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
51 ------------------------------------------------------------------------------
53 ------------------------------------------------------------------------------
55 0.1 Introduction/Credits
56 ------------------------
58 This documentation is part of a soon (or so we hope) to be released book on
59 the SuSE Linux distribution. As there is no complete documentation for the
60 /proc file system and we've used many freely available sources to write these
61 chapters, it seems only fair to give the work back to the Linux community.
62 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
63 afraid it's still far from complete, but we hope it will be useful. As far as
64 we know, it is the first 'all-in-one' document about the /proc file system. It
65 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
66 SPARC, AXP, etc., features, you probably won't find what you are looking for.
67 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
68 additions and patches are welcome and will be added to this document if you
71 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
72 other people for help compiling this documentation. We'd also like to extend a
73 special thank you to Andi Kleen for documentation, which we relied on heavily
74 to create this document, as well as the additional information he provided.
75 Thanks to everybody else who contributed source or docs to the Linux kernel
76 and helped create a great piece of software... :)
78 If you have any comments, corrections or additions, please don't hesitate to
79 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
82 The latest version of this document is available online at
83 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
85 If the above direction does not works for you, you could try the kernel
86 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
87 comandante@zaralinux.com.
92 We don't guarantee the correctness of this document, and if you come to us
93 complaining about how you screwed up your system because of incorrect
94 documentation, we won't feel responsible...
96 ------------------------------------------------------------------------------
97 CHAPTER 1: COLLECTING SYSTEM INFORMATION
98 ------------------------------------------------------------------------------
100 ------------------------------------------------------------------------------
102 ------------------------------------------------------------------------------
103 * Investigating the properties of the pseudo file system /proc and its
104 ability to provide information on the running Linux system
105 * Examining /proc's structure
106 * Uncovering various information about the kernel and the processes running
108 ------------------------------------------------------------------------------
111 The proc file system acts as an interface to internal data structures in the
112 kernel. It can be used to obtain information about the system and to change
113 certain kernel parameters at runtime (sysctl).
115 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
116 show you how you can use /proc/sys to change settings.
118 1.1 Process-Specific Subdirectories
119 -----------------------------------
121 The directory /proc contains (among other things) one subdirectory for each
122 process running on the system, which is named after the process ID (PID).
124 The link self points to the process reading the file system. Each process
125 subdirectory has the entries listed in Table 1-1.
128 Table 1-1: Process specific entries in /proc
129 ..............................................................................
131 clear_refs Clears page referenced bits shown in smaps output
132 cmdline Command line arguments
133 cpu Current and last cpu in which it was executed (2.4)(smp)
134 cwd Link to the current working directory
135 environ Values of environment variables
136 exe Link to the executable of this process
137 fd Directory, which contains all file descriptors
138 maps Memory maps to executables and library files (2.4)
139 mem Memory held by this process
140 root Link to the root directory of this process
142 statm Process memory status information
143 status Process status in human readable form
144 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
145 symbol the task is blocked in - or "0" if not blocked.
147 stack Report full stack trace, enable via CONFIG_STACKTRACE
148 smaps a extension based on maps, showing the memory consumption of
149 each mapping and flags associated with it
150 numa_maps an extension based on maps, showing the memory locality and
151 binding policy as well as mem usage (in pages) of each mapping.
152 ..............................................................................
154 For example, to get the status information of a process, all you have to do is
155 read the file /proc/PID/status:
157 >cat /proc/self/status
185 SigPnd: 0000000000000000
186 ShdPnd: 0000000000000000
187 SigBlk: 0000000000000000
188 SigIgn: 0000000000000000
189 SigCgt: 0000000000000000
190 CapInh: 00000000fffffeff
191 CapPrm: 0000000000000000
192 CapEff: 0000000000000000
193 CapBnd: ffffffffffffffff
195 voluntary_ctxt_switches: 0
196 nonvoluntary_ctxt_switches: 1
198 This shows you nearly the same information you would get if you viewed it with
199 the ps command. In fact, ps uses the proc file system to obtain its
200 information. But you get a more detailed view of the process by reading the
201 file /proc/PID/status. It fields are described in table 1-2.
203 The statm file contains more detailed information about the process
204 memory usage. Its seven fields are explained in Table 1-3. The stat file
205 contains details information about the process itself. Its fields are
206 explained in Table 1-4.
208 (for SMP CONFIG users)
209 For making accounting scalable, RSS related information are handled in an
210 asynchronous manner and the value may not be very precise. To see a precise
211 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
212 It's slow but very precise.
214 Table 1-2: Contents of the status files (as of 4.1)
215 ..............................................................................
217 Name filename of the executable
218 State state (R is running, S is sleeping, D is sleeping
219 in an uninterruptible wait, Z is zombie,
220 T is traced or stopped)
222 Ngid NUMA group ID (0 if none)
224 PPid process id of the parent process
225 TracerPid PID of process tracing this process (0 if not)
226 Uid Real, effective, saved set, and file system UIDs
227 Gid Real, effective, saved set, and file system GIDs
228 Umask file mode creation mask
229 FDSize number of file descriptor slots currently allocated
230 Groups supplementary group list
231 NStgid descendant namespace thread group ID hierarchy
232 NSpid descendant namespace process ID hierarchy
233 NSpgid descendant namespace process group ID hierarchy
234 NSsid descendant namespace session ID hierarchy
235 VmPeak peak virtual memory size
236 VmSize total program size
237 VmLck locked memory size
238 VmHWM peak resident set size ("high water mark")
239 VmRSS size of memory portions. It contains the three
240 following parts (VmRSS = RssAnon + RssFile + RssShmem)
241 RssAnon size of resident anonymous memory
242 RssFile size of resident file mappings
243 RssShmem size of resident shmem memory (includes SysV shm,
244 mapping of tmpfs and shared anonymous mappings)
245 VmData size of private data segments
246 VmStk size of stack segments
247 VmExe size of text segment
248 VmLib size of shared library code
249 VmPTE size of page table entries
250 VmPMD size of second level page tables
251 VmSwap amount of swap used by anonymous private data
252 (shmem swap usage is not included)
253 HugetlbPages size of hugetlb memory portions
254 Threads number of threads
255 SigQ number of signals queued/max. number for queue
256 SigPnd bitmap of pending signals for the thread
257 ShdPnd bitmap of shared pending signals for the process
258 SigBlk bitmap of blocked signals
259 SigIgn bitmap of ignored signals
260 SigCgt bitmap of caught signals
261 CapInh bitmap of inheritable capabilities
262 CapPrm bitmap of permitted capabilities
263 CapEff bitmap of effective capabilities
264 CapBnd bitmap of capabilities bounding set
265 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
266 Cpus_allowed mask of CPUs on which this process may run
267 Cpus_allowed_list Same as previous, but in "list format"
268 Mems_allowed mask of memory nodes allowed to this process
269 Mems_allowed_list Same as previous, but in "list format"
270 voluntary_ctxt_switches number of voluntary context switches
271 nonvoluntary_ctxt_switches number of non voluntary context switches
272 ..............................................................................
