Installing OpenBSD with custom partitioning offers advanced users and system administrators precise control over disk layout, performance optimization, and security hardening. This guide covers essential steps and considerations for tailoring your OpenBSD installation partitions beyond the defaults, helping you create a system that fits your unique needs.
1. Understanding OpenBSD’s Default Disk Layout
Before customizing partitions, it’s important to understand the default OpenBSD disk layout. By default, OpenBSD creates a single disk partition with subpartitions for root (/), swap, and /tmp. This simple layout is easy for beginners but lacks flexibility for isolating system components or optimizing performance.
2. Planning Your Partition Scheme
Custom partitioning starts with planning how to divide your disk space. Consider separating partitions for /var, /home, /usr, and /tmp to improve security and stability. For example, isolating /var limits log file growth from filling the root filesystem, while a dedicated /home partition protects user data during system upgrades.
3. Using the OpenBSD Installer’s Disklabel Editor
The OpenBSD installer includes a disklabel editor accessed during installation. This tool allows you to create, modify, or delete disk partitions (called “slices”) and assign mount points. Familiarity with the disklabel editor is crucial, as it lets you define partition sizes and types tailored to your system’s role.
4. Choosing Partition Sizes for Swap and Root
Allocating swap space depends on your system’s RAM and workload. OpenBSD recommends swap equal to or double your RAM for hibernation support, but modern systems often require less. The root partition should be large enough to hold the base system plus software and logs, typically 10-20GB depending on usage.
5. Creating Separate Partitions for /var and /tmp
Separating /var and /tmp into distinct partitions prevents runaway log files or temporary data from filling critical system space. For servers or systems with heavy logging, /var should be sized generously, often 1-5GB or more. The /tmp partition can be smaller but should still accommodate temporary files safely.
6. Mounting /home on Its Own Partition
Allocating a dedicated /home partition protects user data during system upgrades or reinstallation. This separation simplifies backups and allows users to store large files without impacting system partitions. Size /home based on the number of users and expected data volume, typically tens of gigabytes or more.
7. Considering Filesystem Types and Mount Options
OpenBSD uses the FFS (Fast File System) by default, which is robust and well-tested. When creating partitions, you can specify mount options like soft-updates or noatime to improve performance or reduce disk wear. For example, mounting /tmp with noatime reduces unnecessary writes, benefiting SSD longevity.
8. Handling Disk Encryption with softraid
OpenBSD’s softraid framework allows you to encrypt partitions during installation. Setting up encrypted volumes for sensitive partitions like /home or swap enhances security by protecting data at rest. Encryption requires configuring softraid devices before partitioning, adding a layer of complexity but valuable for privacy.
9. Using Multiple Disks or RAID Configurations
If your system has multiple disks, OpenBSD supports RAID via softraid. You can create mirrored or striped volumes for redundancy or performance. Custom partitioning in this context involves designing partitions atop RAID devices, ensuring critical data is protected while optimizing throughput.
10. Verifying and Testing Your Partition Layout
After creating partitions and completing installation, verify the layout with tools like disklabel -h and mount. Testing includes ensuring all partitions mount correctly and have appropriate permissions. This step prevents boot issues and guarantees that your custom partitioning scheme works as intended.
How to Choose
When selecting a custom partitioning scheme for OpenBSD, focus on your system’s intended use, security requirements, and maintenance preferences. Servers benefit from isolating partitions like /var and /tmp to contain failures, while desktops might prioritize a large /home for user files. Consider disk size, backup strategies, and whether encryption is needed. Avoid overly complex layouts unless justified, as simplicity aids troubleshooting and upgrades.
Frequently Asked Questions
Q: Can I resize OpenBSD partitions after installation?
Not easily. OpenBSD’s disklabel partitions are fixed in size, so resizing typically requires backup, repartitioning, and reinstalling or restoring data.
Q: How much swap space should I allocate?
For most systems, swap equal to RAM size is sufficient. More swap may be needed for hibernation or memory-intensive applications.
Q: Is it necessary to create separate partitions for /var and /tmp?
It’s not mandatory but recommended for stability and security, especially on servers that generate many logs or temporary files.
Q: How do I enable disk encryption during OpenBSD installation?
Use the softraid setup option in the installer before partitioning to create encrypted volumes for your partitions.
Q: What tools can I use to check my partition layout after installation?
Use disklabel -h sd0 (replace sd0 with your disk) and mount to view partitions and mount points.
Final Thoughts
Custom partitioning during OpenBSD installation empowers users to optimize system performance, security, and data management. While it requires careful planning and familiarity with OpenBSD’s disklabel system, the benefits of tailored partitions justify the effort for many use cases. By isolating key directories, allocating appropriate swap, and optionally enabling encryption, you build a resilient and maintainable OpenBSD environment suited to your specific needs.
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