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>
7 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
8 move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
9 ------------------------------------------------------------------------------
10 Version 1.3 Kernel version 2.2.12
11 Kernel version 2.4.0-test11-pre4
12 ------------------------------------------------------------------------------
13 fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
19 0.1 Introduction/Credits
22 1 Collecting System Information
23 1.1 Process-Specific Subdirectories
25 1.3 IDE devices in /proc/ide
26 1.4 Networking info in /proc/net
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
33 2 Modifying System Parameters
35 3 Per-Process Parameters
36 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
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 3.7 /proc/<pid>/task/<tid>/children - Information about task children
44 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
45 3.9 /proc/<pid>/map_files - Information about memory mapped files
46 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
47 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
52 ------------------------------------------------------------------------------
54 ------------------------------------------------------------------------------
56 0.1 Introduction/Credits
57 ------------------------
59 This documentation is part of a soon (or so we hope) to be released book on
60 the SuSE Linux distribution. As there is no complete documentation for the
61 /proc file system and we've used many freely available sources to write these
62 chapters, it seems only fair to give the work back to the Linux community.
63 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
64 afraid it's still far from complete, but we hope it will be useful. As far as
65 we know, it is the first 'all-in-one' document about the /proc file system. It
66 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
67 SPARC, AXP, etc., features, you probably won't find what you are looking for.
68 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
69 additions and patches are welcome and will be added to this document if you
72 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
73 other people for help compiling this documentation. We'd also like to extend a
74 special thank you to Andi Kleen for documentation, which we relied on heavily
75 to create this document, as well as the additional information he provided.
76 Thanks to everybody else who contributed source or docs to the Linux kernel
77 and helped create a great piece of software... :)
79 If you have any comments, corrections or additions, please don't hesitate to
80 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
83 The latest version of this document is available online at
84 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
86 If the above direction does not works for you, you could try the kernel
87 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
88 comandante@zaralinux.com.
93 We don't guarantee the correctness of this document, and if you come to us
94 complaining about how you screwed up your system because of incorrect
95 documentation, we won't feel responsible...
97 ------------------------------------------------------------------------------
98 CHAPTER 1: COLLECTING SYSTEM INFORMATION
99 ------------------------------------------------------------------------------
101 ------------------------------------------------------------------------------
103 ------------------------------------------------------------------------------
104 * Investigating the properties of the pseudo file system /proc and its
105 ability to provide information on the running Linux system
106 * Examining /proc's structure
107 * Uncovering various information about the kernel and the processes running
109 ------------------------------------------------------------------------------
112 The proc file system acts as an interface to internal data structures in the
113 kernel. It can be used to obtain information about the system and to change
114 certain kernel parameters at runtime (sysctl).
116 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
117 show you how you can use /proc/sys to change settings.
119 1.1 Process-Specific Subdirectories
120 -----------------------------------
122 The directory /proc contains (among other things) one subdirectory for each
123 process running on the system, which is named after the process ID (PID).
125 The link self points to the process reading the file system. Each process
126 subdirectory has the entries listed in Table 1-1.
129 Table 1-1: Process specific entries in /proc
130 ..............................................................................
132 clear_refs Clears page referenced bits shown in smaps output
133 cmdline Command line arguments
134 cpu Current and last cpu in which it was executed (2.4)(smp)
135 cwd Link to the current working directory
136 environ Values of environment variables
137 exe Link to the executable of this process
138 fd Directory, which contains all file descriptors
139 maps Memory maps to executables and library files (2.4)
140 mem Memory held by this process
141 root Link to the root directory of this process
143 statm Process memory status information
144 status Process status in human readable form
145 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
146 symbol the task is blocked in - or "0" if not blocked.
148 stack Report full stack trace, enable via CONFIG_STACKTRACE
149 smaps an extension based on maps, showing the memory consumption of
150 each mapping and flags associated with it
151 numa_maps an extension based on maps, showing the memory locality and
152 binding policy as well as mem usage (in pages) of each mapping.
153 ..............................................................................
155 For example, to get the status information of a process, all you have to do is
156 read the file /proc/PID/status:
158 >cat /proc/self/status
186 SigPnd: 0000000000000000
187 ShdPnd: 0000000000000000
188 SigBlk: 0000000000000000
189 SigIgn: 0000000000000000
190 SigCgt: 0000000000000000
191 CapInh: 00000000fffffeff
192 CapPrm: 0000000000000000
193 CapEff: 0000000000000000
194 CapBnd: ffffffffffffffff
197 voluntary_ctxt_switches: 0
198 nonvoluntary_ctxt_switches: 1
200 This shows you nearly the same information you would get if you viewed it with
201 the ps command. In fact, ps uses the proc file system to obtain its
202 information. But you get a more detailed view of the process by reading the
203 file /proc/PID/status. It fields are described in table 1-2.
205 The statm file contains more detailed information about the process
206 memory usage. Its seven fields are explained in Table 1-3. The stat file
207 contains details information about the process itself. Its fields are
208 explained in Table 1-4.
210 (for SMP CONFIG users)
211 For making accounting scalable, RSS related information are handled in an
212 asynchronous manner and the value may not be very precise. To see a precise
213 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
214 It's slow but very precise.
216 Table 1-2: Contents of the status files (as of 4.8)
217 ..............................................................................
219 Name filename of the executable
220 Umask file mode creation mask
221 State state (R is running, S is sleeping, D is sleeping
222 in an uninterruptible wait, Z is zombie,
223 T is traced or stopped)
225 Ngid NUMA group ID (0 if none)
227 PPid process id of the parent process
228 TracerPid PID of process tracing this process (0 if not)
229 Uid Real, effective, saved set, and file system UIDs
230 Gid Real, effective, saved set, and file system GIDs
231 FDSize number of file descriptor slots currently allocated
232 Groups supplementary group list
233 NStgid descendant namespace thread group ID hierarchy
234 NSpid descendant namespace process ID hierarchy
235 NSpgid descendant namespace process group ID hierarchy
236 NSsid descendant namespace session ID hierarchy
237 VmPeak peak virtual memory size
238 VmSize total program size
239 VmLck locked memory size
240 VmPin pinned memory size
241 VmHWM peak resident set size ("high water mark")
242 VmRSS size of memory portions. It contains the three
243 following parts (VmRSS = RssAnon + RssFile + RssShmem)
244 RssAnon size of resident anonymous memory
245 RssFile size of resident file mappings
246 RssShmem size of resident shmem memory (includes SysV shm,
247 mapping of tmpfs and shared anonymous mappings)
248 VmData size of private data segments
249 VmStk size of stack segments
250 VmExe size of text segment
251 VmLib size of shared library code
252 VmPTE size of page table entries
253 VmPMD size of second level page tables
254 VmSwap amount of swap used by anonymous private data
255 (shmem swap usage is not included)
256 HugetlbPages size of hugetlb memory portions
257 Threads number of threads
258 SigQ number of signals queued/max. number for queue
259 SigPnd bitmap of pending signals for the thread
260 ShdPnd bitmap of shared pending signals for the process
261 SigBlk bitmap of blocked signals
262 SigIgn bitmap of ignored signals
263 SigCgt bitmap of caught signals
264 CapInh bitmap of inheritable capabilities
265 CapPrm bitmap of permitted capabilities
266 CapEff bitmap of effective capabilities
267 CapBnd bitmap of capabilities bounding set
268 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
269 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
270 Cpus_allowed mask of CPUs on which this process may run
271 Cpus_allowed_list Same as previous, but in "list format"
272 Mems_allowed mask of memory nodes allowed to this process
273 Mems_allowed_list Same as previous, but in "list format"
274 voluntary_ctxt_switches number of voluntary context switches
275 nonvoluntary_ctxt_switches number of non voluntary context switches
276 ..............................................................................
