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. 567 568"VmFlags" field deserves a separate description. This member represents the 569kernel flags associated with the particular virtual memory area in two letter 570encoded manner. The codes are the following: 571 572 == ============================================================= 573 rd readable 574 wr writeable 575 ex executable 576 sh shared 577 mr may read 578 mw may write 579 me may execute 580 ms may share 581 gd stack segment growns down 582 pf pure PFN range 583 lo pages are locked in memory 584 io memory mapped I/O area 585 sr sequential read advise provided 586 rr random read advise provided 587 dc do not copy area on fork 588 de do not expand area on remapping 589 ac area is accountable 590 nr swap space is not reserved for the area 591 ht area uses huge tlb pages 592 sf synchronous page fault 593 ar architecture specific flag 594 wf wipe on fork 595 dd do not include area into core dump 596 sd soft dirty flag 597 mm mixed map area 598 hg huge page advise flag 599 nh no huge page advise flag 600 mg mergeable advise flag 601 bt arm64 BTI guarded page 602 mt arm64 MTE allocation tags are enabled 603 um userfaultfd missing tracking 604 uw userfaultfd wr-protect tracking 605 ui userfaultfd minor fault 606 ss shadow/guarded control stack page 607 sl sealed 608 lf lock on fault pages 609 dp always lazily freeable mapping 610 gu maybe contains guard regions (if not set, definitely doesn't) 611 == ============================================================= 612 613Note that there is no guarantee that every flag and associated mnemonic will 614be present in all further kernel releases. Things get changed, the flags may 615be vanished or the reverse -- new added. Interpretation of their meaning 616might change in future as well. So each consumer of these flags has to 617follow each specific kernel version for the exact semantic. 618 619This file is only present if the CONFIG_MMU kernel configuration option is 620enabled. 621 622Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent 623output can be achieved only in the single read call). 624 625This typically manifests when doing partial reads of these files while the 626memory map is being modified. Despite the races, we do provide the following 627guarantees: 628 6291) The mapped addresses never go backwards, which implies no two 630 regions will ever overlap. 6312) If there is something at a given vaddr during the entirety of the 632 life of the smaps/maps walk, there will be some output for it. 633 634The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps, 635but their values are the sums of the corresponding values for all mappings of 636the process. Additionally, it contains these fields: 637 638- Pss_Anon 639- Pss_File 640- Pss_Shmem 641 642They represent the proportional shares of anonymous, file, and shmem pages, as 643described for smaps above. These fields are omitted in smaps since each 644mapping identifies the type (anon, file, or shmem) of all pages it contains. 645Thus all information in smaps_rollup can be derived from smaps, but at a 646significantly higher cost. 647 648The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG 649bits on both physical and virtual pages associated with a process, and the 650soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst 651for details). 652To clear the bits for all the pages associated with the process:: 653 654 > echo 1 > /proc/PID/clear_refs 655 656To clear the bits for the anonymous pages associated with the process:: 657 658 > echo 2 > /proc/PID/clear_refs 659 660To clear the bits for the file mapped pages associated with the process:: 661 662 > echo 3 > /proc/PID/clear_refs 663 664To clear the soft-dirty bit:: 665 666 > echo 4 > /proc/PID/clear_refs 667 668To reset the peak resident set size ("high water mark") to the process's 669current value:: 670 671 > echo 5 > /proc/PID/clear_refs 672 673Any other value written to /proc/PID/clear_refs will have no effect. 674 675The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags 676using /proc/kpageflags and number of times a page is mapped using 677/proc/kpagecount. For detailed explanation, see 678Documentation/admin-guide/mm/pagemap.rst. 679 680The /proc/pid/numa_maps is an extension based on maps, showing the memory 681locality and binding policy, as well as the memory usage (in pages) of 682each mapping. The output follows a general format where mapping details get 683summarized separated by blank spaces, one mapping per each file line:: 684 685 address policy mapping details 686 687 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4 688 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4 689 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4 690 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 691 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 692 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4 693 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4 694 320698b000 default file=/lib64/libc-2.12.so 695 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4 696 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 697 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4 698 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4 699 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4 700 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048 701 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4 702 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4 703 704Where: 705 706"address" is the starting address for the mapping; 707 708"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst); 709 710"mapping details" summarizes mapping data such as mapping type, page usage counters, 711node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page 712size, in KB, that is backing the mapping up. 713 714Note that some kernel configurations do not track the precise number of times 715a page part of a larger allocation (e.g., THP) is mapped. In these 716configurations, "mapmax" might corresponds to the average number of mappings 717per page in such a larger allocation instead. 718 7191.2 Kernel data 720--------------- 721 722Similar to the process entries, the kernel data files give information about 723the running kernel. The files used to obtain this information are contained in 724/proc and are listed in Table 1-5. Not all of these will be present in your 725system. It depends on the kernel configuration and the loaded modules, which 726files are there, and which are missing. 727 728.. table:: Table 1-5: Kernel info in /proc 729 730 ============ =============================================================== 731 File Content 732 ============ =============================================================== 733 allocinfo Memory allocations profiling information 734 apm Advanced power management info 735 bootconfig Kernel command line obtained from boot config, 736 and, if there were kernel parameters from the 737 boot loader, a "# Parameters from bootloader:" 738 line followed by a line containing those 739 parameters prefixed by "# ". (5.5) 740 buddyinfo Kernel memory allocator information (see text) (2.5) 741 bus Directory containing bus specific information 742 cmdline Kernel command line, both from bootloader and embedded 743 in the kernel image 744 cpuinfo Info about the CPU 745 devices Available devices (block and character) 746 dma Used DMS channels 747 filesystems Supported filesystems 748 driver Various drivers grouped here, currently rtc (2.4) 749 execdomains Execdomains, related to security (2.4) 750 fb Frame Buffer devices (2.4) 751 fs File system parameters, currently nfs/exports (2.4) 752 ide Directory containing info about the IDE subsystem 753 interrupts Interrupt usage 754 iomem Memory map (2.4) 755 ioports I/O port usage 756 irq Masks for irq to cpu affinity (2.4)(smp?) 757 isapnp ISA PnP (Plug&Play) Info (2.4) 758 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) 759 kmsg Kernel messages 760 ksyms Kernel symbol table 761 loadavg Load average of last 1, 5 & 15 minutes; 762 number of processes currently runnable (running or on ready queue); 763 total number of processes in system; 764 last pid created. 