Top-Level Files in /proc

Below is a list of some of the more useful virtual files in the top-level of the /proc directory.


This file provides information about the state of the Advanced Power Management (APM) system. This information is used by the apm command.

The output of this file on a system without a battery and constantly connected to an AC power source looks similar to this:

1.16 1.2 0x03 0x01 0xff 0x80 -1% -1 ?

Executing apm -v command on these systems results in something similar to this:

APM BIOS 1.2 (kernel driver 1.16)
AC on-line, no system battery

For these systems, apm may be able to do little more than put the machine in standby mode. The apm command is much more useful on laptops. This is also reflected in their /proc/apm files. This is the output from a sample file on a laptop running Linux while plugged into a power outlet:

1.16 1.2 0x03 0x01 0x03 0x09 100% -1 ?

When the same machine is unplugged from its power source and running on its own batteries for a few minutes, you will see the contents of the apm file change:

1.16 1.2 0x03 0x00 0x00 0x01 99% 1792 min

In this state, the apm command yields readable information from this data:

APM BIOS 1.2 (kernel driver 1.16)
AC off-line, battery status high: 99% (1 day, 5:52)

This demonstrates the connection between data located in raw /proc files and the utilities designed to use that information for specific purposes.


This file essentially shows the parameters passed to the kernel at the time it is started. A sample /proc/cmdline file looks similar to this:

ro root=/dev/hda2

The important data contained in the file breaks down in the following way:


This file changes based on the type of processor in your system. The output is fairly easy to understand. A sample file looks like this:

processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 5
model           : 9
model name      : AMD-K6(tm) 3D+ Processor
stepping        : 1
cpu MHz         : 400.919
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr mce cx8 pge mmx syscall 3dnow k6_mtrr
bogomips        : 799.53


This file displays the various character and block devices currently configured for use with the kernel. It does not include modules that are available but not loaded into the kernel. Below is a sample output from this virtual file:

Character devices:
  1 mem
  2 pty
  3 ttyp
  4 ttyS
  5 cua
  7 vcs
 10 misc
 14 sound
 29 fb
 36 netlink
128 ptm
129 ptm
136 pts
137 pts
162 raw
254 iscsictl

Block devices:
  1 ramdisk
  2 fd
  3 ide0
  9 md
 22 ide1

The output from /proc/devices includes the major number and name of the device.

Character devices are similar to block devices, except for two basic differences.

Block devices have a buffer available, allowing them to order requests before dealing with them. This is important for devices designed to store information — such as hard drives — because the ability to order the information before writing it to the device allows it to be placed in more efficient order. Character devices do not require buffering.

The other difference is that block devices can send and receive information in blocks of a size configured per device. Character devices send data with no preconfigured size.

For more information about devices see /usr/src/linux-2.4/Documentation/devices.txt.


This file contains a list of the registered ISA direct memory access (DMA) channels in use. A sample /proc/dma files looks like this:

 4: cascade


This file lists the execution domains currently supported by the Linux kernel, along with the range of personalities they support.

0-0   Linux           [kernel]

Think of execution domains as a kind of "personality" of a particular operating system. Other binary formats, such as Solaris, UnixWare, and FreeBSD, can be used with Linux. By changing the personality of a task running in Linux, a programmer can change the way the operating system treats particular system calls from a certain binary. Except for the PER_LINUX execution domain, they can be implemented as dynamically loadable modules.


This file contains a list of frame buffer devices, with the frame buffer device number and the driver that controls it. Typical output of /proc/fb for systems that contain frame buffer devices looks similar to this:



This file displays a list of the file system types currently supported by the kernel. Sample output from a generic kernel's /proc/filesystems file looks similar to this:

nodev	rootfs
nodev	bdev
nodev	proc
nodev	sockfs
nodev	tmpfs
nodev	shm
nodev	pipefs
nodev	ramfs
nodev	devpts
nodev	autofs
nodev	binfmt_misc

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.


This file records the number of interrupts per IRQ on the x86 architecture. A standard /proc/interrupts looks similar to this:

  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 tells you 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:


This file shows you the current map of the system's memory for its various devices:

00000000-0009fbff : System RAM
0009fc00-0009ffff : reserved
000a0000-000bffff : Video RAM area
000c0000-000c7fff : Video ROM
000f0000-000fffff : System ROM
00100000-07ffffff : System RAM
  00100000-00291ba8 : Kernel code
  00291ba9-002e09cb : Kernel data
e0000000-e3ffffff : VIA Technologies, Inc. VT82C597 [Apollo VP3]
e4000000-e7ffffff : PCI Bus #01
  e4000000-e4003fff : Matrox Graphics, Inc. MGA G200 AGP
  e5000000-e57fffff : Matrox Graphics, Inc. MGA G200 AGP
e8000000-e8ffffff : PCI Bus #01
  e8000000-e8ffffff : Matrox Graphics, Inc. MGA G200 AGP
ea000000-ea00007f : Digital Equipment Corporation DECchip 21140 [FasterNet]
  ea000000-ea00007f : tulip
ffff0000-ffffffff : reserved

The first column displays the memory registers used by each of the different types of memory. The second column tells the kind of memory located within those registers. In particular, this column will even tell you which memory registers are used by the kernel within the system RAM or, if you have multiple Ethernet ports on your NIC, the memory registers assigned for each port.


