The /proc directory also called as /proc
file system contains a hierarchy of files which represent the current state of
the kernel , allowing applications and users to peer into the Kernel view of
the system.
Simply a /proc file system is the view of
your computer. By using the /proc file system we can find various information including
hardware connected to the system , memory,cpus,hard drives and so on.
The Proc file system contains directories
and virtual files. These virtual files can present information from the kernel
to the user and also allows sending information from user to the kernel.
When we view the files in the /proc file
system , like ‘ll /proc’
We can see a series of numbers on the
left hand side. These numbers represent process running in the system. The
first process that starts when the linux starts is ‘init’, hence this process
will have the process ID ‘1’.When the process terminates, the corresponding
number in this location vanishes.
The Important Files in the /proc file
system are
/proc/Cpuinfo contains the
information established by the kernel about the processor at boot time, e.g.,
the type of processor, including CPU family, processor information and features.
/proc/Kcore is like a ‘alias’ for
the memory in the computer. So this has the same size of the amount of RAM we
have and if you read it as a file , the kernel does the memory read. The
contents of the file are designed to be examined by a debugger like gdb and are
not in human readable format.
/proc/loadavg contains the system
load averages for the last 1, 5 and 15 minutes, along with the number of
processes currently running and the total number of processes.
Localhost:root-proc $ cat
loadavg
0.12 0.14 0.10 1/534 15289
/proc/Meminfo contains the memory usage. It contains
information about how much of memory and swap available , in use and various
other information regarding memory usage of the system
localhost:root -proc $ cat
meminfo
MemTotal: 4194304 kB
MemFree: 581520 kB
Buffers: 711776
kB
Cached: 604880 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:
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.
/proc/swaps measures swap space and
its utilization. For a system with only one swap partition, the output of
/proc/swaps may look similar to the following:
[root@ras proc]# cat swaps
Filename Type Size Used
Priority
/dev/sda9 partition 6136788 0 -1
First column tells about 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.
/proc/Stat contains various statistics
about the kernel activity. The amount of usage the kernel has made with the
system resources.
Explaining stat
When you execute
localhost:root-proc $ cat
/proc/stat
cpu 101365990 2076376 119873084 1542606033
8471788 0 2353737 2880442
cpu0 49041138 1251727
39287515 789292472 6962731 0 2140388 1837752
cpu1 52324852 824649 80585569
753313561 1509057 0 213348 1042689
intr 4781453304 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 . . . . (will show a lot of values)
ctxt 8301802579
btime 1338526184
processes 55357479
procs_running 2
procs_blocked 0
The first 3 lines starting with CPU
identify the amount of time CPU has spent performing different kinds of works.
The Columns are
User Nice System Idle IOwait
IRQ SoftIRQ
cpu 101365990 2076376
119873084 1542606033 8471788 0 2353737 2880442
(Not Sure about the last value)
intr 4781453304 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 . . . . (will show a lot of values)
The intr line gives you the count of
interrupts served since boot time for system interrupts.This’4781453304’ is the total of all
interrupts serviced.
ctxt 8301802579
The ‘ctxt’ column gives the
number of context switchs across all the CPU’s.
btime 1338526184
The btime gives you the time
at which system booted in seconds.
processes 55357479
This tells us about the
number of process and threads created.
procs_running 2
This tells us about the
number of process running.
procs_blocked 0
This tells us about the
number of process blocked or waiting for an I/O operation.
/proc/uptime contains the amount of
time in seconds that the system has been running, and the amount of that time
that it has been idle.
Localhost:root-proc $ cat
uptime
8898720.25 7970338.08
/proc/version contains the kernel
version information that lists the version number, when it was compiled and who
compiled it.
Localhost:root-proc $ cat
version
Linux version
2.6.18-308.1.1.el5xen (mockbuild@hs20-bc2-3.build.redhat.com) (gcc version
4.1.2 20080704 (Red Hat 4.1.2-52)) #1 SMP Fri Feb 17 17:11:09 EST 2012
/proc/Cmdline tells us about the
parameters passed to kernel at the time it started.
Localhost:root-proc $ cat
cmdline
ro root=/dev/Vol00_vx1423/root console=xvc0
This tells us that the kernel
is mounted as read only (ro) , located on the logical volume Vol00_vx1423.
Console says the console
booting is supported and no GUI is available.
/proc/Devices This file
displays the various character and block devices currently configured (not
including devices whose modules are not loaded).
