1------------------------------------------------------------------------------ 2 T H E /proc F I L E S Y S T E M 3------------------------------------------------------------------------------ 4/proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999 5 Bodo Bauer <bb@ricochet.net> 6 72.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000 8move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009 9------------------------------------------------------------------------------ 10Version 1.3 Kernel version 2.2.12 11 Kernel version 2.4.0-test11-pre4 12------------------------------------------------------------------------------ 13fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009 14 15Table of Contents 16----------------- 17 18 0 Preface 19 0.1 Introduction/Credits 20 0.2 Legal Stuff 21 22 1 Collecting System Information 23 1.1 Process-Specific Subdirectories 24 1.2 Kernel data 25 1.3 IDE devices in /proc/ide 26 1.4 Networking info in /proc/net 27 1.5 SCSI info 28 1.6 Parallel port info in /proc/parport 29 1.7 TTY info in /proc/tty 30 1.8 Miscellaneous kernel statistics in /proc/stat 31 1.9 Ext4 file system parameters 32 33 2 Modifying System Parameters 34 35 3 Per-Process Parameters 36 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer 37 score 38 3.2 /proc/<pid>/oom_score - Display current oom-killer score 39 3.3 /proc/<pid>/io - Display the IO accounting fields 40 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings 41 3.5 /proc/<pid>/mountinfo - Information about mounts 42 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm 43 44 4 Configuring procfs 45 4.1 Mount options 46 47------------------------------------------------------------------------------ 48Preface 49------------------------------------------------------------------------------ 50 510.1 Introduction/Credits 52------------------------ 53 54This documentation is part of a soon (or so we hope) to be released book on 55the SuSE Linux distribution. As there is no complete documentation for the 56/proc file system and we've used many freely available sources to write these 57chapters, it seems only fair to give the work back to the Linux community. 58This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm 59afraid it's still far from complete, but we hope it will be useful. As far as 60we know, it is the first 'all-in-one' document about the /proc file system. It 61is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, 62SPARC, AXP, etc., features, you probably won't find what you are looking for. 63It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But 64additions and patches are welcome and will be added to this document if you 65mail them to Bodo. 66 67We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of 68other people for help compiling this documentation. We'd also like to extend a 69special thank you to Andi Kleen for documentation, which we relied on heavily 70to create this document, as well as the additional information he provided. 71Thanks to everybody else who contributed source or docs to the Linux kernel 72and helped create a great piece of software... :) 73 74If you have any comments, corrections or additions, please don't hesitate to 75contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this 76document. 77 78The latest version of this document is available online at 79http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html 80 81If the above direction does not works for you, you could try the kernel 82mailing list at linux-kernel@vger.kernel.org and/or try to reach me at 83comandante@zaralinux.com. 84 850.2 Legal Stuff 86--------------- 87 88We don't guarantee the correctness of this document, and if you come to us 89complaining about how you screwed up your system because of incorrect 90documentation, we won't feel responsible... 91 92------------------------------------------------------------------------------ 93CHAPTER 1: COLLECTING SYSTEM INFORMATION 94------------------------------------------------------------------------------ 95 96------------------------------------------------------------------------------ 97In This Chapter 98------------------------------------------------------------------------------ 99* Investigating the properties of the pseudo file system /proc and its 100 ability to provide information on the running Linux system 101* Examining /proc's structure 102* Uncovering various information about the kernel and the processes running 103 on the system 104------------------------------------------------------------------------------ 105 106 107The proc file system acts as an interface to internal data structures in the 108kernel. It can be used to obtain information about the system and to change 109certain kernel parameters at runtime (sysctl). 110 111First, we'll take a look at the read-only parts of /proc. In Chapter 2, we 112show you how you can use /proc/sys to change settings. 113 1141.1 Process-Specific Subdirectories 115----------------------------------- 116 117The directory /proc contains (among other things) one subdirectory for each 118process running on the system, which is named after the process ID (PID). 119 120The link self points to the process reading the file system. Each process 121subdirectory has the entries listed in Table 1-1. 122 123 124Table 1-1: Process specific entries in /proc 125.............................................................................. 126 File Content 127 clear_refs Clears page referenced bits shown in smaps output 128 cmdline Command line arguments 129 cpu Current and last cpu in which it was executed (2.4)(smp) 130 cwd Link to the current working directory 131 environ Values of environment variables 132 exe Link to the executable of this process 133 fd Directory, which contains all file descriptors 134 maps Memory maps to executables and library files (2.4) 135 mem Memory held by this process 136 root Link to the root directory of this process 137 stat Process status 138 statm Process memory status information 139 status Process status in human readable form 140 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan 141 pagemap Page table 142 stack Report full stack trace, enable via CONFIG_STACKTRACE 143 smaps a extension based on maps, showing the memory consumption of 144 each mapping 145.............................................................................. 146 147For example, to get the status information of a process, all you have to do is 148read the file /proc/PID/status: 149 150 >cat /proc/self/status 151 Name: cat 152 State: R (running) 153 Tgid: 5452 154 Pid: 5452 155 PPid: 743 156 TracerPid: 0 (2.4) 157 Uid: 501 501 501 501 158 Gid: 100 100 100 100 159 FDSize: 256 160 Groups: 100 14 16 161 VmPeak: 5004 kB 162 VmSize: 5004 kB 163 VmLck: 0 kB 164 VmHWM: 476 kB 165 VmRSS: 476 kB 166 VmData: 156 kB 167 VmStk: 88 kB 168 VmExe: 68 kB 169 VmLib: 1412 kB 170 VmPTE: 20 kb 171 VmSwap: 0 kB 172 Threads: 1 173 SigQ: 0/28578 174 SigPnd: 0000000000000000 175 ShdPnd: 0000000000000000 176 SigBlk: 0000000000000000 177 SigIgn: 0000000000000000 178 SigCgt: 0000000000000000 179 CapInh: 00000000fffffeff 180 CapPrm: 0000000000000000 181 CapEff: 0000000000000000 182 CapBnd: ffffffffffffffff 183 voluntary_ctxt_switches: 0 184 nonvoluntary_ctxt_switches: 1 185 186This shows you nearly the same information you would get if you viewed it with 187the ps command. In fact, ps uses the proc file system to obtain its 188information. But you get a more detailed view of the process by reading the 189file /proc/PID/status. It fields are described in table 1-2. 190 191The statm file contains more detailed information about the process 192memory usage. Its seven fields are explained in Table 1-3. The stat file 193contains details information about the process itself. Its fields are 194explained in Table 1-4. 195 196(for SMP CONFIG users) 197For making accounting scalable, RSS related information are handled in 198asynchronous manner and the vaule may not be very precise. To see a precise 199snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table. 200It's slow but very precise. 201 202Table 1-2: Contents of the status files (as of 2.6.30-rc7) 203.............................................................................. 