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Chapter 2. The

proc

File System

The first column signifies whether the file system is mounted on a block device. Those beginning with

nodev

are not mounted on a device. The second column lists the name of the file systems supported.

The

mount

command cycles through these file systems when one is not specified as an argument.

2.2.9.

/proc/interrupts

This file records the number of interrupts per IRQ on the x86 architecture. A standard

/proc/interrupts

looks similar to this:

CPU0

0:

80448940

XT PIC

timer

1:

174412

XT PIC

keyboard

2:

0

XT PIC

cascade

8:

1

XT PIC

rtc

10:

410964

XT PIC

eth0

12:

60330

XT PIC

PS/2 Mouse

14:

1314121

XT PIC

ide0

15:

5195422

XT PIC

ide1

NMI:

0

ERR:

0

For a multi processor machine, this file may look slightly different:

CPU0

CPU1

0: 1366814704

0

XT PIC

timer

1:

128

340

IO APIC edge

keyboard

2:

0

0

XT PIC

cascade

8:

0

1

IO APIC edge

rtc

12:

5323

5793

IO APIC edge

PS/2 Mouse

13:

1

0

XT PIC

fpu

16:

11184294

15940594

IO APIC level

Intel EtherExpress Pro 10/100 Ethernet

20:

8450043

11120093

IO APIC level

megaraid

30:

10432

10722

IO APIC level

aic7xxx

31:

23

22

IO APIC level

aic7xxx

NMI:

0

ERR:

0

The first column refers to the IRQ number. Each CPU in the system has its own column and its own

number of interrupts per IRQ. The next column reports the type of interrupt, and the last column

contains the name of the device that is located at that IRQ.

Each of the types of interrupts seen in this file, which are architecture specific, mean something a little

different. For x86 machines, the following values are common:

  XT PIC

  This is the old AT computer interrupts.

  IO APIC edge

  The voltage signal on this interrupt transitions from low to high, creating an

edge, where the interrupt occurs and is only signaled once. This kind of interrupt, as well as the

IO APIC level

interrupt, are only seen on systems with processors from the 586 family and

higher.

  IO APIC level

  Generates interrupts when its voltage signal goes high until the signal goes

low again.