Hardware Management Console
Hardware Management Console
A Hardware Management Console (HMC) is an appliance used to manage Power Systems servers. In particular, it may be used to create or change virtual machines (LPARs), including dynamically altering the hardware assigned to an LPAR (add and remove) without rebooting the operating system running in the LPAR. Please note that the diagram illustrates use of dual redundant HMCs, but one HMC is sufficient if redundancy is not required.
An HMC is an inexpensive custom Intel appliance (stand-alone or 1U rack) with a serial (RS232) card (connected to POWER4 servers) or an Ethernet card (connected to service processors of POWER5, POWER6, and POWER7 servers).
One HMC can control multiple Power Systems servers. See HMC READMEs for the maximum number of servers which can be managed by a single HMC. For example, see the HMC V126.96.36.199 cumulative README for the maximum number of Power Systems servers (48, with a maximum of 1024 total LPARs) which can be managed by HMC Version 7.7.3. If an HMC manages only one Power Systems server, a direct Ethernet connection can be used (no LAN switch is required).
An HMC appliance runs a heavily customized version of Linux provided by IBM. Access to the root userid is disabled by default. The hscroot userid has all the necessary privileges to manage and use the HMC.
An HMC is necessary only to manage Power Systems servers. Once configured, Power Systems servers continue to operate normally even if the HMC is shut down. But please note that larger Power Systems servers (Power 760 and above) require an HMC to successfully power up. Once a server is powered up, the HMC is no longer required for the server to continue to operate normally.
When a modern Power Systems server (managed via a Flexible Service Processor/FSP) is configured, configuration information is saved in both the FSP and the HMC. So if an HMC is replaced, the new HMC can acquire existing configuration information from the FSP in each managed Power Systems server to which it is attached.
In addition to managing Power Systems servers, an HMC also provides access to the console of every virtual machine (LPAR) on every managed server. So there is no need for a terminal server to access virtual machine consoles. And even when a Power Systems server is dedicated (running a single copy of an operating system), the operating system must run in a virtual machine and the HMC can be used to access the console of that virtual machine. (Power Systems virtualization has very low overhead, so even if it were possible, there would be little benefit to running an operating system directly on Power Systems hardware.)
An HMC is also a service focal point, gathering hardware error information and forwarding it to IBM (calling home).
Please note that if a virtual machine is misconfigured and creates a network storm (or other serious network issue), it is very important to be able to access the virtual machine's console to correct the misconfiguration. If an HMC is connected to a Power Systems server via the same Ethernet network as that used by virtual machines, then the network issue will prevent access to the virtual machine's console. Very bad. It is therefore very important that each HMC is connected to its managed Power Systems servers via a dedicated Ethernet network (or private VLAN).
In addition to its private connections to each managed server, each HMC must be able to communicate with each virtual machine. Please see the Types of HMC network connections article for additional information. Please note that the HMC to managed system connection should be private. On the other hand, an HMC's connection to logical partitions (LPARs/virtual machines), to remote users, to other HMCs (if necessary), and to service and support are often via a single public enterprise Ethernet network.
Please note that redundant HMCs illustrated in the diagram above must be configured to use two different DHCP IP address ranges and must be able to communicate with each other, as discussed in the HMC as a DHCP server article.
An HMC can be used via either an X-Windows graphical user interface (GUI) or an SSH command line interface (CLI). Please note that when a virtual machine console is accessed via the HMC GUI, the console session is unencrypted, creating security concerns. System administrators are therefore advised to access virtual machine consoles using the CLI vtmenu command after logging in to the HMC via an SSH session, which is always encrypted. By default, an HMC does not accept SSH sessions. Please see the Configuring the Version 7 HMC to Accept SSH Connections and Remote Commands Technote for a simple procedure to configure HMC V7 to accept SSH sessions.
More HMC Pages in this WIKI
- HMC hints
- HMC reliable communication, sluggish performance, & doing without
- HMC remote client
- HMC and system setup
- LinuxP:ASMI Access
- LinuxP:Firmware Update Control
- LinuxP:Command Line Reboot
- LinuxP:Create LPAR using command line
- LinuxP:Network boot from Open Firmware
- LinuxP:Network boot from HMC - lpar_netboot
- LinuxP:HMC command line
Key sites for more information
For information regarding an HMC running V7 machine code, see the Hardware Management Console Version 7 web page in the IBM Systems Hardware Information Center. For information on using the HMC, follow the link to Managing the Hardware Management Console.
For help when using the HMC command line (after SSHing to the HMC), PDF files can be downloaded for each HMC software level. Each PDF file contains an alphabetical list of HMC commands with the man page for each command. Click here to download. To configure an HMC to accept SSH connections, see the Configuring the Version 7 HMC to Accept SSH Connections and Remote Commands web page. For HMCs running software prior to V7, see the Configuring the Version 6 and Earlier HMC to Accept SSH Connections and Remote Commands web page.
For information regarding an HMC running V6 and V5 machine code, see the Hardware Management Console Version 6 and Version 5 web page in the IBM Systems Hardware Information Center. For information on using the HMC, follow links to Managing the HMC and to Managing your server using the HMC.
For information regarding an HMC running V4 machine code, see the Model 7048 Hardware Management Console for pSeries web page in the IBM Systems Hardware Information Center. For information on using the HMC, follow the link to the eServer Hardware Management Console for pSeries Installation and Operations Guide .
See the Effective System Management Using the IBM Hardware Management Console for pSeries Redbook. From 2003, so somewhat dated.
See the IBM Hardware Management Console (HMC) Best Practices Whitepaper.
See the Hardware Management Console V7 Handbook Redbook.
See the Hardware Management Console (HMC) V7 Technical Update by Ron Barker.