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
187 SigPnd: 0000000000000000
188 ShdPnd: 0000000000000000
189 SigBlk: 0000000000000000
190 SigIgn: 0000000000000000
191 SigCgt: 0000000000000000
192 CapInh: 00000000fffffeff
193 CapPrm: 0000000000000000
194 CapEff: 0000000000000000
195 CapBnd: ffffffffffffffff
198 voluntary_ctxt_switches: 0
199 nonvoluntary_ctxt_switches: 1
201 This shows you nearly the same information you would get if you viewed it with
202 the ps command. In fact, ps uses the proc file system to obtain its
203 information. But you get a more detailed view of the process by reading the
204 file /proc/PID/status. It fields are described in table 1-2.
206 The statm file contains more detailed information about the process
207 memory usage. Its seven fields are explained in Table 1-3. The stat file
208 contains details information about the process itself. Its fields are
209 explained in Table 1-4.
211 (for SMP CONFIG users)
212 For making accounting scalable, RSS related information are handled in an
213 asynchronous manner and the value may not be very precise. To see a precise
214 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
215 It's slow but very precise.
217 Table 1-2: Contents of the status files (as of 4.8)
218 ..............................................................................
220 Name filename of the executable
221 Umask file mode creation mask
222 State state (R is running, S is sleeping, D is sleeping
223 in an uninterruptible wait, Z is zombie,
224 T is traced or stopped)
226 Ngid NUMA group ID (0 if none)
228 PPid process id of the parent process
229 TracerPid PID of process tracing this process (0 if not)
230 Uid Real, effective, saved set, and file system UIDs
231 Gid Real, effective, saved set, and file system GIDs
232 FDSize number of file descriptor slots currently allocated
233 Groups supplementary group list
234 NStgid descendant namespace thread group ID hierarchy
235 NSpid descendant namespace process ID hierarchy
236 NSpgid descendant namespace process group ID hierarchy
237 NSsid descendant namespace session ID hierarchy
238 VmPeak peak virtual memory size
239 VmSize total program size
240 VmLck locked memory size
241 VmPin pinned memory size
242 VmHWM peak resident set size ("high water mark")
243 VmRSS size of memory portions. It contains the three
244 following parts (VmRSS = RssAnon + RssFile + RssShmem)
245 RssAnon size of resident anonymous memory
246 RssFile size of resident file mappings
247 RssShmem size of resident shmem memory (includes SysV shm,
248 mapping of tmpfs and shared anonymous mappings)
249 VmData size of private data segments
250 VmStk size of stack segments
251 VmExe size of text segment
252 VmLib size of shared library code
253 VmPTE size of page table entries
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 CoreDumping process's memory is currently being dumped
258 (killing the process may lead to a corrupted core)
259 Threads number of threads
260 SigQ number of signals queued/max. number for queue
261 SigPnd bitmap of pending signals for the thread
262 ShdPnd bitmap of shared pending signals for the process
263 SigBlk bitmap of blocked signals
264 SigIgn bitmap of ignored signals
265 SigCgt bitmap of caught signals
266 CapInh bitmap of inheritable capabilities
267 CapPrm bitmap of permitted capabilities
268 CapEff bitmap of effective capabilities
269 CapBnd bitmap of capabilities bounding set
270 NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
271 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
272 Cpus_allowed mask of CPUs on which this process may run
273 Cpus_allowed_list Same as previous, but in "list format"
274 Mems_allowed mask of memory nodes allowed to this process
275 Mems_allowed_list Same as previous, but in "list format"
276 voluntary_ctxt_switches number of voluntary context switches
277 nonvoluntary_ctxt_switches number of non voluntary context switches
278 ..............................................................................
280 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
281 ..............................................................................
283 size total program size (pages) (same as VmSize in status)
284 resident size of memory portions (pages) (same as VmRSS in status)
285 shared number of pages that are shared (i.e. backed by a file, same
286 as RssFile+RssShmem in status)
287 trs number of pages that are 'code' (not including libs; broken,
288 includes data segment)
289 lrs number of pages of library (always 0 on 2.6)
290 drs number of pages of data/stack (including libs; broken,
291 includes library text)
292 dt number of dirty pages (always 0 on 2.6)
293 ..............................................................................
