1 ------------------------------------------------------------------------------
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
19 0.1 Introduction/Credits
22 1 Collecting System Information
23 1.1 Process-Specific Subdirectories
25 1.3 IDE devices in /proc/ide
26 1.4 Networking info in /proc/net
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 & /proc/<pid>/oom_score_adj - Adjust the oom-killer
38 3.2 /proc/<pid>/oom_score - Display current oom-killer score
39 3.3 /proc/<pid>/io - Display the IO accounting fields
40 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
41 3.5 /proc/<pid>/mountinfo - Information about mounts
42 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
43 3.7 /proc/<pid>/task/<tid>/children - Information about task children
44 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
49 ------------------------------------------------------------------------------
51 ------------------------------------------------------------------------------
53 0.1 Introduction/Credits
54 ------------------------
56 This documentation is part of a soon (or so we hope) to be released book on
57 the SuSE Linux distribution. As there is no complete documentation for the
58 /proc file system and we've used many freely available sources to write these
59 chapters, it seems only fair to give the work back to the Linux community.
60 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
61 afraid it's still far from complete, but we hope it will be useful. As far as
62 we know, it is the first 'all-in-one' document about the /proc file system. It
63 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
64 SPARC, AXP, etc., features, you probably won't find what you are looking for.
65 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
66 additions and patches are welcome and will be added to this document if you
69 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
70 other people for help compiling this documentation. We'd also like to extend a
71 special thank you to Andi Kleen for documentation, which we relied on heavily
72 to create this document, as well as the additional information he provided.
73 Thanks to everybody else who contributed source or docs to the Linux kernel
74 and helped create a great piece of software... :)
76 If you have any comments, corrections or additions, please don't hesitate to
77 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
80 The latest version of this document is available online at
81 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
83 If the above direction does not works for you, you could try the kernel
84 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
85 comandante@zaralinux.com.
90 We don't guarantee the correctness of this document, and if you come to us
91 complaining about how you screwed up your system because of incorrect
92 documentation, we won't feel responsible...
94 ------------------------------------------------------------------------------
95 CHAPTER 1: COLLECTING SYSTEM INFORMATION
96 ------------------------------------------------------------------------------
98 ------------------------------------------------------------------------------
100 ------------------------------------------------------------------------------
101 * Investigating the properties of the pseudo file system /proc and its
102 ability to provide information on the running Linux system
103 * Examining /proc's structure
104 * Uncovering various information about the kernel and the processes running
106 ------------------------------------------------------------------------------
109 The proc file system acts as an interface to internal data structures in the
110 kernel. It can be used to obtain information about the system and to change
111 certain kernel parameters at runtime (sysctl).
113 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
114 show you how you can use /proc/sys to change settings.
116 1.1 Process-Specific Subdirectories
117 -----------------------------------
119 The directory /proc contains (among other things) one subdirectory for each
120 process running on the system, which is named after the process ID (PID).
122 The link self points to the process reading the file system. Each process
123 subdirectory has the entries listed in Table 1-1.
126 Table 1-1: Process specific entries in /proc
127 ..............................................................................
129 clear_refs Clears page referenced bits shown in smaps output
130 cmdline Command line arguments
131 cpu Current and last cpu in which it was executed (2.4)(smp)
132 cwd Link to the current working directory
133 environ Values of environment variables
134 exe Link to the executable of this process
135 fd Directory, which contains all file descriptors
136 maps Memory maps to executables and library files (2.4)
137 mem Memory held by this process
138 root Link to the root directory of this process
140 statm Process memory status information
141 status Process status in human readable form
142 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
144 stack Report full stack trace, enable via CONFIG_STACKTRACE
145 smaps a extension based on maps, showing the memory consumption of
146 each mapping and flags associated with it
147 ..............................................................................
149 For example, to get the status information of a process, all you have to do is
150 read the file /proc/PID/status:
152 >cat /proc/self/status
176 SigPnd: 0000000000000000
177 ShdPnd: 0000000000000000
178 SigBlk: 0000000000000000
179 SigIgn: 0000000000000000
180 SigCgt: 0000000000000000
181 CapInh: 00000000fffffeff
182 CapPrm: 0000000000000000
183 CapEff: 0000000000000000
184 CapBnd: ffffffffffffffff
186 voluntary_ctxt_switches: 0
187 nonvoluntary_ctxt_switches: 1
189 This shows you nearly the same information you would get if you viewed it with
190 the ps command. In fact, ps uses the proc file system to obtain its
191 information. But you get a more detailed view of the process by reading the
192 file /proc/PID/status. It fields are described in table 1-2.
194 The statm file contains more detailed information about the process
195 memory usage. Its seven fields are explained in Table 1-3. The stat file
196 contains details information about the process itself. Its fields are
197 explained in Table 1-4.
199 (for SMP CONFIG users)
200 For making accounting scalable, RSS related information are handled in
201 asynchronous manner and the vaule may not be very precise. To see a precise
202 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
203 It's slow but very precise.
205 Table 1-2: Contents of the status files (as of 2.6.30-rc7)
206 ..............................................................................
208 Name filename of the executable
209 State state (R is running, S is sleeping, D is sleeping
210 in an uninterruptible wait, Z is zombie,
211 T is traced or stopped)
214 PPid process id of the parent process
215 TracerPid PID of process tracing this process (0 if not)
216 Uid Real, effective, saved set, and file system UIDs
217 Gid Real, effective, saved set, and file system GIDs
218 FDSize number of file descriptor slots currently allocated
219 Groups supplementary group list
220 VmPeak peak virtual memory size
221 VmSize total program size
222 VmLck locked memory size
223 VmHWM peak resident set size ("high water mark")
224 VmRSS size of memory portions
225 VmData size of data, stack, and text segments
226 VmStk size of data, stack, and text segments
227 VmExe size of text segment
228 VmLib size of shared library code
229 VmPTE size of page table entries
230 VmSwap size of swap usage (the number of referred swapents)
231 Threads number of threads
232 SigQ number of signals queued/max. number for queue
233 SigPnd bitmap of pending signals for the thread
234 ShdPnd bitmap of shared pending signals for the process
235 SigBlk bitmap of blocked signals
236 SigIgn bitmap of ignored signals
237 SigCgt bitmap of catched signals
238 CapInh bitmap of inheritable capabilities
239 CapPrm bitmap of permitted capabilities
240 CapEff bitmap of effective capabilities
241 CapBnd bitmap of capabilities bounding set
242 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
243 Cpus_allowed mask of CPUs on which this process may run
244 Cpus_allowed_list Same as previous, but in "list format"
245 Mems_allowed mask of memory nodes allowed to this process
246 Mems_allowed_list Same as previous, but in "list format"
247 voluntary_ctxt_switches number of voluntary context switches
248 nonvoluntary_ctxt_switches number of non voluntary context switches
249 ..............................................................................
