rexecd - remote execution server
Rexecd is the server for the rexec(3X) routine. The server provides
remote execution facilities with authentication based on user names and
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 null (`\0')
byte. The resultant string is interpreted as an ASCII number,
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 null terminated user name of at most 16 characters is
retrieved on the initial socket.
4) A null terminated, encrypted, password of at most 16 characters
is retrieved on the initial socket.
5) A null 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 null byte is returned on the connection associated with the
stderr and the command line is passed to the normal login shell
of the user. The shell inherits the network connections estab-
lished by rexecd.
All diagnostic messages are returned on the connection associated with
the stderr, 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 com-
``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 con-
figured into the system).
No password file entry for the user name existed.
The wrong was password supplied.
``No remote directory.''
The chdir command to the home directory failed.
A fork by the server failed.
The user's login shell could not be started.
Indicating ``Login incorrect'' as opposed to ``Password incorrect'' is
a security breach which allows people to probe a system for users with
A facility to allow all data exchanges to be encrypted should be
4th Berkeley Distribution 4 March 1983 REXECD(8C)