278 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
279 ..............................................................................
281 size total program size (pages) (same as VmSize in status)
282 resident size of memory portions (pages) (same as VmRSS in status)
283 shared number of pages that are shared (i.e. backed by a file, same
284 as RssFile+RssShmem in status)
285 trs number of pages that are 'code' (not including libs; broken,
286 includes data segment)
287 lrs number of pages of library (always 0 on 2.6)
288 drs number of pages of data/stack (including libs; broken,
289 includes library text)
290 dt number of dirty pages (always 0 on 2.6)
291 ..............................................................................
294 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
295 ..............................................................................
298 tcomm filename of the executable
299 state state (R is running, S is sleeping, D is sleeping in an
300 uninterruptible wait, Z is zombie, T is traced or stopped)
301 ppid process id of the parent process
302 pgrp pgrp of the process
304 tty_nr tty the process uses
305 tty_pgrp pgrp of the tty
307 min_flt number of minor faults
308 cmin_flt number of minor faults with child's
309 maj_flt number of major faults
310 cmaj_flt number of major faults with child's
311 utime user mode jiffies
312 stime kernel mode jiffies
313 cutime user mode jiffies with child's
314 cstime kernel mode jiffies with child's
315 priority priority level
317 num_threads number of threads
318 it_real_value (obsolete, always 0)
319 start_time time the process started after system boot
320 vsize virtual memory size
321 rss resident set memory size
322 rsslim current limit in bytes on the rss
323 start_code address above which program text can run
324 end_code address below which program text can run
325 start_stack address of the start of the main process stack
326 esp current value of ESP
327 eip current value of EIP
328 pending bitmap of pending signals
329 blocked bitmap of blocked signals
330 sigign bitmap of ignored signals
331 sigcatch bitmap of caught signals
332 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead)
335 exit_signal signal to send to parent thread on exit
336 task_cpu which CPU the task is scheduled on
337 rt_priority realtime priority
338 policy scheduling policy (man sched_setscheduler)
339 blkio_ticks time spent waiting for block IO
340 gtime guest time of the task in jiffies
341 cgtime guest time of the task children in jiffies
342 start_data address above which program data+bss is placed
343 end_data address below which program data+bss is placed
344 start_brk address above which program heap can be expanded with brk()
345 arg_start address above which program command line is placed
346 arg_end address below which program command line is placed
347 env_start address above which program environment is placed
348 env_end address below which program environment is placed
349 exit_code the thread's exit_code in the form reported by the waitpid system call
350 ..............................................................................
352 The /proc/PID/maps file containing the currently mapped memory regions and
353 their access permissions.
357 address perms offset dev inode pathname
359 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
360 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
361 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
362 a7cb1000-a7cb2000 ---p 00000000 00:00 0
363 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
364 a7eb2000-a7eb3000 ---p 00000000 00:00 0
365 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
366 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
367 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
368 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
369 a800b000-a800e000 rw-p 00000000 00:00 0
370 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
371 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
372 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
373 a8024000-a8027000 rw-p 00000000 00:00 0
374 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
375 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
376 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
377 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
378 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
380 where "address" is the address space in the process that it occupies, "perms"
381 is a set of permissions:
387 p = private (copy on write)
389 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
390 "inode" is the inode on that device. 0 indicates that no inode is associated
391 with the memory region, as the case would be with BSS (uninitialized data).
392 The "pathname" shows the name associated file for this mapping. If the mapping
393 is not associated with a file:
395 [heap] = the heap of the program
396 [stack] = the stack of the main process
397 [vdso] = the "virtual dynamic shared object",
398 the kernel system call handler
400 or if empty, the mapping is anonymous.
402 The /proc/PID/smaps is an extension based on maps, showing the memory
403 consumption for each of the process's mappings. For each of mappings there
404 is a series of lines such as the following:
406 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
420 Private_Hugetlb: 0 kB
426 VmFlags: rd ex mr mw me dw
428 the first of these lines shows the same information as is displayed for the
429 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
430 (size), the amount of the mapping that is currently resident in RAM (RSS), the
431 process' proportional share of this mapping (PSS), the number of clean and
432 dirty private pages in the mapping.
434 The "proportional set size" (PSS) of a process is the count of pages it has
435 in memory, where each page is divided by the number of processes sharing it.
436 So if a process has 1000 pages all to itself, and 1000 shared with one other
437 process, its PSS will be 1500.
438 Note that even a page which is part of a MAP_SHARED mapping, but has only
439 a single pte mapped, i.e. is currently used by only one process, is accounted
440 as private and not as shared.
441 "Referenced" indicates the amount of memory currently marked as referenced or
443 "Anonymous" shows the amount of memory that does not belong to any file. Even
444 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
445 and a page is modified, the file page is replaced by a private anonymous copy.
446 "LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
447 The memory isn't freed immediately with madvise(). It's freed in memory
448 pressure if the memory is clean. Please note that the printed value might
449 be lower than the real value due to optimizations used in the current
450 implementation. If this is not desirable please file a bug report.
451 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
452 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
454 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
455 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
456 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
457 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
458 For shmem mappings, "Swap" includes also the size of the mapped (and not
459 replaced by copy-on-write) part of the underlying shmem object out on swap.
460 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
461 does not take into account swapped out page of underlying shmem objects.
462 "Locked" indicates whether the mapping is locked in memory or not.
464 "VmFlags" field deserves a separate description. This member represents the kernel
465 flags associated with the particular virtual memory area in two letter encoded
466 manner. The codes are the following:
475 gd - stack segment growns down
477 dw - disabled write to the mapped file
478 lo - pages are locked in memory
479 io - memory mapped I/O area
480 sr - sequential read advise provided
481 rr - random read advise provided
482 dc - do not copy area on fork
483 de - do not expand area on remapping
484 ac - area is accountable
485 nr - swap space is not reserved for the area
486 ht - area uses huge tlb pages
487 ar - architecture specific flag
488 dd - do not include area into core dump
491 hg - huge page advise flag
492 nh - no-huge page advise flag
493 mg - mergable advise flag
495 Note that there is no guarantee that every flag and associated mnemonic will
496 be present in all further kernel releases. Things get changed, the flags may
497 be vanished or the reverse -- new added.
499 This file is only present if the CONFIG_MMU kernel configuration option is
502 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
503 output can be achieved only in the single read call).
504 This typically manifests when doing partial reads of these files while the
505 memory map is being modified. Despite the races, we do provide the following
508 1) The mapped addresses never go backwards, which implies no two
509 regions will ever overlap.
510 2) If there is something at a given vaddr during the entirety of the
511 life of the smaps/maps walk, there will be some output for it.