204 Field Content 205 Name filename of the executable 206 State state (R is running, S is sleeping, D is sleeping 207 in an uninterruptible wait, Z is zombie, 208 T is traced or stopped) 209 Tgid thread group ID 210 Pid process id 211 PPid process id of the parent process 212 TracerPid PID of process tracing this process (0 if not) 213 Uid Real, effective, saved set, and file system UIDs 214 Gid Real, effective, saved set, and file system GIDs 215 FDSize number of file descriptor slots currently allocated 216 Groups supplementary group list 217 VmPeak peak virtual memory size 218 VmSize total program size 219 VmLck locked memory size 220 VmHWM peak resident set size ("high water mark") 221 VmRSS size of memory portions 222 VmData size of data, stack, and text segments 223 VmStk size of data, stack, and text segments 224 VmExe size of text segment 225 VmLib size of shared library code 226 VmPTE size of page table entries 227 VmSwap size of swap usage (the number of referred swapents) 228 Threads number of threads 229 SigQ number of signals queued/max. number for queue 230 SigPnd bitmap of pending signals for the thread 231 ShdPnd bitmap of shared pending signals for the process 232 SigBlk bitmap of blocked signals 233 SigIgn bitmap of ignored signals 234 SigCgt bitmap of catched signals 235 CapInh bitmap of inheritable capabilities 236 CapPrm bitmap of permitted capabilities 237 CapEff bitmap of effective capabilities 238 CapBnd bitmap of capabilities bounding set 239 Cpus_allowed mask of CPUs on which this process may run 240 Cpus_allowed_list Same as previous, but in "list format" 241 Mems_allowed mask of memory nodes allowed to this process 242 Mems_allowed_list Same as previous, but in "list format" 243 voluntary_ctxt_switches number of voluntary context switches 244 nonvoluntary_ctxt_switches number of non voluntary context switches 245.............................................................................. 246 247Table 1-3: Contents of the statm files (as of 2.6.8-rc3) 248.............................................................................. 249 Field Content 250 size total program size (pages) (same as VmSize in status) 251 resident size of memory portions (pages) (same as VmRSS in status) 252 shared number of pages that are shared (i.e. backed by a file) 253 trs number of pages that are 'code' (not including libs; broken, 254 includes data segment) 255 lrs number of pages of library (always 0 on 2.6) 256 drs number of pages of data/stack (including libs; broken, 257 includes library text) 258 dt number of dirty pages (always 0 on 2.6) 259.............................................................................. 260 261 262Table 1-4: Contents of the stat files (as of 2.6.30-rc7) 263.............................................................................. 264 Field Content 265 pid process id 266 tcomm filename of the executable 267 state state (R is running, S is sleeping, D is sleeping in an 268 uninterruptible wait, Z is zombie, T is traced or stopped) 269 ppid process id of the parent process 270 pgrp pgrp of the process 271 sid session id 272 tty_nr tty the process uses 273 tty_pgrp pgrp of the tty 274 flags task flags 275 min_flt number of minor faults 276 cmin_flt number of minor faults with child's 277 maj_flt number of major faults 278 cmaj_flt number of major faults with child's 279 utime user mode jiffies 280 stime kernel mode jiffies 281 cutime user mode jiffies with child's 282 cstime kernel mode jiffies with child's 283 priority priority level 284 nice nice level 285 num_threads number of threads 286 it_real_value (obsolete, always 0) 287 start_time time the process started after system boot 288 vsize virtual memory size 289 rss resident set memory size 290 rsslim current limit in bytes on the rss 291 start_code address above which program text can run 292 end_code address below which program text can run 293 start_stack address of the start of the stack 294 esp current value of ESP 295 eip current value of EIP 296 pending bitmap of pending signals 297 blocked bitmap of blocked signals 298 sigign bitmap of ignored signals 299 sigcatch bitmap of catched signals 300 wchan address where process went to sleep 301 0 (place holder) 302 0 (place holder) 303 exit_signal signal to send to parent thread on exit 304 task_cpu which CPU the task is scheduled on 305 rt_priority realtime priority 306 policy scheduling policy (man sched_setscheduler) 307 blkio_ticks time spent waiting for block IO 308 gtime guest time of the task in jiffies 309 cgtime guest time of the task children in jiffies 310 start_data address above which program data+bss is placed 311 end_data address below which program data+bss is placed 312 start_brk address above which program heap can be expanded with brk() 313.............................................................................. 314 315The /proc/PID/maps file containing the currently mapped memory regions and 316their access permissions. 317 318The format is: 319 320address perms offset dev inode pathname 321 32208048000-08049000 r-xp 00000000 03:00 8312 /opt/test 32308049000-0804a000 rw-p 00001000 03:00 8312 /opt/test 3240804a000-0806b000 rw-p 00000000 00:00 0 [heap] 325a7cb1000-a7cb2000 ---p 00000000 00:00 0 326a7cb2000-a7eb2000 rw-p 00000000 00:00 0 327a7eb2000-a7eb3000 ---p 00000000 00:00 0 328a7eb3000-a7ed5000 rw-p 00000000 00:00 0 329a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 330a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 331a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 332a800b000-a800e000 rw-p 00000000 00:00 0 333a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 334a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 335a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 336a8024000-a8027000 rw-p 00000000 00:00 0 337a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 338a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 339a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 340aff35000-aff4a000 rw-p 00000000 00:00 0 [stack] 341ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] 342 343where "address" is the address space in the process that it occupies, "perms" 344is a set of permissions: 345 346 r = read 347 w = write 348 x = execute 349 s = shared 350 p = private (copy on write) 351 352"offset" is the offset into the mapping, "dev" is the device (major:minor), and 353"inode" is the inode on that device. 0 indicates that no inode is associated 354with the memory region, as the case would be with BSS (uninitialized data). 355The "pathname" shows the name associated file for this mapping. If the mapping 356is not associated with a file: 357 358 [heap] = the heap of the program 359 [stack] = the stack of the main process 360 [vdso] = the "virtual dynamic shared object", 361 the kernel system call handler 362 363 or if empty, the mapping is anonymous. 364 365 366The /proc/PID/smaps is an extension based on maps, showing the memory 367consumption for each of the process's mappings. For each of mappings there 368is a series of lines such as the following: 369 37008048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash 371Size: 1084 kB 372Rss: 892 kB 373Pss: 374 kB 374Shared_Clean: 892 kB 375Shared_Dirty: 0 kB 376Private_Clean: 0 kB 377Private_Dirty: 0 kB 378Referenced: 892 kB 379Anonymous: 0 kB 380Swap: 0 kB 381KernelPageSize: 4 kB 382MMUPageSize: 4 kB 383Locked: 374 kB 384 385The first of these lines shows the same information as is displayed for the 386mapping in /proc/PID/maps. The remaining lines show the size of the mapping 387(size), the amount of the mapping that is currently resident in RAM (RSS), the 388process' proportional share of this mapping (PSS), the number of clean and 389dirty private pages in the mapping. Note that even a page which is part of a 390MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used 391by only one process, is accounted as private and not as shared. "Referenced" 392indicates the amount of memory currently marked as referenced or accessed. 393"Anonymous" shows the amount of memory that does not belong to any file. Even 394a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE 395and a page is modified, the file page is replaced by a private anonymous copy. 396"Swap" shows how much would-be-anonymous memory is also used, but out on 397swap. 398 399This file is only present if the CONFIG_MMU kernel configuration option is 400enabled. 