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 3.14 /proc/<pid/ksm_stat - Information about the process's ksm status. 52 53 4 Configuring procfs 54 4.1 Mount options 55 56 5 Filesystem behavior 57 58Preface 59======= 60 610.1 Introduction/Credits 62------------------------ 63 64This documentation is part of a soon (or so we hope) to be released book on 65the SuSE Linux distribution. As there is no complete documentation for the 66/proc file system and we've used many freely available sources to write these 67chapters, it seems only fair to give the work back to the Linux community. 68This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm 69afraid it's still far from complete, but we hope it will be useful. As far as 70we know, it is the first 'all-in-one' document about the /proc file system. It 71is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, 72SPARC, AXP, etc., features, you probably won't find what you are looking for. 73It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But 74additions and patches are welcome and will be added to this document if you 75mail them to Bodo. 76 77We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of 78other people for help compiling this documentation. We'd also like to extend a 79special thank you to Andi Kleen for documentation, which we relied on heavily 80to create this document, as well as the additional information he provided. 81Thanks to everybody else who contributed source or docs to the Linux kernel 82and helped create a great piece of software... :) 83 84If you have any comments, corrections or additions, please don't hesitate to 85contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this 86document. 87 88The latest version of this document is available online at 89https://www.kernel.org/doc/html/latest/filesystems/proc.html 90 91If the above direction does not works for you, you could try the kernel 92mailing list at linux-kernel@vger.kernel.org and/or try to reach me at 93comandante@zaralinux.com. 94 950.2 Legal Stuff 96--------------- 97 98We don't guarantee the correctness of this document, and if you come to us 99complaining about how you screwed up your system because of incorrect 100documentation, we won't feel responsible... 101 102Chapter 1: Collecting System Information 103======================================== 104 105In This Chapter 106--------------- 107* Investigating the properties of the pseudo file system /proc and its 108 ability to provide information on the running Linux system 109* Examining /proc's structure 110* Uncovering various information about the kernel and the processes running 111 on the system 112 113------------------------------------------------------------------------------ 114 115The proc file system acts as an interface to internal data structures in the 116kernel. It can be used to obtain information about the system and to change 117certain kernel parameters at runtime (sysctl). 118 119First, we'll take a look at the read-only parts of /proc. In Chapter 2, we 120show you how you can use /proc/sys to change settings. 121 1221.1 Process-Specific Subdirectories 123----------------------------------- 124 125The directory /proc contains (among other things) one subdirectory for each 126process running on the system, which is named after the process ID (PID). 127 128The link 'self' points to the process reading the file system. Each process 129subdirectory has the entries listed in Table 1-1. 130 131A process can read its own information from /proc/PID/* with no extra 132permissions. When reading /proc/PID/* information for other processes, reading 133process is required to have either CAP_SYS_PTRACE capability with 134PTRACE_MODE_READ access permissions, or, alternatively, CAP_PERFMON 135capability. This applies to all read-only information like `maps`, `environ`, 136`pagemap`, etc. The only exception is `mem` file due to its read-write nature, 137which requires CAP_SYS_PTRACE capabilities with more elevated 138PTRACE_MODE_ATTACH permissions; CAP_PERFMON capability does not grant access 139to /proc/PID/mem for other processes. 140 141Note that an open file descriptor to /proc/<pid> or to any of its 142contained files or subdirectories does not prevent <pid> being reused 143for some other process in the event that <pid> exits. Operations on 144open /proc/<pid> file descriptors corresponding to dead processes 145never act on any new process that the kernel may, through chance, have 146also assigned the process ID <pid>. Instead, operations on these FDs 147usually fail with ESRCH. 148 149.. table:: Table 1-1: Process specific entries in /proc 150 151 ============= =============================================================== 152 File Content 153 ============= =============================================================== 154 clear_refs Clears page referenced bits shown in smaps output 155 cmdline Command line arguments 156 cpu Current and last cpu in which it was executed (2.4)(smp) 157 cwd Link to the current working directory 158 environ Values of environment variables 159 exe Link to the executable of this process 160 fd Directory, which contains all file descriptors 161 maps Memory maps to executables and library files (2.4) 162 mem Memory held by this process 163 root Link to the root directory of this process 164 stat Process status 165 statm Process memory status information 166 status Process status in human readable form 167 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function 168 symbol the task is blocked in - or "0" if not blocked. 169 pagemap Page table 170 stack Report full stack trace, enable via CONFIG_STACKTRACE 171 smaps An extension based on maps, showing the memory consumption of 172 each mapping and flags associated with it 173 smaps_rollup Accumulated smaps stats for all mappings of the process. This 174 can be derived from smaps, but is faster and more convenient 175 numa_maps An extension based on maps, showing the memory locality and 176 binding policy as well as mem usage (in pages) of each mapping. 177 ============= =============================================================== 178 179For example, to get the status information of a process, all you have to do is 180read the file /proc/PID/status:: 181 182 >cat /proc/self/status 183 Name: cat 184 State: R (running) 185 Tgid: 5452 186 Pid: 5452 187 PPid: 743 188 TracerPid: 0 (2.4) 189 Uid: 501 501 501 501 190 Gid: 100 100 100 100 191 FDSize: 256 192 Groups: 100 14 16 193 Kthread: 0 194 VmPeak: 5004 kB 195 VmSize: 5004 kB 196 VmLck: 0 kB 197 VmHWM: 476 kB 198 VmRSS: 476 kB 199 RssAnon: 352 kB 200 RssFile: 120 kB 201 RssShmem: 4 kB 202 VmData: 156 kB 203 VmStk: 88 kB 204 VmExe: 68 kB 205 VmLib: 1412 kB 206 VmPTE: 20 kb 207 VmSwap: 0 kB 208 HugetlbPages: 0 kB 209 CoreDumping: 0 210 THP_enabled: 1 211 Threads: 1 212 SigQ: 0/28578 213 SigPnd: 0000000000000000 214 ShdPnd: 0000000000000000 215 SigBlk: 0000000000000000 216 SigIgn: 0000000000000000 217 SigCgt: 0000000000000000 218 CapInh: 00000000fffffeff 219 CapPrm: 0000000000000000 220 CapEff: 0000000000000000 221 CapBnd: ffffffffffffffff 222 CapAmb: 0000000000000000 223 NoNewPrivs: 0 224 Seccomp: 0 225 Speculation_Store_Bypass: thread vulnerable 226 SpeculationIndirectBranch: conditional enabled 227 voluntary_ctxt_switches: 0 228 nonvoluntary_ctxt_switches: 1 229 230This shows you nearly the same information you would get if you viewed it with 231the ps command. In fact, ps uses the proc file system to obtain its 232information. But you get a more detailed view of the process by reading the 233file /proc/PID/status. It fields are described in table 1-2. 234 235The statm file contains more detailed information about the process 236memory usage. Its seven fields are explained in Table 1-3. The stat file 237contains detailed information about the process itself. Its fields are 238explained in Table 1-4. 239 240(for SMP CONFIG users) 241 242For making accounting scalable, RSS related information are handled in an 243asynchronous manner and the value may not be very precise. To see a precise 244snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table. 245It's slow but very precise. 246 247.. table:: Table 1-2: Contents of the status fields (as of 4.19) 248 249 ========================== =================================================== 250 Field Content 251 ========================== =================================================== 252 Name filename of the executable 253 Umask file mode creation mask 254 State state (R is running, S is sleeping, D is sleeping 255 in an uninterruptible wait, Z is zombie, 256 T is traced or stopped) 257 Tgid thread group ID 258 Ngid NUMA group ID (0 if none) 259 Pid process id 260 PPid process id of the parent process 261 TracerPid PID of process tracing this process (0 if not, or 262 the tracer is outside of the current pid namespace) 263 Uid Real, effective, saved set, and file system UIDs 264 Gid Real, effective, saved set, and file system GIDs 265 FDSize number of file descriptor slots currently allocated 266 Groups supplementary group list 267 NStgid descendant namespace thread group ID hierarchy 268 NSpid descendant namespace process ID hierarchy 269 NSpgid descendant namespace process group ID hierarchy 270 NSsid descendant namespace session ID hierarchy 271 Kthread kernel thread flag, 1 is yes, 0 is no 272 VmPeak peak virtual memory size 273 VmSize total program size 274 VmLck locked memory size 275 VmPin pinned memory size 276 VmHWM peak resident set size ("high water mark") 277 VmRSS size of memory portions. It contains the three 278 following parts 279 (VmRSS = RssAnon + RssFile + RssShmem) 280 RssAnon size of resident anonymous memory 281 RssFile size of resident file mappings 282 RssShmem size of resident shmem memory (includes SysV shm, 283 mapping of tmpfs and shared anonymous mappings) 284 VmData size of private data segments 285 VmStk size of stack segments 286 VmExe size of text segment 287 VmLib size of shared library code 288 VmPTE size of page table entries 289 VmSwap amount of swap used by anonymous private data 290 (shmem swap usage is not included) 291 HugetlbPages size of hugetlb memory portions 292 CoreDumping process's memory is currently being dumped 293 (killing the process may lead to a corrupted core) 294 THP_enabled process is allowed to use THP (returns 0 when 295 PR_SET_THP_DISABLE is set on the process to disable 296 THP completely, not just partially) 297 Threads number of threads 298 SigQ number of signals queued/max. number for queue 299 SigPnd bitmap of pending signals for the thread 300 ShdPnd bitmap of shared pending signals for the process 301 SigBlk bitmap of blocked signals 302 SigIgn bitmap of ignored signals 303 SigCgt bitmap of caught signals 304 CapInh bitmap of inheritable capabilities 305 CapPrm bitmap of permitted capabilities 306 CapEff bitmap of effective capabilities 307 CapBnd bitmap of capabilities bounding set 308 CapAmb bitmap of ambient capabilities 309 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...) 310 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...) 