274 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
275 ..............................................................................
277 size total program size (pages) (same as VmSize in status)
278 resident size of memory portions (pages) (same as VmRSS in status)
279 shared number of pages that are shared (i.e. backed by a file, same
280 as RssFile+RssShmem in status)
281 trs number of pages that are 'code' (not including libs; broken,
282 includes data segment)
283 lrs number of pages of library (always 0 on 2.6)
284 drs number of pages of data/stack (including libs; broken,
285 includes library text)
286 dt number of dirty pages (always 0 on 2.6)
287 ..............................................................................
290 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
291 ..............................................................................
294 tcomm filename of the executable
295 state state (R is running, S is sleeping, D is sleeping in an
296 uninterruptible wait, Z is zombie, T is traced or stopped)
297 ppid process id of the parent process
298 pgrp pgrp of the process
300 tty_nr tty the process uses
301 tty_pgrp pgrp of the tty
303 min_flt number of minor faults
304 cmin_flt number of minor faults with child's
305 maj_flt number of major faults
306 cmaj_flt number of major faults with child's
307 utime user mode jiffies
308 stime kernel mode jiffies
309 cutime user mode jiffies with child's
310 cstime kernel mode jiffies with child's
311 priority priority level
313 num_threads number of threads
314 it_real_value (obsolete, always 0)
315 start_time time the process started after system boot
316 vsize virtual memory size
317 rss resident set memory size
318 rsslim current limit in bytes on the rss
319 start_code address above which program text can run
320 end_code address below which program text can run
321 start_stack address of the start of the main process stack
322 esp current value of ESP
323 eip current value of EIP
324 pending bitmap of pending signals
325 blocked bitmap of blocked signals
326 sigign bitmap of ignored signals
327 sigcatch bitmap of caught signals
328 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead)
331 exit_signal signal to send to parent thread on exit
332 task_cpu which CPU the task is scheduled on
333 rt_priority realtime priority
334 policy scheduling policy (man sched_setscheduler)
335 blkio_ticks time spent waiting for block IO
336 gtime guest time of the task in jiffies
337 cgtime guest time of the task children in jiffies
338 start_data address above which program data+bss is placed
339 end_data address below which program data+bss is placed
340 start_brk address above which program heap can be expanded with brk()
341 arg_start address above which program command line is placed
342 arg_end address below which program command line is placed
343 env_start address above which program environment is placed
344 env_end address below which program environment is placed
345 exit_code the thread's exit_code in the form reported by the waitpid system call
346 ..............................................................................
348 The /proc/PID/maps file containing the currently mapped memory regions and
349 their access permissions.
353 address perms offset dev inode pathname
355 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
356 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
357 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
358 a7cb1000-a7cb2000 ---p 00000000 00:00 0
359 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
360 a7eb2000-a7eb3000 ---p 00000000 00:00 0
361 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
362 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
363 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
364 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
365 a800b000-a800e000 rw-p 00000000 00:00 0
366 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
367 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
368 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
369 a8024000-a8027000 rw-p 00000000 00:00 0
370 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
371 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
372 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
373 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
374 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
376 where "address" is the address space in the process that it occupies, "perms"
377 is a set of permissions:
383 p = private (copy on write)
385 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
386 "inode" is the inode on that device. 0 indicates that no inode is associated
387 with the memory region, as the case would be with BSS (uninitialized data).
388 The "pathname" shows the name associated file for this mapping. If the mapping
389 is not associated with a file:
391 [heap] = the heap of the program
392 [stack] = the stack of the main process
393 [vdso] = the "virtual dynamic shared object",
394 the kernel system call handler
396 or if empty, the mapping is anonymous.
398 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
399 of the individual tasks of a process. In this file you will see a mapping marked
400 as [stack] if that task sees it as a stack. Hence, for the example above, the
401 task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
403 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
404 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
405 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
406 a7cb1000-a7cb2000 ---p 00000000 00:00 0
407 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
408 a7eb2000-a7eb3000 ---p 00000000 00:00 0
409 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack]
410 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
411 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
412 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
413 a800b000-a800e000 rw-p 00000000 00:00 0
414 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
415 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
416 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
417 a8024000-a8027000 rw-p 00000000 00:00 0
418 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
419 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
420 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
421 aff35000-aff4a000 rw-p 00000000 00:00 0
422 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
424 The /proc/PID/smaps is an extension based on maps, showing the memory
425 consumption for each of the process's mappings. For each of mappings there
426 is a series of lines such as the following:
428 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
441 Private_Hugetlb: 0 kB
447 VmFlags: rd ex mr mw me dw
449 the first of these lines shows the same information as is displayed for the
450 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
451 (size), the amount of the mapping that is currently resident in RAM (RSS), the
452 process' proportional share of this mapping (PSS), the number of clean and
453 dirty private pages in the mapping.
455 The "proportional set size" (PSS) of a process is the count of pages it has
456 in memory, where each page is divided by the number of processes sharing it.
457 So if a process has 1000 pages all to itself, and 1000 shared with one other
458 process, its PSS will be 1500.
459 Note that even a page which is part of a MAP_SHARED mapping, but has only
460 a single pte mapped, i.e. is currently used by only one process, is accounted
461 as private and not as shared.
462 "Referenced" indicates the amount of memory currently marked as referenced or
464 "Anonymous" shows the amount of memory that does not belong to any file. Even
465 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
466 and a page is modified, the file page is replaced by a private anonymous copy.
467 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
468 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
470 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
471 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
472 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
473 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
474 For shmem mappings, "Swap" includes also the size of the mapped (and not
475 replaced by copy-on-write) part of the underlying shmem object out on swap.
476 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
477 does not take into account swapped out page of underlying shmem objects.
478 "Locked" indicates whether the mapping is locked in memory or not.
480 "VmFlags" field deserves a separate description. This member represents the kernel
481 flags associated with the particular virtual memory area in two letter encoded
482 manner. The codes are the following:
491 gd - stack segment growns down
493 dw - disabled write to the mapped file
494 lo - pages are locked in memory
495 io - memory mapped I/O area
496 sr - sequential read advise provided
497 rr - random read advise provided
498 dc - do not copy area on fork
499 de - do not expand area on remapping
500 ac - area is accountable
501 nr - swap space is not reserved for the area
502 ht - area uses huge tlb pages
503 ar - architecture specific flag
504 dd - do not include area into core dump
507 hg - huge page advise flag
508 nh - no-huge page advise flag
509 mg - mergable advise flag
511 Note that there is no guarantee that every flag and associated mnemonic will
512 be present in all further kernel releases. Things get changed, the flags may
513 be vanished or the reverse -- new added.
