40

Chapter 2. The

proc

File System

So, for example, a system with a USB bus but no USB devices connected to it has a

/proc/bus/usb/

directory containing several files:

total 0

dr xr xr x

1 root

root

0 May

3 16:25 001

 r  r  r  

1 root

root

0 May

3 16:25 devices

 r  r  r  

1 root

root

0 May

3 16:25 drivers

The

/proc/bus/usb/

directory contains files that track the various devices on any USB buses, as

well as the drivers required to use them. The

/proc/bus/usb/001/

directory contains all devices

on the first USB bus. By looking at the contents of the

devices

file, you can identify the USB root

hub on the motherboard:

T:

Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=

1 Spd=12

MxCh= 2

B:

Alloc=

0/900 us ( 0%), #Int=

0, #Iso=

0

D:

Ver= 1.00 Cls=09(hub

) Sub=00 Prot=00 MxPS= 8 #Cfgs=

1

P:

Vendor=0000 ProdID=0000 Rev= 0.00

S:

Product=USB UHCI Root Hub

S:

SerialNumber=d400

C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=

0mA

I:

If#= 0 Alt= 0 #EPs= 1 Cls=09(hub

) Sub=00 Prot=00 Driver=hub

E:

Ad=81(I) Atr=03(Int.) MxPS=

8 Ivl=255ms

2.3.3.

/proc/driver/

This directory contains information for specific drivers in use by the kernel.

A common file found here is

rtc

, which provides output from the driver for the system's Real Time

Clock (RTC), the device that keeps the time while the system is switched off. Sample output from

/proc/driver/rtc

looks like this:

rtc_time : 01:38:43

rtc_date : 1998 02 13

rtc_epoch : 1900

alarm

: 00:00:00

DST_enable : no

BCD

: yes

24hr

: yes

square_wave : no

alarm_IRQ : no

update_IRQ : no

periodic_IRQ : no

periodic_freq : 1024

batt_status : okay

For more information about the RTC, review

/usr/src/linux 2.4/Documentation/rtc.txt

.

2.3.4.

/proc/fs

This directory shows which file systems are exported. If you are running an NFS server, you can type

cat /proc/fs/nfs/exports

to view the file systems being shared and the permissions granted for

the those file systems. For more on sharing filesystem with NFS, see Chapter 17.