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 64We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of 65other people for help compiling this documentation. We'd also like to extend a 66special thank you to Andi Kleen for documentation, which we relied on heavily 67to create this document, as well as the additional information he provided. 68Thanks to everybody else who contributed source or docs to the Linux kernel 69and helped create a great piece of software... :) 70 71The latest version of this document is available online at 72https://www.kernel.org/doc/html/latest/filesystems/proc.html 73 740.2 Legal Stuff 75--------------- 76 77We don't guarantee the correctness of this document, and if you come to us 78complaining about how you screwed up your system because of incorrect 79documentation, we won't feel responsible... 80 81Chapter 1: Collecting System Information 82======================================== 83 84In This Chapter 85--------------- 86* Investigating the properties of the pseudo file system /proc and its 87 ability to provide information on the running Linux system 88* Examining /proc's structure 89* Uncovering various information about the kernel and the processes running 90 on the system 91 92------------------------------------------------------------------------------ 93 94The proc file system acts as an interface to internal data structures in the 95kernel. It can be used to obtain information about the system and to change 96certain kernel parameters at runtime (sysctl). 97 98First, we'll take a look at the read-only parts of /proc. In Chapter 2, we 99show you how you can use /proc/sys to change settings. 100 1011.1 Process-Specific Subdirectories 102----------------------------------- 103 104The directory /proc contains (among other things) one subdirectory for each 105process running on the system, which is named after the process ID (PID). 106 107The link 'self' points to the process reading the file system. Each process 108subdirectory has the entries listed in Table 1-1. 109 110A process can read its own information from /proc/PID/* with no extra 111permissions. When reading /proc/PID/* information for other processes, reading 112process is required to have either CAP_SYS_PTRACE capability with 113PTRACE_MODE_READ access permissions, or, alternatively, CAP_PERFMON 114capability. This applies to all read-only information like `maps`, `environ`, 115`pagemap`, etc. The only exception is `mem` file due to its read-write nature, 116which requires CAP_SYS_PTRACE capabilities with more elevated 117PTRACE_MODE_ATTACH permissions; CAP_PERFMON capability does not grant access 118to /proc/PID/mem for other processes. 119 120Note that an open file descriptor to /proc/<pid> or to any of its 121contained files or subdirectories does not prevent <pid> being reused 122for some other process in the event that <pid> exits. Operations on 123open /proc/<pid> file descriptors corresponding to dead processes 124never act on any new process that the kernel may, through chance, have 125also assigned the process ID <pid>. Instead, operations on these FDs 126usually fail with ESRCH. 127 128.. table:: Table 1-1: Process specific entries in /proc 129 130 ============= =============================================================== 131 File Content 132 ============= =============================================================== 133 clear_refs Clears page referenced bits shown in smaps output 134 cmdline Command line arguments 135 cpu Current and last cpu in which it was executed (2.4)(smp) 136 cwd Link to the current working directory 137 environ Values of environment variables 138 exe Link to the executable of this process 139 fd Directory, which contains all file descriptors 140 maps Memory maps to executables and library files (2.4) 141 mem Memory held by this process 142 root Link to the root directory of this process 143 stat Process status 144 statm Process memory status information 145 status Process status in human readable form 146 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function 147 symbol the task is blocked in - or "0" if not blocked. 148 pagemap Page table 149 stack Report full stack trace, enable via CONFIG_STACKTRACE 150 smaps An extension based on maps, showing the memory consumption of 151 each mapping and flags associated with it 152 smaps_rollup Accumulated smaps stats for all mappings of the process. This 153 can be derived from smaps, but is faster and more convenient 154 numa_maps An extension based on maps, showing the memory locality and 155 binding policy as well as mem usage (in pages) of each mapping. 156 ============= =============================================================== 157 158For example, to get the status information of a process, all you have to do is 159read the file /proc/PID/status:: 160 161 >cat /proc/self/status 162 Name: cat 163 State: R (running) 164 Tgid: 5452 165 Pid: 5452 166 PPid: 743 167 TracerPid: 0 (2.4) 168 Uid: 501 501 501 501 169 Gid: 100 100 100 100 170 FDSize: 256 171 Groups: 100 14 16 172 Kthread: 0 173 VmPeak: 5004 kB 174 VmSize: 5004 kB 175 VmLck: 0 kB 176 VmHWM: 476 kB 177 VmRSS: 476 kB 178 RssAnon: 352 kB 179 RssFile: 120 kB 180 RssShmem: 4 kB 181 VmData: 156 kB 182 VmStk: 88 kB 183 VmExe: 68 kB 184 VmLib: 1412 kB 185 VmPTE: 20 kb 186 VmSwap: 0 kB 187 HugetlbPages: 0 kB 188 CoreDumping: 0 189 THP_enabled: 1 190 Threads: 1 191 SigQ: 0/28578 192 SigPnd: 0000000000000000 193 ShdPnd: 0000000000000000 194 SigBlk: 0000000000000000 195 SigIgn: 0000000000000000 196 SigCgt: 0000000000000000 197 CapInh: 00000000fffffeff 198 CapPrm: 0000000000000000 199 CapEff: 0000000000000000 200 CapBnd: ffffffffffffffff 201 CapAmb: 0000000000000000 202 NoNewPrivs: 0 203 Seccomp: 0 204 Speculation_Store_Bypass: thread vulnerable 205 SpeculationIndirectBranch: conditional enabled 206 voluntary_ctxt_switches: 0 207 nonvoluntary_ctxt_switches: 1 208 209This shows you nearly the same information you would get if you viewed it with 210the ps command. In fact, ps uses the proc file system to obtain its 211information. But you get a more detailed view of the process by reading the 212file /proc/PID/status. It fields are described in table 1-2. 213 214The statm file contains more detailed information about the process 215memory usage. Its seven fields are explained in Table 1-3. The stat file 216contains detailed information about the process itself. Its fields are 217explained in Table 1-4. 218 219(for SMP CONFIG users) 220 221For making accounting scalable, RSS related information are handled in an 222asynchronous manner and the value may not be very precise. To see a precise 223snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table. 224It's slow but very precise. 225 226.. table:: Table 1-2: Contents of the status fields (as of 4.19) 227 228 ========================== =================================================== 229 Field Content 230 ========================== =================================================== 231 Name filename of the executable 232 Umask file mode creation mask 233 State state (R is running, S is sleeping, D is sleeping 234 in an uninterruptible wait, Z is zombie, 235 T is traced or stopped) 236 Tgid thread group ID 237 Ngid NUMA group ID (0 if none) 238 Pid process id 239 PPid process id of the parent process 240 TracerPid PID of process tracing this process (0 if not, or 241 the tracer is outside of the current pid namespace) 242 Uid Real, effective, saved set, and file system UIDs 243 Gid Real, effective, saved set, and file system GIDs 244 FDSize number of file descriptor slots currently allocated 245 Groups supplementary group list 246 NStgid descendant namespace thread group ID hierarchy 247 NSpid descendant namespace process ID hierarchy 248 NSpgid descendant namespace process group ID hierarchy 249 NSsid descendant namespace session ID hierarchy 250 Kthread kernel thread flag, 1 is yes, 0 is no 251 VmPeak peak virtual memory size 252 VmSize total program size 253 VmLck locked memory size 254 VmPin pinned memory size 255 VmHWM peak resident set size ("high water mark") 256 VmRSS size of memory portions. It contains the three 257 following parts 258 (VmRSS = RssAnon + RssFile + RssShmem) 259 RssAnon size of resident anonymous memory 260 RssFile size of resident file mappings 261 RssShmem size of resident shmem memory (includes SysV shm, 262 mapping of tmpfs and shared anonymous mappings) 263 VmData size of private data segments 264 VmStk size of stack segments 265 VmExe size of text segment 266 VmLib size of shared library code 267 VmPTE size of page table entries 268 VmSwap amount of swap used by anonymous private data 269 (shmem swap usage is not included) 270 HugetlbPages size of hugetlb memory portions 271 CoreDumping process's memory is currently being dumped 272 (killing the process may lead to a corrupted core) 273 THP_enabled process is allowed to use THP (returns 0 when 274 PR_SET_THP_DISABLE is set on the process to disable 275 THP completely, not just partially) 276 Threads number of threads 277 SigQ number of signals queued/max. number for queue 278 SigPnd bitmap of pending signals for the thread 279 ShdPnd bitmap of shared pending signals for the process 280 SigBlk bitmap of blocked signals 281 SigIgn bitmap of ignored signals 282 SigCgt bitmap of caught signals 283 CapInh bitmap of inheritable capabilities 284 CapPrm bitmap of permitted capabilities 285 CapEff bitmap of effective capabilities 286 CapBnd bitmap of capabilities bounding set 287 CapAmb bitmap of ambient capabilities 288 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...) 289 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...) 