Bodo Bauer <bb@ricochet.net>
2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
+move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
------------------------------------------------------------------------------
Version 1.3 Kernel version 2.2.12
Kernel version 2.4.0-test11-pre4
------------------------------------------------------------------------------
+fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
Table of Contents
-----------------
1.6 Parallel port info in /proc/parport
1.7 TTY info in /proc/tty
1.8 Miscellaneous kernel statistics in /proc/stat
+ 1.9 Ext4 file system parameters
2 Modifying System Parameters
- 2.1 /proc/sys/fs - File system data
- 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
- 2.3 /proc/sys/kernel - general kernel parameters
- 2.4 /proc/sys/vm - The virtual memory subsystem
- 2.5 /proc/sys/dev - Device specific parameters
- 2.6 /proc/sys/sunrpc - Remote procedure calls
- 2.7 /proc/sys/net - Networking stuff
- 2.8 /proc/sys/net/ipv4 - IPV4 settings
- 2.9 Appletalk
- 2.10 IPX
- 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
+
+ 3 Per-Process Parameters
+ 3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
+ 3.2 /proc/<pid>/oom_score - Display current oom-killer score
+ 3.3 /proc/<pid>/io - Display the IO accounting fields
+ 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
+ 3.5 /proc/<pid>/mountinfo - Information about mounts
+ 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
+
------------------------------------------------------------------------------
Preface
subdirectory has the entries listed in Table 1-1.
-Table 1-1: Process specific entries in /proc
+Table 1-1: Process specific entries in /proc
..............................................................................
- File Content
- cmdline Command line arguments
- cpu Current and last cpu in wich it was executed (2.4)(smp)
- cwd Link to the current working directory
- environ Values of environment variables
- exe Link to the executable of this process
- fd Directory, which contains all file descriptors
- maps Memory maps to executables and library files (2.4)
- mem Memory held by this process
- root Link to the root directory of this process
- stat Process status
- statm Process memory status information
- status Process status in human readable form
- wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
- smaps Extension based on maps, presenting the rss size for each mapped file
+ File Content
+ clear_refs Clears page referenced bits shown in smaps output
+ cmdline Command line arguments
+ cpu Current and last cpu in which it was executed (2.4)(smp)
+ cwd Link to the current working directory
+ environ Values of environment variables
+ exe Link to the executable of this process
+ fd Directory, which contains all file descriptors
+ maps Memory maps to executables and library files (2.4)
+ mem Memory held by this process
+ root Link to the root directory of this process
+ stat Process status
+ statm Process memory status information
+ status Process status in human readable form
+ wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
+ stack Report full stack trace, enable via CONFIG_STACKTRACE
+ smaps a extension based on maps, showing the memory consumption of
+ each mapping
..............................................................................
For example, to get the status information of a process, all you have to do is
read the file /proc/PID/status:
- >cat /proc/self/status
- Name: cat
- State: R (running)
- Pid: 5452
- PPid: 743
+ >cat /proc/self/status
+ Name: cat
+ State: R (running)
+ Tgid: 5452
+ Pid: 5452
+ PPid: 743
TracerPid: 0 (2.4)
- Uid: 501 501 501 501
- Gid: 100 100 100 100
- Groups: 100 14 16
- VmSize: 1112 kB
- VmLck: 0 kB
- VmRSS: 348 kB
- VmData: 24 kB
- VmStk: 12 kB
- VmExe: 8 kB
- VmLib: 1044 kB
- SigPnd: 0000000000000000
- SigBlk: 0000000000000000
- SigIgn: 0000000000000000
- SigCgt: 0000000000000000
- CapInh: 00000000fffffeff
- CapPrm: 0000000000000000
- CapEff: 0000000000000000
-
+ Uid: 501 501 501 501
+ Gid: 100 100 100 100
+ FDSize: 256
+ Groups: 100 14 16
+ VmPeak: 5004 kB
+ VmSize: 5004 kB
+ VmLck: 0 kB
+ VmHWM: 476 kB
+ VmRSS: 476 kB
+ VmData: 156 kB
+ VmStk: 88 kB
+ VmExe: 68 kB
+ VmLib: 1412 kB
+ VmPTE: 20 kb
+ VmSwap: 0 kB
+ Threads: 1
+ SigQ: 0/28578
+ SigPnd: 0000000000000000
+ ShdPnd: 0000000000000000
+ SigBlk: 0000000000000000
+ SigIgn: 0000000000000000
+ SigCgt: 0000000000000000
+ CapInh: 00000000fffffeff
+ CapPrm: 0000000000000000
+ CapEff: 0000000000000000
+ CapBnd: ffffffffffffffff
+ voluntary_ctxt_switches: 0
+ nonvoluntary_ctxt_switches: 1
This shows you nearly the same information you would get if you viewed it with
the ps command. In fact, ps uses the proc file system to obtain its
-information. The statm file contains more detailed information about the
-process memory usage. Its seven fields are explained in Table 1-2.
+information. But you get a more detailed view of the process by reading the
+file /proc/PID/status. It fields are described in table 1-2.
+
+The statm file contains more detailed information about the process
+memory usage. Its seven fields are explained in Table 1-3. The stat file
+contains details information about the process itself. Its fields are
+explained in Table 1-4.
+(for SMP CONFIG users)
+For making accounting scalable, RSS related information are handled in
+asynchronous manner and the vaule may not be very precise. To see a precise
+snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
+It's slow but very precise.
+
+Table 1-2: Contents of the statm files (as of 2.6.30-rc7)
+..............................................................................
+ Field Content
+ Name filename of the executable
+ State state (R is running, S is sleeping, D is sleeping
+ in an uninterruptible wait, Z is zombie,
+ T is traced or stopped)
+ Tgid thread group ID
+ Pid process id
+ PPid process id of the parent process
+ TracerPid PID of process tracing this process (0 if not)
+ Uid Real, effective, saved set, and file system UIDs
+ Gid Real, effective, saved set, and file system GIDs
+ FDSize number of file descriptor slots currently allocated
+ Groups supplementary group list
+ VmPeak peak virtual memory size
+ VmSize total program size
+ VmLck locked memory size
+ VmHWM peak resident set size ("high water mark")
+ VmRSS size of memory portions
+ VmData size of data, stack, and text segments
+ VmStk size of data, stack, and text segments
+ VmExe size of text segment
+ VmLib size of shared library code
+ VmPTE size of page table entries
+ VmSwap size of swap usage (the number of referred swapents)
+ Threads number of threads
+ SigQ number of signals queued/max. number for queue
+ SigPnd bitmap of pending signals for the thread
+ ShdPnd bitmap of shared pending signals for the process
+ SigBlk bitmap of blocked signals
+ SigIgn bitmap of ignored signals
+ SigCgt bitmap of catched signals
+ CapInh bitmap of inheritable capabilities
+ CapPrm bitmap of permitted capabilities
+ CapEff bitmap of effective capabilities
+ CapBnd bitmap of capabilities bounding set
+ Cpus_allowed mask of CPUs on which this process may run
+ Cpus_allowed_list Same as previous, but in "list format"
+ Mems_allowed mask of memory nodes allowed to this process
+ Mems_allowed_list Same as previous, but in "list format"
+ voluntary_ctxt_switches number of voluntary context switches
+ nonvoluntary_ctxt_switches number of non voluntary context switches
+..............................................................................
-Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
+Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
..............................................................................
Field Content
size total program size (pages) (same as VmSize in status)
dt number of dirty pages (always 0 on 2.6)
..............................................................................
+
+Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
+..............................................................................
