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2 T H E /proc F I L E S Y S T E M
3 ------------------------------------------------------------------------------
4 /proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999
5 Bodo Bauer <bb@ricochet.net>
7 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
8 move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
9 ------------------------------------------------------------------------------
10 Version 1.3 Kernel version 2.2.12
11 Kernel version 2.4.0-test11-pre4
12 ------------------------------------------------------------------------------
13 fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
15 Table of Contents
16 -----------------
18 0 Preface
19 0.1 Introduction/Credits
20 0.2 Legal Stuff
22 1 Collecting System Information
23 1.1 Process-Specific Subdirectories
24 1.2 Kernel data
25 1.3 IDE devices in /proc/ide
26 1.4 Networking info in /proc/net
27 1.5 SCSI info
28 1.6 Parallel port info in /proc/parport
29 1.7 TTY info in /proc/tty
30 1.8 Miscellaneous kernel statistics in /proc/stat
31 1.9 Ext4 file system parameters
33 2 Modifying System Parameters
35 3 Per-Process Parameters
36 3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
37 3.2 /proc/<pid>/oom_score - Display current oom-killer score
38 3.3 /proc/<pid>/io - Display the IO accounting fields
39 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
40 3.5 /proc/<pid>/mountinfo - Information about mounts
41 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
44 ------------------------------------------------------------------------------
45 Preface
46 ------------------------------------------------------------------------------
48 0.1 Introduction/Credits
49 ------------------------
51 This documentation is part of a soon (or so we hope) to be released book on
52 the SuSE Linux distribution. As there is no complete documentation for the
53 /proc file system and we've used many freely available sources to write these
54 chapters, it seems only fair to give the work back to the Linux community.
55 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
56 afraid it's still far from complete, but we hope it will be useful. As far as
57 we know, it is the first 'all-in-one' document about the /proc file system. It
58 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
59 SPARC, AXP, etc., features, you probably won't find what you are looking for.
60 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
61 additions and patches are welcome and will be added to this document if you
62 mail them to Bodo.
64 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
65 other people for help compiling this documentation. We'd also like to extend a
66 special thank you to Andi Kleen for documentation, which we relied on heavily
67 to create this document, as well as the additional information he provided.
68 Thanks to everybody else who contributed source or docs to the Linux kernel
69 and helped create a great piece of software... :)
71 If you have any comments, corrections or additions, please don't hesitate to
72 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
73 document.
75 The latest version of this document is available online at
76 http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
78 If the above direction does not works for you, ypu could try the kernel
79 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
80 comandante@zaralinux.com.
82 0.2 Legal Stuff
83 ---------------
85 We don't guarantee the correctness of this document, and if you come to us
86 complaining about how you screwed up your system because of incorrect
87 documentation, we won't feel responsible...
89 ------------------------------------------------------------------------------
90 CHAPTER 1: COLLECTING SYSTEM INFORMATION
91 ------------------------------------------------------------------------------
93 ------------------------------------------------------------------------------
94 In This Chapter
95 ------------------------------------------------------------------------------
96 * Investigating the properties of the pseudo file system /proc and its
97 ability to provide information on the running Linux system
98 * Examining /proc's structure
99 * Uncovering various information about the kernel and the processes running
100 on the system
101 ------------------------------------------------------------------------------
104 The proc file system acts as an interface to internal data structures in the
105 kernel. It can be used to obtain information about the system and to change
106 certain kernel parameters at runtime (sysctl).
108 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
109 show you how you can use /proc/sys to change settings.
111 1.1 Process-Specific Subdirectories
112 -----------------------------------
114 The directory /proc contains (among other things) one subdirectory for each
115 process running on the system, which is named after the process ID (PID).
117 The link self points to the process reading the file system. Each process
118 subdirectory has the entries listed in Table 1-1.
121 Table 1-1: Process specific entries in /proc
122 ..............................................................................
123 File Content
124 clear_refs Clears page referenced bits shown in smaps output
125 cmdline Command line arguments
126 cpu Current and last cpu in which it was executed (2.4)(smp)
127 cwd Link to the current working directory
128 environ Values of environment variables
129 exe Link to the executable of this process
130 fd Directory, which contains all file descriptors
131 maps Memory maps to executables and library files (2.4)
132 mem Memory held by this process
133 root Link to the root directory of this process
134 stat Process status
135 statm Process memory status information
136 status Process status in human readable form
137 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
138 stack Report full stack trace, enable via CONFIG_STACKTRACE
139 smaps a extension based on maps, showing the memory consumption of
140 each mapping
141 ..............................................................................
143 For example, to get the status information of a process, all you have to do is
144 read the file /proc/PID/status:
146 >cat /proc/self/status
147 Name: cat
148 State: R (running)
149 Tgid: 5452
150 Pid: 5452
151 PPid: 743
152 TracerPid: 0 (2.4)
153 Uid: 501 501 501 501
154 Gid: 100 100 100 100
155 FDSize: 256
156 Groups: 100 14 16
157 VmPeak: 5004 kB
158 VmSize: 5004 kB
159 VmLck: 0 kB
160 VmHWM: 476 kB
161 VmRSS: 476 kB
162 VmData: 156 kB
163 VmStk: 88 kB
164 VmExe: 68 kB
165 VmLib: 1412 kB
166 VmPTE: 20 kb
167 VmSwap: 0 kB
168 Threads: 1
169 SigQ: 0/28578
170 SigPnd: 0000000000000000
171 ShdPnd: 0000000000000000
172 SigBlk: 0000000000000000
173 SigIgn: 0000000000000000
174 SigCgt: 0000000000000000
175 CapInh: 00000000fffffeff
176 CapPrm: 0000000000000000
177 CapEff: 0000000000000000
178 CapBnd: ffffffffffffffff
179 voluntary_ctxt_switches: 0
180 nonvoluntary_ctxt_switches: 1
182 This shows you nearly the same information you would get if you viewed it with
183 the ps command. In fact, ps uses the proc file system to obtain its
184 information. But you get a more detailed view of the process by reading the
185 file /proc/PID/status. It fields are described in table 1-2.
187 The statm file contains more detailed information about the process
188 memory usage. Its seven fields are explained in Table 1-3. The stat file
189 contains details information about the process itself. Its fields are
190 explained in Table 1-4.
192 (for SMP CONFIG users)
193 For making accounting scalable, RSS related information are handled in
194 asynchronous manner and the vaule may not be very precise. To see a precise
195 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
196 It's slow but very precise.
198 Table 1-2: Contents of the status files (as of 2.6.30-rc7)
199 ..............................................................................
