1.. SPDX-License-Identifier: GPL-2.0 2 3==================== 4The /proc Filesystem 5==================== 6 7===================== ======================================= ================ 8/proc/sys Terrehon Bowden <terrehon@pacbell.net>, October 7 1999 9 Bodo Bauer <bb@ricochet.net> 102.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000 11move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009 12fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009 13===================== ======================================= ================ 14 15 16 17.. Table of Contents 18 19 0 Preface 20 0.1 Introduction/Credits 21 0.2 Legal Stuff 22 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 33 34 2 Modifying System Parameters 35 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 51 52 4 Configuring procfs 53 4.1 Mount options 54 55 5 Filesystem behavior 56 57Preface 58======= 59 600.1 Introduction/Credits 61------------------------ 62 63This documentation is part of a soon (or so we hope) to be released book on 64the 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 66chapters, it seems only fair to give the work back to the Linux community. 67This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm 68afraid it's still far from complete, but we hope it will be useful. As far as 69we know, it is the first 'all-in-one' document about the /proc file system. It 70is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, 71SPARC, AXP, etc., features, you probably won't find what you are looking for. 72It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But 73additions and patches are welcome and will be added to this document if you 74mail them to Bodo. 75 76We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of 77other people for help compiling this documentation. We'd also like to extend a 78special thank you to Andi Kleen for documentation, which we relied on heavily 79to create this document, as well as the additional information he provided. 80Thanks to everybody else who contributed source or docs to the Linux kernel 81and helped create a great piece of software... :) 82 83If you have any comments, corrections or additions, please don't hesitate to 84contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this 85document. 86 87The latest version of this document is available online at 88http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html 89 90If the above direction does not works for you, you could try the kernel 91mailing list at linux-kernel@vger.kernel.org and/or try to reach me at 92comandante@zaralinux.com. 93 940.2 Legal Stuff 95--------------- 96 97We don't guarantee the correctness of this document, and if you come to us 98complaining about how you screwed up your system because of incorrect 99documentation, we won't feel responsible... 100 101Chapter 1: Collecting System Information 102======================================== 103 104In 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 111 112------------------------------------------------------------------------------ 113 114The proc file system acts as an interface to internal data structures in the 115kernel. It can be used to obtain information about the system and to change 116certain kernel parameters at runtime (sysctl). 117 118First, we'll take a look at the read-only parts of /proc. In Chapter 2, we 119show you how you can use /proc/sys to change settings. 120 1211.1 Process-Specific Subdirectories 122----------------------------------- 123 124The directory /proc contains (among other things) one subdirectory for each 125process running on the system, which is named after the process ID (PID). 126 127The link 'self' points to the process reading the file system. Each process 128subdirectory has the entries listed in Table 1-1. 129 130Note that an open file descriptor to /proc/<pid> or to any of its 131contained files or subdirectories does not prevent <pid> being reused 132for some other process in the event that <pid> exits. Operations on 133open /proc/<pid> file descriptors corresponding to dead processes 134never act on any new process that the kernel may, through chance, have 135also assigned the process ID <pid>. Instead, operations on these FDs 136usually fail with ESRCH. 137 138.. table:: Table 1-1: Process specific entries in /proc 139 140 ============= =============================================================== 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 ============= =============================================================== 167 168For example, to get the status information of a process, all you have to do is 169read the file /proc/PID/status:: 170 171 >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 VmPeak: 5004 kB 183 VmSize: 5004 kB 184 VmLck: 0 kB 185 VmHWM: 476 kB 186 VmRSS: 476 kB 187 RssAnon: 352 kB 188 RssFile: 120 kB 189 RssShmem: 4 kB 190 VmData: 156 kB 191 VmStk: 88 kB 192 VmExe: 68 kB 193 VmLib: 1412 kB 194 VmPTE: 20 kb 195 VmSwap: 0 kB 196 HugetlbPages: 0 kB 197 CoreDumping: 0 198 THP_enabled: 1 199 Threads: 1 200 SigQ: 0/28578 201 SigPnd: 0000000000000000 202 ShdPnd: 0000000000000000 203 SigBlk: 0000000000000000 204 SigIgn: 0000000000000000 205 SigCgt: 0000000000000000 206 CapInh: 00000000fffffeff 207 CapPrm: 0000000000000000 208 CapEff: 0000000000000000 209 CapBnd: ffffffffffffffff 210 CapAmb: 0000000000000000 211 NoNewPrivs: 0 212 Seccomp: 0 213 Speculation_Store_Bypass: thread vulnerable 214 SpeculationIndirectBranch: conditional enabled 215 voluntary_ctxt_switches: 0 216 nonvoluntary_ctxt_switches: 1 217 218This shows you nearly the same information you would get if you viewed it with 219the ps command. In fact, ps uses the proc file system to obtain its 220information. But you get a more detailed view of the process by reading the 221file /proc/PID/status. It fields are described in table 1-2. 222 223The statm file contains more detailed information about the process 224memory usage. Its seven fields are explained in Table 1-3. The stat file 225contains detailed information about the process itself. Its fields are 226explained in Table 1-4. 227 228(for SMP CONFIG users) 229 230For making accounting scalable, RSS related information are handled in an 231asynchronous manner and the value may not be very precise. To see a precise 232snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table. 233It's slow but very precise. 234 235.. table:: Table 1-2: Contents of the status files (as of 4.19) 236 237 ========================== =================================================== 238 Field Content 239 ========================== =================================================== 240 Name filename of the executable 241 Umask file mode creation mask 242 State state (R is running, S is sleeping, D is sleeping 243 in an uninterruptible wait, Z is zombie, 244 T is traced or stopped) 245 Tgid thread group ID 246 Ngid NUMA group ID (0 if none) 247 Pid process id 248 PPid process id of the parent process 249 TracerPid PID of process tracing this process (0 if not, or 250 the tracer is outside of the current pid namespace) 251 Uid Real, effective, saved set, and file system UIDs 252 Gid Real, effective, saved set, and file system GIDs 253 FDSize number of file descriptor slots currently allocated 254 Groups supplementary group list 255 NStgid descendant namespace thread group ID hierarchy 256 NSpid descendant namespace process ID hierarchy 257 NSpgid descendant namespace process group ID hierarchy 258 NSsid descendant namespace session ID hierarchy 259 VmPeak peak virtual memory size 260 VmSize total program size 261 VmLck locked memory size 262 VmPin pinned memory size 263 VmHWM peak resident set size ("high water mark") 264 VmRSS size of memory portions. It contains the three 265 following parts 266 (VmRSS = RssAnon + RssFile + RssShmem) 267 RssAnon size of resident anonymous memory 268 RssFile size of resident file mappings 269 RssShmem size of resident shmem memory (includes SysV shm, 270 mapping of tmpfs and shared anonymous mappings) 271 VmData size of private data segments 272 VmStk size of stack segments 273 VmExe size of text segment 274 VmLib size of shared library code 275 VmPTE size of page table entries 276 VmSwap amount of swap used by anonymous private data 277 (shmem swap usage is not included) 278 HugetlbPages size of hugetlb memory portions 279 CoreDumping process's memory is currently being dumped 280 (killing the process may lead to a corrupted core) 281 THP_enabled process is allowed to use THP (returns 0 when 282 PR_SET_THP_DISABLE is set on the process 283 Threads number of threads 284 SigQ number of signals queued/max. number for queue 285 SigPnd bitmap of pending signals for the thread 286 ShdPnd bitmap of shared pending signals for the process 287 SigBlk bitmap of blocked signals 288 SigIgn bitmap of ignored signals 289 SigCgt bitmap of caught signals 290 CapInh bitmap of inheritable capabilities 291 CapPrm bitmap of permitted capabilities 292 CapEff bitmap of effective capabilities 293 CapBnd bitmap of capabilities bounding set 294 CapAmb bitmap of ambient capabilities 295 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...) 296 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...) 297 Speculation_Store_Bypass speculative store bypass mitigation status 298 SpeculationIndirectBranch indirect branch speculation mode 299 Cpus_allowed mask of CPUs on which this process may run 300 Cpus_allowed_list Same as previous, but in "list format" 301 Mems_allowed mask of memory nodes allowed to this process 302 Mems_allowed_list Same as previous, but in "list format" 303 voluntary_ctxt_switches number of voluntary context switches 304 nonvoluntary_ctxt_switches number of non voluntary context switches 305 ========================== =================================================== 306 307 308.. table:: Table 1-3: Contents of the statm files (as of 2.6.8-rc3) 309 310 ======== =============================== ============================== 311 Field Content 312 ======== =============================== ============================== 313 size total program size (pages) (same as VmSize in status) 314 resident size of memory portions (pages) (same as VmRSS in status) 315 shared number of pages that are shared (i.e. backed by a file, same 316 as RssFile+RssShmem in status) 317 trs number of pages that are 'code' (not including libs; broken, 318 includes data segment) 319 lrs number of pages of library (always 0 on 2.6) 320 drs number of pages of data/stack (including libs; broken, 321 includes library text) 322 dt number of dirty pages (always 0 on 2.6) 323 ======== =============================== ============================== 324 325 326.. table:: Table 1-4: Contents of the stat files (as of 2.6.30-rc7) 327 328 ============= =============================================================== 329 Field Content 330 ============= =============================================================== 331 pid process id 332 tcomm filename of the executable 333 state state (R is running, S is sleeping, D is sleeping in an 334 uninterruptible wait, Z is zombie, T is traced or stopped) 335 ppid process id of the parent process 336 pgrp pgrp of the process 337 sid session id 338 tty_nr tty the process uses 339 tty_pgrp pgrp of