rexecd(8)rexecd(8)NAMErexecd - The remote execution server
SYNOPSISrexecd [-s]
OPTIONS
Causes rexecd to check for the ptys keyword in the /etc/securettys file
and to deny execution of the request if it is from root and on a pseu‐
doterminal.
DESCRIPTION
The rexecd daemon is the server for the rexec(3) routine. The server
provides remote execution facilities with authentication based on user‐
names and passwords.
The rexecd daemon listens for service requests at the port indicated in
the exec service specification; see services(4). When a service
request is received, the following protocol is initiated: 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. If the number
received in step 1 is nonzero, 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. A null-
terminated username of at most 16 bytes is retrieved on the initial
socket. A null-terminated, unencrypted password of at most 80 bytes is
retrieved on the initial socket. 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. The rexecd server then validates the user as is done at
login time and, if started with the -s option, verifies that the
/etc/securettys file is not setup to deny the user. If the authentica‐
tion was successful, rexecd changes to the user's home directory, and
establishes the user and group protections for the user. If any of
these steps fail, the connection is aborted with a diagnostic message
returned. A null byte is returned on the initial socket and the com‐
mand 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 diagnostic message listed, 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
bytes. The password is longer than 80 bytes. The command line passed
exceeds the size of the argument list (as configured into the system).
No password file entry for the username existed. The wrong password
was supplied. 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 stderr and
is not preceded by a option byte.
CAUTIONS
Indicating Login incorrect as opposed to Password incorrect is a secu‐
rity breach that allows people to probe a system for users with null
passwords.
FILES
Specifies the command path
SEE ALSO
Functions: rexec(3)
Files: securettys(4)rexecd(8)