290 Speculation_Store_Bypass speculative store bypass mitigation status 291 SpeculationIndirectBranch indirect branch speculation mode 292 Cpus_allowed mask of CPUs on which this process may run 293 Cpus_allowed_list Same as previous, but in "list format" 294 Mems_allowed mask of memory nodes allowed to this process 295 Mems_allowed_list Same as previous, but in "list format" 296 voluntary_ctxt_switches number of voluntary context switches 297 nonvoluntary_ctxt_switches number of non voluntary context switches 298 ========================== =================================================== 299 300 301.. table:: Table 1-3: Contents of the statm fields (as of 2.6.8-rc3) 302 303 ======== =============================== ============================== 304 Field Content 305 ======== =============================== ============================== 306 size total program size (pages) (same as VmSize in status) 307 resident size of memory portions (pages) (same as VmRSS in status) 308 shared number of pages that are shared (i.e. backed by a file, same 309 as RssFile+RssShmem in status) 310 trs number of pages that are 'code' (not including libs; broken, 311 includes data segment) 312 lrs number of pages of library (always 0 on 2.6) 313 drs number of pages of data/stack (including libs; broken, 314 includes library text) 315 dt number of dirty pages (always 0 on 2.6) 316 ======== =============================== ============================== 317 318 319.. table:: Table 1-4: Contents of the stat fields (as of 2.6.30-rc7) 320 321 ============= =============================================================== 322 Field Content 323 ============= =============================================================== 324 pid process id 325 tcomm filename of the executable 326 state state (R is running, S is sleeping, D is sleeping in an 327 uninterruptible wait, Z is zombie, T is traced or stopped) 328 ppid process id of the parent process 329 pgrp pgrp of the process 330 sid session id 331 tty_nr tty the process uses 332 tty_pgrp pgrp of the tty 333 flags task flags 334 min_flt number of minor faults 335 cmin_flt number of minor faults with child's 336 maj_flt number of major faults 337 cmaj_flt number of major faults with child's 338 utime user mode jiffies 339 stime kernel mode jiffies 340 cutime user mode jiffies with child's 341 cstime kernel mode jiffies with child's 342 priority priority level 343 nice nice level 344 num_threads number of threads 345 it_real_value (obsolete, always 0) 346 start_time time the process started after system boot 347 vsize virtual memory size 348 rss resident set memory size 349 rsslim current limit in bytes on the rss 350 start_code address above which program text can run 351 end_code address below which program text can run 352 start_stack address of the start of the main process stack 353 esp current value of ESP 354 eip current value of EIP 355 pending bitmap of pending signals 356 blocked bitmap of blocked signals 357 sigign bitmap of ignored signals 358 sigcatch bitmap of caught signals 359 0 (place holder, used to be the wchan address, 360 use /proc/PID/wchan instead) 361 0 (place holder) 362 0 (place holder) 363 exit_signal signal to send to parent thread on exit 364 task_cpu which CPU the task is scheduled on 365 rt_priority realtime priority 366 policy scheduling policy (man sched_setscheduler) 367 blkio_ticks time spent waiting for block IO 368 gtime guest time of the task in jiffies 369 cgtime guest time of the task children in jiffies 370 start_data address above which program data+bss is placed 371 end_data address below which program data+bss is placed 372 start_brk address above which program heap can be expanded with brk() 373 arg_start address above which program command line is placed 374 arg_end address below which program command line is placed 375 env_start address above which program environment is placed 376 env_end address below which program environment is placed 377 exit_code the thread's exit_code in the form reported by the waitpid 378 system call 379 ============= =============================================================== 380 381The /proc/PID/maps file contains the currently mapped memory regions and 382their access permissions. 383 384The format is:: 385 386 address perms offset dev inode pathname 387 388 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test 389 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test 390 0804a000-0806b000 rw-p 00000000 00:00 0 [heap] 391 a7cb1000-a7cb2000 ---p 00000000 00:00 0 392 a7cb2000-a7eb2000 rw-p 00000000 00:00 0 393 a7eb2000-a7eb3000 ---p 00000000 00:00 0 394 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 395 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 396 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 397 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 398 a800b000-a800e000 rw-p 00000000 00:00 0 399 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 400 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 401 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 402 a8024000-a8027000 rw-p 00000000 00:00 0 403 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 404 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 405 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 406 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack] 407 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] 408 409where "address" is the address space in the process that it occupies, "perms" 410is a set of permissions:: 411 412 r = read 413 w = write 414 x = execute 415 s = shared 416 p = private (copy on write) 417 418"offset" is the offset into the mapping, "dev" is the device (major:minor), and 419"inode" is the inode on that device. 0 indicates that no inode is associated 420with the memory region, as the case would be with BSS (uninitialized data). 421The "pathname" shows the name associated file for this mapping. If the mapping 422is not associated with a file: 423 424 =================== =========================================== 425 [heap] the heap of the program 426 [stack] the stack of the main process 427 [vdso] the "virtual dynamic shared object", 428 the kernel system call handler 429 [anon:<name>] a private anonymous mapping that has been 430 named by userspace 431 [anon_shmem:<name>] an anonymous shared memory mapping that has 432 been named by userspace 433 =================== =========================================== 434 435 or if empty, the mapping is anonymous. 436 437Starting with 6.11 kernel, /proc/PID/maps provides an alternative 438ioctl()-based API that gives ability to flexibly and efficiently query and 439filter individual VMAs. This interface is binary and is meant for more 440efficient and easy programmatic use. `struct procmap_query`, defined in 441linux/fs.h UAPI header, serves as an input/output argument to the 442`PROCMAP_QUERY` ioctl() command. See comments in linus/fs.h UAPI header for 443details on query semantics, supported flags, data returned, and general API 444usage information. 445 446The /proc/PID/smaps is an extension based on maps, showing the memory 447consumption for each of the process's mappings. For each mapping (aka Virtual 448Memory Area, or VMA) there is a series of lines such as the following:: 449 450 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash 451 452 Size: 1084 kB 453 KernelPageSize: 4 kB 454 MMUPageSize: 4 kB 455 Rss: 892 kB 456 Pss: 374 kB 457 Pss_Dirty: 0 kB 458 Shared_Clean: 892 kB 459 Shared_Dirty: 0 kB 460 Private_Clean: 0 kB 461 Private_Dirty: 0 kB 462 Referenced: 892 kB 463 Anonymous: 0 kB 464 KSM: 0 kB 465 LazyFree: 0 kB 466 AnonHugePages: 0 kB 467 FilePmdMapped: 0 kB 468 ShmemPmdMapped: 0 kB 469 Shared_Hugetlb: 0 kB 470 Private_Hugetlb: 0 kB 471 Swap: 0 kB 472 SwapPss: 0 kB 473 Locked: 0 kB 474 THPeligible: 0 475 VmFlags: rd ex mr mw me dw 476 477The first of these lines shows the same information as is displayed for 478the mapping in /proc/PID/maps. Following lines show the size of the 479mapping (size); the smallest possible page size allocated when backing a 480VMA (KernelPageSize), which is the granularity in which VMA modifications 481can be performed; the smallest possible page size that could be used by the 482MMU (MMUPageSize) when backing a VMA; the amount of the mapping that is 483currently resident in RAM (RSS); the process's proportional share of this 484mapping (PSS); and the number of clean and dirty shared and private pages 485in the mapping. 486 487"KernelPageSize" always corresponds to "MMUPageSize", except when a larger 488kernel page size is emulated on a system with a smaller page size used by the 489MMU, which is the case for some PPC64 setups with hugetlb. Furthermore, 490"KernelPageSize" and "MMUPageSize" always correspond to the smallest 491possible granularity (fallback) that can be encountered in a VMA throughout 492its lifetime. These values are not affected by Transparent Huge Pages 493being in effect, or any usage of larger MMU page sizes (either through 494architectural huge-page mappings or other explicit/implicit coalescing of 495virtual ranges performed by the MMU). "AnonHugePages", "ShmemPmdMapped" and 496"FilePmdMapped" provide insight into the usage of PMD-level architectural 497huge-page mappings. 498 499The "proportional set size" (PSS) of a process is the count of pages it has 500in memory, where each page is divided by the number of processes sharing it. 501So if a process has 1000 pages all to itself, and 1000 shared with one other 502process, its PSS will be 1500. "Pss_Dirty" is the portion of PSS which 503consists of dirty pages. ("Pss_Clean" is not included, but it can be 504calculated by subtracting "Pss_Dirty" from "Pss".) 505 506Traditionally, a page is accounted as "private" if it is mapped exactly once, 507and a page is accounted as "shared" when mapped multiple times, even when 508mapped in the same process multiple times. Note that this accounting is 509independent of MAP_SHARED. 510 511In some kernel configurations, the semantics of pages part of a larger 512allocation (e.g., THP) can differ: a page is accounted as "private" if all 513pages part of the corresponding large allocation are *certainly* mapped in the 514same process, even if the page is mapped multiple times in that process. A 515page is accounted as "shared" if any page page of the larger allocation 516is *maybe* mapped in a different process. In some cases, a large allocation 517might be treated as "maybe mapped by multiple processes" even though this 518is no longer the case. 519 520Some kernel configurations do not track the precise number of times a page part 521of a larger allocation is mapped. In this case, when calculating the PSS, the 522average number of mappings per page in this larger allocation might be used 523as an approximation for the number of mappings of a page. The PSS calculation 524will be imprecise in this case. 525 526"Referenced" indicates the amount of memory currently marked as referenced or 527accessed. 528 529"Anonymous" shows the amount of memory that does not belong to any file. Even 530a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE 531and a page is modified, the file page is replaced by a private anonymous copy. 532 533"KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages 534are not included, only actual KSM pages. 535 536"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE). 537The memory isn't freed immediately with madvise(). It's freed in memory 538pressure if the memory is clean. Please note that the printed value might 539be lower than the real value due to optimizations used in the current 540implementation. If this is not desirable please file a bug report. 541 542"AnonHugePages", "ShmemPmdMapped" and "FilePmdMapped" show the amount of 543memory backed by Transparent Huge Pages that are currently mapped by 544architectural huge-page mappings at the PMD level. "AnonHugePages" 545corresponds to memory that does not belong to a file, "ShmemPmdMapped" to 546shared memory (shmem/tmpfs) and "FilePmdMapped" to file-backed memory 547(excluding shmem/tmpfs). 548 549There are no dedicated entries for Transparent Huge Pages (or similar concepts) 550that are not mapped by architectural huge-page mappings at the PMD level. 551 552"Shared_Hugetlb" and "Private_Hugetlb" show the amounts of memory backed by 553hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical 554reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field. 