如果我要使用wait()函数,它将最终从proc文件系统中删除信息。我在下面包含了我的代码

#include <time.h>
#include <stdbool.h>
#include <assert.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/resource.h>



void inputted_command(int a, char **b){
 for(int i=1;i<a;i++)
     printf("%s ",b[i]);


}

int main(int argc, char **argv){
    int status; 
  pid_t childpid;
  pid_t get_information;
if (argc < 2)
    {

        return 1;
    }

    bool handle_signals = (signal(SIGINT, SIG_IGN) != SIG_IGN); 
    clock_t t; 
    t= clock(); 
    pid_t pid = fork();

if(pid<0) 
{
printf("fork: error no = %s\n",strerror(errno));
 return 1;

}
else if(pid>0){
    signal(SIGINT,SIG_IGN); 

  sleep(60);

  /*
   get_information=fork();
   if(get_information==0){
     excelp(___);

   }else
  waitpid(pid, &status, 0); 



  */
  waitpid(childpid, &status, 0); 

    t= clock()-t; 
    double real_time_taken = ((double)t)/CLOCKS_PER_SEC;

  printf("The command "); 
  inputted_command(argc,argv);
  if(WIFSIGNALED(status)){

  printf("is interrupted by the signal number = %d (Insert Name Here) real: %.2f, user: , system: , context switch:  \n",WTERMSIG(status),real_time_taken);

}

else{

printf("terminated with return status code = %d real: %.2f, user: , system: , context switch:  \n",WEXITSTATUS(status), real_time_taken);

}

}

else if(pid==0){
       childpid=getpid();
        printf("Process with id: %d created for the command: ",(int)getpid());
        inputted_command(argc,argv);
        printf("\n");
        assert(pid == 0); 
        if (handle_signals) 
        signal(SIGINT, SIG_DFL);
        execvp(argv[1], &argv[1]); 
        printf(" experienced an error in starting the command: ");
        inputted_command(argc,argv);
        printf("\n");
        exit(-1);
      }

}

  • 我的部分代码已被注释,我不确定该怎么做。
  • 我的想法是首先让父进程进入睡眠状态,以便子进程完成终止。
  • 然后,父进程创建一个新的子进程以访问PROC / Fie系统并获取必要的数据(已对此进行了评论) 。
  • 最后,我再次调用wait函数并终止初始子进程

所以我在这里的主要问题是,这是否是获取信息的适当方法子进程的信息,以及如何获取信息(主要是系统时间,用户时间以及自愿和非自愿上下文切换?

2 个答案:

答案 0 :(得分:1)

这是我编写的一个测试程序,可能会有所启发(注意:有点粗糙):

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>

int mode = -1;
pid_t pid;
time_t cur;
FILE *xf;
char dirproc[100];
char dirfd[100];
char status_file[100];
char cmd[100];

void
xsystem(char *cmd)
{

    printf("CMD: %s\n",cmd);
    system(cmd);
}

int
check(int nmode)
{
    struct stat st;
    int errst;
    int errkill;
    char buf[500];

    errkill = kill(pid,0);
    errst = stat(dirproc,&st);

    if (nmode != mode) {
        printf("elap=%d errkill=%d errst=%d\n",cur,errkill,errst);

        sprintf(cmd,"ls -l /proc/%d",pid);
        xsystem(cmd);

        sprintf(cmd,"ls -l /proc/%d/fd",pid);
        xsystem(cmd);

        sprintf(cmd,"cat /proc/%d/status",pid);
        xsystem(cmd);

        printf("fgets\n");

        rewind(xf);
        while (1) {
            char *cp = fgets(buf,sizeof(buf),xf);
            if (cp == NULL)
                break;
            fputs(buf,stdout);
        }

        mode = nmode;
    }

    return errkill;
}

// main -- main program
int
main(int argc,char **argv)
{
    char *cp;

