Linux list all IROs currently in use

Q. How do I list all IRQs currently used under CentOS Linux?

A.. There is a file called /proc/interrupts. The proc filesystem is a pseudo filesystem which is used as an interface to kernel data structures. It is commonly mounted at /proc.

This is used to record the number of interrupts per each IRQ on (at least) the i386 architecture. Very easy to read formatting, done in ASCII.

Display /proc/interrupts

Use cat or less command:
$ cat /proc/interrupts
Output:

           CPU0       CPU1       CPU2       CPU3
  0:        187          0          0          0   IO-APIC-edge      timer
  1:      39922          0          0          0   IO-APIC-edge      i8042
  7:          0          0          0          0   IO-APIC-edge      parport0
  8:          4          0          0          0   IO-APIC-edge      rtc
  9:          1          0          0          0   IO-APIC-fasteoi   acpi
 12:     846774          0          0          0   IO-APIC-edge      i8042
 14:     105048          0          0          0   IO-APIC-edge      libata
 15:          0          0          0          0   IO-APIC-edge      libata
 16:    1069722          0          0          0   IO-APIC-fasteoi   libata, uhci_hcd:usb4, nvidia
 17:     105382          0          0          0   IO-APIC-fasteoi   eth0
 18:      83040          0          0          0   IO-APIC-fasteoi   uhci_hcd:usb2, libata
 19:          0          0          0          0   IO-APIC-fasteoi   uhci_hcd:usb1, ehci_hcd:usb5
 20:     474168          0          0          0   IO-APIC-fasteoi   uhci_hcd:usb3, ohci1394, ra0
 21:      10117          0          0          0   IO-APIC-fasteoi   bttv0
 22:     594327          0          0          0   IO-APIC-fasteoi   HDA Intel
NMI:          0          0          0          0
LOC:    1754492    1545836    2085855    1878596
ERR:          0
MIS:          0