这是我编写的一个测试程序,可能会有所启发(Caveat:这有点粗糙):
#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(稍微)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 的进程如何读取它之后的状态伪文件knows孩子终止了。
Without using wait
,父母不能know明确/轻松/干净地因为检查实时进程的替代方法(例如kill(pid,0)
) 仍然返回 0。这对我来说[有点]令人惊讶。
根据测试程序的输出,一种方法是might工作就是做一个readlink
on /proc/pid/cwd
并检查错误(即错误意味着进程已退出并处于僵尸状态)。
另一种方法是阅读/proc/pid/status
并寻找:State: Z (zombie)
是否需要在等待之前打开状态文件,然后在等待返回后读取它?
之后wait
完成后,即使是pre- 打开流/proc/pid/status
返回EOF。所以,没有喜悦。
或者它比这更不狡猾吗?应该有一些关于 /proc 文件系统的文档 — 例如 man7.org 上的 proc(5) — 应该涵盖这些细节。
手册页还执行一些其他文件,这些文件在进程变为僵尸进程时会发生更改(例如/proc/pid/cmdline
)