515 This file is only present if the CONFIG_MMU kernel configuration option is
518 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
519 bits on both physical and virtual pages associated with a process, and the
520 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
521 To clear the bits for all the pages associated with the process
522 > echo 1 > /proc/PID/clear_refs
524 To clear the bits for the anonymous pages associated with the process
525 > echo 2 > /proc/PID/clear_refs
527 To clear the bits for the file mapped pages associated with the process
528 > echo 3 > /proc/PID/clear_refs
530 To clear the soft-dirty bit
531 > echo 4 > /proc/PID/clear_refs
533 To reset the peak resident set size ("high water mark") to the process's
535 > echo 5 > /proc/PID/clear_refs
537 Any other value written to /proc/PID/clear_refs will have no effect.
539 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
540 using /proc/kpageflags and number of times a page is mapped using
541 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
543 The /proc/pid/numa_maps is an extension based on maps, showing the memory
544 locality and binding policy, as well as the memory usage (in pages) of
545 each mapping. The output follows a general format where mapping details get
546 summarized separated by blank spaces, one mapping per each file line:
548 address policy mapping details
550 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
551 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
552 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
553 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
554 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
555 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
556 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
557 320698b000 default file=/lib64/libc-2.12.so
558 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
559 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
560 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
561 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
562 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
563 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
564 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
565 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
568 "address" is the starting address for the mapping;
569 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
570 "mapping details" summarizes mapping data such as mapping type, page usage counters,
571 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
572 size, in KB, that is backing the mapping up.
577 Similar to the process entries, the kernel data files give information about
578 the running kernel. The files used to obtain this information are contained in
579 /proc and are listed in Table 1-5. Not all of these will be present in your
580 system. It depends on the kernel configuration and the loaded modules, which
581 files are there, and which are missing.
583 Table 1-5: Kernel info in /proc
584 ..............................................................................
586 apm Advanced power management info
587 buddyinfo Kernel memory allocator information (see text) (2.5)
588 bus Directory containing bus specific information
589 cmdline Kernel command line
590 cpuinfo Info about the CPU
591 devices Available devices (block and character)
592 dma Used DMS channels
593 filesystems Supported filesystems
594 driver Various drivers grouped here, currently rtc (2.4)
595 execdomains Execdomains, related to security (2.4)
596 fb Frame Buffer devices (2.4)
597 fs File system parameters, currently nfs/exports (2.4)
598 ide Directory containing info about the IDE subsystem
599 interrupts Interrupt usage
600 iomem Memory map (2.4)
601 ioports I/O port usage
602 irq Masks for irq to cpu affinity (2.4)(smp?)
603 isapnp ISA PnP (Plug&Play) Info (2.4)
604 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
606 ksyms Kernel symbol table
607 loadavg Load average of last 1, 5 & 15 minutes
611 modules List of loaded modules
612 mounts Mounted filesystems
613 net Networking info (see text)
614 pagetypeinfo Additional page allocator information (see text) (2.5)
615 partitions Table of partitions known to the system
616 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
617 decoupled by lspci (2.4)
619 scsi SCSI info (see text)
620 slabinfo Slab pool info
621 softirqs softirq usage
622 stat Overall statistics
623 swaps Swap space utilization
625 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
626 tty Info of tty drivers
627 uptime Wall clock since boot, combined idle time of all cpus
628 version Kernel version
629 video bttv info of video resources (2.4)
630 vmallocinfo Show vmalloced areas
631 ..............................................................................
633 You can, for example, check which interrupts are currently in use and what
634 they are used for by looking in the file /proc/interrupts:
636 > cat /proc/interrupts
638 0: 8728810 XT-PIC timer
639 1: 895 XT-PIC keyboard
641 3: 531695 XT-PIC aha152x
642 4: 2014133 XT-PIC serial
643 5: 44401 XT-PIC pcnet_cs
646 12: 182918 XT-PIC PS/2 Mouse
648 14: 1232265 XT-PIC ide0
652 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
653 output of a SMP machine):
655 > cat /proc/interrupts
658 0: 1243498 1214548 IO-APIC-edge timer
659 1: 8949 8958 IO-APIC-edge keyboard
660 2: 0 0 XT-PIC cascade
661 5: 11286 10161 IO-APIC-edge soundblaster
662 8: 1 0 IO-APIC-edge rtc
663 9: 27422 27407 IO-APIC-edge 3c503
664 12: 113645 113873 IO-APIC-edge PS/2 Mouse
666 14: 22491 24012 IO-APIC-edge ide0
667 15: 2183 2415 IO-APIC-edge ide1
668 17: 30564 30414 IO-APIC-level eth0
669 18: 177 164 IO-APIC-level bttv
674 NMI is incremented in this case because every timer interrupt generates a NMI
675 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
677 LOC is the local interrupt counter of the internal APIC of every CPU.
679 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
680 connects the CPUs in a SMP system. This means that an error has been detected,
681 the IO-APIC automatically retry the transmission, so it should not be a big
682 problem, but you should read the SMP-FAQ.
684 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
685 /proc/interrupts to display every IRQ vector in use by the system, not
686 just those considered 'most important'. The new vectors are:
688 THR -- interrupt raised when a machine check threshold counter
689 (typically counting ECC corrected errors of memory or cache) exceeds
690 a configurable threshold. Only available on some systems.
692 TRM -- a thermal event interrupt occurs when a temperature threshold
693 has been exceeded for the CPU. This interrupt may also be generated
694 when the temperature drops back to normal.
696 SPU -- a spurious interrupt is some interrupt that was raised then lowered
697 by some IO device before it could be fully processed by the APIC. Hence
698 the APIC sees the interrupt but does not know what device it came from.
699 For this case the APIC will generate the interrupt with a IRQ vector
700 of 0xff. This might also be generated by chipset bugs.
702 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
703 sent from one CPU to another per the needs of the OS. Typically,
704 their statistics are used by kernel developers and interested users to
705 determine the occurrence of interrupts of the given type.
707 The above IRQ vectors are displayed only when relevant. For example,
708 the threshold vector does not exist on x86_64 platforms. Others are
709 suppressed when the system is a uniprocessor. As of this writing, only
710 i386 and x86_64 platforms support the new IRQ vector displays.
712 Of some interest is the introduction of the /proc/irq directory to 2.4.
713 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
714 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
715 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
720 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
721 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
725 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
726 IRQ, you can set it by doing:
728 > echo 1 > /proc/irq/10/smp_affinity
730 This means that only the first CPU will handle the IRQ, but you can also echo
731 5 which means that only the first and third CPU can handle the IRQ.
733 The contents of each smp_affinity file is the same by default:
735 > cat /proc/irq/0/smp_affinity
738 There is an alternate interface, smp_affinity_list which allows specifying
739 a cpu range instead of a bitmask:
741 > cat /proc/irq/0/smp_affinity_list
744 The default_smp_affinity mask applies to all non-active IRQs, which are the
745 IRQs which have not yet been allocated/activated, and hence which lack a
746 /proc/irq/[0-9]* directory.
748 The node file on an SMP system shows the node to which the device using the IRQ
749 reports itself as being attached. This hardware locality information does not
750 include information about any possible driver locality preference.
752 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
753 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
755 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
756 between all the CPUs which are allowed to handle it. As usual the kernel has
757 more info than you and does a better job than you, so the defaults are the
758 best choice for almost everyone. [Note this applies only to those IO-APIC's
759 that support "Round Robin" interrupt distribution.]
