Linux使用KILL 0检测进程是否存在

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发布于 2024-03-29 14:35:11

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之前遇到过kill( pid, 0 )的情况，由于平常没注意到kill函数的形参为0的情况，不知道它的作用。后面用man 2 kill命令查看了下kill函数的说明，发现可以用来检测进程的存在情况。

1 关于kill 0的说明1

从上图DESCRIPTION区域的文字可以看出，kill函数中的形参sig是0的话，那么不会向pid进程发送任何信号，但是仍然会继续检测错误（进程ID或者进程组ID是否存在）。kill函数的返回值和具体的错误信息如下：

RETURN VALUE
       On  success  (at least one signal was sent), zero is returned.  On error, -1
       is returned, and errno is set appropriately.

ERRORS
       EINVAL An invalid signal was specified.

       EPERM  The process does not have permission to send the signal to any of the
              target processes.

       ESRCH  The  pid  or  process  group  does  not exist.  Note that an existing
              process might be a zombie, a process which already committed termina‐
              tion, but has not yet been wait(2)ed for.

2 简单测试程序

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/** * @FileName chk_signal_exist.c * @Describe A simple example for checking if a proccess is existing in linux. * @Author vfhky 2016-03-14 11:48 https://typecodes.com/cseries/kill0checkprocessifexist.html * @Compile gcc chk_signal_exist.c -o chk_signal_exist */ #include <stdio.h> #include <signal.h> #include <malloc.h> #include <stdlib.h> #include <string.h> #define GO_FREE(p) \ free(p); \ p = NULL; \ printf( "exit.\n" ); int main( int argc, char **argv ) { if( argc != 2 ) { printf( "Usage: %s %s\n", argv0, "pid" ); exit(-1); } char *p = (char *)malloc( sizeof(char) * 20 ); memcpy( p, argv1, strlen(argv1) ); /** * no signal is sent, but error checking is still performed; * this can be used to check for the existence of a process ID or process group ID. */ if( kill( atoi(p), 0 ) == -1 ) { perror( "error" ); } else { printf( "Signal%s exist.\n", p ); } GO_FREE(p); return 0; }