401 402The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG 403bits on both physical and virtual pages associated with a process. 404To clear the bits for all the pages associated with the process 405 > echo 1 > /proc/PID/clear_refs 406 407To clear the bits for the anonymous pages associated with the process 408 > echo 2 > /proc/PID/clear_refs 409 410To clear the bits for the file mapped pages associated with the process 411 > echo 3 > /proc/PID/clear_refs 412Any other value written to /proc/PID/clear_refs will have no effect. 413 414The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags 415using /proc/kpageflags and number of times a page is mapped using 416/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt. 417 4181.2 Kernel data 419--------------- 420 421Similar to the process entries, the kernel data files give information about 422the running kernel. The files used to obtain this information are contained in 423/proc and are listed in Table 1-5. Not all of these will be present in your 424system. It depends on the kernel configuration and the loaded modules, which 425files are there, and which are missing. 426 427Table 1-5: Kernel info in /proc 428.............................................................................. 429 File Content 430 apm Advanced power management info 431 buddyinfo Kernel memory allocator information (see text) (2.5) 432 bus Directory containing bus specific information 433 cmdline Kernel command line 434 cpuinfo Info about the CPU 435 devices Available devices (block and character) 436 dma Used DMS channels 437 filesystems Supported filesystems 438 driver Various drivers grouped here, currently rtc (2.4) 439 execdomains Execdomains, related to security (2.4) 440 fb Frame Buffer devices (2.4) 441 fs File system parameters, currently nfs/exports (2.4) 442 ide Directory containing info about the IDE subsystem 443 interrupts Interrupt usage 444 iomem Memory map (2.4) 445 ioports I/O port usage 446 irq Masks for irq to cpu affinity (2.4)(smp?) 447 isapnp ISA PnP (Plug&Play) Info (2.4) 448 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) 449 kmsg Kernel messages 450 ksyms Kernel symbol table 451 loadavg Load average of last 1, 5 & 15 minutes 452 locks Kernel locks 453 meminfo Memory info 454 misc Miscellaneous 455 modules List of loaded modules 456 mounts Mounted filesystems 457 net Networking info (see text) 458 pagetypeinfo Additional page allocator information (see text) (2.5) 459 partitions Table of partitions known to the system 460 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, 461 decoupled by lspci (2.4) 462 rtc Real time clock 463 scsi SCSI info (see text) 464 slabinfo Slab pool info 465 softirqs softirq usage 466 stat Overall statistics 467 swaps Swap space utilization 468 sys See chapter 2 469 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) 470 tty Info of tty drivers 471 uptime System uptime 472 version Kernel version 473 video bttv info of video resources (2.4) 474 vmallocinfo Show vmalloced areas 475.............................................................................. 476 477You can, for example, check which interrupts are currently in use and what 478they are used for by looking in the file /proc/interrupts: 479 480 > cat /proc/interrupts 481 CPU0 482 0: 8728810 XT-PIC timer 483 1: 895 XT-PIC keyboard 484 2: 0 XT-PIC cascade 485 3: 531695 XT-PIC aha152x 486 4: 2014133 XT-PIC serial 487 5: 44401 XT-PIC pcnet_cs 488 8: 2 XT-PIC rtc 489 11: 8 XT-PIC i82365 490 12: 182918 XT-PIC PS/2 Mouse 491 13: 1 XT-PIC fpu 492 14: 1232265 XT-PIC ide0 493 15: 7 XT-PIC ide1 494 NMI: 0 495 496In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the 497output of a SMP machine): 498 499 > cat /proc/interrupts 500 501 CPU0 CPU1 502 0: 1243498 1214548 IO-APIC-edge timer 503 1: 8949 8958 IO-APIC-edge keyboard 504 2: 0 0 XT-PIC cascade 505 5: 11286 10161 IO-APIC-edge soundblaster 506 8: 1 0 IO-APIC-edge rtc 507 9: 27422 27407 IO-APIC-edge 3c503 508 12: 113645 113873 IO-APIC-edge PS/2 Mouse 509 13: 0 0 XT-PIC fpu 510 14: 22491 24012 IO-APIC-edge ide0 511 15: 2183 2415 IO-APIC-edge ide1 512 17: 30564 30414 IO-APIC-level eth0 513 18: 177 164 IO-APIC-level bttv 514 NMI: 2457961 2457959 515 LOC: 2457882 2457881 516 ERR: 2155 517 518NMI is incremented in this case because every timer interrupt generates a NMI 519(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. 520 521LOC is the local interrupt counter of the internal APIC of every CPU. 522 523ERR is incremented in the case of errors in the IO-APIC bus (the bus that 524connects the CPUs in a SMP system. This means that an error has been detected, 525the IO-APIC automatically retry the transmission, so it should not be a big 526problem, but you should read the SMP-FAQ. 527 528In 2.6.2* /proc/interrupts was expanded again. This time the goal was for 529/proc/interrupts to display every IRQ vector in use by the system, not 530just those considered 'most important'. The new vectors are: 531 532 THR -- interrupt raised when a machine check threshold counter 533 (typically counting ECC corrected errors of memory or cache) exceeds 534 a configurable threshold. Only available on some systems. 535 536 TRM -- a thermal event interrupt occurs when a temperature threshold 537 has been exceeded for the CPU. This interrupt may also be generated 538 when the temperature drops back to normal. 539 540 SPU -- a spurious interrupt is some interrupt that was raised then lowered 541 by some IO device before it could be fully processed by the APIC. Hence 542 the APIC sees the interrupt but does not know what device it came from. 543 For this case the APIC will generate the interrupt with a IRQ vector 544 of 0xff. This might also be generated by chipset bugs. 545 546 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are 547 sent from one CPU to another per the needs of the OS. Typically, 548 their statistics are used by kernel developers and interested users to 549 determine the occurrence of interrupts of the given type. 550 551The above IRQ vectors are displayed only when relevant. For example, 552the threshold vector does not exist on x86_64 platforms. Others are 553suppressed when the system is a uniprocessor. As of this writing, only 554i386 and x86_64 platforms support the new IRQ vector displays. 555 556Of some interest is the introduction of the /proc/irq directory to 2.4. 557It could be used to set IRQ to CPU affinity, this means that you can "hook" an 558IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the 559irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and 560prof_cpu_mask. 561 562For example 563 > ls /proc/irq/ 564 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask 565 1 11 13 15 17 19 3 5 7 9 default_smp_affinity 566 > ls /proc/irq/0/ 567 smp_affinity 568 569smp_affinity is a bitmask, in which you can specify which CPUs can handle the 570IRQ, you can set it by doing: 571 572 > echo 1 > /proc/irq/10/smp_affinity 573 574This means that only the first CPU will handle the IRQ, but you can also echo 5755 which means that only the first and fourth CPU can handle the IRQ. 576 577The contents of each smp_affinity file is the same by default: 578 579 > cat /proc/irq/0/smp_affinity 580 ffffffff 581 582There is an alternate interface, smp_affinity_list which allows specifying 583a cpu range instead of a bitmask: 584 585 > cat /proc/irq/0/smp_affinity_list 586 1024-1031 587 588The default_smp_affinity mask applies to all non-active IRQs, which are the 589IRQs which have not yet been allocated/activated, and hence which lack a 590/proc/irq/[0-9]* directory. 591 592The node file on an SMP system shows the node to which the device using the IRQ 593reports itself as being attached. This hardware locality information does not 594include information about any possible driver locality preference. 595 596prof_cpu_mask specifies which CPUs are to be profiled by the system wide 597profiler. Default value is ffffffff (all cpus if there are only 32 of them). 598 599The way IRQs are routed is handled by the IO-APIC, and it's Round Robin 600between all the CPUs which are allowed to handle it. As usual the kernel has 601more info than you and does a better job than you, so the defaults are the 602best choice for almost everyone. [Note this applies only to those IO-APIC's 603that support "Round Robin" interrupt distribution.] 