296 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
297 ..............................................................................
300 tcomm filename of the executable
301 state state (R is running, S is sleeping, D is sleeping in an
302 uninterruptible wait, Z is zombie, T is traced or stopped)
303 ppid process id of the parent process
304 pgrp pgrp of the process
306 tty_nr tty the process uses
307 tty_pgrp pgrp of the tty
309 min_flt number of minor faults
310 cmin_flt number of minor faults with child's
311 maj_flt number of major faults
312 cmaj_flt number of major faults with child's
313 utime user mode jiffies
314 stime kernel mode jiffies
315 cutime user mode jiffies with child's
316 cstime kernel mode jiffies with child's
317 priority priority level
319 num_threads number of threads
320 it_real_value (obsolete, always 0)
321 start_time time the process started after system boot
322 vsize virtual memory size
323 rss resident set memory size
324 rsslim current limit in bytes on the rss
325 start_code address above which program text can run
326 end_code address below which program text can run
327 start_stack address of the start of the main process stack
328 esp current value of ESP
329 eip current value of EIP
330 pending bitmap of pending signals
331 blocked bitmap of blocked signals
332 sigign bitmap of ignored signals
333 sigcatch bitmap of caught signals
334 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead)
337 exit_signal signal to send to parent thread on exit
338 task_cpu which CPU the task is scheduled on
339 rt_priority realtime priority
340 policy scheduling policy (man sched_setscheduler)
341 blkio_ticks time spent waiting for block IO
342 gtime guest time of the task in jiffies
343 cgtime guest time of the task children in jiffies
344 start_data address above which program data+bss is placed
345 end_data address below which program data+bss is placed
346 start_brk address above which program heap can be expanded with brk()
347 arg_start address above which program command line is placed
348 arg_end address below which program command line is placed
349 env_start address above which program environment is placed
350 env_end address below which program environment is placed
351 exit_code the thread's exit_code in the form reported by the waitpid system call
352 ..............................................................................
354 The /proc/PID/maps file containing the currently mapped memory regions and
355 their access permissions.
359 address perms offset dev inode pathname
361 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
362 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
363 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
364 a7cb1000-a7cb2000 ---p 00000000 00:00 0
365 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
366 a7eb2000-a7eb3000 ---p 00000000 00:00 0
367 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
368 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
369 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
370 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
371 a800b000-a800e000 rw-p 00000000 00:00 0
372 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
373 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
374 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
375 a8024000-a8027000 rw-p 00000000 00:00 0
376 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
377 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
378 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
379 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
380 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
382 where "address" is the address space in the process that it occupies, "perms"
383 is a set of permissions:
389 p = private (copy on write)
391 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
392 "inode" is the inode on that device. 0 indicates that no inode is associated
393 with the memory region, as the case would be with BSS (uninitialized data).
394 The "pathname" shows the name associated file for this mapping. If the mapping
395 is not associated with a file:
397 [heap] = the heap of the program
398 [stack] = the stack of the main process
399 [vdso] = the "virtual dynamic shared object",
400 the kernel system call handler
402 or if empty, the mapping is anonymous.
404 The /proc/PID/smaps is an extension based on maps, showing the memory
405 consumption for each of the process's mappings. For each of mappings there
406 is a series of lines such as the following:
408 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
422 Private_Hugetlb: 0 kB
429 VmFlags: rd ex mr mw me dw
431 the first of these lines shows the same information as is displayed for the
432 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
433 (size), the amount of the mapping that is currently resident in RAM (RSS), the
434 process' proportional share of this mapping (PSS), the number of clean and
435 dirty private pages in the mapping.
437 The "proportional set size" (PSS) of a process is the count of pages it has
438 in memory, where each page is divided by the number of processes sharing it.
439 So if a process has 1000 pages all to itself, and 1000 shared with one other
440 process, its PSS will be 1500.
441 Note that even a page which is part of a MAP_SHARED mapping, but has only
442 a single pte mapped, i.e. is currently used by only one process, is accounted
443 as private and not as shared.
444 "Referenced" indicates the amount of memory currently marked as referenced or
446 "Anonymous" shows the amount of memory that does not belong to any file. Even
447 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
448 and a page is modified, the file page is replaced by a private anonymous copy.
