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POWER SOLUTIONS March 200476
Remotely Managing UNIX and Linux Servers Using the
Dell RAC Serial/Telnet ConsoleIntroduced in the 3.0 release of Dell remote access controller (RAC) firmware, the RAC
serial/telnet console provides administrators with a standard serial console for remotely
managing Dell PowerEdge servers running UNIX or Linux operating systems. The
console offers system power management capabilities, preoperating system redirec-
tion capabilities, and support for kernel-mode messaging.
Dell remote access controllers (RACs) provide remote
systems management capabilities on supported Dell
PowerEdge servers. Although four types of RACs are
availableDell Remote Access Card III (DRAC III),
DRAC III/XT, Embedded Remote Access (ERA), and
Embedded Remote Access Option (ERA/O)they share
many of the same features and are supported by a common
software stack, which is part of Dell OpenManage Server
Administrator.
One new feature introduced in the 3.0 release of
RAC firmware is the RAC serial/telnet console, which
provides administrators with a standard serial console
for remote management of servers running UNIX or
Linux operating systems. Dell has enhanced its stan-
dard serial console with new functionality, none of
which requires custom software to be installed or run-
ning on the host:
System power management to enable power up,power down, power cycle, or reset
Redirection of preoperating system firmware suchas BIOS screens
Support for kernel-mode messaging using SysRqmagic keys
This article explains how the RAC serial/telnet con-
sole is implemented, provides details on how to config-
ure the console, and includes an example of how to set
up the IT environment for optimal console performance.
Understanding the functionality of the
RAC serial/telnet console
The RAC serial/telnet console provides a means by which
administrators can access the ttyS1 serial console and
video console of a UNIX or Linux host through either a
serial connection (using a VT-100 or ANSI client) or a LAN-
based Telnet connection. The RAC serial/telnet console pro-
vides a rich set of commands for performing system power
management tasks, configuring the RAC, and viewing RAC
and system logs. The serial/telnet console uses the same
set of commands as the Racadm command-line utility that
originally was part of the RAC software stack. Therefore,
administrators need not learn a new set of commands to
use the RAC console.
The RAC acts as a gate between its PowerEdge host
system and the remote administrator, providing optimal
console-redirection performance combined with user-
level security. Depending on the hardware interfaces
and support offered by its host, the RAC can provide
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access to the host console through a serial connection to the RAC,
a Telnet connection, or both. For example, provided that the
RAC is properly configured, the Dell PowerEdge 2650 server offers
connectivity using either a VT-100 or ANSI serial client or a LAN-
based telnet client.
As shown in Figure 1, the RAC hardware features two serial inter-
faces (RAC serial 1 and RAC serial 2) and one video interface
(RAC video interface). The RAC serial 1 interface is used for host-
to-RAC serial communication; the RAC serial 2 interface is used for
RAC-to-client communication. Thus, administrators must properly
set up two baud rates (baud_rate_1 and baud_rate_2) to gain remote
access to the serial console on the host. Baud_rate_1 in the RAC
configuration must be in sync with the Linux ttyS1 baud rate.
Baud_rate_2 must be in sync with the baud rate of the VT-100 or
ANSI client. Any mismatch between these values will make the
RAC serial/telnet console unusable. Note that baud_rate_1 andbaud_rate_2 are not necessarily set to the same value.
For optimal performance, Dell recommends setting baud_rate_1
to 57,600 bps and baud_rate_2 to 115,200 bps, as well as enabling
hardware flow control for the host. RAC relies on hardware flow
control to avoid dropped characters during serial communication;
flow control enables the host to respond to Request To Send/Clear
To Send (RTS/CTS) signals.
Regardless of whether a serial or Telnet connection is established
with the RAC, the console will present the user with a login prompt.
The login is authenticated against the RAC user database, which
resides on the RAC. Because the authentication is RAC-based, not
host-based, administrators can log in to the RAC console even on
a dead server, provided that the server has power. Once authenti-
cated, the administrator connects to the serial console using the
connect com2 command, or to the video console of the host using
the connect video command.
To maintain security, all users are not granted all privileges.
All administrators should be able to access the serial and video
consoles of the host. However, only the root user can power up
the system or configure the RACfor instance, to change a baud
rate. In addition, the root users password and location within the
RAC user database can be changed.
Configuring the RAC serial/telnet console
To set up the RAC serial/telnet console, the following RAC configu-
ration parameters need to be modified in the following sequence:
1. Upgrade the RAC firmware to version 3.0.
2. Upgrade the host system BIOS to the latest version available,
or check to make sure that the current system BIOS supports
the RAC serial/telnet console.
