Below is a list of some of the more useful virtual files in the
top-level of the /proc/ directory.
Note
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 for this documentation effort.
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 1.16ac)
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 content of the apm file changes 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)
This file is used primarily for diagnosing memory fragmentation
issues. Using the buddy algorithm, each column represents the number
of pages of a certain order (a certain size) that are available at any
given time. For example, for zone DMA (direct memory access), there
are 90 of 2^(0*PAGE_SIZE) chunks of memory. Similarly, there are 6 of
2^(1*PAGE_SIZE) chunks, and 2 of 2^(2*PAGE_SIZE) chunks of memory
available.
The
DMA row references the first 16 MB on a system,
the HighMem row references all memory greater
than 4 GB on a system, and the Normal row
references all memory in between.
The following is an example of the output typical of
/proc/buddyinfo:
Node 0, zone DMA 90 6 2 1 1 ...
Node 0, zone Normal 1650 310 5 0 0 ...
Node 0, zone HighMem 2 0 0 1 1 ...
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/VolGroup00/LogVol00 rhgb quiet 3
This tells us that the kernel is mounted read-only (signified by
(ro)), located on the first logical
volume (LogVol00) of the first volume
group
(/dev/VolGroup00). LogVol00
is the equivalent of a disk partition in a non-LVM system (Logical
Volume Management), just as
/dev/VolGroup00 is similar in concept
to /dev/hda1, but much more extensible.
Next, rhgb signals that the
rhgb package has been installed, and graphical
booting is supported, assuming /etc/inittab shows
a default runlevel set to id:5:initdefault:.
Finally, quiet indicates all verbose
kernel messages are suppressed at boot time.
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
processor — Provides
each processor with an identifying number. On systems that have
one processor, only a 0 is
present.
cpu family —
Authoritatively identifies the type of processor in the
system. For an Intel-based system, place the number in front of
"86" to determine the value. This is particularly helpful for
those attempting to identify the architecture of an older system
such as a 586, 486, or 386. Because some RPM packages are compiled
for each of these particular architectures, this value also helps
users determine which packages to install.
model name — Displays
the common name of the processor, including its project name.
cpu MHz — Shows
the precise speed in megahertz for the processor to the
thousandths decimal place.
cache size — Displays
the amount of level 2 memory cache available to the processor.
siblings —
Displays the number of sibling CPUs on the same physical CPU for
architectures which use hyper-threading.
flags — Defines
a number of different qualities about the processor, such as the
presence of a floating point unit (FPU) and the ability to process
MMX instructions.
This file lists all installed cryptographic ciphers used by the Linux
kernel, including additional details for each. A sample
/proc/crypto file looks like the following:
name : sha1
module : kernel
type : digest
blocksize : 64
digestsize : 20
name : md5
module : md5
type : digest
blocksize : 64
digestsize : 16
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:
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:
Character devices do not require buffering. 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 send data with no preconfigured size. Block
devices can send and receive information in blocks of a size
configured per device.
For more information about devices refer to the following installed documentation:
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.
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:
This file displays a list of the file system types currently supported
by the kernel. Sample output from a generic
/proc/filesystems file looks similar to the
following:
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.
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:
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 is high until the
signal is low again.
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.
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:
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 4 KB.
The contents of this file are designed to be examined by a debugger,
such as gdb, and is not human readable.
Caution
Do not view the /proc/kcore virtual file. The
contents of the file scramble 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.
This file provides a look at the load average in regard 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 one,
five, 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 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:
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 and eighth column shows the start and end of the file's
locked region.
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:
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:
MemTotal — Total amount
of physical RAM, in kilobytes.
MemFree — The amount of
physical RAM, in kilobytes, left unused by the system.
Buffers — The amount of
physical RAM, in kilobytes, used for file buffers.
Cached — The amount of
physical RAM, in kilobytes, used as cache memory.
SwapCached — The amount
of swap, in kilobytes, used as cache memory.
Active — The total
amount of buffer or page cache memory, in kilobytes, that is in
active use. This is memory that has been recently used and is
usually not reclaimed for other purposes.
Inactive — The total
amount of buffer or page cache memory, in kilobytes, that are free
and available. This is memory that has not been recently used and
can be reclaimed for other purposes.
HighTotal and
HighFree — The total and
free amount of memory, in kilobytes, that is not directly mapped
into kernel space. The HighTotal
value can vary based on the type of kernel used.
LowTotal and
LowFree — The total and
free amount of memory, in kilobytes, that is directly mapped
into kernel space. The LowTotal
value can vary based on the type of kernel used.
SwapTotal — The total
amount of swap available, in kilobytes.
SwapFree — The total
amount of swap free, in kilobytes.
Dirty — The total
amount of memory, in kilobytes, waiting to be written back to the
disk.
Writeback — The total
amount of memory, in kilobytes, actively being written back to the
disk.
Mapped — The total
amount of memory, in kilobytes, which have been used to map
devices, files, or libraries using the mmap
command.