+ Field Content
+ pid process id
+ tcomm filename of the executable
+ state state (R is running, S is sleeping, D is sleeping in an
+ uninterruptible wait, Z is zombie, T is traced or stopped)
+ ppid process id of the parent process
+ pgrp pgrp of the process
+ sid session id
+ tty_nr tty the process uses
+ tty_pgrp pgrp of the tty
+ flags task flags
+ min_flt number of minor faults
+ cmin_flt number of minor faults with child's
+ maj_flt number of major faults
+ cmaj_flt number of major faults with child's
+ utime user mode jiffies
+ stime kernel mode jiffies
+ cutime user mode jiffies with child's
+ cstime kernel mode jiffies with child's
+ priority priority level
+ nice nice level
+ num_threads number of threads
+ it_real_value (obsolete, always 0)
+ start_time time the process started after system boot
+ vsize virtual memory size
+ rss resident set memory size
+ rsslim current limit in bytes on the rss
+ start_code address above which program text can run
+ end_code address below which program text can run
+ start_stack address of the start of the stack
+ esp current value of ESP
+ eip current value of EIP
+ pending bitmap of pending signals
+ blocked bitmap of blocked signals
+ sigign bitmap of ignored signals
+ sigcatch bitmap of catched signals
+ wchan address where process went to sleep
+ 0 (place holder)
+ 0 (place holder)
+ exit_signal signal to send to parent thread on exit
+ task_cpu which CPU the task is scheduled on
+ rt_priority realtime priority
+ policy scheduling policy (man sched_setscheduler)
+ blkio_ticks time spent waiting for block IO
+ gtime guest time of the task in jiffies
+ cgtime guest time of the task children in jiffies
+..............................................................................
+
+The /proc/PID/map file containing the currently mapped memory regions and
+their access permissions.
+
+The format is:
+
+address perms offset dev inode pathname
+
+08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
+08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
+0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
+a7cb1000-a7cb2000 ---p 00000000 00:00 0
+a7cb2000-a7eb2000 rw-p 00000000 00:00 0 [threadstack:001ff4b4]
+a7eb2000-a7eb3000 ---p 00000000 00:00 0
+a7eb3000-a7ed5000 rw-p 00000000 00:00 0
+a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
+a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
+a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
+a800b000-a800e000 rw-p 00000000 00:00 0
+a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
+a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
+a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
+a8024000-a8027000 rw-p 00000000 00:00 0
+a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
+a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
+a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
+aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
+ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
+
+where "address" is the address space in the process that it occupies, "perms"
+is a set of permissions:
+
+ r = read
+ w = write
+ x = execute
+ s = shared
+ p = private (copy on write)
+
+"offset" is the offset into the mapping, "dev" is the device (major:minor), and
+"inode" is the inode on that device. 0 indicates that no inode is associated
+with the memory region, as the case would be with BSS (uninitialized data).
+The "pathname" shows the name associated file for this mapping. If the mapping
+is not associated with a file:
+
+ [heap] = the heap of the program
+ [stack] = the stack of the main process
+ [vdso] = the "virtual dynamic shared object",
+ the kernel system call handler
+ [threadstack:xxxxxxxx] = the stack of the thread, xxxxxxxx is the stack size
+
+ or if empty, the mapping is anonymous.
+
+
+The /proc/PID/smaps is an extension based on maps, showing the memory
+consumption for each of the process's mappings. For each of mappings there
+is a series of lines such as the following:
+
+08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
+Size: 1084 kB
+Rss: 892 kB
+Pss: 374 kB
+Shared_Clean: 892 kB
+Shared_Dirty: 0 kB
+Private_Clean: 0 kB
+Private_Dirty: 0 kB
+Referenced: 892 kB
+Swap: 0 kB
+KernelPageSize: 4 kB
+MMUPageSize: 4 kB
+
+The first of these lines shows the same information as is displayed for the
+mapping in /proc/PID/maps. The remaining lines show the size of the mapping,
+the amount of the mapping that is currently resident in RAM, the "proportional
+set size” (divide each shared page by the number of processes sharing it), the
+number of clean and dirty shared pages in the mapping, and the number of clean
+and dirty private pages in the mapping. The "Referenced" indicates the amount
+of memory currently marked as referenced or accessed.
+
+This file is only present if the CONFIG_MMU kernel configuration option is
+enabled.
+
+The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
+bits on both physical and virtual pages associated with a process.
+To clear the bits for all the pages associated with the process
+ > echo 1 > /proc/PID/clear_refs
+
+To clear the bits for the anonymous pages associated with the process
+ > echo 2 > /proc/PID/clear_refs
+
+To clear the bits for the file mapped pages associated with the process
+ > echo 3 > /proc/PID/clear_refs
+Any other value written to /proc/PID/clear_refs will have no effect.
+
+
1.2 Kernel data
---------------
Similar to the process entries, the kernel data files give information about
the running kernel. The files used to obtain this information are contained in
-/proc and are listed in Table 1-3. Not all of these will be present in your
+/proc and are listed in Table 1-5. Not all of these will be present in your
system. It depends on the kernel configuration and the loaded modules, which
files are there, and which are missing.
-Table 1-3: Kernel info in /proc
+Table 1-5: Kernel info in /proc
..............................................................................
File Content
apm Advanced power management info
modules List of loaded modules
mounts Mounted filesystems
net Networking info (see text)
+ pagetypeinfo Additional page allocator information (see text) (2.5)
partitions Table of partitions known to the system
- pci Depreciated info of PCI bus (new way -> /proc/bus/pci/,
+ pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
decoupled by lspci (2.4)
rtc Real time clock
scsi SCSI info (see text)
slabinfo Slab pool info
+ softirqs softirq usage
stat Overall statistics
swaps Swap space utilization
sys See chapter 2
uptime System uptime
version Kernel version
video bttv info of video resources (2.4)
+ vmallocinfo Show vmalloced areas
..............................................................................
You can, for example, check which interrupts are currently in use and what
the IO-APIC automatically retry the transmission, so it should not be a big
problem, but you should read the SMP-FAQ.
-In this context it could be interesting to note the new irq directory in 2.4.
+In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
+/proc/interrupts to display every IRQ vector in use by the system, not
+just those considered 'most important'. The new vectors are:
+
+ THR -- interrupt raised when a machine check threshold counter
+ (typically counting ECC corrected errors of memory or cache) exceeds
+ a configurable threshold. Only available on some systems.
+
+ TRM -- a thermal event interrupt occurs when a temperature threshold
+ has been exceeded for the CPU. This interrupt may also be generated
+ when the temperature drops back to normal.
+
+ SPU -- a spurious interrupt is some interrupt that was raised then lowered
+ by some IO device before it could be fully processed by the APIC. Hence
+ the APIC sees the interrupt but does not know what device it came from.
+ For this case the APIC will generate the interrupt with a IRQ vector
+ of 0xff. This might also be generated by chipset bugs.
+
+ RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
+ sent from one CPU to another per the needs of the OS. Typically,
+ their statistics are used by kernel developers and interested users to
+ determine the occurrence of interrupts of the given type.
+
+The above IRQ vectors are displayed only when relevent. For example,
+the threshold vector does not exist on x86_64 platforms. Others are
+suppressed when the system is a uniprocessor. As of this writing, only
+i386 and x86_64 platforms support the new IRQ vector displays.
+
+Of some interest is the introduction of the /proc/irq directory to 2.4.
It could be used to set IRQ to CPU affinity, this means that you can "hook" an
IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
-irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
+irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
+prof_cpu_mask.
For example
> ls /proc/irq/
0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
- 1 11 13 15 17 19 3 5 7 9
+ 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
> ls /proc/irq/0/
smp_affinity
-The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
-is the same by default:
+smp_affinity is a bitmask, in which you can specify which CPUs can handle the
+IRQ, you can set it by doing:
- > cat /proc/irq/0/smp_affinity
- ffffffff
+ > echo 1 > /proc/irq/10/smp_affinity
+
+This means that only the first CPU will handle the IRQ, but you can also echo
+5 which means that only the first and fourth CPU can handle the IRQ.
+
+The contents of each smp_affinity file is the same by default:
-It's a bitmask, in wich you can specify wich CPUs can handle the IRQ, you can
-set it by doing:
+ > cat /proc/irq/0/smp_affinity
+ ffffffff
- > echo 1 > /proc/irq/prof_cpu_mask
+The default_smp_affinity mask applies to all non-active IRQs, which are the
+IRQs which have not yet been allocated/activated, and hence which lack a
+/proc/irq/[0-9]* directory.
-This means that only the first CPU will handle the IRQ, but you can also echo 5
-wich means that only the first and fourth CPU can handle the IRQ.
+prof_cpu_mask specifies which CPUs are to be profiled by the system wide
+profiler. Default value is ffffffff (all cpus).
The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
between all the CPUs which are allowed to handle it. As usual the kernel has
Node 0, zone Normal 1 0 0 1 101 8 ...
Node 0, zone HighMem 2 0 0 1 1 0 ...
