Ubuntu Manpage: rexecd — remote execution server

NAME

       rexecd — remote execution server

SYNOPSIS

       rexecd

DESCRIPTION

Rexecd is the server for the rexec(3) routine. The server provides remote execution facilities with
authentication based on user names and passwords.

Rexecd listens for service requests at the port indicated in the ``exec'' service specification; see
services(5). When a service request is received the following protocol is initiated:

1. The server reads characters from the socket up to a NUL (‘\0’) byte. The resultant string is
interpreted as an ASCII number, base 10.

2. If the number received in step 1 is non-zero, it is interpreted as the port number of a secondary
stream to be used for the stderr. A second connection is then created to the specified port on the
client's machine.

3. A NUL terminated user name of at most 16 characters is retrieved on the initial socket.

4. A NUL terminated, unencrypted password of at most 16 characters is retrieved on the initial socket.

5. A NUL terminated command to be passed to a shell is retrieved on the initial socket. The length of
the command is limited by the upper bound on the size of the system's argument list.

6. Rexecd then validates the user as is done at login time and, if the authentication was successful,
changes to the user's home directory, and establishes the user and group protections of the user.
If any of these steps fail the connection is aborted with a diagnostic message returned.

7. A NUL byte is returned on the initial socket and the command line is passed to the normal login
shell of the user. The shell inherits the network connections established by rexecd.

DIAGNOSTICS

       Except for the last one listed below, all diagnostic messages are returned on the initial  socket,  after
       which  any  network connections are closed.  An error is indicated by a leading byte with a value of 1 (0
       is returned in step 7 above upon successful completion of all the steps prior to the command execution).

       username too long
               The name is longer than 16 characters.

       password too long
               The password is longer than 16 characters.

       command too long
               The command line passed exceeds the size of the argument list (as configured into the system).

       Login incorrect.
               No password file entry for the user name existed or the wrong password was supplied.

       No remote directory.
               The chdir command to the home directory failed.

       Try again.
               A fork by the server failed.

       <shellname>: ...
               The user's login shell could not  be  started.   This  message  is  returned  on  the  connection
               associated with the stderr, and is not preceded by a flag byte.

BUGS

       A facility to allow all data and password exchanges to be encrypted should be present.

HISTORY