200 Field Content
201 Name filename of the executable
202 State state (R is running, S is sleeping, D is sleeping
203 in an uninterruptible wait, Z is zombie,
204 T is traced or stopped)
205 Tgid thread group ID
206 Pid process id
207 PPid process id of the parent process
208 TracerPid PID of process tracing this process (0 if not)
209 Uid Real, effective, saved set, and file system UIDs
210 Gid Real, effective, saved set, and file system GIDs
211 FDSize number of file descriptor slots currently allocated
212 Groups supplementary group list
213 VmPeak peak virtual memory size
214 VmSize total program size
215 VmLck locked memory size
216 VmHWM peak resident set size ("high water mark")
217 VmRSS size of memory portions
218 VmData size of data, stack, and text segments
219 VmStk size of data, stack, and text segments
220 VmExe size of text segment
221 VmLib size of shared library code
222 VmPTE size of page table entries
223 VmSwap size of swap usage (the number of referred swapents)
224 Threads number of threads
225 SigQ number of signals queued/max. number for queue
226 SigPnd bitmap of pending signals for the thread
227 ShdPnd bitmap of shared pending signals for the process
228 SigBlk bitmap of blocked signals
229 SigIgn bitmap of ignored signals
230 SigCgt bitmap of catched signals
231 CapInh bitmap of inheritable capabilities
232 CapPrm bitmap of permitted capabilities
233 CapEff bitmap of effective capabilities
234 CapBnd bitmap of capabilities bounding set
235 Cpus_allowed mask of CPUs on which this process may run
236 Cpus_allowed_list Same as previous, but in "list format"
237 Mems_allowed mask of memory nodes allowed to this process
238 Mems_allowed_list Same as previous, but in "list format"
239 voluntary_ctxt_switches number of voluntary context switches
240 nonvoluntary_ctxt_switches number of non voluntary context switches
241 ..............................................................................
243 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
244 ..............................................................................
245 Field Content
246 size total program size (pages) (same as VmSize in status)
247 resident size of memory portions (pages) (same as VmRSS in status)
248 shared number of pages that are shared (i.e. backed by a file)
249 trs number of pages that are 'code' (not including libs; broken,
250 includes data segment)
251 lrs number of pages of library (always 0 on 2.6)
252 drs number of pages of data/stack (including libs; broken,
253 includes library text)
254 dt number of dirty pages (always 0 on 2.6)
255 ..............................................................................
258 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
259 ..............................................................................
260 Field Content
261 pid process id
262 tcomm filename of the executable
263 state state (R is running, S is sleeping, D is sleeping in an
264 uninterruptible wait, Z is zombie, T is traced or stopped)
265 ppid process id of the parent process
266 pgrp pgrp of the process
267 sid session id
268 tty_nr tty the process uses
269 tty_pgrp pgrp of the tty
270 flags task flags
271 min_flt number of minor faults
272 cmin_flt number of minor faults with child's
273 maj_flt number of major faults
274 cmaj_flt number of major faults with child's
275 utime user mode jiffies
276 stime kernel mode jiffies
277 cutime user mode jiffies with child's
278 cstime kernel mode jiffies with child's
279 priority priority level
280 nice nice level
281 num_threads number of threads
282 it_real_value (obsolete, always 0)
283 start_time time the process started after system boot
284 vsize virtual memory size
285 rss resident set memory size
286 rsslim current limit in bytes on the rss
287 start_code address above which program text can run
288 end_code address below which program text can run
289 start_stack address of the start of the stack
290 esp current value of ESP
291 eip current value of EIP
292 pending bitmap of pending signals
293 blocked bitmap of blocked signals
294 sigign bitmap of ignored signals
295 sigcatch bitmap of catched signals
296 wchan address where process went to sleep
297 0 (place holder)
298 0 (place holder)
299 exit_signal signal to send to parent thread on exit
300 task_cpu which CPU the task is scheduled on
301 rt_priority realtime priority
302 policy scheduling policy (man sched_setscheduler)
303 blkio_ticks time spent waiting for block IO
304 gtime guest time of the task in jiffies
305 cgtime guest time of the task children in jiffies
306 ..............................................................................
308 The /proc/PID/map file containing the currently mapped memory regions and
309 their access permissions.
311 The format is:
313 address perms offset dev inode pathname
315 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
316 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
317 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
318 a7cb1000-a7cb2000 ---p 00000000 00:00 0
319 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
320 a7eb2000-a7eb3000 ---p 00000000 00:00 0
321 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
322 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
323 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
324 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
325 a800b000-a800e000 rw-p 00000000 00:00 0
326 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
327 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
328 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
329 a8024000-a8027000 rw-p 00000000 00:00 0
330 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
331 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
332 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
333 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
334 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
336 where "address" is the address space in the process that it occupies, "perms"
337 is a set of permissions:
339 r = read
340 w = write
341 x = execute
342 s = shared
343 p = private (copy on write)
345 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
346 "inode" is the inode on that device. 0 indicates that no inode is associated
347 with the memory region, as the case would be with BSS (uninitialized data).
348 The "pathname" shows the name associated file for this mapping. If the mapping
349 is not associated with a file:
351 [heap] = the heap of the program
352 [stack] = the stack of the main process
353 [vdso] = the "virtual dynamic shared object",
354 the kernel system call handler
356 or if empty, the mapping is anonymous.
359 The /proc/PID/smaps is an extension based on maps, showing the memory
360 consumption for each of the process's mappings. For each of mappings there
361 is a series of lines such as the following:
363 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
364 Size: 1084 kB
365 Rss: 892 kB
366 Pss: 374 kB
367 Shared_Clean: 892 kB
368 Shared_Dirty: 0 kB
369 Private_Clean: 0 kB
370 Private_Dirty: 0 kB
371 Referenced: 892 kB
372 Swap: 0 kB
373 KernelPageSize: 4 kB
374 MMUPageSize: 4 kB
376 The first of these lines shows the same information as is displayed for the
377 mapping in /proc/PID/maps. The remaining lines show the size of the mapping,
378 the amount of the mapping that is currently resident in RAM, the "proportional
379 set size” (divide each shared page by the number of processes sharing it), the
380 number of clean and dirty shared pages in the mapping, and the number of clean
381 and dirty private pages in the mapping. The "Referenced" indicates the amount
382 of memory currently marked as referenced or accessed.
