rwhod —
system
status server
rwhod |
[-bpaf]
[-i <if>...]
[-u
user] |
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.
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.
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.
rwho(1),
ruptime(1)
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.
The
rwhod command appeared in
4.2BSD.
Philippe Troin <
[email protected]> implemented forwarding and interface
selection flags.