-Memory fragmentation is a problem under some workloads, and buddyinfo is a
+External fragmentation is a problem under some workloads, and buddyinfo is a
useful tool for helping diagnose these problems. Buddyinfo will give you a
clue as to how big an area you can safely allocate, or why a previous
allocation failed.
ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
available in ZONE_NORMAL, etc...
+More information relevant to external fragmentation can be found in
+pagetypeinfo.
+
+> cat /proc/pagetypeinfo
+Page block order: 9
+Pages per block: 512
+
+Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
+Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
+Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
+Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
+Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
+Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
+Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
+Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
+Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
+Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
+Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
+
+Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
+Node 0, zone DMA 2 0 5 1 0
+Node 0, zone DMA32 41 6 967 2 0
+
+Fragmentation avoidance in the kernel works by grouping pages of different
+migrate types into the same contiguous regions of memory called page blocks.
+A page block is typically the size of the default hugepage size e.g. 2MB on
+X86-64. By keeping pages grouped based on their ability to move, the kernel
+can reclaim pages within a page block to satisfy a high-order allocation.
+
+The pagetypinfo begins with information on the size of a page block. It
+then gives the same type of information as buddyinfo except broken down
+by migrate-type and finishes with details on how many page blocks of each
+type exist.
+
+If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
+from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
+make an estimate of the likely number of huge pages that can be allocated
+at a given point in time. All the "Movable" blocks should be allocatable
+unless memory has been mlock()'d. Some of the Reclaimable blocks should
+also be allocatable although a lot of filesystem metadata may have to be
+reclaimed to achieve this.
+
..............................................................................
meminfo:
SwapFree: 0 kB
Dirty: 968 kB
Writeback: 0 kB
+AnonPages: 861800 kB
Mapped: 280372 kB
-Slab: 684068 kB
+Slab: 284364 kB
+SReclaimable: 159856 kB
+SUnreclaim: 124508 kB
+PageTables: 24448 kB
+NFS_Unstable: 0 kB
+Bounce: 0 kB
+WritebackTmp: 0 kB
CommitLimit: 7669796 kB
Committed_AS: 100056 kB
-PageTables: 24448 kB
VmallocTotal: 112216 kB
VmallocUsed: 428 kB
VmallocChunk: 111088 kB
this memory, making it slower to access than lowmem.
LowTotal:
LowFree: Lowmem is memory which can be used for everything that
- highmem can be used for, but it is also availble for the
+ highmem can be used for, but it is also available for the
kernel's use for its own data structures. Among many
other things, it is where everything from the Slab is
allocated. Bad things happen when you're out of lowmem.
on the disk
Dirty: Memory which is waiting to get written back to the disk
Writeback: Memory which is actively being written back to the disk
+ AnonPages: Non-file backed pages mapped into userspace page tables
Mapped: files which have been mmaped, such as libraries
- Slab: in-kernel data structures cache
+ Slab: in-kernel data structures cache
+SReclaimable: Part of Slab, that might be reclaimed, such as caches
+ SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
+ PageTables: amount of memory dedicated to the lowest level of page
+ tables.
+NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
+ storage
+ Bounce: Memory used for block device "bounce buffers"
+WritebackTmp: Memory used by FUSE for temporary writeback buffers
CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
this is the total amount of memory currently available to
be allocated on the system. This limit is only adhered to
above) will not be permitted. This is useful if one needs
to guarantee that processes will not fail due to lack of
memory once that memory has been successfully allocated.
- PageTables: amount of memory dedicated to the lowest level of page
- tables.
VmallocTotal: total size of vmalloc memory area
VmallocUsed: amount of vmalloc area which is used
-VmallocChunk: largest contigious block of vmalloc area which is free
+VmallocChunk: largest contiguous block of vmalloc area which is free
+
+..............................................................................
+
+vmallocinfo:
+
+Provides information about vmalloced/vmaped areas. One line per area,
+containing the virtual address range of the area, size in bytes,
+caller information of the creator, and optional information depending
+on the kind of area :
+
+ pages=nr number of pages
+ phys=addr if a physical address was specified
+ ioremap I/O mapping (ioremap() and friends)
+ vmalloc vmalloc() area
+ vmap vmap()ed pages
+ user VM_USERMAP area
+ vpages buffer for pages pointers was vmalloced (huge area)
+ N<node>=nr (Only on NUMA kernels)
+ Number of pages allocated on memory node <node>
+
+> cat /proc/vmallocinfo
+0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
+ /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
+0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
+ /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
+0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
+ phys=7fee8000 ioremap
+0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
+ phys=7fee7000 ioremap
+0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
+0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
+ /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
+0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
+ pages=2 vmalloc N1=2
+0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
+ /0x130 [x_tables] pages=4 vmalloc N0=4
+0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
+ pages=14 vmalloc N2=14
+0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
+ pages=4 vmalloc N1=4
+0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
+ pages=2 vmalloc N1=2
+0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
+ pages=10 vmalloc N0=10
+
+..............................................................................
+
+softirqs:
+
+Provides counts of softirq handlers serviced since boot time, for each cpu.
+
+> cat /proc/softirqs
+ CPU0 CPU1 CPU2 CPU3
+ HI: 0 0 0 0
+ TIMER: 27166 27120 27097 27034
+ NET_TX: 0 0 0 17
+ NET_RX: 42 0 0 39
+ BLOCK: 0 0 107 1121
+ TASKLET: 0 0 0 290
+ SCHED: 27035 26983 26971 26746
+ HRTIMER: 0 0 0 0
+ RCU: 1678 1769 2178 2250
1.3 IDE devices in /proc/ide
More detailed information can be found in the controller specific
subdirectories. These are named ide0, ide1 and so on. Each of these
-directories contains the files shown in table 1-4.
+directories contains the files shown in table 1-6.
-Table 1-4: IDE controller info in /proc/ide/ide?
+Table 1-6: IDE controller info in /proc/ide/ide?
..............................................................................
File Content
channel IDE channel (0 or 1)
..............................................................................
Each device connected to a controller has a separate subdirectory in the
-controllers directory. The files listed in table 1-5 are contained in these
+controllers directory. The files listed in table 1-7 are contained in these
directories.
-Table 1-5: IDE device information
+Table 1-7: IDE device information
..............................................................................
File Content
cache The cache
1.4 Networking info in /proc/net
--------------------------------
-The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
+The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
additional values you get for IP version 6 if you configure the kernel to
-support this. Table 1-7 lists the files and their meaning.
+support this. Table 1-9 lists the files and their meaning.
-Table 1-6: IPv6 info in /proc/net
+Table 1-8: IPv6 info in /proc/net
..............................................................................
File Content
udp6 UDP sockets (IPv6)
..............................................................................
-Table 1-7: Network info in /proc/net
+Table 1-9: Network info in /proc/net
..............................................................................
File Content
arp Kernel ARP table
your system. It has one subdirectory for each port, named after the port
number (0,1,2,...).
-These directories contain the four files shown in Table 1-8.
+These directories contain the four files shown in Table 1-10.
-Table 1-8: Files in /proc/parport
+Table 1-10: Files in /proc/parport
..............................................................................
File Content
autoprobe Any IEEE-1284 device ID information that has been acquired.
Information about the available and actually used tty's can be found in the
directory /proc/tty.You'll find entries for drivers and line disciplines in
-this directory, as shown in Table 1-9.
+this directory, as shown in Table 1-11.
-Table 1-9: Files in /proc/tty
+Table 1-11: Files in /proc/tty
..............................................................................
File Content
drivers list of drivers and their usage
since the system first booted. For a quick look, simply cat the file:
> cat /proc/stat
- cpu 2255 34 2290 22625563 6290 127 456
- cpu0 1132 34 1441 11311718 3675 127 438
- cpu1 1123 0 849 11313845 2614 0 18
+ cpu 2255 34 2290 22625563 6290 127 456 0 0
+ cpu0 1132 34 1441 11311718 3675 127 438 0 0
+ cpu1 1123 0 849 11313845 2614 0 18 0 0
intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
ctxt 1990473
btime 1062191376
processes 2915
procs_running 1
procs_blocked 0
+ softirq 183433 0 21755 12 39 1137 231 21459 2263
The very first "cpu" line aggregates the numbers in all of the other "cpuN"
lines. These numbers identify the amount of time the CPU has spent performing
- iowait: waiting for I/O to complete
- irq: servicing interrupts
- softirq: servicing softirqs
+- steal: involuntary wait
+- guest: running a normal guest
+- guest_nice: running a niced guest
The "intr" line gives counts of interrupts serviced since boot time, for each
of the possible system interrupts. The first column is the total of all
includes (but is not limited to) those created by calls to the fork() and
clone() system calls.
