rexecd(8c)rexecd(8c)Namerexecd - remote execution server
Syntax
/etc/rexecd
Description
The command is the server for the routine. The server provides remote
execution facilities with authentication based on usernames and
encrypted passwords.
The command is invoked by when it receives a connection on the port
indicated in the ``exec'' service specification. For further informa‐
tion, see 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 username of at most 16 characters is retrieved on
the initial socket.
4) A null terminated 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) The command then validates the user as is done at login time and, if
the authentication was successful, changes to the user's home direc‐
tory, and establishes the user and group protections of the user.
If any of these steps fail the connection is aborted with a diagnos‐
tic 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 established by
Diagnostics
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‐
mand 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 con‐
figured into the system).
Login incorrect
No password file entry for the username existed.
Password incorrect
The wrong was password supplied.
No remote directory
The command to the home directory failed.
Try again
A fork by the server failed.
/bin/sh: ...
The user's login shell could not be started.
Restrictions
Indicating ``Login incorrect'' as opposed to ``Password incorrect'' is
a security breach which allows people to probe a system for users with
null passwords.
See Alsoinetd(8c)rexecd(8c)