251 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
252 ..............................................................................
254 size total program size (pages) (same as VmSize in status)
255 resident size of memory portions (pages) (same as VmRSS in status)
256 shared number of pages that are shared (i.e. backed by a file)
257 trs number of pages that are 'code' (not including libs; broken,
258 includes data segment)
259 lrs number of pages of library (always 0 on 2.6)
260 drs number of pages of data/stack (including libs; broken,
261 includes library text)
262 dt number of dirty pages (always 0 on 2.6)
263 ..............................................................................
266 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
267 ..............................................................................
270 tcomm filename of the executable
271 state state (R is running, S is sleeping, D is sleeping in an
272 uninterruptible wait, Z is zombie, T is traced or stopped)
273 ppid process id of the parent process
274 pgrp pgrp of the process
276 tty_nr tty the process uses
277 tty_pgrp pgrp of the tty
279 min_flt number of minor faults
280 cmin_flt number of minor faults with child's
281 maj_flt number of major faults
282 cmaj_flt number of major faults with child's
283 utime user mode jiffies
284 stime kernel mode jiffies
285 cutime user mode jiffies with child's
286 cstime kernel mode jiffies with child's
287 priority priority level
289 num_threads number of threads
290 it_real_value (obsolete, always 0)
291 start_time time the process started after system boot
292 vsize virtual memory size
293 rss resident set memory size
294 rsslim current limit in bytes on the rss
295 start_code address above which program text can run
296 end_code address below which program text can run
297 start_stack address of the start of the main process stack
298 esp current value of ESP
299 eip current value of EIP
300 pending bitmap of pending signals
301 blocked bitmap of blocked signals
302 sigign bitmap of ignored signals
303 sigcatch bitmap of catched signals
304 wchan address where process went to sleep
307 exit_signal signal to send to parent thread on exit
308 task_cpu which CPU the task is scheduled on
309 rt_priority realtime priority
310 policy scheduling policy (man sched_setscheduler)
311 blkio_ticks time spent waiting for block IO
312 gtime guest time of the task in jiffies
313 cgtime guest time of the task children in jiffies
314 start_data address above which program data+bss is placed
315 end_data address below which program data+bss is placed
316 start_brk address above which program heap can be expanded with brk()
317 arg_start address above which program command line is placed
318 arg_end address below which program command line is placed
319 env_start address above which program environment is placed
320 env_end address below which program environment is placed
321 exit_code the thread's exit_code in the form reported by the waitpid system call
322 ..............................................................................
324 The /proc/PID/maps file containing the currently mapped memory regions and
325 their access permissions.
329 address perms offset dev inode pathname
331 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
332 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
333 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
334 a7cb1000-a7cb2000 ---p 00000000 00:00 0
335 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
336 a7eb2000-a7eb3000 ---p 00000000 00:00 0
337 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack:1001]
338 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
339 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
340 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
341 a800b000-a800e000 rw-p 00000000 00:00 0
342 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
343 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
344 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
345 a8024000-a8027000 rw-p 00000000 00:00 0
346 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
347 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
348 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
349 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
350 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
352 where "address" is the address space in the process that it occupies, "perms"
353 is a set of permissions:
359 p = private (copy on write)
361 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
362 "inode" is the inode on that device. 0 indicates that no inode is associated
363 with the memory region, as the case would be with BSS (uninitialized data).
364 The "pathname" shows the name associated file for this mapping. If the mapping
365 is not associated with a file:
367 [heap] = the heap of the program
368 [stack] = the stack of the main process
369 [stack:1001] = the stack of the thread with tid 1001
370 [vdso] = the "virtual dynamic shared object",
371 the kernel system call handler
373 or if empty, the mapping is anonymous.
375 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
376 of the individual tasks of a process. In this file you will see a mapping marked
377 as [stack] if that task sees it as a stack. This is a key difference from the
378 content of /proc/PID/maps, where you will see all mappings that are being used
379 as stack by all of those tasks. Hence, for the example above, the task-level
380 map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
382 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
383 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
384 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
385 a7cb1000-a7cb2000 ---p 00000000 00:00 0
386 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
387 a7eb2000-a7eb3000 ---p 00000000 00:00 0
388 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack]
389 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
390 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
391 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
392 a800b000-a800e000 rw-p 00000000 00:00 0
393 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
394 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
395 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
396 a8024000-a8027000 rw-p 00000000 00:00 0
397 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
398 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
399 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
400 aff35000-aff4a000 rw-p 00000000 00:00 0
401 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
403 The /proc/PID/smaps is an extension based on maps, showing the memory
404 consumption for each of the process's mappings. For each of mappings there
405 is a series of lines such as the following:
407 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
421 VmFlags: rd ex mr mw me de
423 the first of these lines shows the same information as is displayed for the
424 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
425 (size), the amount of the mapping that is currently resident in RAM (RSS), the
426 process' proportional share of this mapping (PSS), the number of clean and
427 dirty private pages in the mapping. Note that even a page which is part of a
428 MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used
429 by only one process, is accounted as private and not as shared. "Referenced"
430 indicates the amount of memory currently marked as referenced or accessed.
431 "Anonymous" shows the amount of memory that does not belong to any file. Even
432 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
433 and a page is modified, the file page is replaced by a private anonymous copy.
434 "Swap" shows how much would-be-anonymous memory is also used, but out on
437 "VmFlags" field deserves a separate description. This member represents the kernel
438 flags associated with the particular virtual memory area in two letter encoded
439 manner. The codes are the following:
448 gd - stack segment growns down
450 dw - disabled write to the mapped file
451 lo - pages are locked in memory
452 io - memory mapped I/O area
453 sr - sequential read advise provided
454 rr - random read advise provided
455 dc - do not copy area on fork
456 de - do not expand area on remapping
457 ac - area is accountable
458 nr - swap space is not reserved for the area
459 ht - area uses huge tlb pages
460 nl - non-linear mapping
461 ar - architecture specific flag
462 dd - do not include area into core dump
465 hg - huge page advise flag
466 nh - no-huge page advise flag
467 mg - mergable advise flag
469 Note that there is no guarantee that every flag and associated mnemonic will
470 be present in all further kernel releases. Things get changed, the flags may
471 be vanished or the reverse -- new added.