-The "procs_running" line gives the number of processes currently running on
-CPUs.
+The "procs_running" line gives the total number of threads that are
+running or ready to run (i.e., the total number of runnable threads).
The "procs_blocked" line gives the number of processes currently blocked,
waiting for I/O to complete.
+The "softirq" line gives counts of softirqs serviced since boot time, for each
+of the possible system softirqs. The first column is the total of all
+softirqs serviced; each subsequent column is the total for that particular
+softirq.
+
+
+1.9 Ext4 file system parameters
+------------------------------
+
+Information about mounted ext4 file systems can be found in
+/proc/fs/ext4. Each mounted filesystem will have a directory in
+/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
+/proc/fs/ext4/dm-0). The files in each per-device directory are shown
+in Table 1-12, below.
+
+Table 1-12: Files in /proc/fs/ext4/<devname>
+..............................................................................
+ File Content
+ mb_groups details of multiblock allocator buddy cache of free blocks
+..............................................................................
+
------------------------------------------------------------------------------
Summary
This chapter is heavily based on the documentation included in the pre 2.2
kernels, and became part of it in version 2.2.1 of the Linux kernel.
-2.1 /proc/sys/fs - File system data
------------------------------------
-
-This subdirectory contains specific file system, file handle, inode, dentry
-and quota information.
-
-Currently, these files are in /proc/sys/fs:
-
-dentry-state
-------------
-
-Status of the directory cache. Since directory entries are dynamically
-allocated and deallocated, this file indicates the current status. It holds
-six values, in which the last two are not used and are always zero. The others
-are listed in table 2-1.
-
-
-Table 2-1: Status files of the directory cache
-..............................................................................
- File Content
- nr_dentry Almost always zero
- nr_unused Number of unused cache entries
- age_limit
- in seconds after the entry may be reclaimed, when memory is short
- want_pages internally
-..............................................................................
-
-dquot-nr and dquot-max
-----------------------
-
-The file dquot-max shows the maximum number of cached disk quota entries.
-
-The file dquot-nr shows the number of allocated disk quota entries and the
-number of free disk quota entries.
-
-If the number of available cached disk quotas is very low and you have a large
-number of simultaneous system users, you might want to raise the limit.
-
-file-nr and file-max
---------------------
-
-The kernel allocates file handles dynamically, but doesn't free them again at
-this time.
-
-The value in file-max denotes the maximum number of file handles that the
-Linux kernel will allocate. When you get a lot of error messages about running
-out of file handles, you might want to raise this limit. The default value is
-10% of RAM in kilobytes. To change it, just write the new number into the
-file:
-
- # cat /proc/sys/fs/file-max
- 4096
- # echo 8192 > /proc/sys/fs/file-max
- # cat /proc/sys/fs/file-max
- 8192
-
-
-This method of revision is useful for all customizable parameters of the
-kernel - simply echo the new value to the corresponding file.
-
-Historically, the three values in file-nr denoted the number of allocated file
-handles, the number of allocated but unused file handles, and the maximum
-number of file handles. Linux 2.6 always reports 0 as the number of free file
-handles -- this is not an error, it just means that the number of allocated
-file handles exactly matches the number of used file handles.
-
-Attempts to allocate more file descriptors than file-max are reported with
-printk, look for "VFS: file-max limit <number> reached".
-
-inode-state and inode-nr
-------------------------
-
-The file inode-nr contains the first two items from inode-state, so we'll skip
-to that file...
-
-inode-state contains two actual numbers and five dummy values. The numbers
-are nr_inodes and nr_free_inodes (in order of appearance).
-
-nr_inodes
-~~~~~~~~~
-
-Denotes the number of inodes the system has allocated. This number will
-grow and shrink dynamically.
-
-nr_free_inodes
---------------
-
-Represents the number of free inodes. Ie. The number of inuse inodes is
-(nr_inodes - nr_free_inodes).
-
-aio-nr and aio-max-nr
----------------------
-
-aio-nr is the running total of the number of events specified on the
-io_setup system call for all currently active aio contexts. If aio-nr
-reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
-raising aio-max-nr does not result in the pre-allocation or re-sizing
-of any kernel data structures.
-
-2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
------------------------------------------------------------
-
-Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
-handles the kernel support for miscellaneous binary formats.
-
-Binfmt_misc provides the ability to register additional binary formats to the
-Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
-needs to know magic numbers at the beginning or the filename extension of the
-binary.
-
-It works by maintaining a linked list of structs that contain a description of
-a binary format, including a magic with size (or the filename extension),
-offset and mask, and the interpreter name. On request it invokes the given
-interpreter with the original program as argument, as binfmt_java and
-binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
-binary-formats, you have to register an additional binary-format.
-
-There are two general files in binfmt_misc and one file per registered format.
-The two general files are register and status.
-
-Registering a new binary format
--------------------------------
-
-To register a new binary format you have to issue the command
-
- echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
-
+Please see: Documentation/sysctls/ directory for descriptions of these
+entries.
+------------------------------------------------------------------------------
+Summary
+------------------------------------------------------------------------------
+Certain aspects of kernel behavior can be modified at runtime, without the
+need to recompile the kernel, or even to reboot the system. The files in the
+/proc/sys tree can not only be read, but also modified. You can use the echo
+command to write value into these files, thereby changing the default settings
+of the kernel.
+------------------------------------------------------------------------------
-with appropriate name (the name for the /proc-dir entry), offset (defaults to
-0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
-last but not least, the interpreter that is to be invoked (for example and
-testing /bin/echo). Type can be M for usual magic matching or E for filename
-extension matching (give extension in place of magic).
+------------------------------------------------------------------------------
+CHAPTER 3: PER-PROCESS PARAMETERS
+------------------------------------------------------------------------------
-Check or reset the status of the binary format handler
+3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
------------------------------------------------------
-If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
-current status (enabled/disabled) of binfmt_misc. Change the status by echoing
-0 (disables) or 1 (enables) or -1 (caution: this clears all previously
-registered binary formats) to status. For example echo 0 > status to disable
-binfmt_misc (temporarily).
-
-Status of a single handler
---------------------------
-
-Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
-perform the same function as status, but their scope is limited to the actual
-binary format. By cating this file, you also receive all related information
-about the interpreter/magic of the binfmt.
-
-Example usage of binfmt_misc (emulate binfmt_java)
---------------------------------------------------
-
- cd /proc/sys/fs/binfmt_misc
- echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
- echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
- echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
- echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
-
-
-These four lines add support for Java executables and Java applets (like
-binfmt_java, additionally recognizing the .html extension with no need to put
-<!--applet> to every applet file). You have to install the JDK and the
-shell-script /usr/local/java/bin/javawrapper too. It works around the
-brokenness of the Java filename handling. To add a Java binary, just create a
-link to the class-file somewhere in the path.
-
-2.3 /proc/sys/kernel - general kernel parameters
-------------------------------------------------
-
-This directory reflects general kernel behaviors. As I've said before, the
-contents depend on your configuration. Here you'll find the most important
-files, along with descriptions of what they mean and how to use them.
-
-acct
-----
-
-The file contains three values; highwater, lowwater, and frequency.
-
-It exists only when BSD-style process accounting is enabled. These values
-control its behavior. If the free space on the file system where the log lives
-goes below lowwater percentage, accounting suspends. If it goes above
-highwater percentage, accounting resumes. Frequency determines how often you
-check the amount of free space (value is in seconds). Default settings are: 4,
-2, and 30. That is, suspend accounting if there is less than 2 percent free;
-resume it if we have a value of 3 or more percent; consider information about
-the amount of free space valid for 30 seconds
-
-ctrl-alt-del
-------------
-
-When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
-program to handle a graceful restart. However, when the value is greater that
-zero, Linux's reaction to this key combination will be an immediate reboot,
-without syncing its dirty buffers.
-
-[NOTE]
- When a program (like dosemu) has the keyboard in raw mode, the
- ctrl-alt-del is intercepted by the program before it ever reaches the
- kernel tty layer, and it is up to the program to decide what to do with
- it.
