tail head cat sleep
QR code linking to this page

Manual Pages  — RWHOD


rwhod – system status server



rwhod [-i] [-p] [-l] [-m [ttl]]


The rwhod utility is the server which maintains the database used by the rwho(1) and ruptime(1) programs. Its operation is predicated on the ability to broadcast or multicast messages on a network.

The rwhod utility operates as both a producer and consumer of status information, unless the -l (listen mode) option is specified, in which case it acts as a consumer only. As a producer of information it periodically queries the state of the system and constructs status messages which are broadcasted or multicasted on a network. As a consumer of information, it listens for other rwhod servers' status messages, validating them, then recording them in a collection of files located in the directory /var/rwho.

The following options are available:
  Enable insecure mode, which causes rwhod to ignore the source port on incoming packets.
  Ignore all POINTOPOINT interfaces. This is useful if you do not wish to keep dial on demand interfaces permanently active.
  Enable listen mode, which causes rwhod to not broadcast any information. This allows you to monitor other machines' rwhod information, without broadcasting your own.
-m [ttl]
  Cause rwhod to use IP multicast (instead of broadcast) on all interfaces that have the IFF_MULTICAST flag set in their "ifnet" structs (excluding the loopback interface). The multicast reports are sent with a time-to-live of 1, to prevent forwarding beyond the directly-connected subnet(s).

If the optional ttl argument is supplied with the -m flag, rwhod will send IP multicast datagrams with a time-to-live of ttl, via a SINGLE interface rather than all interfaces. ttl must be between 0 and 32 (or MAX_MULTICAST_SCOPE). Note that -m 1 is different from -m, in that -m 1 specifies transmission on one interface only.

When -m is used without a ttl argument, the program accepts multicast rwhod reports from all multicast-capable interfaces. If a ttl argument is given, it accepts multicast reports from only one interface, the one on which reports are sent (which may be controlled via the host's routing table). Regardless of the -m option, the program accepts broadcast or unicast reports from all interfaces. Thus, this program will hear the reports of old, non-multicasting Ns, but, if multicasting is used, those old Ns will not hear the reports generated by this program.

The server transmits and receives messages at the port indicated in the ``who'' service specification; see services(5). The messages sent and received, are of the form:

struct  outmp {
        char    out_line[8];            /* tty name */
        char    out_name[8];            /* user id */
        long    out_time;               /* time on */

struct  whod {         char    wd_vers;         char    wd_type;         char    wd_fill[2];         int     wd_sendtime;         int     wd_recvtime;         char    wd_hostname[32];         int     wd_loadav[3];         int     wd_boottime;         struct  whoent {                 struct  outmp we_utmp;                 int     we_idle;         } wd_we[1024 / sizeof (struct whoent)]; };

All fields are converted to network byte order prior to transmission. The load averages are as calculated by the w(1) program, and represent load averages over the 5, 10, and 15 minute intervals prior to a server's transmission; they are multiplied by 100 for representation in an integer. The host name included is that returned by the gethostname(3) system call, with any trailing domain name omitted. The array at the end of the message contains information about the users logged in to the sending machine. This information includes the contents of the entry from the user accounting database for each non-idle terminal line and a value indicating the time in seconds since a character was last received on the terminal line.

Messages received by the rwho server are discarded unless they originated at an rwho server's port or the -i option was specified. In addition, if the host's name, as specified in the message, contains any unprintable ASCII characters, the message is discarded. Valid messages received by rwhod are placed in files named whod.hostname in the directory /var/rwho. These files contain only the most recent message, in the format described above.

Status messages are generated approximately once every 3 minutes. The rwhod utility performs an nlist(3) on /boot/kernel/kernel every 30 minutes to guard against the possibility that this file is not the system image currently operating.


ruptime(1), rwho(1)


The rwhod utility appeared in BSD 4.2 .


Status information should be sent only upon request rather than continuously. People often interpret the server dying or network communication failures as a machine going down.

RWHOD (8) July 3, 2017

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

Like a classics radio station whose play list spans decades, Unix simultaneously exhibits its mixed and dated heritage. There's Clash-era graphics interfaces; Beatles-era two-letter command names; and systems programs (for example, ps) whose terse and obscure output was designed for slow teletypes; Bing Crosby-era command editing (# and @ are still the default line editing commands), and Scott Joplin-era core dumps.
— The Unix Haters' handbook