rsh(1) rsh(1)
NAME
rsh - remote shell
SYNOPSIS
rsh [-n] [-l username] hostname command
rsh hostname [-n] [-l username] command
hostname [-n] [-l username] command
DESCRIPTION
The rsh command connects to the specified hostname and
executes the specified command.
Files
/etc/hosts
/etc/passwd
/usr/lib/locale/locale/LC_MESSAGES/uxrsh
language-specific message file [See LANG
on environ(5).]
USAGE
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. Interrupt, quit and terminate signals are propagated
to the remote command; rsh normally terminates when the remote
command does.
If you omit command, instead of executing a single command,
rsh logs you in on the remote host using rlogin(1).
Shell metacharacters that are not quoted are interpreted on
the local machine, while quoted metacharacters are interpreted
on the remote machine. See the examples below.
Hostnames are given in the hosts data base, which may be
contained in the /etc/hosts file, the Internet domain name
data base, or both. Each host has one official name (the
first name in the data base entry) and optionally one or more
nicknames. Official host names or nicknames may 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 executed, will invoke a remote shell on
that host. By creating a directory and populating it with
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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.
Each remote machine may have a file named /etc/hosts.equiv
containing a list of trusted host names with which it shares
user names. Users with the same user name on both the local
and remote machine may rsh from the machines listed in the
remote machine's /etc/hosts file without supplying a password.
Individual users may 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. An entry in a remote user's .rhosts
file permits the user named username who is logged into
hostname to use rsh to access the remote machine as the remote
user without supplying a password. 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 host name are not found
in the remote user's .rhosts file, then the remote machine
will prompt for a password. Host names listed in the
/etc/hosts.equiv and .rhosts files must be the official host
names listed in the hosts data base; nicknames may not be used
in either of these files.
To counter security problems, the .rhosts file must be owned
by either the remote user or by a privileged user.
rsh will not prompt for a password if access is denied on the
remote machine unless the command argument is omitted.
Options
rsh takes the following options:
-l username
Use username as the remote user name instead of your
local user name. In the absence of this option, the
remote user name is the same as your local user name.
-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
background without redirecting its input away from the
terminal, it will block even if no reads are posted by
the remote command. The -n option will prevent this.
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The type of remote shell (sh, the restricted shell
/usr/lib/rsh, or other) is determined by the user's entry in
the file /etc/passwd on the remote system.
Examples
The command:
rsh lizard cat lizard.file >> example.file
appends the remote file lizard.file from the machine called
lizard to the file called example.file on the local machine,
while the command:
rsh lizard cat lizard.file ">>" lizard.file2
appends the file lizard.file on the machine called lizard to
the file lizard.file2 which also resides on the machine called
lizard.
Warnings
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 compromise the security of the entire system.
The current local environment is not passed to the remote
shell.
You cannot run an interactive command [such as vi(1)] using
rsh. Use rlogin if you want to do so.
Sometimes the -n option is needed for reasons that are less
than obvious. For example, the command:
rsh somehost dd if=/dev/nrmt0 bs=20b | tar xvpBf -
will put your shell into a strange state. Evidently, what
happens is that the tar terminates before the rsh. The rsh
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
if rsh actually needs to read standard input. For example,
tar cf - . | rsh sundial dd of=/dev/rmt0 obs=20b
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does not produce the bug. If you were to use the -n in a case
like this, rsh would incorrectly read from /dev/null instead
of from the pipe.
Prior to Release 4, the rsh command invoked the restricted
shell. This restricted shell command is /usr/lib/rsh and can
be executed by using the full pathname.
Stop signals stop the local rsh process only; this is arguably
wrong, but currently hard to fix for reasons too complicated
to explain here.
REFERENCES
hosts(4), hosts.equiv(4), named(1M), rlogin(1), vi(1)
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