RSH(1)RSH(1)NAME
rsh, remsh, remote_shell - remote shell
SYNOPSISrsh [-n] [-a] [-K] [-PN | -PO] [-x] [-f | -F] [-l username]
[-k realm] hostname command
rsh hostname [-n] [-a] [-K] [-PN | -PO] [-x] [-f | -F]
[-l username] [-k realm] command
remsh [-n] [-a] [-K] [-PN | -PO] [-x] [-f | -F] [-l username]
[-k realm] hostname command
remsh hostname [-n] [-a] [-K] [-PN | -PO] [-x] [-f | -F]
[-l username] [-k realm] command
hostname [-n] [-a] [-PN | -PO] [-x] [-f | -F]
[-l username] [-k realm] command
DESCRIPTION
The rsh utility connects to the specified hostname and executes the
specified command. rsh copies its standard input to the remote command,
the standard output of the remote command to its standard output, and
the standard error of the remote command to its standard error. Inter‐
rupt, quit, and terminate signals are propagated to the remote command.
rsh normally terminates when the remote command does.
The user can opt for a secure session of rsh which uses Kerberos V5 for
authentication. Encryption of the network session traffic is also pos‐
sible. The rsh session can be kerberized using any of the following
Kerberos specific options: -a, -PN or -PO, -x, -f or -F, and -k realm.
Some of these options (-a, -x, -PN or -PO, and -f or -F) can also be
specified in the [appdefaults] section of krb5.conf(4). The usage of
these options and the expected behavior is discussed in the OPTIONS
section below. If Kerberos authentication is used, authorization to the
account is controlled by rules in krb5_auth_rules(5). If this autho‐
rization fails, fallback to normal rsh using rhosts occurs only if the
-PO option is used explicitly on the command line or is specified in
krb5.conf(4). Also, the -PN or -PO, -x, -f or -F, and -k realm options
are just supersets of the -a option.
If you omit command, instead of executing a single command, rsh logs
you in on the remote host using rlogin(1).
rsh does not return the exit status code of command.
Shell metacharacters which are not quoted are interpreted on the local
machine, while quoted metacharacters are interpreted on the remote
machine. See EXAMPLES.
If there is no locale setting in the initialization file of the login
shell (.cshrc, . . .) for a particular user, rsh always executes the
command in the "C" locale instead of using the default locale of the
remote machine.
The command is sent unencrypted to the remote system. All subsequent
network session traffic is encrypted. See -x.
OPTIONS
The following options are supported:
-a
Explicitly enable Kerberos authentication and trusts the
.k5login file for access-control. If the authorization
check by in.rshd(1M) on the server-side succeeds and if
the .k5login file permits access, the user is allowed to
carry out the command.
-f
Forward a copy of the local credentials (Kerberos Ticket
Granting Ticket) to the remote system. This is a non-
forwardable ticket granting ticket. Forward a ticket
granting ticket if you need to authenticate yourself to
other Kerberized network services on the remote host. An
example would be if your home directory on the remote
host is NFS mounted by way of Kerberos V5. If your local
credentials are not forwarded in this case, you cannot
access your home directory. This option is mutually
exclusive with the -F option.
-F
Forward a forwardable copy of the local credentials
(Kerberos Ticket Granting Ticket) to the remote system.
The -F option provides a superset of the functionality
offered by the -f option. For example, with the -f
option, if, after you connected to the remote host, your
remote command attempted to invoke /usr/bin/ftp,
/usr/bin/telnet, /usr/bin/rlogin, or /usr/bin/rsh, with
the -f or -F options, the attempt would fail. Thus, you
would be unable to push your single network sign on
trust beyond one system. This option is mutually exclu‐
sive with the -f option.
-k realm
Causes rsh to obtain tickets for the remote host in
realm instead of the remote host's realm as determined
by krb5.conf(4).
-K
This option explicitly disables Kerberos authentication.
It can be used to override the autologin variable in
krb5.conf(4).
-l username
Uses username as the remote username instead of your
local username. In the absence of this option, the
remote username is the same as your local username.
-n
Redirect the input of rsh to /dev/null. You sometimes
need this option to avoid unfortunate interactions
between rsh and the shell which invokes it. For example,
if you are running rsh and invoke a rsh in the back‐
ground without redirecting its input away from the ter‐
minal, it blocks even if no reads are posted by the
remote command. The -n option prevents this.
-PO
-PN
Explicitly request new (-PN) or old (-PO) version of the
Kerberos "rcmd" protocol. The new protocol avoids many
security problems prevalant in the old one and is
regarded much more secure, but is not interoperable with
older (MIT/SEAM) servers. The new protocol is used by
default, unless explicitly specified using these options
or through krb5.conf(4). If Kerberos authorization fails
when using the old "rcmd" protocol, there is fallback to
regular, non-kerberized rsh. This is not the case when
the new, more secure "rcmd" protocol is used.
-x
Cause the network session traffic to be encrypted. See
DESCRIPTION.
The type of remote shell (sh, rsh, or other) is determined by the
user's entry in the file /etc/passwd on the remote system.
