我正在学习APUE.2e（UNIX®环境中的高级编程，第二版），现在已经学习了第16章网络IPC：套接字。当我运行程序ruptime（用于客户端）和ruptimed（用于服务器端）时，发生了一些奇怪的事情。客户端程序显示客户端命令，该命令与服务器通信以从a获取输出
系统的uptime命令和服务器程序ruptimed（注意'd'）接收命令，exec的uptime命令并将uptime的输出返回给客户端。这两个程序编译好，我将ruptime 4000/tcp添加到文件/etc/service，这意味着服务ruptime绑定到端口4000/tcp。我在同一台机器上运行了两个程序（Ubuntu 11.04），首先运行ruptimed（当然）：
$ ./ruptimed
$ ./ruptime 127.0.0.1
21:35:48 up 13:06, 3 users, load average: 0.56, 0.85, 0.94
输出是我所期望的。但是，当我跑：
$ ./ruptimed
$ ./ruptime 192.168.1.221
# the terminal blocks here
IP地址192.168.1.221是机器在Intranet中的实际IP。这有什么不对？我搜索了互联网，发现它似乎需要/etc/init.d/中的shell脚本。然后我在ruptime目录中添加一个名为/etc/init.d/的文件。这是：
#! /bin/sh
### BEGIN INIT INFO
# Provides: ruptimed
# Required-Start: $remote_fs $syslog
# Required-Stop: $remote_fs $syslog
# Default-Start: 2 3 4 5
# Default-Stop:
# Short-Description: ruptime
### END INIT INFO
start()
{
echo "start ruptime"
/home/tlh1987/apue-practice/tlh-practice/ruptimed
exit 0;
}
stop()
{
killall ruptimed
echo "stop ruptime"
}
case "$1" in
start)
start
;;
stop)
stop
;;
restart)
stop
start
;;
*)
echo "usage: $0 start|stop|restart"
exit 0;
esac
然而，它没有用，我不知道为什么。我还设置了启用ufw并允许ruptime 像这样：
sudo ufw allow ruptime
它也没用。 ruptime和ruptimed的源代码如下：
// the functions used in the two program
// the connect_retry() function
#include "apue.h"
#include <sys/socket.h>
#define MAXSLEEP 128
int
connect_retry(int sockfd, const struct sockaddr *addr, socklen_t alen)
{
int nsec;
for (nsec = 1; nsec <= MAXSLEEP; nsec <<= 1) {
if (connect(sockfd, addr, alen) == 0) {
return (0);
}
if (nsec <= MAXSLEEP/2)
sleep(nsec);
}
return (-1);
}
// the initserver function
#include "apue.h"
#include <errno.h>
#include <sys/socket.h>
int
initserver(int type, const struct sockaddr *addr, socklen_t alen,
int qlen)
{
int fd;
int err = 0;
if ((fd = socket(addr->sa_family, type, 0)) < 0)
return (-1);
if (bind(fd, addr, alen) < 0) {
err = errno;
goto errout;
}
if (type == SOCK_STREAM || type == SOCK_SEQPACKET) {
if (listen(fd, qlen) < 0) {
err = errno;
goto errout;
}
}
return(fd);
errout:
close(fd);
errno = err;
return (-1);
}
// the client end i.e. ruptime.c
#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <sys/socket.h>
#define MAXADDRLEN 256
#define BUFLEN 128
extern int connect_retry(int, const struct sockaddr *, socklen_t);
void
print_uptime(int sockfd)
{
int n;
char buf[BUFLEN];
while ((n = recv(sockfd, buf, BUFLEN, 0)) > 0)
write(STDOUT_FILENO, buf, n);
if (n < 0)
err_sys("recv error");
}
int
main(int argc, char *argv[])
{
struct addrinfo *ailist, *aip;
struct addrinfo hint;
int sockfd, err;
if (argc !=2 )
err_quit("usage: ruptime hostname");
hint.ai_flags = 0;
hint.ai_family = 0;
hint.ai_socktype = SOCK_STREAM;
hint.ai_protocol = 0;
hint.ai_addrlen = 0;
hint.ai_canonname = NULL;
hint.ai_addr = NULL;
hint.ai_next = NULL;
if ((err = getaddrinfo(argv[1], "ruptime", &hint, &ailist)) != 0)
err_quit("getaddrinfo error: %s", gai_strerror(err));