In a way similar to /proc/iomem, /proc/ioports provides a list of currently registered port regions used for input or output communication with a device. This file can be quite long, with a beginning similar to this:

0000-001f : dma1
0020-003f : pic1
0040-005f : timer
0060-006f : keyboard
0070-007f : rtc
0080-008f : dma page reg
00a0-00bf : pic2
00c0-00df : dma2
00f0-00ff : fpu
0170-0177 : ide1
01f0-01f7 : ide0
02f8-02ff : serial(auto)
0376-0376 : ide1
03c0-03df : vga+
03f6-03f6 : ide0
03f8-03ff : serial(auto)
0cf8-0cff : PCI conf1
d000-dfff : PCI Bus #01
e000-e00f : VIA Technologies, Inc. Bus Master IDE
  e000-e007 : ide0
  e008-e00f : ide1
e800-e87f : Digital Equipment Corporation DECchip 21140 [FasterNet]
  e800-e87f : tulip

The first column gives the actual IO port address range reserved for the device listed in the second column.


This file lists Plug and Play (PnP) cards in ISA slots on the system. This is most often seen with sound cards but may include any number of devices. A /proc/isapnp file with Soundblaster entry in it looks similar to this:

Card 1 'CTL0070:Creative ViBRA16C PnP' PnP version 1.0 Product version 1.0
  Logical device 0 'CTL0001:Audio'
    Device is not active
    Active port 0x220,0x330,0x388
    Active IRQ 5 [0x2]
    Active DMA 1,5
    Resources 0
      Priority preferred
      Port 0x220-0x220, align 0x0, size 0x10, 16-bit address decoding
      Port 0x330-0x330, align 0x0, size 0x2, 16-bit address decoding
      Port 0x388-0x3f8, align 0x0, size 0x4, 16-bit address decoding
      IRQ 5 High-Edge
      DMA 1 8-bit byte-count compatible
      DMA 5 16-bit word-count compatible
      Alternate resources 0:1
        Priority acceptable
        Port 0x220-0x280, align 0x1f, size 0x10, 16-bit address decoding
        Port 0x300-0x330, align 0x2f, size 0x2, 16-bit address decoding
        Port 0x388-0x3f8, align 0x0, size 0x4, 16-bit address decoding
        IRQ 5,7,2/9,10 High-Edge
        DMA 1,3 8-bit byte-count compatible
        DMA 5,7 16-bit word-count compatible

This file can be quite long, depending on the number of devices displayed here and their requirements or requests for resources.

Each card lists its name, PnP version number, and product version number. If the device is active and configured, this file will also reveal the port and IRQ numbers for the device. In addition, to ensure better compatibility, the card will specify preferred and acceptable values for a number of different parameters. The goal here is to allow the PnP cards to work around one another and avoid IRQ and port conflicts.


This file represents the physical memory of the system and is stored in the core file format. Unlike most /proc files, kcore does display a size. This value is given in bytes and is equal to the size of physical memory (RAM) used plus 4KB.


Be sure to avoid viewing the kcore file in /proc. The contents of the file will scramble text output on the terminal. If you accidentally view this file, press [Ctrl]-[C] to stop the process then type reset to bring back the command line prompt.

The contents of this file are designed to be examined by a debugger, such as gdb and is not human readable.


This file is used to hold messages generated by the kernel. These messages are then picked up by other programs, such as klogd.


This file holds the kernel exported symbol definitions used by the modules tools to dynamically link and bind loadable modules.

e003def4 speedo_debug	[eepro100]
e003b04c eepro100_init	[eepro100]
e00390c0 st_template	[st]
e002104c RDINDOOR	[megaraid]
e00210a4 callDone	[megaraid]
e00226cc megaraid_detect	[megaraid]

The second column refers to the name of a kernel function, and the first column lists the memory address of that function in the kernel. The last column reveals the name of the module loaded to provide that function.


This file provides a look at load average on the processor over time and additional data used by uptime and other commands. A sample loadavg file looks similar to this:

0.20 0.18 0.12 1/80 11206

The first three columns measure CPU utilization of the last 1, 5, and 10 minute periods. The fourth column shows the number of currently running processes and the total number of processes. The last column displays the last process ID used.