311 Speculation_Store_Bypass speculative store bypass mitigation status 312 SpeculationIndirectBranch indirect branch speculation mode 313 Cpus_allowed mask of CPUs on which this process may run 314 Cpus_allowed_list Same as previous, but in "list format" 315 Mems_allowed mask of memory nodes allowed to this process 316 Mems_allowed_list Same as previous, but in "list format" 317 voluntary_ctxt_switches number of voluntary context switches 318 nonvoluntary_ctxt_switches number of non voluntary context switches 319 ========================== =================================================== 320 321 322.. table:: Table 1-3: Contents of the statm fields (as of 2.6.8-rc3) 323 324 ======== =============================== ============================== 325 Field Content 326 ======== =============================== ============================== 327 size total program size (pages) (same as VmSize in status) 328 resident size of memory portions (pages) (same as VmRSS in status) 329 shared number of pages that are shared (i.e. backed by a file, same 330 as RssFile+RssShmem in status) 331 trs number of pages that are 'code' (not including libs; broken, 332 includes data segment) 333 lrs number of pages of library (always 0 on 2.6) 334 drs number of pages of data/stack (including libs; broken, 335 includes library text) 336 dt number of dirty pages (always 0 on 2.6) 337 ======== =============================== ============================== 338 339 340.. table:: Table 1-4: Contents of the stat fields (as of 2.6.30-rc7) 341 342 ============= =============================================================== 343 Field Content 344 ============= =============================================================== 345 pid process id 346 tcomm filename of the executable 347 state state (R is running, S is sleeping, D is sleeping in an 348 uninterruptible wait, Z is zombie, T is traced or stopped) 349 ppid process id of the parent process 350 pgrp pgrp of the process 351 sid session id 352 tty_nr tty the process uses 353 tty_pgrp pgrp of the tty 354 flags task flags 355 min_flt number of minor faults 356 cmin_flt number of minor faults with child's 357 maj_flt number of major faults 358 cmaj_flt number of major faults with child's 359 utime user mode jiffies 360 stime kernel mode jiffies 361 cutime user mode jiffies with child's 362 cstime kernel mode jiffies with child's 363 priority priority level 364 nice nice level 365 num_threads number of threads 366 it_real_value (obsolete, always 0) 367 start_time time the process started after system boot 368 vsize virtual memory size 369 rss resident set memory size 370 rsslim current limit in bytes on the rss 371 start_code address above which program text can run 372 end_code address below which program text can run 373 start_stack address of the start of the main process stack 374 esp current value of ESP 375 eip current value of EIP 376 pending bitmap of pending signals 377 blocked bitmap of blocked signals 378 sigign bitmap of ignored signals 379 sigcatch bitmap of caught signals 380 0 (place holder, used to be the wchan address, 381 use /proc/PID/wchan instead) 382 0 (place holder) 383 0 (place holder) 384 exit_signal signal to send to parent thread on exit 385 task_cpu which CPU the task is scheduled on 386 rt_priority realtime priority 387 policy scheduling policy (man sched_setscheduler) 388 blkio_ticks time spent waiting for block IO 389 gtime guest time of the task in jiffies 390 cgtime guest time of the task children in jiffies 391 start_data address above which program data+bss is placed 392 end_data address below which program data+bss is placed 393 start_brk address above which program heap can be expanded with brk() 394 arg_start address above which program command line is placed 395 arg_end address below which program command line is placed 396 env_start address above which program environment is placed 397 env_end address below which program environment is placed 398 exit_code the thread's exit_code in the form reported by the waitpid 399 system call 400 ============= =============================================================== 401 402The /proc/PID/maps file contains the currently mapped memory regions and 403their access permissions. 404 405The format is:: 406 407 address perms offset dev inode pathname 408 409 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test 410 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test 411 0804a000-0806b000 rw-p 00000000 00:00 0 [heap] 412 a7cb1000-a7cb2000 ---p 00000000 00:00 0 413 a7cb2000-a7eb2000 rw-p 00000000 00:00 0 414 a7eb2000-a7eb3000 ---p 00000000 00:00 0 415 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 416 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 417 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 418 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 419 a800b000-a800e000 rw-p 00000000 00:00 0 420 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 421 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 422 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 423 a8024000-a8027000 rw-p 00000000 00:00 0 424 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 425 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 426 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 427 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack] 428 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] 429 430where "address" is the address space in the process that it occupies, "perms" 431is a set of permissions:: 432 433 r = read 434 w = write 435 x = execute 436 s = shared 437 p = private (copy on write) 438 439"offset" is the offset into the mapping, "dev" is the device (major:minor), and 440"inode" is the inode on that device. 0 indicates that no inode is associated 441with the memory region, as the case would be with BSS (uninitialized data). 442The "pathname" shows the name associated file for this mapping. If the mapping 443is not associated with a file: 444 445 =================== =========================================== 446 [heap] the heap of the program 447 [stack] the stack of the main process 448 [vdso] the "virtual dynamic shared object", 449 the kernel system call handler 450 [anon:<name>] a private anonymous mapping that has been 451 named by userspace 452 [anon_shmem:<name>] an anonymous shared memory mapping that has 453 been named by userspace 454 =================== =========================================== 455 456 or if empty, the mapping is anonymous. 457 458Starting with 6.11 kernel, /proc/PID/maps provides an alternative 459ioctl()-based API that gives ability to flexibly and efficiently query and 460filter individual VMAs. This interface is binary and is meant for more 461efficient and easy programmatic use. `struct procmap_query`, defined in 462linux/fs.h UAPI header, serves as an input/output argument to the 463`PROCMAP_QUERY` ioctl() command. See comments in linus/fs.h UAPI header for 464details on query semantics, supported flags, data returned, and general API 465usage information. 466 467The /proc/PID/smaps is an extension based on maps, showing the memory 468consumption for each of the process's mappings. For each mapping (aka Virtual 469Memory Area, or VMA) there is a series of lines such as the following:: 470 471 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash 472 473 Size: 1084 kB 474 KernelPageSize: 4 kB 475 MMUPageSize: 4 kB 476 Rss: 892 kB 477 Pss: 374 kB 478 Pss_Dirty: 0 kB 479 Shared_Clean: 892 kB 480 Shared_Dirty: 0 kB 481 Private_Clean: 0 kB 482 Private_Dirty: 0 kB 483 Referenced: 892 kB 484 Anonymous: 0 kB 485 KSM: 0 kB 486 LazyFree: 0 kB 487 AnonHugePages: 0 kB 488 ShmemPmdMapped: 0 kB 489 Shared_Hugetlb: 0 kB 490 Private_Hugetlb: 0 kB 491 Swap: 0 kB 492 SwapPss: 0 kB 493 KernelPageSize: 4 kB 494 MMUPageSize: 4 kB 495 Locked: 0 kB 496 THPeligible: 0 497 VmFlags: rd ex mr mw me dw 498 499The first of these lines shows the same information as is displayed for 500the mapping in /proc/PID/maps. Following lines show the size of the 501mapping (size); the size of each page allocated when backing a VMA 502(KernelPageSize), which is usually the same as the size in the page table 503entries; the page size used by the MMU when backing a VMA (in most cases, 504the same as KernelPageSize); the amount of the mapping that is currently 505resident in RAM (RSS); the process's proportional share of this mapping 506(PSS); and the number of clean and dirty shared and private pages in the 507mapping. 508 509The "proportional set size" (PSS) of a process is the count of pages it has 510in memory, where each page is divided by the number of processes sharing it. 511So if a process has 1000 pages all to itself, and 1000 shared with one other 512process, its PSS will be 1500. "Pss_Dirty" is the portion of PSS which 513consists of dirty pages. ("Pss_Clean" is not included, but it can be 514calculated by subtracting "Pss_Dirty" from "Pss".) 515 516Traditionally, a page is accounted as "private" if it is mapped exactly once, 517and a page is accounted as "shared" when mapped multiple times, even when 518mapped in the same process multiple times. Note that this accounting is 519independent of MAP_SHARED. 520 521In some kernel configurations, the semantics of pages part of a larger 522allocation (e.g., THP) can differ: a page is accounted as "private" if all 523pages part of the corresponding large allocation are *certainly* mapped in the 524same process, even if the page is mapped multiple times in that process. A 525page is accounted as "shared" if any page page of the larger allocation 526is *maybe* mapped in a different process. In some cases, a large allocation 527might be treated as "maybe mapped by multiple processes" even though this 528is no longer the case. 529 530Some kernel configurations do not track the precise number of times a page part 531of a larger allocation is mapped. In this case, when calculating the PSS, the 532average number of mappings per page in this larger allocation might be used 533as an approximation for the number of mappings of a page. The PSS calculation 534will be imprecise in this case. 535 536"Referenced" indicates the amount of memory currently marked as referenced or 537accessed. 538 539"Anonymous" shows the amount of memory that does not belong to any file. Even 540a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE 541and a page is modified, the file page is replaced by a private anonymous copy. 542 543"KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages 544are not included, only actual KSM pages. 545 546"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE). 547The memory isn't freed immediately with madvise(). It's freed in memory 548pressure if the memory is clean. Please note that the printed value might 549be lower than the real value due to optimizations used in the current 550implementation. If this is not desirable please file a bug report. 551 552"AnonHugePages" shows the amount of memory backed by transparent hugepage. 553 554"ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by 555huge pages. 556 557"Shared_Hugetlb" and "Private_Hugetlb" show the amounts of memory backed by 558hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical 559reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field. 560 561"Swap" shows how much would-be-anonymous memory is also used, but out on swap. 562 563For shmem mappings, "Swap" includes also the size of the mapped (and not 564replaced by copy-on-write) part of the underlying shmem object out on swap. 565"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this 566does not take into account swapped out page of underlying shmem objects. 567"Locked" indicates whether the mapping is locked in memory or not. 568 569"THPeligible" indicates whether the mapping is eligible for allocating 570naturally aligned THP pages of any currently enabled size. 1 if true, 0 571otherwise. 572 573"VmFlags" field deserves a separate description. This member represents the 574kernel flags associated with the particular virtual memory area in two letter 575encoded manner. The codes are the following: 576 577 == ======================================= 578 rd readable 579 wr writeable 580 ex executable 581 sh shared 582 mr may read 583 mw may write 584 me may execute 585 ms may share 586 gd stack segment growns down 587 pf pure PFN range 588 lo pages are locked in memory 589 io memory mapped I/O area 590 sr sequential read advise provided 591 rr random read advise provided 592 dc do not copy area on fork 593 de do not expand area on remapping 594 ac area is accountable 595 nr swap space is not reserved for the area 596 ht area uses huge tlb pages 597 sf synchronous page fault 598 ar architecture specific flag 599 wf wipe on fork 600 dd do not include area into core dump 601 sd soft dirty flag 602 mm mixed map area 603 hg huge page advise flag 604 nh no huge page advise flag 605 mg mergeable advise flag 606 bt arm64 BTI guarded page 607 mt arm64 MTE allocation tags are enabled 608 um userfaultfd missing tracking 609 uw userfaultfd wr-protect tracking 610 ui userfaultfd minor fault 611 ss shadow/guarded control stack page 612 sl sealed 613 lf lock on fault pages 614 dp always lazily freeable mapping 615 == ======================================= 616 617Note that there is no guarantee that every flag and associated mnemonic will 618be present in all further kernel releases. Things get changed, the flags may 619be vanished or the reverse -- new added. Interpretation of their meaning 620might change in future as well. So each consumer of these flags has to 621follow each specific kernel version for the exact semantic. 622 623This file is only present if the CONFIG_MMU kernel configuration option is 624enabled. 625 626Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent 627output can be achieved only in the single read call). 