761 There are three more important subdirectories in /proc: net, scsi, and sys.
762 The general rule is that the contents, or even the existence of these
763 directories, depend on your kernel configuration. If SCSI is not enabled, the
764 directory scsi may not exist. The same is true with the net, which is there
765 only when networking support is present in the running kernel.
767 The slabinfo file gives information about memory usage at the slab level.
768 Linux uses slab pools for memory management above page level in version 2.2.
769 Commonly used objects have their own slab pool (such as network buffers,
770 directory cache, and so on).
772 ..............................................................................
774 > cat /proc/buddyinfo
776 Node 0, zone DMA 0 4 5 4 4 3 ...
777 Node 0, zone Normal 1 0 0 1 101 8 ...
778 Node 0, zone HighMem 2 0 0 1 1 0 ...
780 External fragmentation is a problem under some workloads, and buddyinfo is a
781 useful tool for helping diagnose these problems. Buddyinfo will give you a
782 clue as to how big an area you can safely allocate, or why a previous
785 Each column represents the number of pages of a certain order which are
786 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
787 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
788 available in ZONE_NORMAL, etc...
790 More information relevant to external fragmentation can be found in
793 > cat /proc/pagetypeinfo
797 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
798 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
799 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
800 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
801 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
802 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
803 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
804 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
805 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
806 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
807 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
809 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
810 Node 0, zone DMA 2 0 5 1 0
811 Node 0, zone DMA32 41 6 967 2 0
813 Fragmentation avoidance in the kernel works by grouping pages of different
814 migrate types into the same contiguous regions of memory called page blocks.
815 A page block is typically the size of the default hugepage size e.g. 2MB on
816 X86-64. By keeping pages grouped based on their ability to move, the kernel
817 can reclaim pages within a page block to satisfy a high-order allocation.
819 The pagetypinfo begins with information on the size of a page block. It
820 then gives the same type of information as buddyinfo except broken down
821 by migrate-type and finishes with details on how many page blocks of each
824 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
825 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
826 make an estimate of the likely number of huge pages that can be allocated
827 at a given point in time. All the "Movable" blocks should be allocatable
828 unless memory has been mlock()'d. Some of the Reclaimable blocks should
829 also be allocatable although a lot of filesystem metadata may have to be
830 reclaimed to achieve this.
832 ..............................................................................
836 Provides information about distribution and utilization of memory. This
837 varies by architecture and compile options. The following is from a
838 16GB PIII, which has highmem enabled. You may not have all of these fields.
842 MemTotal: 16344972 kB
844 MemAvailable: 14836172 kB
850 HighTotal: 15597528 kB
851 HighFree: 13629632 kB
862 SReclaimable: 159856 kB
863 SUnreclaim: 124508 kB
868 CommitLimit: 7669796 kB
869 Committed_AS: 100056 kB
870 VmallocTotal: 112216 kB
872 VmallocChunk: 111088 kB
873 AnonHugePages: 49152 kB
878 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
879 bits and the kernel binary code)
880 MemFree: The sum of LowFree+HighFree
881 MemAvailable: An estimate of how much memory is available for starting new
882 applications, without swapping. Calculated from MemFree,
883 SReclaimable, the size of the file LRU lists, and the low
884 watermarks in each zone.
885 The estimate takes into account that the system needs some
886 page cache to function well, and that not all reclaimable
887 slab will be reclaimable, due to items being in use. The
888 impact of those factors will vary from system to system.
889 Buffers: Relatively temporary storage for raw disk blocks
890 shouldn't get tremendously large (20MB or so)
891 Cached: in-memory cache for files read from the disk (the
892 pagecache). Doesn't include SwapCached
893 SwapCached: Memory that once was swapped out, is swapped back in but
894 still also is in the swapfile (if memory is needed it
895 doesn't need to be swapped out AGAIN because it is already
896 in the swapfile. This saves I/O)
897 Active: Memory that has been used more recently and usually not
898 reclaimed unless absolutely necessary.
899 Inactive: Memory which has been less recently used. It is more
900 eligible to be reclaimed for other purposes
902 HighFree: Highmem is all memory above ~860MB of physical memory
903 Highmem areas are for use by userspace programs, or
904 for the pagecache. The kernel must use tricks to access
905 this memory, making it slower to access than lowmem.
907 LowFree: Lowmem is memory which can be used for everything that
908 highmem can be used for, but it is also available for the
909 kernel's use for its own data structures. Among many
910 other things, it is where everything from the Slab is
911 allocated. Bad things happen when you're out of lowmem.
912 SwapTotal: total amount of swap space available
913 SwapFree: Memory which has been evicted from RAM, and is temporarily
915 Dirty: Memory which is waiting to get written back to the disk
916 Writeback: Memory which is actively being written back to the disk
917 AnonPages: Non-file backed pages mapped into userspace page tables
918 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
919 Mapped: files which have been mmaped, such as libraries
920 Shmem: Total memory used by shared memory (shmem) and tmpfs
921 ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
923 ShmemPmdMapped: Shared memory mapped into userspace with huge pages
924 Slab: in-kernel data structures cache
925 SReclaimable: Part of Slab, that might be reclaimed, such as caches
926 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
927 PageTables: amount of memory dedicated to the lowest level of page
929 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
931 Bounce: Memory used for block device "bounce buffers"
932 WritebackTmp: Memory used by FUSE for temporary writeback buffers
933 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
934 this is the total amount of memory currently available to
935 be allocated on the system. This limit is only adhered to
936 if strict overcommit accounting is enabled (mode 2 in
937 'vm.overcommit_memory').
938 The CommitLimit is calculated with the following formula:
939 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
940 overcommit_ratio / 100 + [total swap pages]
941 For example, on a system with 1G of physical RAM and 7G
942 of swap with a `vm.overcommit_ratio` of 30 it would
943 yield a CommitLimit of 7.3G.
944 For more details, see the memory overcommit documentation
945 in vm/overcommit-accounting.
946 Committed_AS: The amount of memory presently allocated on the system.
947 The committed memory is a sum of all of the memory which
948 has been allocated by processes, even if it has not been
949 "used" by them as of yet. A process which malloc()'s 1G
950 of memory, but only touches 300M of it will show up as
951 using 1G. This 1G is memory which has been "committed" to
952 by the VM and can be used at any time by the allocating
953 application. With strict overcommit enabled on the system
954 (mode 2 in 'vm.overcommit_memory'),allocations which would
955 exceed the CommitLimit (detailed above) will not be permitted.
956 This is useful if one needs to guarantee that processes will
957 not fail due to lack of memory once that memory has been
958 successfully allocated.
959 VmallocTotal: total size of vmalloc memory area
960 VmallocUsed: amount of vmalloc area which is used
961 VmallocChunk: largest contiguous block of vmalloc area which is free
963 ..............................................................................