555 556"Swap" shows how much would-be-anonymous memory is also used, but out on swap. 557 558For shmem mappings, "Swap" includes also the size of the mapped (and not 559replaced by copy-on-write) part of the underlying shmem object out on swap. 560"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this 561does not take into account swapped out page of underlying shmem objects. 562"Locked" indicates whether the mapping is locked in memory or not. 563 564"THPeligible" indicates whether the mapping is eligible for allocating 565naturally aligned THP pages of any currently enabled size. 1 if true, 0 566otherwise. 567 568If both the kernel and the CPU support protection keys (pkeys), 569"ProtectionKey" indicates the memory protection key associated with the 570virtual memory area. 571 572"VmFlags" field deserves a separate description. This member represents the 573kernel flags associated with the particular virtual memory area in two letter 574encoded manner. The codes are the following: 575 576 == ============================================================= 577 rd readable 578 wr writeable 579 ex executable 580 sh shared 581 mr may read 582 mw may write 583 me may execute 584 ms may share 585 gd stack segment growns down 586 pf pure PFN range 587 lo pages are locked in memory 588 io memory mapped I/O area 589 sr sequential read advise provided 590 rr random read advise provided 591 dc do not copy area on fork 592 de do not expand area on remapping 593 ac area is accountable 594 nr swap space is not reserved for the area 595 ht area uses huge tlb pages 596 sf synchronous page fault 597 ar architecture specific flag 598 wf wipe on fork 599 dd do not include area into core dump 600 sd soft dirty flag 601 mm mixed map area 602 hg huge page advise flag 603 nh no huge page advise flag 604 mg mergeable advise flag 605 bt arm64 BTI guarded page 606 mt arm64 MTE allocation tags are enabled 607 um userfaultfd missing tracking 608 uw userfaultfd wr-protect tracking 609 ui userfaultfd minor fault 610 ss shadow/guarded control stack page 611 sl sealed 612 lf lock on fault pages 613 dp always lazily freeable mapping 614 gu maybe contains guard regions (if not set, definitely doesn't) 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 DMA 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 default_smp_affinity. 885 886For example:: 887 888 > ls /proc/irq/ 889 0 10 12 14 16 18 2 4 6 8 default_smp_affinity 890 1 11 13 15 17 19 3 5 7 9 891 > ls /proc/irq/0/ 892 smp_affinity 893 894smp_affinity is a bitmask, in which you can specify which CPUs can handle the 895IRQ. You can set it by doing:: 896 897 > echo 1 > /proc/irq/10/smp_affinity 898 899This means that only the first CPU will handle the IRQ, but you can also echo 9005 which means that only the first and third CPU can handle the IRQ. 901 902The contents of each smp_affinity file is the same by default:: 903 904 > cat /proc/irq/0/smp_affinity 905 ffffffff 906 907There is an alternate interface, smp_affinity_list which allows specifying 908a CPU range instead of a bitmask:: 909 910 > cat /proc/irq/0/smp_affinity_list 911 1024-1031 912 913The default_smp_affinity mask applies to all non-active IRQs, which are the 914IRQs which have not yet been allocated/activated, and hence which lack a 915/proc/irq/[0-9]* directory. 916 917The node file on an SMP system shows the node to which the device using the IRQ 918reports itself as being attached. This hardware locality information does not 919include information about any possible driver locality preference. 920 921The way IRQs are routed is handled by the IO-APIC, and it's Round Robin 922between all the CPUs which are allowed to handle it. As usual the kernel has 923more info than you and does a better job than you, so the defaults are the 924best choice for almost everyone. [Note this applies only to those IO-APIC's 925that support "Round Robin" interrupt distribution.] 926 927There are three more important subdirectories in /proc: net, scsi, and sys. 928The general rule is that the contents, or even the existence of these 929directories, depend on your kernel configuration. If SCSI is not enabled, the 930directory scsi may not exist. The same is true with the net, which is there 931only when networking support is present in the running kernel. 932 933The slabinfo file gives information about memory usage at the slab level. 934Linux uses slab pools for memory management above page level in version 2.2. 935Commonly used objects have their own slab pool (such as network buffers, 936directory cache, and so on). 937 938:: 939 940 > cat /proc/buddyinfo 941 942 Node 0, zone DMA 0 4 5 4 4 3 ... 943 Node 0, zone Normal 1 0 0 1 101 8 ... 944 Node 0, zone HighMem 2 0 0 1 1 0 ... 945 946External fragmentation is a problem under some workloads, and buddyinfo is a 947useful tool for helping diagnose these problems. Buddyinfo will give you a 948clue as to how big an area you can safely allocate, or why a previous 949allocation failed. 950 951Each column represents the number of pages of a certain order which are 952available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 953ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 954available in ZONE_NORMAL, etc... 955 956More information relevant to external fragmentation can be found in 957pagetypeinfo:: 958 959 > cat /proc/pagetypeinfo 960 Page block order: 9 961 Pages per block: 512 962 963 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 964 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0 965 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0 966 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2 967 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0 968 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0 969 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9 970 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0 971 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452 972 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0 973 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0 974 975 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate 976 Node 0, zone DMA 2 0 5 1 0 977 Node 0, zone DMA32 41 6 967 2 0 978 979Fragmentation avoidance in the kernel works by grouping pages of different 980migrate types into the same contiguous regions of memory called page blocks. 981A page block is typically the size of the default hugepage size, e.g. 2MB on 982X86-64. By keeping pages grouped based on their ability to move, the kernel 983can reclaim pages within a page block to satisfy a high-order allocation. 984 985The pagetypinfo begins with information on the size of a page block. It 986then gives the same type of information as buddyinfo except broken down 987by migrate-type and finishes with details on how many page blocks of each 988type exist. 989 990If min_free_kbytes has been tuned correctly (recommendations made by hugeadm 991from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can 992make an estimate of the likely number of huge pages that can be allocated 993at a given point in time. All the "Movable" blocks should be allocatable 994unless memory has been mlock()'d. Some of the Reclaimable blocks should 995also be allocatable although a lot of filesystem metadata may have to be 996reclaimed to achieve this. 997 998 999allocinfo 1000~~~~~~~~~ 1001 1002Provides information about memory allocations at all locations in the code 1003base. Each allocation in the code is identified by its source file, line 1004number, module (if originates from a loadable module) and the function calling 1005the allocation. The number of bytes allocated and number of calls at each 1006location are reported. The first line indicates the version of the file, the 1007second line is the header listing fields in the file. 1008If file version is 2.0 or higher then each line may contain additional 1009<key>:<value> pairs representing extra information about the call site. 1010For example if the counters are not accurate, the line will be appended with 1011"accurate:no" pair. 1012 1013Supported markers in v2: 1014accurate:no 1015 1016 Absolute values of the counters in this line are not accurate 1017 because of the failure to allocate memory to track some of the 1018 allocations made at this location. Deltas in these counters are 1019 accurate, therefore counters can be used to track allocation size 1020 and count changes. 1021 1022Example output. 1023 1024:: 1025 1026 > tail -n +3 /proc/allocinfo | sort -rn 1027 127664128 31168 mm/page_ext.c:270 func:alloc_page_ext 1028 56373248 4737 mm/slub.c:2259 func:alloc_slab_page 1029 14880768 3633 mm/readahead.c:247 func:page_cache_ra_unbounded 1030 14417920 3520 mm/mm_init.c:2530 func:alloc_large_system_hash 1031 13377536 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs 1032 11718656 2861 mm/filemap.c:1919 func:__filemap_get_folio 1033 9192960 2800 kernel/fork.c:307 func:alloc_thread_stack_node 1034 4206592 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable 1035 4136960 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start 1036 3940352 962 mm/memory.c:4214 func:alloc_anon_folio 1037 2894464 22613 fs/kernfs/dir.c:615 func:__kernfs_new_node 1038 ... 1039 1040 1041meminfo 1042~~~~~~~ 1043 1044Provides information about distribution and utilization of memory. This 1045varies by architecture and compile options. Some of the counters reported 1046here overlap. The memory reported by the non overlapping counters may not 1047add up to the overall memory usage and the difference for some workloads 1048can be substantial. In many cases there are other means to find out 1049additional memory using subsystem specific interfaces, for instance 1050/proc/net/sockstat for TCP memory allocations. 1051 1052Example output. You may not have all of these fields. 1053 1054:: 1055 1056 > cat /proc/meminfo 1057 1058 MemTotal: 32858820 kB 1059 MemFree: 21001236 kB 1060 MemAvailable: 27214312 kB 1061 Buffers: 581092 kB 1062 Cached: 5587612 kB 1063 SwapCached: 0 kB 1064 Active: 3237152 kB 1065 Inactive: 7586256 kB 1066 Active(anon): 94064 kB 1067 Inactive(anon): 4570616 kB 1068 Active(file): 3143088 kB 1069 Inactive(file): 3015640 kB 1070 Unevictable: 0 kB 1071 Mlocked: 0 kB 1072 SwapTotal: 0 kB 1073 SwapFree: 0 kB 1074 Zswap: 1904 kB 1075 Zswapped: 7792 kB 1076 Dirty: 12 kB 1077 Writeback: 0 kB 1078 AnonPages: 4654780 kB 1079 Mapped: 266244 kB 1080 Shmem: 9976 kB 1081 KReclaimable: 517708 kB 1082 Slab: 660044 kB 1083 SReclaimable: 517708 kB 1084 SUnreclaim: 142336 kB 1085 KernelStack: 11168 kB 1086 PageTables: 20540 kB 1087 SecPageTables: 0 kB 1088 NFS_Unstable: 0 kB 1089 Bounce: 0 kB 1090 WritebackTmp: 0 kB 1091 CommitLimit: 16429408 kB 1092 Committed_AS: 7715148 kB 1093 VmallocTotal: 34359738367 kB 1094 VmallocUsed: 40444 kB 1095 VmallocChunk: 0 kB 1096 Percpu: 29312 kB 1097 EarlyMemtestBad: 0 kB 1098 HardwareCorrupted: 0 kB 1099 AnonHugePages: 4149248 kB 1100 ShmemHugePages: 0 kB 1101 ShmemPmdMapped: 0 kB 1102 FileHugePages: 0 kB 1103 FilePmdMapped: 0 kB 1104 CmaTotal: 0 kB 1105 CmaFree: 0 kB 1106 Unaccepted: 0 kB 1107 Balloon: 0 kB 1108 GPUActive: 0 kB 1109 GPUReclaim: 0 kB 1110 HugePages_Total: 0 1111 HugePages_Free: 0 1112 HugePages_Rsvd: 0 1113 HugePages_Surp: 0 1114 Hugepagesize: 2048 kB 1115 Hugetlb: 0 kB 1116 DirectMap4k: 401152 kB 1117 DirectMap2M: 10008576 kB 1118 DirectMap1G: 24117248 kB 1119 1120MemTotal 1121 Total usable RAM (i.e. physical RAM minus a few reserved 1122 bits and the kernel binary code) 1123MemFree 1124 Total free RAM. On highmem systems, the sum of LowFree+HighFree 1125MemAvailable 1126 An estimate of how much memory is available for starting new 1127 applications, without swapping. Calculated from MemFree, 1128 SReclaimable, the size of the file LRU lists, and the low 1129 watermarks in each zone. 1130 The estimate takes into account that the system needs some 1131 page cache to function well, and that not all reclaimable 1132 slab will be reclaimable, due to items being in use. The 1133 impact of those factors will vary from system to system. 