    --argc;
    ++argv;

    for (;  argc > 0;  --argc, ++argv) {
        cp = *argv;
        if (*cp != '-')
            break;

        switch (cp[1]) {
        default:
            break;
        }
    }

    setlinebuf(stdout);
    setlinebuf(stderr);

    pid = fork();

    if (pid == 0) {
        open("/dev/null",O_RDONLY);
        sleep(1);
        exit(0);
    }

    sprintf(dirproc,"/proc/%d",pid);
    sprintf(dirfd,"/proc/%d/fd",pid);
    sprintf(status_file,"/proc/%d/status",pid);
    xf = fopen(status_file,"r");

    time_t beg = time(NULL);
    cur = 0;

    while (1) {
        cur = time(NULL);

        cur -= beg;
        if (cur >= 4)
            break;

        check(1);
    }

    printf("\n");
    printf("postloop\n");
    check(2);

    waitpid(pid,NULL,0);
    printf("\n");
    printf("postwait\n");
    check(3);

    return 0;
}

这是程序输出:

elap=0 errkill=0 errst=0
CMD: ls -l /proc/94913
total 0
dr-xr-xr-x. 2 xxx xxx 0 Oct 21 15:50 attr
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 autogroup
-r--------. 1 xxx xxx 0 Oct 21 15:50 auxv
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 cgroup
--w-------. 1 xxx xxx 0 Oct 21 15:50 clear_refs
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 cmdline
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 comm
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 coredump_filter
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 cpuset
lrwxrwxrwx. 1 xxx xxx 0 Oct 21 15:50 cwd -> /tmp/cld
-r--------. 1 xxx xxx 0 Oct 21 15:50 environ
lrwxrwxrwx. 1 xxx xxx 0 Oct 21 15:50 exe -> /tmp/cld/pgm2
dr-x------. 2 xxx xxx 0 Oct 21 15:50 fd
dr-x------. 2 xxx xxx 0 Oct 21 15:50 fdinfo
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 gid_map
-r--------. 1 xxx xxx 0 Oct 21 15:50 io
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 latency
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 limits
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 loginuid
dr-x------. 2 xxx xxx 0 Oct 21 15:50 map_files
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 maps
-rw-------. 1 xxx xxx 0 Oct 21 15:50 mem
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 mountinfo
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 mounts
-r--------. 1 xxx xxx 0 Oct 21 15:50 mountstats
dr-xr-xr-x. 6 xxx xxx 0 Oct 21 15:50 net
dr-x--x--x. 2 xxx xxx 0 Oct 21 15:50 ns
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 numa_maps
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 oom_adj
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 oom_score
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 oom_score_adj
-r--------. 1 xxx xxx 0 Oct 21 15:50 pagemap
-r--------. 1 xxx xxx 0 Oct 21 15:50 personality
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 projid_map
lrwxrwxrwx. 1 xxx xxx 0 Oct 21 15:50 root -> /
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 sched