604 605There are three more important subdirectories in /proc: net, scsi, and sys. 606The general rule is that the contents, or even the existence of these 607directories, depend on your kernel configuration. If SCSI is not enabled, the 608directory scsi may not exist. The same is true with the net, which is there 609only when networking support is present in the running kernel. 610 611The slabinfo file gives information about memory usage at the slab level. 612Linux uses slab pools for memory management above page level in version 2.2. 613Commonly used objects have their own slab pool (such as network buffers, 614directory cache, and so on). 615 616.............................................................................. 617 618> cat /proc/buddyinfo 619 620Node 0, zone DMA 0 4 5 4 4 3 ... 621Node 0, zone Normal 1 0 0 1 101 8 ... 622Node 0, zone HighMem 2 0 0 1 1 0 ... 623 624External fragmentation is a problem under some workloads, and buddyinfo is a 625useful tool for helping diagnose these problems. Buddyinfo will give you a 626clue as to how big an area you can safely allocate, or why a previous 627allocation failed. 628 629Each column represents the number of pages of a certain order which are 630available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 631ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 632available in ZONE_NORMAL, etc... 633 634More information relevant to external fragmentation can be found in 635pagetypeinfo. 636 637> cat /proc/pagetypeinfo 638Page block order: 9 639Pages per block: 512 640 641Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 642Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0 643Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0 644Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2 645Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0 646Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0 647Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9 648Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0 649Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452 650Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0 651Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0 652 653Number of blocks type Unmovable Reclaimable Movable Reserve Isolate 654Node 0, zone DMA 2 0 5 1 0 655Node 0, zone DMA32 41 6 967 2 0 656 657Fragmentation avoidance in the kernel works by grouping pages of different 658migrate types into the same contiguous regions of memory called page blocks. 659A page block is typically the size of the default hugepage size e.g. 2MB on 660X86-64. By keeping pages grouped based on their ability to move, the kernel 661can reclaim pages within a page block to satisfy a high-order allocation. 662 663The pagetypinfo begins with information on the size of a page block. It 664then gives the same type of information as buddyinfo except broken down 665by migrate-type and finishes with details on how many page blocks of each 666type exist. 667 668If min_free_kbytes has been tuned correctly (recommendations made by hugeadm 669from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can 670make an estimate of the likely number of huge pages that can be allocated 671at a given point in time. All the "Movable" blocks should be allocatable 672unless memory has been mlock()'d. Some of the Reclaimable blocks should 673also be allocatable although a lot of filesystem metadata may have to be 674reclaimed to achieve this. 675 676.............................................................................. 677 678meminfo: 679 680Provides information about distribution and utilization of memory. This 681varies by architecture and compile options. The following is from a 68216GB PIII, which has highmem enabled. You may not have all of these fields. 683 684> cat /proc/meminfo 685 686The "Locked" indicates whether the mapping is locked in memory or not. 687 688 689MemTotal: 16344972 kB 690MemFree: 13634064 kB 691Buffers: 3656 kB 692Cached: 1195708 kB 693SwapCached: 0 kB 694Active: 891636 kB 695Inactive: 1077224 kB 696HighTotal: 15597528 kB 697HighFree: 13629632 kB 698LowTotal: 747444 kB 699LowFree: 4432 kB 700SwapTotal: 0 kB 701SwapFree: 0 kB 702Dirty: 968 kB 703Writeback: 0 kB 704AnonPages: 861800 kB 705Mapped: 280372 kB 706Slab: 284364 kB 707SReclaimable: 159856 kB 708SUnreclaim: 124508 kB 709PageTables: 24448 kB 710NFS_Unstable: 0 kB 711Bounce: 0 kB 712WritebackTmp: 0 kB 713CommitLimit: 7669796 kB 714Committed_AS: 100056 kB 715VmallocTotal: 112216 kB 716VmallocUsed: 428 kB 717VmallocChunk: 111088 kB 718 719 MemTotal: Total usable ram (i.e. physical ram minus a few reserved 720 bits and the kernel binary code) 721 MemFree: The sum of LowFree+HighFree 722 Buffers: Relatively temporary storage for raw disk blocks 723 shouldn't get tremendously large (20MB or so) 724 Cached: in-memory cache for files read from the disk (the 725 pagecache). Doesn't include SwapCached 726 SwapCached: Memory that once was swapped out, is swapped back in but 727 still also is in the swapfile (if memory is needed it 728 doesn't need to be swapped out AGAIN because it is already 729 in the swapfile. This saves I/O) 730 Active: Memory that has been used more recently and usually not 731 reclaimed unless absolutely necessary. 732 Inactive: Memory which has been less recently used. It is more 733 eligible to be reclaimed for other purposes 734 HighTotal: 735 HighFree: Highmem is all memory above ~860MB of physical memory 736 Highmem areas are for use by userspace programs, or 737 for the pagecache. The kernel must use tricks to access 738 this memory, making it slower to access than lowmem. 739 LowTotal: 740 LowFree: Lowmem is memory which can be used for everything that 741 highmem can be used for, but it is also available for the 742 kernel's use for its own data structures. Among many 743 other things, it is where everything from the Slab is 744 allocated. Bad things happen when you're out of lowmem. 745 SwapTotal: total amount of swap space available 746 SwapFree: Memory which has been evicted from RAM, and is temporarily 747 on the disk 748 Dirty: Memory which is waiting to get written back to the disk 749 Writeback: Memory which is actively being written back to the disk 750 AnonPages: Non-file backed pages mapped into userspace page tables 751 Mapped: files which have been mmaped, such as libraries 752 Slab: in-kernel data structures cache 753SReclaimable: Part of Slab, that might be reclaimed, such as caches 754 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure 755 PageTables: amount of memory dedicated to the lowest level of page 756 tables. 757NFS_Unstable: NFS pages sent to the server, but not yet committed to stable 758 storage 759 Bounce: Memory used for block device "bounce buffers" 760WritebackTmp: Memory used by FUSE for temporary writeback buffers 761 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'), 762 this is the total amount of memory currently available to 763 be allocated on the system. This limit is only adhered to 764 if strict overcommit accounting is enabled (mode 2 in 765 'vm.overcommit_memory'). 766 The CommitLimit is calculated with the following formula: 767 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap 768 For example, on a system with 1G of physical RAM and 7G 769 of swap with a `vm.overcommit_ratio` of 30 it would 770 yield a CommitLimit of 7.3G. 771 For more details, see the memory overcommit documentation 772 in vm/overcommit-accounting. 773Committed_AS: The amount of memory presently allocated on the system. 774 The committed memory is a sum of all of the memory which 775 has been allocated by processes, even if it has not been 776 "used" by them as of yet. A process which malloc()'s 1G 777 of memory, but only touches 300M of it will only show up 778 as using 300M of memory even if it has the address space 779 allocated for the entire 1G. This 1G is memory which has 780 been "committed" to by the VM and can be used at any time 781 by the allocating application. With strict overcommit 782 enabled on the system (mode 2 in 'vm.overcommit_memory'), 783 allocations which would exceed the CommitLimit (detailed 784 above) will not be permitted. This is useful if one needs 785 to guarantee that processes will not fail due to lack of 786 memory once that memory has been successfully allocated. 