Unix-Linux 编程实践教程 第二章 小结

• utmp文件记录当前正在本系统中的用户的登录信息
• wtmp文件记录登录过本系统的用户的登录信息

    PS:man who命令即可查找到utmp和wtmp文件在当前系统的位置

• who命令相关：
  1. who显示当前已登录用户的用户信息
  2. whoami显示当前shell相关的有效用户
  3. who am i显示当前真正已登录用户的用户信息
• utmp和wtmp采用同一结构utmp存储登录信息

             #define EMPTY         0 /* Record does not contain valid info
                                        (formerly known as UT_UNKNOWN on Linux) */
             #define RUN_LVL       1 /* Change in system run-level (see
                                        init(8)) */
             #define BOOT_TIME     2 /* Time of system boot (in ut_tv) */
             #define NEW_TIME      3 /* Time after system clock change
                                        (in ut_tv) */
             #define OLD_TIME      4 /* Time before system clock change
                                        (in ut_tv) */
             #define INIT_PROCESS  5 /* Process spawned by init(8) */
             #define LOGIN_PROCESS 6 /* Session leader process for user login */
             #define USER_PROCESS  7 /* Normal process 此处表明此记录用户当前是处于登录中*/
             #define DEAD_PROCESS  8 /* Terminated process 此处表明此记录用户已经注销 */
             #define ACCOUNTING    9 /* Not implemented */
  
             #define UT_LINESIZE      32
             #define UT_NAMESIZE      32
             #define UT_HOSTSIZE     256
  
             struct exit_status {              /* Type for ut_exit, below */
                 short int e_termination;      /* Process termination status */
                 short int e_exit;             /* Process exit status */
             };
  
             struct utmp {
                 short   ut_type;              /* Type of record */
                 pid_t   ut_pid;               /* PID of login process */
                 char    ut_line[UT_LINESIZE]; /* Device name of tty - "/dev/" */
                 char    ut_id[4];             /* Terminal name suffix,
                                                  or inittab(5) ID */
                 char    ut_user[UT_NAMESIZE]; /* Username */
                 char    ut_host[UT_HOSTSIZE]; /* Hostname for remote login, or
                                                  kernel version for run-level
                                                  messages */
                 struct  exit_status ut_exit;  /* Exit status of a process
                                                  marked as DEAD_PROCESS; not
                                                  used by Linux init (1 */
                 /* 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. */
             #if __WORDSIZE == 64 && defined __WORDSIZE_COMPAT32
                 int32_t ut_session;           /* Session ID (getsid(2)),
                                                  used for windowing */
                 struct {
                     int32_t tv_sec;           /* Seconds 用户处于登陆中则代表用户登录时间，用户已注销则代表用户注销时间*/
                     int32_t tv_usec;          /* Microseconds */
                 } ut_tv;                      /* Time entry was made */
             #else
                  long   ut_session;           /* Session ID */
                  struct timeval ut_tv;        /* Time entry was made */
             #endif
  
                 int32_t ut_addr_v6[4];        /* Internet address of remote
                                                  host; IPv4 address uses
                                                  just ut_addr_v6[0] */
                 char __unused[20];            /* Reserved for future use */
             };
  
             /* Backward compatibility hacks */
             #define ut_name ut_user
             #ifndef _NO_UT_TIME
             #define ut_time ut_tv.tv_sec
             #endif
             #define ut_xtime ut_tv.tv_sec
             #define ut_addr ut_addr_v6[0]