514 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
515 bits on both physical and virtual pages associated with a process, and the
516 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
517 To clear the bits for all the pages associated with the process
518 > echo 1 > /proc/PID/clear_refs
520 To clear the bits for the anonymous pages associated with the process
521 > echo 2 > /proc/PID/clear_refs
523 To clear the bits for the file mapped pages associated with the process
524 > echo 3 > /proc/PID/clear_refs
526 To clear the soft-dirty bit
527 > echo 4 > /proc/PID/clear_refs
529 To reset the peak resident set size ("high water mark") to the process's
531 > echo 5 > /proc/PID/clear_refs
533 Any other value written to /proc/PID/clear_refs will have no effect.
535 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
536 using /proc/kpageflags and number of times a page is mapped using
537 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
539 The /proc/pid/numa_maps is an extension based on maps, showing the memory
540 locality and binding policy, as well as the memory usage (in pages) of
541 each mapping. The output follows a general format where mapping details get
542 summarized separated by blank spaces, one mapping per each file line:
544 address policy mapping details
546 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
547 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
548 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
549 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
550 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
551 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
552 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
553 320698b000 default file=/lib64/libc-2.12.so
554 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
555 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
556 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
557 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
558 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
559 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
560 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
561 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
564 "address" is the starting address for the mapping;
565 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
566 "mapping details" summarizes mapping data such as mapping type, page usage counters,
567 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
568 size, in KB, that is backing the mapping up.
573 Similar to the process entries, the kernel data files give information about
574 the running kernel. The files used to obtain this information are contained in
575 /proc and are listed in Table 1-5. Not all of these will be present in your
576 system. It depends on the kernel configuration and the loaded modules, which
577 files are there, and which are missing.
579 Table 1-5: Kernel info in /proc
580 ..............................................................................
582 apm Advanced power management info
583 buddyinfo Kernel memory allocator information (see text) (2.5)
584 bus Directory containing bus specific information
585 cmdline Kernel command line
586 cpuinfo Info about the CPU
587 devices Available devices (block and character)
588 dma Used DMS channels
589 filesystems Supported filesystems
590 driver Various drivers grouped here, currently rtc (2.4)
591 execdomains Execdomains, related to security (2.4)
592 fb Frame Buffer devices (2.4)
593 fs File system parameters, currently nfs/exports (2.4)
594 ide Directory containing info about the IDE subsystem
595 interrupts Interrupt usage
596 iomem Memory map (2.4)
597 ioports I/O port usage
598 irq Masks for irq to cpu affinity (2.4)(smp?)
599 isapnp ISA PnP (Plug&Play) Info (2.4)
600 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
602 ksyms Kernel symbol table
603 loadavg Load average of last 1, 5 & 15 minutes
607 modules List of loaded modules
608 mounts Mounted filesystems
609 net Networking info (see text)
610 pagetypeinfo Additional page allocator information (see text) (2.5)
611 partitions Table of partitions known to the system
612 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
613 decoupled by lspci (2.4)
615 scsi SCSI info (see text)
616 slabinfo Slab pool info
617 softirqs softirq usage
618 stat Overall statistics
619 swaps Swap space utilization
621 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
622 tty Info of tty drivers
623 uptime Wall clock since boot, combined idle time of all cpus
624 version Kernel version
625 video bttv info of video resources (2.4)
626 vmallocinfo Show vmalloced areas
627 ..............................................................................
629 You can, for example, check which interrupts are currently in use and what
630 they are used for by looking in the file /proc/interrupts:
632 > cat /proc/interrupts
634 0: 8728810 XT-PIC timer
635 1: 895 XT-PIC keyboard
637 3: 531695 XT-PIC aha152x
638 4: 2014133 XT-PIC serial
639 5: 44401 XT-PIC pcnet_cs
642 12: 182918 XT-PIC PS/2 Mouse
644 14: 1232265 XT-PIC ide0
648 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
649 output of a SMP machine):
651 > cat /proc/interrupts
654 0: 1243498 1214548 IO-APIC-edge timer
655 1: 8949 8958 IO-APIC-edge keyboard
656 2: 0 0 XT-PIC cascade
657 5: 11286 10161 IO-APIC-edge soundblaster
658 8: 1 0 IO-APIC-edge rtc
659 9: 27422 27407 IO-APIC-edge 3c503
660 12: 113645 113873 IO-APIC-edge PS/2 Mouse
662 14: 22491 24012 IO-APIC-edge ide0
663 15: 2183 2415 IO-APIC-edge ide1
664 17: 30564 30414 IO-APIC-level eth0
665 18: 177 164 IO-APIC-level bttv
670 NMI is incremented in this case because every timer interrupt generates a NMI
671 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
673 LOC is the local interrupt counter of the internal APIC of every CPU.
675 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
676 connects the CPUs in a SMP system. This means that an error has been detected,
677 the IO-APIC automatically retry the transmission, so it should not be a big
678 problem, but you should read the SMP-FAQ.
680 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
681 /proc/interrupts to display every IRQ vector in use by the system, not
682 just those considered 'most important'. The new vectors are:
684 THR -- interrupt raised when a machine check threshold counter
685 (typically counting ECC corrected errors of memory or cache) exceeds
686 a configurable threshold. Only available on some systems.
688 TRM -- a thermal event interrupt occurs when a temperature threshold
689 has been exceeded for the CPU. This interrupt may also be generated
690 when the temperature drops back to normal.
692 SPU -- a spurious interrupt is some interrupt that was raised then lowered
693 by some IO device before it could be fully processed by the APIC. Hence
694 the APIC sees the interrupt but does not know what device it came from.
695 For this case the APIC will generate the interrupt with a IRQ vector
696 of 0xff. This might also be generated by chipset bugs.
698 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
699 sent from one CPU to another per the needs of the OS. Typically,
700 their statistics are used by kernel developers and interested users to
701 determine the occurrence of interrupts of the given type.
703 The above IRQ vectors are displayed only when relevant. For example,
704 the threshold vector does not exist on x86_64 platforms. Others are
705 suppressed when the system is a uniprocessor. As of this writing, only
706 i386 and x86_64 platforms support the new IRQ vector displays.
708 Of some interest is the introduction of the /proc/irq directory to 2.4.
709 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
710 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
711 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
716 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
717 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
721 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
722 IRQ, you can set it by doing:
724 > echo 1 > /proc/irq/10/smp_affinity
726 This means that only the first CPU will handle the IRQ, but you can also echo
727 5 which means that only the first and third CPU can handle the IRQ.
729 The contents of each smp_affinity file is the same by default:
731 > cat /proc/irq/0/smp_affinity
734 There is an alternate interface, smp_affinity_list which allows specifying
735 a cpu range instead of a bitmask:
737 > cat /proc/irq/0/smp_affinity_list
740 The default_smp_affinity mask applies to all non-active IRQs, which are the
741 IRQs which have not yet been allocated/activated, and hence which lack a
742 /proc/irq/[0-9]* directory.
744 The node file on an SMP system shows the node to which the device using the IRQ
745 reports itself as being attached. This hardware locality information does not
746 include information about any possible driver locality preference.
748 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
749 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
751 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
752 between all the CPUs which are allowed to handle it. As usual the kernel has
753 more info than you and does a better job than you, so the defaults are the
754 best choice for almost everyone. [Note this applies only to those IO-APIC's
755 that support "Round Robin" interrupt distribution.]