-
-domainname and hostname
------------------------
-
-These files can be controlled to set the NIS domainname and hostname of your
-box. For the classic darkstar.frop.org a simple:
-
- # echo "darkstar" > /proc/sys/kernel/hostname
- # echo "frop.org" > /proc/sys/kernel/domainname
-
-
-would suffice to set your hostname and NIS domainname.
-
-osrelease, ostype and version
------------------------------
-
-The names make it pretty obvious what these fields contain:
-
- > cat /proc/sys/kernel/osrelease
- 2.2.12
-
- > cat /proc/sys/kernel/ostype
- Linux
-
- > cat /proc/sys/kernel/version
- #4 Fri Oct 1 12:41:14 PDT 1999
-
-
-The files osrelease and ostype should be clear enough. Version needs a little
-more clarification. The #4 means that this is the 4th kernel built from this
-source base and the date after it indicates the time the kernel was built. The
-only way to tune these values is to rebuild the kernel.
-
-panic
------
-
-The value in this file represents the number of seconds the kernel waits
-before rebooting on a panic. When you use the software watchdog, the
-recommended setting is 60. If set to 0, the auto reboot after a kernel panic
-is disabled, which is the default setting.
-
-printk
-------
-
-The four values in printk denote
-* console_loglevel,
-* default_message_loglevel,
-* minimum_console_loglevel and
-* default_console_loglevel
-respectively.
-
-These values influence printk() behavior when printing or logging error
-messages, which come from inside the kernel. See syslog(2) for more
-information on the different log levels.
-
-console_loglevel
-----------------
-
-Messages with a higher priority than this will be printed to the console.
-
-default_message_level
----------------------
-
-Messages without an explicit priority will be printed with this priority.
-
-minimum_console_loglevel
-------------------------
-
-Minimum (highest) value to which the console_loglevel can be set.
-
-default_console_loglevel
-------------------------
-
-Default value for console_loglevel.
-
-sg-big-buff
------------
-
-This file shows the size of the generic SCSI (sg) buffer. At this point, you
-can't tune it yet, but you can change it at compile time by editing
-include/scsi/sg.h and changing the value of SG_BIG_BUFF.
-
-If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
-this to a higher value. Refer to the SANE documentation on this issue.
-
-modprobe
---------
-
-The location where the modprobe binary is located. The kernel uses this
-program to load modules on demand.
-
-unknown_nmi_panic
------------------
-
-The value in this file affects behavior of handling NMI. When the value is
-non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
-debugging information is displayed on console.
-
-NMI switch that most IA32 servers have fires unknown NMI up, for example.
-If a system hangs up, try pressing the NMI switch.
-
-[NOTE]
- This function and oprofile share a NMI callback. Therefore this function
- cannot be enabled when oprofile is activated.
- And NMI watchdog will be disabled when the value in this file is set to
- non-zero.
-
-
-2.4 /proc/sys/vm - The virtual memory subsystem
------------------------------------------------
-
-The files in this directory can be used to tune the operation of the virtual
-memory (VM) subsystem of the Linux kernel.
-
-vfs_cache_pressure
-------------------
-
-Controls the tendency of the kernel to reclaim the memory which is used for
-caching of directory and inode objects.
-
-At the default value of vfs_cache_pressure=100 the kernel will attempt to
-reclaim dentries and inodes at a "fair" rate with respect to pagecache and
-swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
-to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
-causes the kernel to prefer to reclaim dentries and inodes.
-
-dirty_background_ratio
-----------------------
-
-Contains, as a percentage of total system memory, the number of pages at which
-the pdflush background writeback daemon will start writing out dirty data.
-
-dirty_ratio
------------------
-
-Contains, as a percentage of total system memory, the number of pages at which
-a process which is generating disk writes will itself start writing out dirty
-data.
-
-dirty_writeback_centisecs
--------------------------
-
-The pdflush writeback daemons will periodically wake up and write `old' data
-out to disk. This tunable expresses the interval between those wakeups, in
-100'ths of a second.
-
-Setting this to zero disables periodic writeback altogether.
-
-dirty_expire_centisecs
-----------------------
-
-This tunable is used to define when dirty data is old enough to be eligible
-for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
-Data which has been dirty in-memory for longer than this interval will be
-written out next time a pdflush daemon wakes up.
-
-legacy_va_layout
-----------------
-
-If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
-will use the legacy (2.4) layout for all processes.
-
-lower_zone_protection
----------------------
-
-For some specialised workloads on highmem machines it is dangerous for
-the kernel to allow process memory to be allocated from the "lowmem"
-zone. This is because that memory could then be pinned via the mlock()
-system call, or by unavailability of swapspace.
-
-And on large highmem machines this lack of reclaimable lowmem memory
-can be fatal.
-
-So the Linux page allocator has a mechanism which prevents allocations
-which _could_ use highmem from using too much lowmem. This means that
-a certain amount of lowmem is defended from the possibility of being
-captured into pinned user memory.
-
-(The same argument applies to the old 16 megabyte ISA DMA region. This
-mechanism will also defend that region from allocations which could use
-highmem or lowmem).
-
-The `lower_zone_protection' tunable determines how aggressive the kernel is
-in defending these lower zones. The default value is zero - no
-protection at all.
-
-If you have a machine which uses highmem or ISA DMA and your
-applications are using mlock(), or if you are running with no swap then
-you probably should increase the lower_zone_protection setting.
-
-The units of this tunable are fairly vague. It is approximately equal
-to "megabytes". So setting lower_zone_protection=100 will protect around 100
-megabytes of the lowmem zone from user allocations. It will also make
-those 100 megabytes unavaliable for use by applications and by
-pagecache, so there is a cost.
-
-The effects of this tunable may be observed by monitoring
-/proc/meminfo:LowFree. Write a single huge file and observe the point
-at which LowFree ceases to fall.
-
-A reasonable value for lower_zone_protection is 100.
-
-page-cluster
-------------
-
-page-cluster controls the number of pages which are written to swap in
-a single attempt. The swap I/O size.
-
-It is a logarithmic value - setting it to zero means "1 page", setting
-it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
-
-The default value is three (eight pages at a time). There may be some
-small benefits in tuning this to a different value if your workload is
-swap-intensive.
-
-overcommit_memory
------------------
-
-Controls overcommit of system memory, possibly allowing processes
-to allocate (but not use) more memory than is actually available.
-
-
-0 - Heuristic overcommit handling. Obvious overcommits of
- address space are refused. Used for a typical system. It
- ensures a seriously wild allocation fails while allowing
- overcommit to reduce swap usage. root is allowed to
- allocate slighly more memory in this mode. This is the
- default.
-
-1 - Always overcommit. Appropriate for some scientific
- applications.
-
-2 - Don't overcommit. The total address space commit
- for the system is not permitted to exceed swap plus a
- configurable percentage (default is 50) of physical RAM.
- Depending on the percentage you use, in most situations
- this means a process will not be killed while attempting
- to use already-allocated memory but will receive errors
- on memory allocation as appropriate.
-
-overcommit_ratio
-----------------
-
-Percentage of physical memory size to include in overcommit calculations
-(see above.)
-
-Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
-
- swapspace = total size of all swap areas
- physmem = size of physical memory in system
-
-nr_hugepages and hugetlb_shm_group
-----------------------------------
-
-nr_hugepages configures number of hugetlb page reserved for the system.
-
-hugetlb_shm_group contains group id that is allowed to create SysV shared
-memory segment using hugetlb page.
-
-laptop_mode
------------
-
-laptop_mode is a knob that controls "laptop mode". All the things that are
-controlled by this knob are discussed in Documentation/laptop-mode.txt.
-
-block_dump
-----------
-
-block_dump enables block I/O debugging when set to a nonzero value. More
-information on block I/O debugging is in Documentation/laptop-mode.txt.
-
-swap_token_timeout
-------------------
-
-This file contains valid hold time of swap out protection token. The Linux
-VM has token based thrashing control mechanism and uses the token to prevent
-unnecessary page faults in thrashing situation. The unit of the value is
-second. The value would be useful to tune thrashing behavior.
