《UNIX环境高级编程》笔记第六章系统数据文件和信息-优快云博客

本文链接：https://blog.youkuaiyun.com/day_day_hard_up/article/details/138924842

1. 简介

本章介绍了口令文件（/etc/passwd）、阴影口令(/etc/shadow)、组文件(/etc/group)及其他几个系统数据文件的相关信息、作用和读写接口，后面还涉及了时间和日期相关的API。

2. 函数原型

*struct passwd getpwent(void); void setpwent(void); void endpwent(void);**	操作口令文件 getpwent 读取文件的一个条目，返回值：若成功，返回指针；若出错或到达文件末尾，返回NULL setpwent 反绕文件，重新定位到文件开始处 endpwent 关闭文件
*struct spwd getspnam(const char name);* *struct spwd getspent(void); void setspent(void); void endspent(void);**	操作阴影口令文件
*struct group getgrnam(const char name);* *struct group getgrgid(gid_t gid); struct group getgrent(void);* void setgrent(void); void endgrent(void);	操作组文件
int getgroups(int size, gid_t list[]); int setgroups(size_t size, const gid_t list); int initgroups(const char user, gid_t group);	获取/设置附属组ID
*int getnameinfo(const struct sockaddr addr, socklen_t addrlen,char host, socklen_t hostlen,char serv, socklen_t servlen, int flags); int getaddrinfo(const char node, const char service, const struct addrinfo hints, struct addrinfo res);*	操作/etc/hosts
*struct netent getnetent(void); struct netent getnetbyname(const char name); struct netent getnetbyaddr(uint32_t net, int type);* void setnetent(int stayopen); void endnetent(void);	操作/etc/networks
*struct protoent getprotoent(void); struct protoent getprotobyname(const char name); struct protoent getprotobynumber(int proto);* void setprotoent(int stayopen); void endprotoent(void);	操作/etc/protocols
*struct servent getservent(void); struct servent getservbyname(const char name, const char proto); struct servent getservbyport(int port, const char proto);* void setservent(int stayopen); void endservent(void);	操作/etc/services
*int uname(struct utsname name)**	返回主机和操作系统有关信息
int gethostname(char name, size_t len); int sethostname(const char name, size_t len);	返回/设置主机名字
*time_t time(time_t tloc);**	返回自1970-01-01 00:00:00以来经过的秒数
*int clock_getres(clockid_t clk_id, struct timespec res); int clock_gettime(clockid_t clk_id, struct timespec tp);* *int clock_settime(clockid_t clk_id, const struct timespec tp);**	根据时钟ID来获取/设置时间
*int gettimeofday(struct timeval tv, struct timezone tz);* *int settimeofday(const struct timeval tv, const struct timezone tz);*	获取/设置日历时间，比time函数精度更高
struct tm gmtime(const time_t timep); struct tm localtime(const time_t timep);	将时间转换为世界协调时或本地时间，年、月、日、时、分、秒、周日的分解结构
*time_t mktime(struct tm tm);**	将年、月、日、时、分、秒、周日的分解结构转换为所经历的秒数(1970-01-01 00:00:00)
*size_t strftime(char s, size_t max, const char format, const struct tm tm);**	字符串输出格式化日期和时间

3. 实例

#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <shadow.h>
#include <grp.h>
#include <time.h>
#include <unistd.h>

void scan_passwd()
{
	struct passwd *pwd = NULL;

	printf("scan_passwd*************\n");
	setpwent();
	do {
		pwd = getpwent();
		if (pwd) {
			printf("username: %-20s user id: %04d group id: %04d\n", pwd->pw_name, pwd->pw_uid, pwd->pw_gid);
		}
	} while(pwd != NULL);
	endpwent();
}

// Root user privileges are required
void scan_shadow()
{
	struct spwd *pwd = NULL;

	printf("scan_shadow*************\n");
	setspent();
	do {
		pwd = getspent();
		if (pwd) {
			printf("username: %-20s passwd: %s\n", pwd->sp_namp, pwd->sp_pwdp);
		}
	} while(pwd != NULL);
	endspent();
}

void scan_group()
{
	struct group *grp= NULL;

	printf("scan_group*************\n");
	setgrent();
	do {
		grp = getgrent();
		if (grp) {
			printf("username: %-20s group id: %d\n", grp->gr_name, grp->gr_gid);
		}
	} while(grp != NULL);
	endgrent();
}

int main()
{
	scan_passwd();
	scan_shadow();
	scan_group();

	time_t tim = time(NULL);
	printf("time = %ld\n", tim);
	struct tm *tm = gmtime(&tim);
	if (tm) {
		if (tm->tm_hour > 12) {
			tm->tm_hour -= 12;
		}
		//Run shell command: date -u
		printf("time = %d-%d-%d %d:%d:%d\n",
		tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);

		char buf[64] = {0};
		strftime(buf, sizeof(buf)-1, "%D %T", tm );
		printf("buf time = %s\n", buf);
	}
	

	clockid_t clk_ids[] = {CLOCK_REALTIME, CLOCK_PROCESS_CPUTIME_ID, CLOCK_THREAD_CPUTIME_ID, CLOCK_MONOTONIC};
	for (int i = 0; i < sizeof(clk_ids)/sizeof(clk_ids[0]); i++) {
		struct timespec tp = {0};
		clock_gettime(clk_ids[i], &tp);
		printf("%012ld %ld\n", tp.tv_sec, tp.tv_nsec);
	}
#if 1
	sleep(3);
#else
	int n = 1000000000;
	while (--n);
#endif
	printf("After\n");
	for (int i = 0; i < sizeof(clk_ids)/sizeof(clk_ids[0]); i++) {
		struct timespec tp = {0};
		clock_gettime(clk_ids[i], &tp);
		printf("%012ld %ld\n", tp.tv_sec, tp.tv_nsec);
	}	
}