rwhod Linux Service

rwhod service:

The rwho protocol lets remote users get a list of all users logged onto a machine by running the rwho daemon.
Now lets see the manual of rwhod service.
Manual rwhod:
NAME
rwhod - system status server
SYNOPSIS
rwhod [-bpa] [-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).
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.
If the -u flag is supplied, rwhod will run as the specified user instead of as root.
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.
SEE ALSO
rwho(1), ruptime(1)
BUGS
There should be a way to relay status information between networks. People often interpret the server dying or network communtication failures as a machine going down.
HISTORY
The rwhod command appeared in 4.2BSD.