1134Buffers 1135 Relatively temporary storage for raw disk blocks 1136 shouldn't get tremendously large (20MB or so) 1137Cached 1138 In-memory cache for files read from the disk (the 1139 pagecache) as well as tmpfs & shmem. 1140 Doesn't include SwapCached. 1141SwapCached 1142 Memory that once was swapped out, is swapped back in but 1143 still also is in the swapfile (if memory is needed it 1144 doesn't need to be swapped out AGAIN because it is already 1145 in the swapfile. This saves I/O) 1146Active 1147 Memory that has been used more recently and usually not 1148 reclaimed unless absolutely necessary. 1149Inactive 1150 Memory which has been less recently used. It is more 1151 eligible to be reclaimed for other purposes 1152Unevictable 1153 Memory allocated for userspace which cannot be reclaimed, such 1154 as mlocked pages, ramfs backing pages, secret memfd pages etc. 1155Mlocked 1156 Memory locked with mlock(). 1157HighTotal, HighFree 1158 Highmem is all memory above ~860MB of physical memory. 1159 Highmem areas are for use by userspace programs, or 1160 for the pagecache. The kernel must use tricks to access 1161 this memory, making it slower to access than lowmem. 1162LowTotal, LowFree 1163 Lowmem is memory which can be used for everything that 1164 highmem can be used for, but it is also available for the 1165 kernel's use for its own data structures. Among many 1166 other things, it is where everything from the Slab is 1167 allocated. Bad things happen when you're out of lowmem. 1168SwapTotal 1169 total amount of swap space available 1170SwapFree 1171 Memory which has been evicted from RAM, and is temporarily 1172 on the disk 1173Zswap 1174 Memory consumed by the zswap backend (compressed size) 1175Zswapped 1176 Amount of anonymous memory stored in zswap (original size) 1177Dirty 1178 Memory which is waiting to get written back to the disk 1179Writeback 1180 Memory which is actively being written back to the disk 1181AnonPages 1182 Non-file backed pages mapped into userspace page tables. Note that 1183 some kernel configurations might consider all pages part of a 1184 larger allocation (e.g., THP) as "mapped", as soon as a single 1185 page is mapped. 1186Mapped 1187 files which have been mmapped, such as libraries. Note that some 1188 kernel configurations might consider all pages part of a larger 1189 allocation (e.g., THP) as "mapped", as soon as a single page is 1190 mapped. 1191Shmem 1192 Total memory used by shared memory (shmem) and tmpfs 1193KReclaimable 1194 Kernel allocations that the kernel will attempt to reclaim 1195 under memory pressure. Includes SReclaimable (below), and other 1196 direct allocations with a shrinker. 1197Slab 1198 in-kernel data structures cache 1199SReclaimable 1200 Part of Slab, that might be reclaimed, such as caches 1201SUnreclaim 1202 Part of Slab, that cannot be reclaimed on memory pressure 1203KernelStack 1204 Memory consumed by the kernel stacks of all tasks 1205PageTables 1206 Memory consumed by userspace page tables 1207SecPageTables 1208 Memory consumed by secondary page tables, this currently includes 1209 KVM mmu and IOMMU allocations on x86 and arm64. 1210NFS_Unstable 1211 Always zero. Previously counted pages which had been written to 1212 the server, but has not been committed to stable storage. 1213Bounce 1214 Always zero. Previously memory used for block device 1215 "bounce buffers". 1216WritebackTmp 1217 Always zero. Previously memory used by FUSE for temporary 1218 writeback buffers. 1219CommitLimit 1220 Based on the overcommit ratio ('vm.overcommit_ratio'), 1221 this is the total amount of memory currently available to 1222 be allocated on the system. This limit is only adhered to 1223 if strict overcommit accounting is enabled (mode 2 in 1224 'vm.overcommit_memory'). 1225 1226 The CommitLimit is calculated with the following formula:: 1227 1228 CommitLimit = ([total RAM pages] - [total huge TLB pages]) * 1229 overcommit_ratio / 100 + [total swap pages] 1230 1231 For example, on a system with 1G of physical RAM and 7G 1232 of swap with a `vm.overcommit_ratio` of 30 it would 1233 yield a CommitLimit of 7.3G. 1234 1235 For more details, see the memory overcommit documentation 1236 in mm/overcommit-accounting. 1237Committed_AS 1238 The amount of memory presently allocated on the system. 1239 The committed memory is a sum of all of the memory which 1240 has been allocated by processes, even if it has not been 1241 "used" by them as of yet. A process which malloc()'s 1G 1242 of memory, but only touches 300M of it will show up as 1243 using 1G. This 1G is memory which has been "committed" to 1244 by the VM and can be used at any time by the allocating 1245 application. With strict overcommit enabled on the system 1246 (mode 2 in 'vm.overcommit_memory'), allocations which would 1247 exceed the CommitLimit (detailed above) will not be permitted. 1248 This is useful if one needs to guarantee that processes will 1249 not fail due to lack of memory once that memory has been 1250 successfully allocated. 1251VmallocTotal 1252 total size of vmalloc virtual address space 1253VmallocUsed 1254 amount of vmalloc area which is used 1255VmallocChunk 1256 largest contiguous block of vmalloc area which is free 1257Percpu 1258 Memory allocated to the percpu allocator used to back percpu 1259 allocations. This stat excludes the cost of metadata. 1260EarlyMemtestBad 1261 The amount of RAM/memory in kB, that was identified as corrupted 1262 by early memtest. If memtest was not run, this field will not 1263 be displayed at all. Size is never rounded down to 0 kB. 1264 That means if 0 kB is reported, you can safely assume 1265 there was at least one pass of memtest and none of the passes 1266 found a single faulty byte of RAM. 1267HardwareCorrupted 1268 The amount of RAM/memory in KB, the kernel identifies as 1269 corrupted. 1270AnonHugePages 1271 Non-file backed huge pages mapped into userspace page tables 1272ShmemHugePages 1273 Memory used by shared memory (shmem) and tmpfs allocated 1274 with huge pages 1275ShmemPmdMapped 1276 Shared memory mapped into userspace with huge pages 1277FileHugePages 1278 Memory used for filesystem data (page cache) allocated 1279 with huge pages 1280FilePmdMapped 1281 Page cache mapped into userspace with huge pages 1282CmaTotal 1283 Memory reserved for the Contiguous Memory Allocator (CMA) 1284CmaFree 1285 Free remaining memory in the CMA reserves 1286Unaccepted 1287 Memory that has not been accepted by the guest 1288Balloon 1289 Memory returned to Host by VM Balloon Drivers 1290GPUActive 1291 System memory allocated to active GPU objects 1292GPUReclaim 1293 System memory stored in GPU pools for reuse. This memory is not 1294 counted in GPUActive. It is shrinker reclaimable memory kept in a reuse 1295 pool because it has non-standard page table attributes, like WC or UC. 1296HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb 1297 See Documentation/admin-guide/mm/hugetlbpage.rst. 1298DirectMap4k, DirectMap2M, DirectMap1G 1299 Breakdown of page table sizes used in the kernel's 1300 identity mapping of RAM 1301 1302vmallocinfo 1303~~~~~~~~~~~ 1304 1305Provides information about vmalloced/vmaped areas. One line per area, 1306containing the virtual address range of the area, size in bytes, 1307caller information of the creator, and optional information depending 1308on the kind of area: 1309 1310 ========== =================================================== 1311 pages=nr number of pages 1312 phys=addr if a physical address was specified 1313 ioremap I/O mapping (ioremap() and friends) 1314 vmalloc vmalloc() area 1315 vmap vmap()ed pages 1316 user VM_USERMAP area 1317 vpages buffer for pages pointers was vmalloced (huge area) 1318 N<node>=nr (Only on NUMA kernels) 1319 Number of pages allocated on memory node <node> 1320 ========== =================================================== 1321 1322:: 1323 1324 > cat /proc/vmallocinfo 1325 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... 1326 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 1327 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... 1328 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 1329 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... 1330 phys=7fee8000 ioremap 1331 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... 1332 phys=7fee7000 ioremap 1333 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 1334 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... 1335 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 1336 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... 1337 pages=2 vmalloc N1=2 1338 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... 1339 /0x130 [x_tables] pages=4 vmalloc N0=4 1340 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... 1341 pages=14 vmalloc N2=14 1342 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... 1343 pages=4 vmalloc N1=4 1344 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... 1345 pages=2 vmalloc N1=2 1346 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... 1347 pages=10 vmalloc N0=10 1348 1349 1350softirqs 1351~~~~~~~~ 1352 1353Provides counts of softirq handlers serviced since boot time, for each CPU. 1354 1355:: 1356 1357 > cat /proc/softirqs 1358 CPU0 CPU1 CPU2 CPU3 1359 HI: 0 0 0 0 1360 TIMER: 27166 27120 27097 27034 1361 NET_TX: 0 0 0 17 1362 NET_RX: 42 0 0 39 1363 BLOCK: 0 0 107 1121 1364 TASKLET: 0 0 0 290 1365 SCHED: 27035 26983 26971 26746 1366 HRTIMER: 0 0 0 0 1367 RCU: 1678 1769 2178 2250 1368 13691.3 Networking info in /proc/net 1370-------------------------------- 1371 1372The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the 1373additional values you get for IP version 6 if you configure the kernel to 1374support this. Table 1-9 lists the files and their meaning. 