Warm Reload
The Warm Reload feature allows users to reload their routers without reading images from storage. That is, the Cisco IOS image reboots without ROM monitor mode (ROMMON) intervention by restoring the read-write data from a previously saved copy in the RAM and by starting execution without either copying the image from flash to RAM or self-decompression of the image. Thus, the overall availability of your system improves because the time to reboot your router is significantly reduced.
Finding Feature Information in This Module
Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the “Feature Information for Warm Reload” section on page 8 .
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn . An account on Cisco.com is not required..
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Restrictions for Warm Reload
Additional Memory Consumption
Additional memory is consumed because a copy of the initialized variables must be stored for a warm reboot to function. However, to consume as little memory as possible, a copy of the initialized variables is kept in a compressed form, which is marked as “read-only” to prevent corruption.
Software Support Only
A warm reboot should be used only for forced software crashes. Hardware failure of any kind will result in a cold reboot.
Information About Warm Reload
Benefits of Warm Reload
Quicker Router Reload
By eliminating the need to copy an image from flash to RAM and decompress it, the reload time of a router is reduced by 2 to four minutes. The time savings is greater on platforms that use the BOOTLDR images because tha additional step of loading a BOOTLDR image and parsing the configuration file by the BOOTLDR image can be avoided.
Flash Card Removal
The router is not useless if a flash card is removed because it can still reboot as long as it is not forced into a cold reboot (such as a power failure).
Warm Reload Functionality
When encountering a crash, a Cisco IOS image transfers control to ROMMON, which copies the system image from the storage device (which is typically flash) to main memory, decompresses the system image, and transfers control back to Cisco IOS. Warm rebooting allows the image to return to the start of the text segment in memory and restart execution from that point, thereby, eliminating ROMMON intervention. A copy of the initialized variables is kept in memory and is used to overwrite the existing memory location where the initialized variables are stored. Thus, when the CPU returns to the start of the text segment and begins operating, the information is the same as if execution had begun after the binary had been read from flash and decompressed.
How to Use Warm Reload
Configuring a Warm Reload
Use this task to configure your router for a warm reload in global configuration mode.
DETAILED STEPS
Reloading Your System Without Overriding the Warm-Reload Functionality
If you issue the reload command after you have configured the warm-reboot global command, a cold reboot will occur. Thus, if you wish to reload your system, but do not want to override the warm-reboot functionality, you should specify the warm keyword with the reload command. Use this task to configure your router for a warm reboot while you reload your system.
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
|
|
Example: Router> enable |
Enables privileged EXEC mode.
|
|
|
Example: Router# reload warm at 10:30 |
Reloads the operating system. You must issue the warm keyword if you do not want to override the warm reboot functionality when you reload the router. |
|
|
Example: Router# show reload |
Displays the reload status on the router. |
Configuration Examples for Cisco IOS Warm Reload
Warm Reload Configuration Example
The following example shows how to enable and verify a warm reboot:
Router#(config) warm-reboot count 10 uptime 10 Router#(config) exit ! Router# show warm-reboot Warm Reboot is enabled Statistics: 10 warm reboots have taken place since the last cold reboot XXX KB taken up by warm reboot storage
Additional References
The following sections provide references related to the Warm Reload feature.
Related Documents
| Related Topic |
Document Title |
|---|---|
| Additional information on rebooting your router |
Rebooting and Reloading - Configuring Image Loading Characteristics |
| Additional booting commands |
Cisco IOS Configuration Fundamentals Command Reference |
Standards
| Standards |
Title |
|---|---|
| None |
-- |
MIBs
| MIBs |
MIBs Link |
|---|---|
| None |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
| RFCs |
Title |
|---|---|
| None |
-- |
Technical Assistance
| Description |
Link |
|---|---|
| Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content. |
Glossary
cold reboot --Process of reloading a Cisco IOS image in which the ROMMON copies the configured image from a storage device, such as flash, into main memory. Thereafter, the image is decompressed and execution is started.
warm reboot --Process of reloading a Cisco IOS image without ROMMON intervention in which the image restores read-write data from a previously saved copy in the RAM and starts execution. Unlike a cold reboot, this process does not involve a flash to RAM copy or self-decompression of the image.
 Note |
Refer to Internetworking Terms and Acronyms for terms not included in this glossary. |
Feature Information for Warm Reload
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
| Table 1 | Feature Information for Warm Reload |
| Feature Name |
Releases |
Feature Information |
|---|---|---|
| Warm Reload |
12.3(2)T 12.2(18)S 12.2(27)SBC |
The Warm Reload feature allows users to reload their routers without reading images from storage. The following sections provide information about this feature:
|
Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.
Feedback