384 This file is only present if the CONFIG_MMU kernel configuration option is
385 enabled.
387 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
388 bits on both physical and virtual pages associated with a process.
389 To clear the bits for all the pages associated with the process
390 > echo 1 > /proc/PID/clear_refs
392 To clear the bits for the anonymous pages associated with the process
393 > echo 2 > /proc/PID/clear_refs
395 To clear the bits for the file mapped pages associated with the process
396 > echo 3 > /proc/PID/clear_refs
397 Any other value written to /proc/PID/clear_refs will have no effect.
400 1.2 Kernel data
401 ---------------
403 Similar to the process entries, the kernel data files give information about
404 the running kernel. The files used to obtain this information are contained in
405 /proc and are listed in Table 1-5. Not all of these will be present in your
406 system. It depends on the kernel configuration and the loaded modules, which
407 files are there, and which are missing.
409 Table 1-5: Kernel info in /proc
410 ..............................................................................
411 File Content
412 apm Advanced power management info
413 buddyinfo Kernel memory allocator information (see text) (2.5)
414 bus Directory containing bus specific information
415 cmdline Kernel command line
416 cpuinfo Info about the CPU
417 devices Available devices (block and character)
418 dma Used DMS channels
419 filesystems Supported filesystems
420 driver Various drivers grouped here, currently rtc (2.4)
421 execdomains Execdomains, related to security (2.4)
422 fb Frame Buffer devices (2.4)
423 fs File system parameters, currently nfs/exports (2.4)
424 ide Directory containing info about the IDE subsystem
425 interrupts Interrupt usage
426 iomem Memory map (2.4)
427 ioports I/O port usage
428 irq Masks for irq to cpu affinity (2.4)(smp?)
429 isapnp ISA PnP (Plug&Play) Info (2.4)
430 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
431 kmsg Kernel messages
432 ksyms Kernel symbol table
433 loadavg Load average of last 1, 5 & 15 minutes
434 locks Kernel locks
435 meminfo Memory info
436 misc Miscellaneous
437 modules List of loaded modules
438 mounts Mounted filesystems
439 net Networking info (see text)
440 pagetypeinfo Additional page allocator information (see text) (2.5)
441 partitions Table of partitions known to the system
442 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
443 decoupled by lspci (2.4)
444 rtc Real time clock
445 scsi SCSI info (see text)
446 slabinfo Slab pool info
447 softirqs softirq usage
448 stat Overall statistics
449 swaps Swap space utilization
450 sys See chapter 2
451 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
452 tty Info of tty drivers
453 uptime System uptime
454 version Kernel version
455 video bttv info of video resources (2.4)
456 vmallocinfo Show vmalloced areas
457 ..............................................................................
459 You can, for example, check which interrupts are currently in use and what
460 they are used for by looking in the file /proc/interrupts:
462 > cat /proc/interrupts
463 CPU0
464 0: 8728810 XT-PIC timer
465 1: 895 XT-PIC keyboard
466 2: 0 XT-PIC cascade
467 3: 531695 XT-PIC aha152x
468 4: 2014133 XT-PIC serial
469 5: 44401 XT-PIC pcnet_cs
470 8: 2 XT-PIC rtc
471 11: 8 XT-PIC i82365
472 12: 182918 XT-PIC PS/2 Mouse
473 13: 1 XT-PIC fpu
474 14: 1232265 XT-PIC ide0
475 15: 7 XT-PIC ide1
476 NMI: 0
478 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
479 output of a SMP machine):
481 > cat /proc/interrupts
483 CPU0 CPU1
484 0: 1243498 1214548 IO-APIC-edge timer
485 1: 8949 8958 IO-APIC-edge keyboard
486 2: 0 0 XT-PIC cascade
487 5: 11286 10161 IO-APIC-edge soundblaster
488 8: 1 0 IO-APIC-edge rtc
489 9: 27422 27407 IO-APIC-edge 3c503
490 12: 113645 113873 IO-APIC-edge PS/2 Mouse
491 13: 0 0 XT-PIC fpu
492 14: 22491 24012 IO-APIC-edge ide0
493 15: 2183 2415 IO-APIC-edge ide1
494 17: 30564 30414 IO-APIC-level eth0
495 18: 177 164 IO-APIC-level bttv
496 NMI: 2457961 2457959
497 LOC: 2457882 2457881
498 ERR: 2155
500 NMI is incremented in this case because every timer interrupt generates a NMI
501 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
503 LOC is the local interrupt counter of the internal APIC of every CPU.
505 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
506 connects the CPUs in a SMP system. This means that an error has been detected,
507 the IO-APIC automatically retry the transmission, so it should not be a big
508 problem, but you should read the SMP-FAQ.
510 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
511 /proc/interrupts to display every IRQ vector in use by the system, not
512 just those considered 'most important'. The new vectors are:
514 THR -- interrupt raised when a machine check threshold counter
515 (typically counting ECC corrected errors of memory or cache) exceeds
516 a configurable threshold. Only available on some systems.
518 TRM -- a thermal event interrupt occurs when a temperature threshold
519 has been exceeded for the CPU. This interrupt may also be generated
520 when the temperature drops back to normal.
522 SPU -- a spurious interrupt is some interrupt that was raised then lowered
523 by some IO device before it could be fully processed by the APIC. Hence
524 the APIC sees the interrupt but does not know what device it came from.
525 For this case the APIC will generate the interrupt with a IRQ vector
526 of 0xff. This might also be generated by chipset bugs.
528 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
529 sent from one CPU to another per the needs of the OS. Typically,
530 their statistics are used by kernel developers and interested users to
531 determine the occurrence of interrupts of the given type.
533 The above IRQ vectors are displayed only when relevent. For example,
534 the threshold vector does not exist on x86_64 platforms. Others are
535 suppressed when the system is a uniprocessor. As of this writing, only
536 i386 and x86_64 platforms support the new IRQ vector displays.
538 Of some interest is the introduction of the /proc/irq directory to 2.4.
539 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
540 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
541 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
542 prof_cpu_mask.
544 For example
545 > ls /proc/irq/
546 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
547 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
548 > ls /proc/irq/0/
549 smp_affinity
551 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
552 IRQ, you can set it by doing:
554 > echo 1 > /proc/irq/10/smp_affinity
556 This means that only the first CPU will handle the IRQ, but you can also echo
557 5 which means that only the first and fourth CPU can handle the IRQ.