765 All fields are separated by one space except "number of 766 processes currently runnable" and "total number of processes 767 in system", which are separated by a slash ('/'). Example: 768 0.61 0.61 0.55 3/828 22084 769 locks Kernel locks 770 meminfo Memory info 771 misc Miscellaneous 772 modules List of loaded modules 773 mounts Mounted filesystems 774 net Networking info (see text) 775 pagetypeinfo Additional page allocator information (see text) (2.5) 776 partitions Table of partitions known to the system 777 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, 778 decoupled by lspci (2.4) 779 rtc Real time clock 780 scsi SCSI info (see text) 781 slabinfo Slab pool info 782 softirqs softirq usage 783 stat Overall statistics 784 swaps Swap space utilization 785 sys See chapter 2 786 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) 787 tty Info of tty drivers 788 uptime Wall clock since boot, combined idle time of all cpus 789 version Kernel version 790 video bttv info of video resources (2.4) 791 vmallocinfo Show vmalloced areas 792 ============ =============================================================== 793 794You can, for example, check which interrupts are currently in use and what 795they are used for by looking in the file /proc/interrupts:: 796 797 > cat /proc/interrupts 798 CPU0 799 0: 8728810 XT-PIC timer 800 1: 895 XT-PIC keyboard 801 2: 0 XT-PIC cascade 802 3: 531695 XT-PIC aha152x 803 4: 2014133 XT-PIC serial 804 5: 44401 XT-PIC pcnet_cs 805 8: 2 XT-PIC rtc 806 11: 8 XT-PIC i82365 807 12: 182918 XT-PIC PS/2 Mouse 808 13: 1 XT-PIC fpu 809 14: 1232265 XT-PIC ide0 810 15: 7 XT-PIC ide1 811 NMI: 0 812 813In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the 814output of a SMP machine):: 815 816 > cat /proc/interrupts 817 818 CPU0 CPU1 819 0: 1243498 1214548 IO-APIC-edge timer 820 1: 8949 8958 IO-APIC-edge keyboard 821 2: 0 0 XT-PIC cascade 822 5: 11286 10161 IO-APIC-edge soundblaster 823 8: 1 0 IO-APIC-edge rtc 824 9: 27422 27407 IO-APIC-edge 3c503 825 12: 113645 113873 IO-APIC-edge PS/2 Mouse 826 13: 0 0 XT-PIC fpu 827 14: 22491 24012 IO-APIC-edge ide0 828 15: 2183 2415 IO-APIC-edge ide1 829 17: 30564 30414 IO-APIC-level eth0 830 18: 177 164 IO-APIC-level bttv 831 NMI: 2457961 2457959 832 LOC: 2457882 2457881 833 ERR: 2155 834 835NMI is incremented in this case because every timer interrupt generates a NMI 836(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. 837 838LOC is the local interrupt counter of the internal APIC of every CPU. 839 840ERR is incremented in the case of errors in the IO-APIC bus (the bus that 841connects the CPUs in a SMP system. This means that an error has been detected, 842the IO-APIC automatically retry the transmission, so it should not be a big 843problem, but you should read the SMP-FAQ. 844 845In 2.6.2* /proc/interrupts was expanded again. This time the goal was for 846/proc/interrupts to display every IRQ vector in use by the system, not 847just those considered 'most important'. The new vectors are: 848 849THR 850 interrupt raised when a machine check threshold counter 851 (typically counting ECC corrected errors of memory or cache) exceeds 852 a configurable threshold. Only available on some systems. 853 854TRM 855 a thermal event interrupt occurs when a temperature threshold 856 has been exceeded for the CPU. This interrupt may also be generated 857 when the temperature drops back to normal. 858 859SPU 860 a spurious interrupt is some interrupt that was raised then lowered 861 by some IO device before it could be fully processed by the APIC. Hence 862 the APIC sees the interrupt but does not know what device it came from. 863 For this case the APIC will generate the interrupt with a IRQ vector 864 of 0xff. This might also be generated by chipset bugs. 865 866RES, CAL, TLB 867 rescheduling, call and TLB flush interrupts are 868 sent from one CPU to another per the needs of the OS. Typically, 869 their statistics are used by kernel developers and interested users to 870 determine the occurrence of interrupts of the given type. 871 872The above IRQ vectors are displayed only when relevant. For example, 873the threshold vector does not exist on x86_64 platforms. Others are 874suppressed when the system is a uniprocessor. As of this writing, only 875i386 and x86_64 platforms support the new IRQ vector displays. 876 877Of some interest is the introduction of the /proc/irq directory to 2.4. 878It could be used to set IRQ to CPU affinity. This means that you can "hook" an 879IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the 880irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and 881prof_cpu_mask. 882 883For example:: 884 885 > ls /proc/irq/ 886 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask 887 1 11 13 15 17 19 3 5 7 9 default_smp_affinity 888 > ls /proc/irq/0/ 889 smp_affinity 890 891smp_affinity is a bitmask, in which you can specify which CPUs can handle the 892IRQ. You can set it by doing:: 893 894 > echo 1 > /proc/irq/10/smp_affinity 895 896This means that only the first CPU will handle the IRQ, but you can also echo 8975 which means that only the first and third CPU can handle the IRQ. 898 899The contents of each smp_affinity file is the same by default:: 900 901 > cat /proc/irq/0/smp_affinity 902 ffffffff 903 904There is an alternate interface, smp_affinity_list which allows specifying 905a CPU range instead of a bitmask:: 906 907 > cat /proc/irq/0/smp_affinity_list 908 1024-1031 909 910The default_smp_affinity mask applies to all non-active IRQs, which are the 911IRQs which have not yet been allocated/activated, and hence which lack a 912/proc/irq/[0-9]* directory. 913 914The node file on an SMP system shows the node to which the device using the IRQ 915reports itself as being attached. This hardware locality information does not 916include information about any possible driver locality preference. 917 918prof_cpu_mask specifies which CPUs are to be profiled by the system wide 919profiler. Default value is ffffffff (all CPUs if there are only 32 of them). 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 HugePages_Total: 0 1109 HugePages_Free: 0 1110 HugePages_Rsvd: 0 1111 HugePages_Surp: 0 1112 Hugepagesize: 2048 kB 1113 Hugetlb: 0 kB 1114 DirectMap4k: 401152 kB 1115 DirectMap2M: 10008576 kB 1116 DirectMap1G: 24117248 kB 1117 1118MemTotal 1119 Total usable RAM (i.e. physical RAM minus a few reserved 1120 bits and the kernel binary code) 1121MemFree 1122 Total free RAM. On highmem systems, the sum of LowFree+HighFree 1123MemAvailable 1124 An estimate of how much memory is available for starting new 1125 applications, without swapping. Calculated from MemFree, 1126 SReclaimable, the size of the file LRU lists, and the low 1127 watermarks in each zone. 1128 The estimate takes into account that the system needs some 1129 page cache to function well, and that not all reclaimable 1130 slab will be reclaimable, due to items being in use. The 1131 impact of those factors will vary from system to system. 1132Buffers 1133 Relatively temporary storage for raw disk blocks 1134 shouldn't get tremendously large (20MB or so) 1135Cached 1136 In-memory cache for files read from the disk (the 1137 pagecache) as well as tmpfs & shmem. 1138 Doesn't include SwapCached. 1139SwapCached 1140 Memory that once was swapped out, is swapped back in but 1141 still also is in the swapfile (if memory is needed it 1142 doesn't need to be swapped out AGAIN because it is already 1143 in the swapfile. This saves I/O) 1144Active 1145 Memory that has been used more recently and usually not 1146 reclaimed unless absolutely necessary. 1147Inactive 1148 Memory which has been less recently used. It is more 1149 eligible to be reclaimed for other purposes 1150Unevictable 1151 Memory allocated for userspace which cannot be reclaimed, such 1152 as mlocked pages, ramfs backing pages, secret memfd pages etc. 1153Mlocked 1154 Memory locked with mlock(). 1155HighTotal, HighFree 1156 Highmem is all memory above ~860MB of physical memory. 1157 Highmem areas are for use by userspace programs, or 1158 for the pagecache. The kernel must use tricks to access 1159 this memory, making it slower to access than lowmem. 1160LowTotal, LowFree 1161 Lowmem is memory which can be used for everything that 1162 highmem can be used for, but it is also available for the 1163 kernel's use for its own data structures. Among many 1164 other things, it is where everything from the Slab is 1165 allocated. Bad things happen when you're out of lowmem. 1166SwapTotal 1167 total amount of swap space available 1168SwapFree 1169 Memory which has been evicted from RAM, and is temporarily 1170 on the disk 1171Zswap 1172 Memory consumed by the zswap backend (compressed size) 1173Zswapped 1174 Amount of anonymous memory stored in zswap (original size) 1175Dirty 1176 Memory which is waiting to get written back to the disk 1177Writeback 1178 Memory which is actively being written back to the disk 1179AnonPages 1180 Non-file backed pages mapped into userspace page tables. Note that 1181 some kernel configurations might consider all pages part of a 1182 larger allocation (e.g., THP) as "mapped", as soon as a single 1183 page is mapped. 