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 schedstat
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 sessionid
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 setgroups
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 smaps
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 smaps_rollup
-r--------. 1 xxx xxx 0 Oct 21 15:50 stack
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 stat
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 statm
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 status
-r--------. 1 xxx xxx 0 Oct 21 15:50 syscall
dr-xr-xr-x. 3 xxx xxx 0 Oct 21 15:50 task
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 timers
-rw-rw-rw-. 1 xxx xxx 0 Oct 21 15:50 timerslack_ns
-rw-r--r--. 1 xxx xxx 0 Oct 21 15:50 uid_map
-r--r--r--. 1 xxx xxx 0 Oct 21 15:50 wchan
CMD: ls -l /proc/94913/fd
total 0
lrwx------. 1 xxx xxx 64 Oct 21 15:50 0 -> /dev/pts/0
l-wx------. 1 xxx xxx 64 Oct 21 15:50 1 -> /tmp/out2
l-wx------. 1 xxx xxx 64 Oct 21 15:50 2 -> /tmp/out2
lr-x------. 1 xxx xxx 64 Oct 21 15:50 3 -> /dev/null
CMD: cat /proc/94913/status
Name:   pgm2
Umask:  0022
State:  S (sleeping)
Tgid:   94913
Ngid:   0
Pid:    94913
PPid:   94912
TracerPid:  0
Uid:    500 500 500 500
Gid:    500 500 500 500
FDSize: 64
Groups: 500
NStgid: 94913
NSpid:  94913
NSpgid: 94912
NSsid:  3771
VmPeak:     4136 kB
VmSize:     4136 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:        80 kB
VmRSS:        80 kB
RssAnon:          80 kB
RssFile:           0 kB
RssShmem:          0 kB
VmData:       44 kB
VmStk:       132 kB
VmExe:         8 kB
VmLib:      1872 kB
VmPTE:        52 kB
VmSwap:        0 kB
HugetlbPages:          0 kB
CoreDumping:    0
Threads:    1
SigQ:   0/47895
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000003fffffffff
CapAmb: 0000000000000000
NoNewPrivs: 0
Seccomp:    0
Speculation_Store_Bypass:   thread vulnerable
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    1
nonvoluntary_ctxt_switches: 0
fgets
Name:   pgm2
Umask:  0022
State:  S (sleeping)
Tgid:   94913
Ngid:   0
Pid:    94913
PPid:   94912
TracerPid:  0
Uid:    500 500 500 500
Gid:    500 500 500 500
FDSize: 64
Groups: 500
NStgid: 94913
NSpid:  94913
NSpgid: 94912
NSsid:  3771
VmPeak:     4136 kB
VmSize:     4136 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:        80 kB
VmRSS:        80 kB
RssAnon:          80 kB
RssFile:           0 kB
RssShmem:          0 kB
VmData:       44 kB
VmStk:       132 kB
VmExe:         8 kB
VmLib:      1872 kB
VmPTE:        52 kB
VmSwap:        0 kB
HugetlbPages:          0 kB
CoreDumping:    0
Threads:    1
SigQ:   0/47895
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000003fffffffff
CapAmb: 0000000000000000
NoNewPrivs: 0
Seccomp:    0
Speculation_Store_Bypass:   thread vulnerable
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    1
nonvoluntary_ctxt_switches: 0