This files displays the files currently locked by the kernel. The content of this file contains kernel internal debugging data and can vary greatly, depending on the use of the system. A sample locks file of a very lightly loaded system looks similar to this:

1: FLOCK  ADVISORY  WRITE 807 03:05:308731 0 EOF c2a260c0 c025aa48 c2a26120
2: POSIX  ADVISORY  WRITE 708 03:05:308720 0 EOF c2a2611c c2a260c4 c025aa48

Each lock is assigned a unique number at the beginning of each line. The second column refers to the class of lock used, with FLOCK signifying the older-style UNIX file locks from a flock system call and POSIX representing the newer POSIX locks from the lockf system call.

The third column can have two values. ADVISORY means that the lock does not prevent other people from accessing the data; it only prevents other attempts to lock it. MANDATORY means that no other access to the data is permitted while the lock is held. The fourth column reveals whether the lock is allowing the holder READ or WRITE access to the file, and the fifth column shows the ID of the process holding the lock.

The sixth column shows the ID of the file being locked, in the format of MAJOR-DEVICE:MINOR-DEVICE:INODE-NUMBER. The seventh column shows the start and end of the file's locked region. The remaining columns point to internal kernel data structures used for specialized debugging and can be ignored.


This file contains the current information for multiple-disk, RAID configurations. If your system does not contain such a configuration, then your mdstat file will look similar to this:

Personalities : 
read_ahead not set
unused devices: <none>

This file remains in the state above unless you create a software RAID or md device. In that case, you can use mdstat to give you a picture of what is currently happening with your mdX RAID devices.

The /proc/mdstat file below shows a system with its md0 configured as a RAID 1 device. It is currently re-syncing the disks:

Personalities : [linear] [raid1]
read_ahead 1024 sectors
md0: active raid1 sda2[1] sdb2[0] 9940 blocks [2/2] [UU] resync=1% finish=12.3min
algorithm 2 [3/3] [UUU]
unused devices: <none>


This is one of the more commonly used /proc files, as it reports back plenty of valuable information about the current utilization of RAM on the system. A system with 256MB of RAM and 384MB of swap space might have a /proc/meminfo file similar to this one:

        total:    used:    free:  shared: buffers:  cached:
Mem:  261709824 253407232  8302592        0 120745984 48689152
Swap: 402997248     8192 402989056
MemTotal:       255576 kB
MemFree:          8108 kB
MemShared:           0 kB
Buffers:        117916 kB
Cached:          47548 kB
Active:         135300 kB
Inact_dirty:     29276 kB
Inact_clean:       888 kB
Inact_target:        0 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       255576 kB
LowFree:          8108 kB
SwapTotal:      393552 kB
SwapFree:       393544 kB

Much of the information here is used by the free, top, and ps commands. In fact, the output of the free command is even similar in appearance to the contents and structure of meminfo. By looking directly at meminfo, more memory details are revealed:


This file lists miscellaneous drivers registered on the miscellaneous major device, which is number 10:

135 rtc
  1 psaux
134 apm_bios

The first column is the minor number of each device, and the second column shows the driver in use.


This file displays a list of all modules that have been loaded by the system. Its contents will vary based on the configuration and use of your system, but it should be organized in a similar manner to this sample /proc/modules file output:

ide-cd                 27008   0 (autoclean)
cdrom                  28960   0 (autoclean) [ide-cd]
soundcore               4100   0 (autoclean)
agpgart                31072   0 (unused)
binfmt_misc             5956   1
iscsi                  32672   0 (unused)
scsi_mod               94424   1 [iscsi]
autofs                 10628   0 (autoclean) (unused)
tulip                  48608   1
ext3                   60352   2
jbd                    39192   2 [ext3]

The first column contains the name of the module. The second column refers to the memory size of the module, in bytes. The third column tells you whether the module is currently loaded (1) or unloaded (0). The final column states if the module can unload itself automatically after a period without use (autoclean) or if it is not being utilized (unused). Any module with a line containing a name listed in brackets ([ or ]) tells you that this module depends upon another module to be present in order to function.


This file provides a quick list of all mounts in use by the system:

rootfs / rootfs rw 0 0
/dev/hda2 / ext3 rw 0 0
/proc /proc proc rw 0 0
/dev/hda1 /boot ext3 rw 0 0
none /dev/pts devpts rw 0 0
none /dev/shm tmpfs rw 0 0
none /proc/sys/fs/binfmt_misc binfmt_misc rw 0 0

The output found here is similar to contents of /etc/mtab, except that /proc/mount can be more current.

The first column specifies the device that is mounted, with the second column revealing the mountpoint. The third column tells the file system type, and the fourth column tells you if it is mounted read-only (ro) or read-write (rw). The fifth and sixth columns are dummy values designed to match the format used in /etc/mtab.


