A vendor asks you to confirm which interrupt line a capture card is using and how many interrupts it has taken since boot. Which file gives you both figures?
LPIC-1 Exam 101-500, objective 101. System architecture medium
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct /proc/interrupts
Correct. It lists one row per interrupt source: the IRQ number, a per-CPU count of interrupts delivered, the interrupt controller and the name of the driver or drivers registered on that line.
Not correct /proc/ioports
Wrong. /proc/ioports maps the x86 I/O port ranges that drivers have reserved. It shows an address range, not an IRQ number and no counters.
Not correct /proc/dma
Wrong. /proc/dma lists the registered ISA DMA channels, which on modern hardware is a very short and mostly empty list.
Not correct /proc/iomem
Wrong. /proc/iomem is the physical memory address map, including memory-mapped device regions. It is the memory counterpart of /proc/ioports, and again carries no interrupt data.
Why
The four classic hardware-resource files under /proc each answer one question: interrupts for IRQ lines, ioports for port-mapped I/O ranges, iomem for memory-mapped ranges, and dma for ISA DMA channels. Only /proc/interrupts carries counters, which is what makes it the file to watch when deciding whether a device is generating interrupts at all. Shared IRQs show several driver names on one row, and the counters are cumulative since boot, so read the file twice and compare.
Where this comes from
- Cited
- manual page proc(5)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 101 and space the ones you get wrong.
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