3. Configure and enable the RAC serial/telnet console by saving
the following sample RAC configuration in a text file (for
instance, rac.cfg) and then applying the configuration using
the Racadm interface:
#
# Object Group "cfgSerial"
#
[cfgSerial]
cfgSerialBaudRate=115200
cfgSerialConsoleEnable=1
cfgSerialConsoleQuitKey=,./
cfgSerialTelnetEnable=1
#
# Object Group "cfgRacTuning"
#
[cfgRacTuning]
cfgRacTuneHostCom2BaudRate=57600
The preceding sample configuration file will:
Enable the RAC serial console
Enable the RAC telnet console
Set the RAC-to-client baud rate to 115,200 bps
Set the host-to-RAC baud rate to 57,600 bps
Set the console quit key sequencewhich allows theadministrator to exit the host ttyS1 serial console or
video console redirection and go back to the RAC
serial/telnet consoleto ,./ (comma dot slash)
In the sample configuration file, the names in square brackets
are the groups into which the various configuration parameters
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Telnet clientVT-100 client
Host serialinterface
RAC serial 1(baud_rate_1)
RAC firmware
RAC serial 2(baud_rate_2)
RAC videointerface
RAC networkinterface
card (NIC)
Host videointerface
COM2 RS-232circuitry and
DB-9 connector RAC
Null modem cable LAN
Figure 1. RAC serial/telnet console configuration on PowerEdge 2650 server
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are organized. Refer to theDell Remote Access Controller
Racadm Users Guide for additional information on RACconfiguration parameters.
4. Use the following racadm command to apply these changes:
racadm remote connect options config f
config filename
where remote connect options is -r rac_ip_addr
-u root p passwordand config filename is the name of
the configuration file (for instance, rac.cfg). The remote
connect options variable is needed only for executing
Racadm remotely, for example when configuring a remote
RAC from a management station over a LAN. From the
RACs host console, administrators need not use this vari-
able because Racadm can communicate directly with the
RAC that exists in that system.
5. Reset the RAC using the following command to make the
changes effective:
racadm remote connect options racreset
6. Reboot the RAC host, enter the BIOS configuration page,
and select Integrated Devices. On the PowerEdge 2650,
verify that Serial Port 2 is set to COM2. On the
PowerEdge 1750, verify that Serial Port 1 is set to Off.
7. Select Console Redirection from the main BIOS configu-
ration page. The three settings should be configured as
follows for the PowerEdge 2650 server:
Console Redirection: Serial Port 2
Remote Terminal Type: VT-100
Redirection After Boot: Enabled
For the PowerEdge 1750 server, the administrator must
choose RAC instead of Serial Port 2.
8. Save the changes and reboot the system. The system reboot
is important because it allows the RAC and the BIOS to syn-
chronize their communication parameters. Depending on the
specific configuration of a system, the RAC may not redirect
BIOS screens if the BIOS and the RAC do not sync up.
Because the BIOS and the RAC synchronize when the system
boots, at least one system boot needs to occur after the
administrator enables and configures the RAC serial/telnet
console. No additional reboots are required thereafter.
9. After both the RAC and the BIOS are in sync, at least three
Linux files must be changed to enable ttyS1 serial console
redirection: /etc/grub.conf or /etc/lilo.conf (depending on
the bootloader used), /etc/inittab, and /etc/securetty. How-
ever, none of these changes is required if only access to the
host video console is needed. Required modifications to the
three files are shaded in Figures 2, 3, and 4.
Note: In Figure 2, the Linux host baud rate is set to
57,600 bps in the /etc/grub.conf or /etc/lilo.conf file,
which is in sync with the host-to-RAC baud rate set in
the sample RAC configuration text file (rac.cfg) in the
SYSTEMS MANAGEMENT
POWER SOLUTIONS March 200478
serial --unit=1 --speed=57600
terminal --timeout=10 console serial
title Red Hat Linux Advanced Server (2.4.9-e.3smp)
root (hd0,0)kernel /boot/vmlinuz-2.4.9-e.3smp ro root=/dev/sda1 hda=ide-scsi console=tty0 console=ttyS1,57600
initrd /boot/initrd-2.4.9-e.3smp.img
title Red Hat Linux Advanced Server-up (2.4.9-e.3)
root (hd0,0)
kernel /boot/vmlinuz-2.4.9-e.3 ro root=/dev/sda1 s
initrd /boot/initrd-2.4.9-e.3.im
# Run gettys in standard runlevels
co:2345:respawn:/sbin/agetty h -L 57600 ttyS1 vt100
1:2345:respawn:/sbin/mingetty tty1
2:2345:respawn:/sbin/mingetty tty2
3:2345:respawn:/sbin/mingetty tty3
4:2345:respawn:/sbin/mingetty tty4
5:2345:respawn:/sbin/mingetty tty5
6:2345:respawn:/sbin/mingetty tty6
Figure 2. Modifications to /etc/grub.conf to enable ttyS1 serial console redirection
Figure 3. Modifications to /etc/inittab to enable ttyS1 serial console redirection
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previous example. The same host-to-RAC baud rate of
57,600 bps is used when invoking the agetty command
(see Figure 3). Nevertheless, the h flag, when present on
the same line, forces agetty to use hardware flow controlfor the communication. As explained in Understanding
the functionality of the RAC serial/telnet console, the
RAC relies on hardware flow control for reliable serial
communication with its host.
