17.5 The /proc File System

The /proc file system is a pseudo file system in which the kernel reserves important information in the form of virtual files. For example, display the CPU type with this command:

tester@linux:~> cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 8
model name      : AMD Athlon(tm) XP 2400+
stepping        : 1
cpu MHz         : 2009.343
cache size      : 256 KB
fdiv_bug        : no
[...]
  

Query the allocation and use of interrupts with the following command:

tester@linux:~> cat /proc/interrupts
           CPU0
  0:    3577519          XT-PIC  timer
  1:        130          XT-PIC  i8042
  2:          0          XT-PIC  cascade
  5:     564535          XT-PIC  Intel 82801DB-ICH4
  7:          1          XT-PIC  parport0
  8:          2          XT-PIC  rtc
  9:          1          XT-PIC  acpi, uhci_hcd:usb1, ehci_hcd:usb4
 10:          0          XT-PIC  uhci_hcd:usb3
 11:      71772          XT-PIC  uhci_hcd:usb2, eth0
 12:     101150          XT-PIC  i8042
 14:      33146          XT-PIC  ide0
 15:     149202          XT-PIC  ide1
NMI:          0
LOC:          0
ERR:          0
MIS:          0

Some of the important files and their contents are:

/proc/devices

Available devices

/proc/modules

Kernel modules loaded

/proc/cmdline

Kernel command line

/proc/meminfo

Detailed information about memory usage

/proc/config.gz

gzip-compressed configuration file of the kernel currently running

Further information is available in the text file /usr/src/linux/Documentation/filesystems/proc.txt. Find information about processes currently running in the /proc/NNN directories, where NNN is the process ID (PID) of the relevant process. Every process can find its own characteristics in /proc/self/:

tester@linux:~> ls -l /proc/self
lrwxrwxrwx 1 root root 64 2006-01-09 13:03 /proc/self -> 5356
tester@linux:~> ls -l /proc/self/
total 0
dr-xr-xr-x 2 tester users 0 2006-01-09 17:04 attr
-r-------- 1 tester users 0 2006-01-09 17:04 auxv
-r--r--r-- 1 tester users 0 2006-01-09 17:04 cmdline
lrwxrwxrwx 1 tester users 0 2006-01-09 17:04 cwd -> /home/tester
-r-------- 1 tester users 0 2006-01-09 17:04 environ
lrwxrwxrwx 1 tester users 0 2006-01-09 17:04 exe -> /bin/ls
dr-x------ 2 tester users 0 2006-01-09 17:04 fd
-rw-r--r-- 1 tester users 0 2006-01-09 17:04 loginuid
-r--r--r-- 1 tester users 0 2006-01-09 17:04 maps
-rw------- 1 tester users 0 2006-01-09 17:04 mem
-r--r--r-- 1 tester users 0 2006-01-09 17:04 mounts
-rw-r--r-- 1 tester users 0 2006-01-09 17:04 oom_adj
-r--r--r-- 1 tester users 0 2006-01-09 17:04 oom_score
lrwxrwxrwx 1 tester users 0 2006-01-09 17:04 root -> /
-rw------- 1 tester users 0 2006-01-09 17:04 seccomp
-r--r--r-- 1 tester users 0 2006-01-09 17:04 smaps
-r--r--r-- 1 tester users 0 2006-01-09 17:04 stat
-r--r--r-- 1 tester users 0 2006-01-09 17:04 statm
-r--r--r-- 1 tester users 0 2006-01-09 17:04 status
dr-xr-xr-x 3 tester users 0 2006-01-09 17:04 task
-r--r--r-- 1 tester users 0 2006-01-09 17:04 wchan
  

The address assignment of executables and libraries is contained in the maps file:

tester@linux:~> cat /proc/self/maps
08048000-0804c000 r-xp 00000000 03:03 17753      /bin/cat
0804c000-0804d000 rw-p 00004000 03:03 17753      /bin/cat
0804d000-0806e000 rw-p 0804d000 00:00 0          [heap]
b7d27000-b7d5a000 r--p 00000000 03:03 11867      /usr/lib/locale/en_GB.utf8/
b7d5a000-b7e32000 r--p 00000000 03:03 11868      /usr/lib/locale/en_GB.utf8/
b7e32000-b7e33000 rw-p b7e32000 00:00 0
b7e33000-b7f45000 r-xp 00000000 03:03 8837       /lib/libc-2.3.6.so
b7f45000-b7f46000 r--p 00112000 03:03 8837       /lib/libc-2.3.6.so
b7f46000-b7f48000 rw-p 00113000 03:03 8837       /lib/libc-2.3.6.so
b7f48000-b7f4c000 rw-p b7f48000 00:00 0
b7f52000-b7f53000 r--p 00000000 03:03 11842      /usr/lib/locale/en_GB.utf8/
[...]
b7f5b000-b7f61000 r--s 00000000 03:03 9109       /usr/lib/gconv/gconv-module
b7f61000-b7f62000 r--p 00000000 03:03 9720       /usr/lib/locale/en_GB.utf8/
b7f62000-b7f76000 r-xp 00000000 03:03 8828       /lib/ld-2.3.6.so
b7f76000-b7f78000 rw-p 00013000 03:03 8828       /lib/ld-2.3.6.so
bfd61000-bfd76000 rw-p bfd61000 00:00 0          [stack]
ffffe000-fffff000 ---p 00000000 00:00 0          [vdso]
  

tester@linux:~> procinfo
Linux 2.6.15-rc5-git3-2-default (geeko@buildhost) (gcc 4.1.0 20051129) #1 Wed

Memory:      Total        Used        Free      Shared     Buffers
Mem:        515584      509472        6112           0       73024
Swap:       658656           0      658656

Bootup: Mon Jan  9 12:59:08 2006    Load average: 0.10 0.04 0.05 1/86 5406

user  :       0:02:07.98   0.8%  page in :     442638  disk 1:    20125r 134
nice  :       0:02:20.91   0.9%  page out:     134950
system:       0:00:42.93   0.3%  page act:      70577
IOwait:       0:01:25.40   0.6%  page dea:      11696
hw irq:       0:00:08.94   0.1%  page flt:    1423622
sw irq:       0:00:01.29   0.0%  swap in :          0
idle  :       4:06:30.54  97.3%  swap out:          0
uptime:       4:13:20.72         context :    3813145

irq  0:   3799268 timer                 irq  8:         2 rtc
irq  1:       130 i8042                 irq  9:         1 acpi, uhci_hcd:usb
irq  2:         0 cascade [4]           irq 10:         0 uhci_hcd:usb3
irq  3:         8                       irq 11:     75905 uhci_hcd:usb2, eth
irq  4:         8                       irq 12:    101150 i8042
irq  5:    564535 Intel 82801DB-ICH4    irq 14:     33733 ide0
irq  6:         9                       irq 15:    157045 ide1
irq  7:         1 parport0 [3]