BSD 2.11 - man page for rexecd (bsd section 8)
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rexecd - remote execution server
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 specifi-
cation; see services(5). When a service request is received the following protocol is
1) The server reads characters from the socket up to a null (`\0') byte. The resul-
tant 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 cre-
ated 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
4) A null terminated, unencrypted 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 initial socket and the command line is passed to the
normal login shell of the user. The shell inherits the network connections estab-
lished by rexecd.
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 lead-
ing 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 sys-
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. This message is returned on the connection
associated with the stderr, 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 present.
4.2 Berkeley Distribution November 16, 1996 REXECD(8)
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