loginacct/utmpx_login.c

+/* 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);
 }