1184Mapped 1185 files which have been mmapped, such as libraries. Note that some 1186 kernel configurations might consider all pages part of a larger 1187 allocation (e.g., THP) as "mapped", as soon as a single page is 1188 mapped. 1189Shmem 1190 Total memory used by shared memory (shmem) and tmpfs 1191KReclaimable 1192 Kernel allocations that the kernel will attempt to reclaim 1193 under memory pressure. Includes SReclaimable (below), and other 1194 direct allocations with a shrinker. 1195Slab 1196 in-kernel data structures cache 1197SReclaimable 1198 Part of Slab, that might be reclaimed, such as caches 1199SUnreclaim 1200 Part of Slab, that cannot be reclaimed on memory pressure 1201KernelStack 1202 Memory consumed by the kernel stacks of all tasks 1203PageTables 1204 Memory consumed by userspace page tables 1205SecPageTables 1206 Memory consumed by secondary page tables, this currently includes 1207 KVM mmu and IOMMU allocations on x86 and arm64. 1208NFS_Unstable 1209 Always zero. Previously counted pages which had been written to 1210 the server, but has not been committed to stable storage. 1211Bounce 1212 Always zero. Previously memory used for block device 1213 "bounce buffers". 1214WritebackTmp 1215 Always zero. Previously memory used by FUSE for temporary 1216 writeback buffers. 1217CommitLimit 1218 Based on the overcommit ratio ('vm.overcommit_ratio'), 1219 this is the total amount of memory currently available to 1220 be allocated on the system. This limit is only adhered to 1221 if strict overcommit accounting is enabled (mode 2 in 1222 'vm.overcommit_memory'). 1223 1224 The CommitLimit is calculated with the following formula:: 1225 1226 CommitLimit = ([total RAM pages] - [total huge TLB pages]) * 1227 overcommit_ratio / 100 + [total swap pages] 1228 1229 For example, on a system with 1G of physical RAM and 7G 1230 of swap with a `vm.overcommit_ratio` of 30 it would 1231 yield a CommitLimit of 7.3G. 1232 1233 For more details, see the memory overcommit documentation 1234 in mm/overcommit-accounting. 1235Committed_AS 1236 The amount of memory presently allocated on the system. 1237 The committed memory is a sum of all of the memory which 1238 has been allocated by processes, even if it has not been 1239 "used" by them as of yet. A process which malloc()'s 1G 1240 of memory, but only touches 300M of it will show up as 1241 using 1G. This 1G is memory which has been "committed" to 1242 by the VM and can be used at any time by the allocating 1243 application. With strict overcommit enabled on the system 1244 (mode 2 in 'vm.overcommit_memory'), allocations which would 1245 exceed the CommitLimit (detailed above) will not be permitted. 1246 This is useful if one needs to guarantee that processes will 1247 not fail due to lack of memory once that memory has been 1248 successfully allocated. 1249VmallocTotal 1250 total size of vmalloc virtual address space 1251VmallocUsed 1252 amount of vmalloc area which is used 1253VmallocChunk 1254 largest contiguous block of vmalloc area which is free 1255Percpu 1256 Memory allocated to the percpu allocator used to back percpu 1257 allocations. This stat excludes the cost of metadata. 1258EarlyMemtestBad 1259 The amount of RAM/memory in kB, that was identified as corrupted 1260 by early memtest. If memtest was not run, this field will not 1261 be displayed at all. Size is never rounded down to 0 kB. 1262 That means if 0 kB is reported, you can safely assume 1263 there was at least one pass of memtest and none of the passes 1264 found a single faulty byte of RAM. 1265HardwareCorrupted 1266 The amount of RAM/memory in KB, the kernel identifies as 1267 corrupted. 1268AnonHugePages 1269 Non-file backed huge pages mapped into userspace page tables 1270ShmemHugePages 1271 Memory used by shared memory (shmem) and tmpfs allocated 1272 with huge pages 1273ShmemPmdMapped 1274 Shared memory mapped into userspace with huge pages 1275FileHugePages 1276 Memory used for filesystem data (page cache) allocated 1277 with huge pages 1278FilePmdMapped 1279 Page cache mapped into userspace with huge pages 1280CmaTotal 1281 Memory reserved for the Contiguous Memory Allocator (CMA) 1282CmaFree 1283 Free remaining memory in the CMA reserves 1284Unaccepted 1285 Memory that has not been accepted by the guest 1286Balloon 1287 Memory returned to Host by VM Balloon Drivers 1288HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb 1289 See Documentation/admin-guide/mm/hugetlbpage.rst. 1290DirectMap4k, DirectMap2M, DirectMap1G 1291 Breakdown of page table sizes used in the kernel's 1292 identity mapping of RAM 1293 1294vmallocinfo 1295~~~~~~~~~~~ 1296 1297Provides information about vmalloced/vmaped areas. One line per area, 1298containing the virtual address range of the area, size in bytes, 1299caller information of the creator, and optional information depending 1300on the kind of area: 1301 1302 ========== =================================================== 1303 pages=nr number of pages 1304 phys=addr if a physical address was specified 1305 ioremap I/O mapping (ioremap() and friends) 1306 vmalloc vmalloc() area 1307 vmap vmap()ed pages 1308 user VM_USERMAP area 1309 vpages buffer for pages pointers was vmalloced (huge area) 1310 N<node>=nr (Only on NUMA kernels) 1311 Number of pages allocated on memory node <node> 1312 ========== =================================================== 1313 1314:: 1315 1316 > cat /proc/vmallocinfo 1317 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... 1318 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 1319 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... 1320 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 1321 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... 1322 phys=7fee8000 ioremap 1323 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... 1324 phys=7fee7000 ioremap 1325 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 1326 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... 1327 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 1328 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... 1329 pages=2 vmalloc N1=2 1330 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... 1331 /0x130 [x_tables] pages=4 vmalloc N0=4 1332 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... 1333 pages=14 vmalloc N2=14 1334 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... 1335 pages=4 vmalloc N1=4 1336 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... 1337 pages=2 vmalloc N1=2 1338 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... 1339 pages=10 vmalloc N0=10 1340 1341 1342softirqs 1343~~~~~~~~ 1344 1345Provides counts of softirq handlers serviced since boot time, for each CPU. 1346 1347:: 1348 1349 > cat /proc/softirqs 1350 CPU0 CPU1 CPU2 CPU3 1351 HI: 0 0 0 0 1352 TIMER: 27166 27120 27097 27034 1353 NET_TX: 0 0 0 17 1354 NET_RX: 42 0 0 39 1355 BLOCK: 0 0 107 1121 1356 TASKLET: 0 0 0 290 1357 SCHED: 27035 26983 26971 26746 1358 HRTIMER: 0 0 0 0 1359 RCU: 1678 1769 2178 2250 1360 13611.3 Networking info in /proc/net 1362-------------------------------- 1363 1364The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the 1365additional values you get for IP version 6 if you configure the kernel to 1366support this. Table 1-9 lists the files and their meaning. 1367 1368 1369.. table:: Table 1-8: IPv6 info in /proc/net 1370 1371 ========== ===================================================== 1372 File Content 1373 ========== ===================================================== 1374 udp6 UDP sockets (IPv6) 1375 tcp6 TCP sockets (IPv6) 1376 raw6 Raw device statistics (IPv6) 1377 igmp6 IP multicast addresses, which this host joined (IPv6) 1378 if_inet6 List of IPv6 interface addresses 1379 ipv6_route Kernel routing table for IPv6 1380 rt6_stats Global IPv6 routing tables statistics 1381 sockstat6 Socket statistics (IPv6) 1382 snmp6 Snmp data (IPv6) 1383 ========== ===================================================== 1384 1385.. table:: Table 1-9: Network info in /proc/net 1386 1387 ============= ================================================================ 1388 File Content 1389 ============= ================================================================ 1390 arp Kernel ARP table 1391 dev network devices with statistics 1392 dev_mcast the Layer2 multicast groups a device is listening too 1393 (interface index, label, number of references, number of bound 1394 addresses). 