| blob | 6a882c57a7e736d4fc0fa02cc83fd3691847aee5 |
1 .. SPDX-License-Identifier: GPL-2.0
3 ====================
4 The /proc Filesystem
5 ====================
7 ===================== ======================================= ================
8 /proc/sys Terrehon Bowden <terrehon@pacbell.net>, October 7 1999
9 Bodo Bauer <bb@ricochet.net>
10 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
11 move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
12 fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
13 ===================== ======================================= ================
17 .. Table of Contents
19 0 Preface
20 0.1 Introduction/Credits
21 0.2 Legal Stuff
23 1 Collecting System Information
24 1.1 Process-Specific Subdirectories
25 1.2 Kernel data
26 1.3 IDE devices in /proc/ide
27 1.4 Networking info in /proc/net
28 1.5 SCSI info
29 1.6 Parallel port info in /proc/parport
30 1.7 TTY info in /proc/tty
31 1.8 Miscellaneous kernel statistics in /proc/stat
32 1.9 Ext4 file system parameters
34 2 Modifying System Parameters
36 3 Per-Process Parameters
37 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
38 score
39 3.2 /proc/<pid>/oom_score - Display current oom-killer score
40 3.3 /proc/<pid>/io - Display the IO accounting fields
41 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
42 3.5 /proc/<pid>/mountinfo - Information about mounts
43 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
44 3.7 /proc/<pid>/task/<tid>/children - Information about task children
45 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
46 3.9 /proc/<pid>/map_files - Information about memory mapped files
47 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
48 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
49 3.12 /proc/<pid>/arch_status - Task architecture specific information
50 3.13 /proc/<pid>/fd - List of symlinks to open files
52 4 Configuring procfs
53 4.1 Mount options
55 5 Filesystem behavior
57 Preface
58 =======
60 0.1 Introduction/Credits
61 ------------------------
63 This documentation is part of a soon (or so we hope) to be released book on
64 the SuSE Linux distribution. As there is no complete documentation for the
65 /proc file system and we've used many freely available sources to write these
66 chapters, it seems only fair to give the work back to the Linux community.
67 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
68 afraid it's still far from complete, but we hope it will be useful. As far as
69 we know, it is the first 'all-in-one' document about the /proc file system. It
70 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
71 SPARC, AXP, etc., features, you probably won't find what you are looking for.
72 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
73 additions and patches are welcome and will be added to this document if you
74 mail them to Bodo.
76 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
77 other people for help compiling this documentation. We'd also like to extend a
78 special thank you to Andi Kleen for documentation, which we relied on heavily
79 to create this document, as well as the additional information he provided.
80 Thanks to everybody else who contributed source or docs to the Linux kernel
81 and helped create a great piece of software... :)
83 If you have any comments, corrections or additions, please don't hesitate to
84 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
85 document.
87 The latest version of this document is available online at
88 https://www.kernel.org/doc/html/latest/filesystems/proc.html
90 If the above direction does not works for you, you could try the kernel
91 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
92 comandante@zaralinux.com.
94 0.2 Legal Stuff
95 ---------------
97 We don't guarantee the correctness of this document, and if you come to us
98 complaining about how you screwed up your system because of incorrect
99 documentation, we won't feel responsible...
101 Chapter 1: Collecting System Information
102 ========================================
104 In This Chapter
105 ---------------
106 * Investigating the properties of the pseudo file system /proc and its
107 ability to provide information on the running Linux system
108 * Examining /proc's structure
109 * Uncovering various information about the kernel and the processes running
110 on the system
112 ------------------------------------------------------------------------------
114 The proc file system acts as an interface to internal data structures in the
115 kernel. It can be used to obtain information about the system and to change
116 certain kernel parameters at runtime (sysctl).
118 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
119 show you how you can use /proc/sys to change settings.
121 1.1 Process-Specific Subdirectories
122 -----------------------------------
124 The directory /proc contains (among other things) one subdirectory for each
125 process running on the system, which is named after the process ID (PID).
127 The link 'self' points to the process reading the file system. Each process
128 subdirectory has the entries listed in Table 1-1.
130 Note that an open file descriptor to /proc/<pid> or to any of its
131 contained files or subdirectories does not prevent <pid> being reused
132 for some other process in the event that <pid> exits. Operations on
133 open /proc/<pid> file descriptors corresponding to dead processes
134 never act on any new process that the kernel may, through chance, have
135 also assigned the process ID <pid>. Instead, operations on these FDs
136 usually fail with ESRCH.
138 .. table:: Table 1-1: Process specific entries in /proc
140 ============= ===============================================================
141 File Content
142 ============= ===============================================================
143 clear_refs Clears page referenced bits shown in smaps output
144 cmdline Command line arguments
145 cpu Current and last cpu in which it was executed (2.4)(smp)
146 cwd Link to the current working directory
147 environ Values of environment variables
148 exe Link to the executable of this process
149 fd Directory, which contains all file descriptors
150 maps Memory maps to executables and library files (2.4)
151 mem Memory held by this process
152 root Link to the root directory of this process
153 stat Process status
154 statm Process memory status information
155 status Process status in human readable form
156 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
157 symbol the task is blocked in - or "0" if not blocked.
158 pagemap Page table
159 stack Report full stack trace, enable via CONFIG_STACKTRACE
160 smaps An extension based on maps, showing the memory consumption of
161 each mapping and flags associated with it
162 smaps_rollup Accumulated smaps stats for all mappings of the process. This
163 can be derived from smaps, but is faster and more convenient
164 numa_maps An extension based on maps, showing the memory locality and
165 binding policy as well as mem usage (in pages) of each mapping.
166 ============= ===============================================================
168 For example, to get the status information of a process, all you have to do is
169 read the file /proc/PID/status::
171 >cat /proc/self/status
172 Name: cat
173 State: R (running)
174 Tgid: 5452
175 Pid: 5452
176 PPid: 743
177 TracerPid: 0 (2.4)
178 Uid: 501 501 501 501
179 Gid: 100 100 100 100
180 FDSize: 256
181 Groups: 100 14 16
182 Kthread: 0
183 VmPeak: 5004 kB
184 VmSize: 5004 kB
185 VmLck: 0 kB
186 VmHWM: 476 kB
187 VmRSS: 476 kB
188 RssAnon: 352 kB
189 RssFile: 120 kB
190 RssShmem: 4 kB
191 VmData: 156 kB
192 VmStk: 88 kB
193 VmExe: 68 kB
194 VmLib: 1412 kB
195 VmPTE: 20 kb
196 VmSwap: 0 kB
197 HugetlbPages: 0 kB
198 CoreDumping: 0
199 THP_enabled: 1
200 Threads: 1
201 SigQ: 0/28578
202 SigPnd: 0000000000000000
203 ShdPnd: 0000000000000000
204 SigBlk: 0000000000000000
205 SigIgn: 0000000000000000
206 SigCgt: 0000000000000000
207 CapInh: 00000000fffffeff
208 CapPrm: 0000000000000000
209 CapEff: 0000000000000000
210 CapBnd: ffffffffffffffff
211 CapAmb: 0000000000000000
212 NoNewPrivs: 0
213 Seccomp: 0
214 Speculation_Store_Bypass: thread vulnerable
215 SpeculationIndirectBranch: conditional enabled
216 voluntary_ctxt_switches: 0
217 nonvoluntary_ctxt_switches: 1
219 This shows you nearly the same information you would get if you viewed it with
220 the ps command. In fact, ps uses the proc file system to obtain its
221 information. But you get a more detailed view of the process by reading the
222 file /proc/PID/status. It fields are described in table 1-2.
224 The statm file contains more detailed information about the process
225 memory usage. Its seven fields are explained in Table 1-3. The stat file
226 contains detailed information about the process itself. Its fields are
227 explained in Table 1-4.
229 (for SMP CONFIG users)