473 This file is only present if the CONFIG_MMU kernel configuration option is
476 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
477 bits on both physical and virtual pages associated with a process, and the
478 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
479 To clear the bits for all the pages associated with the process
480 > echo 1 > /proc/PID/clear_refs
482 To clear the bits for the anonymous pages associated with the process
483 > echo 2 > /proc/PID/clear_refs
485 To clear the bits for the file mapped pages associated with the process
486 > echo 3 > /proc/PID/clear_refs
488 To clear the soft-dirty bit
489 > echo 4 > /proc/PID/clear_refs
491 Any other value written to /proc/PID/clear_refs will have no effect.
493 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
494 using /proc/kpageflags and number of times a page is mapped using
495 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
500 Similar to the process entries, the kernel data files give information about
501 the running kernel. The files used to obtain this information are contained in
502 /proc and are listed in Table 1-5. Not all of these will be present in your
503 system. It depends on the kernel configuration and the loaded modules, which
504 files are there, and which are missing.
506 Table 1-5: Kernel info in /proc
507 ..............................................................................
509 apm Advanced power management info
510 buddyinfo Kernel memory allocator information (see text) (2.5)
511 bus Directory containing bus specific information
512 cmdline Kernel command line
513 cpuinfo Info about the CPU
514 devices Available devices (block and character)
515 dma Used DMS channels
516 filesystems Supported filesystems
517 driver Various drivers grouped here, currently rtc (2.4)
518 execdomains Execdomains, related to security (2.4)
519 fb Frame Buffer devices (2.4)
520 fs File system parameters, currently nfs/exports (2.4)
521 ide Directory containing info about the IDE subsystem
522 interrupts Interrupt usage
523 iomem Memory map (2.4)
524 ioports I/O port usage
525 irq Masks for irq to cpu affinity (2.4)(smp?)
526 isapnp ISA PnP (Plug&Play) Info (2.4)
527 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
529 ksyms Kernel symbol table
530 loadavg Load average of last 1, 5 & 15 minutes
534 modules List of loaded modules
535 mounts Mounted filesystems
536 net Networking info (see text)
537 pagetypeinfo Additional page allocator information (see text) (2.5)
538 partitions Table of partitions known to the system
539 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
540 decoupled by lspci (2.4)
542 scsi SCSI info (see text)
543 slabinfo Slab pool info
544 softirqs softirq usage
545 stat Overall statistics
546 swaps Swap space utilization
548 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
549 tty Info of tty drivers
551 version Kernel version
552 video bttv info of video resources (2.4)
553 vmallocinfo Show vmalloced areas
554 ..............................................................................
556 You can, for example, check which interrupts are currently in use and what
557 they are used for by looking in the file /proc/interrupts:
559 > cat /proc/interrupts
561 0: 8728810 XT-PIC timer
562 1: 895 XT-PIC keyboard
564 3: 531695 XT-PIC aha152x
565 4: 2014133 XT-PIC serial
566 5: 44401 XT-PIC pcnet_cs
569 12: 182918 XT-PIC PS/2 Mouse
571 14: 1232265 XT-PIC ide0
575 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
576 output of a SMP machine):
578 > cat /proc/interrupts
581 0: 1243498 1214548 IO-APIC-edge timer
582 1: 8949 8958 IO-APIC-edge keyboard
583 2: 0 0 XT-PIC cascade
584 5: 11286 10161 IO-APIC-edge soundblaster
585 8: 1 0 IO-APIC-edge rtc
586 9: 27422 27407 IO-APIC-edge 3c503
587 12: 113645 113873 IO-APIC-edge PS/2 Mouse
589 14: 22491 24012 IO-APIC-edge ide0
590 15: 2183 2415 IO-APIC-edge ide1
591 17: 30564 30414 IO-APIC-level eth0
592 18: 177 164 IO-APIC-level bttv
597 NMI is incremented in this case because every timer interrupt generates a NMI
598 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
600 LOC is the local interrupt counter of the internal APIC of every CPU.
602 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
603 connects the CPUs in a SMP system. This means that an error has been detected,
604 the IO-APIC automatically retry the transmission, so it should not be a big
605 problem, but you should read the SMP-FAQ.
607 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
608 /proc/interrupts to display every IRQ vector in use by the system, not
609 just those considered 'most important'. The new vectors are:
611 THR -- interrupt raised when a machine check threshold counter
612 (typically counting ECC corrected errors of memory or cache) exceeds
613 a configurable threshold. Only available on some systems.
615 TRM -- a thermal event interrupt occurs when a temperature threshold
616 has been exceeded for the CPU. This interrupt may also be generated
617 when the temperature drops back to normal.
619 SPU -- a spurious interrupt is some interrupt that was raised then lowered
620 by some IO device before it could be fully processed by the APIC. Hence
621 the APIC sees the interrupt but does not know what device it came from.
622 For this case the APIC will generate the interrupt with a IRQ vector
623 of 0xff. This might also be generated by chipset bugs.
625 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
626 sent from one CPU to another per the needs of the OS. Typically,
627 their statistics are used by kernel developers and interested users to
628 determine the occurrence of interrupts of the given type.
630 The above IRQ vectors are displayed only when relevant. For example,
631 the threshold vector does not exist on x86_64 platforms. Others are
632 suppressed when the system is a uniprocessor. As of this writing, only
633 i386 and x86_64 platforms support the new IRQ vector displays.
635 Of some interest is the introduction of the /proc/irq directory to 2.4.
636 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
637 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
638 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
643 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
644 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
648 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
649 IRQ, you can set it by doing:
651 > echo 1 > /proc/irq/10/smp_affinity
653 This means that only the first CPU will handle the IRQ, but you can also echo
654 5 which means that only the first and fourth CPU can handle the IRQ.
656 The contents of each smp_affinity file is the same by default:
658 > cat /proc/irq/0/smp_affinity
661 There is an alternate interface, smp_affinity_list which allows specifying
662 a cpu range instead of a bitmask:
664 > cat /proc/irq/0/smp_affinity_list
667 The default_smp_affinity mask applies to all non-active IRQs, which are the
668 IRQs which have not yet been allocated/activated, and hence which lack a
669 /proc/irq/[0-9]* directory.
671 The node file on an SMP system shows the node to which the device using the IRQ
672 reports itself as being attached. This hardware locality information does not
673 include information about any possible driver locality preference.
675 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
676 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
678 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
679 between all the CPUs which are allowed to handle it. As usual the kernel has
680 more info than you and does a better job than you, so the defaults are the
681 best choice for almost everyone. [Note this applies only to those IO-APIC's
682 that support "Round Robin" interrupt distribution.]