559 The contents of each smp_affinity file is the same by default:
561 > cat /proc/irq/0/smp_affinity
562 ffffffff
564 The default_smp_affinity mask applies to all non-active IRQs, which are the
565 IRQs which have not yet been allocated/activated, and hence which lack a
566 /proc/irq/[0-9]* directory.
568 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
569 profiler. Default value is ffffffff (all cpus).
571 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
572 between all the CPUs which are allowed to handle it. As usual the kernel has
573 more info than you and does a better job than you, so the defaults are the
574 best choice for almost everyone.
576 There are three more important subdirectories in /proc: net, scsi, and sys.
577 The general rule is that the contents, or even the existence of these
578 directories, depend on your kernel configuration. If SCSI is not enabled, the
579 directory scsi may not exist. The same is true with the net, which is there
580 only when networking support is present in the running kernel.
582 The slabinfo file gives information about memory usage at the slab level.
583 Linux uses slab pools for memory management above page level in version 2.2.
584 Commonly used objects have their own slab pool (such as network buffers,
585 directory cache, and so on).
587 ..............................................................................
589 > cat /proc/buddyinfo
591 Node 0, zone DMA 0 4 5 4 4 3 ...
592 Node 0, zone Normal 1 0 0 1 101 8 ...
593 Node 0, zone HighMem 2 0 0 1 1 0 ...
595 External fragmentation is a problem under some workloads, and buddyinfo is a
596 useful tool for helping diagnose these problems. Buddyinfo will give you a
597 clue as to how big an area you can safely allocate, or why a previous
598 allocation failed.
600 Each column represents the number of pages of a certain order which are
601 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
602 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
603 available in ZONE_NORMAL, etc...
605 More information relevant to external fragmentation can be found in
606 pagetypeinfo.
608 > cat /proc/pagetypeinfo
609 Page block order: 9
610 Pages per block: 512
612 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
613 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
614 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
615 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
616 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
617 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
618 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
619 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
620 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
621 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
622 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
624 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
625 Node 0, zone DMA 2 0 5 1 0
626 Node 0, zone DMA32 41 6 967 2 0
628 Fragmentation avoidance in the kernel works by grouping pages of different
629 migrate types into the same contiguous regions of memory called page blocks.
630 A page block is typically the size of the default hugepage size e.g. 2MB on
631 X86-64. By keeping pages grouped based on their ability to move, the kernel
632 can reclaim pages within a page block to satisfy a high-order allocation.
634 The pagetypinfo begins with information on the size of a page block. It
635 then gives the same type of information as buddyinfo except broken down
636 by migrate-type and finishes with details on how many page blocks of each
637 type exist.
639 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
640 from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
641 make an estimate of the likely number of huge pages that can be allocated
642 at a given point in time. All the "Movable" blocks should be allocatable
643 unless memory has been mlock()'d. Some of the Reclaimable blocks should
644 also be allocatable although a lot of filesystem metadata may have to be
645 reclaimed to achieve this.
647 ..............................................................................
649 meminfo:
651 Provides information about distribution and utilization of memory. This
652 varies by architecture and compile options. The following is from a
653 16GB PIII, which has highmem enabled. You may not have all of these fields.
655 > cat /proc/meminfo
658 MemTotal: 16344972 kB
659 MemFree: 13634064 kB
660 Buffers: 3656 kB
661 Cached: 1195708 kB
662 SwapCached: 0 kB
663 Active: 891636 kB
664 Inactive: 1077224 kB
665 HighTotal: 15597528 kB
666 HighFree: 13629632 kB
667 LowTotal: 747444 kB
668 LowFree: 4432 kB
669 SwapTotal: 0 kB
670 SwapFree: 0 kB
671 Dirty: 968 kB
672 Writeback: 0 kB
673 AnonPages: 861800 kB
674 Mapped: 280372 kB
675 Slab: 284364 kB
676 SReclaimable: 159856 kB
677 SUnreclaim: 124508 kB
678 PageTables: 24448 kB
679 NFS_Unstable: 0 kB
680 Bounce: 0 kB
681 WritebackTmp: 0 kB
682 CommitLimit: 7669796 kB
683 Committed_AS: 100056 kB
684 VmallocTotal: 112216 kB
685 VmallocUsed: 428 kB
686 VmallocChunk: 111088 kB
688 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
689 bits and the kernel binary code)
690 MemFree: The sum of LowFree+HighFree
691 Buffers: Relatively temporary storage for raw disk blocks
692 shouldn't get tremendously large (20MB or so)
693 Cached: in-memory cache for files read from the disk (the
694 pagecache). Doesn't include SwapCached
695 SwapCached: Memory that once was swapped out, is swapped back in but
696 still also is in the swapfile (if memory is needed it
697 doesn't need to be swapped out AGAIN because it is already
698 in the swapfile. This saves I/O)
699 Active: Memory that has been used more recently and usually not
700 reclaimed unless absolutely necessary.
701 Inactive: Memory which has been less recently used. It is more
702 eligible to be reclaimed for other purposes
703 HighTotal:
704 HighFree: Highmem is all memory above ~860MB of physical memory
705 Highmem areas are for use by userspace programs, or
706 for the pagecache. The kernel must use tricks to access
707 this memory, making it slower to access than lowmem.
708 LowTotal:
709 LowFree: Lowmem is memory which can be used for everything that
710 highmem can be used for, but it is also available for the
711 kernel's use for its own data structures. Among many
712 other things, it is where everything from the Slab is
713 allocated. Bad things happen when you're out of lowmem.
714 SwapTotal: total amount of swap space available
715 SwapFree: Memory which has been evicted from RAM, and is temporarily
716 on the disk
717 Dirty: Memory which is waiting to get written back to the disk
718 Writeback: Memory which is actively being written back to the disk
719 AnonPages: Non-file backed pages mapped into userspace page tables
720 Mapped: files which have been mmaped, such as libraries
721 Slab: in-kernel data structures cache
722 SReclaimable: Part of Slab, that might be reclaimed, such as caches
723 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
724 PageTables: amount of memory dedicated to the lowest level of page
725 tables.
726 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
727 storage
728 Bounce: Memory used for block device "bounce buffers"
729 WritebackTmp: Memory used by FUSE for temporary writeback buffers
730 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
731 this is the total amount of memory currently available to
732 be allocated on the system. This limit is only adhered to
733 if strict overcommit accounting is enabled (mode 2 in
734 'vm.overcommit_memory').