628 629This typically manifests when doing partial reads of these files while the 630memory map is being modified. Despite the races, we do provide the following 631guarantees: 632 6331) The mapped addresses never go backwards, which implies no two 634 regions will ever overlap. 6352) If there is something at a given vaddr during the entirety of the 636 life of the smaps/maps walk, there will be some output for it. 637 638The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps, 639but their values are the sums of the corresponding values for all mappings of 640the process. Additionally, it contains these fields: 641 642- Pss_Anon 643- Pss_File 644- Pss_Shmem 645 646They represent the proportional shares of anonymous, file, and shmem pages, as 647described for smaps above. These fields are omitted in smaps since each 648mapping identifies the type (anon, file, or shmem) of all pages it contains. 649Thus all information in smaps_rollup can be derived from smaps, but at a 650significantly higher cost. 651 652The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG 653bits on both physical and virtual pages associated with a process, and the 654soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst 655for details). 656To clear the bits for all the pages associated with the process:: 657 658 > echo 1 > /proc/PID/clear_refs 659 660To clear the bits for the anonymous pages associated with the process:: 661 662 > echo 2 > /proc/PID/clear_refs 663 664To clear the bits for the file mapped pages associated with the process:: 665 666 > echo 3 > /proc/PID/clear_refs 667 668To clear the soft-dirty bit:: 669 670 > echo 4 > /proc/PID/clear_refs 671 672To reset the peak resident set size ("high water mark") to the process's 673current value:: 674 675 > echo 5 > /proc/PID/clear_refs 676 677Any other value written to /proc/PID/clear_refs will have no effect. 678 679The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags 680using /proc/kpageflags and number of times a page is mapped using 681/proc/kpagecount. For detailed explanation, see 682Documentation/admin-guide/mm/pagemap.rst. 683 684The /proc/pid/numa_maps is an extension based on maps, showing the memory 685locality and binding policy, as well as the memory usage (in pages) of 686each mapping. The output follows a general format where mapping details get 687summarized separated by blank spaces, one mapping per each file line:: 688 689 address policy mapping details 690 691 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4 692 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4 693 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4 694 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 695 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 696 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4 697 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4 698 320698b000 default file=/lib64/libc-2.12.so 699 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4 700 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 701 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4 702 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4 703 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4 704 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048 705 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4 706 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4 707 708Where: 709 710"address" is the starting address for the mapping; 711 712"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst); 713 714"mapping details" summarizes mapping data such as mapping type, page usage counters, 715node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page 716size, in KB, that is backing the mapping up. 717 718Note that some kernel configurations do not track the precise number of times 719a page part of a larger allocation (e.g., THP) is mapped. In these 720configurations, "mapmax" might corresponds to the average number of mappings 721per page in such a larger allocation instead. 722 7231.2 Kernel data 724--------------- 725 726Similar to the process entries, the kernel data files give information about 727the running kernel. The files used to obtain this information are contained in 728/proc and are listed in Table 1-5. Not all of these will be present in your 729system. It depends on the kernel configuration and the loaded modules, which 730files are there, and which are missing. 731 732.. table:: Table 1-5: Kernel info in /proc 733 734 ============ =============================================================== 735 File Content 736 ============ =============================================================== 737 allocinfo Memory allocations profiling information 738 apm Advanced power management info 739 bootconfig Kernel command line obtained from boot config, 740 and, if there were kernel parameters from the 741 boot loader, a "# Parameters from bootloader:" 742 line followed by a line containing those 743 parameters prefixed by "# ". (5.5) 744 buddyinfo Kernel memory allocator information (see text) (2.5) 745 bus Directory containing bus specific information 746 cmdline Kernel command line, both from bootloader and embedded 747 in the kernel image 748 cpuinfo Info about the CPU 749 devices Available devices (block and character) 750 dma Used DMS channels 751 filesystems Supported filesystems 752 driver Various drivers grouped here, currently rtc (2.4) 753 execdomains Execdomains, related to security (2.4) 754 fb Frame Buffer devices (2.4) 755 fs File system parameters, currently nfs/exports (2.4) 756 ide Directory containing info about the IDE subsystem 757 interrupts Interrupt usage 758 iomem Memory map (2.4) 759 ioports I/O port usage 760 irq Masks for irq to cpu affinity (2.4)(smp?) 761 isapnp ISA PnP (Plug&Play) Info (2.4) 762 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) 763 kmsg Kernel messages 764 ksyms Kernel symbol table 765 loadavg Load average of last 1, 5 & 15 minutes; 766 number of processes currently runnable (running or on ready queue); 767 total number of processes in system; 768 last pid created. 769 All fields are separated by one space except "number of 770 processes currently runnable" and "total number of processes 771 in system", which are separated by a slash ('/'). Example: 772 0.61 0.61 0.55 3/828 22084 773 locks Kernel locks 774 meminfo Memory info 775 misc Miscellaneous 776 modules List of loaded modules 777 mounts Mounted filesystems 778 net Networking info (see text) 779 pagetypeinfo Additional page allocator information (see text) (2.5) 780 partitions Table of partitions known to the system 781 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, 782 decoupled by lspci (2.4) 783 rtc Real time clock 784 scsi SCSI info (see text) 785 slabinfo Slab pool info 786 softirqs softirq usage 787 stat Overall statistics 788 swaps Swap space utilization 789 sys See chapter 2 790 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) 791 tty Info of tty drivers 792 uptime Wall clock since boot, combined idle time of all cpus 793 version Kernel version 794 video bttv info of video resources (2.4) 795 vmallocinfo Show vmalloced areas 796 ============ =============================================================== 797 798You can, for example, check which interrupts are currently in use and what 799they are used for by looking in the file /proc/interrupts:: 800 801 > cat /proc/interrupts 802 CPU0 803 0: 8728810 XT-PIC timer 804 1: 895 XT-PIC keyboard 805 2: 0 XT-PIC cascade 806 3: 531695 XT-PIC aha152x 807 4: 2014133 XT-PIC serial 808 5: 44401 XT-PIC pcnet_cs 809 8: 2 XT-PIC rtc 810 11: 8 XT-PIC i82365 811 12: 182918 XT-PIC PS/2 Mouse 812 13: 1 XT-PIC fpu 813 14: 1232265 XT-PIC ide0 814 15: 7 XT-PIC ide1 815 NMI: 0 816 817In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the 818output of a SMP machine):: 819 820 > cat /proc/interrupts 821 822 CPU0 CPU1 823 0: 1243498 1214548 IO-APIC-edge timer 824 1: 8949 8958 IO-APIC-edge keyboard 825 2: 0 0 XT-PIC cascade 826 5: 11286 10161 IO-APIC-edge soundblaster 827 8: 1 0 IO-APIC-edge rtc 828 9: 27422 27407 IO-APIC-edge 3c503 829 12: 113645 113873 IO-APIC-edge PS/2 Mouse 830 13: 0 0 XT-PIC fpu 831 14: 22491 24012 IO-APIC-edge ide0 832 15: 2183 2415 IO-APIC-edge ide1 833 17: 30564 30414 IO-APIC-level eth0 834 18: 177 164 IO-APIC-level bttv 835 NMI: 2457961 2457959 836 LOC: 2457882 2457881 837 ERR: 2155 838 839NMI is incremented in this case because every timer interrupt generates a NMI 840(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. 841 842LOC is the local interrupt counter of the internal APIC of every CPU. 843 844ERR is incremented in the case of errors in the IO-APIC bus (the bus that 845connects the CPUs in a SMP system. This means that an error has been detected, 846the IO-APIC automatically retry the transmission, so it should not be a big 847problem, but you should read the SMP-FAQ. 848 849In 2.6.2* /proc/interrupts was expanded again. This time the goal was for 850/proc/interrupts to display every IRQ vector in use by the system, not 851just those considered 'most important'. The new vectors are: 852 853THR 854 interrupt raised when a machine check threshold counter 855 (typically counting ECC corrected errors of memory or cache) exceeds 856 a configurable threshold. Only available on some systems. 857 858TRM 859 a thermal event interrupt occurs when a temperature threshold 860 has been exceeded for the CPU. This interrupt may also be generated 861 when the temperature drops back to normal. 862 863SPU 864 a spurious interrupt is some interrupt that was raised then lowered 865 by some IO device before it could be fully processed by the APIC. Hence 866 the APIC sees the interrupt but does not know what device it came from. 867 For this case the APIC will generate the interrupt with a IRQ vector 868 of 0xff. This might also be generated by chipset bugs. 869 870RES, CAL, TLB 871 rescheduling, call and TLB flush interrupts are 872 sent from one CPU to another per the needs of the OS. Typically, 873 their statistics are used by kernel developers and interested users to 874 determine the occurrence of interrupts of the given type. 875 876The above IRQ vectors are displayed only when relevant. For example, 877the threshold vector does not exist on x86_64 platforms. Others are 878suppressed when the system is a uniprocessor. As of this writing, only 879i386 and x86_64 platforms support the new IRQ vector displays. 880 881Of some interest is the introduction of the /proc/irq directory to 2.4. 882It could be used to set IRQ to CPU affinity. This means that you can "hook" an 883IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the 884irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and 885prof_cpu_mask. 886 887For example:: 888 889 > ls /proc/irq/ 890 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask 891 1 11 13 15 17 19 3 5 7 9 default_smp_affinity 892 > ls /proc/irq/0/ 893 smp_affinity 894 895smp_affinity is a bitmask, in which you can specify which CPUs can handle the 896IRQ. You can set it by doing:: 897 898 > echo 1 > /proc/irq/10/smp_affinity 899 900This means that only the first CPU will handle the IRQ, but you can also echo 9015 which means that only the first and third CPU can handle the IRQ. 902 903The contents of each smp_affinity file is the same by default:: 904 905 > cat /proc/irq/0/smp_affinity 906 ffffffff 907 908There is an alternate interface, smp_affinity_list which allows specifying 909a CPU range instead of a bitmask:: 910 911 > cat /proc/irq/0/smp_affinity_list 912 1024-1031 913 914The default_smp_affinity mask applies to all non-active IRQs, which are the 915IRQs which have not yet been allocated/activated, and hence which lack a 916/proc/irq/[0-9]* directory. 917 918The node file on an SMP system shows the node to which the device using the IRQ 919reports itself as being attached. This hardware locality information does not 920include information about any possible driver locality preference. 921 922prof_cpu_mask specifies which CPUs are to be profiled by the system wide 923profiler. Default value is ffffffff (all CPUs if there are only 32 of them). 924 925The way IRQs are routed is handled by the IO-APIC, and it's Round Robin 926between all the CPUs which are allowed to handle it. As usual the kernel has 927more info than you and does a better job than you, so the defaults are the 928best choice for almost everyone. [Note this applies only to those IO-APIC's 929that support "Round Robin" interrupt distribution.] 