1395 dev_stat network device status 1396 ip_fwchains Firewall chain linkage 1397 ip_fwnames Firewall chain names 1398 ip_masq Directory containing the masquerading tables 1399 ip_masquerade Major masquerading table 1400 netstat Network statistics 1401 raw raw device statistics 1402 route Kernel routing table 1403 rpc Directory containing rpc info 1404 rt_cache Routing cache 1405 snmp SNMP data 1406 sockstat Socket statistics 1407 softnet_stat Per-CPU incoming packets queues statistics of online CPUs 1408 tcp TCP sockets 1409 udp UDP sockets 1410 unix UNIX domain sockets 1411 wireless Wireless interface data (Wavelan etc) 1412 igmp IP multicast addresses, which this host joined 1413 psched Global packet scheduler parameters. 1414 netlink List of PF_NETLINK sockets 1415 ip_mr_vifs List of multicast virtual interfaces 1416 ip_mr_cache List of multicast routing cache 1417 ============= ================================================================ 1418 1419You can use this information to see which network devices are available in 1420your system and how much traffic was routed over those devices:: 1421 1422 > cat /proc/net/dev 1423 Inter-|Receive |[... 1424 face |bytes packets errs drop fifo frame compressed multicast|[... 1425 lo: 908188 5596 0 0 0 0 0 0 [... 1426 ppp0:15475140 20721 410 0 0 410 0 0 [... 1427 eth0: 614530 7085 0 0 0 0 0 1 [... 1428 1429 ...] Transmit 1430 ...] bytes packets errs drop fifo colls carrier compressed 1431 ...] 908188 5596 0 0 0 0 0 0 1432 ...] 1375103 17405 0 0 0 0 0 0 1433 ...] 1703981 5535 0 0 0 3 0 0 1434 1435In addition, each Channel Bond interface has its own directory. For 1436example, the bond0 device will have a directory called /proc/net/bond0/. 1437It will contain information that is specific to that bond, such as the 1438current slaves of the bond, the link status of the slaves, and how 1439many times the slaves link has failed. 1440 14411.4 SCSI info 1442------------- 1443 1444If you have a SCSI or ATA host adapter in your system, you'll find a 1445subdirectory named after the driver for this adapter in /proc/scsi. 1446You'll also see a list of all recognized SCSI devices in /proc/scsi:: 1447 1448 >cat /proc/scsi/scsi 1449 Attached devices: 1450 Host: scsi0 Channel: 00 Id: 00 Lun: 00 1451 Vendor: IBM Model: DGHS09U Rev: 03E0 1452 Type: Direct-Access ANSI SCSI revision: 03 1453 Host: scsi0 Channel: 00 Id: 06 Lun: 00 1454 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 1455 Type: CD-ROM ANSI SCSI revision: 02 1456 1457 1458The directory named after the driver has one file for each adapter found in 1459the system. These files contain information about the controller, including 1460the used IRQ and the IO address range. The amount of information shown is 1461dependent on the adapter you use. The example shows the output for an Adaptec 1462AHA-2940 SCSI adapter:: 1463 1464 > cat /proc/scsi/aic7xxx/0 1465 1466 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 1467 Compile Options: 1468 TCQ Enabled By Default : Disabled 1469 AIC7XXX_PROC_STATS : Disabled 1470 AIC7XXX_RESET_DELAY : 5 1471 Adapter Configuration: 1472 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 1473 Ultra Wide Controller 1474 PCI MMAPed I/O Base: 0xeb001000 1475 Adapter SEEPROM Config: SEEPROM found and used. 1476 Adaptec SCSI BIOS: Enabled 1477 IRQ: 10 1478 SCBs: Active 0, Max Active 2, 1479 Allocated 15, HW 16, Page 255 1480 Interrupts: 160328 1481 BIOS Control Word: 0x18b6 1482 Adapter Control Word: 0x005b 1483 Extended Translation: Enabled 1484 Disconnect Enable Flags: 0xffff 1485 Ultra Enable Flags: 0x0001 1486 Tag Queue Enable Flags: 0x0000 1487 Ordered Queue Tag Flags: 0x0000 1488 Default Tag Queue Depth: 8 1489 Tagged Queue By Device array for aic7xxx host instance 0: 1490 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 1491 Actual queue depth per device for aic7xxx host instance 0: 1492 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 1493 Statistics: 1494 (scsi0:0:0:0) 1495 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 1496 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 1497 Total transfers 160151 (74577 reads and 85574 writes) 1498 (scsi0:0:6:0) 1499 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 1500 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 1501 Total transfers 0 (0 reads and 0 writes) 1502 1503 15041.5 Parallel port info in /proc/parport 1505--------------------------------------- 1506 1507The directory /proc/parport contains information about the parallel ports of 1508your system. It has one subdirectory for each port, named after the port 1509number (0,1,2,...). 1510 1511These directories contain the four files shown in Table 1-10. 1512 1513 1514.. table:: Table 1-10: Files in /proc/parport 1515 1516 ========= ==================================================================== 1517 File Content 1518 ========= ==================================================================== 1519 autoprobe Any IEEE-1284 device ID information that has been acquired. 1520 devices list of the device drivers using that port. A + will appear by the 1521 name of the device currently using the port (it might not appear 1522 against any). 1523 hardware Parallel port's base address, IRQ line and DMA channel. 1524 irq IRQ that parport is using for that port. This is in a separate 1525 file to allow you to alter it by writing a new value in (IRQ 1526 number or none). 1527 ========= ==================================================================== 1528 15291.6 TTY info in /proc/tty 1530------------------------- 1531 1532Information about the available and actually used tty's can be found in the 1533directory /proc/tty. You'll find entries for drivers and line disciplines in 1534this directory, as shown in Table 1-11. 1535 1536 1537.. table:: Table 1-11: Files in /proc/tty 1538 1539 ============= ============================================== 1540 File Content 1541 ============= ============================================== 1542 drivers list of drivers and their usage 1543 ldiscs registered line disciplines 1544 driver/serial usage statistic and status of single tty lines 1545 ============= ============================================== 1546 1547To see which tty's are currently in use, you can simply look into the file 1548/proc/tty/drivers:: 1549 1550 > cat /proc/tty/drivers 1551 pty_slave /dev/pts 136 0-255 pty:slave 1552 pty_master /dev/ptm 128 0-255 pty:master 1553 pty_slave /dev/ttyp 3 0-255 pty:slave 1554 pty_master /dev/pty 2 0-255 pty:master 1555 serial /dev/cua 5 64-67 serial:callout 1556 serial /dev/ttyS 4 64-67 serial 1557 /dev/tty0 /dev/tty0 4 0 system:vtmaster 1558 /dev/ptmx /dev/ptmx 5 2 system 1559 /dev/console /dev/console 5 1 system:console 1560 /dev/tty /dev/tty 5 0 system:/dev/tty 1561 unknown /dev/tty 4 1-63 console 1562 1563 15641.7 Miscellaneous kernel statistics in /proc/stat 1565------------------------------------------------- 1566 1567Various pieces of information about kernel activity are available in the 1568/proc/stat file. All of the numbers reported in this file are aggregates 1569since the system first booted. For a quick look, simply cat the file:: 1570 1571 > cat /proc/stat 1572 cpu 237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0 1573 cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0 1574 cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0 1575 cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0 1576 cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0 1577 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> 1578 ctxt 22848221062 1579 btime 1605316999 1580 processes 746787147 1581 procs_running 2 1582 procs_blocked 0 1583 softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354 1584 1585The very first "cpu" line aggregates the numbers in all of the other "cpuN" 1586lines. These numbers identify the amount of time the CPU has spent performing 1587different kinds of work. Time units are in USER_HZ (typically hundredths of a 1588second). The meanings of the columns are as follows, from left to right: 1589 1590- user: normal processes executing in user mode 1591- nice: niced processes executing in user mode 1592- system: processes executing in kernel mode 1593- idle: twiddling thumbs 1594- iowait: In a word, iowait stands for waiting for I/O to complete. But there 1595 are several problems: 1596 1597 1. CPU will not wait for I/O to complete, iowait is the time that a task is 1598 waiting for I/O to complete. When CPU goes into idle state for 1599 outstanding task I/O, another task will be scheduled on this CPU. 1600 2. In a multi-core CPU, the task waiting for I/O to complete is not running 1601 on any CPU, so the iowait of each CPU is difficult to calculate. 1602 3. The value of iowait field in /proc/stat will decrease in certain 1603 conditions. 