postloop
elap=4 errkill=0 errst=0
CMD: ls -l /proc/94913
ls: cannot read symbolic link '/proc/94913/cwd': No such file or directory
ls: cannot read symbolic link '/proc/94913/root': No such file or directory
ls: cannot read symbolic link '/proc/94913/exe': No such file or directory
total 0
dr-xr-xr-x. 2 xxx  xxx  0 Oct 21 15:50 attr
-rw-r--r--. 1 root root 0 Oct 21 15:50 autogroup
-r--------. 1 root root 0 Oct 21 15:50 auxv
-r--r--r--. 1 root root 0 Oct 21 15:50 cgroup
--w-------. 1 root root 0 Oct 21 15:50 clear_refs
-r--r--r--. 1 root root 0 Oct 21 15:50 cmdline
-rw-r--r--. 1 root root 0 Oct 21 15:50 comm
-rw-r--r--. 1 root root 0 Oct 21 15:50 coredump_filter
-r--r--r--. 1 root root 0 Oct 21 15:50 cpuset
lrwxrwxrwx. 1 root root 0 Oct 21 15:50 cwd
-r--------. 1 root root 0 Oct 21 15:50 environ
lrwxrwxrwx. 1 root root 0 Oct 21 15:50 exe
dr-x------. 2 root root 0 Oct 21 15:50 fd
dr-x------. 2 root root 0 Oct 21 15:50 fdinfo
-rw-r--r--. 1 root root 0 Oct 21 15:50 gid_map
-r--------. 1 root root 0 Oct 21 15:50 io
-r--r--r--. 1 root root 0 Oct 21 15:50 latency
-r--r--r--. 1 root root 0 Oct 21 15:50 limits
-rw-r--r--. 1 root root 0 Oct 21 15:50 loginuid
dr-x------. 2 root root 0 Oct 21 15:50 map_files
-r--r--r--. 1 root root 0 Oct 21 15:50 maps
-rw-------. 1 root root 0 Oct 21 15:50 mem
-r--r--r--. 1 root root 0 Oct 21 15:50 mountinfo
-r--r--r--. 1 root root 0 Oct 21 15:50 mounts
-r--------. 1 root root 0 Oct 21 15:50 mountstats
dr-xr-xr-x. 2 xxx  xxx  0 Oct 21 15:50 net
dr-x--x--x. 2 root root 0 Oct 21 15:50 ns
-r--r--r--. 1 root root 0 Oct 21 15:50 numa_maps
-rw-r--r--. 1 root root 0 Oct 21 15:50 oom_adj
-r--r--r--. 1 root root 0 Oct 21 15:50 oom_score
-rw-r--r--. 1 root root 0 Oct 21 15:50 oom_score_adj
-r--------. 1 root root 0 Oct 21 15:50 pagemap
-r--------. 1 root root 0 Oct 21 15:50 personality
-rw-r--r--. 1 root root 0 Oct 21 15:50 projid_map
lrwxrwxrwx. 1 root root 0 Oct 21 15:50 root
-rw-r--r--. 1 root root 0 Oct 21 15:50 sched
-r--r--r--. 1 root root 0 Oct 21 15:50 schedstat
-r--r--r--. 1 root root 0 Oct 21 15:50 sessionid
-rw-r--r--. 1 root root 0 Oct 21 15:50 setgroups
-r--r--r--. 1 root root 0 Oct 21 15:50 smaps
-r--r--r--. 1 root root 0 Oct 21 15:50 smaps_rollup
-r--------. 1 root root 0 Oct 21 15:50 stack
-r--r--r--. 1 root root 0 Oct 21 15:50 stat
-r--r--r--. 1 root root 0 Oct 21 15:50 statm
-r--r--r--. 1 root root 0 Oct 21 15:50 status
-r--------. 1 root root 0 Oct 21 15:50 syscall
dr-xr-xr-x. 3 xxx  xxx  0 Oct 21 15:50 task
-r--r--r--. 1 root root 0 Oct 21 15:50 timers
-rw-rw-rw-. 1 root root 0 Oct 21 15:50 timerslack_ns
-rw-r--r--. 1 root root 0 Oct 21 15:50 uid_map
-r--r--r--. 1 root root 0 Oct 21 15:50 wchan
CMD: ls -l /proc/94913/fd
ls: cannot open directory '/proc/94913/fd': Permission denied
CMD: cat /proc/94913/status
Name:   pgm2
State:  Z (zombie)
Tgid:   94913
Ngid:   0
Pid:    94913
PPid:   94912
TracerPid:  0
Uid:    500 500 500 500
Gid:    500 500 500 500
FDSize: 0
Groups: 500
NStgid: 94913
NSpid:  94913
NSpgid: 94912
NSsid:  3771
Threads:    1
SigQ:   0/47895
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000003fffffffff
CapAmb: 0000000000000000
NoNewPrivs: 0
Seccomp:    0
Speculation_Store_Bypass:   thread vulnerable
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    2
nonvoluntary_ctxt_switches: 0
fgets
Name:   pgm2
State:  Z (zombie)
Tgid:   94913
Ngid:   0
Pid:    94913
PPid:   94912
TracerPid:  0
Uid:    500 500 500 500
Gid:    500 500 500 500
FDSize: 0
Groups: 500
NStgid: 94913
NSpid:  94913
NSpgid: 94912
NSsid:  3771
Threads:    1
SigQ:   0/47895
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000003fffffffff
CapAmb: 0000000000000000
NoNewPrivs: 0
Seccomp:    0
Speculation_Store_Bypass:   thread vulnerable
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    2
nonvoluntary_ctxt_switches: 0