930 931There are three more important subdirectories in /proc: net, scsi, and sys. 932The general rule is that the contents, or even the existence of these 933directories, depend on your kernel configuration. If SCSI is not enabled, the 934directory scsi may not exist. The same is true with the net, which is there 935only when networking support is present in the running kernel. 936 937The slabinfo file gives information about memory usage at the slab level. 938Linux uses slab pools for memory management above page level in version 2.2. 939Commonly used objects have their own slab pool (such as network buffers, 940directory cache, and so on). 941 942:: 943 944 > cat /proc/buddyinfo 945 946 Node 0, zone DMA 0 4 5 4 4 3 ... 947 Node 0, zone Normal 1 0 0 1 101 8 ... 948 Node 0, zone HighMem 2 0 0 1 1 0 ... 949 950External fragmentation is a problem under some workloads, and buddyinfo is a 951useful tool for helping diagnose these problems. Buddyinfo will give you a 952clue as to how big an area you can safely allocate, or why a previous 953allocation failed. 954 955Each column represents the number of pages of a certain order which are 956available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 957ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 958available in ZONE_NORMAL, etc... 959 960More information relevant to external fragmentation can be found in 961pagetypeinfo:: 962 963 > cat /proc/pagetypeinfo 964 Page block order: 9 965 Pages per block: 512 966 967 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 968 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0 969 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0 970 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2 971 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0 972 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0 973 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9 974 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0 975 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452 976 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0 977 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0 978 979 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate 980 Node 0, zone DMA 2 0 5 1 0 981 Node 0, zone DMA32 41 6 967 2 0 982 983Fragmentation avoidance in the kernel works by grouping pages of different 984migrate types into the same contiguous regions of memory called page blocks. 985A page block is typically the size of the default hugepage size, e.g. 2MB on 986X86-64. By keeping pages grouped based on their ability to move, the kernel 987can reclaim pages within a page block to satisfy a high-order allocation. 988 989The pagetypinfo begins with information on the size of a page block. It 990then gives the same type of information as buddyinfo except broken down 991by migrate-type and finishes with details on how many page blocks of each 992type exist. 993 994If min_free_kbytes has been tuned correctly (recommendations made by hugeadm 995from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can 996make an estimate of the likely number of huge pages that can be allocated 997at a given point in time. All the "Movable" blocks should be allocatable 998unless memory has been mlock()'d. Some of the Reclaimable blocks should 999also be allocatable although a lot of filesystem metadata may have to be 1000reclaimed to achieve this. 1001 1002 1003allocinfo 1004~~~~~~~~~ 1005 1006Provides information about memory allocations at all locations in the code 1007base. Each allocation in the code is identified by its source file, line 1008number, module (if originates from a loadable module) and the function calling 1009the allocation. The number of bytes allocated and number of calls at each 1010location are reported. The first line indicates the version of the file, the 1011second line is the header listing fields in the file. 1012If file version is 2.0 or higher then each line may contain additional 1013<key>:<value> pairs representing extra information about the call site. 1014For example if the counters are not accurate, the line will be appended with 1015"accurate:no" pair. 1016 1017Supported markers in v2: 1018accurate:no 1019 1020 Absolute values of the counters in this line are not accurate 1021 because of the failure to allocate memory to track some of the 1022 allocations made at this location. Deltas in these counters are 1023 accurate, therefore counters can be used to track allocation size 1024 and count changes. 1025 1026Example output. 1027 1028:: 1029 1030 > tail -n +3 /proc/allocinfo | sort -rn 1031 127664128 31168 mm/page_ext.c:270 func:alloc_page_ext 1032 56373248 4737 mm/slub.c:2259 func:alloc_slab_page 1033 14880768 3633 mm/readahead.c:247 func:page_cache_ra_unbounded 1034 14417920 3520 mm/mm_init.c:2530 func:alloc_large_system_hash 1035 13377536 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs 1036 11718656 2861 mm/filemap.c:1919 func:__filemap_get_folio 1037 9192960 2800 kernel/fork.c:307 func:alloc_thread_stack_node 1038 4206592 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable 1039 4136960 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start 1040 3940352 962 mm/memory.c:4214 func:alloc_anon_folio 1041 2894464 22613 fs/kernfs/dir.c:615 func:__kernfs_new_node 1042 ... 1043 1044 1045meminfo 1046~~~~~~~ 1047 1048Provides information about distribution and utilization of memory. This 1049varies by architecture and compile options. Some of the counters reported 1050here overlap. The memory reported by the non overlapping counters may not 1051add up to the overall memory usage and the difference for some workloads 1052can be substantial. In many cases there are other means to find out 1053additional memory using subsystem specific interfaces, for instance 1054/proc/net/sockstat for TCP memory allocations. 1055 1056Example output. You may not have all of these fields. 1057 1058:: 1059 1060 > cat /proc/meminfo 1061 1062 MemTotal: 32858820 kB 1063 MemFree: 21001236 kB 1064 MemAvailable: 27214312 kB 1065 Buffers: 581092 kB 1066 Cached: 5587612 kB 1067 SwapCached: 0 kB 1068 Active: 3237152 kB 1069 Inactive: 7586256 kB 1070 Active(anon): 94064 kB 1071 Inactive(anon): 4570616 kB 1072 Active(file): 3143088 kB 1073 Inactive(file): 3015640 kB 1074 Unevictable: 0 kB 1075 Mlocked: 0 kB 1076 SwapTotal: 0 kB 1077 SwapFree: 0 kB 1078 Zswap: 1904 kB 1079 Zswapped: 7792 kB 1080 Dirty: 12 kB 1081 Writeback: 0 kB 1082 AnonPages: 4654780 kB 1083 Mapped: 266244 kB 1084 Shmem: 9976 kB 1085 KReclaimable: 517708 kB 1086 Slab: 660044 kB 1087 SReclaimable: 517708 kB 1088 SUnreclaim: 142336 kB 1089 KernelStack: 11168 kB 1090 PageTables: 20540 kB 1091 SecPageTables: 0 kB 1092 NFS_Unstable: 0 kB 1093 Bounce: 0 kB 1094 WritebackTmp: 0 kB 1095 CommitLimit: 16429408 kB 1096 Committed_AS: 7715148 kB 1097 VmallocTotal: 34359738367 kB 1098 VmallocUsed: 40444 kB 1099 VmallocChunk: 0 kB 1100 Percpu: 29312 kB 1101 EarlyMemtestBad: 0 kB 1102 HardwareCorrupted: 0 kB 1103 AnonHugePages: 4149248 kB 1104 ShmemHugePages: 0 kB 1105 ShmemPmdMapped: 0 kB 1106 FileHugePages: 0 kB 1107 FilePmdMapped: 0 kB 1108 CmaTotal: 0 kB 1109 CmaFree: 0 kB 1110 Unaccepted: 0 kB 1111 Balloon: 0 kB 1112 HugePages_Total: 0 1113 HugePages_Free: 0 1114 HugePages_Rsvd: 0 1115 HugePages_Surp: 0 1116 Hugepagesize: 2048 kB 1117 Hugetlb: 0 kB 1118 DirectMap4k: 401152 kB 1119 DirectMap2M: 10008576 kB 1120 DirectMap1G: 24117248 kB 1121 1122MemTotal 1123 Total usable RAM (i.e. physical RAM minus a few reserved 1124 bits and the kernel binary code) 1125MemFree 1126 Total free RAM. On highmem systems, the sum of LowFree+HighFree 1127MemAvailable 1128 An estimate of how much memory is available for starting new 1129 applications, without swapping. Calculated from MemFree, 1130 SReclaimable, the size of the file LRU lists, and the low 1131 watermarks in each zone. 1132 The estimate takes into account that the system needs some 1133 page cache to function well, and that not all reclaimable 1134 slab will be reclaimable, due to items being in use. The 1135 impact of those factors will vary from system to system. 1136Buffers 1137 Relatively temporary storage for raw disk blocks 1138 shouldn't get tremendously large (20MB or so) 1139Cached 1140 In-memory cache for files read from the disk (the 1141 pagecache) as well as tmpfs & shmem. 1142 Doesn't include SwapCached. 1143SwapCached 1144 Memory that once was swapped out, is swapped back in but 1145 still also is in the swapfile (if memory is needed it 1146 doesn't need to be swapped out AGAIN because it is already 1147 in the swapfile. This saves I/O) 1148Active 1149 Memory that has been used more recently and usually not 1150 reclaimed unless absolutely necessary. 1151Inactive 1152 Memory which has been less recently used. It is more 1153 eligible to be reclaimed for other purposes 1154Unevictable 1155 Memory allocated for userspace which cannot be reclaimed, such 1156 as mlocked pages, ramfs backing pages, secret memfd pages etc. 1157Mlocked 1158 Memory locked with mlock(). 1159HighTotal, HighFree 1160 Highmem is all memory above ~860MB of physical memory. 1161 Highmem areas are for use by userspace programs, or 1162 for the pagecache. The kernel must use tricks to access 1163 this memory, making it slower to access than lowmem. 1164LowTotal, LowFree 1165 Lowmem is memory which can be used for everything that 1166 highmem can be used for, but it is also available for the 1167 kernel's use for its own data structures. Among many 1168 other things, it is where everything from the Slab is 1169 allocated. Bad things happen when you're out of lowmem. 1170SwapTotal 1171 total amount of swap space available 1172SwapFree 1173 Memory which has been evicted from RAM, and is temporarily 1174 on the disk 1175Zswap 1176 Memory consumed by the zswap backend (compressed size) 1177Zswapped 1178 Amount of anonymous memory stored in zswap (original size) 1179Dirty 1180 Memory which is waiting to get written back to the disk 1181Writeback 1182 Memory which is actively being written back to the disk 1183AnonPages 1184 Non-file backed pages mapped into userspace page tables. Note that 1185 some kernel configurations might consider all pages part of a 1186 larger allocation (e.g., THP) as "mapped", as soon as a single 1187 page is mapped. 1188Mapped 1189 files which have been mmapped, such as libraries. Note that some 1190 kernel configurations might consider all pages part of a larger 1191 allocation (e.g., THP) as "mapped", as soon as a single page is 1192 mapped. 1193Shmem 1194 Total memory used by shared memory (shmem) and tmpfs 1195KReclaimable 1196 Kernel allocations that the kernel will attempt to reclaim 1197 under memory pressure. Includes SReclaimable (below), and other 1198 direct allocations with a shrinker. 1199Slab 1200 in-kernel data structures cache 1201SReclaimable 1202 Part of Slab, that might be reclaimed, such as caches 1203SUnreclaim 1204 Part of Slab, that cannot be reclaimed on memory pressure 1205KernelStack 1206 Memory consumed by the kernel stacks of all tasks 1207PageTables 1208 Memory consumed by userspace page tables 1209SecPageTables 1210 Memory consumed by secondary page tables, this currently includes 1211 KVM mmu and IOMMU allocations on x86 and arm64. 1212NFS_Unstable 1213 Always zero. Previously counted pages which had been written to 1214 the server, but has not been committed to stable storage. 1215Bounce 1216 Always zero. Previously memory used for block device 1217 "bounce buffers". 1218WritebackTmp 1219 Always zero. Previously memory used by FUSE for temporary 1220 writeback buffers. 1221CommitLimit 1222 Based on the overcommit ratio ('vm.overcommit_ratio'), 1223 this is the total amount of memory currently available to 1224 be allocated on the system. This limit is only adhered to 1225 if strict overcommit accounting is enabled (mode 2 in 1226 'vm.overcommit_memory'). 1227 1228 The CommitLimit is calculated with the following formula:: 1229 1230 CommitLimit = ([total RAM pages] - [total huge TLB pages]) * 1231 overcommit_ratio / 100 + [total swap pages] 1232 1233 For example, on a system with 1G of physical RAM and 7G 1234 of swap with a `vm.overcommit_ratio` of 30 it would 1235 yield a CommitLimit of 7.3G. 1236 1237 For more details, see the memory overcommit documentation 1238 in mm/overcommit-accounting. 1239Committed_AS 1240 The amount of memory presently allocated on the system. 