the tty 340 flags task flags 341 min_flt number of minor faults 342 cmin_flt number of minor faults with child's 343 maj_flt number of major faults 344 cmaj_flt number of major faults with child's 345 utime user mode jiffies 346 stime kernel mode jiffies 347 cutime user mode jiffies with child's 348 cstime kernel mode jiffies with child's 349 priority priority level 350 nice nice level 351 num_threads number of threads 352 it_real_value (obsolete, always 0) 353 start_time time the process started after system boot 354 vsize virtual memory size 355 rss resident set memory size 356 rsslim current limit in bytes on the rss 357 start_code address above which program text can run 358 end_code address below which program text can run 359 start_stack address of the start of the main process stack 360 esp current value of ESP 361 eip current value of EIP 362 pending bitmap of pending signals 363 blocked bitmap of blocked signals 364 sigign bitmap of ignored signals 365 sigcatch bitmap of caught signals 366 0 (place holder, used to be the wchan address, 367 use /proc/PID/wchan instead) 368 0 (place holder) 369 0 (place holder) 370 exit_signal signal to send to parent thread on exit 371 task_cpu which CPU the task is scheduled on 372 rt_priority realtime priority 373 policy scheduling policy (man sched_setscheduler) 374 blkio_ticks time spent waiting for block IO 375 gtime guest time of the task in jiffies 376 cgtime guest time of the task children in jiffies 377 start_data address above which program data+bss is placed 378 end_data address below which program data+bss is placed 379 start_brk address above which program heap can be expanded with brk() 380 arg_start address above which program command line is placed 381 arg_end address below which program command line is placed 382 env_start address above which program environment is placed 383 env_end address below which program environment is placed 384 exit_code the thread's exit_code in the form reported by the waitpid 385 system call 386 ============= =============================================================== 387 388The /proc/PID/maps file contains the currently mapped memory regions and 389their access permissions. 390 391The format is:: 392 393 address perms offset dev inode pathname 394 395 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test 396 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test 397 0804a000-0806b000 rw-p 00000000 00:00 0 [heap] 398 a7cb1000-a7cb2000 ---p 00000000 00:00 0 399 a7cb2000-a7eb2000 rw-p 00000000 00:00 0 400 a7eb2000-a7eb3000 ---p 00000000 00:00 0 401 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 402 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 403 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 404 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 405 a800b000-a800e000 rw-p 00000000 00:00 0 406 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 407 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 408 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 409 a8024000-a8027000 rw-p 00000000 00:00 0 410 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 411 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 412 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 413 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack] 414 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] 415 416where "address" is the address space in the process that it occupies, "perms" 417is a set of permissions:: 418 419 r = read 420 w = write 421 x = execute 422 s = shared 423 p = private (copy on write) 424 425"offset" is the offset into the mapping, "dev" is the device (major:minor), and 426"inode" is the inode on that device. 0 indicates that no inode is associated 427with the memory region, as the case would be with BSS (uninitialized data). 428The "pathname" shows the name associated file for this mapping. If the mapping 429is not associated with a file: 430 431 =================== =========================================== 432 [heap] the heap of the program 433 [stack] the stack of the main process 434 [vdso] the "virtual dynamic shared object", 435 the kernel system call handler 436 [anon:<name>] a private anonymous mapping that has been 437 named by userspace 438 [anon_shmem:<name>] an anonymous shared memory mapping that has 439 been named by userspace 440 =================== =========================================== 441 442 or if empty, the mapping is anonymous. 443 444The /proc/PID/smaps is an extension based on maps, showing the memory 445consumption for each of the process's mappings. For each mapping (aka Virtual 446Memory Area, or VMA) there is a series of lines such as the following:: 447 448 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash 449 450 Size: 1084 kB 451 KernelPageSize: 4 kB 452 MMUPageSize: 4 kB 453 Rss: 892 kB 454 Pss: 374 kB 455 Pss_Dirty: 0 kB 456 Shared_Clean: 892 kB 457 Shared_Dirty: 0 kB 458 Private_Clean: 0 kB 459 Private_Dirty: 0 kB 460 Referenced: 892 kB 461 Anonymous: 0 kB 462 LazyFree: 0 kB 463 AnonHugePages: 0 kB 464 ShmemPmdMapped: 0 kB 465 Shared_Hugetlb: 0 kB 466 Private_Hugetlb: 0 kB 467 Swap: 0 kB 468 SwapPss: 0 kB 469 KernelPageSize: 4 kB 470 MMUPageSize: 4 kB 471 Locked: 0 kB 472 THPeligible: 0 473 VmFlags: rd ex mr mw me dw 474 475The first of these lines shows the same information as is displayed for the 476mapping in /proc/PID/maps. Following lines show the size of the mapping 477(size); the size of each page allocated when backing a VMA (KernelPageSize), 478which is usually the same as the size in the page table entries; the page size 479used by the MMU when backing a VMA (in most cases, the same as KernelPageSize); 480the amount of the mapping that is currently resident in RAM (RSS); the 481process' proportional share of this mapping (PSS); and the number of clean and 482dirty shared and private pages in the mapping. 483 484The "proportional set size" (PSS) of a process is the count of pages it has 485in memory, where each page is divided by the number of processes sharing it. 486So if a process has 1000 pages all to itself, and 1000 shared with one other 487process, its PSS will be 1500. "Pss_Dirty" is the portion of PSS which 488consists of dirty pages. ("Pss_Clean" is not included, but it can be 489calculated by subtracting "Pss_Dirty" from "Pss".) 490 491Note that even a page which is part of a MAP_SHARED mapping, but has only 492a single pte mapped, i.e. is currently used by only one process, is accounted 493as private and not as shared. 494 495"Referenced" indicates the amount of memory currently marked as referenced or 496accessed. 497 498"Anonymous" shows the amount of memory that does not belong to any file. Even 499a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE 500and a page is modified, the file page is replaced by a private anonymous copy. 501 502"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE). 503The memory isn't freed immediately with madvise(). It's freed in memory 504pressure if the memory is clean. Please note that the printed value might 505be lower than the real value due to optimizations used in the current 506implementation. If this is not desirable please file a bug report. 507 508"AnonHugePages" shows the ammount of memory backed by transparent hugepage. 509 510"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by 511huge pages. 512 513"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by 514hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical 515reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field. 516 517"Swap" shows how much would-be-anonymous memory is also used, but out on swap. 518 519For shmem mappings, "Swap" includes also the size of the mapped (and not 520replaced by copy-on-write) part of the underlying shmem object out on swap. 521"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this 522does not take into account swapped out page of underlying shmem objects. 523"Locked" indicates whether the mapping is locked in memory or not. 524 525"THPeligible" indicates whether the mapping is eligible for allocating THP 526pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise. 527It just shows the current status. 528 529"VmFlags" field deserves a separate description. This member represents the 530kernel flags associated with the particular virtual memory area in two letter 531encoded manner. The codes are the following: 532 533 == ======================================= 534 rd readable 535 wr writeable 536 ex executable 537 sh shared 538 mr may read 539 mw may write 540 me may execute 541 ms may share 542 gd stack segment growns down 543 pf pure PFN range 544 dw disabled write to the mapped file 545 lo pages are locked in memory 546 io memory mapped I/O area 547 sr sequential read advise provided 548 rr random read advise provided 549 dc do not copy area on fork 550 de do not expand area on remapping 551 ac area is accountable 552 nr swap space is not reserved for the area 553 ht area uses huge tlb pages 554 sf synchronous page fault 555 ar architecture specific flag 556 wf wipe on fork 557 dd do not include area into core dump 558 sd soft dirty flag 559 mm mixed map area 560 hg huge page advise flag 561 nh no huge page advise flag 562 mg mergable advise flag 563 bt arm64 BTI guarded page 564 mt arm64 MTE allocation tags are enabled 565 um userfaultfd missing tracking 566 uw userfaultfd wr-protect tracking 567 == ======================================= 568 569Note that there is no guarantee that every flag and associated mnemonic will 570be present in all further kernel releases. Things get changed, the flags may 571be vanished or the reverse -- new added. Interpretation of their meaning 572might change in future as well. So each consumer of these flags has to 573follow each specific kernel version for the exact semantic. 574 575This file is only present if the CONFIG_MMU kernel configuration option is 576enabled. 577 578Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent 579output can be achieved only in the single read call). 580 581This typically manifests when doing partial reads of these files while the 582memory map is being modified. Despite the races, we do provide the following 583guarantees: 584 5851) The mapped addresses never go backwards, which implies no two 586 regions will ever overlap. 5872) If there is something at a given vaddr during the entirety of the 588 life of the smaps/maps walk, there will be some output for it. 589 590The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps, 591but their values are the sums of the corresponding values for all mappings of 592the process. Additionally, it contains these fields: 593 594- Pss_Anon 595- Pss_File 596- Pss_Shmem 597 598They represent the proportional shares of anonymous, file, and shmem pages, as 599described for smaps above. These fields are omitted in smaps since each 600mapping identifies the type (anon, file, or shmem) of all pages it contains. 601Thus all information in smaps_rollup can be derived from smaps, but at a 602significantly higher cost. 603 604The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG 605bits on both physical and virtual pages associated with a process, and the 606soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst 607for details). 