1375 1376 1377.. table:: Table 1-8: IPv6 info in /proc/net 1378 1379 ========== ===================================================== 1380 File Content 1381 ========== ===================================================== 1382 udp6 UDP sockets (IPv6) 1383 tcp6 TCP sockets (IPv6) 1384 raw6 Raw device statistics (IPv6) 1385 igmp6 IP multicast addresses, which this host joined (IPv6) 1386 if_inet6 List of IPv6 interface addresses 1387 ipv6_route Kernel routing table for IPv6 1388 rt6_stats Global IPv6 routing tables statistics 1389 sockstat6 Socket statistics (IPv6) 1390 snmp6 Snmp data (IPv6) 1391 ========== ===================================================== 1392 1393.. table:: Table 1-9: Network info in /proc/net 1394 1395 ============= ================================================================ 1396 File Content 1397 ============= ================================================================ 1398 arp Kernel ARP table 1399 dev network devices with statistics 1400 dev_mcast the Layer2 multicast groups a device is listening too 1401 (interface index, label, number of references, number of bound 1402 addresses). 1403 dev_stat network device status 1404 ip_fwchains Firewall chain linkage 1405 ip_fwnames Firewall chain names 1406 ip_masq Directory containing the masquerading tables 1407 ip_masquerade Major masquerading table 1408 netstat Network statistics 1409 raw raw device statistics 1410 route Kernel routing table 1411 rpc Directory containing rpc info 1412 rt_cache Routing cache 1413 snmp SNMP data 1414 sockstat Socket statistics 1415 softnet_stat Per-CPU incoming packets queues statistics of online CPUs 1416 tcp TCP sockets 1417 udp UDP sockets 1418 unix UNIX domain sockets 1419 wireless Wireless interface data (Wavelan etc) 1420 igmp IP multicast addresses, which this host joined 1421 psched Global packet scheduler parameters. 1422 netlink List of PF_NETLINK sockets 1423 ip_mr_vifs List of multicast virtual interfaces 1424 ip_mr_cache List of multicast routing cache 1425 ============= ================================================================ 1426 1427You can use this information to see which network devices are available in 1428your system and how much traffic was routed over those devices:: 1429 1430 > cat /proc/net/dev 1431 Inter-|Receive |[... 1432 face |bytes packets errs drop fifo frame compressed multicast|[... 1433 lo: 908188 5596 0 0 0 0 0 0 [... 1434 ppp0:15475140 20721 410 0 0 410 0 0 [... 1435 eth0: 614530 7085 0 0 0 0 0 1 [... 1436 1437 ...] Transmit 1438 ...] bytes packets errs drop fifo colls carrier compressed 1439 ...] 908188 5596 0 0 0 0 0 0 1440 ...] 1375103 17405 0 0 0 0 0 0 1441 ...] 1703981 5535 0 0 0 3 0 0 1442 1443In addition, each Channel Bond interface has its own directory. For 1444example, the bond0 device will have a directory called /proc/net/bond0/. 1445It will contain information that is specific to that bond, such as the 1446current slaves of the bond, the link status of the slaves, and how 1447many times the slaves link has failed. 1448 14491.4 SCSI info 1450------------- 1451 1452If you have a SCSI or ATA host adapter in your system, you'll find a 1453subdirectory named after the driver for this adapter in /proc/scsi. 1454You'll also see a list of all recognized SCSI devices in /proc/scsi:: 1455 1456 >cat /proc/scsi/scsi 1457 Attached devices: 1458 Host: scsi0 Channel: 00 Id: 00 Lun: 00 1459 Vendor: IBM Model: DGHS09U Rev: 03E0 1460 Type: Direct-Access ANSI SCSI revision: 03 1461 Host: scsi0 Channel: 00 Id: 06 Lun: 00 1462 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 1463 Type: CD-ROM ANSI SCSI revision: 02 1464 1465 1466The directory named after the driver has one file for each adapter found in 1467the system. These files contain information about the controller, including 1468the used IRQ and the IO address range. The amount of information shown is 1469dependent on the adapter you use. The example shows the output for an Adaptec 1470AHA-2940 SCSI adapter:: 1471 1472 > cat /proc/scsi/aic7xxx/0 1473 1474 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 1475 Compile Options: 1476 TCQ Enabled By Default : Disabled 1477 AIC7XXX_PROC_STATS : Disabled 1478 AIC7XXX_RESET_DELAY : 5 1479 Adapter Configuration: 1480 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 1481 Ultra Wide Controller 1482 PCI MMAPed I/O Base: 0xeb001000 1483 Adapter SEEPROM Config: SEEPROM found and used. 1484 Adaptec SCSI BIOS: Enabled 1485 IRQ: 10 1486 SCBs: Active 0, Max Active 2, 1487 Allocated 15, HW 16, Page 255 1488 Interrupts: 160328 1489 BIOS Control Word: 0x18b6 1490 Adapter Control Word: 0x005b 1491 Extended Translation: Enabled 1492 Disconnect Enable Flags: 0xffff 1493 Ultra Enable Flags: 0x0001 1494 Tag Queue Enable Flags: 0x0000 1495 Ordered Queue Tag Flags: 0x0000 1496 Default Tag Queue Depth: 8 1497 Tagged Queue By Device array for aic7xxx host instance 0: 1498 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 1499 Actual queue depth per device for aic7xxx host instance 0: 1500 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 1501 Statistics: 1502 (scsi0:0:0:0) 1503 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 1504 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 1505 Total transfers 160151 (74577 reads and 85574 writes) 1506 (scsi0:0:6:0) 1507 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 1508 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 1509 Total transfers 0 (0 reads and 0 writes) 1510 1511 15121.5 Parallel port info in /proc/parport 1513--------------------------------------- 1514 1515The directory /proc/parport contains information about the parallel ports of 1516your system. It has one subdirectory for each port, named after the port 1517number (0,1,2,...). 1518 1519These directories contain the four files shown in Table 1-10. 1520 1521 1522.. table:: Table 1-10: Files in /proc/parport 1523 1524 ========= ==================================================================== 1525 File Content 1526 ========= ==================================================================== 1527 autoprobe Any IEEE-1284 device ID information that has been acquired. 1528 devices list of the device drivers using that port. A + will appear by the 1529 name of the device currently using the port (it might not appear 1530 against any). 1531 hardware Parallel port's base address, IRQ line and DMA channel. 1532 irq IRQ that parport is using for that port. This is in a separate 1533 file to allow you to alter it by writing a new value in (IRQ 1534 number or none). 1535 ========= ==================================================================== 1536 15371.6 TTY info in /proc/tty 1538------------------------- 1539 1540Information about the available and actually used tty's can be found in the 1541directory /proc/tty. You'll find entries for drivers and line disciplines in 1542this directory, as shown in Table 1-11. 1543 1544 1545.. table:: Table 1-11: Files in /proc/tty 1546 1547 ============= ============================================== 1548 File Content 1549 ============= ============================================== 1550 drivers list of drivers and their usage 1551 ldiscs registered line disciplines 1552 driver/serial usage statistic and status of single tty lines 1553 ============= ============================================== 1554 1555To see which tty's are currently in use, you can simply look into the file 1556/proc/tty/drivers:: 1557 1558 > cat /proc/tty/drivers 1559 pty_slave /dev/pts 136 0-255 pty:slave 1560 pty_master /dev/ptm 128 0-255 pty:master 1561 pty_slave /dev/ttyp 3 0-255 pty:slave 1562 pty_master /dev/pty 2 0-255 pty:master 1563 serial /dev/cua 5 64-67 serial:callout 1564 serial /dev/ttyS 4 64-67 serial 1565 /dev/tty0 /dev/tty0 4 0 system:vtmaster 1566 /dev/ptmx /dev/ptmx 5 2 system 1567 /dev/console /dev/console 5 1 system:console 1568 /dev/tty /dev/tty 5 0 system:/dev/tty 1569 unknown /dev/tty 4 1-63 console 1570 1571 15721.7 Miscellaneous kernel statistics in /proc/stat 1573------------------------------------------------- 1574 1575Various pieces of information about kernel activity are available in the 1576/proc/stat file. All of the numbers reported in this file are aggregates 1577since the system first booted. For a quick look, simply cat the file:: 1578 1579 > cat /proc/stat 1580 cpu 237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0 1581 cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0 1582 cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0 1583 cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0 1584 cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0 1585 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> 1586 ctxt 22848221062 1587 btime 1605316999 1588 processes 746787147 1589 procs_running 2 1590 procs_blocked 0 1591 softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354 1592 1593The very first "cpu" line aggregates the numbers in all of the other "cpuN" 1594lines. These numbers identify the amount of time the CPU has spent performing 1595different kinds of work. Time units are in USER_HZ (typically hundredths of a 1596second). The meanings of the columns are as follows, from left to right: 1597 1598- user: normal processes executing in user mode 1599- nice: niced processes executing in user mode 1600- system: processes executing in kernel mode 1601- idle: twiddling thumbs 1602- iowait: In a word, iowait stands for waiting for I/O to complete. But there 1603 are several problems: 1604 1605 1. CPU will not wait for I/O to complete, iowait is the time that a task is 1606 waiting for I/O to complete. When CPU goes into idle state for 1607 outstanding task I/O, another task will be scheduled on this CPU. 1608 2. In a multi-core CPU, the task waiting for I/O to complete is not running 1609 on any CPU, so the iowait of each CPU is difficult to calculate. 1610 3. The value of iowait field in /proc/stat will decrease in certain 1611 conditions. 1612 1613 So, the iowait is not reliable by reading from /proc/stat. 1614- irq: servicing interrupts 1615- softirq: servicing softirqs 1616- steal: involuntary wait 1617- guest: running a normal guest 1618- guest_nice: running a niced guest 1619 1620The "intr" line gives counts of interrupts serviced since boot time, for each 1621of the possible system interrupts. The first column is the total of all 1622interrupts serviced including unnumbered architecture specific interrupts; 1623each subsequent column is the total for that particular numbered interrupt. 1624Unnumbered interrupts are not shown, only summed into the total. 1625 1626The "ctxt" line gives the total number of context switches across all CPUs. 1627 1628The "btime" line gives the time at which the system booted, in seconds since 1629the Unix epoch. 1630 1631The "processes" line gives the number of processes and threads created, which 1632includes (but is not limited to) those created by calls to the fork() and 1633clone() system calls. 1634 1635The "procs_running" line gives the total number of threads that are 1636running or ready to run (i.e., the total number of runnable threads). 1637 1638The "procs_blocked" line gives the number of processes currently blocked, 1639waiting for I/O to complete. 1640 1641The "softirq" line gives counts of softirqs serviced since boot time, for each 1642of the possible system softirqs. The first column is the total of all 1643softirqs serviced; each subsequent column is the total for that particular 1644softirq. 