757 There are three more important subdirectories in /proc: net, scsi, and sys.
758 The general rule is that the contents, or even the existence of these
759 directories, depend on your kernel configuration. If SCSI is not enabled, the
760 directory scsi may not exist. The same is true with the net, which is there
761 only when networking support is present in the running kernel.
763 The slabinfo file gives information about memory usage at the slab level.
764 Linux uses slab pools for memory management above page level in version 2.2.
765 Commonly used objects have their own slab pool (such as network buffers,
766 directory cache, and so on).
768 ..............................................................................
770 > cat /proc/buddyinfo
772 Node 0, zone DMA 0 4 5 4 4 3 ...
773 Node 0, zone Normal 1 0 0 1 101 8 ...
774 Node 0, zone HighMem 2 0 0 1 1 0 ...
776 External fragmentation is a problem under some workloads, and buddyinfo is a
777 useful tool for helping diagnose these problems. Buddyinfo will give you a
778 clue as to how big an area you can safely allocate, or why a previous
781 Each column represents the number of pages of a certain order which are
782 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
783 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
784 available in ZONE_NORMAL, etc...
786 More information relevant to external fragmentation can be found in
789 > cat /proc/pagetypeinfo
793 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
794 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
795 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
796 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
797 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
798 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
799 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
800 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
801 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
802 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
803 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
805 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
806 Node 0, zone DMA 2 0 5 1 0
807 Node 0, zone DMA32 41 6 967 2 0
809 Fragmentation avoidance in the kernel works by grouping pages of different
810 migrate types into the same contiguous regions of memory called page blocks.
811 A page block is typically the size of the default hugepage size e.g. 2MB on
812 X86-64. By keeping pages grouped based on their ability to move, the kernel
813 can reclaim pages within a page block to satisfy a high-order allocation.
815 The pagetypinfo begins with information on the size of a page block. It
816 then gives the same type of information as buddyinfo except broken down
817 by migrate-type and finishes with details on how many page blocks of each
820 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
821 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
822 make an estimate of the likely number of huge pages that can be allocated
823 at a given point in time. All the "Movable" blocks should be allocatable
824 unless memory has been mlock()'d. Some of the Reclaimable blocks should
825 also be allocatable although a lot of filesystem metadata may have to be
826 reclaimed to achieve this.
828 ..............................................................................
832 Provides information about distribution and utilization of memory. This
833 varies by architecture and compile options. The following is from a
834 16GB PIII, which has highmem enabled. You may not have all of these fields.
838 MemTotal: 16344972 kB
840 MemAvailable: 14836172 kB
846 HighTotal: 15597528 kB
847 HighFree: 13629632 kB
858 SReclaimable: 159856 kB
859 SUnreclaim: 124508 kB
864 CommitLimit: 7669796 kB
865 Committed_AS: 100056 kB
866 VmallocTotal: 112216 kB
868 VmallocChunk: 111088 kB
869 AnonHugePages: 49152 kB
874 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
875 bits and the kernel binary code)
876 MemFree: The sum of LowFree+HighFree
877 MemAvailable: An estimate of how much memory is available for starting new
878 applications, without swapping. Calculated from MemFree,
879 SReclaimable, the size of the file LRU lists, and the low
880 watermarks in each zone.
881 The estimate takes into account that the system needs some
882 page cache to function well, and that not all reclaimable
883 slab will be reclaimable, due to items being in use. The
884 impact of those factors will vary from system to system.
885 Buffers: Relatively temporary storage for raw disk blocks
886 shouldn't get tremendously large (20MB or so)
887 Cached: in-memory cache for files read from the disk (the
888 pagecache). Doesn't include SwapCached
889 SwapCached: Memory that once was swapped out, is swapped back in but
890 still also is in the swapfile (if memory is needed it
891 doesn't need to be swapped out AGAIN because it is already
892 in the swapfile. This saves I/O)
893 Active: Memory that has been used more recently and usually not
894 reclaimed unless absolutely necessary.
895 Inactive: Memory which has been less recently used. It is more
896 eligible to be reclaimed for other purposes
898 HighFree: Highmem is all memory above ~860MB of physical memory
899 Highmem areas are for use by userspace programs, or
900 for the pagecache. The kernel must use tricks to access
901 this memory, making it slower to access than lowmem.
903 LowFree: Lowmem is memory which can be used for everything that
904 highmem can be used for, but it is also available for the
905 kernel's use for its own data structures. Among many
906 other things, it is where everything from the Slab is
907 allocated. Bad things happen when you're out of lowmem.
908 SwapTotal: total amount of swap space available
909 SwapFree: Memory which has been evicted from RAM, and is temporarily
911 Dirty: Memory which is waiting to get written back to the disk
912 Writeback: Memory which is actively being written back to the disk
913 AnonPages: Non-file backed pages mapped into userspace page tables
914 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
915 Mapped: files which have been mmaped, such as libraries
916 Shmem: Total memory used by shared memory (shmem) and tmpfs
917 ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
919 ShmemPmdMapped: Shared memory mapped into userspace with huge pages
920 Slab: in-kernel data structures cache
921 SReclaimable: Part of Slab, that might be reclaimed, such as caches
922 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
923 PageTables: amount of memory dedicated to the lowest level of page
925 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
927 Bounce: Memory used for block device "bounce buffers"
928 WritebackTmp: Memory used by FUSE for temporary writeback buffers
929 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
930 this is the total amount of memory currently available to
931 be allocated on the system. This limit is only adhered to
932 if strict overcommit accounting is enabled (mode 2 in
933 'vm.overcommit_memory').
934 The CommitLimit is calculated with the following formula:
935 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
936 overcommit_ratio / 100 + [total swap pages]
937 For example, on a system with 1G of physical RAM and 7G
938 of swap with a `vm.overcommit_ratio` of 30 it would
939 yield a CommitLimit of 7.3G.
940 For more details, see the memory overcommit documentation
941 in vm/overcommit-accounting.
942 Committed_AS: The amount of memory presently allocated on the system.
943 The committed memory is a sum of all of the memory which
944 has been allocated by processes, even if it has not been
945 "used" by them as of yet. A process which malloc()'s 1G
946 of memory, but only touches 300M of it will show up as
947 using 1G. This 1G is memory which has been "committed" to
948 by the VM and can be used at any time by the allocating
949 application. With strict overcommit enabled on the system
950 (mode 2 in 'vm.overcommit_memory'),allocations which would
951 exceed the CommitLimit (detailed above) will not be permitted.
952 This is useful if one needs to guarantee that processes will
953 not fail due to lack of memory once that memory has been
954 successfully allocated.
955 VmallocTotal: total size of vmalloc memory area
956 VmallocUsed: amount of vmalloc area which is used
957 VmallocChunk: largest contiguous block of vmalloc area which is free
959 ..............................................................................