231 For making accounting scalable, RSS related information are handled in an
232 asynchronous manner and the value may not be very precise. To see a precise
233 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
234 It's slow but very precise.
236 .. table:: Table 1-2: Contents of the status fields (as of 4.19)
238 ========================== ===================================================
239 Field Content
240 ========================== ===================================================
241 Name filename of the executable
242 Umask file mode creation mask
243 State state (R is running, S is sleeping, D is sleeping
244 in an uninterruptible wait, Z is zombie,
245 T is traced or stopped)
246 Tgid thread group ID
247 Ngid NUMA group ID (0 if none)
248 Pid process id
249 PPid process id of the parent process
250 TracerPid PID of process tracing this process (0 if not, or
251 the tracer is outside of the current pid namespace)
252 Uid Real, effective, saved set, and file system UIDs
253 Gid Real, effective, saved set, and file system GIDs
254 FDSize number of file descriptor slots currently allocated
255 Groups supplementary group list
256 NStgid descendant namespace thread group ID hierarchy
257 NSpid descendant namespace process ID hierarchy
258 NSpgid descendant namespace process group ID hierarchy
259 NSsid descendant namespace session ID hierarchy
260 Kthread kernel thread flag, 1 is yes, 0 is no
261 VmPeak peak virtual memory size
262 VmSize total program size
263 VmLck locked memory size
264 VmPin pinned memory size
265 VmHWM peak resident set size ("high water mark")
266 VmRSS size of memory portions. It contains the three
267 following parts
268 (VmRSS = RssAnon + RssFile + RssShmem)
269 RssAnon size of resident anonymous memory
270 RssFile size of resident file mappings
271 RssShmem size of resident shmem memory (includes SysV shm,
272 mapping of tmpfs and shared anonymous mappings)
273 VmData size of private data segments
274 VmStk size of stack segments
275 VmExe size of text segment
276 VmLib size of shared library code
277 VmPTE size of page table entries
278 VmSwap amount of swap used by anonymous private data
279 (shmem swap usage is not included)
280 HugetlbPages size of hugetlb memory portions
281 CoreDumping process's memory is currently being dumped
282 (killing the process may lead to a corrupted core)
283 THP_enabled process is allowed to use THP (returns 0 when
284 PR_SET_THP_DISABLE is set on the process
285 Threads number of threads
286 SigQ number of signals queued/max. number for queue
287 SigPnd bitmap of pending signals for the thread
288 ShdPnd bitmap of shared pending signals for the process
289 SigBlk bitmap of blocked signals
290 SigIgn bitmap of ignored signals
291 SigCgt bitmap of caught signals
292 CapInh bitmap of inheritable capabilities
293 CapPrm bitmap of permitted capabilities
294 CapEff bitmap of effective capabilities
295 CapBnd bitmap of capabilities bounding set
296 CapAmb bitmap of ambient capabilities
297 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
298 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
299 Speculation_Store_Bypass speculative store bypass mitigation status
300 SpeculationIndirectBranch indirect branch speculation mode
301 Cpus_allowed mask of CPUs on which this process may run
302 Cpus_allowed_list Same as previous, but in "list format"
303 Mems_allowed mask of memory nodes allowed to this process
304 Mems_allowed_list Same as previous, but in "list format"
305 voluntary_ctxt_switches number of voluntary context switches
306 nonvoluntary_ctxt_switches number of non voluntary context switches
307 ========================== ===================================================
310 .. table:: Table 1-3: Contents of the statm fields (as of 2.6.8-rc3)
312 ======== =============================== ==============================
313 Field Content
314 ======== =============================== ==============================
315 size total program size (pages) (same as VmSize in status)
316 resident size of memory portions (pages) (same as VmRSS in status)
317 shared number of pages that are shared (i.e. backed by a file, same
318 as RssFile+RssShmem in status)
319 trs number of pages that are 'code' (not including libs; broken,
320 includes data segment)
321 lrs number of pages of library (always 0 on 2.6)
322 drs number of pages of data/stack (including libs; broken,
323 includes library text)
324 dt number of dirty pages (always 0 on 2.6)
325 ======== =============================== ==============================
328 .. table:: Table 1-4: Contents of the stat fields (as of 2.6.30-rc7)
330 ============= ===============================================================
331 Field Content
332 ============= ===============================================================
333 pid process id
334 tcomm filename of the executable
335 state state (R is running, S is sleeping, D is sleeping in an
336 uninterruptible wait, Z is zombie, T is traced or stopped)
337 ppid process id of the parent process
338 pgrp pgrp of the process
339 sid session id
340 tty_nr tty the process uses
341 tty_pgrp pgrp of the tty
342 flags task flags
343 min_flt number of minor faults
344 cmin_flt number of minor faults with child's
345 maj_flt number of major faults
346 cmaj_flt number of major faults with child's
347 utime user mode jiffies
348 stime kernel mode jiffies
349 cutime user mode jiffies with child's
350 cstime kernel mode jiffies with child's
351 priority priority level
352 nice nice level
353 num_threads number of threads
354 it_real_value (obsolete, always 0)
355 start_time time the process started after system boot
356 vsize virtual memory size
357 rss resident set memory size
358 rsslim current limit in bytes on the rss
359 start_code address above which program text can run
360 end_code address below which program text can run
361 start_stack address of the start of the main process stack
362 esp current value of ESP
363 eip current value of EIP
364 pending bitmap of pending signals
365 blocked bitmap of blocked signals
366 sigign bitmap of ignored signals
367 sigcatch bitmap of caught signals
368 0 (place holder, used to be the wchan address,
369 use /proc/PID/wchan instead)
370 0 (place holder)
371 0 (place holder)
372 exit_signal signal to send to parent thread on exit
373 task_cpu which CPU the task is scheduled on
374 rt_priority realtime priority
375 policy scheduling policy (man sched_setscheduler)
376 blkio_ticks time spent waiting for block IO
377 gtime guest time of the task in jiffies
378 cgtime guest time of the task children in jiffies
379 start_data address above which program data+bss is placed
380 end_data address below which program data+bss is placed
381 start_brk address above which program heap can be expanded with brk()
382 arg_start address above which program command line is placed
383 arg_end address below which program command line is placed
384 env_start address above which program environment is placed
385 env_end address below which program environment is placed
386 exit_code the thread's exit_code in the form reported by the waitpid
387 system call
388 ============= ===============================================================
390 The /proc/PID/maps file contains the currently mapped memory regions and
391 their access permissions.
393 The format is::
395 address perms offset dev inode pathname
397 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
398 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
399 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
400 a7cb1000-a7cb2000 ---p 00000000 00:00 0
401 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
402 a7eb2000-a7eb3000 ---p 00000000 00:00 0
403 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
404 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
405 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
406 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
407 a800b000-a800e000 rw-p 00000000 00:00 0
408 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
409 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
410 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
411 a8024000-a8027000 rw-p 00000000 00:00 0
412 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
413 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
414 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
415 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
416 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
418 where "address" is the address space in the process that it occupies, "perms"
419 is a set of permissions::
421 r = read
422 w = write
423 x = execute
424 s = shared
425 p = private (copy on write)
427 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
428 "inode" is the inode on that device. 0 indicates that no inode is associated
429 with the memory region, as the case would be with BSS (uninitialized data).
430 The "pathname" shows the name associated file for this mapping. If the mapping
431 is not associated with a file:
433 =================== ===========================================
434 [heap] the heap of the program
435 [stack] the stack of the main process
436 [vdso] the "virtual dynamic shared object",
437 the kernel system call handler
438 [anon:<name>] a private anonymous mapping that has been
439 named by userspace
440 [anon_shmem:<name>] an anonymous shared memory mapping that has
441 been named by userspace
442 =================== ===========================================
444 or if empty, the mapping is anonymous.
446 Starting with 6.11 kernel, /proc/PID/maps provides an alternative
447 ioctl()-based API that gives ability to flexibly and efficiently query and
448 filter individual VMAs. This interface is binary and is meant for more
449 efficient and easy programmatic use. `struct procmap_query`, defined in
450 linux/fs.h UAPI header, serves as an input/output argument to the
451 `PROCMAP_QUERY` ioctl() command. See comments in linus/fs.h UAPI header for
452 details on query semantics, supported flags, data returned, and general API
453 usage information.
455 The /proc/PID/smaps is an extension based on maps, showing the memory
456 consumption for each of the process's mappings. For each mapping (aka Virtual
457 Memory Area, or VMA) there is a series of lines such as the following::
459 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
461 Size: 1084 kB
462 KernelPageSize: 4 kB
463 MMUPageSize: 4 kB
464 Rss: 892 kB
465 Pss: 374 kB
466 Pss_Dirty: 0 kB
467 Shared_Clean: 892 kB
468 Shared_Dirty: 0 kB
469 Private_Clean: 0 kB
470 Private_Dirty: 0 kB
471 Referenced: 892 kB
472 Anonymous: 0 kB
473 KSM: 0 kB
474 LazyFree: 0 kB
475 AnonHugePages: 0 kB
476 ShmemPmdMapped: 0 kB
477 Shared_Hugetlb: 0 kB
478 Private_Hugetlb: 0 kB
479 Swap: 0 kB
480 SwapPss: 0 kB
481 KernelPageSize: 4 kB
482 MMUPageSize: 4 kB
483 Locked: 0 kB
484 THPeligible: 0
485 VmFlags: rd ex mr mw me dw
487 The first of these lines shows the same information as is displayed for the
488 mapping in /proc/PID/maps. Following lines show the size of the mapping
489 (size); the size of each page allocated when backing a VMA (KernelPageSize),
490 which is usually the same as the size in the page table entries; the page size
491 used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
492 the amount of the mapping that is currently resident in RAM (RSS); the
493 process' proportional share of this mapping (PSS); and the number of clean and
494 dirty shared and private pages in the mapping.
496 The "proportional set size" (PSS) of a process is the count of pages it has
497 in memory, where each page is divided by the number of processes sharing it.
498 So if a process has 1000 pages all to itself, and 1000 shared with one other
499 process, its PSS will be 1500. "Pss_Dirty" is the portion of PSS which
500 consists of dirty pages. ("Pss_Clean" is not included, but it can be
501 calculated by subtracting "Pss_Dirty" from "Pss".)
503 Note that even a page which is part of a MAP_SHARED mapping, but has only
504 a single pte mapped, i.e. is currently used by only one process, is accounted
505 as private and not as shared.
507 "Referenced" indicates the amount of memory currently marked as referenced or
508 accessed.
510 "Anonymous" shows the amount of memory that does not belong to any file. Even
511 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
512 and a page is modified, the file page is replaced by a private anonymous copy.
514 "KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages
515 are not included, only actual KSM pages.
517 "LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
518 The memory isn't freed immediately with madvise(). It's freed in memory
519 pressure if the memory is clean. Please note that the printed value might
520 be lower than the real value due to optimizations used in the current
521 implementation. If this is not desirable please file a bug report.
523 "AnonHugePages" shows the amount of memory backed by transparent hugepage.
525 "ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by
526 huge pages.
528 "Shared_Hugetlb" and "Private_Hugetlb" show the amounts of memory backed by
529 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
530 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
532 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
534 For shmem mappings, "Swap" includes also the size of the mapped (and not
535 replaced by copy-on-write) part of the underlying shmem object out on swap.
536 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
537 does not take into account swapped out page of underlying shmem objects.
538 "Locked" indicates whether the mapping is locked in memory or not.
540 "THPeligible" indicates whether the mapping is eligible for allocating
541 naturally aligned THP pages of any currently enabled size. 1 if true, 0
542 otherwise.