postwait
elap=4 errkill=-1 errst=-1
CMD: ls -l /proc/94913
ls: cannot access '/proc/94913': No such file or directory
CMD: ls -l /proc/94913/fd
ls: cannot access '/proc/94913/fd': No such file or directory
CMD: cat /proc/94913/status
cat: /proc/94913/status: No such file or directory
fgets

  

谢谢。我对时间问题感到好奇。如果wait-family调用释放了/ proc中PID的信息,那么启动PID的进程在知道终止子进程之后如何读取状态伪文件。

没有使用wait,父级无法确定/轻松/明确地知道,因为存在另一种检查活动进程的方式(例如{ 1}})仍然返回0。这令我有些惊讶。

基于测试程序的输出,可能的一种工作方式是在kill(pid,0)上执行readlink并检查错误(即错误表示进程已退出并处于僵尸状态)。

另一种方法是阅读/proc/pid/cwd并查找:/proc/pid/status

  

是否需要在等待之前打开状态文件,然后在等待返回后再读取它?

完成State: Z (zombie)之后,即使wait上打开 pre 的流也返回EOF。所以,没有喜悦。

  

还是它不那么狡猾? / proc文件系统上应该有一些文档,例如man7.org上的proc(5),应该涵盖这些详细信息。

手册页中还有其他一些文件,这些文件在进程变为僵尸时会更改(例如/proc/pid/status

答案 1 :(得分:0)

有了Craig Esteyanswer的推动力,接着是我的comment,并使用POSIX的信息sigaction(),它指向Signal Actions<signal.h>, 我想出了以下代码,该代码对SA_SIGINFO信号使用SIGCHLD处理,该程序允许程序从/proc文件系统中收集子进程终止后但之前的信息。已经等待了。

siginfo47.c

#define _XOPEN_SOURCE 700

#include "stderr.h"
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

static int       got_signal = 0;
static siginfo_t child_info = { 0 };

static void sigchld(int signum, siginfo_t *info, void *ctxt)
{
    assert(info != 0);
    assert(ctxt != 0);
    assert(signum == info->si_signo);
    got_signal = signum;
    child_info = *info;
}

struct si_code_names
{
    int     si_code;
    char    si_code_name[16];
    char    si_code_meaning[64];
};

static struct si_code_names si_codes[] =
{
    [CLD_EXITED]    = { CLD_EXITED,    "CLD_EXITED",    "Child has exited." },
    [CLD_KILLED]    = { CLD_KILLED,    "CLD_KILLED",    "Child has terminated abnormally and did not create a core file." },
    [CLD_DUMPED]    = { CLD_DUMPED,    "CLD_DUMPED",    "Child has terminated abnormally and created a core file." },
    [CLD_TRAPPED]   = { CLD_TRAPPED,   "CLD_TRAPPED",   "Traced child has trapped." },
    [CLD_STOPPED]   = { CLD_STOPPED,   "CLD_STOPPED",   "Child has stopped." },
    [CLD_CONTINUED] = { CLD_CONTINUED, "CLD_CONTINUED", "Stopped child has continued." },
};

static void cat_proc_file(int pid, const char *base)
{
    char buffer[1024];
    int rc;
    rc = snprintf(buffer, sizeof(buffer), "/proc/%d/%s", pid, base);
    if (rc < 0 || rc >= (int)sizeof(buffer))
        err_error("snprintf() failed - can't happen!?!\n");
    int fd = open(buffer, O_RDONLY);
    if (fd < 0)
        err_syserr("failed to open file '%s' for reading: ", buffer);
    printf("Contents of %s:\n", buffer);
    int nbytes;
    while ((nbytes = read(fd, buffer, sizeof(buffer))) > 0)
        printf("%*.*s", nbytes, nbytes, buffer);
    putchar('\n');
    fflush(stdout);
    close(fd);
}

int main(int argc, char **argv)
{
    char *cmdv[] = { "ls", "-l", 0 };
    err_setarg0(argv[0]);
    if (argc <= 1)
    {
        argc = 2;
        argv = cmdv;
    }
    else
    {
        argc--;
        argv++;
    }

    pid_t pid = fork();

    if (pid < 0)
        err_syserr("failed to fork: ");
    else if (pid > 0)
    {
        struct sigaction sa = { 0 };
        sa.sa_sigaction = sigchld;
        sa.sa_flags = SA_SIGINFO;
        if (sigaction(SIGCHLD, &sa, 0) != 0)
            err_syserr("failed to set signal handling: ");

        printf("Parent PID %d: pausing while PID %d runs\n", (int)getpid(), (int)pid);
        fflush(stdout);
        pause();
        printf("Parent PID %d: unpaused\n", (int)getpid());