963 Provides information about vmalloced/vmaped areas. One line per area,
964 containing the virtual address range of the area, size in bytes,
965 caller information of the creator, and optional information depending
966 on the kind of area :
968 pages=nr number of pages
969 phys=addr if a physical address was specified
970 ioremap I/O mapping (ioremap() and friends)
971 vmalloc vmalloc() area
974 vpages buffer for pages pointers was vmalloced (huge area)
975 N<node>=nr (Only on NUMA kernels)
976 Number of pages allocated on memory node <node>
978 > cat /proc/vmallocinfo
979 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
980 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
981 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
982 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
983 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
984 phys=7fee8000 ioremap
985 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
986 phys=7fee7000 ioremap
987 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
988 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
989 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
990 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
992 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
993 /0x130 [x_tables] pages=4 vmalloc N0=4
994 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
995 pages=14 vmalloc N2=14
996 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
998 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
1000 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
1001 pages=10 vmalloc N0=10
1003 ..............................................................................
1007 Provides counts of softirq handlers serviced since boot time, for each cpu.
1009 > cat /proc/softirqs
1012 TIMER: 27166 27120 27097 27034
1017 SCHED: 27035 26983 26971 26746
1019 RCU: 1678 1769 2178 2250
1022 1.3 IDE devices in /proc/ide
1023 ----------------------------
1025 The subdirectory /proc/ide contains information about all IDE devices of which
1026 the kernel is aware. There is one subdirectory for each IDE controller, the
1027 file drivers and a link for each IDE device, pointing to the device directory
1028 in the controller specific subtree.
1030 The file drivers contains general information about the drivers used for the
1033 > cat /proc/ide/drivers
1034 ide-cdrom version 4.53
1035 ide-disk version 1.08
1037 More detailed information can be found in the controller specific
1038 subdirectories. These are named ide0, ide1 and so on. Each of these
1039 directories contains the files shown in table 1-6.
1042 Table 1-6: IDE controller info in /proc/ide/ide?
1043 ..............................................................................
1045 channel IDE channel (0 or 1)
1046 config Configuration (only for PCI/IDE bridge)
1048 model Type/Chipset of IDE controller
1049 ..............................................................................
1051 Each device connected to a controller has a separate subdirectory in the
1052 controllers directory. The files listed in table 1-7 are contained in these
1056 Table 1-7: IDE device information
1057 ..............................................................................
1060 capacity Capacity of the medium (in 512Byte blocks)
1061 driver driver and version
1062 geometry physical and logical geometry
1063 identify device identify block
1065 model device identifier
1066 settings device setup
1067 smart_thresholds IDE disk management thresholds
1068 smart_values IDE disk management values
1069 ..............................................................................
1071 The most interesting file is settings. This file contains a nice overview of
1072 the drive parameters:
1074 # cat /proc/ide/ide0/hda/settings
1075 name value min max mode
1076 ---- ----- --- --- ----
1077 bios_cyl 526 0 65535 rw
1078 bios_head 255 0 255 rw
1079 bios_sect 63 0 63 rw
1080 breada_readahead 4 0 127 rw
1082 file_readahead 72 0 2097151 rw
1084 keepsettings 0 0 1 rw
1085 max_kb_per_request 122 1 127 rw
1089 pio_mode write-only 0 255 w
1095 1.4 Networking info in /proc/net
1096 --------------------------------
1098 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1099 additional values you get for IP version 6 if you configure the kernel to
1100 support this. Table 1-9 lists the files and their meaning.
1103 Table 1-8: IPv6 info in /proc/net
1104 ..............................................................................
1106 udp6 UDP sockets (IPv6)
1107 tcp6 TCP sockets (IPv6)
1108 raw6 Raw device statistics (IPv6)
1109 igmp6 IP multicast addresses, which this host joined (IPv6)
1110 if_inet6 List of IPv6 interface addresses
1111 ipv6_route Kernel routing table for IPv6
1112 rt6_stats Global IPv6 routing tables statistics
1113 sockstat6 Socket statistics (IPv6)
1114 snmp6 Snmp data (IPv6)
1115 ..............................................................................
1118 Table 1-9: Network info in /proc/net
1119 ..............................................................................
1121 arp Kernel ARP table
1122 dev network devices with statistics
1123 dev_mcast the Layer2 multicast groups a device is listening too
1124 (interface index, label, number of references, number of bound
1126 dev_stat network device status
1127 ip_fwchains Firewall chain linkage
1128 ip_fwnames Firewall chain names
1129 ip_masq Directory containing the masquerading tables
1130 ip_masquerade Major masquerading table
1131 netstat Network statistics
1132 raw raw device statistics
1133 route Kernel routing table
1134 rpc Directory containing rpc info
1135 rt_cache Routing cache
1137 sockstat Socket statistics
1140 unix UNIX domain sockets
1141 wireless Wireless interface data (Wavelan etc)
1142 igmp IP multicast addresses, which this host joined
1143 psched Global packet scheduler parameters.
1144 netlink List of PF_NETLINK sockets
1145 ip_mr_vifs List of multicast virtual interfaces
1146 ip_mr_cache List of multicast routing cache
1147 ..............................................................................
1149 You can use this information to see which network devices are available in
1150 your system and how much traffic was routed over those devices:
1153 Inter-|Receive |[...
1154 face |bytes packets errs drop fifo frame compressed multicast|[...
1155 lo: 908188 5596 0 0 0 0 0 0 [...
1156 ppp0:15475140 20721 410 0 0 410 0 0 [...
1157 eth0: 614530 7085 0 0 0 0 0 1 [...
1160 ...] bytes packets errs drop fifo colls carrier compressed
1161 ...] 908188 5596 0 0 0 0 0 0
1162 ...] 1375103 17405 0 0 0 0 0 0
1163 ...] 1703981 5535 0 0 0 3 0 0
1165 In addition, each Channel Bond interface has its own directory. For
1166 example, the bond0 device will have a directory called /proc/net/bond0/.
1167 It will contain information that is specific to that bond, such as the
1168 current slaves of the bond, the link status of the slaves, and how
1169 many times the slaves link has failed.
1174 If you have a SCSI host adapter in your system, you'll find a subdirectory
1175 named after the driver for this adapter in /proc/scsi. You'll also see a list
1176 of all recognized SCSI devices in /proc/scsi:
1178 >cat /proc/scsi/scsi
1180 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1181 Vendor: IBM Model: DGHS09U Rev: 03E0
1182 Type: Direct-Access ANSI SCSI revision: 03
1183 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1184 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1185 Type: CD-ROM ANSI SCSI revision: 02
1188 The directory named after the driver has one file for each adapter found in
1189 the system. These files contain information about the controller, including
1190 the used IRQ and the IO address range. The amount of information shown is
1191 dependent on the adapter you use. The example shows the output for an Adaptec
1192 AHA-2940 SCSI adapter:
1194 > cat /proc/scsi/aic7xxx/0
1196 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1198 TCQ Enabled By Default : Disabled
1199 AIC7XXX_PROC_STATS : Disabled
1200 AIC7XXX_RESET_DELAY : 5
1201 Adapter Configuration:
1202 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1203 Ultra Wide Controller
1204 PCI MMAPed I/O Base: 0xeb001000
1205 Adapter SEEPROM Config: SEEPROM found and used.
1206 Adaptec SCSI BIOS: Enabled
1208 SCBs: Active 0, Max Active 2,
1209 Allocated 15, HW 16, Page 255
1211 BIOS Control Word: 0x18b6
1212 Adapter Control Word: 0x005b
1213 Extended Translation: Enabled
1214 Disconnect Enable Flags: 0xffff
1215 Ultra Enable Flags: 0x0001
1216 Tag Queue Enable Flags: 0x0000
1217 Ordered Queue Tag Flags: 0x0000
1218 Default Tag Queue Depth: 8
1219 Tagged Queue By Device array for aic7xxx host instance 0:
1220 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1221 Actual queue depth per device for aic7xxx host instance 0:
1222 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1225 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1226 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1227 Total transfers 160151 (74577 reads and 85574 writes)
1229 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1230 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1231 Total transfers 0 (0 reads and 0 writes)
1234 1.6 Parallel port info in /proc/parport
1235 ---------------------------------------
1237 The directory /proc/parport contains information about the parallel ports of
1238 your system. It has one subdirectory for each port, named after the port
1241 These directories contain the four files shown in Table 1-10.
1244 Table 1-10: Files in /proc/parport
1245 ..............................................................................
