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:
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struct |
outmp { |
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char |
out_line[8]; |
/* tty name */ |
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char |
out_name[8]; |
/* user id */ |
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long |
out_time; |
/* time on */ |
};
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struct |
whod { |
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char |
wd_vers; |
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char |
wd_type; |
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char |
wd_fill[2]; |
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int |
wd_sendtime; |
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int |
wd_recvtime; |
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char |
wd_hostname[32]; |
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int |
wd_loadav[3]; |
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int |
wd_boottime; |
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struct |
whoent { |
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struct |
outmp we_utmp; |
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int |
we_idle; |
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} 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
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 [AT] fifi.org> implemented forwarding and interface selection flags.
Linux NetKit (0.17) March 10, 1999 Linux NetKit (0.17)