608To clear the bits for all the pages associated with the process:: 609 610 > echo 1 > /proc/PID/clear_refs 611 612To clear the bits for the anonymous pages associated with the process:: 613 614 > echo 2 > /proc/PID/clear_refs 615 616To clear the bits for the file mapped pages associated with the process:: 617 618 > echo 3 > /proc/PID/clear_refs 619 620To clear the soft-dirty bit:: 621 622 > echo 4 > /proc/PID/clear_refs 623 624To reset the peak resident set size ("high water mark") to the process's 625current value:: 626 627 > echo 5 > /proc/PID/clear_refs 628 629Any other value written to /proc/PID/clear_refs will have no effect. 630 631The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags 632using /proc/kpageflags and number of times a page is mapped using 633/proc/kpagecount. For detailed explanation, see 634Documentation/admin-guide/mm/pagemap.rst. 635 636The /proc/pid/numa_maps is an extension based on maps, showing the memory 637locality and binding policy, as well as the memory usage (in pages) of 638each mapping. The output follows a general format where mapping details get 639summarized separated by blank spaces, one mapping per each file line:: 640 641 address policy mapping details 642 643 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4 644 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4 645 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4 646 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 647 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 648 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4 649 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4 650 320698b000 default file=/lib64/libc-2.12.so 651 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4 652 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 653 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4 654 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4 655 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4 656 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048 657 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4 658 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4 659 660Where: 661 662"address" is the starting address for the mapping; 663 664"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst); 665 666"mapping details" summarizes mapping data such as mapping type, page usage counters, 667node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page 668size, in KB, that is backing the mapping up. 669 6701.2 Kernel data 671--------------- 672 673Similar to the process entries, the kernel data files give information about 674the running kernel. The files used to obtain this information are contained in 675/proc and are listed in Table 1-5. Not all of these will be present in your 676system. It depends on the kernel configuration and the loaded modules, which 677files are there, and which are missing. 678 679.. table:: Table 1-5: Kernel info in /proc 680 681 ============ =============================================================== 682 File Content 683 ============ =============================================================== 684 apm Advanced power management info 685 buddyinfo Kernel memory allocator information (see text) (2.5) 686 bus Directory containing bus specific information 687 cmdline Kernel command line 688 cpuinfo Info about the CPU 689 devices Available devices (block and character) 690 dma Used DMS channels 691 filesystems Supported filesystems 692 driver Various drivers grouped here, currently rtc (2.4) 693 execdomains Execdomains, related to security (2.4) 694 fb Frame Buffer devices (2.4) 695 fs File system parameters, currently nfs/exports (2.4) 696 ide Directory containing info about the IDE subsystem 697 interrupts Interrupt usage 698 iomem Memory map (2.4) 699 ioports I/O port usage 700 irq Masks for irq to cpu affinity (2.4)(smp?) 701 isapnp ISA PnP (Plug&Play) Info (2.4) 702 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) 703 kmsg Kernel messages 704 ksyms Kernel symbol table 705 loadavg Load average of last 1, 5 & 15 minutes; 706 number of processes currently runnable (running or on ready queue); 707 total number of processes in system; 708 last pid created. 709 All fields are separated by one space except "number of 710 processes currently runnable" and "total number of processes 711 in system", which are separated by a slash ('/'). Example: 712 0.61 0.61 0.55 3/828 22084 713 locks Kernel locks 714 meminfo Memory info 715 misc Miscellaneous 716 modules List of loaded modules 717 mounts Mounted filesystems 718 net Networking info (see text) 719 pagetypeinfo Additional page allocator information (see text) (2.5) 720 partitions Table of partitions known to the system 721 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, 722 decoupled by lspci (2.4) 723 rtc Real time clock 724 scsi SCSI info (see text) 725 slabinfo Slab pool info 726 softirqs softirq usage 727 stat Overall statistics 728 swaps Swap space utilization 729 sys See chapter 2 730 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) 731 tty Info of tty drivers 732 uptime Wall clock since boot, combined idle time of all cpus 733 version Kernel version 734 video bttv info of video resources (2.4) 735 vmallocinfo Show vmalloced areas 736 ============ =============================================================== 737 738You can, for example, check which interrupts are currently in use and what 739they are used for by looking in the file /proc/interrupts:: 740 741 > cat /proc/interrupts 742 CPU0 743 0: 8728810 XT-PIC timer 744 1: 895 XT-PIC keyboard 745 2: 0 XT-PIC cascade 746 3: 531695 XT-PIC aha152x 747 4: 2014133 XT-PIC serial 748 5: 44401 XT-PIC pcnet_cs 749 8: 2 XT-PIC rtc 750 11: 8 XT-PIC i82365 751 12: 182918 XT-PIC PS/2 Mouse 752 13: 1 XT-PIC fpu 753 14: 1232265 XT-PIC ide0 754 15: 7 XT-PIC ide1 755 NMI: 0 756 757In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the 758output of a SMP machine):: 759 760 > cat /proc/interrupts 761 762 CPU0 CPU1 763 0: 1243498 1214548 IO-APIC-edge timer 764 1: 8949 8958 IO-APIC-edge keyboard 765 2: 0 0 XT-PIC cascade 766 5: 11286 10161 IO-APIC-edge soundblaster 767 8: 1 0 IO-APIC-edge rtc 768 9: 27422 27407 IO-APIC-edge 3c503 769 12: 113645 113873 IO-APIC-edge PS/2 Mouse 770 13: 0 0 XT-PIC fpu 771 14: 22491 24012 IO-APIC-edge ide0 772 15: 2183 2415 IO-APIC-edge ide1 773 17: 30564 30414 IO-APIC-level eth0 774 18: 177 164 IO-APIC-level bttv 775 NMI: 2457961 2457959 776 LOC: 2457882 2457881 777 ERR: 2155 778 779NMI is incremented in this case because every timer interrupt generates a NMI 780(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. 781 782LOC is the local interrupt counter of the internal APIC of every CPU. 783 784ERR is incremented in the case of errors in the IO-APIC bus (the bus that 785connects the CPUs in a SMP system. This means that an error has been detected, 786the IO-APIC automatically retry the transmission, so it should not be a big 787problem, but you should read the SMP-FAQ. 788 789In 2.6.2* /proc/interrupts was expanded again. This time the goal was for 790/proc/interrupts to display every IRQ vector in use by the system, not 791just those considered 'most important'. The new vectors are: 792 793THR 794 interrupt raised when a machine check threshold counter 795 (typically counting ECC corrected errors of memory or cache) exceeds 796 a configurable threshold. Only available on some systems. 797 798TRM 799 a thermal event interrupt occurs when a temperature threshold 800 has been exceeded for the CPU. This interrupt may also be generated 801 when the temperature drops back to normal. 802 803SPU 804 a spurious interrupt is some interrupt that was raised then lowered 805 by some IO device before it could be fully processed by the APIC. Hence 806 the APIC sees the interrupt but does not know what device it came from. 807 For this case the APIC will generate the interrupt with a IRQ vector 808 of 0xff. This might also be generated by chipset bugs. 809 810RES, CAL, TLB 811 rescheduling, call and TLB flush interrupts are 812 sent from one CPU to another per the needs of the OS. Typically, 813 their statistics are used by kernel developers and interested users to 814 determine the occurrence of interrupts of the given type. 815 816The above IRQ vectors are displayed only when relevant. For example, 817the threshold vector does not exist on x86_64 platforms. Others are 818suppressed when the system is a uniprocessor. As of this writing, only 819i386 and x86_64 platforms support the new IRQ vector displays. 820 821Of some interest is the introduction of the /proc/irq directory to 2.4. 822It could be used to set IRQ to CPU affinity. This means that you can "hook" an 823IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the 824irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and 825prof_cpu_mask. 826 827For example:: 828 829 > ls /proc/irq/ 830 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask 831 1 11 13 15 17 19 3 5 7 9 default_smp_affinity 832 > ls /proc/irq/0/ 833 smp_affinity 834 835smp_affinity is a bitmask, in which you can specify which CPUs can handle the 836IRQ. You can set it by doing:: 837 838 > echo 1 > /proc/irq/10/smp_affinity 839 840This means that only the first CPU will handle the IRQ, but you can also echo 8415 which means that only the first and third CPU can handle the IRQ. 842 843The contents of each smp_affinity file is the same by default:: 844 845 > cat /proc/irq/0/smp_affinity 846 ffffffff 847 848There is an alternate interface, smp_affinity_list which allows specifying 849a CPU range instead of a bitmask:: 850 851 > cat /proc/irq/0/smp_affinity_list 852 1024-1031 853 854The default_smp_affinity mask applies to all non-active IRQs, which are the 855IRQs which have not yet been allocated/activated, and hence which lack a 856/proc/irq/[0-9]* directory. 857 858The node file on an SMP system shows the node to which the device using the IRQ 859reports itself as being attached. This hardware locality information does not 860include information about any possible driver locality preference. 861 862prof_cpu_mask specifies which CPUs are to be profiled by the system wide 863profiler. Default value is ffffffff (all CPUs if there are only 32 of them). 864 865The way IRQs are routed is handled by the IO-APIC, and it's Round Robin 866between all the CPUs which are allowed to handle it. As usual the kernel has 867more info than you and does a better job than you, so the defaults are the 868best choice for almost everyone. [Note this applies only to those IO-APIC's 869that support "Round Robin" interrupt distribution.] 870 871There are three more important subdirectories in /proc: net, scsi, and sys. 872The general rule is that the contents, or even the existence of these 873directories, depend on your kernel configuration. If SCSI is not enabled, the 874directory scsi may not exist. The same is true with the net, which is there 875only when networking support is present in the running kernel. 876 877The slabinfo file gives information about memory usage at the slab level. 878Linux uses slab pools for memory management above page level in version 2.2. 879Commonly used objects have their own slab pool (such as network buffers, 880directory cache, and so on). 