967 Provides information about vmalloced/vmaped areas. One line per area,
968 containing the virtual address range of the area, size in bytes,
969 caller information of the creator, and optional information depending
970 on the kind of area :
972 pages=nr number of pages
973 phys=addr if a physical address was specified
974 ioremap I/O mapping (ioremap() and friends)
975 vmalloc vmalloc() area
978 vpages buffer for pages pointers was vmalloced (huge area)
979 N<node>=nr (Only on NUMA kernels)
980 Number of pages allocated on memory node <node>
982 > cat /proc/vmallocinfo
983 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
984 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
985 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
986 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
987 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
988 phys=7fee8000 ioremap
989 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
990 phys=7fee7000 ioremap
991 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
992 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
993 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
994 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
996 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
997 /0x130 [x_tables] pages=4 vmalloc N0=4
998 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
999 pages=14 vmalloc N2=14
1000 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
1001 pages=4 vmalloc N1=4
1002 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
1003 pages=2 vmalloc N1=2
1004 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
1005 pages=10 vmalloc N0=10
1007 ..............................................................................
1011 Provides counts of softirq handlers serviced since boot time, for each cpu.
1013 > cat /proc/softirqs
1016 TIMER: 27166 27120 27097 27034
1021 SCHED: 27035 26983 26971 26746
1023 RCU: 1678 1769 2178 2250
1026 1.3 IDE devices in /proc/ide
1027 ----------------------------
1029 The subdirectory /proc/ide contains information about all IDE devices of which
1030 the kernel is aware. There is one subdirectory for each IDE controller, the
1031 file drivers and a link for each IDE device, pointing to the device directory
1032 in the controller specific subtree.
1034 The file drivers contains general information about the drivers used for the
1037 > cat /proc/ide/drivers
1038 ide-cdrom version 4.53
1039 ide-disk version 1.08
1041 More detailed information can be found in the controller specific
1042 subdirectories. These are named ide0, ide1 and so on. Each of these
1043 directories contains the files shown in table 1-6.
1046 Table 1-6: IDE controller info in /proc/ide/ide?
1047 ..............................................................................
1049 channel IDE channel (0 or 1)
1050 config Configuration (only for PCI/IDE bridge)
1052 model Type/Chipset of IDE controller
1053 ..............................................................................
1055 Each device connected to a controller has a separate subdirectory in the
1056 controllers directory. The files listed in table 1-7 are contained in these
1060 Table 1-7: IDE device information
1061 ..............................................................................
1064 capacity Capacity of the medium (in 512Byte blocks)
1065 driver driver and version
1066 geometry physical and logical geometry
1067 identify device identify block
1069 model device identifier
1070 settings device setup
1071 smart_thresholds IDE disk management thresholds
1072 smart_values IDE disk management values
1073 ..............................................................................
1075 The most interesting file is settings. This file contains a nice overview of
1076 the drive parameters:
1078 # cat /proc/ide/ide0/hda/settings
1079 name value min max mode
1080 ---- ----- --- --- ----
1081 bios_cyl 526 0 65535 rw
1082 bios_head 255 0 255 rw
1083 bios_sect 63 0 63 rw
1084 breada_readahead 4 0 127 rw
1086 file_readahead 72 0 2097151 rw
1088 keepsettings 0 0 1 rw
1089 max_kb_per_request 122 1 127 rw
1093 pio_mode write-only 0 255 w
1099 1.4 Networking info in /proc/net
1100 --------------------------------
1102 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1103 additional values you get for IP version 6 if you configure the kernel to
1104 support this. Table 1-9 lists the files and their meaning.
1107 Table 1-8: IPv6 info in /proc/net
1108 ..............................................................................
1110 udp6 UDP sockets (IPv6)
1111 tcp6 TCP sockets (IPv6)
1112 raw6 Raw device statistics (IPv6)
1113 igmp6 IP multicast addresses, which this host joined (IPv6)
1114 if_inet6 List of IPv6 interface addresses
1115 ipv6_route Kernel routing table for IPv6
1116 rt6_stats Global IPv6 routing tables statistics
1117 sockstat6 Socket statistics (IPv6)
1118 snmp6 Snmp data (IPv6)
1119 ..............................................................................
1122 Table 1-9: Network info in /proc/net
1123 ..............................................................................
1125 arp Kernel ARP table
1126 dev network devices with statistics
1127 dev_mcast the Layer2 multicast groups a device is listening too
1128 (interface index, label, number of references, number of bound
1130 dev_stat network device status
1131 ip_fwchains Firewall chain linkage
1132 ip_fwnames Firewall chain names
1133 ip_masq Directory containing the masquerading tables
1134 ip_masquerade Major masquerading table
1135 netstat Network statistics
1136 raw raw device statistics
1137 route Kernel routing table
1138 rpc Directory containing rpc info
1139 rt_cache Routing cache
1141 sockstat Socket statistics
1144 unix UNIX domain sockets
1145 wireless Wireless interface data (Wavelan etc)
1146 igmp IP multicast addresses, which this host joined
1147 psched Global packet scheduler parameters.
1148 netlink List of PF_NETLINK sockets
1149 ip_mr_vifs List of multicast virtual interfaces
1150 ip_mr_cache List of multicast routing cache
1151 ..............................................................................
1153 You can use this information to see which network devices are available in
1154 your system and how much traffic was routed over those devices:
1157 Inter-|Receive |[...
1158 face |bytes packets errs drop fifo frame compressed multicast|[...
1159 lo: 908188 5596 0 0 0 0 0 0 [...
1160 ppp0:15475140 20721 410 0 0 410 0 0 [...
1161 eth0: 614530 7085 0 0 0 0 0 1 [...
1164 ...] bytes packets errs drop fifo colls carrier compressed
1165 ...] 908188 5596 0 0 0 0 0 0
1166 ...] 1375103 17405 0 0 0 0 0 0
1167 ...] 1703981 5535 0 0 0 3 0 0
1169 In addition, each Channel Bond interface has its own directory. For
1170 example, the bond0 device will have a directory called /proc/net/bond0/.
1171 It will contain information that is specific to that bond, such as the
1172 current slaves of the bond, the link status of the slaves, and how
1173 many times the slaves link has failed.