1247 autoprobe Any IEEE-1284 device ID information that has been acquired.
1248 devices list of the device drivers using that port. A + will appear by the
1249 name of the device currently using the port (it might not appear
1251 hardware Parallel port's base address, IRQ line and DMA channel.
1252 irq IRQ that parport is using for that port. This is in a separate
1253 file to allow you to alter it by writing a new value in (IRQ
1255 ..............................................................................
1257 1.7 TTY info in /proc/tty
1258 -------------------------
1260 Information about the available and actually used tty's can be found in the
1261 directory /proc/tty.You'll find entries for drivers and line disciplines in
1262 this directory, as shown in Table 1-11.
1265 Table 1-11: Files in /proc/tty
1266 ..............................................................................
1268 drivers list of drivers and their usage
1269 ldiscs registered line disciplines
1270 driver/serial usage statistic and status of single tty lines
1271 ..............................................................................
1273 To see which tty's are currently in use, you can simply look into the file
1276 > cat /proc/tty/drivers
1277 pty_slave /dev/pts 136 0-255 pty:slave
1278 pty_master /dev/ptm 128 0-255 pty:master
1279 pty_slave /dev/ttyp 3 0-255 pty:slave
1280 pty_master /dev/pty 2 0-255 pty:master
1281 serial /dev/cua 5 64-67 serial:callout
1282 serial /dev/ttyS 4 64-67 serial
1283 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1284 /dev/ptmx /dev/ptmx 5 2 system
1285 /dev/console /dev/console 5 1 system:console
1286 /dev/tty /dev/tty 5 0 system:/dev/tty
1287 unknown /dev/tty 4 1-63 console
1290 1.8 Miscellaneous kernel statistics in /proc/stat
1291 -------------------------------------------------
1293 Various pieces of information about kernel activity are available in the
1294 /proc/stat file. All of the numbers reported in this file are aggregates
1295 since the system first booted. For a quick look, simply cat the file:
1298 cpu 2255 34 2290 22625563 6290 127 456 0 0 0
1299 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1300 cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1301 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1307 softirq 183433 0 21755 12 39 1137 231 21459 2263
1309 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1310 lines. These numbers identify the amount of time the CPU has spent performing
1311 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1312 second). The meanings of the columns are as follows, from left to right:
1314 - user: normal processes executing in user mode
1315 - nice: niced processes executing in user mode
1316 - system: processes executing in kernel mode
1317 - idle: twiddling thumbs
1318 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
1319 are several problems:
1320 1. Cpu will not wait for I/O to complete, iowait is the time that a task is
1321 waiting for I/O to complete. When cpu goes into idle state for
1322 outstanding task io, another task will be scheduled on this CPU.
1323 2. In a multi-core CPU, the task waiting for I/O to complete is not running
1324 on any CPU, so the iowait of each CPU is difficult to calculate.
1325 3. The value of iowait field in /proc/stat will decrease in certain
1327 So, the iowait is not reliable by reading from /proc/stat.
1328 - irq: servicing interrupts
1329 - softirq: servicing softirqs
1330 - steal: involuntary wait
1331 - guest: running a normal guest
1332 - guest_nice: running a niced guest
1334 The "intr" line gives counts of interrupts serviced since boot time, for each
1335 of the possible system interrupts. The first column is the total of all
1336 interrupts serviced including unnumbered architecture specific interrupts;
1337 each subsequent column is the total for that particular numbered interrupt.
1338 Unnumbered interrupts are not shown, only summed into the total.
1340 The "ctxt" line gives the total number of context switches across all CPUs.
1342 The "btime" line gives the time at which the system booted, in seconds since
1345 The "processes" line gives the number of processes and threads created, which
1346 includes (but is not limited to) those created by calls to the fork() and
1347 clone() system calls.
1349 The "procs_running" line gives the total number of threads that are
1350 running or ready to run (i.e., the total number of runnable threads).
1352 The "procs_blocked" line gives the number of processes currently blocked,
1353 waiting for I/O to complete.
1355 The "softirq" line gives counts of softirqs serviced since boot time, for each
1356 of the possible system softirqs. The first column is the total of all
1357 softirqs serviced; each subsequent column is the total for that particular
1361 1.9 Ext4 file system parameters
1362 -------------------------------
1364 Information about mounted ext4 file systems can be found in
1365 /proc/fs/ext4. Each mounted filesystem will have a directory in
1366 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1367 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1368 in Table 1-12, below.
1370 Table 1-12: Files in /proc/fs/ext4/<devname>
1371 ..............................................................................
1373 mb_groups details of multiblock allocator buddy cache of free blocks
1374 ..............................................................................
1378 Shows registered system console lines.
1380 To see which character device lines are currently used for the system console
1381 /dev/console, you may simply look into the file /proc/consoles:
1383 > cat /proc/consoles
1389 device name of the device
1390 operations R = can do read operations
1391 W = can do write operations
1393 flags E = it is enabled
1394 C = it is preferred console
1395 B = it is primary boot console
1396 p = it is used for printk buffer
1397 b = it is not a TTY but a Braille device
1398 a = it is safe to use when cpu is offline
1399 major:minor major and minor number of the device separated by a colon
1401 ------------------------------------------------------------------------------
1403 ------------------------------------------------------------------------------
1404 The /proc file system serves information about the running system. It not only
1405 allows access to process data but also allows you to request the kernel status
1406 by reading files in the hierarchy.
1408 The directory structure of /proc reflects the types of information and makes
1409 it easy, if not obvious, where to look for specific data.
1410 ------------------------------------------------------------------------------
1412 ------------------------------------------------------------------------------
1413 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1414 ------------------------------------------------------------------------------
1416 ------------------------------------------------------------------------------
1418 ------------------------------------------------------------------------------
1419 * Modifying kernel parameters by writing into files found in /proc/sys
1420 * Exploring the files which modify certain parameters
1421 * Review of the /proc/sys file tree
1422 ------------------------------------------------------------------------------
1425 A very interesting part of /proc is the directory /proc/sys. This is not only
1426 a source of information, it also allows you to change parameters within the
1427 kernel. Be very careful when attempting this. You can optimize your system,
1428 but you can also cause it to crash. Never alter kernel parameters on a
1429 production system. Set up a development machine and test to make sure that
1430 everything works the way you want it to. You may have no alternative but to
1431 reboot the machine once an error has been made.