449 "LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
450 The memory isn't freed immediately with madvise(). It's freed in memory
451 pressure if the memory is clean. Please note that the printed value might
452 be lower than the real value due to optimizations used in the current
453 implementation. If this is not desirable please file a bug report.
454 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
455 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
457 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
458 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
459 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
460 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
461 For shmem mappings, "Swap" includes also the size of the mapped (and not
462 replaced by copy-on-write) part of the underlying shmem object out on swap.
463 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
464 does not take into account swapped out page of underlying shmem objects.
465 "Locked" indicates whether the mapping is locked in memory or not.
466 "THPeligible" indicates whether the mapping is eligible for THP pages - 1 if
469 "VmFlags" field deserves a separate description. This member represents the kernel
470 flags associated with the particular virtual memory area in two letter encoded
471 manner. The codes are the following:
480 gd - stack segment growns down
482 dw - disabled write to the mapped file
483 lo - pages are locked in memory
484 io - memory mapped I/O area
485 sr - sequential read advise provided
486 rr - random read advise provided
487 dc - do not copy area on fork
488 de - do not expand area on remapping
489 ac - area is accountable
490 nr - swap space is not reserved for the area
491 ht - area uses huge tlb pages
492 ar - architecture specific flag
493 dd - do not include area into core dump
496 hg - huge page advise flag
497 nh - no-huge page advise flag
498 mg - mergable advise flag
500 Note that there is no guarantee that every flag and associated mnemonic will
501 be present in all further kernel releases. Things get changed, the flags may
502 be vanished or the reverse -- new added. Interpretation of their meaning
503 might change in future as well. So each consumer of these flags has to
504 follow each specific kernel version for the exact semantic.
506 This file is only present if the CONFIG_MMU kernel configuration option is
509 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
510 output can be achieved only in the single read call).
511 This typically manifests when doing partial reads of these files while the
512 memory map is being modified. Despite the races, we do provide the following
515 1) The mapped addresses never go backwards, which implies no two
516 regions will ever overlap.
517 2) If there is something at a given vaddr during the entirety of the
518 life of the smaps/maps walk, there will be some output for it.
521 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
522 bits on both physical and virtual pages associated with a process, and the
523 soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
525 To clear the bits for all the pages associated with the process
526 > echo 1 > /proc/PID/clear_refs
528 To clear the bits for the anonymous pages associated with the process
529 > echo 2 > /proc/PID/clear_refs
531 To clear the bits for the file mapped pages associated with the process
532 > echo 3 > /proc/PID/clear_refs
534 To clear the soft-dirty bit
535 > echo 4 > /proc/PID/clear_refs
537 To reset the peak resident set size ("high water mark") to the process's
539 > echo 5 > /proc/PID/clear_refs
541 Any other value written to /proc/PID/clear_refs will have no effect.
543 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
544 using /proc/kpageflags and number of times a page is mapped using
545 /proc/kpagecount. For detailed explanation, see
546 Documentation/admin-guide/mm/pagemap.rst.
548 The /proc/pid/numa_maps is an extension based on maps, showing the memory
549 locality and binding policy, as well as the memory usage (in pages) of
550 each mapping. The output follows a general format where mapping details get
551 summarized separated by blank spaces, one mapping per each file line:
553 address policy mapping details
555 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
556 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
557 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
558 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
559 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
560 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
561 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
562 320698b000 default file=/lib64/libc-2.12.so
563 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
564 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
565 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
566 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
567 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
568 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
569 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
570 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
573 "address" is the starting address for the mapping;
574 "policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
575 "mapping details" summarizes mapping data such as mapping type, page usage counters,
576 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
577 size, in KB, that is backing the mapping up.
582 Similar to the process entries, the kernel data files give information about
583 the running kernel. The files used to obtain this information are contained in
584 /proc and are listed in Table 1-5. Not all of these will be present in your
585 system. It depends on the kernel configuration and the loaded modules, which
586 files are there, and which are missing.
588 Table 1-5: Kernel info in /proc
589 ..............................................................................
