rexecd -- remote execution server
The rexecd utility is the server for the rexec(3) routine. The server
provides remote execution facilities with authentication based on user
names and passwords.
The rexecd utility 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 NUL (`\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
3. A NUL terminated user name of at most 16 characters is retrieved on
the initial socket.
4. A NUL terminated, unencrypted password of at most 16 characters is
retrieved on the initial socket.
5. A NUL 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 rexecd utility 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 NUL 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.
The rexecd utility will not allow root logins unless the -i option is
given on the command line (typically in /etc/inetd.conf). It will also
disallow access for users listed in /etc/ftpusers, or users with no passwords,
which were all serious security holes. The entire concept of
rexec/rexecd is a major security hole and an example of how not to do
things. The rexecd utility is disabled by default in /etc/inetd.conf.
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. [Toc] [Back]
No password file entry for the user name existed.
Password incorrect. [Toc] [Back]
The wrong password was supplied.
No remote directory. [Toc] [Back]
The chdir(1) command to the home directory failed.
Try again. [Toc] [Back]
A fork(2) 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.
A facility to allow all data and password exchanges to be encrypted
should be present.
The rexecd utility appeared in 4.2BSD.
FreeBSD 5.2.1 September 23, 1994 FreeBSD 5.2.1 [ Back ]