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The REMSH Client Functionality
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by Cas Caswell Commercial Systems Division

An Overview of the REMSH Service

The remote shell, or REMSH, service is used to connect to a specified host and execute a command on that remote host. This article describes:

  • Verifying installation

  • Configuring the REMSH client

  • Using REMSH

  • Troubleshooting REMSH

  • Implementation differences between REMSH on MPE/iX and REMSH for HP-UX

  • Available documentation

REMSH is the same service as rsh on BSD UNIX systems. The name was changed due to a conflict with the existing command rsh (restricted shell) on System V UNIX systems.

REMSH allows a user to connect to the remote system and execute a command on that remote system. Output from the remote command is sent to the REMSH standard output so the user can see the results of the command.

Verifying Installation

The REMSH client is part of the Internet Services product with release C.55.03. To verify that REMSH is available on your system, use NMMAINT,73 to list versions of the Internet Services.

Configuring the REMSH Client

There is only one file on the MPE/iX system that you will need to change in order to allow use of the REMSH client. That is the file services.net.sys. However, there are some files that will need to be configured on the remote UNIX systems.

Editing the Services File

The services file associates official service names and aliases with the port number and protocol the services use. To enable REMSH use, you must edit the services file.

To edit the services file:

  1. You may edit the SERVICES.NET.SYS file from MPE/iX. Open the services file with a text editor.

  2. Verify that the following line exists in the file.

    shell   514/tcp  cmd   # remote command, no passwd used

    1. Add the line if it does not exist.

    2. If the line already exists in the file and is preceded by a pound symbol (#), delete the # and any spaces before the service name to enable the service.

  3. Save the file and exit the editor program.

UNIX Configuration

The REMSH service does not prompt for user ID and passwords. That information is handled via the command line parameters and configuration on the UNIX host. See the using REMSH section for details on how the user id is determined and passed to the UNIX host.

Password information is bypassed by use of a .rhosts file in the remote user's home directory or by use of the file /etc/hosts.equiv. See the man pages of the UNIX system for details on how to set up a /etc/hosts.equiv file. A user's .rhosts file entry will consist of the MPE/iX system name and user id.

For example, to access the HP-UX system "taltos" as user "cawti," from the MPE/iX system "jhereg" while user MANAGER.SYS, set up a host equivalency via the /etc/hosts.equiv file, or you will create a .rhosts file in the home directory of user "cawti" on the "taltos" machine. The .rhosts file would look like this:

jhereg  MANAGER.SYS

This will cause the REMSH daemon on the UNIX host to allow a connection from MANAGER.SYS on "jhereg" to the "cawti" user on the host "taltos." The .rhosts file for user "cawti" would contain an entry for every host and userid that you desired to access the "taltos" host as if they were the user "cawti."

NOTE: The MPE/iX equivalent of the UNIX user id is the User.Account. An artifact of the MPE/iX implementation is that the MPE/iX information is usually reported in upper case. So be sure your .rhosts or /etc/hosts.equiv entries use the MPE/iX user ID information in upper case.

Using REMSH

The REMSH service is accessed by running the REMSH.NET.SYS program. You may do so under the MPE/iX CI or under the Posix shell. While the format of the commands will differ depending on how you run the program, the parameter list remains the same. We'll first look at the parameters and then look at running the program under the Posix Shell or from MPE/iX CI.

For the purposes of explaining the parameters, look at a sample invocation from the Posix shell. Detailed examples of both the Posix shell and MPE/iX invocations will follow later.

From the Posix shell you would invoke the REMSH by typing:

/SYS/NET/REMSH remotehost -l remoteuser  remotecommand

In all cases you must provide a remotehost and a remotecommand. The REMSH program will fail and generate an error message otherwise. Unless the remote system has MPE/iX type userids, you will also need to provide a -l remoteuser parameter as well. Otherwise the remote system will not allow the connection.

remotehost

is the name of the remote host you are attempting to connect to. The host name can be either the official name or an alias as understood by gethostbyname().

remoteuser

is the userid on the remote system you wish to be.

NOTE: The traditional UNIX implementation of REMSH makes the -l remoteuser parameter optional. If you do not provide a -l remoteuser parameter, REMSH takes your current userID and assumes that you wish to connect to the same userID on the remote system. Since the MPE version of the userID is USER.ACCOUNT, and the UNIX equivalent is user, it is unlikely that you will find a user on the remote system to match your id. We recommend that you always provide the -l remoteuser argument to REMSH.
remote- command

is the command that you wish to execute on the remote machine. This command may be a CI command, a program (that meets certain criteria) or a shell script. If remotecommand is not specified, REMSH will terminate and provide a usage message.

