REXEC(3) Linux Programmer's Manual REXEC(3)
rexec, rexec_af - return stream to a remote command
int rexec(char **ahost, int inport, const char *user,
const char *passwd, const char *cmd, int *fd2p);
int rexec_af(char **ahost, int inport, const char *user,
const char *passwd, const char *cmd, int *fd2p,
Since glibc 2.19:
In glibc up to and including 2.19:
This interface is obsoleted by rcmd(3).
The rexec() 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. If a username and password are both
specified, then these are used to authenticate to the foreign host;
otherwise the environment and then the .netrc file in user's home
directory are searched for appropriate information. If all this fails,
the user is prompted for the information.
The port inport specifies which well-known DARPA Internet port to use
for the connection; the call getservbyname("exec", "tcp") (see getser-
vent(3)) will return a pointer to a structure that contains the neces-
sary port. The protocol for connection is described in detail in rex-
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 nonzero, then an auxiliary channel to
a control process will be setup, and a file 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. The diagnostic information returned does
not include remote authorization failure, as the secondary connection
is set up after authorization has been verified. 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
The rexec() function works over IPv4 (AF_INET). By contrast, the
rexec_af() function provides an extra argument, af, that allows the
caller to select the protocol. This argument can be specified as
AF_INET, AF_INET6, or AF_UNSPEC (to allow the implementation to select
The rexec_af() function was added to glibc in version 2.2.
For an explanation of the terms used in this section, see
|Interface | Attribute | Value |
|rexec(), rexec_af() | Thread safety | MT-Unsafe |
These functions are not in POSIX.1. The rexec() function first
appeared in 4.2BSD, and is present on the BSDs, Solaris, and many other
systems. The rexec_af() function is more recent, and less widespread.
The rexec() function sends the unencrypted password across the network.
The underlying service is considered a big security hole and therefore
not enabled on many sites; see rexecd(8) for explanations.
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Linux 2017-09-15 REXEC(3)
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