RCMD(3) BSD Library Functions Manual RCMD(3)
rcmd, orcmd, rcmd_af, orcmd_af, rresvport, rresvport_af, iruserok, ruserok, iruserok_sa -- routines for returning a stream to a remote com-
Standard C Library (libc, -lc)
rcmd(char **ahost, int inport, const char *locuser, const char *remuser, const char *cmd, int *fd2p);
orcmd(char **ahost, int inport, const char *locuser, const char *remuser, const char *cmd, int *fd2p);
rcmd_af(char **ahost, int inport, const char *locuser, const char *remuser, const char *cmd, int *fd2p, int af);
orcmd_af(char **ahost, int inport, const char *locuser, const char *remuser, const char *cmd, int *fd2p, int af);
rresvport_af(int *port, int family);
iruserok(uint32_t raddr, int superuser, const char *ruser, const char *luser);
ruserok(const char *rhost, int superuser, const char *ruser, const char *luser);
iruserok_sa(const void *raddr, int rlen, int superuser, const char *ruser, const char *luser);
The rcmd() function is available for use by anyone to run commands on a remote system. It acts like the orcmd() command, with the exception
that it makes a call out to the rcmd(1) command, or any other user-specified command, to perform the actual connection (thus not requiring
that the caller be running as the super-user), and is only available for the ``shell/tcp'' port. The orcmd() function is used by the super-
user to execute a command on a remote machine using an authentication scheme based on reserved port numbers. While rcmd() and orcmd() can
only handle IPv4 address in the first argument, rcmd_af() and orcmd_af() can handle other cases as well. The rresvport() function returns a
descriptor to a socket with an address in the privileged port space. The rresvport_af() function is similar to rresvport(), but you can
explicitly specify the address family to use. Calling rresvport_af() with AF_INET has the same effect as rresvport(). The iruserok() and
ruserok() functions are used by servers to authenticate clients requesting service with rcmd(). All six functions are present in the same
file and are used by the rshd(8) server (among others). iruserok_sa() is an address family independent variant of iruserok().
The rcmd() function looks up the host *ahost using gethostbyname(3), returning -1 if the host does not exist. Otherwise *ahost is set to the
standard name of the host and a connection is established to a server residing at the well-known Internet port inport.
If the connection succeeds, a socket in the Internet domain of type SOCK_STREAM is returned to the caller, and given to the remote command as
stdin and stdout. If fd2p is non-zero, then an auxiliary channel to a control process will be set up, and a descriptor for it will be placed
in *fd2p. The control process will return diagnostic output from the command (unit 2) on this channel, and will also accept bytes on this
channel as being UNIX signal numbers, to be forwarded to the process group of the command. If fd2p is 0, then the stderr (unit 2 of the
remote command) will be made the same as the stdout and no provision is made for sending arbitrary signals to the remote process, although
you may be able to get its attention by using out-of-band data.
rcmd_af() and orcmd_af() take address family in the last argument. If the last argument is PF_UNSPEC, interpretation of *ahost will obey the
underlying address resolution like DNS.
The protocol is described in detail in rshd(8).
The rresvport() and rresvport_af() functions are used to obtain a socket with a privileged address bound to it. This socket is suitable for
use by rcmd() and several other functions. Privileged Internet ports are those in the range 0 to 1023. Only the super-user is allowed to
bind an address of this sort to a socket.
The iruserok() and ruserok() functions take a remote host's IP address or name, respectively, two user names and a flag indicating whether
the local user's name is that of the super-user. Then, if the user is NOT the super-user, it checks the /etc/hosts.equiv file. If that
lookup is not done, or is unsuccessful, the .rhosts in the local user's home directory is checked to see if the request for service is
If this file does not exist, is not a regular file, is owned by anyone other than the user or the super-user, or is writable by anyone other
than the owner, the check automatically fails. Zero is returned if the machine name is listed in the ``hosts.equiv'' file, or the host and
remote user name are found in the ``.rhosts'' file; otherwise iruserok() and ruserok() return -1. If the local domain (as obtained from
gethostname(3)) is the same as the remote domain, only the machine name need be specified.
If the IP address of the remote host is known, iruserok() should be used in preference to ruserok(), as it does not require trusting the DNS
server for the remote host's domain.
While iruserok() can handle IPv4 addresses only, iruserok_sa() and ruserok() can handle other address families as well, like IPv6. The first
argument of iruserok_sa() is typed as void * to avoid dependency between <unistd.h> and <sys/socket.h>.
RCMD_CMD When using the rcmd() function, this variable is used as the program to run instead of rcmd(1).
The rcmd() function returns a valid socket descriptor on success. It returns -1 on error and prints a diagnostic message on the standard
The rresvport() and rresvport_af() function return a valid, bound socket descriptor on success. They return -1 on error with the global
value errno set according to the reason for failure. The error code EAGAIN is overloaded to mean ``All network ports in use.''
rcmd(1), rlogin(1), rsh(1), intro(2), rexec(3), hosts.equiv(5), rhosts(5), rexecd(8), rlogind(8), rshd(8)
The orcmd(), rresvport(), iruserok() and ruserok() functions appeared in 4.2BSD, where the orcmd() function was called rcmd(). The (newer)
rcmd() function appeared in NetBSD 1.3. rcmd_af() and rresvport_af() were defined in RFC2292.
March 30, 2005 BSD