881 882:: 883 884 > cat /proc/buddyinfo 885 886 Node 0, zone DMA 0 4 5 4 4 3 ... 887 Node 0, zone Normal 1 0 0 1 101 8 ... 888 Node 0, zone HighMem 2 0 0 1 1 0 ... 889 890External fragmentation is a problem under some workloads, and buddyinfo is a 891useful tool for helping diagnose these problems. Buddyinfo will give you a 892clue as to how big an area you can safely allocate, or why a previous 893allocation failed. 894 895Each column represents the number of pages of a certain order which are 896available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 897ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 898available in ZONE_NORMAL, etc... 899 900More information relevant to external fragmentation can be found in 901pagetypeinfo:: 902 903 > cat /proc/pagetypeinfo 904 Page block order: 9 905 Pages per block: 512 906 907 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 908 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0 909 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0 910 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2 911 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0 912 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0 913 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9 914 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0 915 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452 916 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0 917 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0 918 919 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate 920 Node 0, zone DMA 2 0 5 1 0 921 Node 0, zone DMA32 41 6 967 2 0 922 923Fragmentation avoidance in the kernel works by grouping pages of different 924migrate types into the same contiguous regions of memory called page blocks. 925A page block is typically the size of the default hugepage size, e.g. 2MB on 926X86-64. By keeping pages grouped based on their ability to move, the kernel 927can reclaim pages within a page block to satisfy a high-order allocation. 928 929The pagetypinfo begins with information on the size of a page block. It 930then gives the same type of information as buddyinfo except broken down 931by migrate-type and finishes with details on how many page blocks of each 932type exist. 933 934If min_free_kbytes has been tuned correctly (recommendations made by hugeadm 935from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can 936make an estimate of the likely number of huge pages that can be allocated 937at a given point in time. All the "Movable" blocks should be allocatable 938unless memory has been mlock()'d. Some of the Reclaimable blocks should 939also be allocatable although a lot of filesystem metadata may have to be 940reclaimed to achieve this. 941 942 943meminfo 944~~~~~~~ 945 946Provides information about distribution and utilization of memory. This 947varies by architecture and compile options. Some of the counters reported 948here overlap. The memory reported by the non overlapping counters may not 949add up to the overall memory usage and the difference for some workloads 950can be substantial. In many cases there are other means to find out 951additional memory using subsystem specific interfaces, for instance 952/proc/net/sockstat for TCP memory allocations. 953 954Example output. You may not have all of these fields. 955 956:: 957 958 > cat /proc/meminfo 959 960 MemTotal: 32858820 kB 961 MemFree: 21001236 kB 962 MemAvailable: 27214312 kB 963 Buffers: 581092 kB 964 Cached: 5587612 kB 965 SwapCached: 0 kB 966 Active: 3237152 kB 967 Inactive: 7586256 kB 968 Active(anon): 94064 kB 969 Inactive(anon): 4570616 kB 970 Active(file): 3143088 kB 971 Inactive(file): 3015640 kB 972 Unevictable: 0 kB 973 Mlocked: 0 kB 974 SwapTotal: 0 kB 975 SwapFree: 0 kB 976 Zswap: 1904 kB 977 Zswapped: 7792 kB 978 Dirty: 12 kB 979 Writeback: 0 kB 980 AnonPages: 4654780 kB 981 Mapped: 266244 kB 982 Shmem: 9976 kB 983 KReclaimable: 517708 kB 984 Slab: 660044 kB 985 SReclaimable: 517708 kB 986 SUnreclaim: 142336 kB 987 KernelStack: 11168 kB 988 PageTables: 20540 kB 989 SecPageTables: 0 kB 990 NFS_Unstable: 0 kB 991 Bounce: 0 kB 992 WritebackTmp: 0 kB 993 CommitLimit: 16429408 kB 994 Committed_AS: 7715148 kB 995 VmallocTotal: 34359738367 kB 996 VmallocUsed: 40444 kB 997 VmallocChunk: 0 kB 998 Percpu: 29312 kB 999 EarlyMemtestBad: 0 kB 1000 HardwareCorrupted: 0 kB 1001 AnonHugePages: 4149248 kB 1002 ShmemHugePages: 0 kB 1003 ShmemPmdMapped: 0 kB 1004 FileHugePages: 0 kB 1005 FilePmdMapped: 0 kB 1006 CmaTotal: 0 kB 1007 CmaFree: 0 kB 1008 HugePages_Total: 0 1009 HugePages_Free: 0 1010 HugePages_Rsvd: 0 1011 HugePages_Surp: 0 1012 Hugepagesize: 2048 kB 1013 Hugetlb: 0 kB 1014 DirectMap4k: 401152 kB 1015 DirectMap2M: 10008576 kB 1016 DirectMap1G: 24117248 kB 1017 1018MemTotal 1019 Total usable RAM (i.e. physical RAM minus a few reserved 1020 bits and the kernel binary code) 1021MemFree 1022 Total free RAM. On highmem systems, the sum of LowFree+HighFree 1023MemAvailable 1024 An estimate of how much memory is available for starting new 1025 applications, without swapping. Calculated from MemFree, 1026 SReclaimable, the size of the file LRU lists, and the low 1027 watermarks in each zone. 1028 The estimate takes into account that the system needs some 1029 page cache to function well, and that not all reclaimable 1030 slab will be reclaimable, due to items being in use. The 1031 impact of those factors will vary from system to system. 1032Buffers 1033 Relatively temporary storage for raw disk blocks 1034 shouldn't get tremendously large (20MB or so) 1035Cached 1036 In-memory cache for files read from the disk (the 1037 pagecache) as well as tmpfs & shmem. 1038 Doesn't include SwapCached. 1039SwapCached 1040 Memory that once was swapped out, is swapped back in but 1041 still also is in the swapfile (if memory is needed it 1042 doesn't need to be swapped out AGAIN because it is already 1043 in the swapfile. This saves I/O) 1044Active 1045 Memory that has been used more recently and usually not 1046 reclaimed unless absolutely necessary. 1047Inactive 1048 Memory which has been less recently used. It is more 1049 eligible to be reclaimed for other purposes 1050Unevictable 1051 Memory allocated for userspace which cannot be reclaimed, such 1052 as mlocked pages, ramfs backing pages, secret memfd pages etc. 1053Mlocked 1054 Memory locked with mlock(). 1055HighTotal, HighFree 1056 Highmem is all memory above ~860MB of physical memory. 1057 Highmem areas are for use by userspace programs, or 1058 for the pagecache. The kernel must use tricks to access 1059 this memory, making it slower to access than lowmem. 1060LowTotal, LowFree 1061 Lowmem is memory which can be used for everything that 1062 highmem can be used for, but it is also available for the 1063 kernel's use for its own data structures. Among many 1064 other things, it is where everything from the Slab is 1065 allocated. Bad things happen when you're out of lowmem. 1066SwapTotal 1067 total amount of swap space available 1068SwapFree 1069 Memory which has been evicted from RAM, and is temporarily 1070 on the disk 1071Zswap 1072 Memory consumed by the zswap backend (compressed size) 1073Zswapped 1074 Amount of anonymous memory stored in zswap (original size) 1075Dirty 1076 Memory which is waiting to get written back to the disk 1077Writeback 1078 Memory which is actively being written back to the disk 1079AnonPages 1080 Non-file backed pages mapped into userspace page tables 1081Mapped 1082 files which have been mmaped, such as libraries 1083Shmem 1084 Total memory used by shared memory (shmem) and tmpfs 1085KReclaimable 1086 Kernel allocations that the kernel will attempt to reclaim 1087 under memory pressure. Includes SReclaimable (below), and other 1088 direct allocations with a shrinker. 1089Slab 1090 in-kernel data structures cache 1091SReclaimable 1092 Part of Slab, that might be reclaimed, such as caches 1093SUnreclaim 1094 Part of Slab, that cannot be reclaimed on memory pressure 1095KernelStack 1096 Memory consumed by the kernel stacks of all tasks 1097PageTables 1098 Memory consumed by userspace page tables 1099SecPageTables 1100 Memory consumed by secondary page tables, this currently 1101 currently includes KVM mmu allocations on x86 and arm64. 1102NFS_Unstable 1103 Always zero. Previous counted pages which had been written to 1104 the server, but has not been committed to stable storage. 1105Bounce 1106 Memory used for block device "bounce buffers" 1107WritebackTmp 1108 Memory used by FUSE for temporary writeback buffers 1109CommitLimit 1110 Based on the overcommit ratio ('vm.overcommit_ratio'), 1111 this is the total amount of memory currently available to 1112 be allocated on the system. This limit is only adhered to 1113 if strict overcommit accounting is enabled (mode 2 in 1114 'vm.overcommit_memory'). 1115 1116 The CommitLimit is calculated with the following formula:: 1117 1118 CommitLimit = ([total RAM pages] - [total huge TLB pages]) * 1119 overcommit_ratio / 100 + [total swap pages] 1120 1121 For example, on a system with 1G of physical RAM and 7G 1122 of swap with a `vm.overcommit_ratio` of 30 it would 1123 yield a CommitLimit of 7.3G. 1124 1125 For more details, see the memory overcommit documentation 1126 in mm/overcommit-accounting. 1127Committed_AS 1128 The amount of memory presently allocated on the system. 1129 The committed memory is a sum of all of the memory which 1130 has been allocated by processes, even if it has not been 1131 "used" by them as of yet. A process which malloc()'s 1G 1132 of memory, but only touches 300M of it will show up as 1133 using 1G. This 1G is memory which has been "committed" to 1134 by the VM and can be used at any time by the allocating 1135 application. With strict overcommit enabled on the system 1136 (mode 2 in 'vm.overcommit_memory'), allocations which would 1137 exceed the CommitLimit (detailed above) will not be permitted. 1138 This is useful if one needs to guarantee that processes will 1139 not fail due to lack of memory once that memory has been 1140 successfully allocated. 1141VmallocTotal 1142 total size of vmalloc virtual address space 1143VmallocUsed 1144 amount of vmalloc area which is used 1145VmallocChunk 1146 largest contiguous block of vmalloc area which is free 1147Percpu 1148 Memory allocated to the percpu allocator used to back percpu 1149 allocations. This stat excludes the cost of metadata. 1150EarlyMemtestBad 1151 The amount of RAM/memory in kB, that was identified as corrupted 1152 by early memtest. If memtest was not run, this field will not 1153 be displayed at all. Size is never rounded down to 0 kB. 1154 That means if 0 kB is reported, you can safely assume 1155 there was at least one pass of memtest and none of the passes 1156 found a single faulty byte of RAM. 1157HardwareCorrupted 1158 The amount of RAM/memory in KB, the kernel identifies as 1159 corrupted. 