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Configuration

Vers uses TOML configuration files to define VM specifications. The primary configuration file is vers.toml, which controls how VMs are created.

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Configuration File Structure

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Complete vers.toml Example

[machine]
mem_size_mib = 2048           # VM memory allocation in MiB
vcpu_count = 4                # Number of virtual CPU cores
fs_size_vm_mib = 4096         # VM filesystem size in MiB

[rootfs]
name = "default"              # Base filesystem image name

[kernel]
name = "default.bin"          # Kernel image file name

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Minimal Configuration

[machine]
mem_size_mib = 512

[rootfs]
name = "default"

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Configuration Sections

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[machine] Section

Controls VM hardware specifications and resource allocation.

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Memory Configuration

  • mem_size_mib - RAM allocation per VM in mebibytes
  • Range - Typically 512-16384 MiB, depending on system capacity
[machine]
mem_size_mib = 1024    # 1 GB RAM per VM

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CPU Configuration

  • vcpu_count - Number of virtual CPU cores per VM
  • Range - 1-16 cores typical, limited by host system
[machine]
vcpu_count = 2         # 2 CPU cores per VM

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Storage Configuration

  • fs_size_vm_mib - Storage allocated to VMs
[machine]
fs_size_vm_mib = 2048         # 2 GB per VM

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[rootfs] Section

Defines the base filesystem image for VMs.
  • name - Identifier for the rootfs image
  • “default” - Uses system default image
[rootfs]
name = "default"

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[kernel] Section

Specifies the kernel image for VM boot.
  • name - Kernel image filename
  • Default - “default.bin” for standard kernel
[kernel]
name = "default.bin"

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Default Values

When values are omitted, Vers uses these defaults: 
[machine]
mem_size_mib = 512
vcpu_count = 1
fs_size_vm_mib = 512

[rootfs]
name = "default"

[kernel]
name = "default.bin"

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Loading Behavior

# If vers.toml exists: load values, use defaults for missing sections
# If vers.toml missing: use all defaults (with warning)
vers run
# Warning: vers.toml not found, using default configuration

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Configuration Override Hierarchy

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Precedence Order (highest to lowest)

  1. Command-line flags - Direct flag values
  2. Configuration file - vers.toml values
  3. System defaults - Built-in fallbacks

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Flag Override Examples

# Override memory from command line
vers run --mem-size 4096
# Uses 4096 MiB regardless of vers.toml value

# Override multiple values
vers run --mem-size 2048 --vcpu-count 4 --rootfs custom-image

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Configuration Validation

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Validation Rules

  • Positive integers - Memory, CPU, and storage values must be > 0
  • Resource constraints - Values must be within system capabilities
  • Image availability - Referenced images must exist

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Common Validation Errors

vers run --mem-size -1
# Error: Invalid memory size (must be positive)

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Environment-Specific Configurations

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Development Configuration

# vers-dev.toml
[machine]
mem_size_mib = 1024
vcpu_count = 2
fs_size_vm_mib = 2048

[rootfs]
name = "default"

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High-Performance Configuration

# vers-perf.toml
[machine]
mem_size_mib = 4096
vcpu_count = 8
fs_size_vm_mib = 8192

[rootfs]
name = "default"

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Configuration Best Practices

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Resource Planning

# Plan resources based on your workload
[machine]
mem_size_mib = 1024           # Per VM
vcpu_count = 2                # Per VM
fs_size_vm_mib = 1024         # Per VM

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Troubleshooting Configuration Issues

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Common Problems

Configuration not loading: 
vers run
# Uses defaults instead of vers.toml values
# Cause: TOML syntax errors or file permission issues
# Solution: Validate TOML syntax and file permissions
Resource allocation failures: 
vers run
# Error: Insufficient system resources
# Cause: Configuration requests more resources than available
# Solution: Reduce memory/CPU requirements or free system resources
Image not found errors: 
vers run --rootfs custom-image
# Error: rootfs image 'custom-image' not found
# Cause: Image name doesn't exist
# Solution: Use "default" or verify the image name exists

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See Also