-
-2.5 /proc/sys/dev - Device specific parameters
-----------------------------------------------
-
-Currently there is only support for CDROM drives, and for those, there is only
-one read-only file containing information about the CD-ROM drives attached to
-the system:
-
- >cat /proc/sys/dev/cdrom/info
- CD-ROM information, Id: cdrom.c 2.55 1999/04/25
-
- drive name: sr0 hdb
- drive speed: 32 40
- drive # of slots: 1 0
- Can close tray: 1 1
- Can open tray: 1 1
- Can lock tray: 1 1
- Can change speed: 1 1
- Can select disk: 0 1
- Can read multisession: 1 1
- Can read MCN: 1 1
- Reports media changed: 1 1
- Can play audio: 1 1
-
-
-You see two drives, sr0 and hdb, along with a list of their features.
-
-2.6 /proc/sys/sunrpc - Remote procedure calls
----------------------------------------------
-
-This directory contains four files, which enable or disable debugging for the
-RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
-be set to one to turn debugging on. (The default value is 0 for each)
-
-2.7 /proc/sys/net - Networking stuff
-------------------------------------
-
-The interface to the networking parts of the kernel is located in
-/proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only
-some of them, depending on your kernel's configuration.
-
-
-Table 2-3: Subdirectories in /proc/sys/net
-..............................................................................
- Directory Content Directory Content
- core General parameter appletalk Appletalk protocol
- unix Unix domain sockets netrom NET/ROM
- 802 E802 protocol ax25 AX25
- ethernet Ethernet protocol rose X.25 PLP layer
- ipv4 IP version 4 x25 X.25 protocol
- ipx IPX token-ring IBM token ring
- bridge Bridging decnet DEC net
- ipv6 IP version 6
-..............................................................................
-
-We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are
-only minor players in the Linux world, we'll skip them in this chapter. You'll
-find some short info on Appletalk and IPX further on in this chapter. Review
-the online documentation and the kernel source to get a detailed view of the
-parameters for those protocols. In this section we'll discuss the
-subdirectories printed in bold letters in the table above. As default values
-are suitable for most needs, there is no need to change these values.
-
-/proc/sys/net/core - Network core options
------------------------------------------
-
-rmem_default
-------------
-
-The default setting of the socket receive buffer in bytes.
-
-rmem_max
---------
-
-The maximum receive socket buffer size in bytes.
-
-wmem_default
-------------
-
-The default setting (in bytes) of the socket send buffer.
-
-wmem_max
---------
-
-The maximum send socket buffer size in bytes.
-
-message_burst and message_cost
-------------------------------
-
-These parameters are used to limit the warning messages written to the kernel
-log from the networking code. They enforce a rate limit to make a
-denial-of-service attack impossible. A higher message_cost factor, results in
-fewer messages that will be written. Message_burst controls when messages will
-be dropped. The default settings limit warning messages to one every five
-seconds.
-
-netdev_max_backlog
-------------------
-
-Maximum number of packets, queued on the INPUT side, when the interface
-receives packets faster than kernel can process them.
-
-optmem_max
-----------
-
-Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
-of struct cmsghdr structures with appended data.
-
-/proc/sys/net/unix - Parameters for Unix domain sockets
+This file can be used to adjust the score used to select which processes
+should be killed in an out-of-memory situation. Giving it a high score will
+increase the likelihood of this process being killed by the oom-killer. Valid
+values are in the range -16 to +15, plus the special value -17, which disables
+oom-killing altogether for this process.
+
+The process to be killed in an out-of-memory situation is selected among all others
+based on its badness score. This value equals the original memory size of the process
+and is then updated according to its CPU time (utime + stime) and the
+run time (uptime - start time). The longer it runs the smaller is the score.
+Badness score is divided by the square root of the CPU time and then by
+the double square root of the run time.
+
+Swapped out tasks are killed first. Half of each child's memory size is added to
+the parent's score if they do not share the same memory. Thus forking servers
+are the prime candidates to be killed. Having only one 'hungry' child will make
+parent less preferable than the child.
+
+/proc/<pid>/oom_score shows process' current badness score.
+
+The following heuristics are then applied:
+ * if the task was reniced, its score doubles
+ * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
+ or CAP_SYS_RAWIO) have their score divided by 4
+ * if oom condition happened in one cpuset and checked process does not belong
+ to it, its score is divided by 8
+ * the resulting score is multiplied by two to the power of oom_adj, i.e.
+ points <<= oom_adj when it is positive and
+ points >>= -(oom_adj) otherwise
+
+The task with the highest badness score is then selected and its children
+are killed, process itself will be killed in an OOM situation when it does
+not have children or some of them disabled oom like described above.
+
+3.2 /proc/<pid>/oom_score - Display current oom-killer score
+-------------------------------------------------------------
+
+This file can be used to check the current score used by the oom-killer is for
+any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
+process should be killed in an out-of-memory situation.
+
+
+3.3 /proc/<pid>/io - Display the IO accounting fields
-------------------------------------------------------
-There are only two files in this subdirectory. They control the delays for
-deleting and destroying socket descriptors.
-
-2.8 /proc/sys/net/ipv4 - IPV4 settings
---------------------------------------
-
-IP version 4 is still the most used protocol in Unix networking. It will be
-replaced by IP version 6 in the next couple of years, but for the moment it's
-the de facto standard for the internet and is used in most networking
-environments around the world. Because of the importance of this protocol,
-we'll have a deeper look into the subtree controlling the behavior of the IPv4
-subsystem of the Linux kernel.
-
-Let's start with the entries in /proc/sys/net/ipv4.
-
-ICMP settings
--------------
-
-icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
-----------------------------------------------------
-
-Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or
-just those to broadcast and multicast addresses.
-
-Please note that if you accept ICMP echo requests with a broadcast/multi\-cast
-destination address your network may be used as an exploder for denial of
-service packet flooding attacks to other hosts.
-
-icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate
----------------------------------------------------------------------------------------
-
-Sets limits for sending ICMP packets to specific targets. A value of zero
-disables all limiting. Any positive value sets the maximum package rate in
-hundredth of a second (on Intel systems).
-
-IP settings
------------
-
-ip_autoconfig
--------------
-
-This file contains the number one if the host received its IP configuration by
-RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero.
-
-ip_default_ttl
---------------
-
-TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of
-hops a packet may travel.
+This file contains IO statistics for each running process
-ip_dynaddr
-----------
-
-Enable dynamic socket address rewriting on interface address change. This is
-useful for dialup interface with changing IP addresses.
-
-ip_forward
-----------
-
-Enable or disable forwarding of IP packages between interfaces. Changing this
-value resets all other parameters to their default values. They differ if the
-kernel is configured as host or router.
-
-ip_local_port_range
--------------------
-
-Range of ports used by TCP and UDP to choose the local port. Contains two
-numbers, the first number is the lowest port, the second number the highest
-local port. Default is 1024-4999. Should be changed to 32768-61000 for
-high-usage systems.
-
-ip_no_pmtu_disc
----------------
-
-Global switch to turn path MTU discovery off. It can also be set on a per
-socket basis by the applications or on a per route basis.
-
-ip_masq_debug
--------------
-
-Enable/disable debugging of IP masquerading.
-
-IP fragmentation settings
--------------------------
-
-ipfrag_high_trash and ipfrag_low_trash
---------------------------------------
-
-Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes
-of memory is allocated for this purpose, the fragment handler will toss
-packets until ipfrag_low_thresh is reached.
-
-ipfrag_time
------------
-
-Time in seconds to keep an IP fragment in memory.
-
-TCP settings
-------------
-
-tcp_ecn
+Example
-------
-This file controls the use of the ECN bit in the IPv4 headers, this is a new
-feature about Explicit Congestion Notification, but some routers and firewalls
-block trafic that has this bit set, so it could be necessary to echo 0 to
-/proc/sys/net/ipv4/tcp_ecn, if you want to talk to this sites. For more info
-you could read RFC2481.
-
-tcp_retrans_collapse
---------------------
-
-Bug-to-bug compatibility with some broken printers. On retransmit, try to send
-larger packets to work around bugs in certain TCP stacks. Can be turned off by
-setting it to zero.
-
-tcp_keepalive_probes
---------------------
-
-Number of keep alive probes TCP sends out, until it decides that the
-connection is broken.
-
-tcp_keepalive_time
-------------------
-
-How often TCP sends out keep alive messages, when keep alive is enabled. The
-default is 2 hours.