684 There are three more important subdirectories in /proc: net, scsi, and sys.
685 The general rule is that the contents, or even the existence of these
686 directories, depend on your kernel configuration. If SCSI is not enabled, the
687 directory scsi may not exist. The same is true with the net, which is there
688 only when networking support is present in the running kernel.
690 The slabinfo file gives information about memory usage at the slab level.
691 Linux uses slab pools for memory management above page level in version 2.2.
692 Commonly used objects have their own slab pool (such as network buffers,
693 directory cache, and so on).
695 ..............................................................................
697 > cat /proc/buddyinfo
699 Node 0, zone DMA 0 4 5 4 4 3 ...
700 Node 0, zone Normal 1 0 0 1 101 8 ...
701 Node 0, zone HighMem 2 0 0 1 1 0 ...
703 External fragmentation is a problem under some workloads, and buddyinfo is a
704 useful tool for helping diagnose these problems. Buddyinfo will give you a
705 clue as to how big an area you can safely allocate, or why a previous
708 Each column represents the number of pages of a certain order which are
709 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
710 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
711 available in ZONE_NORMAL, etc...
713 More information relevant to external fragmentation can be found in
716 > cat /proc/pagetypeinfo
720 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
721 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
722 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
723 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
724 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
725 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
726 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
727 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
728 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
729 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
730 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
732 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
733 Node 0, zone DMA 2 0 5 1 0
734 Node 0, zone DMA32 41 6 967 2 0
736 Fragmentation avoidance in the kernel works by grouping pages of different
737 migrate types into the same contiguous regions of memory called page blocks.
738 A page block is typically the size of the default hugepage size e.g. 2MB on
739 X86-64. By keeping pages grouped based on their ability to move, the kernel
740 can reclaim pages within a page block to satisfy a high-order allocation.
742 The pagetypinfo begins with information on the size of a page block. It
743 then gives the same type of information as buddyinfo except broken down
744 by migrate-type and finishes with details on how many page blocks of each
747 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
748 from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
749 make an estimate of the likely number of huge pages that can be allocated
750 at a given point in time. All the "Movable" blocks should be allocatable
751 unless memory has been mlock()'d. Some of the Reclaimable blocks should
752 also be allocatable although a lot of filesystem metadata may have to be
753 reclaimed to achieve this.
755 ..............................................................................
759 Provides information about distribution and utilization of memory. This
760 varies by architecture and compile options. The following is from a
761 16GB PIII, which has highmem enabled. You may not have all of these fields.
765 The "Locked" indicates whether the mapping is locked in memory or not.
768 MemTotal: 16344972 kB
775 HighTotal: 15597528 kB
776 HighFree: 13629632 kB
786 SReclaimable: 159856 kB
787 SUnreclaim: 124508 kB
792 CommitLimit: 7669796 kB
793 Committed_AS: 100056 kB
794 VmallocTotal: 112216 kB
796 VmallocChunk: 111088 kB
797 AnonHugePages: 49152 kB
799 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
800 bits and the kernel binary code)
801 MemFree: The sum of LowFree+HighFree
802 Buffers: Relatively temporary storage for raw disk blocks
803 shouldn't get tremendously large (20MB or so)
804 Cached: in-memory cache for files read from the disk (the
805 pagecache). Doesn't include SwapCached
806 SwapCached: Memory that once was swapped out, is swapped back in but
807 still also is in the swapfile (if memory is needed it
808 doesn't need to be swapped out AGAIN because it is already
809 in the swapfile. This saves I/O)
810 Active: Memory that has been used more recently and usually not
811 reclaimed unless absolutely necessary.
812 Inactive: Memory which has been less recently used. It is more
813 eligible to be reclaimed for other purposes
815 HighFree: Highmem is all memory above ~860MB of physical memory
816 Highmem areas are for use by userspace programs, or
817 for the pagecache. The kernel must use tricks to access
818 this memory, making it slower to access than lowmem.
820 LowFree: Lowmem is memory which can be used for everything that
821 highmem can be used for, but it is also available for the
822 kernel's use for its own data structures. Among many
823 other things, it is where everything from the Slab is
824 allocated. Bad things happen when you're out of lowmem.
825 SwapTotal: total amount of swap space available
826 SwapFree: Memory which has been evicted from RAM, and is temporarily
828 Dirty: Memory which is waiting to get written back to the disk
829 Writeback: Memory which is actively being written back to the disk
830 AnonPages: Non-file backed pages mapped into userspace page tables
831 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
832 Mapped: files which have been mmaped, such as libraries
833 Slab: in-kernel data structures cache
834 SReclaimable: Part of Slab, that might be reclaimed, such as caches
835 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
836 PageTables: amount of memory dedicated to the lowest level of page
838 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
840 Bounce: Memory used for block device "bounce buffers"
841 WritebackTmp: Memory used by FUSE for temporary writeback buffers
842 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
843 this is the total amount of memory currently available to
844 be allocated on the system. This limit is only adhered to
845 if strict overcommit accounting is enabled (mode 2 in
846 'vm.overcommit_memory').
847 The CommitLimit is calculated with the following formula:
848 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
849 For example, on a system with 1G of physical RAM and 7G
850 of swap with a `vm.overcommit_ratio` of 30 it would
851 yield a CommitLimit of 7.3G.
852 For more details, see the memory overcommit documentation
853 in vm/overcommit-accounting.
854 Committed_AS: The amount of memory presently allocated on the system.
855 The committed memory is a sum of all of the memory which
856 has been allocated by processes, even if it has not been
857 "used" by them as of yet. A process which malloc()'s 1G
858 of memory, but only touches 300M of it will show up as
859 using 1G. This 1G is memory which has been "committed" to
860 by the VM and can be used at any time by the allocating
861 application. With strict overcommit enabled on the system
862 (mode 2 in 'vm.overcommit_memory'),allocations which would
863 exceed the CommitLimit (detailed above) will not be permitted.
864 This is useful if one needs to guarantee that processes will
865 not fail due to lack of memory once that memory has been
866 successfully allocated.
867 VmallocTotal: total size of vmalloc memory area
868 VmallocUsed: amount of vmalloc area which is used
869 VmallocChunk: largest contiguous block of vmalloc area which is free
871 ..............................................................................