591 apm Advanced power management info
592 buddyinfo Kernel memory allocator information (see text) (2.5)
593 bus Directory containing bus specific information
594 cmdline Kernel command line
595 cpuinfo Info about the CPU
596 devices Available devices (block and character)
597 dma Used DMS channels
598 filesystems Supported filesystems
599 driver Various drivers grouped here, currently rtc (2.4)
600 execdomains Execdomains, related to security (2.4)
601 fb Frame Buffer devices (2.4)
602 fs File system parameters, currently nfs/exports (2.4)
603 ide Directory containing info about the IDE subsystem
604 interrupts Interrupt usage
605 iomem Memory map (2.4)
606 ioports I/O port usage
607 irq Masks for irq to cpu affinity (2.4)(smp?)
608 isapnp ISA PnP (Plug&Play) Info (2.4)
609 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
611 ksyms Kernel symbol table
612 loadavg Load average of last 1, 5 & 15 minutes
616 modules List of loaded modules
617 mounts Mounted filesystems
618 net Networking info (see text)
619 pagetypeinfo Additional page allocator information (see text) (2.5)
620 partitions Table of partitions known to the system
621 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
622 decoupled by lspci (2.4)
624 scsi SCSI info (see text)
625 slabinfo Slab pool info
626 softirqs softirq usage
627 stat Overall statistics
628 swaps Swap space utilization
630 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
631 tty Info of tty drivers
632 uptime Wall clock since boot, combined idle time of all cpus
633 version Kernel version
634 video bttv info of video resources (2.4)
635 vmallocinfo Show vmalloced areas
636 ..............................................................................
638 You can, for example, check which interrupts are currently in use and what
639 they are used for by looking in the file /proc/interrupts:
641 > cat /proc/interrupts
643 0: 8728810 XT-PIC timer
644 1: 895 XT-PIC keyboard
646 3: 531695 XT-PIC aha152x
647 4: 2014133 XT-PIC serial
648 5: 44401 XT-PIC pcnet_cs
651 12: 182918 XT-PIC PS/2 Mouse
653 14: 1232265 XT-PIC ide0
657 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
658 output of a SMP machine):
660 > cat /proc/interrupts
663 0: 1243498 1214548 IO-APIC-edge timer
664 1: 8949 8958 IO-APIC-edge keyboard
665 2: 0 0 XT-PIC cascade
666 5: 11286 10161 IO-APIC-edge soundblaster
667 8: 1 0 IO-APIC-edge rtc
668 9: 27422 27407 IO-APIC-edge 3c503
669 12: 113645 113873 IO-APIC-edge PS/2 Mouse
671 14: 22491 24012 IO-APIC-edge ide0
672 15: 2183 2415 IO-APIC-edge ide1
673 17: 30564 30414 IO-APIC-level eth0
674 18: 177 164 IO-APIC-level bttv
679 NMI is incremented in this case because every timer interrupt generates a NMI
680 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
682 LOC is the local interrupt counter of the internal APIC of every CPU.
684 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
685 connects the CPUs in a SMP system. This means that an error has been detected,
686 the IO-APIC automatically retry the transmission, so it should not be a big
687 problem, but you should read the SMP-FAQ.
689 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
690 /proc/interrupts to display every IRQ vector in use by the system, not
691 just those considered 'most important'. The new vectors are:
693 THR -- interrupt raised when a machine check threshold counter
694 (typically counting ECC corrected errors of memory or cache) exceeds
695 a configurable threshold. Only available on some systems.
697 TRM -- a thermal event interrupt occurs when a temperature threshold
698 has been exceeded for the CPU. This interrupt may also be generated
699 when the temperature drops back to normal.
701 SPU -- a spurious interrupt is some interrupt that was raised then lowered
702 by some IO device before it could be fully processed by the APIC. Hence
703 the APIC sees the interrupt but does not know what device it came from.
704 For this case the APIC will generate the interrupt with a IRQ vector
705 of 0xff. This might also be generated by chipset bugs.
707 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
708 sent from one CPU to another per the needs of the OS. Typically,
709 their statistics are used by kernel developers and interested users to
710 determine the occurrence of interrupts of the given type.
712 The above IRQ vectors are displayed only when relevant. For example,
713 the threshold vector does not exist on x86_64 platforms. Others are
714 suppressed when the system is a uniprocessor. As of this writing, only
715 i386 and x86_64 platforms support the new IRQ vector displays.
