1.who是如何工作的
who实际上是通过utmp文件来获取登陆用户的信息的
#include <utmp.h>
信息结构如下:
#define UTMP_FILE /var/adm/utmp
#define ut_name ut_user
struct utmp{
char ut_user[32];//登录名
char ut_id[14];
char ut_line[32];//设备名
short ut_type;//入口类型
pid_t ut_pid;//进程id
struct exit_status{
short e_termination;
short e_exit;
}ut_exit;
time_t ut_time;
char ut_host[64];
};
2.编写实例
#include <stdio.h>
#include <utmp.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#define SHOWHOST
void showtime(long);
void show_info(struct utmp*);
void show_info(struct utmp * utbufp)
{
if(utbufp->ut_type != USER_PROCESS)
{
return;
}
printf("% -8.8s",utbufp->ut_name);
printf(" ");
printf("% -8.8s",utbufp->ut_line);
printf(" ");
showtime(utbufp->ut_time);
printf(" ");
#ifdef SHOWHOST
printf("(%s)",utbufp->ut_host);
#endif
printf("\n");
}
void showtime(long timeval)
{
struct tm *tvp;
tvp = gmtime(&timeval);
printf("%d-%d-%d %d:%d",tvp->tm_year+1990,tvp->tm_mon+1,tvp->tm_mday,tvp->tm_hour,tvp->tm_min);
}
int main()
{
struct utmp current_record;
int utmpfd;
int reclen = sizeof(current_record);
if((utmpfd = open(UTMP_FILE,O_RDONLY)) == -1)
{
perror(UTMP_FILE);
_exit(1);
}
while(read(utmpfd,¤t_record,reclen) == reclen)
{
show_info(¤t_record);
}
close(utmpfd);
return 0;
}
3.测试实例
./who 结果如下:
root pts/0 2102-8-5 8:51 (192.168.1.100)
root pts/1 2102-8-5 12:35 (192.168.1.100)