1160AnonHugePages 1161 Non-file backed huge pages mapped into userspace page tables 1162ShmemHugePages 1163 Memory used by shared memory (shmem) and tmpfs allocated 1164 with huge pages 1165ShmemPmdMapped 1166 Shared memory mapped into userspace with huge pages 1167FileHugePages 1168 Memory used for filesystem data (page cache) allocated 1169 with huge pages 1170FilePmdMapped 1171 Page cache mapped into userspace with huge pages 1172CmaTotal 1173 Memory reserved for the Contiguous Memory Allocator (CMA) 1174CmaFree 1175 Free remaining memory in the CMA reserves 1176HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb 1177 See Documentation/admin-guide/mm/hugetlbpage.rst. 1178DirectMap4k, DirectMap2M, DirectMap1G 1179 Breakdown of page table sizes used in the kernel's 1180 identity mapping of RAM 1181 1182vmallocinfo 1183~~~~~~~~~~~ 1184 1185Provides information about vmalloced/vmaped areas. One line per area, 1186containing the virtual address range of the area, size in bytes, 1187caller information of the creator, and optional information depending 1188on the kind of area: 1189 1190 ========== =================================================== 1191 pages=nr number of pages 1192 phys=addr if a physical address was specified 1193 ioremap I/O mapping (ioremap() and friends) 1194 vmalloc vmalloc() area 1195 vmap vmap()ed pages 1196 user VM_USERMAP area 1197 vpages buffer for pages pointers was vmalloced (huge area) 1198 N<node>=nr (Only on NUMA kernels) 1199 Number of pages allocated on memory node <node> 1200 ========== =================================================== 1201 1202:: 1203 1204 > cat /proc/vmallocinfo 1205 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... 1206 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 1207 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... 1208 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 1209 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... 1210 phys=7fee8000 ioremap 1211 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... 1212 phys=7fee7000 ioremap 1213 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 1214 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... 1215 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 1216 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... 1217 pages=2 vmalloc N1=2 1218 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... 1219 /0x130 [x_tables] pages=4 vmalloc N0=4 1220 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... 1221 pages=14 vmalloc N2=14 1222 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... 1223 pages=4 vmalloc N1=4 1224 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... 1225 pages=2 vmalloc N1=2 1226 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... 1227 pages=10 vmalloc N0=10 1228 1229 1230softirqs 1231~~~~~~~~ 1232 1233Provides counts of softirq handlers serviced since boot time, for each CPU. 1234 1235:: 1236 1237 > cat /proc/softirqs 1238 CPU0 CPU1 CPU2 CPU3 1239 HI: 0 0 0 0 1240 TIMER: 27166 27120 27097 27034 1241 NET_TX: 0 0 0 17 1242 NET_RX: 42 0 0 39 1243 BLOCK: 0 0 107 1121 1244 TASKLET: 0 0 0 290 1245 SCHED: 27035 26983 26971 26746 1246 HRTIMER: 0 0 0 0 1247 RCU: 1678 1769 2178 2250 1248 12491.3 Networking info in /proc/net 1250-------------------------------- 1251 1252The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the 1253additional values you get for IP version 6 if you configure the kernel to 1254support this. Table 1-9 lists the files and their meaning. 1255 1256 1257.. table:: Table 1-8: IPv6 info in /proc/net 1258 1259 ========== ===================================================== 1260 File Content 1261 ========== ===================================================== 1262 udp6 UDP sockets (IPv6) 1263 tcp6 TCP sockets (IPv6) 1264 raw6 Raw device statistics (IPv6) 1265 igmp6 IP multicast addresses, which this host joined (IPv6) 1266 if_inet6 List of IPv6 interface addresses 1267 ipv6_route Kernel routing table for IPv6 1268 rt6_stats Global IPv6 routing tables statistics 1269 sockstat6 Socket statistics (IPv6) 1270 snmp6 Snmp data (IPv6) 1271 ========== ===================================================== 1272 1273.. table:: Table 1-9: Network info in /proc/net 1274 1275 ============= ================================================================ 1276 File Content 1277 ============= ================================================================ 1278 arp Kernel ARP table 1279 dev network devices with statistics 1280 dev_mcast the Layer2 multicast groups a device is listening too 1281 (interface index, label, number of references, number of bound 1282 addresses). 1283 dev_stat network device status 1284 ip_fwchains Firewall chain linkage 1285 ip_fwnames Firewall chain names 1286 ip_masq Directory containing the masquerading tables 1287 ip_masquerade Major masquerading table 1288 netstat Network statistics 1289 raw raw device statistics 1290 route Kernel routing table 1291 rpc Directory containing rpc info 1292 rt_cache Routing cache 1293 snmp SNMP data 1294 sockstat Socket statistics 1295 softnet_stat Per-CPU incoming packets queues statistics of online CPUs 1296 tcp TCP sockets 1297 udp UDP sockets 1298 unix UNIX domain sockets 1299 wireless Wireless interface data (Wavelan etc) 1300 igmp IP multicast addresses, which this host joined 1301 psched Global packet scheduler parameters. 1302 netlink List of PF_NETLINK sockets 1303 ip_mr_vifs List of multicast virtual interfaces 1304 ip_mr_cache List of multicast routing cache 1305 ============= ================================================================ 1306 1307You can use this information to see which network devices are available in 1308your system and how much traffic was routed over those devices:: 1309 1310 > cat /proc/net/dev 1311 Inter-|Receive |[... 1312 face |bytes packets errs drop fifo frame compressed multicast|[... 1313 lo: 908188 5596 0 0 0 0 0 0 [... 1314 ppp0:15475140 20721 410 0 0 410 0 0 [... 1315 eth0: 614530 7085 0 0 0 0 0 1 [... 1316 1317 ...] Transmit 1318 ...] bytes packets errs drop fifo colls carrier compressed 1319 ...] 908188 5596 0 0 0 0 0 0 1320 ...] 1375103 17405 0 0 0 0 0 0 1321 ...] 1703981 5535 0 0 0 3 0 0 1322 1323In addition, each Channel Bond interface has its own directory. For 1324example, the bond0 device will have a directory called /proc/net/bond0/. 1325It will contain information that is specific to that bond, such as the 1326current slaves of the bond, the link status of the slaves, and how 1327many times the slaves link has failed. 1328 13291.4 SCSI info 1330------------- 1331 1332If you have a SCSI host adapter in your system, you'll find a subdirectory 1333named after the driver for this adapter in /proc/scsi. You'll also see a list 1334of all recognized SCSI devices in /proc/scsi:: 1335 1336 >cat /proc/scsi/scsi 1337 Attached devices: 1338 Host: scsi0 Channel: 00 Id: 00 Lun: 00 1339 Vendor: IBM Model: DGHS09U Rev: 03E0 1340 Type: Direct-Access ANSI SCSI revision: 03 1341 Host: scsi0 Channel: 00 Id: 06 Lun: 00 1342 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 1343 Type: CD-ROM ANSI SCSI revision: 02 1344 1345 1346The directory named after the driver has one file for each adapter found in 1347the system. These files contain information about the controller, including 1348the used IRQ and the IO address range. The amount of information shown is 1349dependent on the adapter you use. The example shows the output for an Adaptec 1350AHA-2940 SCSI adapter:: 1351 1352 > cat /proc/scsi/aic7xxx/0 1353 1354 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 1355 Compile Options: 1356 TCQ Enabled By Default : Disabled 1357 AIC7XXX_PROC_STATS : Disabled 1358 AIC7XXX_RESET_DELAY : 5 1359 Adapter Configuration: 1360 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 1361 Ultra Wide Controller 1362 PCI MMAPed I/O Base: 0xeb001000 1363 Adapter SEEPROM Config: SEEPROM found and used. 1364 Adaptec SCSI BIOS: Enabled 1365 IRQ: 10 1366 SCBs: Active 0, Max Active 2, 1367 Allocated 15, HW 16, Page 255 1368 Interrupts: 160328 1369 BIOS Control Word: 0x18b6 1370 Adapter Control Word: 0x005b 1371 Extended Translation: Enabled 1372 Disconnect Enable Flags: 0xffff 1373 Ultra Enable Flags: 0x0001 1374 Tag Queue Enable Flags: 0x0000 1375 Ordered Queue Tag Flags: 0x0000 1376 Default Tag Queue Depth: 8 1377 Tagged Queue By Device array for aic7xxx host instance 0: 1378 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 1379 Actual queue depth per device for aic7xxx host instance 0: 1380 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 1381 Statistics: 1382 (scsi0:0:0:0) 1383 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 1384 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 1385 Total transfers 160151 (74577 reads and 85574 writes) 1386 (scsi0:0:6:0) 1387 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 1388 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 1389 Total transfers 0 (0 reads and 0 writes) 1390 1391 13921.5 Parallel port info in /proc/parport 1393--------------------------------------- 1394 1395The directory /proc/parport contains information about the parallel ports of 1396your system. It has one subdirectory for each port, named after the port 1397number (0,1,2,...). 1398 1399These directories contain the four files shown in Table 1-10. 1400 1401 1402.. table:: Table 1-10: Files in /proc/parport 1403 1404 ========= ==================================================================== 1405 File Content 1406 ========= ==================================================================== 1407 autoprobe Any IEEE-1284 device ID information that has been acquired. 1408 devices list of the device drivers using that port. A + will appear by the 1409 name of the device currently using the port (it might not appear 1410 against any). 1411 hardware Parallel port's base address, IRQ line and DMA channel. 1412 irq IRQ that parport is using for that port. This is in a separate 1413 file to allow you to alter it by writing a new value in (IRQ 1414 number or none). 1415 ========= ==================================================================== 1416 14171.6 TTY info in /proc/tty 1418------------------------- 1419 1420Information about the available and actually used tty's can be found in the 1421directory /proc/tty. You'll find entries for drivers and line disciplines in 1422this directory, as shown in Table 1-11. 