544 "VmFlags" field deserves a separate description. This member represents the
545 kernel flags associated with the particular virtual memory area in two letter
546 encoded manner. The codes are the following:
548 == =======================================
549 rd readable
550 wr writeable
551 ex executable
552 sh shared
553 mr may read
554 mw may write
555 me may execute
556 ms may share
557 gd stack segment growns down
558 pf pure PFN range
559 dw disabled write to the mapped file
560 lo pages are locked in memory
561 io memory mapped I/O area
562 sr sequential read advise provided
563 rr random read advise provided
564 dc do not copy area on fork
565 de do not expand area on remapping
566 ac area is accountable
567 nr swap space is not reserved for the area
568 ht area uses huge tlb pages
569 sf synchronous page fault
570 ar architecture specific flag
571 wf wipe on fork
572 dd do not include area into core dump
573 sd soft dirty flag
574 mm mixed map area
575 hg huge page advise flag
576 nh no huge page advise flag
577 mg mergeable advise flag
578 bt arm64 BTI guarded page
579 mt arm64 MTE allocation tags are enabled
580 um userfaultfd missing tracking
581 uw userfaultfd wr-protect tracking
582 ss shadow/guarded control stack page
583 sl sealed
584 == =======================================
586 Note that there is no guarantee that every flag and associated mnemonic will
587 be present in all further kernel releases. Things get changed, the flags may
588 be vanished or the reverse -- new added. Interpretation of their meaning
589 might change in future as well. So each consumer of these flags has to
590 follow each specific kernel version for the exact semantic.
592 This file is only present if the CONFIG_MMU kernel configuration option is
593 enabled.
595 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
596 output can be achieved only in the single read call).
598 This typically manifests when doing partial reads of these files while the
599 memory map is being modified. Despite the races, we do provide the following
600 guarantees:
602 1) The mapped addresses never go backwards, which implies no two
603 regions will ever overlap.
604 2) If there is something at a given vaddr during the entirety of the
605 life of the smaps/maps walk, there will be some output for it.
607 The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
608 but their values are the sums of the corresponding values for all mappings of
609 the process. Additionally, it contains these fields:
611 - Pss_Anon
612 - Pss_File
613 - Pss_Shmem
615 They represent the proportional shares of anonymous, file, and shmem pages, as
616 described for smaps above. These fields are omitted in smaps since each
617 mapping identifies the type (anon, file, or shmem) of all pages it contains.
618 Thus all information in smaps_rollup can be derived from smaps, but at a
619 significantly higher cost.
621 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
622 bits on both physical and virtual pages associated with a process, and the
623 soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
624 for details).
625 To clear the bits for all the pages associated with the process::
627 > echo 1 > /proc/PID/clear_refs
629 To clear the bits for the anonymous pages associated with the process::
631 > echo 2 > /proc/PID/clear_refs
633 To clear the bits for the file mapped pages associated with the process::
635 > echo 3 > /proc/PID/clear_refs
637 To clear the soft-dirty bit::
639 > echo 4 > /proc/PID/clear_refs
641 To reset the peak resident set size ("high water mark") to the process's
642 current value::
644 > echo 5 > /proc/PID/clear_refs
646 Any other value written to /proc/PID/clear_refs will have no effect.
648 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
649 using /proc/kpageflags and number of times a page is mapped using
650 /proc/kpagecount. For detailed explanation, see
651 Documentation/admin-guide/mm/pagemap.rst.
653 The /proc/pid/numa_maps is an extension based on maps, showing the memory
654 locality and binding policy, as well as the memory usage (in pages) of
655 each mapping. The output follows a general format where mapping details get
656 summarized separated by blank spaces, one mapping per each file line::
658 address policy mapping details
660 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
661 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
662 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
663 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
664 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
665 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
666 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
667 320698b000 default file=/lib64/libc-2.12.so
668 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
669 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
670 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
671 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
672 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
673 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
674 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
675 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
677 Where:
679 "address" is the starting address for the mapping;
681 "policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
683 "mapping details" summarizes mapping data such as mapping type, page usage counters,
684 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
685 size, in KB, that is backing the mapping up.
687 1.2 Kernel data
688 ---------------
690 Similar to the process entries, the kernel data files give information about
691 the running kernel. The files used to obtain this information are contained in
692 /proc and are listed in Table 1-5. Not all of these will be present in your
693 system. It depends on the kernel configuration and the loaded modules, which
694 files are there, and which are missing.
696 .. table:: Table 1-5: Kernel info in /proc
698 ============ ===============================================================
699 File Content
700 ============ ===============================================================
701 allocinfo Memory allocations profiling information
702 apm Advanced power management info
703 bootconfig Kernel command line obtained from boot config,
704 and, if there were kernel parameters from the
705 boot loader, a "# Parameters from bootloader:"
706 line followed by a line containing those
707 parameters prefixed by "# ". (5.5)
708 buddyinfo Kernel memory allocator information (see text) (2.5)
709 bus Directory containing bus specific information
710 cmdline Kernel command line, both from bootloader and embedded
711 in the kernel image
712 cpuinfo Info about the CPU
713 devices Available devices (block and character)
714 dma Used DMS channels
715 filesystems Supported filesystems
716 driver Various drivers grouped here, currently rtc (2.4)
717 execdomains Execdomains, related to security (2.4)
718 fb Frame Buffer devices (2.4)
719 fs File system parameters, currently nfs/exports (2.4)
720 ide Directory containing info about the IDE subsystem
721 interrupts Interrupt usage
722 iomem Memory map (2.4)
723 ioports I/O port usage
724 irq Masks for irq to cpu affinity (2.4)(smp?)
725 isapnp ISA PnP (Plug&Play) Info (2.4)
726 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
727 kmsg Kernel messages
728 ksyms Kernel symbol table
729 loadavg Load average of last 1, 5 & 15 minutes;
730 number of processes currently runnable (running or on ready queue);
731 total number of processes in system;
732 last pid created.
733 All fields are separated by one space except "number of
734 processes currently runnable" and "total number of processes
735 in system", which are separated by a slash ('/'). Example:
736 0.61 0.61 0.55 3/828 22084
737 locks Kernel locks
738 meminfo Memory info
739 misc Miscellaneous
740 modules List of loaded modules
741 mounts Mounted filesystems
742 net Networking info (see text)
743 pagetypeinfo Additional page allocator information (see text) (2.5)
744 partitions Table of partitions known to the system
745 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
746 decoupled by lspci (2.4)
747 rtc Real time clock
748 scsi SCSI info (see text)
749 slabinfo Slab pool info
750 softirqs softirq usage
751 stat Overall statistics
752 swaps Swap space utilization
753 sys See chapter 2
754 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
755 tty Info of tty drivers
756 uptime Wall clock since boot, combined idle time of all cpus
757 version Kernel version
758 video bttv info of video resources (2.4)
759 vmallocinfo Show vmalloced areas
760 ============ ===============================================================
762 You can, for example, check which interrupts are currently in use and what
763 they are used for by looking in the file /proc/interrupts::
765 > cat /proc/interrupts
766 CPU0
767 0: 8728810 XT-PIC timer
768 1: 895 XT-PIC keyboard
769 2: 0 XT-PIC cascade
770 3: 531695 XT-PIC aha152x
771 4: 2014133 XT-PIC serial
772 5: 44401 XT-PIC pcnet_cs
773 8: 2 XT-PIC rtc
774 11: 8 XT-PIC i82365
775 12: 182918 XT-PIC PS/2 Mouse
776 13: 1 XT-PIC fpu
777 14: 1232265 XT-PIC ide0
778 15: 7 XT-PIC ide1
779 NMI: 0
781 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
782 output of a SMP machine)::
784 > cat /proc/interrupts
786 CPU0 CPU1
787 0: 1243498 1214548 IO-APIC-edge timer
788 1: 8949 8958 IO-APIC-edge keyboard
789 2: 0 0 XT-PIC cascade
790 5: 11286 10161 IO-APIC-edge soundblaster
791 8: 1 0 IO-APIC-edge rtc
792 9: 27422 27407 IO-APIC-edge 3c503
793 12: 113645 113873 IO-APIC-edge PS/2 Mouse
794 13: 0 0 XT-PIC fpu
795 14: 22491 24012 IO-APIC-edge ide0
796 15: 2183 2415 IO-APIC-edge ide1
797 17: 30564 30414 IO-APIC-level eth0
798 18: 177 164 IO-APIC-level bttv
799 NMI: 2457961 2457959
800 LOC: 2457882 2457881
801 ERR: 2155
803 NMI is incremented in this case because every timer interrupt generates a NMI
804 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
806 LOC is the local interrupt counter of the internal APIC of every CPU.
808 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
809 connects the CPUs in a SMP system. This means that an error has been detected,
810 the IO-APIC automatically retry the transmission, so it should not be a big
811 problem, but you should read the SMP-FAQ.
813 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
814 /proc/interrupts to display every IRQ vector in use by the system, not
815 just those considered 'most important'. The new vectors are:
817 THR
818 interrupt raised when a machine check threshold counter
819 (typically counting ECC corrected errors of memory or cache) exceeds
820 a configurable threshold. Only available on some systems.
822 TRM
823 a thermal event interrupt occurs when a temperature threshold
824 has been exceeded for the CPU. This interrupt may also be generated
825 when the temperature drops back to normal.
827 SPU
828 a spurious interrupt is some interrupt that was raised then lowered
829 by some IO device before it could be fully processed by the APIC. Hence
830 the APIC sees the interrupt but does not know what device it came from.
831 For this case the APIC will generate the interrupt with a IRQ vector
832 of 0xff. This might also be generated by chipset bugs.
834 RES, CAL, TLB
835 rescheduling, call and TLB flush interrupts are
836 sent from one CPU to another per the needs of the OS. Typically,
837 their statistics are used by kernel developers and interested users to
838 determine the occurrence of interrupts of the given type.
840 The above IRQ vectors are displayed only when relevant. For example,
841 the threshold vector does not exist on x86_64 platforms. Others are
842 suppressed when the system is a uniprocessor. As of this writing, only
843 i386 and x86_64 platforms support the new IRQ vector displays.
845 Of some interest is the introduction of the /proc/irq directory to 2.4.
846 It could be used to set IRQ to CPU affinity. This means that you can "hook" an
847 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
848 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
849 prof_cpu_mask.
851 For example::
853 > ls /proc/irq/
854 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
855 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
856 > ls /proc/irq/0/
857 smp_affinity
859 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
860 IRQ. You can set it by doing::
862 > echo 1 > /proc/irq/10/smp_affinity
864 This means that only the first CPU will handle the IRQ, but you can also echo
865 5 which means that only the first and third CPU can handle the IRQ.