Localhost:root-proc $ cat
devices
Character devices:
1 mem
4 /dev/vc/0
4 tty
5 /dev/tty
5 /dev/console
5 /dev/ptmx
6 lp
7 vcs
10 misc
13 input
29 fb
128 ptm
136 pts
162 raw
180 usb
189 usb_device
202 cpu/msr
203 cpu/cpuid
204 xvc
253 hidraw
254 pcmcia
Block devices:
1 ramdisk
9 md
202 xvd
253 device-mapper
254 mdp
The output shows u the major number and
the device. The output of the /proc/devices is divided into 2 sections:
character devices and block devices
/proc/Device Files: Under linux each and every hardware device is treated as a
file. a device file allows users to access hardware devices so that the users
do not need to get into the details of the hardware. There are 2 types of
device files available,
Block Special Files: These
files talk to the device block by block.
Ex : hard disk
Character Files: These files talk to the device character by character.
Ex : terminal
A character file contains the first
letter as 'c' and block files contain 'b' as first letter.
/proc/filesystems lists all
the file systems that were compiled into our kernel.
Localhost:root-proc $ cat
filesystems
nodev sysfs
nodev rootfs
nodev bdev
nodev proc
nodev cpuset
nodev binfmt_misc
nodev debugfs
nodev securityfs
nodev sockfs
nodev usbfs
nodev pipefs
nodev anon_inodefs
nodev futexfs
nodev tmpfs
nodev inotifyfs
nodev eventpollfs
nodev devpts
ext2
nodev ramfs
iso9660
nodev mqueue
ext3
nodev rpc_pipefs
the ‘nodev’ column says that the file
system does not require a device for mounting (virtual file system)
/proc/ crypto tells us about the
installed cryptographic ciphers installed in the system
Localhost:root-proc $ cat
crypto
name : crc32c
driver :
crc32c-generic
module : kernel
priority : 0
type : digest
blocksize : 32
digestsize : 4
name : sha1
driver : sha1-generic
module :
kernel
priority : 0
type : digest
blocksize : 64
digestsize : 20
/proc/dma tells us about the
registered DMA channels in use
Localhost:root-proc $ cat dma
4: cascade
/proc/ interrupts records the
number of interrupts per IRQ.
Localhost:root-proc $ cat
interrupts
CPU0 CPU1
256: 1583733226 0
Dynamic-irq timer0
257: 26747867
0 Dynamic-irq resched0
258: 37 0
Dynamic-irq callfunc0
259: 325 0
Dynamic-irq xenbus
The first column is the IRQ number,
the second and third says about the cpu in the system which has its own column
and its own number of interrupts per IRQ. The next column is the type of the interrupt
and last column is the device that is located at that interrupt.
/proc/ iomem shows you the current
map of system memory for each physical device.
Localhost:root-proc $ cat iomem
000a0000-000bffff : Video RAM
area
/proc/ ioports lists ports
that are registered for input and output communication for a device.
Localhost:root-proc $ cat
ioports
0000-001f : dma1
0020-0021 : pic1
0040-0043 : timer0
0050-0053 : timer1
0060-0060 : keyboard
0064-0064 : keyboard
0080-008f : dma page reg
/proc/kmg is used to hold message
generated by the kernel. These messages are then picked up by dmesg
/proc/ modules list all the modules
loaded into the kernel. The same information can be viewed using ‘lsmod’
command.
/proc/ mounts list all the mounts in use by
system.
/proc/partitions contain
partition block allocation information.
Localhost:root-proc $ cat
partitions
major minor #blocks
name
202
0 44040192 xvda
202
1 522081 xvda1
202
2 41415570 xvda2
253
0 2097152 dm-0
/proc/fs specifies which file
system are exported much like nfs and so on.
/proc/tty specifies the available
and currently being used tty devices on the system.
/proc/PID
As we said earlier, each
process running will have a corresponding number in the /proc file system. Each
process directory contains
Cmdline : command line issued when starting the process
Cwd : a sym link to the current working directory
Environ : a list of environment variables for the process. The variable
is shown in caps where as the value is shown in small case
Exe: a sym link to the executable of this process
Mem : memory held by the process. This cant be viewed by users.
Root : a link to the root directory of the process
Stat : the status of the process
Statm : the status of the memory in use for the process
Localhost:root-4105 $ cat
statm
159358 24073 2418 10 0 154807
0
The seven columns relate to
different memory statistics for the process. From left to right, they report
the following aspects of the memory used:
Total program size, in
kilobytes.
Size of memory portions, in
kilobytes.
Number of pages that are
shared.
Number of pages that are
code.
Number of pages of
data/stack.
Number of library pages.
Number of dirty pages.
Status : the status of the process in detailed format.
Fd : information containing all of the file descriptors for a particular
process.
Maps : list of memory maps to the various executables and library associated
with the process.
Wchan: contains the name of the sys call the process is currently executing.
It contains ‘-‘ if the process is not in any sys call.
More To Come , Happy Learning