1241 The committed memory is a sum of all of the memory which 1242 has been allocated by processes, even if it has not been 1243 "used" by them as of yet. A process which malloc()'s 1G 1244 of memory, but only touches 300M of it will show up as 1245 using 1G. This 1G is memory which has been "committed" to 1246 by the VM and can be used at any time by the allocating 1247 application. With strict overcommit enabled on the system 1248 (mode 2 in 'vm.overcommit_memory'), allocations which would 1249 exceed the CommitLimit (detailed above) will not be permitted. 1250 This is useful if one needs to guarantee that processes will 1251 not fail due to lack of memory once that memory has been 1252 successfully allocated. 1253VmallocTotal 1254 total size of vmalloc virtual address space 1255VmallocUsed 1256 amount of vmalloc area which is used 1257VmallocChunk 1258 largest contiguous block of vmalloc area which is free 1259Percpu 1260 Memory allocated to the percpu allocator used to back percpu 1261 allocations. This stat excludes the cost of metadata. 1262EarlyMemtestBad 1263 The amount of RAM/memory in kB, that was identified as corrupted 1264 by early memtest. If memtest was not run, this field will not 1265 be displayed at all. Size is never rounded down to 0 kB. 1266 That means if 0 kB is reported, you can safely assume 1267 there was at least one pass of memtest and none of the passes 1268 found a single faulty byte of RAM. 1269HardwareCorrupted 1270 The amount of RAM/memory in KB, the kernel identifies as 1271 corrupted. 1272AnonHugePages 1273 Non-file backed huge pages mapped into userspace page tables 1274ShmemHugePages 1275 Memory used by shared memory (shmem) and tmpfs allocated 1276 with huge pages 1277ShmemPmdMapped 1278 Shared memory mapped into userspace with huge pages 1279FileHugePages 1280 Memory used for filesystem data (page cache) allocated 1281 with huge pages 1282FilePmdMapped 1283 Page cache mapped into userspace with huge pages 1284CmaTotal 1285 Memory reserved for the Contiguous Memory Allocator (CMA) 1286CmaFree 1287 Free remaining memory in the CMA reserves 1288Unaccepted 1289 Memory that has not been accepted by the guest 1290Balloon 1291 Memory returned to Host by VM Balloon Drivers 1292HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb 1293 See Documentation/admin-guide/mm/hugetlbpage.rst. 1294DirectMap4k, DirectMap2M, DirectMap1G 1295 Breakdown of page table sizes used in the kernel's 1296 identity mapping of RAM 1297 1298vmallocinfo 1299~~~~~~~~~~~ 1300 1301Provides information about vmalloced/vmaped areas. One line per area, 1302containing the virtual address range of the area, size in bytes, 1303caller information of the creator, and optional information depending 1304on the kind of area: 1305 1306 ========== =================================================== 1307 pages=nr number of pages 1308 phys=addr if a physical address was specified 1309 ioremap I/O mapping (ioremap() and friends) 1310 vmalloc vmalloc() area 1311 vmap vmap()ed pages 1312 user VM_USERMAP area 1313 vpages buffer for pages pointers was vmalloced (huge area) 1314 N<node>=nr (Only on NUMA kernels) 1315 Number of pages allocated on memory node <node> 1316 ========== =================================================== 1317 1318:: 1319 1320 > cat /proc/vmallocinfo 1321 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... 1322 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 1323 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... 1324 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 1325 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... 1326 phys=7fee8000 ioremap 1327 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... 1328 phys=7fee7000 ioremap 1329 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 1330 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... 1331 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 1332 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... 1333 pages=2 vmalloc N1=2 1334 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... 1335 /0x130 [x_tables] pages=4 vmalloc N0=4 1336 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... 1337 pages=14 vmalloc N2=14 1338 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... 1339 pages=4 vmalloc N1=4 1340 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... 1341 pages=2 vmalloc N1=2 1342 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... 1343 pages=10 vmalloc N0=10 1344 1345 1346softirqs 1347~~~~~~~~ 1348 1349Provides counts of softirq handlers serviced since boot time, for each CPU. 1350 1351:: 1352 1353 > cat /proc/softirqs 1354 CPU0 CPU1 CPU2 CPU3 1355 HI: 0 0 0 0 1356 TIMER: 27166 27120 27097 27034 1357 NET_TX: 0 0 0 17 1358 NET_RX: 42 0 0 39 1359 BLOCK: 0 0 107 1121 1360 TASKLET: 0 0 0 290 1361 SCHED: 27035 26983 26971 26746 1362 HRTIMER: 0 0 0 0 1363 RCU: 1678 1769 2178 2250 1364 13651.3 Networking info in /proc/net 1366-------------------------------- 1367 1368The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the 1369additional values you get for IP version 6 if you configure the kernel to 1370support this. Table 1-9 lists the files and their meaning. 1371 1372 1373.. table:: Table 1-8: IPv6 info in /proc/net 1374 1375 ========== ===================================================== 1376 File Content 1377 ========== ===================================================== 1378 udp6 UDP sockets (IPv6) 1379 tcp6 TCP sockets (IPv6) 1380 raw6 Raw device statistics (IPv6) 1381 igmp6 IP multicast addresses, which this host joined (IPv6) 1382 if_inet6 List of IPv6 interface addresses 1383 ipv6_route Kernel routing table for IPv6 1384 rt6_stats Global IPv6 routing tables statistics 1385 sockstat6 Socket statistics (IPv6) 1386 snmp6 Snmp data (IPv6) 1387 ========== ===================================================== 1388 1389.. table:: Table 1-9: Network info in /proc/net 1390 1391 ============= ================================================================ 1392 File Content 1393 ============= ================================================================ 1394 arp Kernel ARP table 1395 dev network devices with statistics 1396 dev_mcast the Layer2 multicast groups a device is listening too 1397 (interface index, label, number of references, number of bound 1398 addresses). 1399 dev_stat network device status 1400 ip_fwchains Firewall chain linkage 1401 ip_fwnames Firewall chain names 1402 ip_masq Directory containing the masquerading tables 1403 ip_masquerade Major masquerading table 1404 netstat Network statistics 1405 raw raw device statistics 1406 route Kernel routing table 1407 rpc Directory containing rpc info 1408 rt_cache Routing cache 1409 snmp SNMP data 1410 sockstat Socket statistics 1411 softnet_stat Per-CPU incoming packets queues statistics of online CPUs 1412 tcp TCP sockets 1413 udp UDP sockets 1414 unix UNIX domain sockets 1415 wireless Wireless interface data (Wavelan etc) 1416 igmp IP multicast addresses, which this host joined 1417 psched Global packet scheduler parameters. 1418 netlink List of PF_NETLINK sockets 1419 ip_mr_vifs List of multicast virtual interfaces 1420 ip_mr_cache List of multicast routing cache 1421 ============= ================================================================ 1422 1423You can use this information to see which network devices are available in 1424your system and how much traffic was routed over those devices:: 1425 1426 > cat /proc/net/dev 1427 Inter-|Receive |[... 1428 face |bytes packets errs drop fifo frame compressed multicast|[... 1429 lo: 908188 5596 0 0 0 0 0 0 [... 1430 ppp0:15475140 20721 410 0 0 410 0 0 [... 1431 eth0: 614530 7085 0 0 0 0 0 1 [... 1432 1433 ...] Transmit 1434 ...] bytes packets errs drop fifo colls carrier compressed 1435 ...] 908188 5596 0 0 0 0 0 0 1436 ...] 1375103 17405 0 0 0 0 0 0 1437 ...] 1703981 5535 0 0 0 3 0 0 1438 1439In addition, each Channel Bond interface has its own directory. For 1440example, the bond0 device will have a directory called /proc/net/bond0/. 1441It will contain information that is specific to that bond, such as the 1442current slaves of the bond, the link status of the slaves, and how 1443many times the slaves link has failed. 1444 14451.4 SCSI info 1446------------- 1447 1448If you have a SCSI or ATA host adapter in your system, you'll find a 1449subdirectory named after the driver for this adapter in /proc/scsi. 1450You'll also see a list of all recognized SCSI devices in /proc/scsi:: 1451 1452 >cat /proc/scsi/scsi 1453 Attached devices: 1454 Host: scsi0 Channel: 00 Id: 00 Lun: 00 1455 Vendor: IBM Model: DGHS09U Rev: 03E0 1456 Type: Direct-Access ANSI SCSI revision: 03 1457 Host: scsi0 Channel: 00 Id: 06 Lun: 00 1458 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 1459 Type: CD-ROM ANSI SCSI revision: 02 1460 1461 1462The directory named after the driver has one file for each adapter found in 1463the system. These files contain information about the controller, including 1464the used IRQ and the IO address range. The amount of information shown is 1465dependent on the adapter you use. The example shows the output for an Adaptec 1466AHA-2940 SCSI adapter:: 1467 1468 > cat /proc/scsi/aic7xxx/0 1469 1470 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 1471 Compile Options: 1472 TCQ Enabled By Default : Disabled 1473 AIC7XXX_PROC_STATS : Disabled 1474 AIC7XXX_RESET_DELAY : 5 1475 Adapter Configuration: 1476 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 1477 Ultra Wide Controller 1478 PCI MMAPed I/O Base: 0xeb001000 1479 Adapter SEEPROM Config: SEEPROM found and used. 1480 Adaptec SCSI BIOS: Enabled 1481 IRQ: 10 1482 SCBs: Active 0, Max Active 2, 1483 Allocated 15, HW 16, Page 255 1484 Interrupts: 160328 1485 BIOS Control Word: 0x18b6 1486 Adapter Control Word: 0x005b 1487 Extended Translation: Enabled 1488 Disconnect Enable Flags: 0xffff 1489 Ultra Enable Flags: 0x0001 1490 Tag Queue Enable Flags: 0x0000 1491 Ordered Queue Tag Flags: 0x0000 1492 Default Tag Queue Depth: 8 1493 Tagged Queue By Device array for aic7xxx host instance 0: 1494 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 1495 Actual queue depth per device for aic7xxx host instance 0: 1496 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 1497 Statistics: 1498 (scsi0:0:0:0) 1499 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 1500 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 1501 Total transfers 160151 (74577 reads and 85574 writes) 1502 (scsi0:0:6:0) 1503 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 1504 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 1505 Total transfers 0 (0 reads and 0 writes) 1506 1507 15081.5 Parallel port info in /proc/parport 1509--------------------------------------- 1510 1511The directory /proc/parport contains information about the parallel ports of 1512your system. It has one subdirectory for each port, named after the port 1513number (0,1,2,...). 1514 1515These directories contain the four files shown in Table 1-10. 1516 1517 1518.. table:: Table 1-10: Files in /proc/parport 1519 1520 ========= ==================================================================== 1521 File Content 1522 ========= ==================================================================== 1523 autoprobe Any IEEE-1284 device ID information that has been acquired. 1524 devices list of the device drivers using that port. A + will appear by the 1525 name of the device currently using the port (it might not appear 1526 against any). 1527 hardware Parallel port's base address, IRQ line and DMA channel. 1528 irq IRQ that parport is using for that port. This is in a separate 1529 file to allow you to alter it by writing a new value in (IRQ 1530 number or none). 1531 ========= ==================================================================== 1532 15331.6 TTY info in /proc/tty 1534------------------------- 1535 1536Information about the available and actually used tty's can be found in the 1537directory /proc/tty. You'll find entries for drivers and line disciplines in 1538this directory, as shown in Table 1-11. 