-
-tcp_syn_retries
----------------
-
-Number of times initial SYNs for a TCP connection attempt will be
-retransmitted. Should not be higher than 255. This is only the timeout for
-outgoing connections, for incoming connections the number of retransmits is
-defined by tcp_retries1.
-
-tcp_sack
---------
-
-Enable select acknowledgments after RFC2018.
-
-tcp_timestamps
---------------
-
-Enable timestamps as defined in RFC1323.
-
-tcp_stdurg
-----------
-
-Enable the strict RFC793 interpretation of the TCP urgent pointer field. The
-default is to use the BSD compatible interpretation of the urgent pointer
-pointing to the first byte after the urgent data. The RFC793 interpretation is
-to have it point to the last byte of urgent data. Enabling this option may
-lead to interoperatibility problems. Disabled by default.
-
-tcp_syncookies
---------------
-
-Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out
-syncookies when the syn backlog queue of a socket overflows. This is to ward
-off the common 'syn flood attack'. Disabled by default.
-
-Note that the concept of a socket backlog is abandoned. This means the peer
-may not receive reliable error messages from an over loaded server with
-syncookies enabled.
-
-tcp_window_scaling
-------------------
-
-Enable window scaling as defined in RFC1323.
-
-tcp_fin_timeout
----------------
-
-The length of time in seconds it takes to receive a final FIN before the
-socket is always closed. This is strictly a violation of the TCP
-specification, but required to prevent denial-of-service attacks.
-
-tcp_max_ka_probes
------------------
-
-Indicates how many keep alive probes are sent per slow timer run. Should not
-be set too high to prevent bursts.
-
-tcp_max_syn_backlog
--------------------
-
-Length of the per socket backlog queue. Since Linux 2.2 the backlog specified
-in listen(2) only specifies the length of the backlog queue of already
-established sockets. When more connection requests arrive Linux starts to drop
-packets. When syncookies are enabled the packets are still answered and the
-maximum queue is effectively ignored.
-
-tcp_retries1
-------------
-
-Defines how often an answer to a TCP connection request is retransmitted
-before giving up.
-
-tcp_retries2
-------------
-
-Defines how often a TCP packet is retransmitted before giving up.
-
-Interface specific settings
----------------------------
-
-In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each
-interface the system knows about and one directory calls all. Changes in the
-all subdirectory affect all interfaces, whereas changes in the other
-subdirectories affect only one interface. All directories have the same
-entries:
-
-accept_redirects
-----------------
-
-This switch decides if the kernel accepts ICMP redirect messages or not. The
-default is 'yes' if the kernel is configured for a regular host and 'no' for a
-router configuration.
-
-accept_source_route
--------------------
-
-Should source routed packages be accepted or declined. The default is
-dependent on the kernel configuration. It's 'yes' for routers and 'no' for
-hosts.
+test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
+[1] 3828
-bootp_relay
-~~~~~~~~~~~
+test:/tmp # cat /proc/3828/io
+rchar: 323934931
+wchar: 323929600
+syscr: 632687
+syscw: 632675
+read_bytes: 0
+write_bytes: 323932160
+cancelled_write_bytes: 0
-Accept packets with source address 0.b.c.d with destinations not to this host
-as local ones. It is supposed that a BOOTP relay daemon will catch and forward
-such packets.
-The default is 0, since this feature is not implemented yet (kernel version
-2.2.12).
-
-forwarding
-----------
-
-Enable or disable IP forwarding on this interface.
-
-log_martians
-------------
-
-Log packets with source addresses with no known route to kernel log.
-
-mc_forwarding
--------------
-
-Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a
-multicast routing daemon is required.
-
-proxy_arp
----------
-
-Does (1) or does not (0) perform proxy ARP.
-
-rp_filter
----------
-
-Integer value determines if a source validation should be made. 1 means yes, 0
-means no. Disabled by default, but local/broadcast address spoofing is always
-on.
-
-If you set this to 1 on a router that is the only connection for a network to
-the net, it will prevent spoofing attacks against your internal networks
-(external addresses can still be spoofed), without the need for additional
-firewall rules.
-
-secure_redirects
-----------------
-
-Accept ICMP redirect messages only for gateways, listed in default gateway
-list. Enabled by default.
-
-shared_media
-------------
-
-If it is not set the kernel does not assume that different subnets on this
-device can communicate directly. Default setting is 'yes'.
-
-send_redirects
---------------
-
-Determines whether to send ICMP redirects to other hosts.
-
-Routing settings
-----------------
-
-The directory /proc/sys/net/ipv4/route contains several file to control
-routing issues.
-
-error_burst and error_cost
---------------------------
-
-These parameters are used to limit how many ICMP destination unreachable to
-send from the host in question. ICMP destination unreachable messages are
-sent when we can not reach the next hop, while trying to transmit a packet.
-It will also print some error messages to kernel logs if someone is ignoring
-our ICMP redirects. The higher the error_cost factor is, the fewer
-destination unreachable and error messages will be let through. Error_burst
-controls when destination unreachable messages and error messages will be
-dropped. The default settings limit warning messages to five every second.
+Description
+-----------
-flush
+rchar
-----
-Writing to this file results in a flush of the routing cache.
+I/O counter: chars read
+The number of bytes which this task has caused to be read from storage. This
+is simply the sum of bytes which this process passed to read() and pread().
+It includes things like tty IO and it is unaffected by whether or not actual
+physical disk IO was required (the read might have been satisfied from
+pagecache)
-gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh
----------------------------------------------------------------------
-Values to control the frequency and behavior of the garbage collection
-algorithm for the routing cache. gc_min_interval is deprecated and replaced
-by gc_min_interval_ms.
-
-
-max_size
---------
-
-Maximum size of the routing cache. Old entries will be purged once the cache
-reached has this size.
-
-max_delay, min_delay
---------------------
-
-Delays for flushing the routing cache.
-
-redirect_load, redirect_number
-------------------------------
-
-Factors which determine if more ICPM redirects should be sent to a specific
-host. No redirects will be sent once the load limit or the maximum number of
-redirects has been reached.
-
-redirect_silence
-----------------
-
-Timeout for redirects. After this period redirects will be sent again, even if
-this has been stopped, because the load or number limit has been reached.
-
-Network Neighbor handling
--------------------------
-
-Settings about how to handle connections with direct neighbors (nodes attached
-to the same link) can be found in the directory /proc/sys/net/ipv4/neigh.
+wchar
+-----
-As we saw it in the conf directory, there is a default subdirectory which
-holds the default values, and one directory for each interface. The contents
-of the directories are identical, with the single exception that the default
-settings contain additional options to set garbage collection parameters.
+I/O counter: chars written
+The number of bytes which this task has caused, or shall cause to be written
+to disk. Similar caveats apply here as with rchar.
-In the interface directories you'll find the following entries:
-base_reachable_time, base_reachable_time_ms
--------------------------------------------
+syscr
+-----
-A base value used for computing the random reachable time value as specified
-in RFC2461.
+I/O counter: read syscalls
+Attempt to count the number of read I/O operations, i.e. syscalls like read()
+and pread().
-Expression of base_reachable_time, which is deprecated, is in seconds.
-Expression of base_reachable_time_ms is in milliseconds.
-retrans_time, retrans_time_ms
------------------------------
+syscw
+-----
-The time between retransmitted Neighbor Solicitation messages.
-Used for address resolution and to determine if a neighbor is
-unreachable.
+I/O counter: write syscalls
+Attempt to count the number of write I/O operations, i.e. syscalls like
+write() and pwrite().
-Expression of retrans_time, which is deprecated, is in 1/100 seconds (for
-IPv4) or in jiffies (for IPv6).
-Expression of retrans_time_ms is in milliseconds.
-unres_qlen
+read_bytes
----------
-Maximum queue length for a pending arp request - the number of packets which
-are accepted from other layers while the ARP address is still resolved.
-
-anycast_delay
--------------
-
-Maximum for random delay of answers to neighbor solicitation messages in
-jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support
-yet).
-
-ucast_solicit
--------------
-
-Maximum number of retries for unicast solicitation.
-
-mcast_solicit
--------------
-
-Maximum number of retries for multicast solicitation.
