rwhod(8)
NAME
rwhod --- system status server
SYNOPSIS
rwhod [-bpaf] [-i <if>...] [-u user]
DESCRIPTION
Rwhod 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 messages on a network.
Rwhod operates as both a producer and consumer of status information. As
a producer of information it periodically queries the state of the system
and constructs status messages which are broadcast 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/spool/rwho.
The server transmits and receives messages at the port indicated in the
``rwho'' 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(2)
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 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. 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/spool/rwho. These files contain only
the most recent message, in the format described above.
Status messages are generated approximately once every 3 minutes. Rwhod
recomputes the system boot time every 30 minutes because on some (non-
Linux) systems it is not a totally reliable process.
FLAGS
If the -b flag is supplied, only broadcast interfaces, such as ethernets,
will be used. If the -p flag is supplied, only point-to-point interfaces
will be used. If the -a flag is supplied, or no flags are supplied, all
interfaces will be used.
Alternately, you may specify interfaces by name by providing one or more
-i options followed by the interface name.
If the -u flag is supplied, rwhod will run as the specified user instead
of as rwhod. The initial user until the daemon drops privileges is root.
Rwhod can also forward packets between interfaces if started with -f.
Please read the CAVEATS section before enabling rwhod forwarding.
CAVEATS
While rwhod listens on any interface present on the host, it will only
send (or forward) to the interfaces determined by the -a -b -p -i flags.
When operating in forwarding mode (with -f ), rwhod forwards all correct
rwhod packets received on an interface to all the other interfaces. You
can create a broadcast storm if there is a loop in your network and all
the routers in the loop run in forwarding mode. To prevent this from
happenning, rwhod will shut down forwarding (and log the event to the
syslog) if more than one rwhod packet is forwarded per second on average
over the last three minutes. If this happens, you must break the loop of
forwarding routers.
SEE ALSO
rwho(1), ruptime(1)
BUGS
Some kind of proxying feature might be useful if your router doesn't run
rwhod.
People often interpret the server dying or network communication failures
as a machine going down.
Rwhod doesn't refresh its interface list, which might be useful when
using -a -b -p.
HISTORY
The rwhod command appeared in 4.2BSD.
Philippe Troin <phil@fifi.org> implemented forwarding and interface
selection flags.
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