RWHOD(8) BSD System Manager's Manual RWHOD(8)NAMErwhod — system status server
SYNOPSISrwhod [-i] [-p] [-l] [-g time] [-m [ttl]]
DESCRIPTION
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 period‐
ically 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, vali‐
dating them, then recording them in a collection of files located in the
directory /var/rwho.
The -i option enables insecure mode, which causes rwhod to ignore the
source port on incoming packets.
The -g option allows for the broadcast time for rwhod to be reduced below
3 minutes. This enables for more 'real' time statistics of the host. The
time operand can be given as 30 (30 seconds) or 1m (1 minute), for exam‐
ple.
The -p option tells rwhod to ignore all POINTOPOINT interfaces. This is
useful if you do not wish to keep dial on demand interfaces permanently
active.
The -l option enables listen mode, which causes rwhod to not broadcast
any information. This allows you to monitor other machines' rwhod infor‐
mation, without broadcasting your own.
The -m option causes 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 rwhods, but, if multicasting is used,
those old rwhods won't 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 inte‐
ger. The host name included is that returned by the gethostname(3) sys‐
tem 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 utmp(5) entry 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 by default approximately once every 3 min‐
utes. Rwhod performs an nlist(3) on /boot/kernel every 30 minutes to
guard against the possibility that this file is not the system image cur‐
rently operating.
SEE ALSOruptime(1), rwho(1)HISTORY
The rwhod utility appeared in 4.2BSD.
BUGS
Status information should be sent only upon request rather than continu‐
ously. People often interpret the server dying or network communication
failures as a machine going down.
BSD September 2, 2008 BSD