for (aip = ailist; aip != NULL; aip = aip->ai_next) {
if ((sockfd = socket(aip->ai_family, SOCK_STREAM, 0)) < 0)
err = errno;
if (connect_retry(sockfd, aip->ai_addr, aip->ai_addrlen) < 0) {
err = errno;
} else {
print_uptime(sockfd);
exit(0);
}
}
fprintf(stderr, "can't connect to %s: %s\n", argv[1],
strerror(err));
exit(1);
}
//the server end i.e. ruptimed is as follows:
#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <syslog.h>
#include <sys/socket.h>
#define BUFLEN 128
#define QLEN 10
#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 256
#endif
extern int initserver(int, struct sockaddr *, socklen_t, int);
void
serve(int sockfd)
{
int clfd;
FILE *fp;
char buf[BUFLEN];
for ( ; ; ) {
clfd = accept(sockfd, NULL, NULL);
if (clfd < 0) {
syslog(LOG_ERR, "ruptimed: accept error: %s",
strerror(errno));
exit(1);
}
if ((fp = popen("/usr/bin/uptime", "r")) == NULL) {
sprintf(buf, "error: %s\n", strerror(errno));
send(clfd, buf, strlen(buf), 0);
} else {
while (fgets(buf, BUFLEN, fp) != NULL)
send(clfd, buf, strlen(buf), 0);
pclose(fp);
}
close(clfd);
}
}
int
main(int argc, char *argv[])
{
struct addrinfo *ailist, *aip;
struct addrinfo hint;
int sockfd, err, n;
char *host;
if (argc != 1)
err_quit("usage: ruptimed");
#ifdef _SC_HOST_NAME_MAX
n = sysconf(_SC_HOST_NAME_MAX);
if (n < 0)
#endif
n = HOST_NAME_MAX;
host = malloc(n);
if (host == NULL)
err_sys("malloc error");
if (gethostname(host, n) < 0)
err_sys("gethostname error");
daemonize("ruptimed");
hint.ai_flags = AI_CANONNAME;
hint.ai_family = 0;
hint.ai_socktype = SOCK_STREAM;
hint.ai_protocol = 0;
hint.ai_addrlen = 0;
hint.ai_canonname = NULL;
hint.ai_addr = NULL;
hint.ai_next = NULL;
if ((err = getaddrinfo(host, "ruptime", &hint, &ailist)) != 0) {
syslog(LOG_ERR, "ruptimed: getaddrinfo error: %s",
gai_strerror(err));
exit(1);
}
for (aip = ailist; aip != NULL; aip = aip->ai_next) {
if ((sockfd = initserver(SOCK_STREAM, aip->ai_addr,
aip->ai_addrlen, QLEN)) >= 0)
serve(sockfd);
exit(0);
}
exit(1);
}
有人可以提供帮助吗？
命令netstat -nap的标题行：
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN -
tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN -
tcp 0 0 127.0.0.1:4000 0.0.0.0:* LISTEN 2252/ruptimed
tcp 0 13033 192.168.1.221:47380 91.189.89.114:443 LAST_ACK -
tcp 74 0 192.168.1.221:43914 91.189.89.76:443 ESTABLISHED 1846/python
tcp 0 0 127.0.0.1:4000 127.0.0.1:56344 TIME_WAIT -
tcp 0 1 192.168.1.221:35442 192.168.1.89:24800 SYN_SENT 1478/synergyc
tcp 0 0 192.168.1.221:34957 74.125.71.125:5222 ESTABLISHED 1618/chrome
tcp 0 0 192.168.1.221:57795 203.208.46.163:443 ESTABLISHED 1618/chrome
tcp6 0 0 :::22 :::* LISTEN -
第3条记录是我的服务ruptime。这有什么不对吗？我对它的意思不太了解。
答案 0 :(得分：5)
我不是C专家，但我知道一件事：您的守护程序可能只绑定到一个地址/接口，并且仅接受来自它的连接。
使用netstat -nap检查守护程序绑定到的地址。
如果它正在监听0.0.0.0，那么它接受来自每个接口的连接，包括localhost。
如果正在收听127.0.0.1，则只接受来自localhost。
我打赌它只限于127.0.0.1，这就是为什么你不能与任何其他地址联系的原因。
答案 1 :(得分：1)
这几乎肯定是防火墙问题，而不是编码问题。您可能需要查看some ufw documentation并在ufw行上指定端口或IP地址。