867 The contents of each smp_affinity file is the same by default::
869 > cat /proc/irq/0/smp_affinity
870 ffffffff
872 There is an alternate interface, smp_affinity_list which allows specifying
873 a CPU range instead of a bitmask::
875 > cat /proc/irq/0/smp_affinity_list
876 1024-1031
878 The default_smp_affinity mask applies to all non-active IRQs, which are the
879 IRQs which have not yet been allocated/activated, and hence which lack a
880 /proc/irq/[0-9]* directory.
882 The node file on an SMP system shows the node to which the device using the IRQ
883 reports itself as being attached. This hardware locality information does not
884 include information about any possible driver locality preference.
886 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
887 profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
889 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
890 between all the CPUs which are allowed to handle it. As usual the kernel has
891 more info than you and does a better job than you, so the defaults are the
892 best choice for almost everyone. [Note this applies only to those IO-APIC's
893 that support "Round Robin" interrupt distribution.]
895 There are three more important subdirectories in /proc: net, scsi, and sys.
896 The general rule is that the contents, or even the existence of these
897 directories, depend on your kernel configuration. If SCSI is not enabled, the
898 directory scsi may not exist. The same is true with the net, which is there
899 only when networking support is present in the running kernel.
901 The slabinfo file gives information about memory usage at the slab level.
902 Linux uses slab pools for memory management above page level in version 2.2.
903 Commonly used objects have their own slab pool (such as network buffers,
904 directory cache, and so on).
906 ::
908 > cat /proc/buddyinfo
910 Node 0, zone DMA 0 4 5 4 4 3 ...
911 Node 0, zone Normal 1 0 0 1 101 8 ...
912 Node 0, zone HighMem 2 0 0 1 1 0 ...
914 External fragmentation is a problem under some workloads, and buddyinfo is a
915 useful tool for helping diagnose these problems. Buddyinfo will give you a
916 clue as to how big an area you can safely allocate, or why a previous
917 allocation failed.
919 Each column represents the number of pages of a certain order which are
920 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
921 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
922 available in ZONE_NORMAL, etc...
924 More information relevant to external fragmentation can be found in
925 pagetypeinfo::
927 > cat /proc/pagetypeinfo
928 Page block order: 9
929 Pages per block: 512
931 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
932 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
933 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
934 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
935 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
936 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
937 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
938 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
939 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
940 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
941 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
943 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
944 Node 0, zone DMA 2 0 5 1 0
945 Node 0, zone DMA32 41 6 967 2 0
947 Fragmentation avoidance in the kernel works by grouping pages of different
948 migrate types into the same contiguous regions of memory called page blocks.
949 A page block is typically the size of the default hugepage size, e.g. 2MB on
950 X86-64. By keeping pages grouped based on their ability to move, the kernel
951 can reclaim pages within a page block to satisfy a high-order allocation.
953 The pagetypinfo begins with information on the size of a page block. It
954 then gives the same type of information as buddyinfo except broken down
955 by migrate-type and finishes with details on how many page blocks of each
956 type exist.
958 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
959 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
960 make an estimate of the likely number of huge pages that can be allocated
961 at a given point in time. All the "Movable" blocks should be allocatable
962 unless memory has been mlock()'d. Some of the Reclaimable blocks should
963 also be allocatable although a lot of filesystem metadata may have to be
964 reclaimed to achieve this.
967 allocinfo
968 ~~~~~~~~~
970 Provides information about memory allocations at all locations in the code
971 base. Each allocation in the code is identified by its source file, line
972 number, module (if originates from a loadable module) and the function calling
973 the allocation. The number of bytes allocated and number of calls at each
974 location are reported. The first line indicates the version of the file, the
975 second line is the header listing fields in the file.
977 Example output.
979 ::
981 > tail -n +3 /proc/allocinfo | sort -rn
982 127664128 31168 mm/page_ext.c:270 func:alloc_page_ext
983 56373248 4737 mm/slub.c:2259 func:alloc_slab_page
984 14880768 3633 mm/readahead.c:247 func:page_cache_ra_unbounded
985 14417920 3520 mm/mm_init.c:2530 func:alloc_large_system_hash
986 13377536 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
987 11718656 2861 mm/filemap.c:1919 func:__filemap_get_folio
988 9192960 2800 kernel/fork.c:307 func:alloc_thread_stack_node
989 4206592 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
990 4136960 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
991 3940352 962 mm/memory.c:4214 func:alloc_anon_folio
992 2894464 22613 fs/kernfs/dir.c:615 func:__kernfs_new_node
993 ...
996 meminfo
997 ~~~~~~~
999 Provides information about distribution and utilization of memory. This
1000 varies by architecture and compile options. Some of the counters reported
1001 here overlap. The memory reported by the non overlapping counters may not
1002 add up to the overall memory usage and the difference for some workloads
1003 can be substantial. In many cases there are other means to find out
1004 additional memory using subsystem specific interfaces, for instance
1005 /proc/net/sockstat for TCP memory allocations.
1007 Example output. You may not have all of these fields.
1009 ::
1011 > cat /proc/meminfo
1013 MemTotal: 32858820 kB
1014 MemFree: 21001236 kB
1015 MemAvailable: 27214312 kB
1016 Buffers: 581092 kB
1017 Cached: 5587612 kB
1018 SwapCached: 0 kB
1019 Active: 3237152 kB
1020 Inactive: 7586256 kB
1021 Active(anon): 94064 kB
1022 Inactive(anon): 4570616 kB
1023 Active(file): 3143088 kB
1024 Inactive(file): 3015640 kB
1025 Unevictable: 0 kB
1026 Mlocked: 0 kB
1027 SwapTotal: 0 kB
1028 SwapFree: 0 kB
1029 Zswap: 1904 kB
1030 Zswapped: 7792 kB
1031 Dirty: 12 kB
1032 Writeback: 0 kB
1033 AnonPages: 4654780 kB
1034 Mapped: 266244 kB
1035 Shmem: 9976 kB
1036 KReclaimable: 517708 kB
1037 Slab: 660044 kB
1038 SReclaimable: 517708 kB
1039 SUnreclaim: 142336 kB
1040 KernelStack: 11168 kB
1041 PageTables: 20540 kB
1042 SecPageTables: 0 kB
1043 NFS_Unstable: 0 kB
1044 Bounce: 0 kB
1045 WritebackTmp: 0 kB
1046 CommitLimit: 16429408 kB
1047 Committed_AS: 7715148 kB
1048 VmallocTotal: 34359738367 kB
1049 VmallocUsed: 40444 kB
1050 VmallocChunk: 0 kB
1051 Percpu: 29312 kB
1052 EarlyMemtestBad: 0 kB
1053 HardwareCorrupted: 0 kB
1054 AnonHugePages: 4149248 kB
1055 ShmemHugePages: 0 kB
1056 ShmemPmdMapped: 0 kB
1057 FileHugePages: 0 kB
1058 FilePmdMapped: 0 kB
1059 CmaTotal: 0 kB
1060 CmaFree: 0 kB
1061 HugePages_Total: 0
1062 HugePages_Free: 0
1063 HugePages_Rsvd: 0
1064 HugePages_Surp: 0
1065 Hugepagesize: 2048 kB
1066 Hugetlb: 0 kB
1067 DirectMap4k: 401152 kB
1068 DirectMap2M: 10008576 kB
1069 DirectMap1G: 24117248 kB
1071 MemTotal
1072 Total usable RAM (i.e. physical RAM minus a few reserved
1073 bits and the kernel binary code)
1074 MemFree
1075 Total free RAM. On highmem systems, the sum of LowFree+HighFree
1076 MemAvailable
1077 An estimate of how much memory is available for starting new
1078 applications, without swapping. Calculated from MemFree,
1079 SReclaimable, the size of the file LRU lists, and the low
1080 watermarks in each zone.
1081 The estimate takes into account that the system needs some
1082 page cache to function well, and that not all reclaimable
1083 slab will be reclaimable, due to items being in use. The
1084 impact of those factors will vary from system to system.
1085 Buffers
1086 Relatively temporary storage for raw disk blocks
1087 shouldn't get tremendously large (20MB or so)
1088 Cached
1089 In-memory cache for files read from the disk (the
1090 pagecache) as well as tmpfs & shmem.
1091 Doesn't include SwapCached.
1092 SwapCached
1093 Memory that once was swapped out, is swapped back in but
1094 still also is in the swapfile (if memory is needed it
1095 doesn't need to be swapped out AGAIN because it is already
1096 in the swapfile. This saves I/O)
1097 Active
1098 Memory that has been used more recently and usually not
1099 reclaimed unless absolutely necessary.
1100 Inactive
1101 Memory which has been less recently used. It is more
1102 eligible to be reclaimed for other purposes
1103 Unevictable
1104 Memory allocated for userspace which cannot be reclaimed, such
1105 as mlocked pages, ramfs backing pages, secret memfd pages etc.
1106 Mlocked
1107 Memory locked with mlock().
1108 HighTotal, HighFree
1109 Highmem is all memory above ~860MB of physical memory.
1110 Highmem areas are for use by userspace programs, or
1111 for the pagecache. The kernel must use tricks to access
1112 this memory, making it slower to access than lowmem.
1113 LowTotal, LowFree
1114 Lowmem is memory which can be used for everything that
1115 highmem can be used for, but it is also available for the
1116 kernel's use for its own data structures. Among many
1117 other things, it is where everything from the Slab is
1118 allocated. Bad things happen when you're out of lowmem.
1119 SwapTotal
1120 total amount of swap space available
1121 SwapFree
1122 Memory which has been evicted from RAM, and is temporarily
1123 on the disk
1124 Zswap
1125 Memory consumed by the zswap backend (compressed size)
1126 Zswapped
1127 Amount of anonymous memory stored in zswap (original size)
1128 Dirty
1129 Memory which is waiting to get written back to the disk
1130 Writeback
1131 Memory which is actively being written back to the disk
1132 AnonPages
1133 Non-file backed pages mapped into userspace page tables
1134 Mapped
1135 files which have been mmapped, such as libraries
1136 Shmem
1137 Total memory used by shared memory (shmem) and tmpfs
1138 KReclaimable
1139 Kernel allocations that the kernel will attempt to reclaim
1140 under memory pressure. Includes SReclaimable (below), and other
1141 direct allocations with a shrinker.