1423 1424 1425.. table:: Table 1-11: Files in /proc/tty 1426 1427 ============= ============================================== 1428 File Content 1429 ============= ============================================== 1430 drivers list of drivers and their usage 1431 ldiscs registered line disciplines 1432 driver/serial usage statistic and status of single tty lines 1433 ============= ============================================== 1434 1435To see which tty's are currently in use, you can simply look into the file 1436/proc/tty/drivers:: 1437 1438 > cat /proc/tty/drivers 1439 pty_slave /dev/pts 136 0-255 pty:slave 1440 pty_master /dev/ptm 128 0-255 pty:master 1441 pty_slave /dev/ttyp 3 0-255 pty:slave 1442 pty_master /dev/pty 2 0-255 pty:master 1443 serial /dev/cua 5 64-67 serial:callout 1444 serial /dev/ttyS 4 64-67 serial 1445 /dev/tty0 /dev/tty0 4 0 system:vtmaster 1446 /dev/ptmx /dev/ptmx 5 2 system 1447 /dev/console /dev/console 5 1 system:console 1448 /dev/tty /dev/tty 5 0 system:/dev/tty 1449 unknown /dev/tty 4 1-63 console 1450 1451 14521.7 Miscellaneous kernel statistics in /proc/stat 1453------------------------------------------------- 1454 1455Various pieces of information about kernel activity are available in the 1456/proc/stat file. All of the numbers reported in this file are aggregates 1457since the system first booted. For a quick look, simply cat the file:: 1458 1459 > cat /proc/stat 1460 cpu 2255 34 2290 22625563 6290 127 456 0 0 0 1461 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0 1462 cpu1 1123 0 849 11313845 2614 0 18 0 0 0 1463 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] 1464 ctxt 1990473 1465 btime 1062191376 1466 processes 2915 1467 procs_running 1 1468 procs_blocked 0 1469 softirq 183433 0 21755 12 39 1137 231 21459 2263 1470 1471The very first "cpu" line aggregates the numbers in all of the other "cpuN" 1472lines. These numbers identify the amount of time the CPU has spent performing 1473different kinds of work. Time units are in USER_HZ (typically hundredths of a 1474second). The meanings of the columns are as follows, from left to right: 1475 1476- user: normal processes executing in user mode 1477- nice: niced processes executing in user mode 1478- system: processes executing in kernel mode 1479- idle: twiddling thumbs 1480- iowait: In a word, iowait stands for waiting for I/O to complete. But there 1481 are several problems: 1482 1483 1. CPU will not wait for I/O to complete, iowait is the time that a task is 1484 waiting for I/O to complete. When CPU goes into idle state for 1485 outstanding task I/O, another task will be scheduled on this CPU. 1486 2. In a multi-core CPU, the task waiting for I/O to complete is not running 1487 on any CPU, so the iowait of each CPU is difficult to calculate. 1488 3. The value of iowait field in /proc/stat will decrease in certain 1489 conditions. 1490 1491 So, the iowait is not reliable by reading from /proc/stat. 1492- irq: servicing interrupts 1493- softirq: servicing softirqs 1494- steal: involuntary wait 1495- guest: running a normal guest 1496- guest_nice: running a niced guest 1497 1498The "intr" line gives counts of interrupts serviced since boot time, for each 1499of the possible system interrupts. The first column is the total of all 1500interrupts serviced including unnumbered architecture specific interrupts; 1501each subsequent column is the total for that particular numbered interrupt. 1502Unnumbered interrupts are not shown, only summed into the total. 1503 1504The "ctxt" line gives the total number of context switches across all CPUs. 1505 1506The "btime" line gives the time at which the system booted, in seconds since 1507the Unix epoch. 1508 1509The "processes" line gives the number of processes and threads created, which 1510includes (but is not limited to) those created by calls to the fork() and 1511clone() system calls. 1512 1513The "procs_running" line gives the total number of threads that are 1514running or ready to run (i.e., the total number of runnable threads). 1515 1516The "procs_blocked" line gives the number of processes currently blocked, 1517waiting for I/O to complete. 1518 1519The "softirq" line gives counts of softirqs serviced since boot time, for each 1520of the possible system softirqs. The first column is the total of all 1521softirqs serviced; each subsequent column is the total for that particular 1522softirq. 1523 1524 15251.8 Ext4 file system parameters 1526------------------------------- 1527 1528Information about mounted ext4 file systems can be found in 1529/proc/fs/ext4. Each mounted filesystem will have a directory in 1530/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or 1531/proc/fs/ext4/dm-0). The files in each per-device directory are shown 1532in Table 1-12, below. 1533 1534.. table:: Table 1-12: Files in /proc/fs/ext4/<devname> 1535 1536 ============== ========================================================== 1537 File Content 1538 mb_groups details of multiblock allocator buddy cache of free blocks 1539 ============== ========================================================== 1540 15411.9 /proc/consoles 1542------------------- 1543Shows registered system console lines. 1544 1545To see which character device lines are currently used for the system console 1546/dev/console, you may simply look into the file /proc/consoles:: 1547 1548 > cat /proc/consoles 1549 tty0 -WU (ECp) 4:7 1550 ttyS0 -W- (Ep) 4:64 1551 1552The columns are: 1553 1554+--------------------+-------------------------------------------------------+ 1555| device | name of the device | 1556+====================+=======================================================+ 1557| operations | * R = can do read operations | 1558| | * W = can do write operations | 1559| | * U = can do unblank | 1560+--------------------+-------------------------------------------------------+ 1561| flags | * E = it is enabled | 1562| | * C = it is preferred console | 1563| | * B = it is primary boot console | 1564| | * p = it is used for printk buffer | 1565| | * b = it is not a TTY but a Braille device | 1566| | * a = it is safe to use when cpu is offline | 1567+--------------------+-------------------------------------------------------+ 1568| major:minor | major and minor number of the device separated by a | 1569| | colon | 1570+--------------------+-------------------------------------------------------+ 1571 1572Summary 1573------- 1574 1575The /proc file system serves information about the running system. It not only 1576allows access to process data but also allows you to request the kernel status 1577by reading files in the hierarchy. 1578 1579The directory structure of /proc reflects the types of information and makes 1580it easy, if not obvious, where to look for specific data. 1581 1582Chapter 2: Modifying System Parameters 1583====================================== 1584 1585In This Chapter 1586--------------- 1587 1588* Modifying kernel parameters by writing into files found in /proc/sys 1589* Exploring the files which modify certain parameters 1590* Review of the /proc/sys file tree 1591 1592------------------------------------------------------------------------------ 1593 1594A very interesting part of /proc is the directory /proc/sys. This is not only 1595a source of information, it also allows you to change parameters within the 1596kernel. Be very careful when attempting this. You can optimize your system, 1597but you can also cause it to crash. Never alter kernel parameters on a 1598production system. Set up a development machine and test to make sure that 1599everything works the way you want it to. You may have no alternative but to 1600reboot the machine once an error has been made. 1601 1602To change a value, simply echo the new value into the file. 1603You need to be root to do this. You can create your own boot script 1604to perform this every time your system boots. 1605 1606The files in /proc/sys can be used to fine tune and monitor miscellaneous and 1607general things in the operation of the Linux kernel. Since some of the files 1608can inadvertently disrupt your system, it is advisable to read both 1609documentation and source before actually making adjustments. In any case, be 1610very careful when writing to any of these files. The entries in /proc may 1611change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt 1612review the kernel documentation in the directory /usr/src/linux/Documentation. 1613This chapter is heavily based on the documentation included in the pre 2.2 1614kernels, and became part of it in version 2.2.1 of the Linux kernel. 1615 1616Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these 1617entries. 1618 1619Summary 1620------- 1621 1622Certain aspects of kernel behavior can be modified at runtime, without the 1623need to recompile the kernel, or even to reboot the system. The files in the 1624/proc/sys tree can not only be read, but also modified. You can use the echo 1625command to write value into these files, thereby changing the default settings 1626of the kernel. 1627 1628 1629Chapter 3: Per-process Parameters 1630================================= 1631 16323.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score 1633-------------------------------------------------------------------------------- 1634 1635These files can be used to adjust the badness heuristic used to select which 1636process gets killed in out of memory (oom) conditions. 1637 1638The badness heuristic assigns a value to each candidate task ranging from 0 1639(never kill) to 1000 (always kill) to determine which process is targeted. The 1640units are roughly a proportion along that range of allowed memory the process 1641may allocate from based on an estimation of its current memory and swap use. 1642For example, if a task is using all allowed memory, its badness score will be 16431000. If it is using half of its allowed memory, its score will be 500. 1644 1645The amount of "allowed" memory depends on the context in which the oom killer 1646was called. If it is due to the memory assigned to the allocating task's cpuset 1647being exhausted, the allowed memory represents the set of mems assigned to that 1648cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed 1649memory represents the set of mempolicy nodes. If it is due to a memory 1650limit (or swap limit) being reached, the allowed memory is that configured 1651limit. Finally, if it is due to the entire system being out of memory, the 1652allowed memory represents all allocatable resources. 1653 1654The value of /proc/<pid>/oom_score_adj is added to the badness score before it 1655is used to determine which task to kill. Acceptable values range from -1000 1656(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to 1657polarize the preference for oom killing either by always preferring a certain 1658task or completely disabling it. The lowest possible value, -1000, is 1659equivalent to disabling oom killing entirely for that task since it will always 1660report a badness score of 0. 1661 1662Consequently, it is very simple for userspace to define the amount of memory to 1663consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for 1664example, is roughly equivalent to allowing the remainder of tasks sharing the 1665same system, cpuset, mempolicy, or memory controller resources to use at least 166650% more memory. A value of -500, on the other hand, would be roughly 1667equivalent to discounting 50% of the task's allowed memory from being considered 1668as scoring against the task. 1669 1670For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also 1671be used to tune the badness score. Its acceptable values range from -16 1672(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 1673(OOM_DISABLE) to disable oom killing entirely for that task. Its value is 1674scaled linearly with /proc/<pid>/oom_score_adj. 1675 1676The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last 1677value set by a CAP_SYS_RESOURCE process. To reduce the value any lower 1678requires CAP_SYS_RESOURCE. 1679 1680 16813.2 /proc/<pid>/oom_score - Display current oom-killer score 1682------------------------------------------------------------- 1683 1684This file can be used to check the current score used by the oom-killer for 1685any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which 1686process should be killed in an out-of-memory situation. 