5.2. Top-level Files within the proc File System

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


In most cases, the content of the files listed in this section are not the same as those installed on your machine. This is because much of the information is specific to the hardware on which Red Hat Enterprise Linux is running.

5.2.1. /proc/apm

This file provides information about the state of the Advanced Power Management (APM) system and is used by the apm command. If a system with no battery is connected to an AC power source, this virtual file would look similar to the following:

1.16 1.2 0x07 0x01 0xff 0x80 -1% -1 ?

Running the apm -v command on such a system results in output similar to the following:

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

For systems which do not use a battery as a power source, apm is able do little more than put the machine in standby mode. The apm command is much more useful on laptops. For example, the following output is from the command cat /proc/apm on a laptop while plugged into a power outlet:

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

When the same laptop is unplugged from its power source for a few minutes, the contents of the apm file change to something like the following:

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

The apm -v command now yields more useful data, such as the following:

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

5.2.2. /proc/cmdline

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

ro root=/dev/hda2

This tells us that the kernel is mounted read-only (signified by (ro)) off of the second partition on the first IDE device (/dev/hda2).

5.2.3. /proc/cpuinfo

This virtual file identifies the type of processor used by your system. The following is an example of the output typical of /proc/cpuinfo:

processor	: 0
vendor_id	: GenuineIntel
cpu family	: 15
model		: 2
model name	: Intel(R) Xeon(TM) CPU 2.40GHz
stepping	: 7
cpu MHz		: 2392.371
cache size	: 512 KB
physical id	: 0
siblings	: 2
runqueue	: 0
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca 
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips	: 4771.02

5.2.4. /proc/devices

This file displays the various character and block devices currently configured (not including devices whose modules are not loaded). Below is a sample output from this 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, and is broken into two major sections: Character devices and Block devices.

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

  1. Block devices have a buffer available, allowing them to order requests before addressing 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 a more efficient order. Character devices do not require buffering.

  2. 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 refer to the following installed documentation:


5.2.5. /proc/dma

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

 4: cascade

5.2.6. /proc/execdomains

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 the "personality" for an operating system. Because other binary formats, such as Solaris, UnixWare, and FreeBSD, can be used with Linux, programmers can change the way the operating system treats system calls from these binaries by changing the personality of the task. Except for the PER_LINUX execution domain, different personalities can be implemented as dynamically loadable modules.

5.2.7. /proc/fb

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 which contain frame buffer devices looks similar to the following:


5.2.8. /proc/filesystems

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

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 names of the file systems supported.

The mount command cycles through the file systems listed here when one is not specified as an argument.

5.2.9. /proc/interrupts

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

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

5.2.10. /proc/iomem

This file shows you the current map of the system's memory for each physical device:

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 lists the kind of memory located within those registers and displays which memory registers are used by the kernel within the system RAM or, if the network interface card has multiple Ethernet ports, the memory registers assigned for each port.

5.2.11. /proc/ioports

The output of /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. The following is a partial listing:

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 I/O port address range reserved for the device listed in the second column.

5.2.12. /proc/isapnp

This file lists installed 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. The following is an example /proc/isapnp file with a sound card installed:

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 and their resource requirements.

Each card lists its name, PnP version number, and product version number. If the device is active and configured, this file also reveals the port and IRQ numbers for the device. In addition, to ensure better compatibility, the card specifies 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.

5.2.13. /proc/kcore

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

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


Do not view the /proc/kcore virtual file. The contents of the file scrambles text output on the terminal. If this file is accidentally viewed, press [Ctrl]-[C] to stop the process and then type reset to bring back the command line prompt.

5.2.14. /proc/kmsg

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

5.2.15. /proc/ksyms

This file contains the symbol definitions used by the module tools to dynamically link and bind kernel modules.

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

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

5.2.16. /proc/loadavg

This file provides a look the load average in regards to both the CPU and IO over time, as well as additional data used by uptime and other commands. A sample /proc/loadavg file looks similar to the following:

0.20 0.18 0.12 1/80 11206

The first three columns measure CPU and IO 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.

5.2.17. /proc/locks

This file displays the files currently locked by the kernel. The contents of this file contain internal kernel debugging data and can vary tremendously, depending on the use of the system. A sample /proc/locks file for a lightly loaded system looks similar to the following:

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 has its own line which starts with a unique number. 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 or MANDATORY. 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. 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.

5.2.18. /proc/mdstat

This file contains the current information for multiple-disk, RAID configurations. If the system does not contain such a configuration, then /proc/mdstat looks similar to the following:

Personalities : 
read_ahead not set
unused devices: <none>

This file remains in the same state as seen above unless a software RAID or md device is present. In that case, view /proc/mdstat to find the current status of mdX RAID devices.