875 Provides information about vmalloced/vmaped areas. One line per area,
876 containing the virtual address range of the area, size in bytes,
877 caller information of the creator, and optional information depending
878 on the kind of area :
880 pages=nr number of pages
881 phys=addr if a physical address was specified
882 ioremap I/O mapping (ioremap() and friends)
883 vmalloc vmalloc() area
886 vpages buffer for pages pointers was vmalloced (huge area)
887 N<node>=nr (Only on NUMA kernels)
888 Number of pages allocated on memory node <node>
890 > cat /proc/vmallocinfo
891 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
892 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
893 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
894 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
895 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
896 phys=7fee8000 ioremap
897 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
898 phys=7fee7000 ioremap
899 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
900 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
901 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
902 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
904 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
905 /0x130 [x_tables] pages=4 vmalloc N0=4
906 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
907 pages=14 vmalloc N2=14
908 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
910 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
912 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
913 pages=10 vmalloc N0=10
915 ..............................................................................
919 Provides counts of softirq handlers serviced since boot time, for each cpu.
924 TIMER: 27166 27120 27097 27034
929 SCHED: 27035 26983 26971 26746
931 RCU: 1678 1769 2178 2250
934 1.3 IDE devices in /proc/ide
935 ----------------------------
937 The subdirectory /proc/ide contains information about all IDE devices of which
938 the kernel is aware. There is one subdirectory for each IDE controller, the
939 file drivers and a link for each IDE device, pointing to the device directory
940 in the controller specific subtree.
942 The file drivers contains general information about the drivers used for the
945 > cat /proc/ide/drivers
946 ide-cdrom version 4.53
947 ide-disk version 1.08
949 More detailed information can be found in the controller specific
950 subdirectories. These are named ide0, ide1 and so on. Each of these
951 directories contains the files shown in table 1-6.
954 Table 1-6: IDE controller info in /proc/ide/ide?
955 ..............................................................................
957 channel IDE channel (0 or 1)
958 config Configuration (only for PCI/IDE bridge)
960 model Type/Chipset of IDE controller
961 ..............................................................................
963 Each device connected to a controller has a separate subdirectory in the
964 controllers directory. The files listed in table 1-7 are contained in these
968 Table 1-7: IDE device information
969 ..............................................................................
972 capacity Capacity of the medium (in 512Byte blocks)
973 driver driver and version
974 geometry physical and logical geometry
975 identify device identify block
977 model device identifier
978 settings device setup
979 smart_thresholds IDE disk management thresholds
980 smart_values IDE disk management values
981 ..............................................................................
983 The most interesting file is settings. This file contains a nice overview of
984 the drive parameters:
986 # cat /proc/ide/ide0/hda/settings
987 name value min max mode
988 ---- ----- --- --- ----
989 bios_cyl 526 0 65535 rw
990 bios_head 255 0 255 rw
992 breada_readahead 4 0 127 rw
994 file_readahead 72 0 2097151 rw
996 keepsettings 0 0 1 rw
997 max_kb_per_request 122 1 127 rw
1001 pio_mode write-only 0 255 w
1007 1.4 Networking info in /proc/net
1008 --------------------------------
1010 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1011 additional values you get for IP version 6 if you configure the kernel to
1012 support this. Table 1-9 lists the files and their meaning.
1015 Table 1-8: IPv6 info in /proc/net
1016 ..............................................................................
1018 udp6 UDP sockets (IPv6)
1019 tcp6 TCP sockets (IPv6)
1020 raw6 Raw device statistics (IPv6)
1021 igmp6 IP multicast addresses, which this host joined (IPv6)
1022 if_inet6 List of IPv6 interface addresses
1023 ipv6_route Kernel routing table for IPv6
1024 rt6_stats Global IPv6 routing tables statistics
1025 sockstat6 Socket statistics (IPv6)
1026 snmp6 Snmp data (IPv6)
1027 ..............................................................................
1030 Table 1-9: Network info in /proc/net
1031 ..............................................................................
1033 arp Kernel ARP table
1034 dev network devices with statistics
1035 dev_mcast the Layer2 multicast groups a device is listening too
1036 (interface index, label, number of references, number of bound
1038 dev_stat network device status
1039 ip_fwchains Firewall chain linkage
1040 ip_fwnames Firewall chain names
1041 ip_masq Directory containing the masquerading tables
1042 ip_masquerade Major masquerading table
1043 netstat Network statistics
1044 raw raw device statistics
1045 route Kernel routing table
1046 rpc Directory containing rpc info
1047 rt_cache Routing cache
1049 sockstat Socket statistics
1052 unix UNIX domain sockets
1053 wireless Wireless interface data (Wavelan etc)
1054 igmp IP multicast addresses, which this host joined
1055 psched Global packet scheduler parameters.
1056 netlink List of PF_NETLINK sockets
1057 ip_mr_vifs List of multicast virtual interfaces
1058 ip_mr_cache List of multicast routing cache
1059 ..............................................................................
1061 You can use this information to see which network devices are available in
1062 your system and how much traffic was routed over those devices:
1065 Inter-|Receive |[...
1066 face |bytes packets errs drop fifo frame compressed multicast|[...
1067 lo: 908188 5596 0 0 0 0 0 0 [...
1068 ppp0:15475140 20721 410 0 0 410 0 0 [...
1069 eth0: 614530 7085 0 0 0 0 0 1 [...
1072 ...] bytes packets errs drop fifo colls carrier compressed
1073 ...] 908188 5596 0 0 0 0 0 0
1074 ...] 1375103 17405 0 0 0 0 0 0
1075 ...] 1703981 5535 0 0 0 3 0 0
1077 In addition, each Channel Bond interface has its own directory. For
1078 example, the bond0 device will have a directory called /proc/net/bond0/.
1079 It will contain information that is specific to that bond, such as the
1080 current slaves of the bond, the link status of the slaves, and how
1081 many times the slaves link has failed.