735 The CommitLimit is calculated with the following formula:
736 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
737 For example, on a system with 1G of physical RAM and 7G
738 of swap with a `vm.overcommit_ratio` of 30 it would
739 yield a CommitLimit of 7.3G.
740 For more details, see the memory overcommit documentation
741 in vm/overcommit-accounting.
742 Committed_AS: The amount of memory presently allocated on the system.
743 The committed memory is a sum of all of the memory which
744 has been allocated by processes, even if it has not been
745 "used" by them as of yet. A process which malloc()'s 1G
746 of memory, but only touches 300M of it will only show up
747 as using 300M of memory even if it has the address space
748 allocated for the entire 1G. This 1G is memory which has
749 been "committed" to by the VM and can be used at any time
750 by the allocating application. With strict overcommit
751 enabled on the system (mode 2 in 'vm.overcommit_memory'),
752 allocations which would exceed the CommitLimit (detailed
753 above) will not be permitted. This is useful if one needs
754 to guarantee that processes will not fail due to lack of
755 memory once that memory has been successfully allocated.
756 VmallocTotal: total size of vmalloc memory area
757 VmallocUsed: amount of vmalloc area which is used
758 VmallocChunk: largest contiguous block of vmalloc area which is free
760 ..............................................................................
762 vmallocinfo:
764 Provides information about vmalloced/vmaped areas. One line per area,
765 containing the virtual address range of the area, size in bytes,
766 caller information of the creator, and optional information depending
767 on the kind of area :
769 pages=nr number of pages
770 phys=addr if a physical address was specified
771 ioremap I/O mapping (ioremap() and friends)
772 vmalloc vmalloc() area
773 vmap vmap()ed pages
774 user VM_USERMAP area
775 vpages buffer for pages pointers was vmalloced (huge area)
776 N<node>=nr (Only on NUMA kernels)
777 Number of pages allocated on memory node <node>
779 > cat /proc/vmallocinfo
780 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
781 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
782 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
783 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
784 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
785 phys=7fee8000 ioremap
786 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
787 phys=7fee7000 ioremap
788 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
789 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
790 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
791 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
792 pages=2 vmalloc N1=2
793 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
794 /0x130 [x_tables] pages=4 vmalloc N0=4
795 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
796 pages=14 vmalloc N2=14
797 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
798 pages=4 vmalloc N1=4
799 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
800 pages=2 vmalloc N1=2
801 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
802 pages=10 vmalloc N0=10
804 ..............................................................................
806 softirqs:
808 Provides counts of softirq handlers serviced since boot time, for each cpu.
810 > cat /proc/softirqs
811 CPU0 CPU1 CPU2 CPU3
812 HI: 0 0 0 0
813 TIMER: 27166 27120 27097 27034
814 NET_TX: 0 0 0 17
815 NET_RX: 42 0 0 39
816 BLOCK: 0 0 107 1121
817 TASKLET: 0 0 0 290
818 SCHED: 27035 26983 26971 26746
819 HRTIMER: 0 0 0 0
820 RCU: 1678 1769 2178 2250
823 1.3 IDE devices in /proc/ide
824 ----------------------------
826 The subdirectory /proc/ide contains information about all IDE devices of which
827 the kernel is aware. There is one subdirectory for each IDE controller, the
828 file drivers and a link for each IDE device, pointing to the device directory
829 in the controller specific subtree.
831 The file drivers contains general information about the drivers used for the
832 IDE devices:
834 > cat /proc/ide/drivers
835 ide-cdrom version 4.53
836 ide-disk version 1.08
838 More detailed information can be found in the controller specific
839 subdirectories. These are named ide0, ide1 and so on. Each of these
840 directories contains the files shown in table 1-6.
843 Table 1-6: IDE controller info in /proc/ide/ide?
844 ..............................................................................
845 File Content
846 channel IDE channel (0 or 1)
847 config Configuration (only for PCI/IDE bridge)
848 mate Mate name
849 model Type/Chipset of IDE controller
850 ..............................................................................
852 Each device connected to a controller has a separate subdirectory in the
853 controllers directory. The files listed in table 1-7 are contained in these
854 directories.
857 Table 1-7: IDE device information
858 ..............................................................................
859 File Content
860 cache The cache
861 capacity Capacity of the medium (in 512Byte blocks)
862 driver driver and version
863 geometry physical and logical geometry
864 identify device identify block
865 media media type
866 model device identifier
867 settings device setup
868 smart_thresholds IDE disk management thresholds
869 smart_values IDE disk management values
870 ..............................................................................
872 The most interesting file is settings. This file contains a nice overview of
873 the drive parameters:
875 # cat /proc/ide/ide0/hda/settings
876 name value min max mode
877 ---- ----- --- --- ----
878 bios_cyl 526 0 65535 rw
879 bios_head 255 0 255 rw
880 bios_sect 63 0 63 rw
881 breada_readahead 4 0 127 rw
882 bswap 0 0 1 r
883 file_readahead 72 0 2097151 rw
884 io_32bit 0 0 3 rw
885 keepsettings 0 0 1 rw
886 max_kb_per_request 122 1 127 rw
887 multcount 0 0 8 rw
888 nice1 1 0 1 rw
889 nowerr 0 0 1 rw
890 pio_mode write-only 0 255 w
891 slow 0 0 1 rw
892 unmaskirq 0 0 1 rw
893 using_dma 0 0 1 rw
896 1.4 Networking info in /proc/net
897 --------------------------------
899 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
900 additional values you get for IP version 6 if you configure the kernel to
901 support this. Table 1-9 lists the files and their meaning.
904 Table 1-8: IPv6 info in /proc/net
905 ..............................................................................
906 File Content
907 udp6 UDP sockets (IPv6)
908 tcp6 TCP sockets (IPv6)
909 raw6 Raw device statistics (IPv6)
910 igmp6 IP multicast addresses, which this host joined (IPv6)
911 if_inet6 List of IPv6 interface addresses
912 ipv6_route Kernel routing table for IPv6
913 rt6_stats Global IPv6 routing tables statistics
914 sockstat6 Socket statistics (IPv6)
915 snmp6 Snmp data (IPv6)
916 ..............................................................................
919 Table 1-9: Network info in /proc/net
920 ..............................................................................
921 File Content
922 arp Kernel ARP table
923 dev network devices with statistics
924 dev_mcast the Layer2 multicast groups a device is listening too
925 (interface index, label, number of references, number of bound
926 addresses).