787VmallocTotal: total size of vmalloc memory area 788 VmallocUsed: amount of vmalloc area which is used 789VmallocChunk: largest contiguous block of vmalloc area which is free 790 791.............................................................................. 792 793vmallocinfo: 794 795Provides information about vmalloced/vmaped areas. One line per area, 796containing the virtual address range of the area, size in bytes, 797caller information of the creator, and optional information depending 798on the kind of area : 799 800 pages=nr number of pages 801 phys=addr if a physical address was specified 802 ioremap I/O mapping (ioremap() and friends) 803 vmalloc vmalloc() area 804 vmap vmap()ed pages 805 user VM_USERMAP area 806 vpages buffer for pages pointers was vmalloced (huge area) 807 N<node>=nr (Only on NUMA kernels) 808 Number of pages allocated on memory node <node> 809 810> cat /proc/vmallocinfo 8110xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... 812 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 8130xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... 814 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 8150xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... 816 phys=7fee8000 ioremap 8170xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... 818 phys=7fee7000 ioremap 8190xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 8200xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... 821 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 8220xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... 823 pages=2 vmalloc N1=2 8240xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... 825 /0x130 [x_tables] pages=4 vmalloc N0=4 8260xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... 827 pages=14 vmalloc N2=14 8280xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... 829 pages=4 vmalloc N1=4 8300xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... 831 pages=2 vmalloc N1=2 8320xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... 833 pages=10 vmalloc N0=10 834 835.............................................................................. 836 837softirqs: 838 839Provides counts of softirq handlers serviced since boot time, for each cpu. 840 841> cat /proc/softirqs 842 CPU0 CPU1 CPU2 CPU3 843 HI: 0 0 0 0 844 TIMER: 27166 27120 27097 27034 845 NET_TX: 0 0 0 17 846 NET_RX: 42 0 0 39 847 BLOCK: 0 0 107 1121 848 TASKLET: 0 0 0 290 849 SCHED: 27035 26983 26971 26746 850 HRTIMER: 0 0 0 0 851 RCU: 1678 1769 2178 2250 852 853 8541.3 IDE devices in /proc/ide 855---------------------------- 856 857The subdirectory /proc/ide contains information about all IDE devices of which 858the kernel is aware. There is one subdirectory for each IDE controller, the 859file drivers and a link for each IDE device, pointing to the device directory 860in the controller specific subtree. 861 862The file drivers contains general information about the drivers used for the 863IDE devices: 864 865 > cat /proc/ide/drivers 866 ide-cdrom version 4.53 867 ide-disk version 1.08 868 869More detailed information can be found in the controller specific 870subdirectories. These are named ide0, ide1 and so on. Each of these 871directories contains the files shown in table 1-6. 872 873 874Table 1-6: IDE controller info in /proc/ide/ide? 875.............................................................................. 876 File Content 877 channel IDE channel (0 or 1) 878 config Configuration (only for PCI/IDE bridge) 879 mate Mate name 880 model Type/Chipset of IDE controller 881.............................................................................. 882 883Each device connected to a controller has a separate subdirectory in the 884controllers directory. The files listed in table 1-7 are contained in these 885directories. 886 887 888Table 1-7: IDE device information 889.............................................................................. 890 File Content 891 cache The cache 892 capacity Capacity of the medium (in 512Byte blocks) 893 driver driver and version 894 geometry physical and logical geometry 895 identify device identify block 896 media media type 897 model device identifier 898 settings device setup 899 smart_thresholds IDE disk management thresholds 900 smart_values IDE disk management values 901.............................................................................. 902 903The most interesting file is settings. This file contains a nice overview of 904the drive parameters: 905 906 # cat /proc/ide/ide0/hda/settings 907 name value min max mode 908 ---- ----- --- --- ---- 909 bios_cyl 526 0 65535 rw 910 bios_head 255 0 255 rw 911 bios_sect 63 0 63 rw 912 breada_readahead 4 0 127 rw 913 bswap 0 0 1 r 914 file_readahead 72 0 2097151 rw 915 io_32bit 0 0 3 rw 916 keepsettings 0 0 1 rw 917 max_kb_per_request 122 1 127 rw 918 multcount 0 0 8 rw 919 nice1 1 0 1 rw 920 nowerr 0 0 1 rw 921 pio_mode write-only 0 255 w 922 slow 0 0 1 rw 923 unmaskirq 0 0 1 rw 924 using_dma 0 0 1 rw 925 926 9271.4 Networking info in /proc/net 928-------------------------------- 929 930The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the 931additional values you get for IP version 6 if you configure the kernel to 932support this. Table 1-9 lists the files and their meaning. 933 934 935Table 1-8: IPv6 info in /proc/net 936.............................................................................. 937 File Content 938 udp6 UDP sockets (IPv6) 939 tcp6 TCP sockets (IPv6) 940 raw6 Raw device statistics (IPv6) 941 igmp6 IP multicast addresses, which this host joined (IPv6) 942 if_inet6 List of IPv6 interface addresses 943 ipv6_route Kernel routing table for IPv6 944 rt6_stats Global IPv6 routing tables statistics 945 sockstat6 Socket statistics (IPv6) 946 snmp6 Snmp data (IPv6) 947.............................................................................. 948 949 950Table 1-9: Network info in /proc/net 951.............................................................................. 952 File Content 953 arp Kernel ARP table 954 dev network devices with statistics 955 dev_mcast the Layer2 multicast groups a device is listening too 956 (interface index, label, number of references, number of bound 957 addresses). 958 dev_stat network device status 959 ip_fwchains Firewall chain linkage 960 ip_fwnames Firewall chain names 961 ip_masq Directory containing the masquerading tables 962 ip_masquerade Major masquerading table 963 netstat Network statistics 964 raw raw device statistics 965 route Kernel routing table 966 rpc Directory containing rpc info 967 rt_cache Routing cache 968 snmp SNMP data 969 sockstat Socket statistics 970 tcp TCP sockets 971 tr_rif Token ring RIF routing table 972 udp UDP sockets 973 unix UNIX domain sockets 974 wireless Wireless interface data (Wavelan etc) 975 igmp IP multicast addresses, which this host joined 976 psched Global packet scheduler parameters. 977 netlink List of PF_NETLINK sockets 978 ip_mr_vifs List of multicast virtual interfaces 979 ip_mr_cache List of multicast routing cache 980.............................................................................. 981 982You can use this information to see which network devices are available in 983your system and how much traffic was routed over those devices: 984 985 > cat /proc/net/dev 986 Inter-|Receive |[... 987 face |bytes packets errs drop fifo frame compressed multicast|[... 988 lo: 908188 5596 0 0 0 0 0 0 [... 989 ppp0:15475140 20721 410 0 0 410 0 0 [... 990 eth0: 614530 7085 0 0 0 0 0 1 [... 991 992 ...] Transmit 993 ...] bytes packets errs drop fifo colls carrier compressed 994 ...] 908188 5596 0 0 0 0 0 0 995 ...] 1375103 17405 0 0 0 0 0 0 996 ...] 1703981 5535 0 0 0 3 0 0 997 998In addition, each Channel Bond interface has its own directory. For 999example, the bond0 device will have a directory called /proc/net/bond0/. 1000It will contain information that is specific to that bond, such as the 1001current slaves of the bond, the link status of the slaves, and how 1002many times the slaves link has failed. 