1645 1646 16471.8 Ext4 file system parameters 1648------------------------------- 1649 1650Information about mounted ext4 file systems can be found in 1651/proc/fs/ext4. Each mounted filesystem will have a directory in 1652/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or 1653/proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0). The files in each per-device 1654directory are shown in Table 1-12, below. 1655 1656.. table:: Table 1-12: Files in /proc/fs/ext4/<devname> 1657 1658 ============== ========================================================== 1659 File Content 1660 mb_groups details of multiblock allocator buddy cache of free blocks 1661 ============== ========================================================== 1662 16631.9 /proc/consoles 1664------------------- 1665Shows registered system console lines. 1666 1667To see which character device lines are currently used for the system console 1668/dev/console, you may simply look into the file /proc/consoles:: 1669 1670 > cat /proc/consoles 1671 tty0 -WU (ECp) 4:7 1672 ttyS0 -W- (Ep) 4:64 1673 1674The columns are: 1675 1676+--------------------+-------------------------------------------------------+ 1677| device | name of the device | 1678+====================+=======================================================+ 1679| operations | * R = can do read operations | 1680| | * W = can do write operations | 1681| | * U = can do unblank | 1682+--------------------+-------------------------------------------------------+ 1683| flags | * E = it is enabled | 1684| | * C = it is preferred console | 1685| | * B = it is primary boot console | 1686| | * p = it is used for printk buffer | 1687| | * b = it is not a TTY but a Braille device | 1688| | * a = it is safe to use when cpu is offline | 1689+--------------------+-------------------------------------------------------+ 1690| major:minor | major and minor number of the device separated by a | 1691| | colon | 1692+--------------------+-------------------------------------------------------+ 1693 1694Summary 1695------- 1696 1697The /proc file system serves information about the running system. It not only 1698allows access to process data but also allows you to request the kernel status 1699by reading files in the hierarchy. 1700 1701The directory structure of /proc reflects the types of information and makes 1702it easy, if not obvious, where to look for specific data. 1703 1704Chapter 2: Modifying System Parameters 1705====================================== 1706 1707In This Chapter 1708--------------- 1709 1710* Modifying kernel parameters by writing into files found in /proc/sys 1711* Exploring the files which modify certain parameters 1712* Review of the /proc/sys file tree 1713 1714------------------------------------------------------------------------------ 1715 1716A very interesting part of /proc is the directory /proc/sys. This is not only 1717a source of information, it also allows you to change parameters within the 1718kernel. Be very careful when attempting this. You can optimize your system, 1719but you can also cause it to crash. Never alter kernel parameters on a 1720production system. Set up a development machine and test to make sure that 1721everything works the way you want it to. You may have no alternative but to 1722reboot the machine once an error has been made. 1723 1724To change a value, simply echo the new value into the file. 1725You need to be root to do this. You can create your own boot script 1726to perform this every time your system boots. 1727 1728The files in /proc/sys can be used to fine tune and monitor miscellaneous and 1729general things in the operation of the Linux kernel. Since some of the files 1730can inadvertently disrupt your system, it is advisable to read both 1731documentation and source before actually making adjustments. In any case, be 1732very careful when writing to any of these files. The entries in /proc may 1733change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt 1734review the kernel documentation in the directory linux/Documentation. 1735This chapter is heavily based on the documentation included in the pre 2.2 1736kernels, and became part of it in version 2.2.1 of the Linux kernel. 1737 1738Please see: Documentation/admin-guide/sysctl/ directory for descriptions of 1739these entries. 1740 1741Summary 1742------- 1743 1744Certain aspects of kernel behavior can be modified at runtime, without the 1745need to recompile the kernel, or even to reboot the system. The files in the 1746/proc/sys tree can not only be read, but also modified. You can use the echo 1747command to write value into these files, thereby changing the default settings 1748of the kernel. 1749 1750 1751Chapter 3: Per-process Parameters 1752================================= 1753 17543.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score 1755-------------------------------------------------------------------------------- 1756 1757These files can be used to adjust the badness heuristic used to select which 1758process gets killed in out of memory (oom) conditions. 1759 1760The badness heuristic assigns a value to each candidate task ranging from 0 1761(never kill) to 1000 (always kill) to determine which process is targeted. The 1762units are roughly a proportion along that range of allowed memory the process 1763may allocate from based on an estimation of its current memory and swap use. 1764For example, if a task is using all allowed memory, its badness score will be 17651000. If it is using half of its allowed memory, its score will be 500. 1766 1767The amount of "allowed" memory depends on the context in which the oom killer 1768was called. If it is due to the memory assigned to the allocating task's cpuset 1769being exhausted, the allowed memory represents the set of mems assigned to that 1770cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed 1771memory represents the set of mempolicy nodes. If it is due to a memory 1772limit (or swap limit) being reached, the allowed memory is that configured 1773limit. Finally, if it is due to the entire system being out of memory, the 1774allowed memory represents all allocatable resources. 1775 1776The value of /proc/<pid>/oom_score_adj is added to the badness score before it 1777is used to determine which task to kill. Acceptable values range from -1000 1778(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to 1779polarize the preference for oom killing either by always preferring a certain 1780task or completely disabling it. The lowest possible value, -1000, is 1781equivalent to disabling oom killing entirely for that task since it will always 1782report a badness score of 0. 1783 1784Consequently, it is very simple for userspace to define the amount of memory to 1785consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for 1786example, is roughly equivalent to allowing the remainder of tasks sharing the 1787same system, cpuset, mempolicy, or memory controller resources to use at least 178850% more memory. A value of -500, on the other hand, would be roughly 1789equivalent to discounting 50% of the task's allowed memory from being considered 1790as scoring against the task. 1791 1792For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also 1793be used to tune the badness score. Its acceptable values range from -16 1794(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 1795(OOM_DISABLE) to disable oom killing entirely for that task. Its value is 1796scaled linearly with /proc/<pid>/oom_score_adj. 1797 1798The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last 1799value set by a CAP_SYS_RESOURCE process. To reduce the value any lower 1800requires CAP_SYS_RESOURCE. 1801 1802 18033.2 /proc/<pid>/oom_score - Display current oom-killer score 1804------------------------------------------------------------- 1805 1806This file can be used to check the current score used by the oom-killer for 1807any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which 1808process should be killed in an out-of-memory situation. 1809 1810Please note that the exported value includes oom_score_adj so it is 1811effectively in range [0,2000]. 1812 1813 18143.3 /proc/<pid>/io - Display the IO accounting fields 1815------------------------------------------------------- 1816 1817This file contains IO statistics for each running process. 1818 1819Example 1820~~~~~~~ 1821 1822:: 1823 1824 test:/tmp # dd if=/dev/zero of=/tmp/test.dat & 1825 [1] 3828 1826 1827 test:/tmp # cat /proc/3828/io 1828 rchar: 323934931 1829 wchar: 323929600 1830 syscr: 632687 1831 syscw: 632675 1832 read_bytes: 0 1833 write_bytes: 323932160 1834 cancelled_write_bytes: 0 1835 1836 1837Description 1838~~~~~~~~~~~ 1839 1840rchar 1841^^^^^ 1842 1843I/O counter: chars read 1844The number of bytes which this task has caused to be read from storage. This 1845is simply the sum of bytes which this process passed to read() and pread(). 1846It includes things like tty IO and it is unaffected by whether or not actual 1847physical disk IO was required (the read might have been satisfied from 1848pagecache). 1849 1850 1851wchar 1852^^^^^ 1853 1854I/O counter: chars written 1855The number of bytes which this task has caused, or shall cause to be written 1856to disk. Similar caveats apply here as with rchar. 1857 1858 1859syscr 1860^^^^^ 1861 1862I/O counter: read syscalls 1863Attempt to count the number of read I/O operations, i.e. syscalls like read() 1864and pread(). 1865 1866 1867syscw 1868^^^^^ 1869 1870I/O counter: write syscalls 1871Attempt to count the number of write I/O operations, i.e. syscalls like 1872write() and pwrite(). 1873 1874 1875read_bytes 1876^^^^^^^^^^ 1877 1878I/O counter: bytes read 1879Attempt to count the number of bytes which this process really did cause to 1880be fetched from the storage layer. Done at the submit_bio() level, so it is 1881accurate for block-backed filesystems. <please add status regarding NFS and 1882CIFS at a later time> 1883 1884 1885write_bytes 1886^^^^^^^^^^^ 1887 1888I/O counter: bytes written 1889Attempt to count the number of bytes which this process caused to be sent to 1890the storage layer. This is done at page-dirtying time. 1891 1892 1893cancelled_write_bytes 1894^^^^^^^^^^^^^^^^^^^^^ 1895 1896The big inaccuracy here is truncate. If a process writes 1MB to a file and 1897then deletes the file, it will in fact perform no writeout. But it will have 1898been accounted as having caused 1MB of write. 1899In other words: The number of bytes which this process caused to not happen, 1900by truncating pagecache. A task can cause "negative" IO too. If this task 1901truncates some dirty pagecache, some IO which another task has been accounted 1902for (in its write_bytes) will not be happening. We _could_ just subtract that 1903from the truncating task's write_bytes, but there is information loss in doing 1904that. 1905 1906 1907.. Note:: 1908 1909 At its current implementation state, this is a bit racy on 32-bit machines: 1910 if process A reads process B's /proc/pid/io while process B is updating one 1911 of those 64-bit counters, process A could see an intermediate result. 1912 1913 1914More information about this can be found within the taskstats documentation in 1915Documentation/accounting. 