How to Check PCIe Link Speed and Bus Width in Ubuntu Terminal Using lspci

When installing high-performance hardware components—such as NVMe solid-state storage drives, dedicated graphics cards, 10GbE network interface cards (NICs), or hardware RAID controllers—in an Ubuntu server or desktop, physical hardware installation does not always guarantee full operational bandwidth. Bent socket pins, motherboard PCIe slot lane sharing, or improper BIOS configuration can cause a card capable of PCIe 4.0 x16 to downgrade silently to PCIe 3.0 x4. In Ubuntu, you can audit negotiated PCIe link capabilities directly in terminal using lspci.

Locating the Target PCI Device Address

Every peripheral component connected to your motherboard PCI bus is assigned a unique hardware domain, bus, device, and function address (BDF, e.g. 01:00.0):

1. Launch your Ubuntu terminal session.
2. Search the PCI hardware bus for your target component (for example, an NVIDIA GPU or Samsung NVMe controller):

   lspci | grep -iE 'vga|3d|non-volatile'

3. Identify the slot address at the beginning of the line (e.g. 01:00.0 for a graphics card or 04:00.0 for an NVMe drive).

Inspecting Link Capabilities and Negotiated Link Status

To extract granular PCI Express physical layer telemetry, invoke lspci in verbose mode (-vv) filtered through grep:

sudo lspci -s 01:00.0 -vv | grep -E "LnkCap:|LnkSta:"

The terminal will output two vital configuration strings:

LnkCap: Port #0, Speed 16GT/s, Width x16, ASPM L0s L1, Exit Latency L0s <512ns, L1 <16us
LnkSta: Speed 16GT/s (ok), Width x16 (ok)

Interpreting LinkCap vs LinkSta Metrics

Understanding the distinction between these two output metrics reveals whether your hardware is throttled:

• LnkCap (Link Capabilities): The maximum theoretical performance supported by the physical peripheral device itself. For example, Speed 16GT/s, Width x16 indicates a PCIe Generation 4.0 card supporting up to 16 full lanes.
• LnkSta (Link Status): The actual real-time connection negotiated between the device and the motherboard chipset. If LnkSta reports lower numbers than LnkCap (such as Speed 8GT/s, Width x8 on a 16GT/s x16 card), the connection is throttled.

Understanding Common PCIe Transfer Speeds

The gigatransfers per second (GT/s) rating maps directly to PCIe generations:

• 2.5 GT/s: PCIe 1.0 (Approx. 250 MB/s per lane)
• 5.0 GT/s: PCIe 2.0 (Approx. 500 MB/s per lane)
• 8.0 GT/s: PCIe 3.0 (Approx. 985 MB/s per lane)
• 16.0 GT/s: PCIe 4.0 (Approx. 1.97 GB/s per lane)
• 32.0 GT/s: PCIe 5.0 (Approx. 3.94 GB/s per lane)

If an idle GPU temporarily downclocks to 2.5 GT/s to conserve power via Active State Power Management (ASPM), run a minor compute task in another window to verify if LnkSta scales up to full rated speed under load.