in.rshd(1M)
NAME
in.rshd, rshd - remote shell server
SYNOPSIS
in.rshd host.port
DESCRIPTION
in.rshd is the server for the rsh(1) program. The server
provides remote execution facilities with authentication
based on privileged port numbers.
in.rshd is invoked by inetd(1M) each time a shell service is
requested, and executes the following protocol:
1. The server checks the client's source port. If the port
is not in the range 512-1023, the server aborts the con-
nection. The client's host address (in hex) and port
number (in decimal) are the arguments passed to in.rshd.
2. The server reads characters from the socket up to a null
( \0 ) byte. The resultant string is interpreted as an
ASCII number, base 10.
3. If the number received in step 2 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.
The source port of this second connection is also in the
range 512-1023.
4. A null-terminated user name of at most 16 characters is
retrieved on the initial socket. This user name is
interpreted as the user identity on the client's machine.
5. A null terminated user name of at most 16 characters is
retrieved on the initial socket. This user name is
interpreted as a user identity to use on the server's
machine.
6. A null terminated command to be passed to a shell is
retrieved on the initial socket. The length of the com-
mand is limited by the upper bound on the size of the
system's argument list.
7. in.rshd then validates the user according to the follow-
ing steps. The remote user name is looked up in the pass-
word file and a chdir is performed to the user's home
directory. If the lookup fails, the connection is ter-
minated. If the chdir fails, it does a chdir to / (root).
If the user is not the superuser, (user ID 0), and if the
pam_rhosts_auth PAM module is configured for authentica-
tion, the file /etc/hosts.equiv is consulted for a list
of hosts considered "equivalent". If the client's host
name is present in this file, the authentication is con-
sidered successful. See the SECURITY section below for a
discussion of PAM authentication.
If the lookup fails, or the user is the superuser, then
the file .rhosts in the home directory of the remote user
is checked for the machine name and identity of the user
on the client's machine. If this lookup fails, the con-
nection is terminated
8. 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 PATH variable is set to
/usr/bin.) The shell inherits the network connections
established by in.rshd.
USAGE
rshd and in.rshd are IPv6-enabled. See ip6(7P).
SECURITY
in.rshd uses pam(3PAM) for authentication, account manage-
ment, and session management. The PAM configuration policy,
listed through /etc/pam.conf, specifies the modules to be
used for in.rshd. Here is a partial pam.conf file with
entries for the rsh command using rhosts authentication,
UNIX account management, and session management module.
rsh auth required pam_rhosts_auth.so.1
rsh account required pam_unix_roles.so.1
rsh session required pam_unix_projects.so.1
rsh session required pam_unix_account.so.1
rsh session required pam_unix_session.so.1
If there are no entries for the rsh service, then the
entries for the "other" service are used. To maintain the
authentication requirement for in.rshd, the rsh entry must
always be configured with the pam_rhosts_auth.so.1 module.
FILES
/etc/hosts.equiv
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWrcmds |
|_____________________________|_____________________________|
SEE ALSO
rsh(1), inetd(1M), pam(3PAM), hosts(4), inetd.conf(4),
pam.conf(4), attributes(5), environ(5),
pam_authtok_check(5), pam_authtok_get(5),
pam_authtok_store(5), pam_dhkeys(5), pam_passwd_auth(5),
pam_rhosts_auth(5), pam_unix(5), pam_unix_account(5),
pam_unix_auth(5), pam_unix_session(5)ip6(7P)
DIAGNOSTICS
The following diagnostic messages are returned on the con-
nection associated with stderr, after which any network
connections are closed. An error is indicated by a leading
byte with a value of 1 in step 8 above (0 is returned above
upon successful completion of all the steps prior to the
command execution).
locuser too long
The name of the user on the client's machine is
longer than 16 characters.
remuser too long
The name of the user on the remote machine is
longer than 16 characters.
command too long
The command line passed exceeds the size of the
argument list (as configured into the system).
Hostname for your address unknown.
No entry in the host name database existed for
the client's machine.
Login incorrect.
No password file entry for the user name existed.
Permission denied.
The authentication procedure described above
failed.
Can't make pipe.
The pipe needed for the stderr was not created.
Try again.
A fork by the server failed.
NOTES
The authentication procedure used here assumes the integrity
of each client machine and the connecting medium. This is
insecure, but it is useful in an "open" environment.
A facility to allow all data exchanges to be encrypted
should be present.
The pam_unix(5) module might not be supported in a future
release. Similar functionality is provided by
pam_authtok_check(5), pam_authtok_get(5),
pam_authtok_store(5), pam_dhkeys(5), pam_passwd_auth(5),
pam_unix_account(5), pam_unix_auth(5), and
pam_unix_session(5).
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