rwhod(1Mtcp)

rwhod -- system status server

Synopsis

in.rwhod

Description

The rwhod command is the server which maintains the database used by the rwho(1tcp) and ruptime(1tcp) 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 rwho server transmits and receives messages at the port indicated in the rwho service specification; see services(4tcp). 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(1bsd) program, and represent load averages over the 5, 10, and 15 minute intervals prior to a server's transmission. The host name included is that returned by gethostname(3C). 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(4) and a value indicating the time since a character was last received on the terminal line.

Messages received by the rwho server are discarded unless they originated at a 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 60 seconds. rwhod performs an nlist(3elf) on /stand/unix every 10 minutes to guard against the possibility that this file is not the system image currently operating.

Files

/var/spool/rwho

Usage

This service takes up progressively more network bandwidth as the number of hosts on the local net increases. For large networks, the cost becomes prohibitive.

No updates will be sent through ignored network interfaces specified in /etc/inet/if.ignore.

Warnings

For rwhod to work properly, the directory /var/spool/rwho must be created by the system administrator. Given the adverse effect rwho can have on system and network performance, the system administrator must decide whether the benefits of the rwho feature are worth the performance cost.

References

gethostname(3C), nlist(3elf), ruptime(1tcp), rwho(1tcp), utmp(4), w(1bsd)

Notices

Ideally, rwhod would relay status information between networks. People often interpret the server dying as a machine going down.