How to Use the Command 'nvram' (with Examples)

The nvram command is a powerful tool that enables users to manage firmware variables stored in the non-volatile random-access memory (NVRAM) of Apple computers. This memory stores configuration settings that need to persist even when the computer is powered off. The nvram command provides a means to view, modify, delete, or reset these values as needed, often aiding in troubleshooting, system configuration, or resetting hardware settings.

Use Case 1: Print All the Variables Stored in the NVRAM

Code:

nvram -p

Motivation:

Printing all the variables stored in the NVRAM is beneficial for system administrators or users when they want to audit current system settings or diagnose issues related to system startup, hardware configurations, or other persistent settings. It provides a clear overview of all settings at once, which is useful for troubleshooting or documenting system configurations.

Explanation:

• nvram: Invokes the command.
• -p: Stands for “print,” instructing the command to display all the stored NVRAM variables in a human-readable format.

Example Output:

The output will be a list of key-value pairs representing current NVRAM settings.

boot-args    debug=0x144
SystemAudioVolume    %80
BacklightLevel    %00

Use Case 2: Print All the Variables Stored in the NVRAM Using XML Format

Code:

nvram -xp

Motivation:

Using XML format to print all the NVRAM variables can be particularly advantageous for developers or advanced users who might want to further process the output programmatically. XML provides structured data that can be easily parsed, transformed, or integrated into other systems or processes.

Explanation:

• nvram: Invokes the command.
• -xp: Combines the “print” flag with “XML,” specifying that the output should be presented in XML format.

Example Output:

The output will be an XML-formatted list of the NVRAM variables.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>boot-args</key>
    <string>debug=0x144</string>
    <key>SystemAudioVolume</key>
    <data>l80=</data>
    <key>BacklightLevel</key>
    <data>lAA=</data>
</dict>
</plist>

Use Case 3: Modify the Value of a Firmware Variable

Code:

sudo nvram name="value"

Motivation:

Modifying the value of a firmware variable is crucial when users need to change system behavior or settings that are defined at a hardware level. For instance, changing boot arguments can enable or disable certain debugging features or alter the boot configuration, which can be instrumental in more technical troubleshooting scenarios or system tuning.

Explanation:

• sudo: Grants administrative privileges necessary to modify NVRAM settings.
• nvram: Invokes the command.
• name="value": Specifies the name of the variable to change and its new value.

Example Output:

No output is shown if successful, indicating the variable was updated.

Use Case 4: Delete a Firmware Variable

Code:

sudo nvram -d name

Motivation:

Deleting a firmware variable is useful when certain settings or configurations need to be reset to their default state. This can be necessary in resolving conflicts caused by custom settings or reverting changes made for temporary troubleshooting purposes.

Explanation:

• sudo: Grants administrative privileges needed for modifying NVRAM.
• nvram: Invokes the command.
• -d: Indicates deletion.
• name: Specifies the name of the variable to be removed.

Example Output:

Successful execution typically results in no output, signifying the variable was deleted.

Use Case 5: Clear All the Firmware Variables

Code:

sudo nvram -c

Motivation:

Clearing all firmware variables is often used as a last resort to restore default system settings, especially when facing persistent hardware or startup issues. This acts as a factory reset for the NVRAM, which can help resolve settings-related conflicts or errors.

Explanation:

• sudo: Provides the necessary administrative rights.
• nvram: Calls the command.
• -c: Stands for “clear,” directing the command to erase all NVRAM variables.

Example Output:

Completion without any errors serves as a confirmation that all variables have been cleared.

Use Case 6: Set a Firmware Variable From a Specific XML File

Code:

sudo nvram -xf path/to/file.xml

Motivation:

Setting a firmware variable from a specific XML file can streamline the process of reconfiguring systems, particularly if the desired settings are complex or need to be replicated across multiple systems. This functionality allows importing predefined configurations smoothly via XML.

Explanation:

• sudo: Provides administrative access required for this operation.
• nvram: Initiates the command.
• -xf: Designates an external XML file from which to read the variables.
• path/to/file.xml: Indicates the path to the XML file containing the desired NVRAM configurations.

Example Output:

If executed successfully, no output is returned, confirming that settings from the XML file were applied.

Conclusion:

The nvram command offers a comprehensive toolset for managing firmware variables on Apple systems. Mastering its use can significantly support system administration, allowing for effective viewing, modifying, and resetting of persistent system configurations stored in NVRAM.