1604 1605 So, the iowait is not reliable by reading from /proc/stat. 1606- irq: servicing interrupts 1607- softirq: servicing softirqs 1608- steal: involuntary wait 1609- guest: running a normal guest 1610- guest_nice: running a niced guest 1611 1612The "intr" line gives counts of interrupts serviced since boot time, for each 1613of the possible system interrupts. The first column is the total of all 1614interrupts serviced including unnumbered architecture specific interrupts; 1615each subsequent column is the total for that particular numbered interrupt. 1616Unnumbered interrupts are not shown, only summed into the total. 1617 1618The "ctxt" line gives the total number of context switches across all CPUs. 1619 1620The "btime" line gives the time at which the system booted, in seconds since 1621the Unix epoch. 1622 1623The "processes" line gives the number of processes and threads created, which 1624includes (but is not limited to) those created by calls to the fork() and 1625clone() system calls. 1626 1627The "procs_running" line gives the total number of threads that are 1628running or ready to run (i.e., the total number of runnable threads). 1629 1630The "procs_blocked" line gives the number of processes currently blocked, 1631waiting for I/O to complete. 1632 1633The "softirq" line gives counts of softirqs serviced since boot time, for each 1634of the possible system softirqs. The first column is the total of all 1635softirqs serviced; each subsequent column is the total for that particular 1636softirq. 1637 1638 16391.8 Ext4 file system parameters 1640------------------------------- 1641 1642Information about mounted ext4 file systems can be found in 1643/proc/fs/ext4. Each mounted filesystem will have a directory in 1644/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or 1645/proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0). The files in each per-device 1646directory are shown in Table 1-12, below. 1647 1648.. table:: Table 1-12: Files in /proc/fs/ext4/<devname> 1649 1650 ============== ========================================================== 1651 File Content 1652 mb_groups details of multiblock allocator buddy cache of free blocks 1653 ============== ========================================================== 1654 16551.9 /proc/consoles 1656------------------- 1657Shows registered system console lines. 1658 1659To see which character device lines are currently used for the system console 1660/dev/console, you may simply look into the file /proc/consoles:: 1661 1662 > cat /proc/consoles 1663 tty0 -WU (ECp) 4:7 1664 ttyS0 -W- (Ep) 4:64 1665 1666The columns are: 1667 1668+--------------------+-------------------------------------------------------+ 1669| device | name of the device | 1670+====================+=======================================================+ 1671| operations | * R = can do read operations | 1672| | * W = can do write operations | 1673| | * U = can do unblank | 1674+--------------------+-------------------------------------------------------+ 1675| flags | * E = it is enabled | 1676| | * C = it is preferred console | 1677| | * B = it is primary boot console | 1678| | * p = it is used for printk buffer | 1679| | * b = it is not a TTY but a Braille device | 1680| | * a = it is safe to use when cpu is offline | 1681+--------------------+-------------------------------------------------------+ 1682| major:minor | major and minor number of the device separated by a | 1683| | colon | 1684+--------------------+-------------------------------------------------------+ 1685 1686Summary 1687------- 1688 1689The /proc file system serves information about the running system. It not only 1690allows access to process data but also allows you to request the kernel status 1691by reading files in the hierarchy. 1692 1693The directory structure of /proc reflects the types of information and makes 1694it easy, if not obvious, where to look for specific data. 1695 1696Chapter 2: Modifying System Parameters 1697====================================== 1698 1699In This Chapter 1700--------------- 1701 1702* Modifying kernel parameters by writing into files found in /proc/sys 1703* Exploring the files which modify certain parameters 1704* Review of the /proc/sys file tree 1705 1706------------------------------------------------------------------------------ 1707 1708A very interesting part of /proc is the directory /proc/sys. This is not only 1709a source of information, it also allows you to change parameters within the 1710kernel. Be very careful when attempting this. You can optimize your system, 1711but you can also cause it to crash. Never alter kernel parameters on a 1712production system. Set up a development machine and test to make sure that 1713everything works the way you want it to. You may have no alternative but to 1714reboot the machine once an error has been made. 1715 1716To change a value, simply echo the new value into the file. 1717You need to be root to do this. You can create your own boot script 1718to perform this every time your system boots. 1719 1720The files in /proc/sys can be used to fine tune and monitor miscellaneous and 1721general things in the operation of the Linux kernel. Since some of the files 1722can inadvertently disrupt your system, it is advisable to read both 1723documentation and source before actually making adjustments. In any case, be 1724very careful when writing to any of these files. The entries in /proc may 1725change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt 1726review the kernel documentation in the directory linux/Documentation. 1727This chapter is heavily based on the documentation included in the pre 2.2 1728kernels, and became part of it in version 2.2.1 of the Linux kernel. 1729 1730Please see: Documentation/admin-guide/sysctl/ directory for descriptions of 1731these entries. 1732 1733Summary 1734------- 1735 1736Certain aspects of kernel behavior can be modified at runtime, without the 1737need to recompile the kernel, or even to reboot the system. The files in the 1738/proc/sys tree can not only be read, but also modified. You can use the echo 1739command to write value into these files, thereby changing the default settings 1740of the kernel. 1741 1742 1743Chapter 3: Per-process Parameters 1744================================= 1745 17463.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score 1747-------------------------------------------------------------------------------- 1748 1749These files can be used to adjust the badness heuristic used to select which 1750process gets killed in out of memory (oom) conditions. 1751 1752The badness heuristic assigns a value to each candidate task ranging from 0 1753(never kill) to 1000 (always kill) to determine which process is targeted. The 1754units are roughly a proportion along that range of allowed memory the process 1755may allocate from based on an estimation of its current memory and swap use. 1756For example, if a task is using all allowed memory, its badness score will be 17571000. If it is using half of its allowed memory, its score will be 500. 1758 1759The amount of "allowed" memory depends on the context in which the oom killer 1760was called. If it is due to the memory assigned to the allocating task's cpuset 1761being exhausted, the allowed memory represents the set of mems assigned to that 1762cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed 1763memory represents the set of mempolicy nodes. If it is due to a memory 1764limit (or swap limit) being reached, the allowed memory is that configured 1765limit. Finally, if it is due to the entire system being out of memory, the 1766allowed memory represents all allocatable resources. 1767 1768The value of /proc/<pid>/oom_score_adj is added to the badness score before it 1769is used to determine which task to kill. Acceptable values range from -1000 1770(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to 1771polarize the preference for oom killing either by always preferring a certain 1772task or completely disabling it. The lowest possible value, -1000, is 1773equivalent to disabling oom killing entirely for that task since it will always 1774report a badness score of 0. 1775 1776Consequently, it is very simple for userspace to define the amount of memory to 1777consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for 1778example, is roughly equivalent to allowing the remainder of tasks sharing the 1779same system, cpuset, mempolicy, or memory controller resources to use at least 178050% more memory. A value of -500, on the other hand, would be roughly 1781equivalent to discounting 50% of the task's allowed memory from being considered 1782as scoring against the task. 1783 1784For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also 1785be used to tune the badness score. Its acceptable values range from -16 1786(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 1787(OOM_DISABLE) to disable oom killing entirely for that task. Its value is 1788scaled linearly with /proc/<pid>/oom_score_adj. 1789 1790The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last 1791value set by a CAP_SYS_RESOURCE process. To reduce the value any lower 1792requires CAP_SYS_RESOURCE. 