1916 19173.4 /proc/<pid>/coredump_filter - Core dump filtering settings 1918--------------------------------------------------------------- 1919When a process is dumped, all anonymous memory is written to a core file as 1920long as the size of the core file isn't limited. But sometimes we don't want 1921to dump some memory segments, for example, huge shared memory or DAX. 1922Conversely, sometimes we want to save file-backed memory segments into a core 1923file, not only the individual files. 1924 1925/proc/<pid>/coredump_filter allows you to customize which memory segments 1926will be dumped when the <pid> process is dumped. coredump_filter is a bitmask 1927of memory types. If a bit of the bitmask is set, memory segments of the 1928corresponding memory type are dumped, otherwise they are not dumped. 1929 1930The following 9 memory types are supported: 1931 1932 - (bit 0) anonymous private memory 1933 - (bit 1) anonymous shared memory 1934 - (bit 2) file-backed private memory 1935 - (bit 3) file-backed shared memory 1936 - (bit 4) ELF header pages in file-backed private memory areas (it is 1937 effective only if the bit 2 is cleared) 1938 - (bit 5) hugetlb private memory 1939 - (bit 6) hugetlb shared memory 1940 - (bit 7) DAX private memory 1941 - (bit 8) DAX shared memory 1942 1943 Note that MMIO pages such as frame buffer are never dumped and vDSO pages 1944 are always dumped regardless of the bitmask status. 1945 1946 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is 1947 only affected by bit 5-6, and DAX is only affected by bits 7-8. 1948 1949The default value of coredump_filter is 0x33; this means all anonymous memory 1950segments, ELF header pages and hugetlb private memory are dumped. 1951 1952If you don't want to dump all shared memory segments attached to pid 1234, 1953write 0x31 to the process's proc file:: 1954 1955 $ echo 0x31 > /proc/1234/coredump_filter 1956 1957When a new process is created, the process inherits the bitmask status from its 1958parent. It is useful to set up coredump_filter before the program runs. 1959For example:: 1960 1961 $ echo 0x7 > /proc/self/coredump_filter 1962 $ ./some_program 1963 19643.5 /proc/<pid>/mountinfo - Information about mounts 1965-------------------------------------------------------- 1966 1967This file contains lines of the form:: 1968 1969 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue 1970 (1)(2)(3) (4) (5) (6) (n…m) (m+1)(m+2) (m+3) (m+4) 1971 1972 (1) mount ID: unique identifier of the mount (may be reused after umount) 1973 (2) parent ID: ID of parent (or of self for the top of the mount tree) 1974 (3) major:minor: value of st_dev for files on filesystem 1975 (4) root: root of the mount within the filesystem 1976 (5) mount point: mount point relative to the process's root 1977 (6) mount options: per mount options 1978 (n…m) optional fields: zero or more fields of the form "tag[:value]" 1979 (m+1) separator: marks the end of the optional fields 1980 (m+2) filesystem type: name of filesystem of the form "type[.subtype]" 1981 (m+3) mount source: filesystem specific information or "none" 1982 (m+4) super options: per super block options 1983 1984Parsers should ignore all unrecognised optional fields. Currently the 1985possible optional fields are: 1986 1987================ ============================================================== 1988shared:X mount is shared in peer group X 1989master:X mount is slave to peer group X 1990propagate_from:X mount is slave and receives propagation from peer group X [#]_ 1991unbindable mount is unbindable 1992================ ============================================================== 1993 1994.. [#] X is the closest dominant peer group under the process's root. If 1995 X is the immediate master of the mount, or if there's no dominant peer 1996 group under the same root, then only the "master:X" field is present 1997 and not the "propagate_from:X" field. 1998 1999For more information on mount propagation see: 2000 2001 Documentation/filesystems/sharedsubtree.rst 2002 2003 20043.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm 2005-------------------------------------------------------- 2006These files provide a method to access a task's comm value. It also allows for 2007a task to set its own or one of its thread siblings comm value. The comm value 2008is limited in size compared to the cmdline value, so writing anything longer 2009then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL 2010terminator) will result in a truncated comm value. 2011 2012 20133.7 /proc/<pid>/task/<tid>/children - Information about task children 2014------------------------------------------------------------------------- 2015This file provides a fast way to retrieve first level children pids 2016of a task pointed by <pid>/<tid> pair. The format is a space separated 2017stream of pids. 2018 2019Note the "first level" here -- if a child has its own children they will 2020not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children 2021to obtain the descendants. 2022 2023Since this interface is intended to be fast and cheap it doesn't 2024guarantee to provide precise results and some children might be 2025skipped, especially if they've exited right after we printed their 2026pids, so one needs to either stop or freeze processes being inspected 2027if precise results are needed. 2028 2029 20303.8 /proc/<pid>/fdinfo/<fd> - Information about opened file 2031--------------------------------------------------------------- 2032This file provides information associated with an opened file. The regular 2033files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. 2034The 'pos' represents the current offset of the opened file in decimal 2035form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the 2036file has been created with [see open(2) for details] and 'mnt_id' represents 2037mount ID of the file system containing the opened file [see 3.5 2038/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of 2039the file. 2040 2041A typical output is:: 2042 2043 pos: 0 2044 flags: 0100002 2045 mnt_id: 19 2046 ino: 63107 2047 2048All locks associated with a file descriptor are shown in its fdinfo too:: 2049 2050 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF 2051 2052The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags 2053pair provide additional information particular to the objects they represent. 2054 2055Eventfd files 2056~~~~~~~~~~~~~ 2057 2058:: 2059 2060 pos: 0 2061 flags: 04002 2062 mnt_id: 9 2063 ino: 63107 2064 eventfd-count: 5a 2065 2066where 'eventfd-count' is hex value of a counter. 2067 2068Signalfd files 2069~~~~~~~~~~~~~~ 2070 2071:: 2072 2073 pos: 0 2074 flags: 04002 2075 mnt_id: 9 2076 ino: 63107 2077 sigmask: 0000000000000200 2078 2079where 'sigmask' is hex value of the signal mask associated 2080with a file. 2081 2082Epoll files 2083~~~~~~~~~~~ 2084 2085:: 2086 2087 pos: 0 2088 flags: 02 2089 mnt_id: 9 2090 ino: 63107 2091 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 2092 2093where 'tfd' is a target file descriptor number in decimal form, 2094'events' is events mask being watched and the 'data' is data 2095associated with a target [see epoll(7) for more details]. 2096 2097The 'pos' is current offset of the target file in decimal form 2098[see lseek(2)], 'ino' and 'sdev' are inode and device numbers 2099where target file resides, all in hex format. 2100 2101Fsnotify files 2102~~~~~~~~~~~~~~ 2103For inotify files the format is the following:: 2104 2105 pos: 0 2106 flags: 02000000 2107 mnt_id: 9 2108 ino: 63107 2109 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d 2110 2111where 'wd' is a watch descriptor in decimal form, i.e. a target file 2112descriptor number, 'ino' and 'sdev' are inode and device where the 2113target file resides and the 'mask' is the mask of events, all in hex 2114form [see inotify(7) for more details]. 2115 2116If the kernel was built with exportfs support, the path to the target 2117file is encoded as a file handle. The file handle is provided by three 2118fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex 2119format. 2120 2121If the kernel is built without exportfs support the file handle won't be 2122printed out. 2123 2124If there is no inotify mark attached yet the 'inotify' line will be omitted. 2125 2126For fanotify files the format is:: 2127 2128 pos: 0 2129 flags: 02 2130 mnt_id: 9 2131 ino: 63107 2132 fanotify flags:10 event-flags:0 2133 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003 2134 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4 2135 2136where fanotify 'flags' and 'event-flags' are values used in fanotify_init 2137call, 'mnt_id' is the mount point identifier, 'mflags' is the value of 2138flags associated with mark which are tracked separately from events 2139mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events 2140mask and 'ignored_mask' is the mask of events which are to be ignored. 2141All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask' 2142provide information about flags and mask used in fanotify_mark 2143call [see fsnotify manpage for details]. 2144 2145While the first three lines are mandatory and always printed, the rest is 2146optional and may be omitted if no marks created yet. 2147 2148Timerfd files 2149~~~~~~~~~~~~~ 2150 2151:: 2152 2153 pos: 0 2154 flags: 02 2155 mnt_id: 9 2156 ino: 63107 2157 clockid: 0 2158 ticks: 0 2159 settime flags: 01 2160 it_value: (0, 49406829) 2161 it_interval: (1, 0) 2162 2163where 'clockid' is the clock type and 'ticks' is the number of the timer expirations 2164that have occurred [see timerfd_create(2) for details]. 'settime flags' are 2165flags in octal form been used to setup the timer [see timerfd_settime(2) for 2166details]. 'it_value' is remaining time until the timer expiration. 2167'it_interval' is the interval for the timer. Note the timer might be set up 2168with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value' 2169still exhibits timer's remaining time. 2170 2171DMA Buffer files 2172~~~~~~~~~~~~~~~~ 2173 2174:: 2175 2176 pos: 0 2177 flags: 04002 2178 mnt_id: 9 2179 ino: 63107 2180 size: 32768 2181 count: 2 2182 exp_name: system-heap 2183 2184where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of 2185the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter. 2186 2187VFIO Device files 2188~~~~~~~~~~~~~~~~~ 2189 2190:: 2191 2192 pos: 0 2193 flags: 02000002 2194 mnt_id: 17 2195 ino: 5122 2196 vfio-device-syspath: /sys/devices/pci0000:e0/0000:e0:01.1/0000:e1:00.0/0000:e2:05.0/0000:e8:00.0 2197 2198where 'vfio-device-syspath' is the sysfs path corresponding to the VFIO device 2199file. 2200 22013.9 /proc/<pid>/map_files - Information about memory mapped files 2202--------------------------------------------------------------------- 2203This directory contains symbolic links which represent memory mapped files 2204the process is maintaining. Example output:: 2205 2206 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so 2207 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so 2208 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so 2209 | ... 