1539 1540 1541.. table:: Table 1-11: Files in /proc/tty 1542 1543 ============= ============================================== 1544 File Content 1545 ============= ============================================== 1546 drivers list of drivers and their usage 1547 ldiscs registered line disciplines 1548 driver/serial usage statistic and status of single tty lines 1549 ============= ============================================== 1550 1551To see which tty's are currently in use, you can simply look into the file 1552/proc/tty/drivers:: 1553 1554 > cat /proc/tty/drivers 1555 pty_slave /dev/pts 136 0-255 pty:slave 1556 pty_master /dev/ptm 128 0-255 pty:master 1557 pty_slave /dev/ttyp 3 0-255 pty:slave 1558 pty_master /dev/pty 2 0-255 pty:master 1559 serial /dev/cua 5 64-67 serial:callout 1560 serial /dev/ttyS 4 64-67 serial 1561 /dev/tty0 /dev/tty0 4 0 system:vtmaster 1562 /dev/ptmx /dev/ptmx 5 2 system 1563 /dev/console /dev/console 5 1 system:console 1564 /dev/tty /dev/tty 5 0 system:/dev/tty 1565 unknown /dev/tty 4 1-63 console 1566 1567 15681.7 Miscellaneous kernel statistics in /proc/stat 1569------------------------------------------------- 1570 1571Various pieces of information about kernel activity are available in the 1572/proc/stat file. All of the numbers reported in this file are aggregates 1573since the system first booted. For a quick look, simply cat the file:: 1574 1575 > cat /proc/stat 1576 cpu 237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0 1577 cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0 1578 cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0 1579 cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0 1580 cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0 1581 intr 8688370575 8 3373 0 0 0 0 0 0 1 40791 0 0 353317 0 0 0 0 224789828 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 190974333 41958554 123983334 43 0 224593 0 0 0 <more 0's deleted> 1582 ctxt 22848221062 1583 btime 1605316999 1584 processes 746787147 1585 procs_running 2 1586 procs_blocked 0 1587 softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354 1588 1589The very first "cpu" line aggregates the numbers in all of the other "cpuN" 1590lines. These numbers identify the amount of time the CPU has spent performing 1591different kinds of work. Time units are in USER_HZ (typically hundredths of a 1592second). The meanings of the columns are as follows, from left to right: 1593 1594- user: normal processes executing in user mode 1595- nice: niced processes executing in user mode 1596- system: processes executing in kernel mode 1597- idle: twiddling thumbs 1598- iowait: In a word, iowait stands for waiting for I/O to complete. But there 1599 are several problems: 1600 1601 1. CPU will not wait for I/O to complete, iowait is the time that a task is 1602 waiting for I/O to complete. When CPU goes into idle state for 1603 outstanding task I/O, another task will be scheduled on this CPU. 1604 2. In a multi-core CPU, the task waiting for I/O to complete is not running 1605 on any CPU, so the iowait of each CPU is difficult to calculate. 1606 3. The value of iowait field in /proc/stat will decrease in certain 1607 conditions. 1608 1609 So, the iowait is not reliable by reading from /proc/stat. 1610- irq: servicing interrupts 1611- softirq: servicing softirqs 1612- steal: involuntary wait 1613- guest: running a normal guest 1614- guest_nice: running a niced guest 1615 1616The "intr" line gives counts of interrupts serviced since boot time, for each 1617of the possible system interrupts. The first column is the total of all 1618interrupts serviced including unnumbered architecture specific interrupts; 1619each subsequent column is the total for that particular numbered interrupt. 1620Unnumbered interrupts are not shown, only summed into the total. 1621 1622The "ctxt" line gives the total number of context switches across all CPUs. 1623 1624The "btime" line gives the time at which the system booted, in seconds since 1625the Unix epoch. 1626 1627The "processes" line gives the number of processes and threads created, which 1628includes (but is not limited to) those created by calls to the fork() and 1629clone() system calls. 1630 1631The "procs_running" line gives the total number of threads that are 1632running or ready to run (i.e., the total number of runnable threads). 1633 1634The "procs_blocked" line gives the number of processes currently blocked, 1635waiting for I/O to complete. 1636 1637The "softirq" line gives counts of softirqs serviced since boot time, for each 1638of the possible system softirqs. The first column is the total of all 1639softirqs serviced; each subsequent column is the total for that particular 1640softirq. 1641 1642 16431.8 Ext4 file system parameters 1644------------------------------- 1645 1646Information about mounted ext4 file systems can be found in 1647/proc/fs/ext4. Each mounted filesystem will have a directory in 1648/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or 1649/proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0). The files in each per-device 1650directory are shown in Table 1-12, below. 1651 1652.. table:: Table 1-12: Files in /proc/fs/ext4/<devname> 1653 1654 ============== ========================================================== 1655 File Content 1656 mb_groups details of multiblock allocator buddy cache of free blocks 1657 ============== ========================================================== 1658 16591.9 /proc/consoles 1660------------------- 1661Shows registered system console lines. 1662 1663To see which character device lines are currently used for the system console 1664/dev/console, you may simply look into the file /proc/consoles:: 1665 1666 > cat /proc/consoles 1667 tty0 -WU (ECp) 4:7 1668 ttyS0 -W- (Ep) 4:64 1669 1670The columns are: 1671 1672+--------------------+-------------------------------------------------------+ 1673| device | name of the device | 1674+====================+=======================================================+ 1675| operations | * R = can do read operations | 1676| | * W = can do write operations | 1677| | * U = can do unblank | 1678+--------------------+-------------------------------------------------------+ 1679| flags | * E = it is enabled | 1680| | * C = it is preferred console | 1681| | * B = it is primary boot console | 1682| | * p = it is used for printk buffer | 1683| | * b = it is not a TTY but a Braille device | 1684| | * a = it is safe to use when cpu is offline | 1685+--------------------+-------------------------------------------------------+ 1686| major:minor | major and minor number of the device separated by a | 1687| | colon | 1688+--------------------+-------------------------------------------------------+ 1689 1690Summary 1691------- 1692 1693The /proc file system serves information about the running system. It not only 1694allows access to process data but also allows you to request the kernel status 1695by reading files in the hierarchy. 1696 1697The directory structure of /proc reflects the types of information and makes 1698it easy, if not obvious, where to look for specific data. 1699 1700Chapter 2: Modifying System Parameters 1701====================================== 1702 1703In This Chapter 1704--------------- 1705 1706* Modifying kernel parameters by writing into files found in /proc/sys 1707* Exploring the files which modify certain parameters 1708* Review of the /proc/sys file tree 1709 1710------------------------------------------------------------------------------ 1711 1712A very interesting part of /proc is the directory /proc/sys. This is not only 1713a source of information, it also allows you to change parameters within the 1714kernel. Be very careful when attempting this. You can optimize your system, 1715but you can also cause it to crash. Never alter kernel parameters on a 1716production system. Set up a development machine and test to make sure that 1717everything works the way you want it to. You may have no alternative but to 1718reboot the machine once an error has been made. 1719 1720To change a value, simply echo the new value into the file. 1721You need to be root to do this. You can create your own boot script 1722to perform this every time your system boots. 1723 1724The files in /proc/sys can be used to fine tune and monitor miscellaneous and 1725general things in the operation of the Linux kernel. Since some of the files 1726can inadvertently disrupt your system, it is advisable to read both 1727documentation and source before actually making adjustments. In any case, be 1728very careful when writing to any of these files. The entries in /proc may 1729change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt 1730review the kernel documentation in the directory linux/Documentation. 1731This chapter is heavily based on the documentation included in the pre 2.2 1732kernels, and became part of it in version 2.2.1 of the Linux kernel. 1733 1734Please see: Documentation/admin-guide/sysctl/ directory for descriptions of 1735these entries. 1736 1737Summary 1738------- 1739 1740Certain aspects of kernel behavior can be modified at runtime, without the 1741need to recompile the kernel, or even to reboot the system. The files in the 1742/proc/sys tree can not only be read, but also modified. You can use the echo 1743command to write value into these files, thereby changing the default settings 1744of the kernel. 1745 1746 1747Chapter 3: Per-process Parameters 1748================================= 1749 17503.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score 1751-------------------------------------------------------------------------------- 1752 1753These files can be used to adjust the badness heuristic used to select which 1754process gets killed in out of memory (oom) conditions. 1755 1756The badness heuristic assigns a value to each candidate task ranging from 0 1757(never kill) to 1000 (always kill) to determine which process is targeted. The 1758units are roughly a proportion along that range of allowed memory the process 1759may allocate from based on an estimation of its current memory and swap use. 1760For example, if a task is using all allowed memory, its badness score will be 17611000. If it is using half of its allowed memory, its score will be 500. 1762 1763The amount of "allowed" memory depends on the context in which the oom killer 1764was called. If it is due to the memory assigned to the allocating task's cpuset 1765being exhausted, the allowed memory represents the set of mems assigned to that 1766cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed 1767memory represents the set of mempolicy nodes. If it is due to a memory 1768limit (or swap limit) being reached, the allowed memory is that configured 1769limit. Finally, if it is due to the entire system being out of memory, the 1770allowed memory represents all allocatable resources. 1771 1772The value of /proc/<pid>/oom_score_adj is added to the badness score before it 1773is used to determine which task to kill. Acceptable values range from -1000 1774(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to 1775polarize the preference for oom killing either by always preferring a certain 1776task or completely disabling it. The lowest possible value, -1000, is 1777equivalent to disabling oom killing entirely for that task since it will always 1778report a badness score of 0. 1779 1780Consequently, it is very simple for userspace to define the amount of memory to 1781consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for 1782example, is roughly equivalent to allowing the remainder of tasks sharing the 1783same system, cpuset, mempolicy, or memory controller resources to use at least 178450% more memory. A value of -500, on the other hand, would be roughly 1785equivalent to discounting 50% of the task's allowed memory from being considered 1786as scoring against the task. 1787 1788For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also 1789be used to tune the badness score. Its acceptable values range from -16 1790(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 1791(OOM_DISABLE) to disable oom killing entirely for that task. Its value is 1792scaled linearly with /proc/<pid>/oom_score_adj. 1793 1794The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last 1795value set by a CAP_SYS_RESOURCE process. To reduce the value any lower 1796requires CAP_SYS_RESOURCE. 1797 1798 17993.2 /proc/<pid>/oom_score - Display current oom-killer score 1800------------------------------------------------------------- 1801 1802This file can be used to check the current score used by the oom-killer for 1803any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which 1804process should be killed in an out-of-memory situation. 1805 1806Please note that the exported value includes oom_score_adj so it is 1807effectively in range [0,2000]. 