1793 1794 17953.2 /proc/<pid>/oom_score - Display current oom-killer score 1796------------------------------------------------------------- 1797 1798This file can be used to check the current score used by the oom-killer for 1799any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which 1800process should be killed in an out-of-memory situation. 1801 1802Please note that the exported value includes oom_score_adj so it is 1803effectively in range [0,2000]. 1804 1805 18063.3 /proc/<pid>/io - Display the IO accounting fields 1807------------------------------------------------------- 1808 1809This file contains IO statistics for each running process. 1810 1811Example 1812~~~~~~~ 1813 1814:: 1815 1816 test:/tmp # dd if=/dev/zero of=/tmp/test.dat & 1817 [1] 3828 1818 1819 test:/tmp # cat /proc/3828/io 1820 rchar: 323934931 1821 wchar: 323929600 1822 syscr: 632687 1823 syscw: 632675 1824 read_bytes: 0 1825 write_bytes: 323932160 1826 cancelled_write_bytes: 0 1827 1828 1829Description 1830~~~~~~~~~~~ 1831 1832rchar 1833^^^^^ 1834 1835I/O counter: chars read 1836The number of bytes which this task has caused to be read from storage. This 1837is simply the sum of bytes which this process passed to read() and pread(). 1838It includes things like tty IO and it is unaffected by whether or not actual 1839physical disk IO was required (the read might have been satisfied from 1840pagecache). 1841 1842 1843wchar 1844^^^^^ 1845 1846I/O counter: chars written 1847The number of bytes which this task has caused, or shall cause to be written 1848to disk. Similar caveats apply here as with rchar. 1849 1850 1851syscr 1852^^^^^ 1853 1854I/O counter: read syscalls 1855Attempt to count the number of read I/O operations, i.e. syscalls like read() 1856and pread(). 1857 1858 1859syscw 1860^^^^^ 1861 1862I/O counter: write syscalls 1863Attempt to count the number of write I/O operations, i.e. syscalls like 1864write() and pwrite(). 1865 1866 1867read_bytes 1868^^^^^^^^^^ 1869 1870I/O counter: bytes read 1871Attempt to count the number of bytes which this process really did cause to 1872be fetched from the storage layer. Done at the submit_bio() level, so it is 1873accurate for block-backed filesystems. <please add status regarding NFS and 1874CIFS at a later time> 1875 1876 1877write_bytes 1878^^^^^^^^^^^ 1879 1880I/O counter: bytes written 1881Attempt to count the number of bytes which this process caused to be sent to 1882the storage layer. This is done at page-dirtying time. 1883 1884 1885cancelled_write_bytes 1886^^^^^^^^^^^^^^^^^^^^^ 1887 1888The big inaccuracy here is truncate. If a process writes 1MB to a file and 1889then deletes the file, it will in fact perform no writeout. But it will have 1890been accounted as having caused 1MB of write. 1891In other words: The number of bytes which this process caused to not happen, 1892by truncating pagecache. A task can cause "negative" IO too. If this task 1893truncates some dirty pagecache, some IO which another task has been accounted 1894for (in its write_bytes) will not be happening. We _could_ just subtract that 1895from the truncating task's write_bytes, but there is information loss in doing 1896that. 1897 1898 1899.. Note:: 1900 1901 At its current implementation state, this is a bit racy on 32-bit machines: 1902 if process A reads process B's /proc/pid/io while process B is updating one 1903 of those 64-bit counters, process A could see an intermediate result. 1904 1905 1906More information about this can be found within the taskstats documentation in 1907Documentation/accounting. 1908 19093.4 /proc/<pid>/coredump_filter - Core dump filtering settings 1910--------------------------------------------------------------- 1911When a process is dumped, all anonymous memory is written to a core file as 1912long as the size of the core file isn't limited. But sometimes we don't want 1913to dump some memory segments, for example, huge shared memory or DAX. 1914Conversely, sometimes we want to save file-backed memory segments into a core 1915file, not only the individual files. 1916 1917/proc/<pid>/coredump_filter allows you to customize which memory segments 1918will be dumped when the <pid> process is dumped. coredump_filter is a bitmask 1919of memory types. If a bit of the bitmask is set, memory segments of the 1920corresponding memory type are dumped, otherwise they are not dumped. 1921 1922The following 9 memory types are supported: 1923 1924 - (bit 0) anonymous private memory 1925 - (bit 1) anonymous shared memory 1926 - (bit 2) file-backed private memory 1927 - (bit 3) file-backed shared memory 1928 - (bit 4) ELF header pages in file-backed private memory areas (it is 1929 effective only if the bit 2 is cleared) 1930 - (bit 5) hugetlb private memory 1931 - (bit 6) hugetlb shared memory 1932 - (bit 7) DAX private memory 1933 - (bit 8) DAX shared memory 1934 1935 Note that MMIO pages such as frame buffer are never dumped and vDSO pages 1936 are always dumped regardless of the bitmask status. 1937 1938 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is 1939 only affected by bit 5-6, and DAX is only affected by bits 7-8. 1940 1941The default value of coredump_filter is 0x33; this means all anonymous memory 1942segments, ELF header pages and hugetlb private memory are dumped. 1943 1944If you don't want to dump all shared memory segments attached to pid 1234, 1945write 0x31 to the process's proc file:: 1946 1947 $ echo 0x31 > /proc/1234/coredump_filter 1948 1949When a new process is created, the process inherits the bitmask status from its 1950parent. It is useful to set up coredump_filter before the program runs. 1951For example:: 1952 1953 $ echo 0x7 > /proc/self/coredump_filter 1954 $ ./some_program 1955 19563.5 /proc/<pid>/mountinfo - Information about mounts 1957-------------------------------------------------------- 1958 1959This file contains lines of the form:: 1960 1961 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue 1962 (1)(2)(3) (4) (5) (6) (n…m) (m+1)(m+2) (m+3) (m+4) 1963 1964 (1) mount ID: unique identifier of the mount (may be reused after umount) 1965 (2) parent ID: ID of parent (or of self for the top of the mount tree) 1966 (3) major:minor: value of st_dev for files on filesystem 1967 (4) root: root of the mount within the filesystem 1968 (5) mount point: mount point relative to the process's root 1969 (6) mount options: per mount options 1970 (n…m) optional fields: zero or more fields of the form "tag[:value]" 1971 (m+1) separator: marks the end of the optional fields 1972 (m+2) filesystem type: name of filesystem of the form "type[.subtype]" 1973 (m+3) mount source: filesystem specific information or "none" 1974 (m+4) super options: per super block options 1975 1976Parsers should ignore all unrecognised optional fields. Currently the 1977possible optional fields are: 1978 1979================ ============================================================== 1980shared:X mount is shared in peer group X 1981master:X mount is slave to peer group X 1982propagate_from:X mount is slave and receives propagation from peer group X [#]_ 1983unbindable mount is unbindable 1984================ ============================================================== 1985 1986.. [#] X is the closest dominant peer group under the process's root. If 1987 X is the immediate master of the mount, or if there's no dominant peer 1988 group under the same root, then only the "master:X" field is present 1989 and not the "propagate_from:X" field. 1990 1991For more information on mount propagation see: 1992 1993 Documentation/filesystems/sharedsubtree.rst 1994 1995 19963.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm 1997-------------------------------------------------------- 1998These files provide a method to access a task's comm value. It also allows for 1999a task to set its own or one of its thread siblings comm value. The comm value 2000is limited in size compared to the cmdline value, so writing anything longer 2001then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL 2002terminator) will result in a truncated comm value. 2003 2004 20053.7 /proc/<pid>/task/<tid>/children - Information about task children 2006------------------------------------------------------------------------- 2007This file provides a fast way to retrieve first level children pids 2008of a task pointed by <pid>/<tid> pair. The format is a space separated 2009stream of pids. 2010 2011Note the "first level" here -- if a child has its own children they will 2012not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children 2013to obtain the descendants. 