1086 If you have a SCSI host adapter in your system, you'll find a subdirectory
1087 named after the driver for this adapter in /proc/scsi. You'll also see a list
1088 of all recognized SCSI devices in /proc/scsi:
1090 >cat /proc/scsi/scsi
1092 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1093 Vendor: IBM Model: DGHS09U Rev: 03E0
1094 Type: Direct-Access ANSI SCSI revision: 03
1095 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1096 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1097 Type: CD-ROM ANSI SCSI revision: 02
1100 The directory named after the driver has one file for each adapter found in
1101 the system. These files contain information about the controller, including
1102 the used IRQ and the IO address range. The amount of information shown is
1103 dependent on the adapter you use. The example shows the output for an Adaptec
1104 AHA-2940 SCSI adapter:
1106 > cat /proc/scsi/aic7xxx/0
1108 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1110 TCQ Enabled By Default : Disabled
1111 AIC7XXX_PROC_STATS : Disabled
1112 AIC7XXX_RESET_DELAY : 5
1113 Adapter Configuration:
1114 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1115 Ultra Wide Controller
1116 PCI MMAPed I/O Base: 0xeb001000
1117 Adapter SEEPROM Config: SEEPROM found and used.
1118 Adaptec SCSI BIOS: Enabled
1120 SCBs: Active 0, Max Active 2,
1121 Allocated 15, HW 16, Page 255
1123 BIOS Control Word: 0x18b6
1124 Adapter Control Word: 0x005b
1125 Extended Translation: Enabled
1126 Disconnect Enable Flags: 0xffff
1127 Ultra Enable Flags: 0x0001
1128 Tag Queue Enable Flags: 0x0000
1129 Ordered Queue Tag Flags: 0x0000
1130 Default Tag Queue Depth: 8
1131 Tagged Queue By Device array for aic7xxx host instance 0:
1132 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1133 Actual queue depth per device for aic7xxx host instance 0:
1134 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1137 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1138 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1139 Total transfers 160151 (74577 reads and 85574 writes)
1141 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1142 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1143 Total transfers 0 (0 reads and 0 writes)
1146 1.6 Parallel port info in /proc/parport
1147 ---------------------------------------
1149 The directory /proc/parport contains information about the parallel ports of
1150 your system. It has one subdirectory for each port, named after the port
1153 These directories contain the four files shown in Table 1-10.
1156 Table 1-10: Files in /proc/parport
1157 ..............................................................................
1159 autoprobe Any IEEE-1284 device ID information that has been acquired.
1160 devices list of the device drivers using that port. A + will appear by the
1161 name of the device currently using the port (it might not appear
1163 hardware Parallel port's base address, IRQ line and DMA channel.
1164 irq IRQ that parport is using for that port. This is in a separate
1165 file to allow you to alter it by writing a new value in (IRQ
1167 ..............................................................................
1169 1.7 TTY info in /proc/tty
1170 -------------------------
1172 Information about the available and actually used tty's can be found in the
1173 directory /proc/tty.You'll find entries for drivers and line disciplines in
1174 this directory, as shown in Table 1-11.
1177 Table 1-11: Files in /proc/tty
1178 ..............................................................................
1180 drivers list of drivers and their usage
1181 ldiscs registered line disciplines
1182 driver/serial usage statistic and status of single tty lines
1183 ..............................................................................
1185 To see which tty's are currently in use, you can simply look into the file
1188 > cat /proc/tty/drivers
1189 pty_slave /dev/pts 136 0-255 pty:slave
1190 pty_master /dev/ptm 128 0-255 pty:master
1191 pty_slave /dev/ttyp 3 0-255 pty:slave
1192 pty_master /dev/pty 2 0-255 pty:master
1193 serial /dev/cua 5 64-67 serial:callout
1194 serial /dev/ttyS 4 64-67 serial
1195 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1196 /dev/ptmx /dev/ptmx 5 2 system
1197 /dev/console /dev/console 5 1 system:console
1198 /dev/tty /dev/tty 5 0 system:/dev/tty
1199 unknown /dev/tty 4 1-63 console
1202 1.8 Miscellaneous kernel statistics in /proc/stat
1203 -------------------------------------------------
1205 Various pieces of information about kernel activity are available in the
1206 /proc/stat file. All of the numbers reported in this file are aggregates
1207 since the system first booted. For a quick look, simply cat the file:
1210 cpu 2255 34 2290 22625563 6290 127 456 0 0
1211 cpu0 1132 34 1441 11311718 3675 127 438 0 0
1212 cpu1 1123 0 849 11313845 2614 0 18 0 0
1213 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1219 softirq 183433 0 21755 12 39 1137 231 21459 2263
1221 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1222 lines. These numbers identify the amount of time the CPU has spent performing
1223 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1224 second). The meanings of the columns are as follows, from left to right:
1226 - user: normal processes executing in user mode
1227 - nice: niced processes executing in user mode
1228 - system: processes executing in kernel mode
1229 - idle: twiddling thumbs
1230 - iowait: waiting for I/O to complete
1231 - irq: servicing interrupts
1232 - softirq: servicing softirqs
1233 - steal: involuntary wait
1234 - guest: running a normal guest
1235 - guest_nice: running a niced guest
1237 The "intr" line gives counts of interrupts serviced since boot time, for each
1238 of the possible system interrupts. The first column is the total of all
1239 interrupts serviced; each subsequent column is the total for that particular
1242 The "ctxt" line gives the total number of context switches across all CPUs.
1244 The "btime" line gives the time at which the system booted, in seconds since
1247 The "processes" line gives the number of processes and threads created, which
1248 includes (but is not limited to) those created by calls to the fork() and
1249 clone() system calls.
1251 The "procs_running" line gives the total number of threads that are
1252 running or ready to run (i.e., the total number of runnable threads).
1254 The "procs_blocked" line gives the number of processes currently blocked,
1255 waiting for I/O to complete.
1257 The "softirq" line gives counts of softirqs serviced since boot time, for each
1258 of the possible system softirqs. The first column is the total of all
1259 softirqs serviced; each subsequent column is the total for that particular
1263 1.9 Ext4 file system parameters
1264 ------------------------------
1266 Information about mounted ext4 file systems can be found in
1267 /proc/fs/ext4. Each mounted filesystem will have a directory in
1268 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1269 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1270 in Table 1-12, below.
1272 Table 1-12: Files in /proc/fs/ext4/<devname>
1273 ..............................................................................
1275 mb_groups details of multiblock allocator buddy cache of free blocks
1276 ..............................................................................
1280 Shows registered system console lines.
1282 To see which character device lines are currently used for the system console
1283 /dev/console, you may simply look into the file /proc/consoles:
1285 > cat /proc/consoles
1291 device name of the device
1292 operations R = can do read operations
1293 W = can do write operations
1295 flags E = it is enabled
1296 C = it is preferred console
1297 B = it is primary boot console
1298 p = it is used for printk buffer
1299 b = it is not a TTY but a Braille device
1300 a = it is safe to use when cpu is offline
1301 major:minor major and minor number of the device separated by a colon
1303 ------------------------------------------------------------------------------
1305 ------------------------------------------------------------------------------
1306 The /proc file system serves information about the running system. It not only
1307 allows access to process data but also allows you to request the kernel status
1308 by reading files in the hierarchy.
1310 The directory structure of /proc reflects the types of information and makes
1311 it easy, if not obvious, where to look for specific data.