1433 To change a value, simply echo the new value into the file. An example is
1434 given below in the section on the file system data. You need to be root to do
1435 this. You can create your own boot script to perform this every time your
1438 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1439 general things in the operation of the Linux kernel. Since some of the files
1440 can inadvertently disrupt your system, it is advisable to read both
1441 documentation and source before actually making adjustments. In any case, be
1442 very careful when writing to any of these files. The entries in /proc may
1443 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1444 review the kernel documentation in the directory /usr/src/linux/Documentation.
1445 This chapter is heavily based on the documentation included in the pre 2.2
1446 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1448 Please see: Documentation/sysctl/ directory for descriptions of these
1451 ------------------------------------------------------------------------------
1453 ------------------------------------------------------------------------------
1454 Certain aspects of kernel behavior can be modified at runtime, without the
1455 need to recompile the kernel, or even to reboot the system. The files in the
1456 /proc/sys tree can not only be read, but also modified. You can use the echo
1457 command to write value into these files, thereby changing the default settings
1459 ------------------------------------------------------------------------------
1461 ------------------------------------------------------------------------------
1462 CHAPTER 3: PER-PROCESS PARAMETERS
1463 ------------------------------------------------------------------------------
1465 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1466 --------------------------------------------------------------------------------
1468 These file can be used to adjust the badness heuristic used to select which
1469 process gets killed in out of memory conditions.
1471 The badness heuristic assigns a value to each candidate task ranging from 0
1472 (never kill) to 1000 (always kill) to determine which process is targeted. The
1473 units are roughly a proportion along that range of allowed memory the process
1474 may allocate from based on an estimation of its current memory and swap use.
1475 For example, if a task is using all allowed memory, its badness score will be
1476 1000. If it is using half of its allowed memory, its score will be 500.
1478 There is an additional factor included in the badness score: the current memory
1479 and swap usage is discounted by 3% for root processes.
1481 The amount of "allowed" memory depends on the context in which the oom killer
1482 was called. If it is due to the memory assigned to the allocating task's cpuset
1483 being exhausted, the allowed memory represents the set of mems assigned to that
1484 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1485 memory represents the set of mempolicy nodes. If it is due to a memory
1486 limit (or swap limit) being reached, the allowed memory is that configured
1487 limit. Finally, if it is due to the entire system being out of memory, the
1488 allowed memory represents all allocatable resources.
1490 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1491 is used to determine which task to kill. Acceptable values range from -1000
1492 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1493 polarize the preference for oom killing either by always preferring a certain
1494 task or completely disabling it. The lowest possible value, -1000, is
1495 equivalent to disabling oom killing entirely for that task since it will always
1496 report a badness score of 0.
1498 Consequently, it is very simple for userspace to define the amount of memory to
1499 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1500 example, is roughly equivalent to allowing the remainder of tasks sharing the
1501 same system, cpuset, mempolicy, or memory controller resources to use at least
1502 50% more memory. A value of -500, on the other hand, would be roughly
1503 equivalent to discounting 50% of the task's allowed memory from being considered
1504 as scoring against the task.
1506 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1507 be used to tune the badness score. Its acceptable values range from -16
1508 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1509 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1510 scaled linearly with /proc/<pid>/oom_score_adj.
1512 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1513 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1514 requires CAP_SYS_RESOURCE.
1516 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1517 generation children with separate address spaces instead, if possible. This
1518 avoids servers and important system daemons from being killed and loses the
1519 minimal amount of work.
1522 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1523 -------------------------------------------------------------
1525 This file can be used to check the current score used by the oom-killer is for
1526 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1527 process should be killed in an out-of-memory situation.
1530 3.3 /proc/<pid>/io - Display the IO accounting fields
1531 -------------------------------------------------------
1533 This file contains IO statistics for each running process
1538 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1541 test:/tmp # cat /proc/3828/io
1547 write_bytes: 323932160
1548 cancelled_write_bytes: 0
1557 I/O counter: chars read
1558 The number of bytes which this task has caused to be read from storage. This
1559 is simply the sum of bytes which this process passed to read() and pread().
1560 It includes things like tty IO and it is unaffected by whether or not actual
1561 physical disk IO was required (the read might have been satisfied from
1568 I/O counter: chars written
1569 The number of bytes which this task has caused, or shall cause to be written
1570 to disk. Similar caveats apply here as with rchar.
1576 I/O counter: read syscalls
1577 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1584 I/O counter: write syscalls
1585 Attempt to count the number of write I/O operations, i.e. syscalls like
1586 write() and pwrite().
1592 I/O counter: bytes read
1593 Attempt to count the number of bytes which this process really did cause to
1594 be fetched from the storage layer. Done at the submit_bio() level, so it is
1595 accurate for block-backed filesystems. <please add status regarding NFS and
1596 CIFS at a later time>
1602 I/O counter: bytes written
1603 Attempt to count the number of bytes which this process caused to be sent to
1604 the storage layer. This is done at page-dirtying time.
1607 cancelled_write_bytes
1608 ---------------------
1610 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1611 then deletes the file, it will in fact perform no writeout. But it will have
1612 been accounted as having caused 1MB of write.
1613 In other words: The number of bytes which this process caused to not happen,
1614 by truncating pagecache. A task can cause "negative" IO too. If this task
1615 truncates some dirty pagecache, some IO which another task has been accounted
1616 for (in its write_bytes) will not be happening. We _could_ just subtract that
1617 from the truncating task's write_bytes, but there is information loss in doing
1624 At its current implementation state, this is a bit racy on 32-bit machines: if
1625 process A reads process B's /proc/pid/io while process B is updating one of
1626 those 64-bit counters, process A could see an intermediate result.
1629 More information about this can be found within the taskstats documentation in
1630 Documentation/accounting.
1632 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1633 ---------------------------------------------------------------
1634 When a process is dumped, all anonymous memory is written to a core file as
1635 long as the size of the core file isn't limited. But sometimes we don't want
1636 to dump some memory segments, for example, huge shared memory or DAX.
1637 Conversely, sometimes we want to save file-backed memory segments into a core
1638 file, not only the individual files.
1640 /proc/<pid>/coredump_filter allows you to customize which memory segments
1641 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1642 of memory types. If a bit of the bitmask is set, memory segments of the
1643 corresponding memory type are dumped, otherwise they are not dumped.
1645 The following 9 memory types are supported:
1646 - (bit 0) anonymous private memory
1647 - (bit 1) anonymous shared memory
1648 - (bit 2) file-backed private memory
1649 - (bit 3) file-backed shared memory
1650 - (bit 4) ELF header pages in file-backed private memory areas (it is
1651 effective only if the bit 2 is cleared)
1652 - (bit 5) hugetlb private memory
1653 - (bit 6) hugetlb shared memory
1654 - (bit 7) DAX private memory
1655 - (bit 8) DAX shared memory
1657 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1658 are always dumped regardless of the bitmask status.
1660 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1661 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1663 The default value of coredump_filter is 0x33; this means all anonymous memory
1664 segments, ELF header pages and hugetlb private memory are dumped.
1666 If you don't want to dump all shared memory segments attached to pid 1234,
1667 write 0x31 to the process's proc file.
1669 $ echo 0x31 > /proc/1234/coredump_filter
1671 When a new process is created, the process inherits the bitmask status from its
1672 parent. It is useful to set up coredump_filter before the program runs.