OPERANDS
The following operand is supported:
command
The command to be executed on the specified hostname.
USAGE
See largefile(5) for the description of the behavior of rsh and remsh
when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
The rsh and remsh commands are IPv6-enabled. See ip6(7P). IPv6 is not
currently supported with Kerberos V5 authentication.
Hostnames are given in the hosts database, which can be contained in
the /etc/hosts file, the Internet domain name database, or both. Each
host has one official name (the first name in the database entry) and
optionally one or more nicknames. Official hostnames or nicknames can
be given as hostname.
If the name of the file from which rsh is executed is anything other
than rsh, rsh takes this name as its hostname argument. This allows you
to create a symbolic link to rsh in the name of a host which, when exe‐
cuted, invokes a remote shell on that host. By creating a directory and
populating it with symbolic links in the names of commonly used hosts,
then including the directory in your shell's search path, you can run
rsh by typing hostname to your shell.
If rsh is invoked with the basename remsh, rsh checks for the existence
of the file /usr/bin/remsh. If this file exists, rsh behaves as if
remsh is an alias for rsh. If /usr/bin/remsh does not exist, rsh
behaves as if remsh is a host name.
For the kerberized rsh session, each user can have a private authoriza‐
tion list in a file .k5login in their home directory. Each line in this
file should contain a Kerberos principal name of the form princi‐
pal/instance@realm. If there is a ~/.k5login file, then access is
granted to the account if and only if the originater user is authenti‐
cated to one of the principals named in the ~/.k5login file. Other‐
wise, the originating user is granted access to the account if and only
if the authenticated principal name of the user can be mapped to the
local account name using the authenticated-principal-name → local-user-
name mapping rules. The .k5login file (for access control) comes into
play only when Kerberos authentication is being done.
For the non-secure rsh session, each remote machine can have a file
named /etc/hosts.equiv containing a list of trusted hostnames with
which it shares usernames. Users with the same username on both the
local and remote machine can run rsh from the machines listed in the
remote machine's /etc/hosts.equiv file. Individual users can set up a
similar private equivalence list with the file .rhosts in their home
directories. Each line in this file contains two names: a hostname and
a username separated by a space. The entry permits the user named
username who is logged into hostname to use rsh to access the remote
machine as the remote user. If the name of the local host is not found
in the /etc/hosts.equiv file on the remote machine, and the local user‐
name and hostname are not found in the remote user's .rhosts file, then
the access is denied. The hostnames listed in the /etc/hosts.equiv and
.rhosts files must be the official hostnames listed in the hosts data‐
base; nicknames can not be used in either of these files.
You cannot log in using rsh as a trusted user from a trusted hostname
if the trusted user account is locked.
rsh does not prompt for a password if access is denied on the remote
machine unless the command argument is omitted.
EXAMPLES
Example 1 Using rsh to Append Files
The following command appends the remote file lizard.file from the
machine called lizard to the file called example.file on the machine
called example:
example% rsh lizard cat lizard.file >> example.file
The following command appends the file lizard.file on the machine
called lizard to the file lizard.file2 which also resides on the
machine called lizard:
example% rsh lizard cat lizard.file ">>" lizard.file2
EXIT STATUS
The following exit values are returned:
0
Successful completion.
1
An error occurred.
FILES
/etc/hosts
Internet host table
/etc/hosts.equiv
Trusted remote hosts and users
/etc/passwd
System password file
$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 │
├───────────────┼─────────────────┤
│CSI │ Enabled │
└───────────────┴─────────────────┘
SEE ALSOon(1), rlogin(1), ssh(1), telnet(1), vi(1), in.rshd(1M), hosts(4),
hosts.equiv(4), krb5.conf(4), attributes(5), krb5_auth_rules(5), large‐
file(5), ip6(7P)NOTES
When a system is listed in hosts.equiv, its security must be as good as
local security. One insecure system listed in hosts.equiv can compro‐
mise the security of the entire system.
You cannot run an interactive command (such as vi(1)). Use rlogin if
you wish to do this.
Stop signals stop the local rsh process only. This is arguably wrong,
but currently hard to fix for reasons too complicated to explain here.
The current local environment is not passed to the remote shell.
Sometimes the -n option is needed for reasons that are less than obvi‐
ous. For example, the command:
example% rsh somehost dd if=/dev/nrmt0 bs=20b | tar xvpBf −
puts your shell into a strange state. Evidently, the tar process termi‐
nates before the rsh process. The rsh command then tries to write into
the ``broken pipe'' and, instead of terminating neatly, proceeds to
compete with your shell for its standard input. Invoking rsh with the
-n option avoids such incidents.
This bug occurs only when rsh is at the beginning of a pipeline and is
not reading standard input. Do not use the -n option if rsh actually
needs to read standard input. For example:
example% tar cf − . | rsh sundial dd of=/dev/rmt0 obs=20b
does not produce the bug. If you were to use the -n option in a case
like this, rsh would incorrectly read from /dev/null instead of from
the pipe.
For most purposes, ssh(1) is preferred over rsh.
Dec 23, 2008 RSH(1)
