rexec, rexec_af — return stream to a remote command


#include <netdb.h>

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,
             sa_family_t af);

rexec(), rexec_af():

    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 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 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 out-of-band data.


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 protocol).


The rexec_af() function was added to glibc in version 2.2.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
rexec(), rexec_af() Thread safety MT-Unsafe

Conforming to

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.

See Also

rcmd(3), rexecd(8)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

in.rexecd(8), rcmd(3), rexec(1), rmt(1).

The man page rexec_af(3) is an alias of rexec(3).

2017-09-15 Linux Programmer's Manual