        printf("Stashed information:\n");
        printf("  Signal:       %d\n", got_signal);
        printf("  si_signo:     %d\n", child_info.si_signo);
        printf("  si_code:      %d\n", child_info.si_code);
        if (child_info.si_signo == SIGCHLD)
        {
            struct si_code_names *code = &si_codes[child_info.si_code];
            printf("                [%s] %s\n", code->si_code_name,
                   code->si_code_meaning);
        }
        printf("  si_pid:       %d\n", (int)child_info.si_pid);
        printf("  si_uid:       %d\n", (int)child_info.si_uid);
        printf("  si_addr:      0x%12" PRIXPTR "\n", (uintptr_t)child_info.si_addr);
        printf("  si_status:    %d\n", child_info.si_code);
        printf("  si_value.int: %d\n", child_info.si_value.sival_int);

        cat_proc_file(pid, "stat");
        cat_proc_file(pid, "status");

        int status;
        int corpse;
        if ((corpse = waitpid(pid, &status, 0)) != pid)
            err_syserr("failed to wait for child %d", pid);

        if (WIFSIGNALED(status))
            printf("PID %d died from signal number = %d (0x%.4X)\n",
                   corpse, WTERMSIG(status), status);
        else if (WIFEXITED(status))
            printf("PID %d exited normally with status = %d (0x%.4X)\n",
                   corpse, WEXITSTATUS(status), status);
        else
            printf("PID %d was neither signalled nor exited normally (0x%.4X)\n",
                   corpse, status);
    }
    else if (pid == 0)
    {
        printf("PID: %d:", (int)getpid());
        for (int i = 0; argv[i] != 0; i++)
            printf(" %s", argv[i]);
        putchar('\n');
        fflush(stdout);
        execvp(argv[0], &argv[0]);
        err_syserr("failed to execute %s: ", argv[0]);
        /*NOTREACHED*/
    }
}

其中一些代码可从我在GitHub上的SOQ(堆栈溢出问题)存储库中获得。具体来说,文件stderr.cstderr.h可以在src/libsoq子目录中找到。它们极大地简化了错误报告。

示例运行包括:

$ siginfo47
Parent PID 15016: pausing while PID 15017 runs
PID: 15017: ls -l
total 400
drwxr-xr-x   2 jleffler pd  4096 Oct 21 15:16 bin
drwxr-xr-x   5 jleffler pd   256 Oct 21 15:15 doc
drwxr-xr-x   2 jleffler pd  4096 Oct 21 15:15 etc
drwxr-xr-x   2 jleffler pd  4096 Oct 21 15:16 inc
drwxr-xr-x   2 jleffler pd   256 Oct 21 15:16 lib
-rw-r--r--   1 jleffler pd 22072 Oct 21 15:15 LICENSE.md
-rw-r--r--   1 jleffler pd   390 Oct 21 15:15 makefile
drwxr-xr-x   2 jleffler pd   256 Oct 21 15:15 packages
-rw-r--r--   1 jleffler pd  2694 Oct 21 15:15 README.md
-rwxr-xr-x   1 jleffler pd 64968 Oct 21 15:17 siginfo41
-rw-r--r--   1 jleffler pd  5990 Oct 21 15:17 siginfo41.c
-rwxr-xr-x   1 jleffler pd 66104 Oct 21 15:34 siginfo47
-rw-r--r--   1 jleffler pd  7417 Oct 21 15:33 siginfo47.c
drwxr-xr-x 230 jleffler pd  8192 Oct 21 15:15 src
Parent PID 15016: unpaused
Stashed information:
  Signal:       17
  si_signo:     17
  si_code:      1
                [CLD_EXITED] Child has exited.
  si_pid:       15017
  si_uid:       9508
  si_addr:      0x252400003AA9
  si_status:    1
  si_value.int: 0
Contents of /proc/15017/stat:
15017 (ls) Z 15016 15016 13211 34827 15016 4227084 452 0 0 0 0 0 0 0 20 0 1 0 511347844 0 0 18446744073709551615 0 0 0 0 0 0 0 0 0 18446744073709551615 0 0 17 6 0 0 0 0 0 0 0 0 0 0 0 0 0

