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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



rexec, rexec_af - return stream to a remote command


#include <netdb.h>
#include <unistd.h>

int rexec(char **ahost, unsigned short inport, const char *user,
     const char *passwd, const char *cmd, int *fd2p);
int rexec_af(char **ahost, unsigned short inport, const char *user,
     const char *passwd, const char *cmd, int *fd2p, int af);


These functions open a connection to a remote host to execute a command, and return a socket connected to the remote command's standard input and output file descriptors. The protocol for connection is described in detail in in.rexecd(8).

The rexec() and rexec_af() functions first look up the host ahost using getaddrinfo(3C) and return −1 if the host does not exist. Otherwise ahost is set to the standard name of the host. The user and passwd parameters are used as the username and password in remote host authentication. When a username and password are not specified, the .netrc file in the user's home directory is searched for the appropriate information. If the search fails, the user is prompted for the information.

The rexec() function always returns a socket of the AF_INET address family. The rexec_af() function accepts AF_INET, AF_INET6, or AF_UNSPEC for the address family parameter af. An application can choose which type of socket is returned by passing AF_INET or AF_INET6 as the address family. The use of AF_UNSPEC means that the caller will accept any address family. Choosing AF_UNSPEC provides a socket that best suits the connectivity to the remote host.

The parameter inport specifies which TCP port to use for the connection. The port number used must be in network byte order, as supplied by a call to htons(3C).

If the call succeeds, a socket of type SOCK_STREAM is returned to the caller, and given to the remote command as its standard input and standard output. If fd2p is non-null, an auxiliary channel to a control process is set up and a file descriptor for it is placed in *fd2p. The control process returns diagnostic output (file descriptor 2), from the command on the auxiliary channel. The control process also accepts bytes on this channel as signal numbers to be forwarded to the process group of the command. If fd2p is NULL, the standard error (file descriptor 2) of the remote command is made the same as its standard output, and no provision is made for sending arbitrary signals to the remote process, other than possibly sending out-of-band data.

There is no way to specify options to the socket() call made by the rexec() or rexec_af() functions.

Return Values

If rexec() succeeds, a file descriptor number is returned of the socket type SOCK_STREAM and the address family AF_INET. The parameter *ahost is set to the standard name of the host. If the value of fd2p is other than NULL, a file descriptor number is placed in *fd2p which represents the standard error stream of the command.

If rexec_af() succeeds, the routine returns a file descriptor number of the socket type SOCK_STREAM in the address family AF_INET or AF_INET6, as determined by the value of the af parameter.

If either rexec() or rexec_af() fails, −1 is returned.


The protocol underlying these functions uses weak authentication and offers no protection against spoofing or snooping of traffic. The in.rexecd(8) server is disabled by default on Oracle Solaris and most other modern operating systems, and may be removed in future versions of Oracle Solaris. Use of the sshd(8) server is strongly recommended instead, and a programming interface to it is available via the libssh2 library.


See attributes(7) for descriptions of the following attributes:

Interface Stability

This interface is Unsafe in multithreaded applications. Unsafe interfaces should be called only from the main thread.

See Also

getaddrinfo(3C), htons(3C), socket(3C), attributes(7), in.rexecd(8)


The rexec() function has been present since the initial release of Solaris.

The rexec_af() function was added to Oracle Solaris in the Solaris 8 release.