AVML (Acquire Volatile Memory for Linux)

Summary

A portable volatile memory acquisition tool for Linux.

AVML is an X86_64 userland volatile memory acquisition tool written in Rust, intended to be deployed as a static binary. AVML can be used to acquire memory without knowing the target OS distribution or kernel a priori. No on-target compilation or fingerprinting is needed.

Features

• Save recorded images to external locations via Azure Blob Store or HTTP PUT
• Azure Blob Storage uploads retry transient failures via the Azure SDK's default exponential backoff policy (8 attempts, capped at one minute total elapsed).
• Optional page level compression using Snappy.
• Uses LiME output format (when not using compression).

Memory Sources

• /dev/crash
• /proc/kcore
• /dev/mem

If the memory source is not specified on the commandline, AVML will iterate over the memory sources to find a functional source.

NOTE: If the kernel feature kernel_lockdown is enabled, AVML will not be able to acquire memory.

Tested Distributions

• Ubuntu: 12.04, 14.04, 16.04, 18.04, 18.10, 19.04, 19.10, 20.04, 21.04, 22.04
• Centos: 6.5, 6.6, 6.7, 6.8, 6.9, 6.10, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.9
• RHEL: 6.7, 6.8, 6.9, 7.0, 7.2, 7.3, 7.4, 7.5, 7.7, 8.5, 9.0
• Debian: 8, 9, 10, 11, 12
• Oracle Linux: 6.8, 6.9, 6.10, 7.3, 7.4, 7.5, 7.6, 7.9, 8.5, 9.0
• CBL-Mariner: 1.0, 2.0

Subcommands

avml is a single binary with subcommands. Each subcommand is gated by a Cargo feature so a minimal build only includes the capability you need:

Build a minimal acquire-only binary with cargo build --release --no-default-features.

Getting Started

Capturing a compressed memory image

On the target host:

avml acquire --compress output.lime.compressed

Capturing an uncompressed memory image

On the target host:

avml acquire output.lime

Capturing a memory image & uploading to Azure Blob Store

On a secure host with az cli credentials, generate a SAS URL.

EXPIRY=$(date -d '1 day' '+%Y-%m-%dT%H:%MZ')
SAS_URL=$(az storage blob generate-sas --account-name ACCOUNT --container CONTAINER test.lime --full-uri --permissions c --output tsv --expiry ${EXPIRY})

On the target host, execute avml with the generated SAS token.

avml acquire --sas-url ${SAS_URL} --delete output.lime

Streaming a memory image without writing to local disk

For hosts where writing the snapshot to a local file first is undesirable (read-only root, limited disk, forensic chain-of-custody concerns), use the stream subcommand. It picks the memory source once up front (same preference order as acquire's /dev/stdout path — /proc/kcore, then /dev/crash, then /dev/mem; pass --source to override) and writes bytes sequentially to the chosen destination. The source cannot be changed mid-stream, so there is no automatic source fallback.

To Azure Block Blob Storage

avml stream blob ${SAS_URL}

• The block size is derived automatically so the snapshot fits within Azure's per-blob 50,000-block limit. --sas-block-size (MiB) acts as a floor; if the derived minimum is larger, the larger value wins.
• --sas-block-concurrency caps the number of in-flight stage_block calls. Peak RAM is approximately (concurrency + 1) * block_size.
• If the snapshot fails mid-upload, staged blocks are abandoned without being committed; Azure discards them automatically per its standard policy.

To a remote TCP listener

On the collector host:

nc -l 9000 > snapshot.lime

On the target host:

avml stream tcp collector.example.com:9000

avml connects once and writes the snapshot sequentially. If the connection drops mid-stream, the snapshot aborts; there is no resume. No TLS — pair with an SSH tunnel or stunnel for confidentiality and integrity if needed.

Uploading a previously-captured snapshot

avml upload put  ./output.lime ${URL}              # HTTP PUT
avml upload blob ./output.lime ${SAS_URL}          # Azure Block Blob

Capturing a memory image of an Azure VM using VM Extensions

On a secure host with az cli credentials, do the following:

1. Generate a SAS URL (see above)
2. Create config.json containing the following information:

{
    "commandToExecute": "./avml acquire --compress --sas-url <GENERATED_SAS_URL> --delete",
    "fileUris": ["https://FULL.URL.TO.AVML.example.com/avml"]
}

3. Execute the customScript extension with the specified config.json

az vm extension set -g RESOURCE_GROUP --vm-name VM_NAME --publisher Microsoft.Azure.Extensions -n customScript --settings config.json

To upload to AWS S3 or GCP Cloud Storage

On a secure host, generate a S3 pre-signed URL or generate a GCP pre-signed URL.

On the target host, execute avml with the generated pre-signed URL.

avml acquire --url ${URL} --delete output.lime

To decompress an AVML-compressed image

avml convert ./compressed.lime ./uncompressed.lime

To compress an uncompressed LiME image

avml convert --source-format lime --format lime_compressed ./uncompressed.lime ./compressed.lime

Usage

A portable volatile memory acquisition tool for Linux

Usage: avml <COMMAND>

Commands:
  acquire  Acquire a memory snapshot to a local file (and optionally upload it)
  convert  Convert between AVML and LiME snapshot formats and a raw memory image
  upload   Upload an already-acquired snapshot file to remote storage
  stream   Stream a memory snapshot directly to remote storage, without writing it to a local file
  help     Print this message or the help of the given subcommand(s)

Run avml <COMMAND> --help for per-command options.

Building on Ubuntu

# Install MUSL
sudo apt-get install musl-dev musl-tools musl

# Install Rust via rustup
curl https://sh.rustup.rs -sSf | sh -s -- -y

# Add the MUSL target for Rust
rustup target add x86_64-unknown-linux-musl

# Build
cargo build --release --target x86_64-unknown-linux-musl

# Build without upload functionality
cargo build --release --target x86_64-unknown-linux-musl --no-default-features

Testing on Azure

The testing scripts will create, use, and cleanup a number of resource groups, virtual machines, and a storage account.

1. Install az cli
2. Login to your Azure subscription using: az login
3. Build avml (see above)
4. ./eng/test-on-azure.sh

Contributing

This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.

When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repositories using our CLA.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact [email protected] with any additional questions or comments.

Reporting Security Issues

Security issues and bugs should be reported privately, via email, to the Microsoft Security Response Center (MSRC) at [email protected]. You should receive a response within 24 hours. If for some reason you do not, please follow up via email to ensure we received your original message. Further information, including the MSRC PGP key, can be found in the Security TechCenter.