1003 10041.5 SCSI info 1005------------- 1006 1007If you have a SCSI host adapter in your system, you'll find a subdirectory 1008named after the driver for this adapter in /proc/scsi. You'll also see a list 1009of all recognized SCSI devices in /proc/scsi: 1010 1011 >cat /proc/scsi/scsi 1012 Attached devices: 1013 Host: scsi0 Channel: 00 Id: 00 Lun: 00 1014 Vendor: IBM Model: DGHS09U Rev: 03E0 1015 Type: Direct-Access ANSI SCSI revision: 03 1016 Host: scsi0 Channel: 00 Id: 06 Lun: 00 1017 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 1018 Type: CD-ROM ANSI SCSI revision: 02 1019 1020 1021The directory named after the driver has one file for each adapter found in 1022the system. These files contain information about the controller, including 1023the used IRQ and the IO address range. The amount of information shown is 1024dependent on the adapter you use. The example shows the output for an Adaptec 1025AHA-2940 SCSI adapter: 1026 1027 > cat /proc/scsi/aic7xxx/0 1028 1029 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 1030 Compile Options: 1031 TCQ Enabled By Default : Disabled 1032 AIC7XXX_PROC_STATS : Disabled 1033 AIC7XXX_RESET_DELAY : 5 1034 Adapter Configuration: 1035 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 1036 Ultra Wide Controller 1037 PCI MMAPed I/O Base: 0xeb001000 1038 Adapter SEEPROM Config: SEEPROM found and used. 1039 Adaptec SCSI BIOS: Enabled 1040 IRQ: 10 1041 SCBs: Active 0, Max Active 2, 1042 Allocated 15, HW 16, Page 255 1043 Interrupts: 160328 1044 BIOS Control Word: 0x18b6 1045 Adapter Control Word: 0x005b 1046 Extended Translation: Enabled 1047 Disconnect Enable Flags: 0xffff 1048 Ultra Enable Flags: 0x0001 1049 Tag Queue Enable Flags: 0x0000 1050 Ordered Queue Tag Flags: 0x0000 1051 Default Tag Queue Depth: 8 1052 Tagged Queue By Device array for aic7xxx host instance 0: 1053 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 1054 Actual queue depth per device for aic7xxx host instance 0: 1055 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 1056 Statistics: 1057 (scsi0:0:0:0) 1058 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 1059 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 1060 Total transfers 160151 (74577 reads and 85574 writes) 1061 (scsi0:0:6:0) 1062 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 1063 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 1064 Total transfers 0 (0 reads and 0 writes) 1065 1066 10671.6 Parallel port info in /proc/parport 1068--------------------------------------- 1069 1070The directory /proc/parport contains information about the parallel ports of 1071your system. It has one subdirectory for each port, named after the port 1072number (0,1,2,...). 1073 1074These directories contain the four files shown in Table 1-10. 1075 1076 1077Table 1-10: Files in /proc/parport 1078.............................................................................. 1079 File Content 1080 autoprobe Any IEEE-1284 device ID information that has been acquired. 1081 devices list of the device drivers using that port. A + will appear by the 1082 name of the device currently using the port (it might not appear 1083 against any). 1084 hardware Parallel port's base address, IRQ line and DMA channel. 1085 irq IRQ that parport is using for that port. This is in a separate 1086 file to allow you to alter it by writing a new value in (IRQ 1087 number or none). 1088.............................................................................. 1089 10901.7 TTY info in /proc/tty 1091------------------------- 1092 1093Information about the available and actually used tty's can be found in the 1094directory /proc/tty.You'll find entries for drivers and line disciplines in 1095this directory, as shown in Table 1-11. 1096 1097 1098Table 1-11: Files in /proc/tty 1099.............................................................................. 1100 File Content 1101 drivers list of drivers and their usage 1102 ldiscs registered line disciplines 1103 driver/serial usage statistic and status of single tty lines 1104.............................................................................. 1105 1106To see which tty's are currently in use, you can simply look into the file 1107/proc/tty/drivers: 1108 1109 > cat /proc/tty/drivers 1110 pty_slave /dev/pts 136 0-255 pty:slave 1111 pty_master /dev/ptm 128 0-255 pty:master 1112 pty_slave /dev/ttyp 3 0-255 pty:slave 1113 pty_master /dev/pty 2 0-255 pty:master 1114 serial /dev/cua 5 64-67 serial:callout 1115 serial /dev/ttyS 4 64-67 serial 1116 /dev/tty0 /dev/tty0 4 0 system:vtmaster 1117 /dev/ptmx /dev/ptmx 5 2 system 1118 /dev/console /dev/console 5 1 system:console 1119 /dev/tty /dev/tty 5 0 system:/dev/tty 1120 unknown /dev/tty 4 1-63 console 1121 1122 11231.8 Miscellaneous kernel statistics in /proc/stat 1124------------------------------------------------- 1125 1126Various pieces of information about kernel activity are available in the 1127/proc/stat file. All of the numbers reported in this file are aggregates 1128since the system first booted. For a quick look, simply cat the file: 1129 1130 > cat /proc/stat 1131 cpu 2255 34 2290 22625563 6290 127 456 0 0 1132 cpu0 1132 34 1441 11311718 3675 127 438 0 0 1133 cpu1 1123 0 849 11313845 2614 0 18 0 0 1134 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] 1135 ctxt 1990473 1136 btime 1062191376 1137 processes 2915 1138 procs_running 1 1139 procs_blocked 0 1140 softirq 183433 0 21755 12 39 1137 231 21459 2263 1141 1142The very first "cpu" line aggregates the numbers in all of the other "cpuN" 1143lines. These numbers identify the amount of time the CPU has spent performing 1144different kinds of work. Time units are in USER_HZ (typically hundredths of a 1145second). The meanings of the columns are as follows, from left to right: 1146 1147- user: normal processes executing in user mode 1148- nice: niced processes executing in user mode 1149- system: processes executing in kernel mode 1150- idle: twiddling thumbs 1151- iowait: waiting for I/O to complete 1152- irq: servicing interrupts 1153- softirq: servicing softirqs 1154- steal: involuntary wait 1155- guest: running a normal guest 1156- guest_nice: running a niced guest 1157 1158The "intr" line gives counts of interrupts serviced since boot time, for each 1159of the possible system interrupts. The first column is the total of all 1160interrupts serviced; each subsequent column is the total for that particular 1161interrupt. 1162 1163The "ctxt" line gives the total number of context switches across all CPUs. 1164 1165The "btime" line gives the time at which the system booted, in seconds since 1166the Unix epoch. 1167 1168The "processes" line gives the number of processes and threads created, which 1169includes (but is not limited to) those created by calls to the fork() and 1170clone() system calls. 1171 1172The "procs_running" line gives the total number of threads that are 1173running or ready to run (i.e., the total number of runnable threads). 1174 1175The "procs_blocked" line gives the number of processes currently blocked, 1176waiting for I/O to complete. 1177 1178The "softirq" line gives counts of softirqs serviced since boot time, for each 1179of the possible system softirqs. The first column is the total of all 1180softirqs serviced; each subsequent column is the total for that particular 1181softirq. 1182 1183 11841.9 Ext4 file system parameters 1185------------------------------ 1186 1187Information about mounted ext4 file systems can be found in 1188/proc/fs/ext4. Each mounted filesystem will have a directory in 1189/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or 1190/proc/fs/ext4/dm-0). The files in each per-device directory are shown 1191in Table 1-12, below. 1192 1193Table 1-12: Files in /proc/fs/ext4/<devname> 1194.............................................................................. 1195 File Content 1196 mb_groups details of multiblock allocator buddy cache of free blocks 1197.............................................................................. 1198 11992.0 /proc/consoles 1200------------------ 1201Shows registered system console lines. 1202 1203To see which character device lines are currently used for the system console 1204/dev/console, you may simply look into the file /proc/consoles: 1205 1206 > cat /proc/consoles 1207 tty0 -WU (ECp) 4:7 1208 ttyS0 -W- (Ep) 4:64 1209 1210The columns are: 1211 1212 device name of the device 1213 operations R = can do read operations 1214 W = can do write operations 1215 U = can do unblank 1216 flags E = it is enabled 1217 C = it is preferred console 1218 B = it is primary boot console 1219 p = it is used for printk buffer 1220 b = it is not a TTY but a Braille device 1221 a = it is safe to use when cpu is offline 1222 major:minor major and minor number of the device separated by a colon 1223 1224------------------------------------------------------------------------------ 1225Summary 1226------------------------------------------------------------------------------ 1227The /proc file system serves information about the running system. It not only 1228allows access to process data but also allows you to request the kernel status 1229by reading files in the hierarchy. 