This file refers to the current Memory Type Range Registers (MTRRs) in use with the system. If your system's architecture supports MTRRs, your mtrr might look something like this:

reg00: base=0x00000000 (   0MB), size=  64MB: write-back, count=1

MTRRs are used with Intel P6 family of processors (Pentium Pro and higher), and they are used to control processor access to memory ranges. When using a video card on a PCI or AGP bus, a properly configured mtrr file can increase performance over 150%.

Most of the time, this value is properly configured for you. For more information on MTRRs and manually configuring this file, please see


Most of the information here is of little importance to most users, except for the following columns:


This file contains a full listing of every PCI device on your system. Depending on the number of PCI devices you have, /proc/pci can get rather long. An example from this file on a basic system looks similar to this:

  Bus  0, device   0, function  0:
    Host bridge: Intel Corporation 440BX/ZX - 82443BX/ZX Host bridge (rev 3).
      Master Capable.  Latency=64.  
      Prefetchable 32 bit memory at 0xe4000000 [0xe7ffffff].
  Bus  0, device   1, function  0:
    PCI bridge: Intel Corporation 440BX/ZX - 82443BX/ZX AGP bridge (rev 3).
      Master Capable.  Latency=64.  Min Gnt=128.
  Bus  0, device   4, function  0:
    ISA bridge: Intel Corporation 82371AB PIIX4 ISA (rev 2).
  Bus  0, device   4, function  1:
    IDE interface: Intel Corporation 82371AB PIIX4 IDE (rev 1).
      Master Capable.  Latency=32.  
      I/O at 0xd800 [0xd80f].
  Bus  0, device   4, function  2:
    USB Controller: Intel Corporation 82371AB PIIX4 USB (rev 1).
      IRQ 5.
      Master Capable.  Latency=32.  
      I/O at 0xd400 [0xd41f].
  Bus  0, device   4, function  3:
    Bridge: Intel Corporation 82371AB PIIX4 ACPI (rev 2).
      IRQ 9.
  Bus  0, device   9, function  0:
    Ethernet controller: Lite-On Communications Inc LNE100TX (rev 33).
      IRQ 5.
      Master Capable.  Latency=32.  
      I/O at 0xd000 [0xd0ff].
      Non-prefetchable 32 bit memory at 0xe3000000 [0xe30000ff].
  Bus  0, device  12, function  0:
    VGA compatible controller: S3 Inc. ViRGE/DX or /GX (rev 1).
      IRQ 11.
      Master Capable.  Latency=32.  Min Gnt=4.Max Lat=255.
      Non-prefetchable 32 bit memory at 0xdc000000 [0xdfffffff].

This output shows a list of all PCI devices, sorted in the order of bus, device, and function. Beyond providing the name and version of the device, this list also gives you detailed IRQ information so you can quickly look for conflicts.


To get a more readable version of this informations, type:

lspci -vb


This file gives information about memory usage on the slab level. Linux kernels greater than 2.2 use slab pools to manage memory above the page level. Commonly used objects have their own slab pools.

The values in this file occur in the following order: cache name, number of active objects, number of total objects, size of the object, number of active slabs (blocks) of the objects, total number of slabs of the objects, and the number of pages per slab.

It should be noted that active in this case means in use. An active object is one that is in use, and an active slab is one that contains any used objects.


This file keeps track of a variety of different statistics about the system since it was last restarted. The contents of /proc/stat, which can be quite long, begins something like this:

cpu  1139111 3689 234449 84378914
cpu0 1139111 3689 234449 84378914
page 2675248 8567956
swap 10022 19226
intr 93326523 85756163 174412 0 3 3 0 6 0 1 0 428620 0 60330 0 1368304 5538681
disk_io: (3,0):(1408049,445601,5349480,962448,17135856) 
ctxt 27269477
btime 886490134
processes 206458

Some of the more popular statistics include:


This file measures swap space and its utilization. For a system with only one swap partition, the output of /proc/swap may look similar to this:

Filename			Type		Size	Used	Priority
/dev/hda6                       partition	136512	20024	-1

While some of this information can be found in other /proc files, swap provides for a very quick snapshot of every swap filename, type of swap space, and total and used sizes (in kilobytes). The priority column is useful when multiple swap files are in use, and some of them are preferred over others, such as if they are on faster hard disks. The lower the priority, the more likely the swap file will be used.


This file contains information about how long the system has on since its last restart. The output of /proc/uptime is quite minimal:

350735.47 234388.90

The first number tells you the total number of seconds the system has been up. The second number tells you how much of that time, also in seconds, the machine has spent idle.


This files tells you the versions of the Linux kernel and gcc, as well as the version of Red Hat Linux installed on the system:

Linux version 2.4.18-0.4 ( (gcc version 2.96 20000731
(Red Hat Linux 7.2 2.96-106)) #1 Wed Mar 13 10:47:08 EST 2002

This information is used for a variety of purposes, including the version data presented when a user logs in.