1312 ------------------------------------------------------------------------------
1314 ------------------------------------------------------------------------------
1315 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1316 ------------------------------------------------------------------------------
1318 ------------------------------------------------------------------------------
1320 ------------------------------------------------------------------------------
1321 * Modifying kernel parameters by writing into files found in /proc/sys
1322 * Exploring the files which modify certain parameters
1323 * Review of the /proc/sys file tree
1324 ------------------------------------------------------------------------------
1327 A very interesting part of /proc is the directory /proc/sys. This is not only
1328 a source of information, it also allows you to change parameters within the
1329 kernel. Be very careful when attempting this. You can optimize your system,
1330 but you can also cause it to crash. Never alter kernel parameters on a
1331 production system. Set up a development machine and test to make sure that
1332 everything works the way you want it to. You may have no alternative but to
1333 reboot the machine once an error has been made.
1335 To change a value, simply echo the new value into the file. An example is
1336 given below in the section on the file system data. You need to be root to do
1337 this. You can create your own boot script to perform this every time your
1340 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1341 general things in the operation of the Linux kernel. Since some of the files
1342 can inadvertently disrupt your system, it is advisable to read both
1343 documentation and source before actually making adjustments. In any case, be
1344 very careful when writing to any of these files. The entries in /proc may
1345 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1346 review the kernel documentation in the directory /usr/src/linux/Documentation.
1347 This chapter is heavily based on the documentation included in the pre 2.2
1348 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1350 Please see: Documentation/sysctl/ directory for descriptions of these
1353 ------------------------------------------------------------------------------
1355 ------------------------------------------------------------------------------
1356 Certain aspects of kernel behavior can be modified at runtime, without the
1357 need to recompile the kernel, or even to reboot the system. The files in the
1358 /proc/sys tree can not only be read, but also modified. You can use the echo
1359 command to write value into these files, thereby changing the default settings
1361 ------------------------------------------------------------------------------
1363 ------------------------------------------------------------------------------
1364 CHAPTER 3: PER-PROCESS PARAMETERS
1365 ------------------------------------------------------------------------------
1367 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1368 --------------------------------------------------------------------------------
1370 These file can be used to adjust the badness heuristic used to select which
1371 process gets killed in out of memory conditions.
1373 The badness heuristic assigns a value to each candidate task ranging from 0
1374 (never kill) to 1000 (always kill) to determine which process is targeted. The
1375 units are roughly a proportion along that range of allowed memory the process
1376 may allocate from based on an estimation of its current memory and swap use.
1377 For example, if a task is using all allowed memory, its badness score will be
1378 1000. If it is using half of its allowed memory, its score will be 500.
1380 There is an additional factor included in the badness score: root
1381 processes are given 3% extra memory over other tasks.
1383 The amount of "allowed" memory depends on the context in which the oom killer
1384 was called. If it is due to the memory assigned to the allocating task's cpuset
1385 being exhausted, the allowed memory represents the set of mems assigned to that
1386 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1387 memory represents the set of mempolicy nodes. If it is due to a memory
1388 limit (or swap limit) being reached, the allowed memory is that configured
1389 limit. Finally, if it is due to the entire system being out of memory, the
1390 allowed memory represents all allocatable resources.
1392 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1393 is used to determine which task to kill. Acceptable values range from -1000
1394 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1395 polarize the preference for oom killing either by always preferring a certain
1396 task or completely disabling it. The lowest possible value, -1000, is
1397 equivalent to disabling oom killing entirely for that task since it will always
1398 report a badness score of 0.
1400 Consequently, it is very simple for userspace to define the amount of memory to
1401 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1402 example, is roughly equivalent to allowing the remainder of tasks sharing the
1403 same system, cpuset, mempolicy, or memory controller resources to use at least
1404 50% more memory. A value of -500, on the other hand, would be roughly
1405 equivalent to discounting 50% of the task's allowed memory from being considered
1406 as scoring against the task.
1408 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1409 be used to tune the badness score. Its acceptable values range from -16
1410 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1411 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1412 scaled linearly with /proc/<pid>/oom_score_adj.
1414 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1415 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1416 requires CAP_SYS_RESOURCE.
1418 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1419 generation children with separate address spaces instead, if possible. This
1420 avoids servers and important system daemons from being killed and loses the
1421 minimal amount of work.
1424 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1425 -------------------------------------------------------------
1427 This file can be used to check the current score used by the oom-killer is for
1428 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1429 process should be killed in an out-of-memory situation.
1432 3.3 /proc/<pid>/io - Display the IO accounting fields
1433 -------------------------------------------------------
1435 This file contains IO statistics for each running process
1440 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1443 test:/tmp # cat /proc/3828/io
1449 write_bytes: 323932160
1450 cancelled_write_bytes: 0
1459 I/O counter: chars read
1460 The number of bytes which this task has caused to be read from storage. This
1461 is simply the sum of bytes which this process passed to read() and pread().
1462 It includes things like tty IO and it is unaffected by whether or not actual
1463 physical disk IO was required (the read might have been satisfied from
1470 I/O counter: chars written
1471 The number of bytes which this task has caused, or shall cause to be written
1472 to disk. Similar caveats apply here as with rchar.
1478 I/O counter: read syscalls
1479 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1486 I/O counter: write syscalls
1487 Attempt to count the number of write I/O operations, i.e. syscalls like
1488 write() and pwrite().
1494 I/O counter: bytes read
1495 Attempt to count the number of bytes which this process really did cause to
1496 be fetched from the storage layer. Done at the submit_bio() level, so it is
1497 accurate for block-backed filesystems. <please add status regarding NFS and
1498 CIFS at a later time>
1504 I/O counter: bytes written
1505 Attempt to count the number of bytes which this process caused to be sent to
1506 the storage layer. This is done at page-dirtying time.
1509 cancelled_write_bytes
1510 ---------------------
1512 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1513 then deletes the file, it will in fact perform no writeout. But it will have
1514 been accounted as having caused 1MB of write.
1515 In other words: The number of bytes which this process caused to not happen,
1516 by truncating pagecache. A task can cause "negative" IO too. If this task
1517 truncates some dirty pagecache, some IO which another task has been accounted
1518 for (in its write_bytes) will not be happening. We _could_ just subtract that
1519 from the truncating task's write_bytes, but there is information loss in doing
1526 At its current implementation state, this is a bit racy on 32-bit machines: if
1527 process A reads process B's /proc/pid/io while process B is updating one of
1528 those 64-bit counters, process A could see an intermediate result.