1178 If you have a SCSI host adapter in your system, you'll find a subdirectory
1179 named after the driver for this adapter in /proc/scsi. You'll also see a list
1180 of all recognized SCSI devices in /proc/scsi:
1182 >cat /proc/scsi/scsi
1184 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1185 Vendor: IBM Model: DGHS09U Rev: 03E0
1186 Type: Direct-Access ANSI SCSI revision: 03
1187 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1188 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1189 Type: CD-ROM ANSI SCSI revision: 02
1192 The directory named after the driver has one file for each adapter found in
1193 the system. These files contain information about the controller, including
1194 the used IRQ and the IO address range. The amount of information shown is
1195 dependent on the adapter you use. The example shows the output for an Adaptec
1196 AHA-2940 SCSI adapter:
1198 > cat /proc/scsi/aic7xxx/0
1200 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1202 TCQ Enabled By Default : Disabled
1203 AIC7XXX_PROC_STATS : Disabled
1204 AIC7XXX_RESET_DELAY : 5
1205 Adapter Configuration:
1206 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1207 Ultra Wide Controller
1208 PCI MMAPed I/O Base: 0xeb001000
1209 Adapter SEEPROM Config: SEEPROM found and used.
1210 Adaptec SCSI BIOS: Enabled
1212 SCBs: Active 0, Max Active 2,
1213 Allocated 15, HW 16, Page 255
1215 BIOS Control Word: 0x18b6
1216 Adapter Control Word: 0x005b
1217 Extended Translation: Enabled
1218 Disconnect Enable Flags: 0xffff
1219 Ultra Enable Flags: 0x0001
1220 Tag Queue Enable Flags: 0x0000
1221 Ordered Queue Tag Flags: 0x0000
1222 Default Tag Queue Depth: 8
1223 Tagged Queue By Device array for aic7xxx host instance 0:
1224 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1225 Actual queue depth per device for aic7xxx host instance 0:
1226 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1229 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1230 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1231 Total transfers 160151 (74577 reads and 85574 writes)
1233 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1234 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1235 Total transfers 0 (0 reads and 0 writes)
1238 1.6 Parallel port info in /proc/parport
1239 ---------------------------------------
1241 The directory /proc/parport contains information about the parallel ports of
1242 your system. It has one subdirectory for each port, named after the port
1245 These directories contain the four files shown in Table 1-10.
1248 Table 1-10: Files in /proc/parport
1249 ..............................................................................
1251 autoprobe Any IEEE-1284 device ID information that has been acquired.
1252 devices list of the device drivers using that port. A + will appear by the
1253 name of the device currently using the port (it might not appear
1255 hardware Parallel port's base address, IRQ line and DMA channel.
1256 irq IRQ that parport is using for that port. This is in a separate
1257 file to allow you to alter it by writing a new value in (IRQ
1259 ..............................................................................
1261 1.7 TTY info in /proc/tty
1262 -------------------------
1264 Information about the available and actually used tty's can be found in the
1265 directory /proc/tty.You'll find entries for drivers and line disciplines in
1266 this directory, as shown in Table 1-11.
1269 Table 1-11: Files in /proc/tty
1270 ..............................................................................
1272 drivers list of drivers and their usage
1273 ldiscs registered line disciplines
1274 driver/serial usage statistic and status of single tty lines
1275 ..............................................................................
1277 To see which tty's are currently in use, you can simply look into the file
1280 > cat /proc/tty/drivers
1281 pty_slave /dev/pts 136 0-255 pty:slave
1282 pty_master /dev/ptm 128 0-255 pty:master
1283 pty_slave /dev/ttyp 3 0-255 pty:slave
1284 pty_master /dev/pty 2 0-255 pty:master
1285 serial /dev/cua 5 64-67 serial:callout
1286 serial /dev/ttyS 4 64-67 serial
1287 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1288 /dev/ptmx /dev/ptmx 5 2 system
1289 /dev/console /dev/console 5 1 system:console
1290 /dev/tty /dev/tty 5 0 system:/dev/tty
1291 unknown /dev/tty 4 1-63 console
1294 1.8 Miscellaneous kernel statistics in /proc/stat
1295 -------------------------------------------------
1297 Various pieces of information about kernel activity are available in the
1298 /proc/stat file. All of the numbers reported in this file are aggregates
1299 since the system first booted. For a quick look, simply cat the file:
1302 cpu 2255 34 2290 22625563 6290 127 456 0 0 0
1303 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1304 cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1305 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1311 softirq 183433 0 21755 12 39 1137 231 21459 2263
1313 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1314 lines. These numbers identify the amount of time the CPU has spent performing
1315 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1316 second). The meanings of the columns are as follows, from left to right:
1318 - user: normal processes executing in user mode
1319 - nice: niced processes executing in user mode
1320 - system: processes executing in kernel mode
1321 - idle: twiddling thumbs
1322 - iowait: waiting for I/O to complete
1323 - irq: servicing interrupts
1324 - softirq: servicing softirqs
1325 - steal: involuntary wait
1326 - guest: running a normal guest
1327 - guest_nice: running a niced guest
1329 The "intr" line gives counts of interrupts serviced since boot time, for each
1330 of the possible system interrupts. The first column is the total of all
1331 interrupts serviced including unnumbered architecture specific interrupts;
1332 each subsequent column is the total for that particular numbered interrupt.
1333 Unnumbered interrupts are not shown, only summed into the total.
1335 The "ctxt" line gives the total number of context switches across all CPUs.
1337 The "btime" line gives the time at which the system booted, in seconds since
1340 The "processes" line gives the number of processes and threads created, which
1341 includes (but is not limited to) those created by calls to the fork() and
1342 clone() system calls.
1344 The "procs_running" line gives the total number of threads that are
1345 running or ready to run (i.e., the total number of runnable threads).
1347 The "procs_blocked" line gives the number of processes currently blocked,
1348 waiting for I/O to complete.
1350 The "softirq" line gives counts of softirqs serviced since boot time, for each
1351 of the possible system softirqs. The first column is the total of all
1352 softirqs serviced; each subsequent column is the total for that particular
1356 1.9 Ext4 file system parameters
1357 -------------------------------
1359 Information about mounted ext4 file systems can be found in
1360 /proc/fs/ext4. Each mounted filesystem will have a directory in
1361 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1362 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1363 in Table 1-12, below.
1365 Table 1-12: Files in /proc/fs/ext4/<devname>
1366 ..............................................................................
1368 mb_groups details of multiblock allocator buddy cache of free blocks
1369 ..............................................................................
1373 Shows registered system console lines.
1375 To see which character device lines are currently used for the system console
1376 /dev/console, you may simply look into the file /proc/consoles:
1378 > cat /proc/consoles
1384 device name of the device
1385 operations R = can do read operations
1386 W = can do write operations
1388 flags E = it is enabled
1389 C = it is preferred console
1390 B = it is primary boot console
1391 p = it is used for printk buffer
1392 b = it is not a TTY but a Braille device
1393 a = it is safe to use when cpu is offline
1394 major:minor major and minor number of the device separated by a colon
1396 ------------------------------------------------------------------------------
1398 ------------------------------------------------------------------------------
1399 The /proc file system serves information about the running system. It not only
1400 allows access to process data but also allows you to request the kernel status
1401 by reading files in the hierarchy.
1403 The directory structure of /proc reflects the types of information and makes
1404 it easy, if not obvious, where to look for specific data.
1405 ------------------------------------------------------------------------------
1407 ------------------------------------------------------------------------------
1408 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1409 ------------------------------------------------------------------------------
1411 ------------------------------------------------------------------------------
1413 ------------------------------------------------------------------------------
1414 * Modifying kernel parameters by writing into files found in /proc/sys
1415 * Exploring the files which modify certain parameters
1416 * Review of the /proc/sys file tree
1417 ------------------------------------------------------------------------------
1420 A very interesting part of /proc is the directory /proc/sys. This is not only
1421 a source of information, it also allows you to change parameters within the
1422 kernel. Be very careful when attempting this. You can optimize your system,
1423 but you can also cause it to crash. Never alter kernel parameters on a
1424 production system. Set up a development machine and test to make sure that
1425 everything works the way you want it to. You may have no alternative but to
1426 reboot the machine once an error has been made.
