/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2026.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* utmpx_login.c

   Demonstrate the steps required to update the utmp and wtmp files on user
   login and logout.

   Note: updating utmp and wtmp (normally) requires root privileges.

   This program is Linux-specific.
*/
#define _GNU_SOURCE
#include <time.h>
#include <utmpx.h>
#include <paths.h>              /* Definitions of _PATH_UTMP and _PATH_WTMP */
#include "tlpi_hdr.h"

int
main(int argc, char *argv[])
{
    struct utmpx ut;
    char *devName;

    if (argc < 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s username [sleep-time]\n", argv[0]);

    /* Initialize login record for utmp and wtmp files */

    memset(&ut, 0, sizeof(struct utmpx));
    ut.ut_type = USER_PROCESS;          /* This is a user login */
    strncpy(ut.ut_user, argv[1], sizeof(ut.ut_user));
    ut.ut_tv.tv_sec = time(NULL);       /* Stamp with current time */
    ut.ut_pid = getpid();

    /* Set ut_line and ut_id based on the terminal associated with
       'stdin'. This code assumes terminals named "/dev/[pt]t[sy]*".
       The "/dev/" dirname is 5 characters; the "[pt]t[sy]" filename
       prefix is 3 characters (making 8 characters in all). */

    devName = ttyname(STDIN_FILENO);
    if (devName == NULL)
        errExit("ttyname");
    if (strlen(devName) <= 8)           /* Should never happen */
        fatal("Terminal name is too short: %s", devName);

    strncpy(ut.ut_line, devName + 5, sizeof(ut.ut_line));
    strncpy(ut.ut_id, devName + 8, sizeof(ut.ut_id));

    printf("Creating login entries in utmp and wtmp\n");
    printf("        using pid %ld, line %.*s, id %.*s\n",
            (long) ut.ut_pid, (int) sizeof(ut.ut_line), ut.ut_line,
            (int) sizeof(ut.ut_id), ut.ut_id);

    setutxent();                        /* Rewind to start of utmp file */
    if (pututxline(&ut) == NULL)        /* Write login record to utmp */
        errExit("pututxline");
    updwtmpx(_PATH_WTMP, &ut);          /* Append login record to wtmp */

    /* Sleep a while, so we can examine utmp and wtmp files */

    sleep((argc > 2) ? getInt(argv[2], GN_NONNEG, "sleep-time") : 15);

    /* Now do a "logout"; use values from previously initialized 'ut',
       except for changes below */

    ut.ut_type = DEAD_PROCESS;          /* Required for logout record */
    ut.ut_tv.tv_sec = time(NULL);       /* Stamp with logout time */
    memset(&ut.ut_user, 0, sizeof(ut.ut_user));
                                        /* Logout record has null username */

    printf("Creating logout entries in utmp and wtmp\n");
    setutxent();                        /* Rewind to start of utmp file */
    if (pututxline(&ut) == NULL)        /* Overwrite previous utmp record */
        errExit("pututxline");
    updwtmpx(_PATH_WTMP, &ut);          /* Append logout record to wtmp */

    endutxent();
    exit(EXIT_SUCCESS);
}