2210 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1 2211 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls 2212 2213The name of a link represents the virtual memory bounds of a mapping, i.e. 2214vm_area_struct::vm_start-vm_area_struct::vm_end. 2215 2216The main purpose of the map_files is to retrieve a set of memory mapped 2217files in a fast way instead of parsing /proc/<pid>/maps or 2218/proc/<pid>/smaps, both of which contain many more records. At the same 2219time one can open(2) mappings from the listings of two processes and 2220comparing their inode numbers to figure out which anonymous memory areas 2221are actually shared. 2222 22233.10 /proc/<pid>/timerslack_ns - Task timerslack value 2224--------------------------------------------------------- 2225This file provides the value of the task's timerslack value in nanoseconds. 2226This value specifies an amount of time that normal timers may be deferred 2227in order to coalesce timers and avoid unnecessary wakeups. 2228 2229This allows a task's interactivity vs power consumption tradeoff to be 2230adjusted. 2231 2232Writing 0 to the file will set the task's timerslack to the default value. 2233 2234Valid values are from 0 - ULLONG_MAX 2235 2236An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level 2237permissions on the task specified to change its timerslack_ns value. 2238 22393.11 /proc/<pid>/patch_state - Livepatch patch operation state 2240----------------------------------------------------------------- 2241When CONFIG_LIVEPATCH is enabled, this file displays the value of the 2242patch state for the task. 2243 2244A value of '-1' indicates that no patch is in transition. 2245 2246A value of '0' indicates that a patch is in transition and the task is 2247unpatched. If the patch is being enabled, then the task hasn't been 2248patched yet. If the patch is being disabled, then the task has already 2249been unpatched. 2250 2251A value of '1' indicates that a patch is in transition and the task is 2252patched. If the patch is being enabled, then the task has already been 2253patched. If the patch is being disabled, then the task hasn't been 2254unpatched yet. 2255 22563.12 /proc/<pid>/arch_status - task architecture specific status 2257------------------------------------------------------------------- 2258When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the 2259architecture specific status of the task. 2260 2261Example 2262~~~~~~~ 2263 2264:: 2265 2266 $ cat /proc/6753/arch_status 2267 AVX512_elapsed_ms: 8 2268 2269Description 2270~~~~~~~~~~~ 2271 2272x86 specific entries 2273~~~~~~~~~~~~~~~~~~~~~ 2274 2275AVX512_elapsed_ms 2276^^^^^^^^^^^^^^^^^^ 2277 2278 If AVX512 is supported on the machine, this entry shows the milliseconds 2279 elapsed since the last time AVX512 usage was recorded. The recording 2280 happens on a best effort basis when a task is scheduled out. This means 2281 that the value depends on two factors: 2282 2283 1) The time which the task spent on the CPU without being scheduled 2284 out. With CPU isolation and a single runnable task this can take 2285 several seconds. 2286 2287 2) The time since the task was scheduled out last. Depending on the 2288 reason for being scheduled out (time slice exhausted, syscall ...) 2289 this can be arbitrary long time. 2290 2291 As a consequence the value cannot be considered precise and authoritative 2292 information. The application which uses this information has to be aware 2293 of the overall scenario on the system in order to determine whether a 2294 task is a real AVX512 user or not. Precise information can be obtained 2295 with performance counters. 2296 2297 A special value of '-1' indicates that no AVX512 usage was recorded, thus 2298 the task is unlikely an AVX512 user, but depends on the workload and the 2299 scheduling scenario, it also could be a false negative mentioned above. 2300 23013.13 /proc/<pid>/fd - List of symlinks to open files 2302------------------------------------------------------- 2303This directory contains symbolic links which represent open files 2304the process is maintaining. Example output:: 2305 2306 lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null 2307 l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null 2308 lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]' 2309 lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]' 2310 lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]' 2311 2312The number of open files for the process is stored in 'size' member 2313of stat() output for /proc/<pid>/fd for fast access. 2314------------------------------------------------------- 2315 23163.14 /proc/<pid>/ksm_stat - Information about the process's ksm status 2317---------------------------------------------------------------------- 2318When CONFIG_KSM is enabled, each process has this file which displays 2319the information of ksm merging status. 2320 2321Example 2322~~~~~~~ 2323 2324:: 2325 2326 / # cat /proc/self/ksm_stat 2327 ksm_rmap_items 0 2328 ksm_zero_pages 0 2329 ksm_merging_pages 0 2330 ksm_process_profit 0 2331 ksm_merge_any: no 2332 ksm_mergeable: no 2333 2334Description 2335~~~~~~~~~~~ 2336 2337ksm_rmap_items 2338^^^^^^^^^^^^^^ 2339 2340The number of ksm_rmap_item structures in use. The structure 2341ksm_rmap_item stores the reverse mapping information for virtual 2342addresses. KSM will generate a ksm_rmap_item for each ksm-scanned page of 2343the process. 2344 2345ksm_zero_pages 2346^^^^^^^^^^^^^^ 2347 2348When /sys/kernel/mm/ksm/use_zero_pages is enabled, it represent how many 2349empty pages are merged with kernel zero pages by KSM. 2350 2351ksm_merging_pages 2352^^^^^^^^^^^^^^^^^ 2353 2354It represents how many pages of this process are involved in KSM merging 2355(not including ksm_zero_pages). It is the same with what 2356/proc/<pid>/ksm_merging_pages shows. 2357 2358ksm_process_profit 2359^^^^^^^^^^^^^^^^^^ 2360 2361The profit that KSM brings (Saved bytes). KSM can save memory by merging 2362identical pages, but also can consume additional memory, because it needs 2363to generate a number of rmap_items to save each scanned page's brief rmap 2364information. Some of these pages may be merged, but some may not be abled 2365to be merged after being checked several times, which are unprofitable 2366memory consumed. 2367 2368ksm_merge_any 2369^^^^^^^^^^^^^ 2370 2371It specifies whether the process's 'mm is added by prctl() into the 2372candidate list of KSM or not, and if KSM scanning is fully enabled at 2373process level. 2374 2375ksm_mergeable 2376^^^^^^^^^^^^^ 2377 2378It specifies whether any VMAs of the process''s mms are currently 2379applicable to KSM. 2380 2381More information about KSM can be found in 2382Documentation/admin-guide/mm/ksm.rst. 2383 2384 2385Chapter 4: Configuring procfs 2386============================= 2387 23884.1 Mount options 2389--------------------- 2390 2391The following mount options are supported: 2392 2393 ========= ======================================================== 2394 hidepid= Set /proc/<pid>/ access mode. 2395 gid= Set the group authorized to learn processes information. 2396 subset= Show only the specified subset of procfs. 2397 pidns= Specify a the namespace used by this procfs. 2398 ========= ======================================================== 2399 2400hidepid=off or hidepid=0 means classic mode - everybody may access all 2401/proc/<pid>/ directories (default). 2402 2403hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ 2404directories but their own. Sensitive files like cmdline, sched*, status are now 2405protected against other users. This makes it impossible to learn whether any 2406user runs specific program (given the program doesn't reveal itself by its 2407behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for 2408other users, poorly written programs passing sensitive information via program 2409arguments are now protected against local eavesdroppers. 2410 2411hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be 2412fully invisible to other users. It doesn't mean that it hides a fact whether a 2413process with a specific pid value exists (it can be learned by other means, e.g. 2414by "kill -0 $PID"), but it hides process's uid and gid, which may be learned by 2415stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of 2416gathering information about running processes, whether some daemon runs with 2417elevated privileges, whether other user runs some sensitive program, whether 2418other users run any program at all, etc. 2419 2420hidepid=ptraceable or hidepid=4 means that procfs should only contain 2421/proc/<pid>/ directories that the caller can ptrace. 2422 2423gid= defines a group authorized to learn processes information otherwise 2424prohibited by hidepid=. If you use some daemon like identd which needs to learn 2425information about processes information, just add identd to this group. 2426 2427subset=pid hides all top level files and directories in the procfs that 2428are not related to tasks. 2429 2430pidns= specifies a pid namespace (either as a string path to something like 2431`/proc/$pid/ns/pid`, or a file descriptor when using `FSCONFIG_SET_FD`) that 2432will be used by the procfs instance when translating pids. By default, procfs 2433will use the calling process's active pid namespace. Note that the pid 2434namespace of an existing procfs instance cannot be modified (attempting to do 2435so will give an `-EBUSY` error). 2436 2437Chapter 5: Filesystem behavior 2438============================== 2439 2440Originally, before the advent of pid namespace, procfs was a global file 2441system. It means that there was only one procfs instance in the system. 2442 2443When pid namespace was added, a separate procfs instance was mounted in 2444each pid namespace. So, procfs mount options are global among all 2445mountpoints within the same namespace:: 2446 2447 # grep ^proc /proc/mounts 2448 proc /proc proc rw,relatime,hidepid=2 0 0 2449 2450 # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc 2451 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0 2452 +++ exited with 0 +++ 2453 2454 # grep ^proc /proc/mounts 2455 proc /proc proc rw,relatime,hidepid=2 0 0 2456 proc /tmp/proc proc rw,relatime,hidepid=2 0 0 2457 2458and only after remounting procfs mount options will change at all 2459mountpoints:: 2460 2461 # mount -o remount,hidepid=1 -t proc proc /tmp/proc 2462 2463 # grep ^proc /proc/mounts 2464 proc /proc proc rw,relatime,hidepid=1 0 0 2465 proc /tmp/proc proc rw,relatime,hidepid=1 0 0 2466 2467This behavior is different from the behavior of other filesystems. 2468 2469The new procfs behavior is more like other filesystems. Each procfs mount 2470creates a new procfs instance. Mount options affect own procfs instance. 2471It means that it became possible to have several procfs instances 2472displaying tasks with different filtering options in one pid namespace:: 2473 2474 # mount -o hidepid=invisible -t proc proc /proc 2475 # mount -o hidepid=noaccess -t proc proc /tmp/proc 2476 # grep ^proc /proc/mounts 2477 proc /proc proc rw,relatime,hidepid=invisible 0 0 2478 proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 2479