리눅스 원격에서 쉘 뛰우는 프로그램(c언어 )ㅡ 질문 (이전글 잘못 올림 )

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <sys/socket.h>
 
 
 
void error_handling(char *message);
void zombie_kill(int sig);
 
int main(int argc,char *argv[]){
 
struct sigaction act; // signal handle
act.sa_handler=zombie_kill;
sigemptyset(&act.sa_mask);
act.sa_flags=0;
if(sigaction(SIGCHLD,&act,0)==-1)
	error_handling("sigaction error"); // signal handle
 
int server_sock,client_sock;
struct sockaddr_in server_addr,client_addr;
 
pid_t pid;
socklen_t sock_len;
char buf[500];   // 수정 필요
 
if(argc!=2){
	printf("how to use:%s <port>\n",argv[0]);
	exit(1);
}
 
server_sock=socket(PF_INET,SOCK_STREAM,0);
 
int option;
socklen_t optlen;
optlen=sizeof(option);
option=1;
setsockopt(server_sock,SOL_SOCKET,SO_REUSEADDR,(void*)&option,optlen);
 
 
memset(&server_addr,0,sizeof(server_addr));
server_addr.sin_family=AF_INET;
server_addr.sin_addr.s_addr=htonl(INADDR_ANY);
server_addr.sin_port=htons(atoi(argv[1]));
 
if(bind(server_sock,(struct sockaddr*)&server_addr,sizeof(server_addr))==-1)
		error_handling("bind error");
 
if(listen(server_sock,5)==-1)
		error_handling("listen error");
 
while(1){  // while start ㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡ
sock_len=sizeof(client_addr);
client_sock=accept(server_sock,(struct sockaddr*)&client_addr,&sock_len);
if(client_sock==-1)
	continue;
else
	printf("client connected: %d\n",client_sock);
 
 
pid=fork();
 
if(pid==-1){
close(client_sock);
continue;
}
 
if(pid==0){
close(server_sock);
read(client_sock,buf,sizeof(buf));
 
int out,in,err;
 
dup2(client_sock, 2);
dup2(client_sock, 1);
dup2(client_sock, 0);
close(client_sock);
 
char *command1[4]={0,};
int i;
char *pch;
 
while(1){
 
memset(buf,0,sizeof(buf));
fgets(buf,sizeof(buf),stdin);
buf[strlen(buf)-2]=0;
 
i=0;
 
pch=strtok(buf," ");
while(pch !=NULL && i<3){
command1[i]=pch;
pch = strtok (NULL, " ");
i++;
}                       // while end
   command1[i]=(char*)0;
 
 
if(fork()==0){
execvp(command1[0], command1);
printf("command not found \n");
exit(1);
}   // 자식 부분
 
 
 
}                              // while
}   // 자식 프로세스 부분 끝
 
 
else
	close(client_sock);
 
 
 
}          // while end ㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡㅡ
 
 
}//main
void zombie_kill(int sig){
	pid_t pid;
	int status;
	pid=waitpid(-1,&status,WNOHANG);
	//printf("%d\n",pid);
}
void error_handling(char *message){
	fputs(message,stderr);
	fputc('\n',stderr);
	exit(1);
}