1230 1231The directory structure of /proc reflects the types of information and makes 1232it easy, if not obvious, where to look for specific data. 1233------------------------------------------------------------------------------ 1234 1235------------------------------------------------------------------------------ 1236CHAPTER 2: MODIFYING SYSTEM PARAMETERS 1237------------------------------------------------------------------------------ 1238 1239------------------------------------------------------------------------------ 1240In This Chapter 1241------------------------------------------------------------------------------ 1242* Modifying kernel parameters by writing into files found in /proc/sys 1243* Exploring the files which modify certain parameters 1244* Review of the /proc/sys file tree 1245------------------------------------------------------------------------------ 1246 1247 1248A very interesting part of /proc is the directory /proc/sys. This is not only 1249a source of information, it also allows you to change parameters within the 1250kernel. Be very careful when attempting this. You can optimize your system, 1251but you can also cause it to crash. Never alter kernel parameters on a 1252production system. Set up a development machine and test to make sure that 1253everything works the way you want it to. You may have no alternative but to 1254reboot the machine once an error has been made. 1255 1256To change a value, simply echo the new value into the file. An example is 1257given below in the section on the file system data. You need to be root to do 1258this. You can create your own boot script to perform this every time your 1259system boots. 1260 1261The files in /proc/sys can be used to fine tune and monitor miscellaneous and 1262general things in the operation of the Linux kernel. Since some of the files 1263can inadvertently disrupt your system, it is advisable to read both 1264documentation and source before actually making adjustments. In any case, be 1265very careful when writing to any of these files. The entries in /proc may 1266change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt 1267review the kernel documentation in the directory /usr/src/linux/Documentation. 1268This chapter is heavily based on the documentation included in the pre 2.2 1269kernels, and became part of it in version 2.2.1 of the Linux kernel. 1270 1271Please see: Documentation/sysctl/ directory for descriptions of these 1272entries. 1273 1274------------------------------------------------------------------------------ 1275Summary 1276------------------------------------------------------------------------------ 1277Certain aspects of kernel behavior can be modified at runtime, without the 1278need to recompile the kernel, or even to reboot the system. The files in the 1279/proc/sys tree can not only be read, but also modified. You can use the echo 1280command to write value into these files, thereby changing the default settings 1281of the kernel. 1282------------------------------------------------------------------------------ 1283 1284------------------------------------------------------------------------------ 1285CHAPTER 3: PER-PROCESS PARAMETERS 1286------------------------------------------------------------------------------ 1287 12883.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score 1289-------------------------------------------------------------------------------- 1290 1291These file can be used to adjust the badness heuristic used to select which 1292process gets killed in out of memory conditions. 1293 1294The badness heuristic assigns a value to each candidate task ranging from 0 1295(never kill) to 1000 (always kill) to determine which process is targeted. The 1296units are roughly a proportion along that range of allowed memory the process 1297may allocate from based on an estimation of its current memory and swap use. 1298For example, if a task is using all allowed memory, its badness score will be 12991000. If it is using half of its allowed memory, its score will be 500. 1300 1301There is an additional factor included in the badness score: root 1302processes are given 3% extra memory over other tasks. 1303 1304The amount of "allowed" memory depends on the context in which the oom killer 1305was called. If it is due to the memory assigned to the allocating task's cpuset 1306being exhausted, the allowed memory represents the set of mems assigned to that 1307cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed 1308memory represents the set of mempolicy nodes. If it is due to a memory 1309limit (or swap limit) being reached, the allowed memory is that configured 1310limit. Finally, if it is due to the entire system being out of memory, the 1311allowed memory represents all allocatable resources. 1312 1313The value of /proc/<pid>/oom_score_adj is added to the badness score before it 1314is used to determine which task to kill. Acceptable values range from -1000 1315(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to 1316polarize the preference for oom killing either by always preferring a certain 1317task or completely disabling it. The lowest possible value, -1000, is 1318equivalent to disabling oom killing entirely for that task since it will always 1319report a badness score of 0. 1320 1321Consequently, it is very simple for userspace to define the amount of memory to 1322consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for 1323example, is roughly equivalent to allowing the remainder of tasks sharing the 1324same system, cpuset, mempolicy, or memory controller resources to use at least 132550% more memory. A value of -500, on the other hand, would be roughly 1326equivalent to discounting 50% of the task's allowed memory from being considered 1327as scoring against the task. 1328 1329For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also 1330be used to tune the badness score. Its acceptable values range from -16 1331(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 1332(OOM_DISABLE) to disable oom killing entirely for that task. Its value is 1333scaled linearly with /proc/<pid>/oom_score_adj. 1334 1335Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the 1336other with its scaled value. 1337 1338The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last 1339value set by a CAP_SYS_RESOURCE process. To reduce the value any lower 1340requires CAP_SYS_RESOURCE. 1341 1342NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see 1343Documentation/feature-removal-schedule.txt. 1344 1345Caveat: when a parent task is selected, the oom killer will sacrifice any first 1346generation children with separate address spaces instead, if possible. This 1347avoids servers and important system daemons from being killed and loses the 1348minimal amount of work. 1349 1350 13513.2 /proc/<pid>/oom_score - Display current oom-killer score 1352------------------------------------------------------------- 1353 1354This file can be used to check the current score used by the oom-killer is for 1355any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which 1356process should be killed in an out-of-memory situation. 1357 1358 13593.3 /proc/<pid>/io - Display the IO accounting fields 1360------------------------------------------------------- 1361 1362This file contains IO statistics for each running process 1363 1364Example 1365------- 1366 1367test:/tmp # dd if=/dev/zero of=/tmp/test.dat & 1368[1] 3828 1369 1370test:/tmp # cat /proc/3828/io 1371rchar: 323934931 1372wchar: 323929600 1373syscr: 632687 1374syscw: 632675 1375read_bytes: 0 1376write_bytes: 323932160 1377cancelled_write_bytes: 0 1378 1379 1380Description 1381----------- 1382 1383rchar 1384----- 1385 1386I/O counter: chars read 1387The number of bytes which this task has caused to be read from storage. This 1388is simply the sum of bytes which this process passed to read() and pread(). 