927 dev_stat network device status
928 ip_fwchains Firewall chain linkage
929 ip_fwnames Firewall chain names
930 ip_masq Directory containing the masquerading tables
931 ip_masquerade Major masquerading table
932 netstat Network statistics
933 raw raw device statistics
934 route Kernel routing table
935 rpc Directory containing rpc info
936 rt_cache Routing cache
937 snmp SNMP data
938 sockstat Socket statistics
939 tcp TCP sockets
940 tr_rif Token ring RIF routing table
941 udp UDP sockets
942 unix UNIX domain sockets
943 wireless Wireless interface data (Wavelan etc)
944 igmp IP multicast addresses, which this host joined
945 psched Global packet scheduler parameters.
946 netlink List of PF_NETLINK sockets
947 ip_mr_vifs List of multicast virtual interfaces
948 ip_mr_cache List of multicast routing cache
949 ..............................................................................
951 You can use this information to see which network devices are available in
952 your system and how much traffic was routed over those devices:
954 > cat /proc/net/dev
955 Inter-|Receive |[...
956 face |bytes packets errs drop fifo frame compressed multicast|[...
957 lo: 908188 5596 0 0 0 0 0 0 [...
958 ppp0:15475140 20721 410 0 0 410 0 0 [...
959 eth0: 614530 7085 0 0 0 0 0 1 [...
961 ...] Transmit
962 ...] bytes packets errs drop fifo colls carrier compressed
963 ...] 908188 5596 0 0 0 0 0 0
964 ...] 1375103 17405 0 0 0 0 0 0
965 ...] 1703981 5535 0 0 0 3 0 0
967 In addition, each Channel Bond interface has it's own directory. For
968 example, the bond0 device will have a directory called /proc/net/bond0/.
969 It will contain information that is specific to that bond, such as the
970 current slaves of the bond, the link status of the slaves, and how
971 many times the slaves link has failed.
973 1.5 SCSI info
974 -------------
976 If you have a SCSI host adapter in your system, you'll find a subdirectory
977 named after the driver for this adapter in /proc/scsi. You'll also see a list
978 of all recognized SCSI devices in /proc/scsi:
980 >cat /proc/scsi/scsi
981 Attached devices:
982 Host: scsi0 Channel: 00 Id: 00 Lun: 00
983 Vendor: IBM Model: DGHS09U Rev: 03E0
984 Type: Direct-Access ANSI SCSI revision: 03
985 Host: scsi0 Channel: 00 Id: 06 Lun: 00
986 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
987 Type: CD-ROM ANSI SCSI revision: 02
990 The directory named after the driver has one file for each adapter found in
991 the system. These files contain information about the controller, including
992 the used IRQ and the IO address range. The amount of information shown is
993 dependent on the adapter you use. The example shows the output for an Adaptec
994 AHA-2940 SCSI adapter:
996 > cat /proc/scsi/aic7xxx/0
998 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
999 Compile Options:
1000 TCQ Enabled By Default : Disabled
1001 AIC7XXX_PROC_STATS : Disabled
1002 AIC7XXX_RESET_DELAY : 5
1003 Adapter Configuration:
1004 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1005 Ultra Wide Controller
1006 PCI MMAPed I/O Base: 0xeb001000
1007 Adapter SEEPROM Config: SEEPROM found and used.
1008 Adaptec SCSI BIOS: Enabled
1009 IRQ: 10
1010 SCBs: Active 0, Max Active 2,
1011 Allocated 15, HW 16, Page 255
1012 Interrupts: 160328
1013 BIOS Control Word: 0x18b6
1014 Adapter Control Word: 0x005b
1015 Extended Translation: Enabled
1016 Disconnect Enable Flags: 0xffff
1017 Ultra Enable Flags: 0x0001
1018 Tag Queue Enable Flags: 0x0000
1019 Ordered Queue Tag Flags: 0x0000
1020 Default Tag Queue Depth: 8
1021 Tagged Queue By Device array for aic7xxx host instance 0:
1022 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1023 Actual queue depth per device for aic7xxx host instance 0:
1024 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1025 Statistics:
1026 (scsi0:0:0:0)
1027 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1028 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1029 Total transfers 160151 (74577 reads and 85574 writes)
1030 (scsi0:0:6:0)
1031 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1032 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1033 Total transfers 0 (0 reads and 0 writes)
1036 1.6 Parallel port info in /proc/parport
1037 ---------------------------------------
1039 The directory /proc/parport contains information about the parallel ports of
1040 your system. It has one subdirectory for each port, named after the port
1041 number (0,1,2,...).
1043 These directories contain the four files shown in Table 1-10.
1046 Table 1-10: Files in /proc/parport
1047 ..............................................................................
1048 File Content
1049 autoprobe Any IEEE-1284 device ID information that has been acquired.
1050 devices list of the device drivers using that port. A + will appear by the
1051 name of the device currently using the port (it might not appear
1052 against any).
1053 hardware Parallel port's base address, IRQ line and DMA channel.
1054 irq IRQ that parport is using for that port. This is in a separate
1055 file to allow you to alter it by writing a new value in (IRQ
1056 number or none).
1057 ..............................................................................
1059 1.7 TTY info in /proc/tty
1060 -------------------------
1062 Information about the available and actually used tty's can be found in the
1063 directory /proc/tty.You'll find entries for drivers and line disciplines in
1064 this directory, as shown in Table 1-11.
1067 Table 1-11: Files in /proc/tty
1068 ..............................................................................
1069 File Content
1070 drivers list of drivers and their usage
1071 ldiscs registered line disciplines
1072 driver/serial usage statistic and status of single tty lines
1073 ..............................................................................