1687 1688Please note that the exported value includes oom_score_adj so it is 1689effectively in range [0,2000]. 1690 1691 16923.3 /proc/<pid>/io - Display the IO accounting fields 1693------------------------------------------------------- 1694 1695This file contains IO statistics for each running process. 1696 1697Example 1698~~~~~~~ 1699 1700:: 1701 1702 test:/tmp # dd if=/dev/zero of=/tmp/test.dat & 1703 [1] 3828 1704 1705 test:/tmp # cat /proc/3828/io 1706 rchar: 323934931 1707 wchar: 323929600 1708 syscr: 632687 1709 syscw: 632675 1710 read_bytes: 0 1711 write_bytes: 323932160 1712 cancelled_write_bytes: 0 1713 1714 1715Description 1716~~~~~~~~~~~ 1717 1718rchar 1719^^^^^ 1720 1721I/O counter: chars read 1722The number of bytes which this task has caused to be read from storage. This 1723is simply the sum of bytes which this process passed to read() and pread(). 1724It includes things like tty IO and it is unaffected by whether or not actual 1725physical disk IO was required (the read might have been satisfied from 1726pagecache). 1727 1728 1729wchar 1730^^^^^ 1731 1732I/O counter: chars written 1733The number of bytes which this task has caused, or shall cause to be written 1734to disk. Similar caveats apply here as with rchar. 1735 1736 1737syscr 1738^^^^^ 1739 1740I/O counter: read syscalls 1741Attempt to count the number of read I/O operations, i.e. syscalls like read() 1742and pread(). 1743 1744 1745syscw 1746^^^^^ 1747 1748I/O counter: write syscalls 1749Attempt to count the number of write I/O operations, i.e. syscalls like 1750write() and pwrite(). 1751 1752 1753read_bytes 1754^^^^^^^^^^ 1755 1756I/O counter: bytes read 1757Attempt to count the number of bytes which this process really did cause to 1758be fetched from the storage layer. Done at the submit_bio() level, so it is 1759accurate for block-backed filesystems. <please add status regarding NFS and 1760CIFS at a later time> 1761 1762 1763write_bytes 1764^^^^^^^^^^^ 1765 1766I/O counter: bytes written 1767Attempt to count the number of bytes which this process caused to be sent to 1768the storage layer. This is done at page-dirtying time. 1769 1770 1771cancelled_write_bytes 1772^^^^^^^^^^^^^^^^^^^^^ 1773 1774The big inaccuracy here is truncate. If a process writes 1MB to a file and 1775then deletes the file, it will in fact perform no writeout. But it will have 1776been accounted as having caused 1MB of write. 1777In other words: The number of bytes which this process caused to not happen, 1778by truncating pagecache. A task can cause "negative" IO too. If this task 1779truncates some dirty pagecache, some IO which another task has been accounted 1780for (in its write_bytes) will not be happening. We _could_ just subtract that 1781from the truncating task's write_bytes, but there is information loss in doing 1782that. 1783 1784 1785.. Note:: 1786 1787 At its current implementation state, this is a bit racy on 32-bit machines: 1788 if process A reads process B's /proc/pid/io while process B is updating one 1789 of those 64-bit counters, process A could see an intermediate result. 1790 1791 1792More information about this can be found within the taskstats documentation in 1793Documentation/accounting. 1794 17953.4 /proc/<pid>/coredump_filter - Core dump filtering settings 1796--------------------------------------------------------------- 1797When a process is dumped, all anonymous memory is written to a core file as 1798long as the size of the core file isn't limited. But sometimes we don't want 1799to dump some memory segments, for example, huge shared memory or DAX. 1800Conversely, sometimes we want to save file-backed memory segments into a core 1801file, not only the individual files. 1802 1803/proc/<pid>/coredump_filter allows you to customize which memory segments 1804will be dumped when the <pid> process is dumped. coredump_filter is a bitmask 1805of memory types. If a bit of the bitmask is set, memory segments of the 1806corresponding memory type are dumped, otherwise they are not dumped. 1807 1808The following 9 memory types are supported: 1809 1810 - (bit 0) anonymous private memory 1811 - (bit 1) anonymous shared memory 1812 - (bit 2) file-backed private memory 1813 - (bit 3) file-backed shared memory 1814 - (bit 4) ELF header pages in file-backed private memory areas (it is 1815 effective only if the bit 2 is cleared) 1816 - (bit 5) hugetlb private memory 1817 - (bit 6) hugetlb shared memory 1818 - (bit 7) DAX private memory 1819 - (bit 8) DAX shared memory 1820 1821 Note that MMIO pages such as frame buffer are never dumped and vDSO pages 1822 are always dumped regardless of the bitmask status. 1823 1824 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is 1825 only affected by bit 5-6, and DAX is only affected by bits 7-8. 1826 1827The default value of coredump_filter is 0x33; this means all anonymous memory 1828segments, ELF header pages and hugetlb private memory are dumped. 1829 1830If you don't want to dump all shared memory segments attached to pid 1234, 1831write 0x31 to the process's proc file:: 1832 1833 $ echo 0x31 > /proc/1234/coredump_filter 1834 1835When a new process is created, the process inherits the bitmask status from its 1836parent. It is useful to set up coredump_filter before the program runs. 1837For example:: 1838 1839 $ echo 0x7 > /proc/self/coredump_filter 1840 $ ./some_program 1841 18423.5 /proc/<pid>/mountinfo - Information about mounts 1843-------------------------------------------------------- 1844 1845This file contains lines of the form:: 1846 1847 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue 1848 (1)(2)(3) (4) (5) (6) (n…m) (m+1)(m+2) (m+3) (m+4) 1849 1850 (1) mount ID: unique identifier of the mount (may be reused after umount) 1851 (2) parent ID: ID of parent (or of self for the top of the mount tree) 1852 (3) major:minor: value of st_dev for files on filesystem 1853 (4) root: root of the mount within the filesystem 1854 (5) mount point: mount point relative to the process's root 1855 (6) mount options: per mount options 1856 (n…m) optional fields: zero or more fields of the form "tag[:value]" 1857 (m+1) separator: marks the end of the optional fields 1858 (m+2) filesystem type: name of filesystem of the form "type[.subtype]" 1859 (m+3) mount source: filesystem specific information or "none" 1860 (m+4) super options: per super block options 1861 1862Parsers should ignore all unrecognised optional fields. Currently the 1863possible optional fields are: 1864 1865================ ============================================================== 1866shared:X mount is shared in peer group X 1867master:X mount is slave to peer group X 1868propagate_from:X mount is slave and receives propagation from peer group X [#]_ 1869unbindable mount is unbindable 1870================ ============================================================== 1871 1872.. [#] X is the closest dominant peer group under the process's root. If 1873 X is the immediate master of the mount, or if there's no dominant peer 1874 group under the same root, then only the "master:X" field is present 1875 and not the "propagate_from:X" field. 1876 1877For more information on mount propagation see: 1878 1879 Documentation/filesystems/sharedsubtree.rst 1880 1881 18823.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm 1883-------------------------------------------------------- 1884These files provide a method to access a task's comm value. It also allows for 1885a task to set its own or one of its thread siblings comm value. The comm value 1886is limited in size compared to the cmdline value, so writing anything longer 1887then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated 1888comm value. 1889 1890 18913.7 /proc/<pid>/task/<tid>/children - Information about task children 1892------------------------------------------------------------------------- 1893This file provides a fast way to retrieve first level children pids 1894of a task pointed by <pid>/<tid> pair. The format is a space separated 1895stream of pids. 1896 1897Note the "first level" here -- if a child has its own children they will 1898not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children 1899to obtain the descendants. 1900 1901Since this interface is intended to be fast and cheap it doesn't 1902guarantee to provide precise results and some children might be 1903skipped, especially if they've exited right after we printed their 1904pids, so one needs to either stop or freeze processes being inspected 1905if precise results are needed. 1906 1907 19083.8 /proc/<pid>/fdinfo/<fd> - Information about opened file 1909--------------------------------------------------------------- 1910This file provides information associated with an opened file. The regular 1911files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. 1912The 'pos' represents the current offset of the opened file in decimal 1913form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the 1914file has been created with [see open(2) for details] and 'mnt_id' represents 1915mount ID of the file system containing the opened file [see 3.5 1916/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of 1917the file. 1918 1919A typical output is:: 1920 1921 pos: 0 1922 flags: 0100002 1923 mnt_id: 19 1924 ino: 63107 1925 1926All locks associated with a file descriptor are shown in its fdinfo too:: 1927 1928 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF 1929 1930The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags 1931pair provide additional information particular to the objects they represent. 1932 1933Eventfd files 1934~~~~~~~~~~~~~ 1935 1936:: 1937 1938 pos: 0 1939 flags: 04002 1940 mnt_id: 9 1941 ino: 63107 1942 eventfd-count: 5a 1943 1944where 'eventfd-count' is hex value of a counter. 1945 1946Signalfd files 1947~~~~~~~~~~~~~~ 1948 1949:: 1950 1951 pos: 0 1952 flags: 04002 1953 mnt_id: 9 1954 ino: 63107 1955 sigmask: 0000000000000200 1956 1957where 'sigmask' is hex value of the signal mask associated 1958with a file. 1959 1960Epoll files 1961~~~~~~~~~~~ 1962 1963:: 1964 1965 pos: 0 1966 flags: 02 1967 mnt_id: 9 1968 ino: 63107 1969 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 1970 1971where 'tfd' is a target file descriptor number in decimal form, 1972'events' is events mask being watched and the 'data' is data 1973associated with a target [see epoll(7) for more details]. 1974 1975The 'pos' is current offset of the target file in decimal form 1976[see lseek(2)], 'ino' and 'sdev' are inode and device numbers 1977where target file resides, all in hex format. 1978 1979Fsnotify files 1980~~~~~~~~~~~~~~ 1981For inotify files the format is the following:: 1982 1983 pos: 0 1984 flags: 02000000 1985 mnt_id: 9 1986 ino: 63107 1987 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d 1988 1989where 'wd' is a watch descriptor in decimal form, i.e. a target file 1990descriptor number, 'ino' and 'sdev' are inode and device where the 1991target file resides and the 'mask' is the mask of events, all in hex 1992form [see inotify(7) for more details]. 1993 1994If the kernel was built with exportfs support, the path to the target 1995file is encoded as a file handle. The file handle is provided by three 1996fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex 1997format. 