2014 2015Since this interface is intended to be fast and cheap it doesn't 2016guarantee to provide precise results and some children might be 2017skipped, especially if they've exited right after we printed their 2018pids, so one needs to either stop or freeze processes being inspected 2019if precise results are needed. 2020 2021 20223.8 /proc/<pid>/fdinfo/<fd> - Information about opened file 2023--------------------------------------------------------------- 2024This file provides information associated with an opened file. The regular 2025files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. 2026The 'pos' represents the current offset of the opened file in decimal 2027form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the 2028file has been created with [see open(2) for details] and 'mnt_id' represents 2029mount ID of the file system containing the opened file [see 3.5 2030/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of 2031the file. 2032 2033A typical output is:: 2034 2035 pos: 0 2036 flags: 0100002 2037 mnt_id: 19 2038 ino: 63107 2039 2040All locks associated with a file descriptor are shown in its fdinfo too:: 2041 2042 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF 2043 2044The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags 2045pair provide additional information particular to the objects they represent. 2046 2047Eventfd files 2048~~~~~~~~~~~~~ 2049 2050:: 2051 2052 pos: 0 2053 flags: 04002 2054 mnt_id: 9 2055 ino: 63107 2056 eventfd-count: 5a 2057 2058where 'eventfd-count' is hex value of a counter. 2059 2060Signalfd files 2061~~~~~~~~~~~~~~ 2062 2063:: 2064 2065 pos: 0 2066 flags: 04002 2067 mnt_id: 9 2068 ino: 63107 2069 sigmask: 0000000000000200 2070 2071where 'sigmask' is hex value of the signal mask associated 2072with a file. 2073 2074Epoll files 2075~~~~~~~~~~~ 2076 2077:: 2078 2079 pos: 0 2080 flags: 02 2081 mnt_id: 9 2082 ino: 63107 2083 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 2084 2085where 'tfd' is a target file descriptor number in decimal form, 2086'events' is events mask being watched and the 'data' is data 2087associated with a target [see epoll(7) for more details]. 2088 2089The 'pos' is current offset of the target file in decimal form 2090[see lseek(2)], 'ino' and 'sdev' are inode and device numbers 2091where target file resides, all in hex format. 2092 2093Fsnotify files 2094~~~~~~~~~~~~~~ 2095For inotify files the format is the following:: 2096 2097 pos: 0 2098 flags: 02000000 2099 mnt_id: 9 2100 ino: 63107 2101 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d 2102 2103where 'wd' is a watch descriptor in decimal form, i.e. a target file 2104descriptor number, 'ino' and 'sdev' are inode and device where the 2105target file resides and the 'mask' is the mask of events, all in hex 2106form [see inotify(7) for more details]. 2107 2108If the kernel was built with exportfs support, the path to the target 2109file is encoded as a file handle. The file handle is provided by three 2110fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex 2111format. 2112 2113If the kernel is built without exportfs support the file handle won't be 2114printed out. 2115 2116If there is no inotify mark attached yet the 'inotify' line will be omitted. 2117 2118For fanotify files the format is:: 2119 2120 pos: 0 2121 flags: 02 2122 mnt_id: 9 2123 ino: 63107 2124 fanotify flags:10 event-flags:0 2125 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003 2126 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4 2127 2128where fanotify 'flags' and 'event-flags' are values used in fanotify_init 2129call, 'mnt_id' is the mount point identifier, 'mflags' is the value of 2130flags associated with mark which are tracked separately from events 2131mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events 2132mask and 'ignored_mask' is the mask of events which are to be ignored. 2133All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask' 2134provide information about flags and mask used in fanotify_mark 2135call [see fsnotify manpage for details]. 2136 2137While the first three lines are mandatory and always printed, the rest is 2138optional and may be omitted if no marks created yet. 2139 2140Timerfd files 2141~~~~~~~~~~~~~ 2142 2143:: 2144 2145 pos: 0 2146 flags: 02 2147 mnt_id: 9 2148 ino: 63107 2149 clockid: 0 2150 ticks: 0 2151 settime flags: 01 2152 it_value: (0, 49406829) 2153 it_interval: (1, 0) 2154 2155where 'clockid' is the clock type and 'ticks' is the number of the timer expirations 2156that have occurred [see timerfd_create(2) for details]. 'settime flags' are 2157flags in octal form been used to setup the timer [see timerfd_settime(2) for 2158details]. 'it_value' is remaining time until the timer expiration. 2159'it_interval' is the interval for the timer. Note the timer might be set up 2160with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value' 2161still exhibits timer's remaining time. 2162 2163DMA Buffer files 2164~~~~~~~~~~~~~~~~ 2165 2166:: 2167 2168 pos: 0 2169 flags: 04002 2170 mnt_id: 9 2171 ino: 63107 2172 size: 32768 2173 count: 2 2174 exp_name: system-heap 2175 2176where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of 2177the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter. 2178 2179VFIO Device files 2180~~~~~~~~~~~~~~~~~ 2181 2182:: 2183 2184 pos: 0 2185 flags: 02000002 2186 mnt_id: 17 2187 ino: 5122 2188 vfio-device-syspath: /sys/devices/pci0000:e0/0000:e0:01.1/0000:e1:00.0/0000:e2:05.0/0000:e8:00.0 2189 2190where 'vfio-device-syspath' is the sysfs path corresponding to the VFIO device 2191file. 2192 21933.9 /proc/<pid>/map_files - Information about memory mapped files 2194--------------------------------------------------------------------- 2195This directory contains symbolic links which represent memory mapped files 2196the process is maintaining. Example output:: 2197 2198 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so 2199 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so 2200 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so 2201 | ... 2202 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1 2203 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls 2204 2205The name of a link represents the virtual memory bounds of a mapping, i.e. 2206vm_area_struct::vm_start-vm_area_struct::vm_end. 2207 2208The main purpose of the map_files is to retrieve a set of memory mapped 2209files in a fast way instead of parsing /proc/<pid>/maps or 2210/proc/<pid>/smaps, both of which contain many more records. At the same 2211time one can open(2) mappings from the listings of two processes and 2212comparing their inode numbers to figure out which anonymous memory areas 2213are actually shared. 2214 22153.10 /proc/<pid>/timerslack_ns - Task timerslack value 2216--------------------------------------------------------- 2217This file provides the value of the task's timerslack value in nanoseconds. 2218This value specifies an amount of time that normal timers may be deferred 2219in order to coalesce timers and avoid unnecessary wakeups. 2220 2221This allows a task's interactivity vs power consumption tradeoff to be 2222adjusted. 2223 2224Writing 0 to the file will set the task's timerslack to the default value. 2225 2226Valid values are from 0 - ULLONG_MAX 2227 2228An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level 2229permissions on the task specified to change its timerslack_ns value. 2230 22313.11 /proc/<pid>/patch_state - Livepatch patch operation state 2232----------------------------------------------------------------- 2233When CONFIG_LIVEPATCH is enabled, this file displays the value of the 2234patch state for the task. 2235 2236A value of '-1' indicates that no patch is in transition. 2237 2238A value of '0' indicates that a patch is in transition and the task is 2239unpatched. If the patch is being enabled, then the task hasn't been 2240patched yet. If the patch is being disabled, then the task has already 2241been unpatched. 