Linux exec简介

冷不防 2022-06-14 06:48 121阅读 0赞

# exec系列函数简介 #

`fork`子进程之后，子进程要调用`exec`系列函数执行程序，这个调用用新程序替换了当前进程的正文段、数据段、堆段、栈段。

#include <unistd.h>
    
    extern char **environ;
    int execl(const char *path, const char *arg, ...);
    int execle(const char *path, const char *arg, ..., char * const envp[]);
    int execv(const char *path, char *const argv[]);
    
    int execlp(const char *file, const char *arg, ...);
    int execvp(const char *file, char *const argv[]);
    int execvpe(const char *file, char *const argv[],char *const envp[]);

第一个参数为`path`的是需要加路径  
第一个参数为`filename`的是在`PATH`环境变量中搜索

执行`exec`后，进程ID没有变。新程序从调用的子进程继承了下面属性：  
进程ID和父进程ID  
实际用户ID和实际组ID  
附属组ID  
进程组ID  
回话ID  
等等

下面写个程序，进行简单验证，代码也可以：[github][]

#include <stdio.h>
    #include <stdlib.h>
    #include <assert.h>
    #include <unistd.h>
    #include <sys/time.h>
    #include <malloc.h>
    
    int main(int argc, char **argv)
    {
        pid_t pid;
        if((pid=fork())<0)
        {
            printf("fork error\r\n");
            return -1;
        }
        else if(pid == 0)
        {
            printf("child  pid = %ld\r\n",(long)getpid());
            printf("child  uid = %ld\r\n",(long)getuid());
            printf("child  gid = %ld\r\n",(long)getgid());
        //  execl("/bin/ls", "ls", "-l", (char *)0);
            execlp("ls", "ls", "-l", (char *)0);
        }
        else
        {
            int stat;
            pid_t pid=wait(&stat);
            printf("child terminate pid = %ld\r\n",(long)pid);
            printf("child terminate uid = %ld\r\n",(long)getuid());
            printf("child terminate gid = %ld\r\n",(long)getgid());
        }
        return 0;
    }

[github]: https://github.com/NearXdu/APUE