1075 To see which tty's are currently in use, you can simply look into the file
1076 /proc/tty/drivers:
1078 > cat /proc/tty/drivers
1079 pty_slave /dev/pts 136 0-255 pty:slave
1080 pty_master /dev/ptm 128 0-255 pty:master
1081 pty_slave /dev/ttyp 3 0-255 pty:slave
1082 pty_master /dev/pty 2 0-255 pty:master
1083 serial /dev/cua 5 64-67 serial:callout
1084 serial /dev/ttyS 4 64-67 serial
1085 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1086 /dev/ptmx /dev/ptmx 5 2 system
1087 /dev/console /dev/console 5 1 system:console
1088 /dev/tty /dev/tty 5 0 system:/dev/tty
1089 unknown /dev/tty 4 1-63 console
1092 1.8 Miscellaneous kernel statistics in /proc/stat
1093 -------------------------------------------------
1095 Various pieces of information about kernel activity are available in the
1096 /proc/stat file. All of the numbers reported in this file are aggregates
1097 since the system first booted. For a quick look, simply cat the file:
1099 > cat /proc/stat
1100 cpu 2255 34 2290 22625563 6290 127 456 0 0
1101 cpu0 1132 34 1441 11311718 3675 127 438 0 0
1102 cpu1 1123 0 849 11313845 2614 0 18 0 0
1103 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1104 ctxt 1990473
1105 btime 1062191376
1106 processes 2915
1107 procs_running 1
1108 procs_blocked 0
1109 softirq 183433 0 21755 12 39 1137 231 21459 2263
1111 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1112 lines. These numbers identify the amount of time the CPU has spent performing
1113 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1114 second). The meanings of the columns are as follows, from left to right:
1116 - user: normal processes executing in user mode
1117 - nice: niced processes executing in user mode
1118 - system: processes executing in kernel mode
1119 - idle: twiddling thumbs
1120 - iowait: waiting for I/O to complete
1121 - irq: servicing interrupts
1122 - softirq: servicing softirqs
1123 - steal: involuntary wait
1124 - guest: running a normal guest
1125 - guest_nice: running a niced guest
1127 The "intr" line gives counts of interrupts serviced since boot time, for each
1128 of the possible system interrupts. The first column is the total of all
1129 interrupts serviced; each subsequent column is the total for that particular
1130 interrupt.
1132 The "ctxt" line gives the total number of context switches across all CPUs.
1134 The "btime" line gives the time at which the system booted, in seconds since
1135 the Unix epoch.
1137 The "processes" line gives the number of processes and threads created, which
1138 includes (but is not limited to) those created by calls to the fork() and
1139 clone() system calls.
1141 The "procs_running" line gives the total number of threads that are
1142 running or ready to run (i.e., the total number of runnable threads).
1144 The "procs_blocked" line gives the number of processes currently blocked,
1145 waiting for I/O to complete.
1147 The "softirq" line gives counts of softirqs serviced since boot time, for each
1148 of the possible system softirqs. The first column is the total of all
1149 softirqs serviced; each subsequent column is the total for that particular
1150 softirq.
1153 1.9 Ext4 file system parameters
1154 ------------------------------
1156 Information about mounted ext4 file systems can be found in
1157 /proc/fs/ext4. Each mounted filesystem will have a directory in
1158 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1159 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1160 in Table 1-12, below.
1162 Table 1-12: Files in /proc/fs/ext4/<devname>
1163 ..............................................................................
1164 File Content
1165 mb_groups details of multiblock allocator buddy cache of free blocks
1166 ..............................................................................
1169 ------------------------------------------------------------------------------
1170 Summary
1171 ------------------------------------------------------------------------------
1172 The /proc file system serves information about the running system. It not only
1173 allows access to process data but also allows you to request the kernel status
1174 by reading files in the hierarchy.
1176 The directory structure of /proc reflects the types of information and makes
1177 it easy, if not obvious, where to look for specific data.
1178 ------------------------------------------------------------------------------
1180 ------------------------------------------------------------------------------
1181 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1182 ------------------------------------------------------------------------------
1184 ------------------------------------------------------------------------------
1185 In This Chapter
1186 ------------------------------------------------------------------------------
1187 * Modifying kernel parameters by writing into files found in /proc/sys
1188 * Exploring the files which modify certain parameters
1189 * Review of the /proc/sys file tree
1190 ------------------------------------------------------------------------------
1193 A very interesting part of /proc is the directory /proc/sys. This is not only
1194 a source of information, it also allows you to change parameters within the
1195 kernel. Be very careful when attempting this. You can optimize your system,
1196 but you can also cause it to crash. Never alter kernel parameters on a
1197 production system. Set up a development machine and test to make sure that
1198 everything works the way you want it to. You may have no alternative but to
1199 reboot the machine once an error has been made.
1201 To change a value, simply echo the new value into the file. An example is
1202 given below in the section on the file system data. You need to be root to do
1203 this. You can create your own boot script to perform this every time your
1204 system boots.
1206 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1207 general things in the operation of the Linux kernel. Since some of the files
1208 can inadvertently disrupt your system, it is advisable to read both
1209 documentation and source before actually making adjustments. In any case, be
1210 very careful when writing to any of these files. The entries in /proc may
1211 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1212 review the kernel documentation in the directory /usr/src/linux/Documentation.
1213 This chapter is heavily based on the documentation included in the pre 2.2
1214 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1216 Please see: Documentation/sysctls/ directory for descriptions of these
1217 entries.
1219 ------------------------------------------------------------------------------
1220 Summary
1221 ------------------------------------------------------------------------------
1222 Certain aspects of kernel behavior can be modified at runtime, without the
1223 need to recompile the kernel, or even to reboot the system. The files in the
1224 /proc/sys tree can not only be read, but also modified. You can use the echo
1225 command to write value into these files, thereby changing the default settings
1226 of the kernel.
1227 ------------------------------------------------------------------------------
1229 ------------------------------------------------------------------------------
1230 CHAPTER 3: PER-PROCESS PARAMETERS
1231 ------------------------------------------------------------------------------
1233 3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
1234 ------------------------------------------------------
1236 This file can be used to adjust the score used to select which processes
1237 should be killed in an out-of-memory situation. Giving it a high score will
1238 increase the likelihood of this process being killed by the oom-killer. Valid
1239 values are in the range -16 to +15, plus the special value -17, which disables
1240 oom-killing altogether for this process.
1242 The process to be killed in an out-of-memory situation is selected among all others
1243 based on its badness score. This value equals the original memory size of the process
1244 and is then updated according to its CPU time (utime + stime) and the
1245 run time (uptime - start time). The longer it runs the smaller is the score.
1246 Badness score is divided by the square root of the CPU time and then by
1247 the double square root of the run time.
1249 Swapped out tasks are killed first. Half of each child's memory size is added to
1250 the parent's score if they do not share the same memory. Thus forking servers
1251 are the prime candidates to be killed. Having only one 'hungry' child will make
1252 parent less preferable than the child.
1254 /proc/<pid>/oom_score shows process' current badness score.
1256 The following heuristics are then applied:
1257 * if the task was reniced, its score doubles
1258 * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
1259 or CAP_SYS_RAWIO) have their score divided by 4
1260 * if oom condition happened in one cpuset and checked process does not belong
1261 to it, its score is divided by 8
1262 * the resulting score is multiplied by two to the power of oom_adj, i.e.
