Gfilui

I have a Dell XPS 13 on which I have installed Ubuntu. I would like to know if it has PCIe x4 or x2.

Edit 1:
I already know that it is Thunderbolt, just don't know how many PCIe lanes it has.

Edit 2:
This is what I got after trying the suggested command.

$ sudo dmidecode | grep PCI
PCI is supported
Type: x16 PCI Express
Type: x1 PCI Express
Type: x1 PCI Express
Type: x1 PCI Express
Type: x1 PCI Express
Type: x1 PCI Express
Type: x1 PCI Express
Type: 32-bit PCI
 SA - PCIe Version

Edit 3: After trying, sudo lspci -vv | grep -E 'PCI bridge|LnkCap'

00:1c.0 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port (rev f1) (prog-if 00 [Normal decode])
 LnkCap: Port #1, Speed 8GT/s, Width x2, ASPM not supported, Exit Latency L0s unlimited, L1 <16us
00:1c.4 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port #5 (rev f1) (prog-if 00 [Normal decode])
 LnkCap: Port #5, Speed 8GT/s, Width x1, ASPM L1, Exit Latency L0s <1us, L1 <16us
00:1c.5 PCI bridge: Intel Corporation Sunrise Point-LP PCI Express Root Port #6 (rev f1) (prog-if 00 [Normal decode])
 LnkCap: Port #6, Speed 8GT/s, Width x1, ASPM L1, Exit Latency L0s <1us, L1 <16us
 LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s <4us, L1 <64us
 LnkCap: Port #0, Speed 5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s unlimited, L1 <64us

Type this in a terminal sudo dmidecode | grep PCI it will tell you which Pci-e slots you have.

Edit: This should work in an indirect way. Type sudo lspci -vv | grep -E 'PCI bridge|LnkCap' in a terminal it should show you something like this:

00:14.4 PCI bridge: Advanced Micro Devices, Inc. [AMD] FCH PCI Bridge (rev 40) (prog-if 01 [Subtractive decode])
00:15.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] Hudson PCI to PCI bridge (PCIE port 0) (prog-if 00 [Normal decode])
 LnkCap: Port #247, Speed 5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s <64ns, L1 <1us
 Capabilities: [b0] Subsystem: Advanced Micro Devices, Inc. [AMD] Hudson PCI to PCI bridge (PCIE port 0)
00:15.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Hudson PCI to PCI bridge (PCIE port 1) (prog-if 00 [Normal decode])
 LnkCap: Port #1, Speed 5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s <64ns, L1 <1us
 Capabilities: [b0] Subsystem: Advanced Micro Devices, Inc. [AMD] Hudson PCI to PCI bridge (PCIE port 1)
 LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s unlimited, L1 unlimited

Now just check what version corresponds to the specs you have here and you should be good to go.