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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.
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..
•Information About Warm Reload
•Configuration Examples for Cisco IOS Warm Reload
•Feature Information 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.
To use the warm-reboot functionality, you should understand the following concepts:
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).
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.
This section contains the following procedures:
•Reloading Your System Without Overriding the Warm-Reload Functionality
Use this task to configure your router for a warm reload in global configuration mode.
1. enable
2. configure terminal
3. warm-reboot [count number] [uptime minutes]
4. exit
5. show warm-reboot
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.
1. enable
2. reload [[warm] text | [warm] in [hh:]mm [text] | [warm] at hh:mm [month day | day month] [text] | [warm] cancel]
3. show reload
This section contains the following configuration example:
•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
The following sections provide references related to the Warm Reload feature.
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Additional information on rebooting your router |
Rebooting and Reloading - Configuring Image Loading Characteristics |
Additional booting commands |
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None |
— |
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None |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
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None |
— |
The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS Configuration Fundamentals Command Reference at http://www.cisco.com/en/US/docs/ios/fundamentals/command/reference/cf_book.html. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.
•reload
•show warm-reboot
•warm-reboot
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.
Table 1 lists the release history for this feature.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.
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Warm Reload |
12.3(2)T |
The Warm Reload feature allows users to reload their routers without reading images from storage. The following sections provide information about this feature: •Information About Warm Reload |