REXEC(3) Linux Programmer's Manual REXEC(3)
rexec, rexec_af - return stream to a remote command
#define _BSD_SOURCE /* See feature_test_macros(7) */
int rexec(char **ahost, int inport, char *user,
char *passwd, char *cmd, int *fd2p);
int rexec_af(char **ahost, int inport, char *user,
char *passwd, char *cmd, int *fd2p,
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 for-
eign 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
The port inport specifies which well-known DARPA Internet port to use for the connection;
the call getservbyname("exec", "tcp") (see getservent(3)) will return a pointer to a
structure that contains the necessary port. The protocol for connection is described in
detail in rexecd(8).
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 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 con-
nection 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 out-of-band data.
The rexec() function works over IPv4 (AF_INET). By contrast, the rexec_af() function pro-
vides 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.
Multithreading (see pthreads(7))
The rexec() and rexec_af() functions are not thread-safe.
These functions are not in POSIX.1-2001. 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.
This page is part of release 3.55 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
Linux 2013-09-26 REXEC(3)