1142 Slab
1143 in-kernel data structures cache
1144 SReclaimable
1145 Part of Slab, that might be reclaimed, such as caches
1146 SUnreclaim
1147 Part of Slab, that cannot be reclaimed on memory pressure
1148 KernelStack
1149 Memory consumed by the kernel stacks of all tasks
1150 PageTables
1151 Memory consumed by userspace page tables
1152 SecPageTables
1153 Memory consumed by secondary page tables, this currently includes
1154 KVM mmu and IOMMU allocations on x86 and arm64.
1155 NFS_Unstable
1156 Always zero. Previous counted pages which had been written to
1157 the server, but has not been committed to stable storage.
1158 Bounce
1159 Memory used for block device "bounce buffers"
1160 WritebackTmp
1161 Memory used by FUSE for temporary writeback buffers
1162 CommitLimit
1163 Based on the overcommit ratio ('vm.overcommit_ratio'),
1164 this is the total amount of memory currently available to
1165 be allocated on the system. This limit is only adhered to
1166 if strict overcommit accounting is enabled (mode 2 in
1167 'vm.overcommit_memory').
1169 The CommitLimit is calculated with the following formula::
1171 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1172 overcommit_ratio / 100 + [total swap pages]
1174 For example, on a system with 1G of physical RAM and 7G
1175 of swap with a `vm.overcommit_ratio` of 30 it would
1176 yield a CommitLimit of 7.3G.
1178 For more details, see the memory overcommit documentation
1179 in mm/overcommit-accounting.
1180 Committed_AS
1181 The amount of memory presently allocated on the system.
1182 The committed memory is a sum of all of the memory which
1183 has been allocated by processes, even if it has not been
1184 "used" by them as of yet. A process which malloc()'s 1G
1185 of memory, but only touches 300M of it will show up as
1186 using 1G. This 1G is memory which has been "committed" to
1187 by the VM and can be used at any time by the allocating
1188 application. With strict overcommit enabled on the system
1189 (mode 2 in 'vm.overcommit_memory'), allocations which would
1190 exceed the CommitLimit (detailed above) will not be permitted.
1191 This is useful if one needs to guarantee that processes will
1192 not fail due to lack of memory once that memory has been
1193 successfully allocated.
1194 VmallocTotal
1195 total size of vmalloc virtual address space
1196 VmallocUsed
1197 amount of vmalloc area which is used
1198 VmallocChunk
1199 largest contiguous block of vmalloc area which is free
1200 Percpu
1201 Memory allocated to the percpu allocator used to back percpu
1202 allocations. This stat excludes the cost of metadata.
1203 EarlyMemtestBad
1204 The amount of RAM/memory in kB, that was identified as corrupted
1205 by early memtest. If memtest was not run, this field will not
1206 be displayed at all. Size is never rounded down to 0 kB.
1207 That means if 0 kB is reported, you can safely assume
1208 there was at least one pass of memtest and none of the passes
1209 found a single faulty byte of RAM.
1210 HardwareCorrupted
1211 The amount of RAM/memory in KB, the kernel identifies as
1212 corrupted.
1213 AnonHugePages
1214 Non-file backed huge pages mapped into userspace page tables
1215 ShmemHugePages
1216 Memory used by shared memory (shmem) and tmpfs allocated
1217 with huge pages
1218 ShmemPmdMapped
1219 Shared memory mapped into userspace with huge pages
1220 FileHugePages
1221 Memory used for filesystem data (page cache) allocated
1222 with huge pages
1223 FilePmdMapped
1224 Page cache mapped into userspace with huge pages
1225 CmaTotal
1226 Memory reserved for the Contiguous Memory Allocator (CMA)
1227 CmaFree
1228 Free remaining memory in the CMA reserves
1229 HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
1230 See Documentation/admin-guide/mm/hugetlbpage.rst.
1231 DirectMap4k, DirectMap2M, DirectMap1G
1232 Breakdown of page table sizes used in the kernel's
1233 identity mapping of RAM
1235 vmallocinfo
1236 ~~~~~~~~~~~
1238 Provides information about vmalloced/vmaped areas. One line per area,
1239 containing the virtual address range of the area, size in bytes,
1240 caller information of the creator, and optional information depending
1241 on the kind of area:
1243 ========== ===================================================
1244 pages=nr number of pages
1245 phys=addr if a physical address was specified
1246 ioremap I/O mapping (ioremap() and friends)
1247 vmalloc vmalloc() area
1248 vmap vmap()ed pages
1249 user VM_USERMAP area
1250 vpages buffer for pages pointers was vmalloced (huge area)
1251 N<node>=nr (Only on NUMA kernels)
1252 Number of pages allocated on memory node <node>
1253 ========== ===================================================
1255 ::
1257 > cat /proc/vmallocinfo
1258 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1259 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1260 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1261 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1262 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
1263 phys=7fee8000 ioremap
1264 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
1265 phys=7fee7000 ioremap
1266 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
1267 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
1268 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1269 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
1270 pages=2 vmalloc N1=2
1271 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
1272 /0x130 [x_tables] pages=4 vmalloc N0=4
1273 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
1274 pages=14 vmalloc N2=14
1275 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
1276 pages=4 vmalloc N1=4
1277 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
1278 pages=2 vmalloc N1=2
1279 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
1280 pages=10 vmalloc N0=10
1283 softirqs
1284 ~~~~~~~~
1286 Provides counts of softirq handlers serviced since boot time, for each CPU.
1288 ::
1290 > cat /proc/softirqs
1291 CPU0 CPU1 CPU2 CPU3
1292 HI: 0 0 0 0
1293 TIMER: 27166 27120 27097 27034
1294 NET_TX: 0 0 0 17
1295 NET_RX: 42 0 0 39
1296 BLOCK: 0 0 107 1121
1297 TASKLET: 0 0 0 290
1298 SCHED: 27035 26983 26971 26746
1299 HRTIMER: 0 0 0 0
1300 RCU: 1678 1769 2178 2250
1302 1.3 Networking info in /proc/net
1303 --------------------------------
1305 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1306 additional values you get for IP version 6 if you configure the kernel to
1307 support this. Table 1-9 lists the files and their meaning.
1310 .. table:: Table 1-8: IPv6 info in /proc/net
1312 ========== =====================================================
1313 File Content
1314 ========== =====================================================
1315 udp6 UDP sockets (IPv6)
1316 tcp6 TCP sockets (IPv6)
1317 raw6 Raw device statistics (IPv6)
1318 igmp6 IP multicast addresses, which this host joined (IPv6)
1319 if_inet6 List of IPv6 interface addresses
1320 ipv6_route Kernel routing table for IPv6
1321 rt6_stats Global IPv6 routing tables statistics
1322 sockstat6 Socket statistics (IPv6)
1323 snmp6 Snmp data (IPv6)
1324 ========== =====================================================
1326 .. table:: Table 1-9: Network info in /proc/net
1328 ============= ================================================================
1329 File Content
1330 ============= ================================================================
1331 arp Kernel ARP table
1332 dev network devices with statistics
1333 dev_mcast the Layer2 multicast groups a device is listening too
1334 (interface index, label, number of references, number of bound
1335 addresses).
1336 dev_stat network device status
1337 ip_fwchains Firewall chain linkage
1338 ip_fwnames Firewall chain names
1339 ip_masq Directory containing the masquerading tables
1340 ip_masquerade Major masquerading table
1341 netstat Network statistics
1342 raw raw device statistics
1343 route Kernel routing table
1344 rpc Directory containing rpc info
1345 rt_cache Routing cache
1346 snmp SNMP data
1347 sockstat Socket statistics
1348 softnet_stat Per-CPU incoming packets queues statistics of online CPUs
1349 tcp TCP sockets
1350 udp UDP sockets
1351 unix UNIX domain sockets
1352 wireless Wireless interface data (Wavelan etc)
1353 igmp IP multicast addresses, which this host joined
1354 psched Global packet scheduler parameters.
1355 netlink List of PF_NETLINK sockets
1356 ip_mr_vifs List of multicast virtual interfaces
1357 ip_mr_cache List of multicast routing cache
1358 ============= ================================================================
1360 You can use this information to see which network devices are available in
1361 your system and how much traffic was routed over those devices::
1363 > cat /proc/net/dev
1364 Inter-|Receive |[...
1365 face |bytes packets errs drop fifo frame compressed multicast|[...
1366 lo: 908188 5596 0 0 0 0 0 0 [...
1367 ppp0:15475140 20721 410 0 0 410 0 0 [...
1368 eth0: 614530 7085 0 0 0 0 0 1 [...
1370 ...] Transmit
1371 ...] bytes packets errs drop fifo colls carrier compressed
1372 ...] 908188 5596 0 0 0 0 0 0
1373 ...] 1375103 17405 0 0 0 0 0 0
1374 ...] 1703981 5535 0 0 0 3 0 0
1376 In addition, each Channel Bond interface has its own directory. For
1377 example, the bond0 device will have a directory called /proc/net/bond0/.
1378 It will contain information that is specific to that bond, such as the
1379 current slaves of the bond, the link status of the slaves, and how
1380 many times the slaves link has failed.
1382 1.4 SCSI info
1383 -------------
1385 If you have a SCSI or ATA host adapter in your system, you'll find a
1386 subdirectory named after the driver for this adapter in /proc/scsi.