1808 1809 18103.3 /proc/<pid>/io - Display the IO accounting fields 1811------------------------------------------------------- 1812 1813This file contains IO statistics for each running process. 1814 1815Example 1816~~~~~~~ 1817 1818:: 1819 1820 test:/tmp # dd if=/dev/zero of=/tmp/test.dat & 1821 [1] 3828 1822 1823 test:/tmp # cat /proc/3828/io 1824 rchar: 323934931 1825 wchar: 323929600 1826 syscr: 632687 1827 syscw: 632675 1828 read_bytes: 0 1829 write_bytes: 323932160 1830 cancelled_write_bytes: 0 1831 1832 1833Description 1834~~~~~~~~~~~ 1835 1836rchar 1837^^^^^ 1838 1839I/O counter: chars read 1840The number of bytes which this task has caused to be read from storage. This 1841is simply the sum of bytes which this process passed to read() and pread(). 1842It includes things like tty IO and it is unaffected by whether or not actual 1843physical disk IO was required (the read might have been satisfied from 1844pagecache). 1845 1846 1847wchar 1848^^^^^ 1849 1850I/O counter: chars written 1851The number of bytes which this task has caused, or shall cause to be written 1852to disk. Similar caveats apply here as with rchar. 1853 1854 1855syscr 1856^^^^^ 1857 1858I/O counter: read syscalls 1859Attempt to count the number of read I/O operations, i.e. syscalls like read() 1860and pread(). 1861 1862 1863syscw 1864^^^^^ 1865 1866I/O counter: write syscalls 1867Attempt to count the number of write I/O operations, i.e. syscalls like 1868write() and pwrite(). 1869 1870 1871read_bytes 1872^^^^^^^^^^ 1873 1874I/O counter: bytes read 1875Attempt to count the number of bytes which this process really did cause to 1876be fetched from the storage layer. Done at the submit_bio() level, so it is 1877accurate for block-backed filesystems. <please add status regarding NFS and 1878CIFS at a later time> 1879 1880 1881write_bytes 1882^^^^^^^^^^^ 1883 1884I/O counter: bytes written 1885Attempt to count the number of bytes which this process caused to be sent to 1886the storage layer. This is done at page-dirtying time. 1887 1888 1889cancelled_write_bytes 1890^^^^^^^^^^^^^^^^^^^^^ 1891 1892The big inaccuracy here is truncate. If a process writes 1MB to a file and 1893then deletes the file, it will in fact perform no writeout. But it will have 1894been accounted as having caused 1MB of write. 1895In other words: The number of bytes which this process caused to not happen, 1896by truncating pagecache. A task can cause "negative" IO too. If this task 1897truncates some dirty pagecache, some IO which another task has been accounted 1898for (in its write_bytes) will not be happening. We _could_ just subtract that 1899from the truncating task's write_bytes, but there is information loss in doing 1900that. 1901 1902 1903.. Note:: 1904 1905 At its current implementation state, this is a bit racy on 32-bit machines: 1906 if process A reads process B's /proc/pid/io while process B is updating one 1907 of those 64-bit counters, process A could see an intermediate result. 1908 1909 1910More information about this can be found within the taskstats documentation in 1911Documentation/accounting. 1912 19133.4 /proc/<pid>/coredump_filter - Core dump filtering settings 1914--------------------------------------------------------------- 1915When a process is dumped, all anonymous memory is written to a core file as 1916long as the size of the core file isn't limited. But sometimes we don't want 1917to dump some memory segments, for example, huge shared memory or DAX. 1918Conversely, sometimes we want to save file-backed memory segments into a core 1919file, not only the individual files. 1920 1921/proc/<pid>/coredump_filter allows you to customize which memory segments 1922will be dumped when the <pid> process is dumped. coredump_filter is a bitmask 1923of memory types. If a bit of the bitmask is set, memory segments of the 1924corresponding memory type are dumped, otherwise they are not dumped. 1925 1926The following 9 memory types are supported: 1927 1928 - (bit 0) anonymous private memory 1929 - (bit 1) anonymous shared memory 1930 - (bit 2) file-backed private memory 1931 - (bit 3) file-backed shared memory 1932 - (bit 4) ELF header pages in file-backed private memory areas (it is 1933 effective only if the bit 2 is cleared) 1934 - (bit 5) hugetlb private memory 1935 - (bit 6) hugetlb shared memory 1936 - (bit 7) DAX private memory 1937 - (bit 8) DAX shared memory 1938 1939 Note that MMIO pages such as frame buffer are never dumped and vDSO pages 1940 are always dumped regardless of the bitmask status. 1941 1942 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is 1943 only affected by bit 5-6, and DAX is only affected by bits 7-8. 1944 1945The default value of coredump_filter is 0x33; this means all anonymous memory 1946segments, ELF header pages and hugetlb private memory are dumped. 1947 1948If you don't want to dump all shared memory segments attached to pid 1234, 1949write 0x31 to the process's proc file:: 1950 1951 $ echo 0x31 > /proc/1234/coredump_filter 1952 1953When a new process is created, the process inherits the bitmask status from its 1954parent. It is useful to set up coredump_filter before the program runs. 1955For example:: 1956 1957 $ echo 0x7 > /proc/self/coredump_filter 1958 $ ./some_program 1959 19603.5 /proc/<pid>/mountinfo - Information about mounts 1961-------------------------------------------------------- 1962 1963This file contains lines of the form:: 1964 1965 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue 1966 (1)(2)(3) (4) (5) (6) (n…m) (m+1)(m+2) (m+3) (m+4) 1967 1968 (1) mount ID: unique identifier of the mount (may be reused after umount) 1969 (2) parent ID: ID of parent (or of self for the top of the mount tree) 1970 (3) major:minor: value of st_dev for files on filesystem 1971 (4) root: root of the mount within the filesystem 1972 (5) mount point: mount point relative to the process's root 1973 (6) mount options: per mount options 1974 (n…m) optional fields: zero or more fields of the form "tag[:value]" 1975 (m+1) separator: marks the end of the optional fields 1976 (m+2) filesystem type: name of filesystem of the form "type[.subtype]" 1977 (m+3) mount source: filesystem specific information or "none" 1978 (m+4) super options: per super block options 1979 1980Parsers should ignore all unrecognised optional fields. Currently the 1981possible optional fields are: 1982 1983================ ============================================================== 1984shared:X mount is shared in peer group X 1985master:X mount is slave to peer group X 1986propagate_from:X mount is slave and receives propagation from peer group X [#]_ 1987unbindable mount is unbindable 1988================ ============================================================== 1989 1990.. [#] X is the closest dominant peer group under the process's root. If 1991 X is the immediate master of the mount, or if there's no dominant peer 1992 group under the same root, then only the "master:X" field is present 1993 and not the "propagate_from:X" field. 1994 1995For more information on mount propagation see: 1996 1997 Documentation/filesystems/sharedsubtree.rst 1998 1999 20003.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm 2001-------------------------------------------------------- 2002These files provide a method to access a task's comm value. It also allows for 2003a task to set its own or one of its thread siblings comm value. The comm value 2004is limited in size compared to the cmdline value, so writing anything longer 2005then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL 2006terminator) will result in a truncated comm value. 2007 2008 20093.7 /proc/<pid>/task/<tid>/children - Information about task children 2010------------------------------------------------------------------------- 2011This file provides a fast way to retrieve first level children pids 2012of a task pointed by <pid>/<tid> pair. The format is a space separated 2013stream of pids. 2014 2015Note the "first level" here -- if a child has its own children they will 2016not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children 2017to obtain the descendants. 2018 2019Since this interface is intended to be fast and cheap it doesn't 2020guarantee to provide precise results and some children might be 2021skipped, especially if they've exited right after we printed their 2022pids, so one needs to either stop or freeze processes being inspected 2023if precise results are needed. 2024 2025 20263.8 /proc/<pid>/fdinfo/<fd> - Information about opened file 2027--------------------------------------------------------------- 2028This file provides information associated with an opened file. The regular 2029files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. 2030The 'pos' represents the current offset of the opened file in decimal 2031form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the 2032file has been created with [see open(2) for details] and 'mnt_id' represents 2033mount ID of the file system containing the opened file [see 3.5 2034/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of 2035the file. 2036 2037A typical output is:: 2038 2039 pos: 0 2040 flags: 0100002 2041 mnt_id: 19 2042 ino: 63107 2043 2044All locks associated with a file descriptor are shown in its fdinfo too:: 2045 2046 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF 2047 2048The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags 2049pair provide additional information particular to the objects they represent. 2050 2051Eventfd files 2052~~~~~~~~~~~~~ 2053 2054:: 2055 2056 pos: 0 2057 flags: 04002 2058 mnt_id: 9 2059 ino: 63107 2060 eventfd-count: 5a 2061 2062where 'eventfd-count' is hex value of a counter. 2063 2064Signalfd files 2065~~~~~~~~~~~~~~ 2066 2067:: 2068 2069 pos: 0 2070 flags: 04002 2071 mnt_id: 9 2072 ino: 63107 2073 sigmask: 0000000000000200 2074 2075where 'sigmask' is hex value of the signal mask associated 2076with a file. 2077 2078Epoll files 2079~~~~~~~~~~~ 2080 2081:: 2082 2083 pos: 0 2084 flags: 02 2085 mnt_id: 9 2086 ino: 63107 2087 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 2088 2089where 'tfd' is a target file descriptor number in decimal form, 2090'events' is events mask being watched and the 'data' is data 2091associated with a target [see epoll(7) for more details]. 2092 2093The 'pos' is current offset of the target file in decimal form 2094[see lseek(2)], 'ino' and 'sdev' are inode and device numbers 2095where target file resides, all in hex format. 2096 2097Fsnotify files 2098~~~~~~~~~~~~~~ 2099For inotify files the format is the following:: 2100 2101 pos: 0 2102 flags: 02000000 2103 mnt_id: 9 2104 ino: 63107 2105 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d 2106 2107where 'wd' is a watch descriptor in decimal form, i.e. a target file 2108descriptor number, 'ino' and 'sdev' are inode and device where the 2109target file resides and the 'mask' is the mask of events, all in hex 2110form [see inotify(7) for more details]. 2111 2112If the kernel was built with exportfs support, the path to the target 2113file is encoded as a file handle. The file handle is provided by three 2114fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex 2115format. 2116 2117If the kernel is built without exportfs support the file handle won't be 2118printed out. 2119 2120If there is no inotify mark attached yet the 'inotify' line will be omitted. 2121 2122For fanotify files the format is:: 2123 2124 pos: 0 2125 flags: 02 2126 mnt_id: 9 2127 ino: 63107 2128 fanotify flags:10 event-flags:0 2129 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003 2130 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4 2131 2132where fanotify 'flags' and 'event-flags' are values used in fanotify_init 2133call, 'mnt_id' is the mount point identifier, 'mflags' is the value of 2134flags associated with mark which are tracked separately from events 2135mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events 2136mask and 'ignored_mask' is the mask of events which are to be ignored. 2137All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask' 2138provide information about flags and mask used in fanotify_mark 2139call [see fsnotify manpage for details]. 2140 2141While the first three lines are mandatory and always printed, the rest is 2142optional and may be omitted if no marks created yet. 2143 2144Timerfd files 2145~~~~~~~~~~~~~ 2146 2147:: 2148 2149 pos: 0 2150 flags: 02 2151 mnt_id: 9 2152 ino: 63107 2153 clockid: 0 2154 ticks: 0 2155 settime flags: 01 2156 it_value: (0, 49406829) 2157 it_interval: (1, 0) 2158 2159where 'clockid' is the clock type and 'ticks' is the number of the timer expirations 2160that have occurred [see timerfd_create(2) for details]. 