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rsh(1)

Name
     rsh, remsh, remote_shell - remote shell

Synopsis
     rsh [-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  exe-
     cutes  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.  Interrupt,  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 Ker-
     beros  V5 for authentication. Encryption of the network ses-
     sion traffic is also possible. The rsh session can  be  ker-
     berized   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 dis-
     cussed in the OPTIONS section below. If Kerberos authentica-
     tion  is used, authorization to the account is controlled by
     rules in krb5_auth_rules(5). If  this  authorization  fails,
     fallback  to  normal rsh using rhosts occurs only if the -PO
     option is used explicitly on the command line or  is  speci-
     fied  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 inter-
     preted 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 (Ker-
                    beros  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  creden-
                    tials  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  net-
                    work  sign  on  trust beyond one system. This
                    option is  mutually  exclusive  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 unfor-
                    tunate 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 terminal, 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" proto-
                    col 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 host-
                name.

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 authentica-
     tion.


     Hostnames are given in the hosts database, which can be con-
     tained  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  any-
     thing  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, 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
     authorization  list  in a file .k5login in their home direc-
     tory. Each line in this file should contain a Kerberos prin-
     cipal name of the form principal/instance@realm. If there is
     a ~/.k5login file, then access is granted to the account  if
     and  only  if the originater user is authenticated to one of
     the principals named in the ~/.k5login file. Otherwise,  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 per-
     mits  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
     username  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  database;  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  attri-
     butes:



     tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i)  ATTRI-
     BUTE             TYPEATTRIBUTE            VALUE            _
     Availabilityservice/network/network-clients _ CSIEnabled

See Also
     on(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), largefile(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 compromise the security of the  entire  sys-
     tem.


     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  argu-
     ably  wrong,  but currently hard to fix for reasons too com-
     plicated 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 obvious. 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  terminates  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 pipe-
     line  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.
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