1998 1999If the kernel is built without exportfs support the file handle won't be 2000printed out. 2001 2002If there is no inotify mark attached yet the 'inotify' line will be omitted. 2003 2004For fanotify files the format is:: 2005 2006 pos: 0 2007 flags: 02 2008 mnt_id: 9 2009 ino: 63107 2010 fanotify flags:10 event-flags:0 2011 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003 2012 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4 2013 2014where fanotify 'flags' and 'event-flags' are values used in fanotify_init 2015call, 'mnt_id' is the mount point identifier, 'mflags' is the value of 2016flags associated with mark which are tracked separately from events 2017mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events 2018mask and 'ignored_mask' is the mask of events which are to be ignored. 2019All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask' 2020provide information about flags and mask used in fanotify_mark 2021call [see fsnotify manpage for details]. 2022 2023While the first three lines are mandatory and always printed, the rest is 2024optional and may be omitted if no marks created yet. 2025 2026Timerfd files 2027~~~~~~~~~~~~~ 2028 2029:: 2030 2031 pos: 0 2032 flags: 02 2033 mnt_id: 9 2034 ino: 63107 2035 clockid: 0 2036 ticks: 0 2037 settime flags: 01 2038 it_value: (0, 49406829) 2039 it_interval: (1, 0) 2040 2041where 'clockid' is the clock type and 'ticks' is the number of the timer expirations 2042that have occurred [see timerfd_create(2) for details]. 'settime flags' are 2043flags in octal form been used to setup the timer [see timerfd_settime(2) for 2044details]. 'it_value' is remaining time until the timer expiration. 2045'it_interval' is the interval for the timer. Note the timer might be set up 2046with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value' 2047still exhibits timer's remaining time. 2048 2049DMA Buffer files 2050~~~~~~~~~~~~~~~~ 2051 2052:: 2053 2054 pos: 0 2055 flags: 04002 2056 mnt_id: 9 2057 ino: 63107 2058 size: 32768 2059 count: 2 2060 exp_name: system-heap 2061 2062where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of 2063the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter. 2064 20653.9 /proc/<pid>/map_files - Information about memory mapped files 2066--------------------------------------------------------------------- 2067This directory contains symbolic links which represent memory mapped files 2068the process is maintaining. Example output:: 2069 2070 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so 2071 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so 2072 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so 2073 | ... 2074 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1 2075 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls 2076 2077The name of a link represents the virtual memory bounds of a mapping, i.e. 2078vm_area_struct::vm_start-vm_area_struct::vm_end. 2079 2080The main purpose of the map_files is to retrieve a set of memory mapped 2081files in a fast way instead of parsing /proc/<pid>/maps or 2082/proc/<pid>/smaps, both of which contain many more records. At the same 2083time one can open(2) mappings from the listings of two processes and 2084comparing their inode numbers to figure out which anonymous memory areas 2085are actually shared. 2086 20873.10 /proc/<pid>/timerslack_ns - Task timerslack value 2088--------------------------------------------------------- 2089This file provides the value of the task's timerslack value in nanoseconds. 2090This value specifies an amount of time that normal timers may be deferred 2091in order to coalesce timers and avoid unnecessary wakeups. 2092 2093This allows a task's interactivity vs power consumption tradeoff to be 2094adjusted. 2095 2096Writing 0 to the file will set the task's timerslack to the default value. 2097 2098Valid values are from 0 - ULLONG_MAX 2099 2100An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level 2101permissions on the task specified to change its timerslack_ns value. 2102 21033.11 /proc/<pid>/patch_state - Livepatch patch operation state 2104----------------------------------------------------------------- 2105When CONFIG_LIVEPATCH is enabled, this file displays the value of the 2106patch state for the task. 2107 2108A value of '-1' indicates that no patch is in transition. 2109 2110A value of '0' indicates that a patch is in transition and the task is 2111unpatched. If the patch is being enabled, then the task hasn't been 2112patched yet. If the patch is being disabled, then the task has already 2113been unpatched. 2114 2115A value of '1' indicates that a patch is in transition and the task is 2116patched. If the patch is being enabled, then the task has already been 2117patched. If the patch is being disabled, then the task hasn't been 2118unpatched yet. 2119 21203.12 /proc/<pid>/arch_status - task architecture specific status 2121------------------------------------------------------------------- 2122When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the 2123architecture specific status of the task. 2124 2125Example 2126~~~~~~~ 2127 2128:: 2129 2130 $ cat /proc/6753/arch_status 2131 AVX512_elapsed_ms: 8 2132 2133Description 2134~~~~~~~~~~~ 2135 2136x86 specific entries 2137~~~~~~~~~~~~~~~~~~~~~ 2138 2139AVX512_elapsed_ms 2140^^^^^^^^^^^^^^^^^^ 2141 2142 If AVX512 is supported on the machine, this entry shows the milliseconds 2143 elapsed since the last time AVX512 usage was recorded. The recording 2144 happens on a best effort basis when a task is scheduled out. This means 2145 that the value depends on two factors: 2146 2147 1) The time which the task spent on the CPU without being scheduled 2148 out. With CPU isolation and a single runnable task this can take 2149 several seconds. 2150 2151 2) The time since the task was scheduled out last. Depending on the 2152 reason for being scheduled out (time slice exhausted, syscall ...) 2153 this can be arbitrary long time. 2154 2155 As a consequence the value cannot be considered precise and authoritative 2156 information. The application which uses this information has to be aware 2157 of the overall scenario on the system in order to determine whether a 2158 task is a real AVX512 user or not. Precise information can be obtained 2159 with performance counters. 2160 2161 A special value of '-1' indicates that no AVX512 usage was recorded, thus 2162 the task is unlikely an AVX512 user, but depends on the workload and the 2163 scheduling scenario, it also could be a false negative mentioned above. 2164 21653.13 /proc/<pid>/fd - List of symlinks to open files 2166------------------------------------------------------- 2167This directory contains symbolic links which represent open files 2168the process is maintaining. Example output:: 2169 2170 lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null 2171 l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null 2172 lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]' 2173 lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]' 2174 lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]' 2175 2176The number of open files for the process is stored in 'size' member 2177of stat() output for /proc/<pid>/fd for fast access. 2178------------------------------------------------------- 2179 2180 2181Chapter 4: Configuring procfs 2182============================= 2183 21844.1 Mount options 2185--------------------- 2186 2187The following mount options are supported: 2188 2189 ========= ======================================================== 2190 hidepid= Set /proc/<pid>/ access mode. 2191 gid= Set the group authorized to learn processes information. 2192 subset= Show only the specified subset of procfs. 2193 ========= ======================================================== 2194 2195hidepid=off or hidepid=0 means classic mode - everybody may access all 2196/proc/<pid>/ directories (default). 2197 2198hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ 2199directories but their own. Sensitive files like cmdline, sched*, status are now 2200protected against other users. This makes it impossible to learn whether any 2201user runs specific program (given the program doesn't reveal itself by its 2202behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for 2203other users, poorly written programs passing sensitive information via program 2204arguments are now protected against local eavesdroppers. 2205 2206hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be 2207fully invisible to other users. It doesn't mean that it hides a fact whether a 2208process with a specific pid value exists (it can be learned by other means, e.g. 2209by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by 2210stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of 2211gathering information about running processes, whether some daemon runs with 2212elevated privileges, whether other user runs some sensitive program, whether 2213other users run any program at all, etc. 2214 2215hidepid=ptraceable or hidepid=4 means that procfs should only contain 2216/proc/<pid>/ directories that the caller can ptrace. 2217 2218gid= defines a group authorized to learn processes information otherwise 2219prohibited by hidepid=. If you use some daemon like identd which needs to learn 2220information about processes information, just add identd to this group. 2221 2222subset=pid hides all top level files and directories in the procfs that 2223are not related to tasks. 2224 2225Chapter 5: Filesystem behavior 2226============================== 2227 2228Originally, before the advent of pid namepsace, procfs was a global file 2229system. It means that there was only one procfs instance in the system. 2230 2231When pid namespace was added, a separate procfs instance was mounted in 2232each pid namespace. So, procfs mount options are global among all 2233mountpoints within the same namespace:: 2234 2235 # grep ^proc /proc/mounts 2236 proc /proc proc rw,relatime,hidepid=2 0 0 2237 2238 # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc 2239 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0 2240 +++ exited with 0 +++ 2241 2242 # grep ^proc /proc/mounts 2243 proc /proc proc rw,relatime,hidepid=2 0 0 2244 proc /tmp/proc proc rw,relatime,hidepid=2 0 0 2245 2246and only after remounting procfs mount options will change at all 2247mountpoints:: 2248 2249 # mount -o remount,hidepid=1 -t proc proc /tmp/proc 2250 2251 # grep ^proc /proc/mounts 2252 proc /proc proc rw,relatime,hidepid=1 0 0 2253 proc /tmp/proc proc rw,relatime,hidepid=1 0 0 2254 2255This behavior is different from the behavior of other filesystems. 2256 2257The new procfs behavior is more like other filesystems. Each procfs mount 2258creates a new procfs instance. Mount options affect own procfs instance. 2259It means that it became possible to have several procfs instances 2260displaying tasks with different filtering options in one pid namespace:: 2261 2262 # mount -o hidepid=invisible -t proc proc /proc 2263 # mount -o hidepid=noaccess -t proc proc /tmp/proc 2264 # grep ^proc /proc/mounts 2265 proc /proc proc rw,relatime,hidepid=invisible 0 0 2266 proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 2267