+I/O counter: bytes read
+Attempt to count the number of bytes which this process really did cause to
+be fetched from the storage layer. Done at the submit_bio() level, so it is
+accurate for block-backed filesystems. <please add status regarding NFS and
+CIFS at a later time>
-delay_first_probe_time
-----------------------
-Delay for the first time probe if the neighbor is reachable. (see
-gc_stale_time)
-
-locktime
---------
-
-An ARP/neighbor entry is only replaced with a new one if the old is at least
-locktime old. This prevents ARP cache thrashing.
-
-proxy_delay
+write_bytes
-----------
-Maximum time (real time is random [0..proxytime]) before answering to an ARP
-request for which we have an proxy ARP entry. In some cases, this is used to
-prevent network flooding.
-
-proxy_qlen
-----------
-
-Maximum queue length of the delayed proxy arp timer. (see proxy_delay).
+I/O counter: bytes written
+Attempt to count the number of bytes which this process caused to be sent to
+the storage layer. This is done at page-dirtying time.
-app_solcit
-----------
-
-Determines the number of requests to send to the user level ARP daemon. Use 0
-to turn off.
-
-gc_stale_time
--------------
-Determines how often to check for stale ARP entries. After an ARP entry is
-stale it will be resolved again (which is useful when an IP address migrates
-to another machine). When ucast_solicit is greater than 0 it first tries to
-send an ARP packet directly to the known host When that fails and
-mcast_solicit is greater than 0, an ARP request is broadcasted.
+cancelled_write_bytes
+---------------------
-2.9 Appletalk
--------------
+The big inaccuracy here is truncate. If a process writes 1MB to a file and
+then deletes the file, it will in fact perform no writeout. But it will have
+been accounted as having caused 1MB of write.
+In other words: The number of bytes which this process caused to not happen,
+by truncating pagecache. A task can cause "negative" IO too. If this task
+truncates some dirty pagecache, some IO which another task has been accounted
+for (in it's write_bytes) will not be happening. We _could_ just subtract that
+from the truncating task's write_bytes, but there is information loss in doing
+that.
-The /proc/sys/net/appletalk directory holds the Appletalk configuration data
-when Appletalk is loaded. The configurable parameters are:
-aarp-expiry-time
-----------------
+Note
+----
-The amount of time we keep an ARP entry before expiring it. Used to age out
-old hosts.
+At its current implementation state, this is a bit racy on 32-bit machines: if
+process A reads process B's /proc/pid/io while process B is updating one of
+those 64-bit counters, process A could see an intermediate result.
-aarp-resolve-time
------------------
-The amount of time we will spend trying to resolve an Appletalk address.
+More information about this can be found within the taskstats documentation in
+Documentation/accounting.
-aarp-retransmit-limit
----------------------
+3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
+---------------------------------------------------------------
+When a process is dumped, all anonymous memory is written to a core file as
+long as the size of the core file isn't limited. But sometimes we don't want
+to dump some memory segments, for example, huge shared memory. Conversely,
+sometimes we want to save file-backed memory segments into a core file, not
+only the individual files.
-The number of times we will retransmit a query before giving up.
+/proc/<pid>/coredump_filter allows you to customize which memory segments
+will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
+of memory types. If a bit of the bitmask is set, memory segments of the
+corresponding memory type are dumped, otherwise they are not dumped.
-aarp-tick-time
---------------
+The following 7 memory types are supported:
+ - (bit 0) anonymous private memory
+ - (bit 1) anonymous shared memory
+ - (bit 2) file-backed private memory
+ - (bit 3) file-backed shared memory
+ - (bit 4) ELF header pages in file-backed private memory areas (it is
+ effective only if the bit 2 is cleared)
+ - (bit 5) hugetlb private memory
+ - (bit 6) hugetlb shared memory
-Controls the rate at which expires are checked.
+ Note that MMIO pages such as frame buffer are never dumped and vDSO pages
+ are always dumped regardless of the bitmask status.
-The directory /proc/net/appletalk holds the list of active Appletalk sockets
-on a machine.
+ Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
+ effected by bit 5-6.
-The fields indicate the DDP type, the local address (in network:node format)
-the remote address, the size of the transmit pending queue, the size of the
-received queue (bytes waiting for applications to read) the state and the uid
-owning the socket.
+Default value of coredump_filter is 0x23; this means all anonymous memory
+segments and hugetlb private memory are dumped.
-/proc/net/atalk_iface lists all the interfaces configured for appletalk.It
-shows the name of the interface, its Appletalk address, the network range on
-that address (or network number for phase 1 networks), and the status of the
-interface.
+If you don't want to dump all shared memory segments attached to pid 1234,
+write 0x21 to the process's proc file.
-/proc/net/atalk_route lists each known network route. It lists the target
-(network) that the route leads to, the router (may be directly connected), the
-route flags, and the device the route is using.
+ $ echo 0x21 > /proc/1234/coredump_filter
-2.10 IPX
---------
+When a new process is created, the process inherits the bitmask status from its
+parent. It is useful to set up coredump_filter before the program runs.
+For example:
-The IPX protocol has no tunable values in proc/sys/net.
+ $ echo 0x7 > /proc/self/coredump_filter
+ $ ./some_program
-The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
-socket giving the local and remote addresses in Novell format (that is
-network:node:port). In accordance with the strange Novell tradition,
-everything but the port is in hex. Not_Connected is displayed for sockets that
-are not tied to a specific remote address. The Tx and Rx queue sizes indicate
-the number of bytes pending for transmission and reception. The state
-indicates the state the socket is in and the uid is the owning uid of the
-socket.
+3.5 /proc/<pid>/mountinfo - Information about mounts
+--------------------------------------------------------
-The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
-it gives the network number, the node number, and indicates if the network is
-the primary network. It also indicates which device it is bound to (or
-Internal for internal networks) and the Frame Type if appropriate. Linux
-supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
-IPX.
+This file contains lines of the form:
-The /proc/net/ipx_route table holds a list of IPX routes. For each route it
-gives the destination network, the router node (or Directly) and the network
-address of the router (or Connected) for internal networks.
+36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
+(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
-2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
-----------------------------------------------------------
+(1) mount ID: unique identifier of the mount (may be reused after umount)
+(2) parent ID: ID of parent (or of self for the top of the mount tree)
+(3) major:minor: value of st_dev for files on filesystem
+(4) root: root of the mount within the filesystem
+(5) mount point: mount point relative to the process's root
+(6) mount options: per mount options
+(7) optional fields: zero or more fields of the form "tag[:value]"
+(8) separator: marks the end of the optional fields
+(9) filesystem type: name of filesystem of the form "type[.subtype]"
+(10) mount source: filesystem specific information or "none"
+(11) super options: per super block options
-The "mqueue" filesystem provides the necessary kernel features to enable the
-creation of a user space library that implements the POSIX message queues
-API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
-Interfaces specification.)
+Parsers should ignore all unrecognised optional fields. Currently the
+possible optional fields are:
-The "mqueue" filesystem contains values for determining/setting the amount of
-resources used by the file system.
+shared:X mount is shared in peer group X
+master:X mount is slave to peer group X
+propagate_from:X mount is slave and receives propagation from peer group X (*)
+unbindable mount is unbindable
-/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
-maximum number of message queues allowed on the system.
+(*) X is the closest dominant peer group under the process's root. If
+X is the immediate master of the mount, or if there's no dominant peer
+group under the same root, then only the "master:X" field is present
+and not the "propagate_from:X" field.
-/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
-maximum number of messages in a queue value. In fact it is the limiting value
-for another (user) limit which is set in mq_open invocation. This attribute of
-a queue must be less or equal then msg_max.
+For more information on mount propagation see:
-/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
-maximum message size value (it is every message queue's attribute set during
-its creation).
+ Documentation/filesystems/sharedsubtree.txt
-------------------------------------------------------------------------------
-Summary
-------------------------------------------------------------------------------
-Certain aspects of kernel behavior can be modified at runtime, without the
-need to recompile the kernel, or even to reboot the system. The files in the
-/proc/sys tree can not only be read, but also modified. You can use the echo
-command to write value into these files, thereby changing the default settings
-of the kernel.
-------------------------------------------------------------------------------
+3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
+--------------------------------------------------------
+These files provide a method to access a tasks comm value. It also allows for
+a task to set its own or one of its thread siblings comm value. The comm value
+is limited in size compared to the cmdline value, so writing anything longer
+then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
+comm value.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff