NAME¶
rexecd
—
remote execution server
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:
- The server reads characters from the socket up to a NUL
(‘
\0
’) byte. The resultant string is
interpreted as an ASCII number, base 10.
- 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.
- A NUL terminated user name of at most 16 characters is retrieved on the
initial socket.
- A NUL terminated, unencrypted password of at most 16 characters is
retrieved on the initial socket.
- 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.
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.
- 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¶
The rexecd
command appeared in
4.2BSD.