1531 More information about this can be found within the taskstats documentation in
1532 Documentation/accounting.
1534 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1535 ---------------------------------------------------------------
1536 When a process is dumped, all anonymous memory is written to a core file as
1537 long as the size of the core file isn't limited. But sometimes we don't want
1538 to dump some memory segments, for example, huge shared memory. Conversely,
1539 sometimes we want to save file-backed memory segments into a core file, not
1540 only the individual files.
1542 /proc/<pid>/coredump_filter allows you to customize which memory segments
1543 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1544 of memory types. If a bit of the bitmask is set, memory segments of the
1545 corresponding memory type are dumped, otherwise they are not dumped.
1547 The following 7 memory types are supported:
1548 - (bit 0) anonymous private memory
1549 - (bit 1) anonymous shared memory
1550 - (bit 2) file-backed private memory
1551 - (bit 3) file-backed shared memory
1552 - (bit 4) ELF header pages in file-backed private memory areas (it is
1553 effective only if the bit 2 is cleared)
1554 - (bit 5) hugetlb private memory
1555 - (bit 6) hugetlb shared memory
1557 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1558 are always dumped regardless of the bitmask status.
1560 Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1561 effected by bit 5-6.
1563 Default value of coredump_filter is 0x23; this means all anonymous memory
1564 segments and hugetlb private memory are dumped.
1566 If you don't want to dump all shared memory segments attached to pid 1234,
1567 write 0x21 to the process's proc file.
1569 $ echo 0x21 > /proc/1234/coredump_filter
1571 When a new process is created, the process inherits the bitmask status from its
1572 parent. It is useful to set up coredump_filter before the program runs.
1575 $ echo 0x7 > /proc/self/coredump_filter
1578 3.5 /proc/<pid>/mountinfo - Information about mounts
1579 --------------------------------------------------------
1581 This file contains lines of the form:
1583 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1584 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1586 (1) mount ID: unique identifier of the mount (may be reused after umount)
1587 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1588 (3) major:minor: value of st_dev for files on filesystem
1589 (4) root: root of the mount within the filesystem
1590 (5) mount point: mount point relative to the process's root
1591 (6) mount options: per mount options
1592 (7) optional fields: zero or more fields of the form "tag[:value]"
1593 (8) separator: marks the end of the optional fields
1594 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1595 (10) mount source: filesystem specific information or "none"
1596 (11) super options: per super block options
1598 Parsers should ignore all unrecognised optional fields. Currently the
1599 possible optional fields are:
1601 shared:X mount is shared in peer group X
1602 master:X mount is slave to peer group X
1603 propagate_from:X mount is slave and receives propagation from peer group X (*)
1604 unbindable mount is unbindable
1606 (*) X is the closest dominant peer group under the process's root. If
1607 X is the immediate master of the mount, or if there's no dominant peer
1608 group under the same root, then only the "master:X" field is present
1609 and not the "propagate_from:X" field.
1611 For more information on mount propagation see:
1613 Documentation/filesystems/sharedsubtree.txt
1616 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1617 --------------------------------------------------------
1618 These files provide a method to access a tasks comm value. It also allows for
1619 a task to set its own or one of its thread siblings comm value. The comm value
1620 is limited in size compared to the cmdline value, so writing anything longer
1621 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1625 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1626 -------------------------------------------------------------------------
1627 This file provides a fast way to retrieve first level children pids
1628 of a task pointed by <pid>/<tid> pair. The format is a space separated
1631 Note the "first level" here -- if a child has own children they will
1632 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1633 to obtain the descendants.
1635 Since this interface is intended to be fast and cheap it doesn't
1636 guarantee to provide precise results and some children might be
1637 skipped, especially if they've exited right after we printed their
1638 pids, so one need to either stop or freeze processes being inspected
1639 if precise results are needed.
1642 3.7 /proc/<pid>/fdinfo/<fd> - Information about opened file
1643 ---------------------------------------------------------------
1644 This file provides information associated with an opened file. The regular
1645 files have at least two fields -- 'pos' and 'flags'. The 'pos' represents
1646 the current offset of the opened file in decimal form [see lseek(2) for
1647 details] and 'flags' denotes the octal O_xxx mask the file has been
1648 created with [see open(2) for details].
1655 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1656 pair provide additional information particular to the objects they represent.
1664 where 'eventfd-count' is hex value of a counter.
1670 sigmask: 0000000000000200
1672 where 'sigmask' is hex value of the signal mask associated
1679 tfd: 5 events: 1d data: ffffffffffffffff
1681 where 'tfd' is a target file descriptor number in decimal form,
1682 'events' is events mask being watched and the 'data' is data
1683 associated with a target [see epoll(7) for more details].
1687 For inotify files the format is the following
1691 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1693 where 'wd' is a watch descriptor in decimal form, ie a target file
1694 descriptor number, 'ino' and 'sdev' are inode and device where the
1695 target file resides and the 'mask' is the mask of events, all in hex
1696 form [see inotify(7) for more details].
1698 If the kernel was built with exportfs support, the path to the target
1699 file is encoded as a file handle. The file handle is provided by three
1700 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1703 If the kernel is built without exportfs support the file handle won't be
1706 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1708 For fanotify files the format is
1712 fanotify flags:10 event-flags:0
1713 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1714 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1716 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1717 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1718 flags associated with mark which are tracked separately from events
1719 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1720 mask and 'ignored_mask' is the mask of events which are to be ignored.
1721 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1722 does provide information about flags and mask used in fanotify_mark
1723 call [see fsnotify manpage for details].
1725 While the first three lines are mandatory and always printed, the rest is
1726 optional and may be omitted if no marks created yet.
1729 ------------------------------------------------------------------------------
1731 ------------------------------------------------------------------------------
1734 ---------------------
1736 The following mount options are supported:
1738 hidepid= Set /proc/<pid>/ access mode.
1739 gid= Set the group authorized to learn processes information.
1741 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1744 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1745 own. Sensitive files like cmdline, sched*, status are now protected against
1746 other users. This makes it impossible to learn whether any user runs
1747 specific program (given the program doesn't reveal itself by its behaviour).
1748 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1749 poorly written programs passing sensitive information via program arguments are
1750 now protected against local eavesdroppers.
1752 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1753 users. It doesn't mean that it hides a fact whether a process with a specific
1754 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1755 but it hides process' uid and gid, which may be learned by stat()'ing
1756 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1757 information about running processes, whether some daemon runs with elevated
1758 privileges, whether other user runs some sensitive program, whether other users
1759 run any program at all, etc.
1761 gid= defines a group authorized to learn processes information otherwise
1762 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1763 information about processes information, just add identd to this group.
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