1387 You'll also see a list of all recognized SCSI devices in /proc/scsi::
1389 >cat /proc/scsi/scsi
1390 Attached devices:
1391 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1392 Vendor: IBM Model: DGHS09U Rev: 03E0
1393 Type: Direct-Access ANSI SCSI revision: 03
1394 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1395 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1396 Type: CD-ROM ANSI SCSI revision: 02
1399 The directory named after the driver has one file for each adapter found in
1400 the system. These files contain information about the controller, including
1401 the used IRQ and the IO address range. The amount of information shown is
1402 dependent on the adapter you use. The example shows the output for an Adaptec
1403 AHA-2940 SCSI adapter::
1405 > cat /proc/scsi/aic7xxx/0
1407 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1408 Compile Options:
1409 TCQ Enabled By Default : Disabled
1410 AIC7XXX_PROC_STATS : Disabled
1411 AIC7XXX_RESET_DELAY : 5
1412 Adapter Configuration:
1413 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1414 Ultra Wide Controller
1415 PCI MMAPed I/O Base: 0xeb001000
1416 Adapter SEEPROM Config: SEEPROM found and used.
1417 Adaptec SCSI BIOS: Enabled
1418 IRQ: 10
1419 SCBs: Active 0, Max Active 2,
1420 Allocated 15, HW 16, Page 255
1421 Interrupts: 160328
1422 BIOS Control Word: 0x18b6
1423 Adapter Control Word: 0x005b
1424 Extended Translation: Enabled
1425 Disconnect Enable Flags: 0xffff
1426 Ultra Enable Flags: 0x0001
1427 Tag Queue Enable Flags: 0x0000
1428 Ordered Queue Tag Flags: 0x0000
1429 Default Tag Queue Depth: 8
1430 Tagged Queue By Device array for aic7xxx host instance 0:
1431 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1432 Actual queue depth per device for aic7xxx host instance 0:
1433 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1434 Statistics:
1435 (scsi0:0:0:0)
1436 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1437 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1438 Total transfers 160151 (74577 reads and 85574 writes)
1439 (scsi0:0:6:0)
1440 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1441 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1442 Total transfers 0 (0 reads and 0 writes)
1445 1.5 Parallel port info in /proc/parport
1446 ---------------------------------------
1448 The directory /proc/parport contains information about the parallel ports of
1449 your system. It has one subdirectory for each port, named after the port
1450 number (0,1,2,...).
1452 These directories contain the four files shown in Table 1-10.
1455 .. table:: Table 1-10: Files in /proc/parport
1457 ========= ====================================================================
1458 File Content
1459 ========= ====================================================================
1460 autoprobe Any IEEE-1284 device ID information that has been acquired.
1461 devices list of the device drivers using that port. A + will appear by the
1462 name of the device currently using the port (it might not appear
1463 against any).
1464 hardware Parallel port's base address, IRQ line and DMA channel.
1465 irq IRQ that parport is using for that port. This is in a separate
1466 file to allow you to alter it by writing a new value in (IRQ
1467 number or none).
1468 ========= ====================================================================
1470 1.6 TTY info in /proc/tty
1471 -------------------------
1473 Information about the available and actually used tty's can be found in the
1474 directory /proc/tty. You'll find entries for drivers and line disciplines in
1475 this directory, as shown in Table 1-11.
1478 .. table:: Table 1-11: Files in /proc/tty
1480 ============= ==============================================
1481 File Content
1482 ============= ==============================================
1483 drivers list of drivers and their usage
1484 ldiscs registered line disciplines
1485 driver/serial usage statistic and status of single tty lines
1486 ============= ==============================================
1488 To see which tty's are currently in use, you can simply look into the file
1489 /proc/tty/drivers::
1491 > cat /proc/tty/drivers
1492 pty_slave /dev/pts 136 0-255 pty:slave
1493 pty_master /dev/ptm 128 0-255 pty:master
1494 pty_slave /dev/ttyp 3 0-255 pty:slave
1495 pty_master /dev/pty 2 0-255 pty:master
1496 serial /dev/cua 5 64-67 serial:callout
1497 serial /dev/ttyS 4 64-67 serial
1498 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1499 /dev/ptmx /dev/ptmx 5 2 system
1500 /dev/console /dev/console 5 1 system:console
1501 /dev/tty /dev/tty 5 0 system:/dev/tty
1502 unknown /dev/tty 4 1-63 console
1505 1.7 Miscellaneous kernel statistics in /proc/stat
1506 -------------------------------------------------
1508 Various pieces of information about kernel activity are available in the
1509 /proc/stat file. All of the numbers reported in this file are aggregates
1510 since the system first booted. For a quick look, simply cat the file::
1512 > cat /proc/stat
1513 cpu 237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0
1514 cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0
1515 cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0
1516 cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0
1517 cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0
1518 intr 8688370575 8 3373 0 0 0 0 0 0 1 40791 0 0 353317 0 0 0 0 224789828 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 190974333 41958554 123983334 43 0 224593 0 0 0 <more 0's deleted>
1519 ctxt 22848221062
1520 btime 1605316999
1521 processes 746787147
1522 procs_running 2
1523 procs_blocked 0
1524 softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354
1526 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1527 lines. These numbers identify the amount of time the CPU has spent performing
1528 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1529 second). The meanings of the columns are as follows, from left to right:
1531 - user: normal processes executing in user mode
1532 - nice: niced processes executing in user mode
1533 - system: processes executing in kernel mode
1534 - idle: twiddling thumbs
1535 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
1536 are several problems:
1538 1. CPU will not wait for I/O to complete, iowait is the time that a task is
1539 waiting for I/O to complete. When CPU goes into idle state for
1540 outstanding task I/O, another task will be scheduled on this CPU.
1541 2. In a multi-core CPU, the task waiting for I/O to complete is not running
1542 on any CPU, so the iowait of each CPU is difficult to calculate.
1543 3. The value of iowait field in /proc/stat will decrease in certain
1544 conditions.
1546 So, the iowait is not reliable by reading from /proc/stat.
1547 - irq: servicing interrupts
1548 - softirq: servicing softirqs
1549 - steal: involuntary wait
1550 - guest: running a normal guest
1551 - guest_nice: running a niced guest
1553 The "intr" line gives counts of interrupts serviced since boot time, for each
1554 of the possible system interrupts. The first column is the total of all
1555 interrupts serviced including unnumbered architecture specific interrupts;
1556 each subsequent column is the total for that particular numbered interrupt.
1557 Unnumbered interrupts are not shown, only summed into the total.
1559 The "ctxt" line gives the total number of context switches across all CPUs.
1561 The "btime" line gives the time at which the system booted, in seconds since
1562 the Unix epoch.
1564 The "processes" line gives the number of processes and threads created, which
1565 includes (but is not limited to) those created by calls to the fork() and
1566 clone() system calls.
1568 The "procs_running" line gives the total number of threads that are
1569 running or ready to run (i.e., the total number of runnable threads).
1571 The "procs_blocked" line gives the number of processes currently blocked,
1572 waiting for I/O to complete.
1574 The "softirq" line gives counts of softirqs serviced since boot time, for each
1575 of the possible system softirqs. The first column is the total of all
1576 softirqs serviced; each subsequent column is the total for that particular
1577 softirq.
1580 1.8 Ext4 file system parameters
1581 -------------------------------
1583 Information about mounted ext4 file systems can be found in
1584 /proc/fs/ext4. Each mounted filesystem will have a directory in
1585 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1586 /proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0). The files in each per-device
1587 directory are shown in Table 1-12, below.
1589 .. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1591 ============== ==========================================================
1592 File Content
1593 mb_groups details of multiblock allocator buddy cache of free blocks
1594 ============== ==========================================================
1596 1.9 /proc/consoles
1597 -------------------
1598 Shows registered system console lines.
1600 To see which character device lines are currently used for the system console
1601 /dev/console, you may simply look into the file /proc/consoles::
1603 > cat /proc/consoles
1604 tty0 -WU (ECp) 4:7
1605 ttyS0 -W- (Ep) 4:64
1607 The columns are:
1609 +--------------------+-------------------------------------------------------+
1610 | device | name of the device |
1611 +====================+=======================================================+
1612 | operations | * R = can do read operations |
1613 | | * W = can do write operations |
1614 | | * U = can do unblank |
1615 +--------------------+-------------------------------------------------------+
1616 | flags | * E = it is enabled |
1617 | | * C = it is preferred console |
1618 | | * B = it is primary boot console |
1619 | | * p = it is used for printk buffer |
1620 | | * b = it is not a TTY but a Braille device |
1621 | | * a = it is safe to use when cpu is offline |
1622 +--------------------+-------------------------------------------------------+
1623 | major:minor | major and minor number of the device separated by a |
1624 | | colon |
1625 +--------------------+-------------------------------------------------------+
1627 Summary
1628 -------
1630 The /proc file system serves information about the running system. It not only
1631 allows access to process data but also allows you to request the kernel status
1632 by reading files in the hierarchy.
1634 The directory structure of /proc reflects the types of information and makes
1635 it easy, if not obvious, where to look for specific data.
1637 Chapter 2: Modifying System Parameters
1638 ======================================
1640 In This Chapter
1641 ---------------
1643 * Modifying kernel parameters by writing into files found in /proc/sys
1644 * Exploring the files which modify certain parameters
1645 * Review of the /proc/sys file tree
1647 ------------------------------------------------------------------------------
1649 A very interesting part of /proc is the directory /proc/sys. This is not only
1650 a source of information, it also allows you to change parameters within the
1651 kernel. Be very careful when attempting this. You can optimize your system,
1652 but you can also cause it to crash. Never alter kernel parameters on a
1653 production system. Set up a development machine and test to make sure that
1654 everything works the way you want it to. You may have no alternative but to
1655 reboot the machine once an error has been made.
1657 To change a value, simply echo the new value into the file.
1658 You need to be root to do this. You can create your own boot script
1659 to perform this every time your system boots.
1661 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1662 general things in the operation of the Linux kernel. Since some of the files
1663 can inadvertently disrupt your system, it is advisable to read both
1664 documentation and source before actually making adjustments. In any case, be
1665 very careful when writing to any of these files. The entries in /proc may
1666 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1667 review the kernel documentation in the directory linux/Documentation.
1668 This chapter is heavily based on the documentation included in the pre 2.2
1669 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1671 Please see: Documentation/admin-guide/sysctl/ directory for descriptions of
1672 these entries.
1674 Summary
1675 -------
1677 Certain aspects of kernel behavior can be modified at runtime, without the
1678 need to recompile the kernel, or even to reboot the system. The files in the
1679 /proc/sys tree can not only be read, but also modified. You can use the echo
1680 command to write value into these files, thereby changing the default settings
1681 of the kernel.