'settime flags' are 2161flags in octal form been used to setup the timer [see timerfd_settime(2) for 2162details]. 'it_value' is remaining time until the timer expiration. 2163'it_interval' is the interval for the timer. Note the timer might be set up 2164with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value' 2165still exhibits timer's remaining time. 2166 2167DMA Buffer files 2168~~~~~~~~~~~~~~~~ 2169 2170:: 2171 2172 pos: 0 2173 flags: 04002 2174 mnt_id: 9 2175 ino: 63107 2176 size: 32768 2177 count: 2 2178 exp_name: system-heap 2179 2180where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of 2181the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter. 2182 21833.9 /proc/<pid>/map_files - Information about memory mapped files 2184--------------------------------------------------------------------- 2185This directory contains symbolic links which represent memory mapped files 2186the process is maintaining. Example output:: 2187 2188 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so 2189 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so 2190 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so 2191 | ... 2192 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1 2193 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls 2194 2195The name of a link represents the virtual memory bounds of a mapping, i.e. 2196vm_area_struct::vm_start-vm_area_struct::vm_end. 2197 2198The main purpose of the map_files is to retrieve a set of memory mapped 2199files in a fast way instead of parsing /proc/<pid>/maps or 2200/proc/<pid>/smaps, both of which contain many more records. At the same 2201time one can open(2) mappings from the listings of two processes and 2202comparing their inode numbers to figure out which anonymous memory areas 2203are actually shared. 2204 22053.10 /proc/<pid>/timerslack_ns - Task timerslack value 2206--------------------------------------------------------- 2207This file provides the value of the task's timerslack value in nanoseconds. 2208This value specifies an amount of time that normal timers may be deferred 2209in order to coalesce timers and avoid unnecessary wakeups. 2210 2211This allows a task's interactivity vs power consumption tradeoff to be 2212adjusted. 2213 2214Writing 0 to the file will set the task's timerslack to the default value. 2215 2216Valid values are from 0 - ULLONG_MAX 2217 2218An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level 2219permissions on the task specified to change its timerslack_ns value. 2220 22213.11 /proc/<pid>/patch_state - Livepatch patch operation state 2222----------------------------------------------------------------- 2223When CONFIG_LIVEPATCH is enabled, this file displays the value of the 2224patch state for the task. 2225 2226A value of '-1' indicates that no patch is in transition. 2227 2228A value of '0' indicates that a patch is in transition and the task is 2229unpatched. If the patch is being enabled, then the task hasn't been 2230patched yet. If the patch is being disabled, then the task has already 2231been unpatched. 2232 2233A value of '1' indicates that a patch is in transition and the task is 2234patched. If the patch is being enabled, then the task has already been 2235patched. If the patch is being disabled, then the task hasn't been 2236unpatched yet. 2237 22383.12 /proc/<pid>/arch_status - task architecture specific status 2239------------------------------------------------------------------- 2240When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the 2241architecture specific status of the task. 2242 2243Example 2244~~~~~~~ 2245 2246:: 2247 2248 $ cat /proc/6753/arch_status 2249 AVX512_elapsed_ms: 8 2250 2251Description 2252~~~~~~~~~~~ 2253 2254x86 specific entries 2255~~~~~~~~~~~~~~~~~~~~~ 2256 2257AVX512_elapsed_ms 2258^^^^^^^^^^^^^^^^^^ 2259 2260 If AVX512 is supported on the machine, this entry shows the milliseconds 2261 elapsed since the last time AVX512 usage was recorded. The recording 2262 happens on a best effort basis when a task is scheduled out. This means 2263 that the value depends on two factors: 2264 2265 1) The time which the task spent on the CPU without being scheduled 2266 out. With CPU isolation and a single runnable task this can take 2267 several seconds. 2268 2269 2) The time since the task was scheduled out last. Depending on the 2270 reason for being scheduled out (time slice exhausted, syscall ...) 2271 this can be arbitrary long time. 2272 2273 As a consequence the value cannot be considered precise and authoritative 2274 information. The application which uses this information has to be aware 2275 of the overall scenario on the system in order to determine whether a 2276 task is a real AVX512 user or not. Precise information can be obtained 2277 with performance counters. 2278 2279 A special value of '-1' indicates that no AVX512 usage was recorded, thus 2280 the task is unlikely an AVX512 user, but depends on the workload and the 2281 scheduling scenario, it also could be a false negative mentioned above. 2282 22833.13 /proc/<pid>/fd - List of symlinks to open files 2284------------------------------------------------------- 2285This directory contains symbolic links which represent open files 2286the process is maintaining. Example output:: 2287 2288 lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null 2289 l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null 2290 lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]' 2291 lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]' 2292 lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]' 2293 2294The number of open files for the process is stored in 'size' member 2295of stat() output for /proc/<pid>/fd for fast access. 2296------------------------------------------------------- 2297 22983.14 /proc/<pid/ksm_stat - Information about the process's ksm status 2299--------------------------------------------------------------------- 2300When CONFIG_KSM is enabled, each process has this file which displays 2301the information of ksm merging status. 2302 2303Example 2304~~~~~~~ 2305 2306:: 2307 2308 / # cat /proc/self/ksm_stat 2309 ksm_rmap_items 0 2310 ksm_zero_pages 0 2311 ksm_merging_pages 0 2312 ksm_process_profit 0 2313 ksm_merge_any: no 2314 ksm_mergeable: no 2315 2316Description 2317~~~~~~~~~~~ 2318 2319ksm_rmap_items 2320^^^^^^^^^^^^^^ 2321 2322The number of ksm_rmap_item structures in use. The structure 2323ksm_rmap_item stores the reverse mapping information for virtual 2324addresses. KSM will generate a ksm_rmap_item for each ksm-scanned page of 2325the process. 2326 2327ksm_zero_pages 2328^^^^^^^^^^^^^^ 2329 2330When /sys/kernel/mm/ksm/use_zero_pages is enabled, it represent how many 2331empty pages are merged with kernel zero pages by KSM. 2332 2333ksm_merging_pages 2334^^^^^^^^^^^^^^^^^ 2335 2336It represents how many pages of this process are involved in KSM merging 2337(not including ksm_zero_pages). It is the same with what 2338/proc/<pid>/ksm_merging_pages shows. 2339 2340ksm_process_profit 2341^^^^^^^^^^^^^^^^^^ 2342 2343The profit that KSM brings (Saved bytes). KSM can save memory by merging 2344identical pages, but also can consume additional memory, because it needs 2345to generate a number of rmap_items to save each scanned page's brief rmap 2346information. Some of these pages may be merged, but some may not be abled 2347to be merged after being checked several times, which are unprofitable 2348memory consumed. 2349 2350ksm_merge_any 2351^^^^^^^^^^^^^ 2352 2353It specifies whether the process's 'mm is added by prctl() into the 2354candidate list of KSM or not, and if KSM scanning is fully enabled at 2355process level. 2356 2357ksm_mergeable 2358^^^^^^^^^^^^^ 2359 2360It specifies whether any VMAs of the process''s mms are currently 2361applicable to KSM. 2362 2363More information about KSM can be found in 2364Documentation/admin-guide/mm/ksm.rst. 2365 2366 2367Chapter 4: Configuring procfs 2368============================= 2369 23704.1 Mount options 2371--------------------- 2372 2373The following mount options are supported: 2374 2375 ========= ======================================================== 2376 hidepid= Set /proc/<pid>/ access mode. 2377 gid= Set the group authorized to learn processes information. 2378 subset= Show only the specified subset of procfs. 2379 pidns= Specify a the namespace used by this procfs. 2380 ========= ======================================================== 2381 2382hidepid=off or hidepid=0 means classic mode - everybody may access all 2383/proc/<pid>/ directories (default). 2384 2385hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ 2386directories but their own. Sensitive files like cmdline, sched*, status are now 2387protected against other users. This makes it impossible to learn whether any 2388user runs specific program (given the program doesn't reveal itself by its 2389behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for 2390other users, poorly written programs passing sensitive information via program 2391arguments are now protected against local eavesdroppers. 2392 2393hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be 2394fully invisible to other users. It doesn't mean that it hides a fact whether a 2395process with a specific pid value exists (it can be learned by other means, e.g. 2396by "kill -0 $PID"), but it hides process's uid and gid, which may be learned by 2397stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of 2398gathering information about running processes, whether some daemon runs with 2399elevated privileges, whether other user runs some sensitive program, whether 2400other users run any program at all, etc. 2401 2402hidepid=ptraceable or hidepid=4 means that procfs should only contain 2403/proc/<pid>/ directories that the caller can ptrace. 2404 2405gid= defines a group authorized to learn processes information otherwise 2406prohibited by hidepid=. If you use some daemon like identd which needs to learn 2407information about processes information, just add identd to this group. 2408 2409subset=pid hides all top level files and directories in the procfs that 2410are not related to tasks. 2411 2412pidns= specifies a pid namespace (either as a string path to something like 2413`/proc/$pid/ns/pid`, or a file descriptor when using `FSCONFIG_SET_FD`) that 2414will be used by the procfs instance when translating pids. By default, procfs 2415will use the calling process's active pid namespace. Note that the pid 2416namespace of an existing procfs instance cannot be modified (attempting to do 2417so will give an `-EBUSY` error). 2418 2419Chapter 5: Filesystem behavior 2420============================== 2421 2422Originally, before the advent of pid namespace, procfs was a global file 2423system. It means that there was only one procfs instance in the system. 2424 2425When pid namespace was added, a separate procfs instance was mounted in 2426each pid namespace. So, procfs mount options are global among all 2427mountpoints within the same namespace:: 2428 2429 # grep ^proc /proc/mounts 2430 proc /proc proc rw,relatime,hidepid=2 0 0 2431 2432 # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc 2433 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0 2434 +++ exited with 0 +++ 2435 2436 # grep ^proc /proc/mounts 2437 proc /proc proc rw,relatime,hidepid=2 0 0 2438 proc /tmp/proc proc rw,relatime,hidepid=2 0 0 2439 2440and only after remounting procfs mount options will change at all 2441mountpoints:: 2442 2443 # mount -o remount,hidepid=1 -t proc proc /tmp/proc 2444 2445 # grep ^proc /proc/mounts 2446 proc /proc proc rw,relatime,hidepid=1 0 0 2447 proc /tmp/proc proc rw,relatime,hidepid=1 0 0 2448 2449This behavior is different from the behavior of other filesystems. 2450 2451The new procfs behavior is more like other filesystems. Each procfs mount 2452creates a new procfs instance. Mount options affect own procfs instance. 2453It means that it became possible to have several procfs instances 2454displaying tasks with different filtering options in one pid namespace:: 2455 2456 # mount -o hidepid=invisible -t proc proc /proc 2457 # mount -o hidepid=noaccess -t proc proc /tmp/proc 2458 # grep ^proc /proc/mounts 2459 proc /proc proc rw,relatime,hidepid=invisible 0 0 2460 proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 2461