NOTE: REMSH cannot be used to run commands that require a terminal interface (such as VI) or commands that read their standard error (such as more).

MPE/iX Examples

To run REMSH from MPE/iX prompt, type:

run remsh.net.sys;info="remotehost -l remoteuser [-n] 
remotecommand"
 
jhereg(PUB): run remsh.net.sys;info="taltos -l cawti -n pwd"
/u2/home/cawti
jhereg(PUB):

Posix Examples

From the Posix Shell prompt, type:

/SYS/NET/REMSH remotehost -l remoteuser [-n] remotecommand
shell/iX> /SYS/NET/REMSH taltos -l cawti -n pwd
/u2/home/cawti
shell/iX>

Since you are running under the Posix shell, there are a number of shell features that you can take advantage of.

Shell metacharacters that are not quoted are interpreted on the local host; quoted metacharacters are interpreted on the remote host. The following command line appends the remotefile to the local file localfile:

SYS/NET/REMSH taltos -l cawti cat remotefile >> localfile

The following command line appends remotefile to the otherremotefile:

/SYS/NET/REMSH taltos -l cawti cat remotefile ">>" otherremotefile

The following command line runs REMSH in the background on the local system, and the output of the remote command comes to your terminal asynchronously:

/SYS/NET/REMSH otherhost -l remoteuser  -n remotecommand

The following command line causes REMSH to return immediately without waiting for the remote command to complete:

/SYS/NET/REMSH otherhost -l remoteuser  -n 
"remotecommand 1>&- 2>&- &"

In REMSH, if the first parameter in its argument vector is not REMSH, it will use the value as a host name. You may symbolically link the host name to the REMSH program. A typical BSD UNIX implementation will have these links under the /usr/hosts directory.

If you have made a symbolic link to the REMSH program that is the host name (that is in our examples, ln -s /SYS/NET/REMSH taltos), you could generate the same result as the first example with the following:

shell/iX>taltos -l cawti -n pwd
/u2/home/cawti
shell/iX>

Troubleshooting REMSH

These are the REMSH messages with an explanation of the meaning and suggested action, if any.

Message

remsh: MPE/iX/X version won't support rlogin or rexec 
functionality
usage: remsh host -l login -n command

Meaning

Be sure to provide a command to execute.

Message

remshd: Login incorrect

Meaning

There is probably an invalid entry in remote .rhosts file. Be sure host name and userid are correct. Userid must be in upper case. Be sure you provided an -l userid parameter, or that the remote system has a userid that matches your MPE/iX logon.

Message

Program requires more capabilities than allowed for the group, the user
of a temporary file, or the hierarchical directory user. (LDRERR 505)
Native mode loader message 505
Unable to load program to be run. (CIERR 625)
 
**** EXEC FUNCTION FAILED; subsys =517; info = 48
ABORT: REMSH.NET.SYS
NM SYS   a.00aa0270 dbg_abort_trace+$24
NM UNKN  150.00366f6c
NM UNKN  2dd.0004bbd8
[1] + Done (134) REMSH hpcsyn24 -l casc -n pwd
  262204        Abort   REMSH

Meaning

The first message is from running REMSH from MPE/iX name space, and the second is from running under the Posix Shell. The cause is typically lack of PM capability on the group where REMSH resides. Since REMSH is in NET.SYS, it is unlikely you will see this problem unless someone changes the capability of the NET.SYS group.

Message

shell/tcp: Unknown service

Meaning

The shell service specification is not present in the services file. Edit /etc/services or SERVICES.NET.SYS to fix.

Message

Can't establish stderr

Meaning

REMSH cannot establish secondary socket connection for stderr.

Message

Couldn't reopen stderr

Meaning

The remote command tried to reopen stderror. This is not allowed under REMSH.

Message

 <system call>: ...

Meaning

Error in executing system call. Appended to this error is a message specifying the cause of the failure.

Implementation Differences

The full remote shell service typically consists of two parts: the REMSH client which allows a user on this machine to access remote hosts, and the remshd server which allows REMSH clients on other hosts to access the local host. Only the REMSH client functionality has been implemented on the MPE/iX system.

The HP-UX version of the REMSH client has an optional -n parameter that tells the client to not read from STDIN. Due to differences between MPE IO and UNIX IO the -n parameter has been hard coded into the MPE/iX client.

The HP-UX REMSH client also allows rlogin and rexec functionality. Since this implementation was designed to address the needs of users attempting to access HP-UX commands and scripts from MPE/iX stream jobs, we chose not to implement any feature needing interactive input with the remote system.



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