11 Advanced Topics

This chapter covers topics intended for the advanced user. This chapter addresses the following topics:

•“Enabling Remote Execution with OpenSSH” (page 107)•“Running an X Terminal Session from a Remote Node” (page 107)•“Using the GNU Parallel Make Capability” (page 109)•“Local Disks on Compute Nodes” (page 112)•“I/O Performance Considerations” (page 113)•“Communication Between Nodes” (page 113)

11.1Enabling Remote Execution with OpenSSH

To reduce the risk of network attacks and increase the security of your HP XC system, the traditional rsh, rlogin, and telnet tools are disabled by default, and OpenSSH is provided instead. HP XC systems use the OpenSSH package to provide a more secure environment than the traditional rsh, rlogin, and telnet tools. OpenSSH provides a secure, encrypted connection between your system and the HP XC system.

However, OpenSSH requires, by default, that users enter their password every time that they attempt to access a remote system. When first you use the ssh command to access the system, or when attempting to use a tool such as TotalView to debug an application on the cluster, you may be prompted to enter your password multiple times. To eliminate the multiple requests, use the procedure described below. Alternatively, you can use the ssh_create_shared_keys command, which is described in “Using the Secure Shell to Log In”

There are a number of ways in which to manage an OpenSSH environment. If you have not already established your own procedures, the following procedure will help you to get started. This procedure must be executed by each user, and assumes that your home directory is on a file system that is shared across the cluster.

Log in to your account on the system and execute the following commands. Press the ENTER key in response to all questions.

$ ssh-keygen -t dsa $ cd ~/.ssh

$ cat id_dsa.pub >>authorized_keys $ chmod go-rwx authorized_keys

11.2 Running an X Terminal Session from a Remote Node

This section illustrates running an X terminal session from a remote node. An X terminal session can be invoked through SLURM or through LSF. Note that the procedure described in this section creates an unencrypted X terminal session, which is considered unsecure. The information in this section assumes the following:

•You are on a Linux, UNIX, or UNIX-like machine.•You are on a non-HP XC machine, which is serving your local display.•Your machine is on a trusted network.
Step 1. Determining IP Address of Your Local Machine

To begin, you need to determine the IP address of your monitor's display server (the machine serving your monitor), as shown in the following steps. You will use this IP address in later commands to run the X terminal session.

First, echo the display:

11.1 Enabling Remote Execution with OpenSSH 107