1389It includes things like tty IO and it is unaffected by whether or not actual 1390physical disk IO was required (the read might have been satisfied from 1391pagecache) 1392 1393 1394wchar 1395----- 1396 1397I/O counter: chars written 1398The number of bytes which this task has caused, or shall cause to be written 1399to disk. Similar caveats apply here as with rchar. 1400 1401 1402syscr 1403----- 1404 1405I/O counter: read syscalls 1406Attempt to count the number of read I/O operations, i.e. syscalls like read() 1407and pread(). 1408 1409 1410syscw 1411----- 1412 1413I/O counter: write syscalls 1414Attempt to count the number of write I/O operations, i.e. syscalls like 1415write() and pwrite(). 1416 1417 1418read_bytes 1419---------- 1420 1421I/O counter: bytes read 1422Attempt to count the number of bytes which this process really did cause to 1423be fetched from the storage layer. Done at the submit_bio() level, so it is 1424accurate for block-backed filesystems. <please add status regarding NFS and 1425CIFS at a later time> 1426 1427 1428write_bytes 1429----------- 1430 1431I/O counter: bytes written 1432Attempt to count the number of bytes which this process caused to be sent to 1433the storage layer. This is done at page-dirtying time. 1434 1435 1436cancelled_write_bytes 1437--------------------- 1438 1439The big inaccuracy here is truncate. If a process writes 1MB to a file and 1440then deletes the file, it will in fact perform no writeout. But it will have 1441been accounted as having caused 1MB of write. 1442In other words: The number of bytes which this process caused to not happen, 1443by truncating pagecache. A task can cause "negative" IO too. If this task 1444truncates some dirty pagecache, some IO which another task has been accounted 1445for (in its write_bytes) will not be happening. We _could_ just subtract that 1446from the truncating task's write_bytes, but there is information loss in doing 1447that. 1448 1449 1450Note 1451---- 1452 1453At its current implementation state, this is a bit racy on 32-bit machines: if 1454process A reads process B's /proc/pid/io while process B is updating one of 1455those 64-bit counters, process A could see an intermediate result. 1456 1457 1458More information about this can be found within the taskstats documentation in 1459Documentation/accounting. 1460 14613.4 /proc/<pid>/coredump_filter - Core dump filtering settings 1462--------------------------------------------------------------- 1463When a process is dumped, all anonymous memory is written to a core file as 1464long as the size of the core file isn't limited. But sometimes we don't want 1465to dump some memory segments, for example, huge shared memory. Conversely, 1466sometimes we want to save file-backed memory segments into a core file, not 1467only the individual files. 1468 1469/proc/<pid>/coredump_filter allows you to customize which memory segments 1470will be dumped when the <pid> process is dumped. coredump_filter is a bitmask 1471of memory types. If a bit of the bitmask is set, memory segments of the 1472corresponding memory type are dumped, otherwise they are not dumped. 1473 1474The following 7 memory types are supported: 1475 - (bit 0) anonymous private memory 1476 - (bit 1) anonymous shared memory 1477 - (bit 2) file-backed private memory 1478 - (bit 3) file-backed shared memory 1479 - (bit 4) ELF header pages in file-backed private memory areas (it is 1480 effective only if the bit 2 is cleared) 1481 - (bit 5) hugetlb private memory 1482 - (bit 6) hugetlb shared memory 1483 1484 Note that MMIO pages such as frame buffer are never dumped and vDSO pages 1485 are always dumped regardless of the bitmask status. 1486 1487 Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only 1488 effected by bit 5-6. 1489 1490Default value of coredump_filter is 0x23; this means all anonymous memory 1491segments and hugetlb private memory are dumped. 1492 1493If you don't want to dump all shared memory segments attached to pid 1234, 1494write 0x21 to the process's proc file. 1495 1496 $ echo 0x21 > /proc/1234/coredump_filter 1497 1498When a new process is created, the process inherits the bitmask status from its 1499parent. It is useful to set up coredump_filter before the program runs. 1500For example: 1501 1502 $ echo 0x7 > /proc/self/coredump_filter 1503 $ ./some_program 1504 15053.5 /proc/<pid>/mountinfo - Information about mounts 1506-------------------------------------------------------- 1507 1508This file contains lines of the form: 1509 151036 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue 1511(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11) 1512 1513(1) mount ID: unique identifier of the mount (may be reused after umount) 1514(2) parent ID: ID of parent (or of self for the top of the mount tree) 1515(3) major:minor: value of st_dev for files on filesystem 1516(4) root: root of the mount within the filesystem 1517(5) mount point: mount point relative to the process's root 1518(6) mount options: per mount options 1519(7) optional fields: zero or more fields of the form "tag[:value]" 1520(8) separator: marks the end of the optional fields 1521(9) filesystem type: name of filesystem of the form "type[.subtype]" 1522(10) mount source: filesystem specific information or "none" 1523(11) super options: per super block options 1524 1525Parsers should ignore all unrecognised optional fields. Currently the 1526possible optional fields are: 1527 1528shared:X mount is shared in peer group X 1529master:X mount is slave to peer group X 1530propagate_from:X mount is slave and receives propagation from peer group X (*) 1531unbindable mount is unbindable 1532 1533(*) X is the closest dominant peer group under the process's root. If 1534X is the immediate master of the mount, or if there's no dominant peer 1535group under the same root, then only the "master:X" field is present 1536and not the "propagate_from:X" field. 1537 1538For more information on mount propagation see: 1539 1540 Documentation/filesystems/sharedsubtree.txt 1541 1542 15433.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm 1544-------------------------------------------------------- 1545These files provide a method to access a tasks comm value. It also allows for 1546a task to set its own or one of its thread siblings comm value. The comm value 1547is limited in size compared to the cmdline value, so writing anything longer 1548then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated 1549comm value. 1550 1551 1552------------------------------------------------------------------------------ 1553Configuring procfs 1554------------------------------------------------------------------------------ 1555 15564.1 Mount options 1557--------------------- 1558 1559The following mount options are supported: 1560 1561 hidepid= Set /proc/<pid>/ access mode. 1562 gid= Set the group authorized to learn processes information. 1563 1564hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories 1565(default). 1566 1567hidepid=1 means users may not access any /proc/<pid>/ directories but their 1568own. Sensitive files like cmdline, sched*, status are now protected against 1569other users. This makes it impossible to learn whether any user runs 1570specific program (given the program doesn't reveal itself by its behaviour). 1571As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users, 1572poorly written programs passing sensitive information via program arguments are 1573now protected against local eavesdroppers. 1574 1575hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other 1576users. It doesn't mean that it hides a fact whether a process with a specific 1577pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), 1578but it hides process' uid and gid, which may be learned by stat()'ing 1579/proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering 1580information about running processes, whether some daemon runs with elevated 1581privileges, whether other user runs some sensitive program, whether other users 1582run any program at all, etc. 1583 1584gid= defines a group authorized to learn processes information otherwise 1585prohibited by hidepid=. If you use some daemon like identd which needs to learn 1586information about processes information, just add identd to this group. 1587