1263 points <<= oom_adj when it is positive and
1264 points >>= -(oom_adj) otherwise
1266 The task with the highest badness score is then selected and its children
1267 are killed, process itself will be killed in an OOM situation when it does
1268 not have children or some of them disabled oom like described above.
1270 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1271 -------------------------------------------------------------
1273 This file can be used to check the current score used by the oom-killer is for
1274 any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
1275 process should be killed in an out-of-memory situation.
1278 3.3 /proc/<pid>/io - Display the IO accounting fields
1279 -------------------------------------------------------
1281 This file contains IO statistics for each running process
1283 Example
1284 -------
1286 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1287 [1] 3828
1289 test:/tmp # cat /proc/3828/io
1290 rchar: 323934931
1291 wchar: 323929600
1292 syscr: 632687
1293 syscw: 632675
1294 read_bytes: 0
1295 write_bytes: 323932160
1296 cancelled_write_bytes: 0
1299 Description
1300 -----------
1302 rchar
1303 -----
1305 I/O counter: chars read
1306 The number of bytes which this task has caused to be read from storage. This
1307 is simply the sum of bytes which this process passed to read() and pread().
1308 It includes things like tty IO and it is unaffected by whether or not actual
1309 physical disk IO was required (the read might have been satisfied from
1310 pagecache)
1313 wchar
1314 -----
1316 I/O counter: chars written
1317 The number of bytes which this task has caused, or shall cause to be written
1318 to disk. Similar caveats apply here as with rchar.
1321 syscr
1322 -----
1324 I/O counter: read syscalls
1325 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1326 and pread().
1329 syscw
1330 -----
1332 I/O counter: write syscalls
1333 Attempt to count the number of write I/O operations, i.e. syscalls like
1334 write() and pwrite().
1337 read_bytes
1338 ----------
1340 I/O counter: bytes read
1341 Attempt to count the number of bytes which this process really did cause to
1342 be fetched from the storage layer. Done at the submit_bio() level, so it is
1343 accurate for block-backed filesystems. <please add status regarding NFS and
1344 CIFS at a later time>
1347 write_bytes
1348 -----------
1350 I/O counter: bytes written
1351 Attempt to count the number of bytes which this process caused to be sent to
1352 the storage layer. This is done at page-dirtying time.
1355 cancelled_write_bytes
1356 ---------------------
1358 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1359 then deletes the file, it will in fact perform no writeout. But it will have
1360 been accounted as having caused 1MB of write.
1361 In other words: The number of bytes which this process caused to not happen,
1362 by truncating pagecache. A task can cause "negative" IO too. If this task
1363 truncates some dirty pagecache, some IO which another task has been accounted
1364 for (in it's write_bytes) will not be happening. We _could_ just subtract that
1365 from the truncating task's write_bytes, but there is information loss in doing
1366 that.
1369 Note
1370 ----
1372 At its current implementation state, this is a bit racy on 32-bit machines: if
1373 process A reads process B's /proc/pid/io while process B is updating one of
1374 those 64-bit counters, process A could see an intermediate result.
1377 More information about this can be found within the taskstats documentation in
1378 Documentation/accounting.
1380 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1381 ---------------------------------------------------------------
1382 When a process is dumped, all anonymous memory is written to a core file as
1383 long as the size of the core file isn't limited. But sometimes we don't want
1384 to dump some memory segments, for example, huge shared memory. Conversely,
1385 sometimes we want to save file-backed memory segments into a core file, not
1386 only the individual files.
1388 /proc/<pid>/coredump_filter allows you to customize which memory segments
1389 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1390 of memory types. If a bit of the bitmask is set, memory segments of the
1391 corresponding memory type are dumped, otherwise they are not dumped.
1393 The following 7 memory types are supported:
1394 - (bit 0) anonymous private memory
1395 - (bit 1) anonymous shared memory
1396 - (bit 2) file-backed private memory
1397 - (bit 3) file-backed shared memory
1398 - (bit 4) ELF header pages in file-backed private memory areas (it is
1399 effective only if the bit 2 is cleared)
1400 - (bit 5) hugetlb private memory
1401 - (bit 6) hugetlb shared memory
1403 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1404 are always dumped regardless of the bitmask status.
1406 Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1407 effected by bit 5-6.
1409 Default value of coredump_filter is 0x23; this means all anonymous memory
1410 segments and hugetlb private memory are dumped.
1412 If you don't want to dump all shared memory segments attached to pid 1234,
1413 write 0x21 to the process's proc file.
1415 $ echo 0x21 > /proc/1234/coredump_filter
1417 When a new process is created, the process inherits the bitmask status from its
1418 parent. It is useful to set up coredump_filter before the program runs.
1419 For example:
1421 $ echo 0x7 > /proc/self/coredump_filter
1422 $ ./some_program
1424 3.5 /proc/<pid>/mountinfo - Information about mounts
1425 --------------------------------------------------------
1427 This file contains lines of the form:
1429 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1430 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1432 (1) mount ID: unique identifier of the mount (may be reused after umount)
1433 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1434 (3) major:minor: value of st_dev for files on filesystem
1435 (4) root: root of the mount within the filesystem
1436 (5) mount point: mount point relative to the process's root
1437 (6) mount options: per mount options
1438 (7) optional fields: zero or more fields of the form "tag[:value]"
1439 (8) separator: marks the end of the optional fields
1440 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1441 (10) mount source: filesystem specific information or "none"
1442 (11) super options: per super block options
1444 Parsers should ignore all unrecognised optional fields. Currently the
1445 possible optional fields are:
1447 shared:X mount is shared in peer group X
1448 master:X mount is slave to peer group X
1449 propagate_from:X mount is slave and receives propagation from peer group X (*)
1450 unbindable mount is unbindable
1452 (*) X is the closest dominant peer group under the process's root. If
1453 X is the immediate master of the mount, or if there's no dominant peer
1454 group under the same root, then only the "master:X" field is present
1455 and not the "propagate_from:X" field.
1457 For more information on mount propagation see:
1459 Documentation/filesystems/sharedsubtree.txt
1462 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1463 --------------------------------------------------------
1464 These files provide a method to access a tasks comm value. It also allows for
1465 a task to set its own or one of its thread siblings comm value. The comm value
1466 is limited in size compared to the cmdline value, so writing anything longer
1467 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1468 comm value.