Contents of /proc/15017/status:
Name:   ls
State:  Z (zombie)
Tgid:   15017
Ngid:   0
Pid:    15017
PPid:   15016
TracerPid:  0
Uid:    9508    9508    9508    9508
Gid:    1240    1240    1240    1240
FDSize: 0
Groups: 297 1240 1360 8714 
Threads:    1
SigQ:   0/71487
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000180000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000001fffffffff
CapAmb: 0000000000000000
Seccomp:    0
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    3
nonvoluntary_ctxt_switches: 1

PID 15017 exited normally with status = 0 (0x0000)
$ siginfo47 exitcode 23
Parent PID 15032: pausing while PID 15033 runs
PID: 15033: exitcode 23
Parent PID 15032: unpaused
Stashed information:
  Signal:       17
  si_signo:     17
  si_code:      1
                [CLD_EXITED] Child has exited.
  si_pid:       15033
  si_uid:       9508
  si_addr:      0x252400003AB9
  si_status:    1
  si_value.int: 23
Contents of /proc/15033/stat:
15033 (exitcode) Z 15032 15032 13211 34827 15032 4227084 179 0 0 0 0 0 0 0 20 0 1 0 511349111 0 0 18446744073709551615 0 0 0 0 0 0 0 0 0 18446744073709551615 0 0 17 5 0 0 0 0 0 0 0 0 0 0 0 0 0

Contents of /proc/15033/status:
Name:   exitcode
State:  Z (zombie)
Tgid:   15033
Ngid:   0
Pid:    15033
PPid:   15032
TracerPid:  0
Uid:    9508    9508    9508    9508
Gid:    1240    1240    1240    1240
FDSize: 0
Groups: 297 1240 1360 8714 
Threads:    1
SigQ:   0/71487
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000001fffffffff
CapAmb: 0000000000000000
Seccomp:    0
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    3
nonvoluntary_ctxt_switches: 1

PID 15033 exited normally with status = 23 (0x1700)
$ siginfo47 exitcode -s 13
PID: 15057: exitcode -s 13
Parent PID 15056: pausing while PID 15057 runs
Parent PID 15056: unpaused
Stashed information:
  Signal:       17
  si_signo:     17
  si_code:      2
                [CLD_KILLED] Child has terminated abnormally and did not create a core file.
  si_pid:       15057
  si_uid:       9508
  si_addr:      0x252400003AD1
  si_status:    2
  si_value.int: 13
Contents of /proc/15057/stat:
15057 (exitcode) Z 15056 15056 13211 34827 15056 4228108 177 0 0 0 0 0 0 0 20 0 1 0 511350462 0 0 18446744073709551615 0 0 0 0 0 4096 0 0 0 18446744073709551615 0 0 17 5 0 0 0 0 0 0 0 0 0 0 0 0 0

Contents of /proc/15057/status:
Name:   exitcode
State:  Z (zombie)
Tgid:   15057
Ngid:   0
Pid:    15057
PPid:   15056
TracerPid:  0
Uid:    9508    9508    9508    9508
Gid:    1240    1240    1240    1240
FDSize: 0
Groups: 297 1240 1360 8714 
Threads:    1
SigQ:   1/71487
SigPnd: 0000000000001000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: 0000001fffffffff
CapAmb: 0000000000000000
Seccomp:    0
Cpus_allowed:   ff
Cpus_allowed_list:  0-7
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list:  0
voluntary_ctxt_switches:    2
nonvoluntary_ctxt_switches: 1

PID 15057 died from signal number = 13 (0x000D)
$ exitcode -h
Usage: exitcode [-hV] [-s signal] [exit-status]
  -h         Print this help message and exit
  -s signal  Kill self with signal number
  -V         Print version information and exit

$

如帮助消息所示,exitcode程序以退出状态死掉,退出状态通常是(exitcode 23)或由于信号(exitcode -s 13)导致的。