REXECD(8C)REXECD(8C)NAMErexecd - remote execution server
SYNOPSIS
/usr/etc/rexecd
DESCRIPTION
Rexecd is the server for the rexec(3X) 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 null (`\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 null terminated user name of at most 16 characters is
retrieved on the initial socket.
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 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.
``Password incorrect.''
The wrong was password 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.
SEE ALSOrexec(3X)BUGS
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 May 9, 1986 REXECD(8C)