rcmd, rcmd_r - Allow execution of commands on a remote
#include <sys/types.h> #include <netdb.h> #include
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(
struct hostent_data *host_data );
Standard C Library (libc)
Specifies the name of a remote host. 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 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 messages 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 provision 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
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 connection 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. A user 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.
Alternatively, the rcmd() function can use a Secure Shell
connection to authenticate users. In addition to authenticating
users, a Secure Shell connection also authenticates
the client and server and provides data encryption, data
integrity, and nonrepudiation. You configure the rcmd()
function (and the rsh, rlogin, and rcp commands) to automatically
use a Secure Shell connection by enabling the
Secure Shell EnforceSecureRutils keyword in the
/etc/ssh2/ssh2_config file or in a user's
$HOME/.ssh2/ssh2_config file. When the EnforceSecureRutils
keyword is enabled: The sshd daemon runs and spawns the
srcmd child process; the rshd and rlogind daemons do not
run. The rcmd() function can use only Secure Shell hostbased
authentication to authenticate users.
See Security Administration for more information about
configuring Secure Shell host-based authentication and the
The rcmd_r() function is the reentrant version of rcmd().
It is supported in order to maintain backward compatibility
with previous versions of the operating system.
The netdb.h header file defines the hostent_data structures.
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.
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.
Specifies remote users that can use a local user account.
Specifies Secure Shell client configuration information.
Specifies Secure Shell server configuration information.
Functions: gethostname(2), rresvport(3), rresvport_af(3),
Commands: rlogin(1), rsh(1)
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