Apue Chapter 6 习题答案
Q6.1 如果系统使用阴影文件，那么如何取得加密口令？
If the system uses a shadow file and we need to obtain the encrypted password, how do we do so ?
我们可以用 struct spwd *getspnam(const char *name); 去/etc/shadow 里去查看用户密码部分。
[root@clstore3 ~]# ./getspwnam root
argc is 2
the string is root
the string is $6$z5AyhdWr$9V0IBMBGLDE82.ueFZVv5WQRAwiTOYhXk..RtmHR7xUqlAGPTneEuILxqxxzbJIhRkkXoVmbs4yUyCq839KZR0
the string is 16584
[root@clstore3 ~]# cat getspwnam.c
#include <apue.h>
#include <shadow.h>
int
main (int argc, char *argv[])
{
struct spwd *
getspnam(const char *name)
{
struct spwd *ptr;
setpwent();
while (( ptr = getspent()) != NULL )
if ( strcmp(name, ptr->sp_namp) == 0)
break;
printf("the string is %s\n", ptr->sp_namp);
printf("the string is %s\n", ptr->sp_pwdp);
printf("the string is %ld\n", ptr->sp_lstchg);
printf("the string is %ld\n", ptr->sp_expire);
printf("the string is %ld\n", ptr->sp_inact);
printf("the string is %ld\n", ptr->sp_expire);
endspent();
return(ptr);
}
printf("argc is %ld\n", argc);
if (argc != 2 )
{
printf("usage: getspnam <user account>\n");
exit(1);
}
if ( getspnam(argv[1]) < 0 )
printf("get error");
}
Q6.2 假设你有超级用户权限，并且系统使用的阴影口令，重新考虑上一道题？
If you have superuser access and your system uses shadow passowords, implement the previous exercise.
只有你有超级用户权限才能去取，看标准答案多简洁，其实我的也还行，:) :)
522868 $ ./getspnam1 root
getspnam error: Permission denied
[root@clstore3 ~]# ./getspnam1 root
sp_pwdp = $6$z5AyhdWr$9V0IBMBGLDE82.ueFZVv5WQRAwiTOYhXk..RtmHR7xUqlAGPTneEuILxqxxzbJIhRkkXoVmbs4yUyCq839KZR0
代码部分，
[root@clstore3 ~]# cat getspnam1.c
#include "apue.h"
#include <shadow.h>
int
main (int argc, char *argv[])
{
struct spwd *ptr;
if(( ptr = getspnam(argv[1])) == NULL)
err_sys("getspnam error");
printf("sp_pwdp = %s\n", ptr->sp_pwdp == NULL || ptr->sp_pwdp[0] == 0 ? "(null)" : ptr->sp_pwdp);
exit(0);
}
Q6.3 编写一个程序，它调用uname 并输出utsname 结构中的所以字段，将该输出与uname命令的输出结果进行比较。
[root@clstore3 ~]# ./uname
system name = Linux
nodename = clstore3.sha.chin.seagate.com
release = 2.6.32-431.el6.x86_64
version = #1 SMP Fri Nov 22 03:15:09 UTC 2013
machine = x86_64
uname 是这样的。
[root@clstore3 ~]# uname -a
Linux clstore3.sha.chin.seagate.com 2.6.32-431.el6.x86_64 #1 SMP Fri Nov 22 03:15:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
[root@clstore3 ~]# cat uname.c
#include "apue.h"
#include <shadow.h>
#include <sys/utsname.h>
int
main (int argc, char *argv[])
{
int uname ( struct utsname *name);
struct utsname ptr;
int fb;
fb = uname(&ptr);
if ( fb < 0 )
printf("error ");
else
{
printf("system name = %s\n", ptr.sysname);
printf("nodename = %s\n", ptr.nodename);
printf("release = %s\n", ptr.release);
printf("version = %s\n", ptr.version);
printf("machine = %s\n", ptr.machine);
#if _UTSNAME_DOMAIN_LENGTH - 0
/* Name of the domain of this node on the network. */
# ifdef __USE_GNU
printf("domain name = %s\n", ptr.domainname);
#endif
#endif
}
exit(0);
}
Q6.4 计算可有time_t 数据类型表示的最近时间，如果超出了这一时间将会如果？
Q6.5 编写一程序，获取当前时间，并使用 strftime将输出结果转换为类似的data 命令的默认输出，将环境变量TZ 设置为不同值，观察输出结果/
可以看到，TZ 不同，它的输出也不同， 这个和6.11的脚本是一模一样的，重标准答案抄过来的。
[root@clstore3 ~]# date
Thu Nov 26 10:50:12 CST 2015
[root@clstore3 ~]# TZ=Japan ./date
Thu Nov 26 11:50:25 JST 2015
[root@clstore3 ~]# cat date.c
#include "apue.h"
#include <time.h>
int
main (void)
{
time_t caltime;
struct tm *tm;
char line[MAXLINE];
if (( caltime = time(NULL)) == -1 )
err_sys("time error");
if ((tm = localtime(&caltime)) == NULL)
err_sys("localtime error");
if(strftime(line, MAXLINE, "%a %b %d %X %Z %Y\n", tm) == 0 )
err_sys("strftime error");
fputs(line, stdout);
exit(0);
}