RWHOD(8)

NAME
rwhod - system status server

SYNOPSIS
rwhod [-46bMpa] [-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).

IPv4 support will be enabled by the -4 flag, and IPv6 support will be enabled by the -6 flag. If the -M flag is supplied, IPv6 support with ipv4-mapped ipv6 address feature will be enabled. If neither -4 flag or -4 flag are supplied, IPv4 and IPv6 feature will be enabled by default. Note that on many Linux based system, you need the -m flag because kernel will not accept ipv4 and ipv6 socket on the same port at the same time.

If the -b flag is supplied, only broadcast interfaces, such as ethernets, will be used for ipv4 support and only multicast interfaces should will be used for ipv6 support. 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. IPv6 support was developed by USAGI Project.