Software Maintenance Upgrade (SMU)
The Software Maintenance Upgrade (SMU) is a package that can be installed on a system to provide a patch fix or security resolution to a released image for a specific defect in order to respond to immediate issues. It does not contain new features.
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SMU installation was supported in both bundle boot and install mode. From Cisco IOS XE Release 17.9.x, SMU installation will be stopped if the router is booted up in bundle mode. If the router is booted up in install mode, SMU installation will keep working as it is in previous releases. |
Some of the caveats of the SMU are:
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Provided on a per release, per component basis and is specific to the platform. SMU versions are synchronized to the package major, minor, and maintenance versions they upgrade.
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SMUs are not an alternative to maintenance releases. All defects fixed by SMUs are then automatically integrated into the upcoming maintenance releases.
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The Cisco IOS XE platform internally validates the SMU compatibility and does not allow you to install non-compatible SMUs. This is based on rules/limitations for a SMU change-set.
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An SMU provides a significant benefit over classic IOS software as it allows you to address the network issue quickly while reducing the time and scope of the testing required.
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SMU is a method to fix bugs in an existing release, and allows the application of a PSIRT fix in an existing release.
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SMU is NOT an upgrade path from release X to maintenance release X.1
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SMU is NOT an upgrade path from release X to release Y
The device only supports “Hot Patching”. This means:
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The running image is modified in-place or in-service
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This avoids downtime and interruption of service
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The updated code to fix the defect is written in a different location, and where the patch redirects the program run