1428 To change a value, simply echo the new value into the file. An example is
1429 given below in the section on the file system data. You need to be root to do
1430 this. You can create your own boot script to perform this every time your
1433 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1434 general things in the operation of the Linux kernel. Since some of the files
1435 can inadvertently disrupt your system, it is advisable to read both
1436 documentation and source before actually making adjustments. In any case, be
1437 very careful when writing to any of these files. The entries in /proc may
1438 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1439 review the kernel documentation in the directory /usr/src/linux/Documentation.
1440 This chapter is heavily based on the documentation included in the pre 2.2
1441 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1443 Please see: Documentation/sysctl/ directory for descriptions of these
1446 ------------------------------------------------------------------------------
1448 ------------------------------------------------------------------------------
1449 Certain aspects of kernel behavior can be modified at runtime, without the
1450 need to recompile the kernel, or even to reboot the system. The files in the
1451 /proc/sys tree can not only be read, but also modified. You can use the echo
1452 command to write value into these files, thereby changing the default settings
1454 ------------------------------------------------------------------------------
1456 ------------------------------------------------------------------------------
1457 CHAPTER 3: PER-PROCESS PARAMETERS
1458 ------------------------------------------------------------------------------
1460 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1461 --------------------------------------------------------------------------------
1463 These file can be used to adjust the badness heuristic used to select which
1464 process gets killed in out of memory conditions.
1466 The badness heuristic assigns a value to each candidate task ranging from 0
1467 (never kill) to 1000 (always kill) to determine which process is targeted. The
1468 units are roughly a proportion along that range of allowed memory the process
1469 may allocate from based on an estimation of its current memory and swap use.
1470 For example, if a task is using all allowed memory, its badness score will be
1471 1000. If it is using half of its allowed memory, its score will be 500.
1473 There is an additional factor included in the badness score: the current memory
1474 and swap usage is discounted by 3% for root processes.
1476 The amount of "allowed" memory depends on the context in which the oom killer
1477 was called. If it is due to the memory assigned to the allocating task's cpuset
1478 being exhausted, the allowed memory represents the set of mems assigned to that
1479 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1480 memory represents the set of mempolicy nodes. If it is due to a memory
1481 limit (or swap limit) being reached, the allowed memory is that configured
1482 limit. Finally, if it is due to the entire system being out of memory, the
1483 allowed memory represents all allocatable resources.
1485 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1486 is used to determine which task to kill. Acceptable values range from -1000
1487 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1488 polarize the preference for oom killing either by always preferring a certain
1489 task or completely disabling it. The lowest possible value, -1000, is
1490 equivalent to disabling oom killing entirely for that task since it will always
1491 report a badness score of 0.
1493 Consequently, it is very simple for userspace to define the amount of memory to
1494 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1495 example, is roughly equivalent to allowing the remainder of tasks sharing the
1496 same system, cpuset, mempolicy, or memory controller resources to use at least
1497 50% more memory. A value of -500, on the other hand, would be roughly
1498 equivalent to discounting 50% of the task's allowed memory from being considered
1499 as scoring against the task.
1501 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1502 be used to tune the badness score. Its acceptable values range from -16
1503 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1504 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1505 scaled linearly with /proc/<pid>/oom_score_adj.
1507 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1508 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1509 requires CAP_SYS_RESOURCE.
1511 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1512 generation children with separate address spaces instead, if possible. This
1513 avoids servers and important system daemons from being killed and loses the
1514 minimal amount of work.
1517 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1518 -------------------------------------------------------------
1520 This file can be used to check the current score used by the oom-killer is for
1521 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1522 process should be killed in an out-of-memory situation.
1525 3.3 /proc/<pid>/io - Display the IO accounting fields
1526 -------------------------------------------------------
1528 This file contains IO statistics for each running process
1533 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1536 test:/tmp # cat /proc/3828/io
1542 write_bytes: 323932160
1543 cancelled_write_bytes: 0
1552 I/O counter: chars read
1553 The number of bytes which this task has caused to be read from storage. This
1554 is simply the sum of bytes which this process passed to read() and pread().
1555 It includes things like tty IO and it is unaffected by whether or not actual
1556 physical disk IO was required (the read might have been satisfied from
1563 I/O counter: chars written
1564 The number of bytes which this task has caused, or shall cause to be written
1565 to disk. Similar caveats apply here as with rchar.
1571 I/O counter: read syscalls
1572 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1579 I/O counter: write syscalls
1580 Attempt to count the number of write I/O operations, i.e. syscalls like
1581 write() and pwrite().
1587 I/O counter: bytes read
1588 Attempt to count the number of bytes which this process really did cause to
1589 be fetched from the storage layer. Done at the submit_bio() level, so it is
1590 accurate for block-backed filesystems. <please add status regarding NFS and
1591 CIFS at a later time>
1597 I/O counter: bytes written
1598 Attempt to count the number of bytes which this process caused to be sent to
1599 the storage layer. This is done at page-dirtying time.
1602 cancelled_write_bytes
1603 ---------------------
1605 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1606 then deletes the file, it will in fact perform no writeout. But it will have
1607 been accounted as having caused 1MB of write.
1608 In other words: The number of bytes which this process caused to not happen,
1609 by truncating pagecache. A task can cause "negative" IO too. If this task
1610 truncates some dirty pagecache, some IO which another task has been accounted
1611 for (in its write_bytes) will not be happening. We _could_ just subtract that
1612 from the truncating task's write_bytes, but there is information loss in doing
1619 At its current implementation state, this is a bit racy on 32-bit machines: if
1620 process A reads process B's /proc/pid/io while process B is updating one of
1621 those 64-bit counters, process A could see an intermediate result.
1624 More information about this can be found within the taskstats documentation in
1625 Documentation/accounting.
1627 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1628 ---------------------------------------------------------------
1629 When a process is dumped, all anonymous memory is written to a core file as
1630 long as the size of the core file isn't limited. But sometimes we don't want
1631 to dump some memory segments, for example, huge shared memory or DAX.
1632 Conversely, sometimes we want to save file-backed memory segments into a core
1633 file, not only the individual files.
1635 /proc/<pid>/coredump_filter allows you to customize which memory segments
1636 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1637 of memory types. If a bit of the bitmask is set, memory segments of the
1638 corresponding memory type are dumped, otherwise they are not dumped.
1640 The following 9 memory types are supported:
1641 - (bit 0) anonymous private memory
1642 - (bit 1) anonymous shared memory
1643 - (bit 2) file-backed private memory
1644 - (bit 3) file-backed shared memory
1645 - (bit 4) ELF header pages in file-backed private memory areas (it is
1646 effective only if the bit 2 is cleared)
1647 - (bit 5) hugetlb private memory
1648 - (bit 6) hugetlb shared memory
1649 - (bit 7) DAX private memory
1650 - (bit 8) DAX shared memory
1652 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1653 are always dumped regardless of the bitmask status.