1684 Chapter 3: Per-process Parameters
1685 =================================
1687 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1688 --------------------------------------------------------------------------------
1690 These files can be used to adjust the badness heuristic used to select which
1691 process gets killed in out of memory (oom) conditions.
1693 The badness heuristic assigns a value to each candidate task ranging from 0
1694 (never kill) to 1000 (always kill) to determine which process is targeted. The
1695 units are roughly a proportion along that range of allowed memory the process
1696 may allocate from based on an estimation of its current memory and swap use.
1697 For example, if a task is using all allowed memory, its badness score will be
1698 1000. If it is using half of its allowed memory, its score will be 500.
1700 The amount of "allowed" memory depends on the context in which the oom killer
1701 was called. If it is due to the memory assigned to the allocating task's cpuset
1702 being exhausted, the allowed memory represents the set of mems assigned to that
1703 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1704 memory represents the set of mempolicy nodes. If it is due to a memory
1705 limit (or swap limit) being reached, the allowed memory is that configured
1706 limit. Finally, if it is due to the entire system being out of memory, the
1707 allowed memory represents all allocatable resources.
1709 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1710 is used to determine which task to kill. Acceptable values range from -1000
1711 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1712 polarize the preference for oom killing either by always preferring a certain
1713 task or completely disabling it. The lowest possible value, -1000, is
1714 equivalent to disabling oom killing entirely for that task since it will always
1715 report a badness score of 0.
1717 Consequently, it is very simple for userspace to define the amount of memory to
1718 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1719 example, is roughly equivalent to allowing the remainder of tasks sharing the
1720 same system, cpuset, mempolicy, or memory controller resources to use at least
1721 50% more memory. A value of -500, on the other hand, would be roughly
1722 equivalent to discounting 50% of the task's allowed memory from being considered
1723 as scoring against the task.
1725 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1726 be used to tune the badness score. Its acceptable values range from -16
1727 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1728 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1729 scaled linearly with /proc/<pid>/oom_score_adj.
1731 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1732 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1733 requires CAP_SYS_RESOURCE.
1736 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1737 -------------------------------------------------------------
1739 This file can be used to check the current score used by the oom-killer for
1740 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1741 process should be killed in an out-of-memory situation.
1743 Please note that the exported value includes oom_score_adj so it is
1744 effectively in range [0,2000].
1747 3.3 /proc/<pid>/io - Display the IO accounting fields
1748 -------------------------------------------------------
1750 This file contains IO statistics for each running process.
1752 Example
1753 ~~~~~~~
1755 ::
1757 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1758 [1] 3828
1760 test:/tmp # cat /proc/3828/io
1761 rchar: 323934931
1762 wchar: 323929600
1763 syscr: 632687
1764 syscw: 632675
1765 read_bytes: 0
1766 write_bytes: 323932160
1767 cancelled_write_bytes: 0
1770 Description
1771 ~~~~~~~~~~~
1773 rchar
1774 ^^^^^
1776 I/O counter: chars read
1777 The number of bytes which this task has caused to be read from storage. This
1778 is simply the sum of bytes which this process passed to read() and pread().
1779 It includes things like tty IO and it is unaffected by whether or not actual
1780 physical disk IO was required (the read might have been satisfied from
1781 pagecache).
1784 wchar
1785 ^^^^^
1787 I/O counter: chars written
1788 The number of bytes which this task has caused, or shall cause to be written
1789 to disk. Similar caveats apply here as with rchar.
1792 syscr
1793 ^^^^^
1795 I/O counter: read syscalls
1796 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1797 and pread().
1800 syscw
1801 ^^^^^
1803 I/O counter: write syscalls
1804 Attempt to count the number of write I/O operations, i.e. syscalls like
1805 write() and pwrite().
1808 read_bytes
1809 ^^^^^^^^^^
1811 I/O counter: bytes read
1812 Attempt to count the number of bytes which this process really did cause to
1813 be fetched from the storage layer. Done at the submit_bio() level, so it is
1814 accurate for block-backed filesystems. <please add status regarding NFS and
1815 CIFS at a later time>
1818 write_bytes
1819 ^^^^^^^^^^^
1821 I/O counter: bytes written
1822 Attempt to count the number of bytes which this process caused to be sent to
1823 the storage layer. This is done at page-dirtying time.
1826 cancelled_write_bytes
1827 ^^^^^^^^^^^^^^^^^^^^^
1829 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1830 then deletes the file, it will in fact perform no writeout. But it will have
1831 been accounted as having caused 1MB of write.
1832 In other words: The number of bytes which this process caused to not happen,
1833 by truncating pagecache. A task can cause "negative" IO too. If this task
1834 truncates some dirty pagecache, some IO which another task has been accounted
1835 for (in its write_bytes) will not be happening. We _could_ just subtract that
1836 from the truncating task's write_bytes, but there is information loss in doing
1837 that.
1840 .. Note::
1842 At its current implementation state, this is a bit racy on 32-bit machines:
1843 if process A reads process B's /proc/pid/io while process B is updating one
1844 of those 64-bit counters, process A could see an intermediate result.
1847 More information about this can be found within the taskstats documentation in
1848 Documentation/accounting.
1850 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1851 ---------------------------------------------------------------
1852 When a process is dumped, all anonymous memory is written to a core file as
1853 long as the size of the core file isn't limited. But sometimes we don't want
1854 to dump some memory segments, for example, huge shared memory or DAX.
1855 Conversely, sometimes we want to save file-backed memory segments into a core
1856 file, not only the individual files.
1858 /proc/<pid>/coredump_filter allows you to customize which memory segments
1859 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1860 of memory types. If a bit of the bitmask is set, memory segments of the
1861 corresponding memory type are dumped, otherwise they are not dumped.
1863 The following 9 memory types are supported:
1865 - (bit 0) anonymous private memory
1866 - (bit 1) anonymous shared memory
1867 - (bit 2) file-backed private memory
1868 - (bit 3) file-backed shared memory
1869 - (bit 4) ELF header pages in file-backed private memory areas (it is
1870 effective only if the bit 2 is cleared)
1871 - (bit 5) hugetlb private memory
1872 - (bit 6) hugetlb shared memory
1873 - (bit 7) DAX private memory
1874 - (bit 8) DAX shared memory
1876 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1877 are always dumped regardless of the bitmask status.
1879 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1880 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1882 The default value of coredump_filter is 0x33; this means all anonymous memory
1883 segments, ELF header pages and hugetlb private memory are dumped.
1885 If you don't want to dump all shared memory segments attached to pid 1234,
1886 write 0x31 to the process's proc file::
1888 $ echo 0x31 > /proc/1234/coredump_filter
1890 When a new process is created, the process inherits the bitmask status from its
1891 parent. It is useful to set up coredump_filter before the program runs.
1892 For example::
1894 $ echo 0x7 > /proc/self/coredump_filter
1895 $ ./some_program
1897 3.5 /proc/<pid>/mountinfo - Information about mounts
1898 --------------------------------------------------------
1900 This file contains lines of the form::
1902 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1903 (1)(2)(3) (4) (5) (6) (n…m) (m+1)(m+2) (m+3) (m+4)
1905 (1) mount ID: unique identifier of the mount (may be reused after umount)
1906 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1907 (3) major:minor: value of st_dev for files on filesystem
1908 (4) root: root of the mount within the filesystem
1909 (5) mount point: mount point relative to the process's root
1910 (6) mount options: per mount options
1911 (n…m) optional fields: zero or more fields of the form "tag[:value]"
1912 (m+1) separator: marks the end of the optional fields
1913 (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
1914 (m+3) mount source: filesystem specific information or "none"
1915 (m+4) super options: per super block options
1917 Parsers should ignore all unrecognised optional fields. Currently the
1918 possible optional fields are:
1920 ================ ==============================================================
1921 shared:X mount is shared in peer group X
1922 master:X mount is slave to peer group X
1923 propagate_from:X mount is slave and receives propagation from peer group X [#]_
1924 unbindable mount is unbindable
1925 ================ ==============================================================
1927 .. [#] X is the closest dominant peer group under the process's root. If
1928 X is the immediate master of the mount, or if there's no dominant peer
1929 group under the same root, then only the "master:X" field is present
1930 and not the "propagate_from:X" field.
1932 For more information on mount propagation see:
1934 Documentation/filesystems/sharedsubtree.rst
1937 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1938 --------------------------------------------------------
1939 These files provide a method to access a task's comm value. It also allows for
1940 a task to set its own or one of its thread siblings comm value. The comm value
1941 is limited in size compared to the cmdline value, so writing anything longer
1942 then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL
1943 terminator) will result in a truncated comm value.
1946 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1947 -------------------------------------------------------------------------
1948 This file provides a fast way to retrieve first level children pids
1949 of a task pointed by <pid>/<tid> pair. The format is a space separated
1950 stream of pids.
1952 Note the "first level" here -- if a child has its own children they will
1953 not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1954 to obtain the descendants.
1956 Since this interface is intended to be fast and cheap it doesn't
1957 guarantee to provide precise results and some children might be
1958 skipped, especially if they've exited right after we printed their
1959 pids, so one needs to either stop or freeze processes being inspected
1960 if precise results are needed.
1963 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1964 ---------------------------------------------------------------
1965 This file provides information associated with an opened file. The regular
1966 files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
1967 The 'pos' represents the current offset of the opened file in decimal
1968 form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
1969 file has been created with [see open(2) for details] and 'mnt_id' represents
1970 mount ID of the file system containing the opened file [see 3.5
1971 /proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
1972 the file.
1974 A typical output is::
1976 pos: 0
1977 flags: 0100002
1978 mnt_id: 19
1979 ino: 63107
1981 All locks associated with a file descriptor are shown in its fdinfo too::
1983 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1985 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1986 pair provide additional information particular to the objects they represent.
1988 Eventfd files
1989 ~~~~~~~~~~~~~
1991 ::
1993 pos: 0
1994 flags: 04002
1995 mnt_id: 9
1996 ino: 63107
1997 eventfd-count: 5a
1999 where 'eventfd-count' is hex value of a counter.