2242 2243A value of '1' indicates that a patch is in transition and the task is 2244patched. If the patch is being enabled, then the task has already been 2245patched. If the patch is being disabled, then the task hasn't been 2246unpatched yet. 2247 22483.12 /proc/<pid>/arch_status - task architecture specific status 2249------------------------------------------------------------------- 2250When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the 2251architecture specific status of the task. 2252 2253Example 2254~~~~~~~ 2255 2256:: 2257 2258 $ cat /proc/6753/arch_status 2259 AVX512_elapsed_ms: 8 2260 2261Description 2262~~~~~~~~~~~ 2263 2264x86 specific entries 2265~~~~~~~~~~~~~~~~~~~~~ 2266 2267AVX512_elapsed_ms 2268^^^^^^^^^^^^^^^^^^ 2269 2270 If AVX512 is supported on the machine, this entry shows the milliseconds 2271 elapsed since the last time AVX512 usage was recorded. The recording 2272 happens on a best effort basis when a task is scheduled out. This means 2273 that the value depends on two factors: 2274 2275 1) The time which the task spent on the CPU without being scheduled 2276 out. With CPU isolation and a single runnable task this can take 2277 several seconds. 2278 2279 2) The time since the task was scheduled out last. Depending on the 2280 reason for being scheduled out (time slice exhausted, syscall ...) 2281 this can be arbitrary long time. 2282 2283 As a consequence the value cannot be considered precise and authoritative 2284 information. The application which uses this information has to be aware 2285 of the overall scenario on the system in order to determine whether a 2286 task is a real AVX512 user or not. Precise information can be obtained 2287 with performance counters. 2288 2289 A special value of '-1' indicates that no AVX512 usage was recorded, thus 2290 the task is unlikely an AVX512 user, but depends on the workload and the 2291 scheduling scenario, it also could be a false negative mentioned above. 2292 22933.13 /proc/<pid>/fd - List of symlinks to open files 2294------------------------------------------------------- 2295This directory contains symbolic links which represent open files 2296the process is maintaining. Example output:: 2297 2298 lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null 2299 l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null 2300 lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]' 2301 lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]' 2302 lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]' 2303 2304The number of open files for the process is stored in 'size' member 2305of stat() output for /proc/<pid>/fd for fast access. 2306------------------------------------------------------- 2307 23083.14 /proc/<pid>/ksm_stat - Information about the process's ksm status 2309---------------------------------------------------------------------- 2310When CONFIG_KSM is enabled, each process has this file which displays 2311the information of ksm merging status. 2312 2313Example 2314~~~~~~~ 2315 2316:: 2317 2318 / # cat /proc/self/ksm_stat 2319 ksm_rmap_items 0 2320 ksm_zero_pages 0 2321 ksm_merging_pages 0 2322 ksm_process_profit 0 2323 ksm_merge_any: no 2324 ksm_mergeable: no 2325 2326Description 2327~~~~~~~~~~~ 2328 2329ksm_rmap_items 2330^^^^^^^^^^^^^^ 2331 2332The number of ksm_rmap_item structures in use. The structure 2333ksm_rmap_item stores the reverse mapping information for virtual 2334addresses. KSM will generate a ksm_rmap_item for each ksm-scanned page of 2335the process. 2336 2337ksm_zero_pages 2338^^^^^^^^^^^^^^ 2339 2340When /sys/kernel/mm/ksm/use_zero_pages is enabled, it represent how many 2341empty pages are merged with kernel zero pages by KSM. 2342 2343ksm_merging_pages 2344^^^^^^^^^^^^^^^^^ 2345 2346It represents how many pages of this process are involved in KSM merging 2347(not including ksm_zero_pages). It is the same with what 2348/proc/<pid>/ksm_merging_pages shows. 2349 2350ksm_process_profit 2351^^^^^^^^^^^^^^^^^^ 2352 2353The profit that KSM brings (Saved bytes). KSM can save memory by merging 2354identical pages, but also can consume additional memory, because it needs 2355to generate a number of rmap_items to save each scanned page's brief rmap 2356information. Some of these pages may be merged, but some may not be abled 2357to be merged after being checked several times, which are unprofitable 2358memory consumed. 2359 2360ksm_merge_any 2361^^^^^^^^^^^^^ 2362 2363It specifies whether the process's 'mm is added by prctl() into the 2364candidate list of KSM or not, and if KSM scanning is fully enabled at 2365process level. 2366 2367ksm_mergeable 2368^^^^^^^^^^^^^ 2369 2370It specifies whether any VMAs of the process''s mms are currently 2371applicable to KSM. 2372 2373More information about KSM can be found in 2374Documentation/admin-guide/mm/ksm.rst. 2375 2376 2377Chapter 4: Configuring procfs 2378============================= 2379 23804.1 Mount options 2381--------------------- 2382 2383The following mount options are supported: 2384 2385 ========= ======================================================== 2386 hidepid= Set /proc/<pid>/ access mode. 2387 gid= Set the group authorized to learn processes information. 2388 subset= Show only the specified subset of procfs. 2389 pidns= Specify a the namespace used by this procfs. 2390 ========= ======================================================== 2391 2392hidepid=off or hidepid=0 means classic mode - everybody may access all 2393/proc/<pid>/ directories (default). 2394 2395hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/ 2396directories but their own. Sensitive files like cmdline, sched*, status are now 2397protected against other users. This makes it impossible to learn whether any 2398user runs specific program (given the program doesn't reveal itself by its 2399behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for 2400other users, poorly written programs passing sensitive information via program 2401arguments are now protected against local eavesdroppers. 2402 2403hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be 2404fully invisible to other users. It doesn't mean that it hides a fact whether a 2405process with a specific pid value exists (it can be learned by other means, e.g. 2406by "kill -0 $PID"), but it hides process's uid and gid, which may be learned by 2407stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of 2408gathering information about running processes, whether some daemon runs with 2409elevated privileges, whether other user runs some sensitive program, whether 2410other users run any program at all, etc. 2411 2412hidepid=ptraceable or hidepid=4 means that procfs should only contain 2413/proc/<pid>/ directories that the caller can ptrace. 2414 2415gid= defines a group authorized to learn processes information otherwise 2416prohibited by hidepid=. If you use some daemon like identd which needs to learn 2417information about processes information, just add identd to this group. 2418 2419subset=pid hides all top level files and directories in the procfs that 2420are not related to tasks. 2421 2422pidns= specifies a pid namespace (either as a string path to something like 2423`/proc/$pid/ns/pid`, or a file descriptor when using `FSCONFIG_SET_FD`) that 2424will be used by the procfs instance when translating pids. By default, procfs 2425will use the calling process's active pid namespace. Note that the pid 2426namespace of an existing procfs instance cannot be modified (attempting to do 2427so will give an `-EBUSY` error). 2428 2429Chapter 5: Filesystem behavior 2430============================== 2431 2432Originally, before the advent of pid namespace, procfs was a global file 2433system. It means that there was only one procfs instance in the system. 2434 2435When pid namespace was added, a separate procfs instance was mounted in 2436each pid namespace. So, procfs mount options are global among all 2437mountpoints within the same namespace:: 2438 2439 # grep ^proc /proc/mounts 2440 proc /proc proc rw,relatime,hidepid=2 0 0 2441 2442 # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc 2443 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0 2444 +++ exited with 0 +++ 2445 2446 # grep ^proc /proc/mounts 2447 proc /proc proc rw,relatime,hidepid=2 0 0 2448 proc /tmp/proc proc rw,relatime,hidepid=2 0 0 2449 2450and only after remounting procfs mount options will change at all 2451mountpoints:: 2452 2453 # mount -o remount,hidepid=1 -t proc proc /tmp/proc 2454 2455 # grep ^proc /proc/mounts 2456 proc /proc proc rw,relatime,hidepid=1 0 0 2457 proc /tmp/proc proc rw,relatime,hidepid=1 0 0 2458 2459This behavior is different from the behavior of other filesystems. 2460 2461The new procfs behavior is more like other filesystems. Each procfs mount 2462creates a new procfs instance. Mount options affect own procfs instance. 2463It means that it became possible to have several procfs instances 2464displaying tasks with different filtering options in one pid namespace:: 2465 2466 # mount -o hidepid=invisible -t proc proc /proc 2467 # mount -o hidepid=noaccess -t proc proc /tmp/proc 2468 # grep ^proc /proc/mounts 2469 proc /proc proc rw,relatime,hidepid=invisible 0 0 2470 proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 2471