1655 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1656 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1658 The default value of coredump_filter is 0x33; this means all anonymous memory
1659 segments, ELF header pages and hugetlb private memory are dumped.
1661 If you don't want to dump all shared memory segments attached to pid 1234,
1662 write 0x31 to the process's proc file.
1664 $ echo 0x31 > /proc/1234/coredump_filter
1666 When a new process is created, the process inherits the bitmask status from its
1667 parent. It is useful to set up coredump_filter before the program runs.
1670 $ echo 0x7 > /proc/self/coredump_filter
1673 3.5 /proc/<pid>/mountinfo - Information about mounts
1674 --------------------------------------------------------
1676 This file contains lines of the form:
1678 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1679 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1681 (1) mount ID: unique identifier of the mount (may be reused after umount)
1682 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1683 (3) major:minor: value of st_dev for files on filesystem
1684 (4) root: root of the mount within the filesystem
1685 (5) mount point: mount point relative to the process's root
1686 (6) mount options: per mount options
1687 (7) optional fields: zero or more fields of the form "tag[:value]"
1688 (8) separator: marks the end of the optional fields
1689 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1690 (10) mount source: filesystem specific information or "none"
1691 (11) super options: per super block options
1693 Parsers should ignore all unrecognised optional fields. Currently the
1694 possible optional fields are:
1696 shared:X mount is shared in peer group X
1697 master:X mount is slave to peer group X
1698 propagate_from:X mount is slave and receives propagation from peer group X (*)
1699 unbindable mount is unbindable
1701 (*) X is the closest dominant peer group under the process's root. If
1702 X is the immediate master of the mount, or if there's no dominant peer
1703 group under the same root, then only the "master:X" field is present
1704 and not the "propagate_from:X" field.
1706 For more information on mount propagation see:
1708 Documentation/filesystems/sharedsubtree.txt
1711 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1712 --------------------------------------------------------
1713 These files provide a method to access a tasks comm value. It also allows for
1714 a task to set its own or one of its thread siblings comm value. The comm value
1715 is limited in size compared to the cmdline value, so writing anything longer
1716 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1720 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1721 -------------------------------------------------------------------------
1722 This file provides a fast way to retrieve first level children pids
1723 of a task pointed by <pid>/<tid> pair. The format is a space separated
1726 Note the "first level" here -- if a child has own children they will
1727 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1728 to obtain the descendants.
1730 Since this interface is intended to be fast and cheap it doesn't
1731 guarantee to provide precise results and some children might be
1732 skipped, especially if they've exited right after we printed their
1733 pids, so one need to either stop or freeze processes being inspected
1734 if precise results are needed.
1737 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1738 ---------------------------------------------------------------
1739 This file provides information associated with an opened file. The regular
1740 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1741 represents the current offset of the opened file in decimal form [see lseek(2)
1742 for details], 'flags' denotes the octal O_xxx mask the file has been
1743 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1744 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1753 All locks associated with a file descriptor are shown in its fdinfo too.
1755 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1757 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1758 pair provide additional information particular to the objects they represent.
1767 where 'eventfd-count' is hex value of a counter.
1774 sigmask: 0000000000000200
1776 where 'sigmask' is hex value of the signal mask associated
1784 tfd: 5 events: 1d data: ffffffffffffffff
1786 where 'tfd' is a target file descriptor number in decimal form,
1787 'events' is events mask being watched and the 'data' is data
1788 associated with a target [see epoll(7) for more details].
1792 For inotify files the format is the following
1796 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1798 where 'wd' is a watch descriptor in decimal form, ie a target file
1799 descriptor number, 'ino' and 'sdev' are inode and device where the
1800 target file resides and the 'mask' is the mask of events, all in hex
1801 form [see inotify(7) for more details].
1803 If the kernel was built with exportfs support, the path to the target
1804 file is encoded as a file handle. The file handle is provided by three
1805 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1808 If the kernel is built without exportfs support the file handle won't be
1811 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1813 For fanotify files the format is
1818 fanotify flags:10 event-flags:0
1819 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1820 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1822 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1823 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1824 flags associated with mark which are tracked separately from events
1825 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1826 mask and 'ignored_mask' is the mask of events which are to be ignored.
1827 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1828 does provide information about flags and mask used in fanotify_mark
1829 call [see fsnotify manpage for details].
1831 While the first three lines are mandatory and always printed, the rest is
1832 optional and may be omitted if no marks created yet.
1843 it_value: (0, 49406829)
1846 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1847 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1848 flags in octal form been used to setup the timer [see timerfd_settime(2) for
1849 details]. 'it_value' is remaining time until the timer exiration.
1850 'it_interval' is the interval for the timer. Note the timer might be set up
1851 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1852 still exhibits timer's remaining time.
1854 3.9 /proc/<pid>/map_files - Information about memory mapped files
1855 ---------------------------------------------------------------------
1856 This directory contains symbolic links which represent memory mapped files
1857 the process is maintaining. Example output:
1859 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1860 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1861 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1863 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1864 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1866 The name of a link represents the virtual memory bounds of a mapping, i.e.
1867 vm_area_struct::vm_start-vm_area_struct::vm_end.
1869 The main purpose of the map_files is to retrieve a set of memory mapped
1870 files in a fast way instead of parsing /proc/<pid>/maps or
1871 /proc/<pid>/smaps, both of which contain many more records. At the same
1872 time one can open(2) mappings from the listings of two processes and
1873 comparing their inode numbers to figure out which anonymous memory areas
1874 are actually shared.
1876 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
1877 ---------------------------------------------------------
1878 This file provides the value of the task's timerslack value in nanoseconds.
1879 This value specifies a amount of time that normal timers may be deferred
1880 in order to coalesce timers and avoid unnecessary wakeups.
1882 This allows a task's interactivity vs power consumption trade off to be
1885 Writing 0 to the file will set the tasks timerslack to the default value.
1887 Valid values are from 0 - ULLONG_MAX
1889 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1890 permissions on the task specified to change its timerslack_ns value.
1893 ------------------------------------------------------------------------------
1895 ------------------------------------------------------------------------------
1898 ---------------------
1900 The following mount options are supported:
1902 hidepid= Set /proc/<pid>/ access mode.
1903 gid= Set the group authorized to learn processes information.
1905 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1908 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1909 own. Sensitive files like cmdline, sched*, status are now protected against
1910 other users. This makes it impossible to learn whether any user runs
1911 specific program (given the program doesn't reveal itself by its behaviour).
1912 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1913 poorly written programs passing sensitive information via program arguments are
1914 now protected against local eavesdroppers.
1916 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1917 users. It doesn't mean that it hides a fact whether a process with a specific
1918 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1919 but it hides process' uid and gid, which may be learned by stat()'ing
1920 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1921 information about running processes, whether some daemon runs with elevated
1922 privileges, whether other user runs some sensitive program, whether other users
1923 run any program at all, etc.
1925 gid= defines a group authorized to learn processes information otherwise
1926 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1927 information about processes information, just add identd to this group.
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