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Reloading Your System Without Overriding the Warm-Reload Functionality
Configuration Examples for Cisco IOS Warm Reload
Warm Reload Configuration: Example
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.
Feature History for Warm Reload
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.
Contents
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Information About Warm Reload
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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
To use the warm-reboot functionality, you should understand the following concepts:
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
This section contains the following procedures:
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Configuring a Warm Reload
Use this task to configure your router for a warm reload in global configuration mode.
SUMMARY STEPS
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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.
SUMMARY STEPS
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DETAILED STEPS
Configuration Examples for Cisco IOS Warm Reload
This section contains the following configuration example:
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Warm Reload Configuration: Example
The following example shows how to enable and verify a warm reboot:
Router#(config) warm-reboot count 10 uptime 10Router#(config) exit!Router# show warm-rebootWarm Reboot is enabledStatistics:10 warm reboots have taken place since the last cold rebootXXX KB taken up by warm reboot storageAdditional References
The following sections provide references related to the Warm Reload feature.
Related Documents
Standards
MIBs
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
Technical Assistance
Command Reference
This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.3 T command reference publications.
reload
To reload the operating system, use the reload command in EXEC mode.
reload [[warm] [/verify | /noverify] text | [warm] [/verify | /noverify] in [hh:]mm [text] | [warm] [/verify | /noverify] at hh:mm [month day | day month] [text] | [warm] [/verify | /noverify] cancel]
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
The reload command halts the system. If the system is set to restart on error, it reboots itself. Use the reload command after configuration information is entered into a file and saved to the startup configuration.
You cannot reload from a virtual terminal if the system is not set up for automatic booting. This prevents the system from dropping to the ROM monitor and thereby taking the system out of the remote user's control.
If you modify your configuration file, the system prompts you to save the configuration. During a save operation, the system asks you if you want to proceed with the save if the CONFIG_FILE variable points to a startup configuration file that no longer exists. If you say "yes" in this situation, the system goes to setup mode upon reload.
When you schedule a reload to occur at a later time, it must take place within approximately 24 days.
The at keyword can be used only if the system clock has be set on the router (either through NTP, the hardware calendar, or manually). The time is relative to the configured time zone on the router. To schedule reloads across several routers to occur simultaneously, the time on each router must be synchronized with NTP.
To display information about a scheduled reload, use the show reload EXEC command.
The warm Keyword
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. The warm keyword configures the router for warm reboot, which allows a Cisco IOS image to reload without ROMMON intervention. That is, read-write data is saved in RAM during cold startup and restored during a warm reboot. Warm reboot allows the router to reboot quicker than conventional rebooting (where control is transferred to ROMMON and back to the image) because nothing is copied from flash to RAM.
The /verify and /noverify Keywords
If the /verify keyword is specified, the integrity of the image will be verified before it is reloaded onto a router. If verification fails, the image reload will not occur. Image verification is important because it assures the user that the image is protected from accidental corruption, which can occur at any time during transit, starting from the moment the files are generated by Cisco until they reach the user.
The /noverify keyword overrides any global automatic image verification that may enabled via the file verify auto command.
Examples
The following example immediately reloads the software on the router:
Router# reloadThe following example reloads the software on the router in 10 minutes:
Router# reload in 10Router# Reload scheduled for 11:57:08 PDT Fri Apr 21 1996 (in 10 minutes)Proceed with reload? [confirm]Router#The following example reloads the software on the router at 1:00 p.m. today:
Router# reload at 13:00Router# Reload scheduled for 13:00:00 PDT Fri Apr 21 1996 (in 1 hour and 2 minutes)Proceed with reload? [confirm]Router#The following example reloads the software on the router on April 20 at 2:00 a.m.:
Router# reload at 02:00 apr 20Router# Reload scheduled for 02:00:00 PDT Sat Apr 20 1996 (in 38 hours and 9 minutes)Proceed with reload? [confirm]Router#The following example cancels a pending reload:
Router# reload cancel%Reload cancelled.The following example shows how to configure the router for warm reboot at 4:00 today:
Router# reload warm at 4:00
The following example shows how to specify image verification via the /verify keyword before reloading an image onto the router:
Router# reload /verifyVerifying file bootflash:c7200-kboot-mz.121-8a.E%ERROR:Signature not found in file bootflash:c7200-kboot-mz.121-8a.E.Signature not present. Proceed with verify? [confirm]Verifying file disk0:c7200-js-mz ......................................................................................................................................Done!Embedded Hash MD5 :CFA258948C4ECE52085DCF428A426DCDComputed Hash MD5 :CFA258948C4ECE52085DCF428A426DCDCCO Hash MD5 :44A7B9BDDD9638128C35528466318183Signature VerifiedProceed with reload? [confirm]nRouter#
Related Commands
show warm-reboot
To display the statistics for attempted warm reboots, use the show warm-reboot command in privileged EXEC mode.
show warm-reboot
Syntax Description
This command has no arguments or keywords.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Use the show warm-reboot command to see if warm rebooting is enabled, and, if so, how many warm reloads have occurred and how much space in kilobytes (KB) is consumed by warm-reboot storage, which is the RAM area used to store the data segment that enables warm reloading to function.
Examples
The following example is sample output from the show warm-reboot command:
Router# show warm-rebootWarm Reboot is enabledStatistics:10 warm reboots have taken place since the last cold rebootXXX KB taken up by warm reboot storageRelated Commands
warm-reboot
To enable a router to warm-reboot, use the warm-reboot command in global configuration mode. To disable warm rebooting, use the no form of this command.
warm-reboot [count number] [uptime minutes]
no warm-reboot count number uptime minutes
Syntax Description
Defaults
Warm rebooting is disabled.
If warm rebooting is enabled, the default value for the count number option is 5 times, and the default value for the uptime minutes option is 5 minutes.
Command Modes
Global configuration
Command History
Usage Guidelines
Use the warm-reboot command to enable the router to reload a Cisco IOS image without ROM monitor mode (ROMMON) intervention, in which the image restores read-write data from a previously saved copy in the RAM and starts execution from that point. Unlike a cold reboot, this process does not involve a flash to RAM copy or self-decompression of the image.
Note
Note
Examples
The following example shows how to enable a warm reboot on the router:
Router#(config) warm-reboot count 10 uptime 10Related Commands
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
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