2001 Signalfd files
2002 ~~~~~~~~~~~~~~
2004 ::
2006 pos: 0
2007 flags: 04002
2008 mnt_id: 9
2009 ino: 63107
2010 sigmask: 0000000000000200
2012 where 'sigmask' is hex value of the signal mask associated
2013 with a file.
2015 Epoll files
2016 ~~~~~~~~~~~
2018 ::
2020 pos: 0
2021 flags: 02
2022 mnt_id: 9
2023 ino: 63107
2024 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
2026 where 'tfd' is a target file descriptor number in decimal form,
2027 'events' is events mask being watched and the 'data' is data
2028 associated with a target [see epoll(7) for more details].
2030 The 'pos' is current offset of the target file in decimal form
2031 [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
2032 where target file resides, all in hex format.
2034 Fsnotify files
2035 ~~~~~~~~~~~~~~
2036 For inotify files the format is the following::
2038 pos: 0
2039 flags: 02000000
2040 mnt_id: 9
2041 ino: 63107
2042 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
2044 where 'wd' is a watch descriptor in decimal form, i.e. a target file
2045 descriptor number, 'ino' and 'sdev' are inode and device where the
2046 target file resides and the 'mask' is the mask of events, all in hex
2047 form [see inotify(7) for more details].
2049 If the kernel was built with exportfs support, the path to the target
2050 file is encoded as a file handle. The file handle is provided by three
2051 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
2052 format.
2054 If the kernel is built without exportfs support the file handle won't be
2055 printed out.
2057 If there is no inotify mark attached yet the 'inotify' line will be omitted.
2059 For fanotify files the format is::
2061 pos: 0
2062 flags: 02
2063 mnt_id: 9
2064 ino: 63107
2065 fanotify flags:10 event-flags:0
2066 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
2067 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
2069 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2070 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
2071 flags associated with mark which are tracked separately from events
2072 mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2073 mask and 'ignored_mask' is the mask of events which are to be ignored.
2074 All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2075 provide information about flags and mask used in fanotify_mark
2076 call [see fsnotify manpage for details].
2078 While the first three lines are mandatory and always printed, the rest is
2079 optional and may be omitted if no marks created yet.
2081 Timerfd files
2082 ~~~~~~~~~~~~~
2084 ::
2086 pos: 0
2087 flags: 02
2088 mnt_id: 9
2089 ino: 63107
2090 clockid: 0
2091 ticks: 0
2092 settime flags: 01
2093 it_value: (0, 49406829)
2094 it_interval: (1, 0)
2096 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2097 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2098 flags in octal form been used to setup the timer [see timerfd_settime(2) for
2099 details]. 'it_value' is remaining time until the timer expiration.
2100 'it_interval' is the interval for the timer. Note the timer might be set up
2101 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2102 still exhibits timer's remaining time.
2104 DMA Buffer files
2105 ~~~~~~~~~~~~~~~~
2107 ::
2109 pos: 0
2110 flags: 04002
2111 mnt_id: 9
2112 ino: 63107
2113 size: 32768
2114 count: 2
2115 exp_name: system-heap
2117 where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
2118 the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
2120 3.9 /proc/<pid>/map_files - Information about memory mapped files
2121 ---------------------------------------------------------------------
2122 This directory contains symbolic links which represent memory mapped files
2123 the process is maintaining. Example output::
2125 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2126 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2127 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2128 | ...
2129 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2130 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2132 The name of a link represents the virtual memory bounds of a mapping, i.e.
2133 vm_area_struct::vm_start-vm_area_struct::vm_end.
2135 The main purpose of the map_files is to retrieve a set of memory mapped
2136 files in a fast way instead of parsing /proc/<pid>/maps or
2137 /proc/<pid>/smaps, both of which contain many more records. At the same
2138 time one can open(2) mappings from the listings of two processes and
2139 comparing their inode numbers to figure out which anonymous memory areas
2140 are actually shared.
2142 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
2143 ---------------------------------------------------------
2144 This file provides the value of the task's timerslack value in nanoseconds.
2145 This value specifies an amount of time that normal timers may be deferred
2146 in order to coalesce timers and avoid unnecessary wakeups.
2148 This allows a task's interactivity vs power consumption tradeoff to be
2149 adjusted.
2151 Writing 0 to the file will set the task's timerslack to the default value.
2153 Valid values are from 0 - ULLONG_MAX
2155 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2156 permissions on the task specified to change its timerslack_ns value.
2158 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
2159 -----------------------------------------------------------------
2160 When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2161 patch state for the task.
2163 A value of '-1' indicates that no patch is in transition.
2165 A value of '0' indicates that a patch is in transition and the task is
2166 unpatched. If the patch is being enabled, then the task hasn't been
2167 patched yet. If the patch is being disabled, then the task has already
2168 been unpatched.
2170 A value of '1' indicates that a patch is in transition and the task is
2171 patched. If the patch is being enabled, then the task has already been
2172 patched. If the patch is being disabled, then the task hasn't been
2173 unpatched yet.
2175 3.12 /proc/<pid>/arch_status - task architecture specific status
2176 -------------------------------------------------------------------
2177 When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2178 architecture specific status of the task.
2180 Example
2181 ~~~~~~~
2183 ::
2185 $ cat /proc/6753/arch_status
2186 AVX512_elapsed_ms: 8
2188 Description
2189 ~~~~~~~~~~~
2191 x86 specific entries
2192 ~~~~~~~~~~~~~~~~~~~~~
2194 AVX512_elapsed_ms
2195 ^^^^^^^^^^^^^^^^^^
2197 If AVX512 is supported on the machine, this entry shows the milliseconds
2198 elapsed since the last time AVX512 usage was recorded. The recording
2199 happens on a best effort basis when a task is scheduled out. This means
2200 that the value depends on two factors:
2202 1) The time which the task spent on the CPU without being scheduled
2203 out. With CPU isolation and a single runnable task this can take
2204 several seconds.
2206 2) The time since the task was scheduled out last. Depending on the
2207 reason for being scheduled out (time slice exhausted, syscall ...)
2208 this can be arbitrary long time.
2210 As a consequence the value cannot be considered precise and authoritative
2211 information. The application which uses this information has to be aware
2212 of the overall scenario on the system in order to determine whether a
2213 task is a real AVX512 user or not. Precise information can be obtained
2214 with performance counters.
2216 A special value of '-1' indicates that no AVX512 usage was recorded, thus
2217 the task is unlikely an AVX512 user, but depends on the workload and the
2218 scheduling scenario, it also could be a false negative mentioned above.
2220 3.13 /proc/<pid>/fd - List of symlinks to open files
2221 -------------------------------------------------------
2222 This directory contains symbolic links which represent open files
2223 the process is maintaining. Example output::
2225 lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null
2226 l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null
2227 lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]'
2228 lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]'
2229 lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]'
2231 The number of open files for the process is stored in 'size' member
2232 of stat() output for /proc/<pid>/fd for fast access.
2233 -------------------------------------------------------
2236 Chapter 4: Configuring procfs
2237 =============================
2239 4.1 Mount options
2240 ---------------------
2242 The following mount options are supported:
2244 ========= ========================================================
2245 hidepid= Set /proc/<pid>/ access mode.
2246 gid= Set the group authorized to learn processes information.
2247 subset= Show only the specified subset of procfs.
2248 ========= ========================================================
2250 hidepid=off or hidepid=0 means classic mode - everybody may access all
2251 /proc/<pid>/ directories (default).
2253 hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2254 directories but their own. Sensitive files like cmdline, sched*, status are now
2255 protected against other users. This makes it impossible to learn whether any
2256 user runs specific program (given the program doesn't reveal itself by its
2257 behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2258 other users, poorly written programs passing sensitive information via program
2259 arguments are now protected against local eavesdroppers.
2261 hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2262 fully invisible to other users. It doesn't mean that it hides a fact whether a
2263 process with a specific pid value exists (it can be learned by other means, e.g.
2264 by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2265 stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of
2266 gathering information about running processes, whether some daemon runs with
2267 elevated privileges, whether other user runs some sensitive program, whether
2268 other users run any program at all, etc.
2270 hidepid=ptraceable or hidepid=4 means that procfs should only contain
2271 /proc/<pid>/ directories that the caller can ptrace.
2273 gid= defines a group authorized to learn processes information otherwise
2274 prohibited by hidepid=. If you use some daemon like identd which needs to learn
2275 information about processes information, just add identd to this group.
2277 subset=pid hides all top level files and directories in the procfs that
2278 are not related to tasks.
2280 Chapter 5: Filesystem behavior
2281 ==============================
2283 Originally, before the advent of pid namespace, procfs was a global file
2284 system. It means that there was only one procfs instance in the system.
2286 When pid namespace was added, a separate procfs instance was mounted in
2287 each pid namespace. So, procfs mount options are global among all
2288 mountpoints within the same namespace::
2290 # grep ^proc /proc/mounts
2291 proc /proc proc rw,relatime,hidepid=2 0 0
2293 # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2294 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2295 +++ exited with 0 +++
2297 # grep ^proc /proc/mounts
2298 proc /proc proc rw,relatime,hidepid=2 0 0
2299 proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2301 and only after remounting procfs mount options will change at all
2302 mountpoints::
2304 # mount -o remount,hidepid=1 -t proc proc /tmp/proc
2306 # grep ^proc /proc/mounts
2307 proc /proc proc rw,relatime,hidepid=1 0 0
2308 proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2310 This behavior is different from the behavior of other filesystems.
2312 The new procfs behavior is more like other filesystems. Each procfs mount
2313 creates a new procfs instance. Mount options affect own procfs instance.
2314 It means that it became possible to have several procfs instances
2315 displaying tasks with different filtering options in one pid namespace::
2317 # mount -o hidepid=invisible -t proc proc /proc
2318 # mount -o hidepid=noaccess -t proc proc /tmp/proc
2319 # grep ^proc /proc/mounts
2320 proc /proc proc rw,relatime,hidepid=invisible 0 0
2321 proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0