in.rshd(1M) System Administration Commands in.rshd(1M)NAME
in.rshd, rshd - remote shell server
SYNOPSIS
in.rshd [-k5eciU] [-s tos] [-S keytab] [-M realm] [-L env_var]
host.port
DESCRIPTION
in.rshd is the server for the rsh(1) program. The server provides
remote execution facilities with authentication based on Kerberos V5 or
privileged port numbers.
in.rshd is invoked by inetd(1M) each time a shell service is requested.
When Kerberos V5 authentication is required (this can be set with Ker‐
beros-specific options listed below), the following protocol is initi‐
ated:
1. Check Kerberos V5 authentication.
2. Check authorization according to rules in krb5_auth_rules(5).
3. A null byte is returned on the initial socket 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.
In order for Kerberos authentication to work, a host/<FQDN> Kerberos
principal must exist for each Fully Qualified Domain Name associated
with the in.rshd server. Each of these host/<FQDN> principals must have
a keytab entry in the /etc/krb5/krb5.keytab file on the in.rshd server.
An example principal might be:
host/bigmachine.eng.example.com
See kadmin(1M) or gkadmin(1M) for instructions on adding a principal to
a krb5.keytab file. See System Administration Guide: Security Services
for a discussion of Kerberos authentication.
If Kerberos V5 authentication is not enabled, then in.rshd 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 connection. The client's
host address (in hex) and port number (in decimal) are the argu‐
ments passed to in.rshd.
2. The server reads characters from the socket up to a null ( ) 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 command 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 following steps.
The remote user name is looked up in the password file and a chdir
is performed to the user's home directory. If the lookup fails, the
connection is terminated. 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 authentication, 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 considered successful. See the SECURITY sec‐
tion 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 connection is terminated
8. A null byte is returned on the initial connection 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 connec‐
tions established by in.rshd.
OPTIONS
The following options are supported:
-5 Same as -k, for backwards compatibility
-c Requires Kerberos V5 clients to present a cryptographic
checksum of initial connection information like the
name of the user that the client is trying to access in
the initial authenticator. This checksum provides addi‐
tionl security by preventing an attacker from changing
the initial connection information. This option is
mutually exclusive with the -i option.
-e Requires the client to encrypt the connection.
-i Ignores authenticator checksums if provided. This
option ignores authenticator checksums presented by
current Kerberos clients to protect initial connection
information. Option -i is the opposite of option -c.
-k Allows Kerberos V5 authentication with the .k5login
access control file to be trusted. If this authentica‐
tion system is used by the client and the authorization
check is passed, then the user is allowed to log in.
-L env_var List of environment variables that need to be saved and
passed along.
-M realm Uses the indicated Kerberos V5 realm. By default, the
daemon will determine its realm from the settings in
the krb5.conf(4) file.
-s tos Sets the IP TOS option.
-S keytab Sets the KRB5 keytab file to use.
The/etc/krb5/krb5.keytab file is used by default.
-U Refuses connections that cannot be mapped to a name
through the getnameinfo(3SOCKET) function.
USAGErshd and in.rshd are IPv6-enabled. See ip6(7P). IPv6 is not currently
supported with Kerberos V5 authentication.
The Kerberized rshd service runs on port 544 (kshell). The correspond‐
ing FMRI entry is: :
svc:/network/shell:kshell (rshd with kerberos (ipv4 only))
SECURITY
in.rshd uses pam(3PAM) for authentication, account management, and ses‐
sion 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.
in.rshd can authenticate using Kerberos V5 authentication or pam(3PAM).
For Kerberized rsh service, the appropriate PAM service name is krsh.
FILES
/etc/hosts.equiv
$HOME/.k5login File containing Kerberos principals that are
allowed access.
/etc/krb5/krb5.conf Kerberos configuration file.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWrcmds │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOrsh(1), svcs(1), gkadmin(1M), inetadm(1M), inetd(1M), kadmin(1M),
svcadm(1M), pam(3PAM), getnameinfo(3SOCKET), hosts(4), krb5.conf(4),
pam.conf(4), attributes(5), environ(5), krb5_auth_rules(5), pam_auth‐
tok_check(5), pam_authtok_get(5), pam_authtok_store(5), pam_dhkeys(5),
pam_passwd_auth(5), pam_rhosts_auth(5), pam_unix_account(5),
pam_unix_auth(5), pam_unix_session(5), smf(5), ip6(7P)
System Administration Guide: Security Services
DIAGNOSTICS
The following diagnostic messages are returned on the connection asso‐
ciated 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 char‐
acters.
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 is no longer supported. Similar functionality is
provided by pam_authtok_check(5), pam_authtok_get(5), pam_auth‐
tok_store(5), pam_dhkeys(5), pam_passwd_auth(5), pam_unix_account(5),
pam_unix_auth(5), and pam_unix_session(5).
The in.rshd service is managed by the service management facility,
smf(5), under the service identifier:
svc:/network/shell:default
Administrative actions on this service, such as enabling, disabling, or
requesting restart, can be performed using svcadm(1M). Responsibility
for initiating and restarting this service is delegated to inetd(1M).
Use inetadm(1M) to make configuration changes and to view configuration
information for this service. The service's status can be queried using
the svcs(1) command.
SunOS 5.10 10 Nov 2005 in.rshd(1M)