who 命令

最新推荐文章于 2021-08-21 17:07:27 发布

原创最新推荐文章于 2021-08-21 17:07:27 发布 · 400 阅读

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who命令用于显示当前系统中已经登录的用户信息，用户登录信息存储在utmp文件中，utmp.h在/usr/include/bits/下，utmp文件的结构如下：

{

short int ut_type; /* Type of login. */

pid_t ut_pid; /* Process ID of login process. */

char ut_line[UT_LINESIZE]; /* Devicename. */

char ut_id[4]; /* Inittab ID. */

char ut_user[UT_NAMESIZE]; /* Username. */

char ut_host[UT_HOSTSIZE]; /* Hostname for remote login. */

struct exit_status ut_exit; /* Exit status of a process marked

as DEAD_PROCESS. */

/* The ut_session and ut_tv fields must be the same size when compiled

32- and 64-bit. This allows data files and shared memory to be

shared between 32- and 64-bit applications. */

#ifdef __WORDSIZE_TIME64_COMPAT32

int32_t ut_session; /* Session ID, used for windowing. */

struct

{

int32_t tv_sec; /* Seconds. */

int32_t tv_usec; /* Microseconds. */

} ut_tv; /* Time entry was made. */

#else

long int ut_session; /* Session ID, used for windowing. */

struct timeval ut_tv; /* Time entry was made. */

#endif

int32_t ut_addr_v6[4]; /* Internet address of remote host. */

char __unused[20]; /* Reserved for future use. */

};

主要的字段有ut_user: 登录名， ut_line:终端类型， ut_time:登录时间， ut_host: 登录计算机

who的实现如下：who1.c

#include <unistd.h>
#include <utmp.h>
#include <fcntl.h>
#include <time.h>

void showtime(long);
void show_info(struct utmp *);

int main()
{
    struct utmp utbuf;
    int utmpfd;
    if ((utmpfd = open(UTMP_FILE, O_RDONLY)) == -1){
        perror(UTMP_FILE);
        exit(1);
    }

    while (read(utmpfd, &utbuf, sizeof(utbuf)) == sizeof(utbuf))
        show_info(&utbuf);
    close(utmpfd);
    return 0;
}

void showtime(long timeval)
{
    char *cp;
    cp = ctime(&timeval);
    printf("%12.12s", cp+4);
}

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");
}

编译：

gcc who1.c -o who1

运行：

who1

结果：

root pts/1 Nov 19 20:19

root pts/3 Nov 19 21:38

参考文献：

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