is the server for the
routine. The server provides remote execution facilities
with authentication based on user names and
listens for service requests at the port indicated in
the ``exec'' service specification; see
When a service request is received the following protocol
The server reads characters from the socket up
to a NUL
byte. The resultant string is
interpreted as an
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
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.
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
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).
The name is
longer than 16 characters.
The password is longer than 16 characters.
The command line passed exceeds the size of the argument
list (as configured into the system).
No password file entry for the user name existed.
The wrong password was supplied.
command to the home directory failed.
by the server failed.
The user's login shell could not be started.
This message is returned
on the connection associated with the
and is not preceded by a flag byte.
Indicating ``Login incorrect'' as opposed to ``Password incorrect''
is a security breach which allows people to probe a system for users
with null passwords.
A facility to allow all data and password exchanges to be encrypted should be
command appeared in
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