1675 $ echo 0x7 > /proc/self/coredump_filter
1678 3.5 /proc/<pid>/mountinfo - Information about mounts
1679 --------------------------------------------------------
1681 This file contains lines of the form:
1683 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1684 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1686 (1) mount ID: unique identifier of the mount (may be reused after umount)
1687 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1688 (3) major:minor: value of st_dev for files on filesystem
1689 (4) root: root of the mount within the filesystem
1690 (5) mount point: mount point relative to the process's root
1691 (6) mount options: per mount options
1692 (7) optional fields: zero or more fields of the form "tag[:value]"
1693 (8) separator: marks the end of the optional fields
1694 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1695 (10) mount source: filesystem specific information or "none"
1696 (11) super options: per super block options
1698 Parsers should ignore all unrecognised optional fields. Currently the
1699 possible optional fields are:
1701 shared:X mount is shared in peer group X
1702 master:X mount is slave to peer group X
1703 propagate_from:X mount is slave and receives propagation from peer group X (*)
1704 unbindable mount is unbindable
1706 (*) X is the closest dominant peer group under the process's root. If
1707 X is the immediate master of the mount, or if there's no dominant peer
1708 group under the same root, then only the "master:X" field is present
1709 and not the "propagate_from:X" field.
1711 For more information on mount propagation see:
1713 Documentation/filesystems/sharedsubtree.txt
1716 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1717 --------------------------------------------------------
1718 These files provide a method to access a tasks comm value. It also allows for
1719 a task to set its own or one of its thread siblings comm value. The comm value
1720 is limited in size compared to the cmdline value, so writing anything longer
1721 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1725 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1726 -------------------------------------------------------------------------
1727 This file provides a fast way to retrieve first level children pids
1728 of a task pointed by <pid>/<tid> pair. The format is a space separated
1731 Note the "first level" here -- if a child has own children they will
1732 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1733 to obtain the descendants.
1735 Since this interface is intended to be fast and cheap it doesn't
1736 guarantee to provide precise results and some children might be
1737 skipped, especially if they've exited right after we printed their
1738 pids, so one need to either stop or freeze processes being inspected
1739 if precise results are needed.
1742 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1743 ---------------------------------------------------------------
1744 This file provides information associated with an opened file. The regular
1745 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1746 represents the current offset of the opened file in decimal form [see lseek(2)
1747 for details], 'flags' denotes the octal O_xxx mask the file has been
1748 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1749 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1758 All locks associated with a file descriptor are shown in its fdinfo too.
1760 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1762 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1763 pair provide additional information particular to the objects they represent.
1772 where 'eventfd-count' is hex value of a counter.
1779 sigmask: 0000000000000200
1781 where 'sigmask' is hex value of the signal mask associated
1789 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1791 where 'tfd' is a target file descriptor number in decimal form,
1792 'events' is events mask being watched and the 'data' is data
1793 associated with a target [see epoll(7) for more details].
1795 The 'pos' is current offset of the target file in decimal form
1796 [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1797 where target file resides, all in hex format.
1801 For inotify files the format is the following
1805 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1807 where 'wd' is a watch descriptor in decimal form, ie a target file
1808 descriptor number, 'ino' and 'sdev' are inode and device where the
1809 target file resides and the 'mask' is the mask of events, all in hex
1810 form [see inotify(7) for more details].
1812 If the kernel was built with exportfs support, the path to the target
1813 file is encoded as a file handle. The file handle is provided by three
1814 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1817 If the kernel is built without exportfs support the file handle won't be
1820 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1822 For fanotify files the format is
1827 fanotify flags:10 event-flags:0
1828 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1829 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1831 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1832 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1833 flags associated with mark which are tracked separately from events
1834 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1835 mask and 'ignored_mask' is the mask of events which are to be ignored.
1836 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1837 does provide information about flags and mask used in fanotify_mark
1838 call [see fsnotify manpage for details].
1840 While the first three lines are mandatory and always printed, the rest is
1841 optional and may be omitted if no marks created yet.
1852 it_value: (0, 49406829)
1855 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1856 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1857 flags in octal form been used to setup the timer [see timerfd_settime(2) for
1858 details]. 'it_value' is remaining time until the timer exiration.
1859 'it_interval' is the interval for the timer. Note the timer might be set up
1860 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1861 still exhibits timer's remaining time.
1863 3.9 /proc/<pid>/map_files - Information about memory mapped files
1864 ---------------------------------------------------------------------
1865 This directory contains symbolic links which represent memory mapped files
1866 the process is maintaining. Example output:
1868 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1869 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1870 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1872 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1873 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1875 The name of a link represents the virtual memory bounds of a mapping, i.e.
1876 vm_area_struct::vm_start-vm_area_struct::vm_end.
1878 The main purpose of the map_files is to retrieve a set of memory mapped
1879 files in a fast way instead of parsing /proc/<pid>/maps or
1880 /proc/<pid>/smaps, both of which contain many more records. At the same
1881 time one can open(2) mappings from the listings of two processes and
1882 comparing their inode numbers to figure out which anonymous memory areas
1883 are actually shared.
1885 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
1886 ---------------------------------------------------------
1887 This file provides the value of the task's timerslack value in nanoseconds.
1888 This value specifies a amount of time that normal timers may be deferred
1889 in order to coalesce timers and avoid unnecessary wakeups.
1891 This allows a task's interactivity vs power consumption trade off to be
1894 Writing 0 to the file will set the tasks timerslack to the default value.
1896 Valid values are from 0 - ULLONG_MAX
1898 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1899 permissions on the task specified to change its timerslack_ns value.
1901 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
1902 -----------------------------------------------------------------
1903 When CONFIG_LIVEPATCH is enabled, this file displays the value of the
1904 patch state for the task.
1906 A value of '-1' indicates that no patch is in transition.
1908 A value of '0' indicates that a patch is in transition and the task is
1909 unpatched. If the patch is being enabled, then the task hasn't been
1910 patched yet. If the patch is being disabled, then the task has already
1913 A value of '1' indicates that a patch is in transition and the task is
1914 patched. If the patch is being enabled, then the task has already been
1915 patched. If the patch is being disabled, then the task hasn't been
1919 ------------------------------------------------------------------------------
1921 ------------------------------------------------------------------------------
1924 ---------------------
1926 The following mount options are supported:
1928 hidepid= Set /proc/<pid>/ access mode.
1929 gid= Set the group authorized to learn processes information.
1931 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1934 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1935 own. Sensitive files like cmdline, sched*, status are now protected against
1936 other users. This makes it impossible to learn whether any user runs
1937 specific program (given the program doesn't reveal itself by its behaviour).
1938 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1939 poorly written programs passing sensitive information via program arguments are
1940 now protected against local eavesdroppers.
1942 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1943 users. It doesn't mean that it hides a fact whether a process with a specific
1944 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1945 but it hides process' uid and gid, which may be learned by stat()'ing
1946 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1947 information about running processes, whether some daemon runs with elevated
1948 privileges, whether other user runs some sensitive program, whether other users
1949 run any program at all, etc.
1951 gid= defines a group authorized to learn processes information otherwise
1952 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1953 information about processes information, just add identd to this group.
git.samba.org / sfrench / cifs-2.6.git / blob