The /proc/mdstat file below shows a system with its md0 configured as a RAID 1 device, while 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>

5.2.19. /proc/meminfo

This is one of the more commonly used files in the /proc/ directory, as it reports a large amount of valuable information about the systems RAM usage.

The following sample /proc/meminfo virtual file is from a system with 256MB of RAM and 384MB of swap space:

       total:     used:    free:   shared: buffers:  cached:
Mem:  128692224 121212928  7479296        0  9293824 47964160
Swap: 1103093760 32772096 1070321664
MemTotal:       125676 kB
MemFree:          7304 kB
MemShared:           0 kB
Buffers:          9076 kB
Cached:          34204 kB
SwapCached:      12636 kB
Active:          79352 kB
ActiveAnon:      57308 kB
ActiveCache:     22044 kB
Inact_dirty:       240 kB
Inact_laundry:   17468 kB
Inact_clean:       984 kB
Inact_target:    19608 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       125676 kB
LowFree:          7304 kB
SwapTotal:     1077240 kB
SwapFree:      1045236 kB
HugePages_Total:     2
HugePages_Free:      2
Hugepagesize:     2096 kB

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

5.2.20. /proc/misc

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

135 rtc
  1 psaux
134 apm_bios

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

5.2.21. /proc/modules

This file displays a list of all modules loaded into the kernel. Its contents 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 lists 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). A module with a line containing a name listed in brackets ([ or ]) indicates that the module depends upon another module to be present in order to function.

This information can also be viewed via the /sbin/lsmod command.

5.2.22. /proc/mounts

This file provides a 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 is more up-to-date.

The first column specifies the device that is mounted, the second column reveals the mount point, and 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.

5.2.23. /proc/mtrr

This file refers to the current Memory Type Range Registers (MTRRs) in use with the system. If the system architecture supports MTRRs, then the /proc/mtrr file may look similar to the following:

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

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

Most of the time, this value is properly configured by default. More information on manually configuring this file, can be found online at the following URL:


5.2.24. /proc/partitions

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

5.2.25. /proc/pci

This file contains a full listing of every PCI device on the system. Depending on the number of PCI devices, /proc/pci can be rather long. A sampling of this file from a basic system looks similar to the following:

  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 detailed IRQ information so an administrator can quickly look for conflicts.


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

/sbin/lspci -vb

5.2.26. /proc/slabinfo

This file gives information about memory usage on the slab level. Linux kernels greater than version 2.2 use slab pools to manage memory above the page level. Commonly used objects have their own slab pools. The following is a portion of a typical /proc/slabinfo virtual file:

slabinfo - version: 1.1 (statistics)
kmem_cache            64     68    112    2    2    1
nfs_write_data         0      0    384    0    0    1
nfs_read_data          0    160    384    0   16    1
nfs_page               0    200     96    0    5    1
ip_fib_hash           10    113     32    1    1    1
journal_head          51   7020     48    2   90    1
revoke_table           2    253     12    1    1    1
revoke_record          0      0     32    0    0    1
clip_arp_cache         0      0    128    0    0    1
ip_mrt_cache           0      0     96    0    0    1

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.

Note that active in this case means an object is in use.

5.2.27. /proc/stat

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, usually begins like the following example:

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 commonly used statistics include:

5.2.28. /proc/sysrq-trigger

Using the echo command to wrote to this file, a remote root user can execute most System Request Key commands remotely as if at the local terminal. To echo values to this file, the /proc/sys/kernel/sysrq must be set to a value other than 0. For more information about the System Request Key, refer to Section /proc/sys/kernel/.

Although it is possible to write to this file, it cannot be read, even by the root user.

5.2.29. /proc/swaps

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 the following:

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

While some of this information can be found in other files in the /proc/ directory, /proc/swap provides a snapshot of every swap file name, the type of swap space, the total size, and the amount of space is in use (in kilobytes). The priority column is useful when multiple swap files are in use. The lower the priority, the more likely the swap file is to be used.

5.2.30. /proc/uptime

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

350735.47 234388.90

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

5.2.31. /proc/version

This file specifies the version of the Linux kernel and gcc in use, as well as the version of Red Hat Enterprise Linux installed on the system:

Linux version 2.4.20-1.1931. (user@foo.redhat.com) (gcc version 3.2.3 20030422 
(Red Hat Enterprise Linux 3.2.3-7)) #1 Thu Jun 19 14:57:04 EDT 2003

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