10. After modifying the files, restart agetty or reboot the RAC
host to complete the configuration process. The RAC is now
ready to redirect its host serial console.
Optimizing the IT environment for serial/telnet console performance
Depending on the IT environment and the hardware capabili-
ties of the RAC host, administrators may choose to use either
a serial connection or a Telnet connection to the RAC. Many
organizations use serial concentrators, or terminal servers, to
consolidate multiple serial connections. Unfortunately, not all
serial concentrators are alike: they vary with respect to
configuration parameters, configuration interface, and wiring.
Most serial concentrators use an RJ-45toDB-9 adapter. For
connection schematics for two adapters that can be used to
connect a RAC to a Cisco 2511 serial concentrator, visit Dell
Power Solutions online at http://www.dell.com/magazines_extras.
Regardless of whether a serial or Telnet connection is used,
administrators must first log in to the RAC prompt to view
RAC system logs, then redirect either ttyS1 serial consoles or
video consoles, andif logged in as rootconfigure the RAC or
reboot the system. Some organizations also use SysRq magic
keys to capture kernel-level status information as part of the
IT support process.
The RAC serial/telnet console supports SysRq functionality,
although the methodology is slightly different for a remote con-
nection than for a local console. At the local console, the adminis-
trator normally would press the Alt + SysRq + magic_key sequence
to get the expected SysRq output. If using the remote connection, the
administrator enters the send break command on the serial or
telnet client and then presses one of the SysRq magic keys. This
SysRq functionality will work only when redirecting ttyS1; it will
not be present if the administrator connects to the remote con-
sole and then redirects the hosts video console. To gain access to
ttyS1, administrators must use the connect com2 command in the
RAC console.
For example, an administrator may want to collect as much
information as possible to assist with a problem diagnosis and
to store this information in a file. Generally the problems encoun-
tered can be divided into two areas: an unresponsive system or
a system that has crashed. In either case, the administrator may
need to connect to the RAC and then access the host ttyS1 serial
console or video console. If the system appears to be hung, the
administrator probably requires output from the b, m, p,
and t SysRq magic keys. Once that information is gathered, theRAC can be used remotely to restart the server, after which the
administrator can examine the boot screens for further clues. If
the system appears to have crashed, then the best approach may
be to examine the RAC system logs. Depending on the state of
the system, the administrator may choose to use the RAC to
restart the server.
Enabling server recovery and configuration management
through RAC
The RAC serial/telnet console can be a valuable remote management
tool for IT administrators. Besides supporting industry-wide systems
management practices, the RAC serial/telnet console is enhanced with
features that allow for server recovery, system configuration man-
agement, and RAC configuration management. The RAC serial/telnet
console is software-independent and helps administrators interact
smoothly with the RAC host.
Aurelian Dumitru ([email protected]) is a senior software engineer with the Custom
Solutions Engineering team at Dell, where he works to deploy and customize systems man-
agement for medium to large enterprises. Before joining the Custom Solutions Engineering
team, he held the lead engineer position for the Remote Management Delivery team.
Aurelian has 12 years of experience in hardware, software, and system design and integra-
tion. He has an M.S.E.E. degree from the Technical University of Iasi, Romania.
SYSTEMS MANAGEMENT
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Figure 4. Modifications to /etc/securetty to enable ttyS1 serial console redirection
.
.
.
tty8
tty9
tty10
tty11
ttyS1
F O R M O R E I N F O R M A T I O N
Dell Remote Access Controller Racadm Users Guide :
http://docs.us.dell.com/docs/software/smdrac3/RAC/en/index.htm
Remote serial console how-to:
http://www.faqs.org/docs/Linux-HOWTO/Remote-Serial-Console-HOWTO.html