rcmd(3) Library Functions Manual rcmd(3)
NAME
rcmd, rcmd_r - Allow execution of commands on a remote host
LIBRARY
Standard C Library (libc.a)
SYNOPSIS
#include <sys/types.h> #include <netdb.h> #include <unistd.h>
int rcmd( char **host, u_short port, char *local_user, char *remote_user, char *command, int *err_file_desc);
The following function is supported in order to maintain backward compatibility with previous versions of the operating system. int
rcmd_r( char **host, u_short port, char *local_user, char *remote_user, char *command, int *err_file_desc,
struct hostent_data *host_data);
PARAMETERS
Specifies the name of a remote host that is listed in the /etc/hosts file. The function sets the host parameter to be the fully qualified
hostname. Specifies the well-known port to use for the connection. The /etc/services file contains the DARPA Internet services, their
ports, and socket types. Points to usernames that are valid at the local host. Any valid username can be given. Points to usernames that
are valid at the remote host. Any valid username can be given. Specifies the name of the command to be executed at the remote host.
Points to an address used by rcmd() to store a pointer to the file descriptor for a channel used by the remote process to write stderr mes-
sages and to accept bytes as signal numbers to be forwarded to the process group of the command.
If a null pointer is specified, the standard error (stderr) of the remote command is the same as the standard output (stdout). No provi-
sion is made for sending arbitrary signals to the remote process. However, it is possible to send out-of-band data to the remote command.
Per-thread data for reentrant version.
DESCRIPTION
The rcmd() (remote command) function allows execution of certain commands on a remote host. For example, the rcmd() function is used by
rsh and rlogin, among others.
The rcmd() function looks up a host via the name server or, if the local name server is not running, via the /etc/hosts file. If the con-
nection succeeds, a socket in the Internet domain of type SOCK_STREAM is returned to the calling process and given to the remote command as
standard input (stdin) and standard output (stdout).
Always specify the host name. If the local domain and remote domain are the same, specifying the domain parts is optional. The rcmd()
function returns the fully qualified hostname in the host parameter. To reuse the host name in another rcmd() call, you should make a
string copy of the host parameter. For example: rcmd ( &host, .... ); first_host = strdup(host); ... rcmd ( &host, .... );
Only processes with an effective user ID of root user can use the rcmd() function. An authentication scheme based on remote port numbers
is used to verify permissions. Ports in the range from 0 to 1023 can only be used by a root user.
NOTES
The rcmd_r() function is the reentrant version of rcmd(). It is supported in order to maintain backward compatibility with previous ver-
sions of the operating system.
The netdb.h header file defines the hostent_data structures.
RETURN VALUES
Upon successful completion, the rcmd() function returns a valid socket descriptor. The function returns a value of -1 if the effective
user ID of the calling process is not root user, if the function fails to resolve the host, or if it encounters a socket connection error.
FILES
Contains the service names, ports, and socket types. Contains hostnames and their addresses for the hosts in a network. Contains the name
server and the domain name.
RELATED INFORMATION
Functions: gethostname(2), rresvport(3), rresvport_af(3), ruserok(3), sethostname(2).
Commands: rlogin(1), rsh(1). delim off
rcmd(3)