Slab — The total amount
of memory, in kilobytes, used by the kernel to cache data
structures for its own use.
Committed_AS — The
total amount of memory, in kilobytes, estimated to complete the
workload. This value represents the worst case scenario value, and
also includes swap memory.
PageTables — The total
amount of memory, in kilobytes, dedicated to the lowest page table
level.
VMallocTotal — The
total amount of memory, in kilobytes, of total allocated virtual
address space.
VMallocUsed — The total
amount of memory, in kilobytes, of used virtual address space.
VMallocChunk — The
largest contiguous block of memory, in kilobytes, of available
virtual address space.
HugePages_Total — The
total number of hugepages for the system. The number is derived by
dividing Hugepagesize by the
megabytes set aside for hugepages specified in
/proc/sys/vm/hugetlb_pool. This
statistic only appears on the x86, Itanium, and AMD64
architectures.
HugePages_Free — The
total number of hugepages available for the system. This
statistic only appears on the x86, Itanium, and AMD64
architectures.
Hugepagesize — The size
for each hugepages unit in kilobytes. By default, the value is
4096 KB on uniprocessor kernels for 32 bit architectures. For SMP,
hugemem kernels, and AMD64, the default is 2048 KB. For Itanium
architectures, the default is 262144 KB. This statistic
only appears on the x86, Itanium, and AMD64
architectures.
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:
Note
This example has been reformatted into a readable format. Most of
this information can also be viewed via the
/sbin/lsmod command.
nfs 170109 0 - Live 0x129b0000
lockd 51593 1 nfs, Live 0x128b0000
nls_utf8 1729 0 - Live 0x12830000
vfat 12097 0 - Live 0x12823000
fat 38881 1 vfat, Live 0x1287b000
autofs4 20293 2 - Live 0x1284f000
sunrpc 140453 3 nfs,lockd, Live 0x12954000
3c59x 33257 0 - Live 0x12871000
uhci_hcd 28377 0 - Live 0x12869000
md5 3777 1 - Live 0x1282c000
ipv6 211845 16 - Live 0x128de000
ext3 92585 2 - Live 0x12886000
jbd 65625 1 ext3, Live 0x12857000
dm_mod 46677 3 - Live 0x12833000
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 how many instances of the module are currently
loaded. A value of zero represents an unloaded module.
The fourth column states if the module depends upon another module to
be present in order to function, and lists those other modules.
The fifth column lists what load state the module is in:
Live, Loading, or
Unloading are the only possible values.
The sixth column lists the current kernel memory offset for the loaded
module. This information can be useful for debugging purposes, or for
profiling tools such as oprofile.
The output found here is similar to the 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.
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:
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 locally at
the following location:
This file contains partition block allocation information. A sampling
of this file from a basic system looks similar to the following:
major minor #blocks name
3 0 19531250 hda
3 1 104391 hda1
3 2 19422585 hda2
253 0 22708224 dm-0
253 1 524288 dm-1
Most of the information here is of little importance to the user,
except for the following columns:
major — The major
number of the device with this partition. The major number in the
/proc/partitions,
(3), corresponds with the block
device ide0, in
/proc/devices.
minor — The minor number
of the device with this partition. This serves to separate the
partitions into different physical devices and relates to the
number at the end of the name of the partition.
#blocks — Lists the
number of physical disk blocks contained in a particular
partition.
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.
Tip
To get a more readable version of this information, type:
This file gives full 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.
Instead of parsing the highly verbose
/proc/slabinfo file manually, the
/usr/bin/slabtop program displays kernel slab
cache information in real time. This program allows for custom
configurations, including column sorting and screen refreshing.
A sample screen shot of /usr/bin/slabtop usually
looks like the following example:
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:
Some of the more commonly used statistics include:
cpu — Measures the
number of jiffies (1/100 of a second for
x86 systems) that the system has been in user mode, user mode with
low priority (nice), system mode, idle task, I/O wait, IRQ
(hardirq), and softirq respectively. The IRQ (hardirq) is the
direct response to a hardware event. The IRQ takes minimal work
for queuing the "heavy" work up for the softirq to execute. The
softirq runs at a lower priority than the IRQ and therefore may be
interrupted more frequently. The total for all CPUs is given at
the top, while each individual CPU is listed below with its own
statistics. The following example is a 4-way Intel Pentium Xeon
configuration with multi-threading enabled, therefore showing four
physical processors and four virtual processors totaling eight
processors.
page — The number of
memory pages the system has written in and out to disk.
swap — The number of swap
pages the system has brought in and out.
intr — The number of
interrupts the system has experienced.
btime — The boot time,
measured in the number of seconds since January 1, 1970,
otherwise known as the epoch.
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/mapper/VolGroup00-LogVol01 partition 524280 0 -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 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.
Using the echo command to write 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 5.3.9.3 /proc/sys/kernel/.
Although it is possible to write to this file, it cannot be read, even
by the root user.
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.