717 Of some interest is the introduction of the /proc/irq directory to 2.4.
718 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
719 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
720 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
725 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
726 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
730 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
731 IRQ, you can set it by doing:
733 > echo 1 > /proc/irq/10/smp_affinity
735 This means that only the first CPU will handle the IRQ, but you can also echo
736 5 which means that only the first and third CPU can handle the IRQ.
738 The contents of each smp_affinity file is the same by default:
740 > cat /proc/irq/0/smp_affinity
743 There is an alternate interface, smp_affinity_list which allows specifying
744 a cpu range instead of a bitmask:
746 > cat /proc/irq/0/smp_affinity_list
749 The default_smp_affinity mask applies to all non-active IRQs, which are the
750 IRQs which have not yet been allocated/activated, and hence which lack a
751 /proc/irq/[0-9]* directory.
753 The node file on an SMP system shows the node to which the device using the IRQ
754 reports itself as being attached. This hardware locality information does not
755 include information about any possible driver locality preference.
757 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
758 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
760 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
761 between all the CPUs which are allowed to handle it. As usual the kernel has
762 more info than you and does a better job than you, so the defaults are the
763 best choice for almost everyone. [Note this applies only to those IO-APIC's
764 that support "Round Robin" interrupt distribution.]
766 There are three more important subdirectories in /proc: net, scsi, and sys.
767 The general rule is that the contents, or even the existence of these
768 directories, depend on your kernel configuration. If SCSI is not enabled, the
769 directory scsi may not exist. The same is true with the net, which is there
770 only when networking support is present in the running kernel.
772 The slabinfo file gives information about memory usage at the slab level.
773 Linux uses slab pools for memory management above page level in version 2.2.
774 Commonly used objects have their own slab pool (such as network buffers,
775 directory cache, and so on).
777 ..............................................................................
779 > cat /proc/buddyinfo
781 Node 0, zone DMA 0 4 5 4 4 3 ...
782 Node 0, zone Normal 1 0 0 1 101 8 ...
783 Node 0, zone HighMem 2 0 0 1 1 0 ...
785 External fragmentation is a problem under some workloads, and buddyinfo is a
786 useful tool for helping diagnose these problems. Buddyinfo will give you a
787 clue as to how big an area you can safely allocate, or why a previous
790 Each column represents the number of pages of a certain order which are
791 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
792 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
793 available in ZONE_NORMAL, etc...
795 More information relevant to external fragmentation can be found in
798 > cat /proc/pagetypeinfo
802 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
803 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
804 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
805 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
806 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
807 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
808 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
809 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
810 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
811 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
812 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
814 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
815 Node 0, zone DMA 2 0 5 1 0
816 Node 0, zone DMA32 41 6 967 2 0
818 Fragmentation avoidance in the kernel works by grouping pages of different
819 migrate types into the same contiguous regions of memory called page blocks.
820 A page block is typically the size of the default hugepage size e.g. 2MB on
821 X86-64. By keeping pages grouped based on their ability to move, the kernel
822 can reclaim pages within a page block to satisfy a high-order allocation.
824 The pagetypinfo begins with information on the size of a page block. It
825 then gives the same type of information as buddyinfo except broken down
826 by migrate-type and finishes with details on how many page blocks of each
829 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
830 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
831 make an estimate of the likely number of huge pages that can be allocated
832 at a given point in time. All the "Movable" blocks should be allocatable
833 unless memory has been mlock()'d. Some of the Reclaimable blocks should
834 also be allocatable although a lot of filesystem metadata may have to be
835 reclaimed to achieve this.
837 ..............................................................................
841 Provides information about distribution and utilization of memory. This
842 varies by architecture and compile options. The following is from a
843 16GB PIII, which has highmem enabled. You may not have all of these fields.
847 MemTotal: 16344972 kB
849 MemAvailable: 14836172 kB
855 HighTotal: 15597528 kB
856 HighFree: 13629632 kB
867 SReclaimable: 159856 kB
868 SUnreclaim: 124508 kB
873 CommitLimit: 7669796 kB
874 Committed_AS: 100056 kB
875 VmallocTotal: 112216 kB
877 VmallocChunk: 111088 kB
879 HardwareCorrupted: 0 kB
880 AnonHugePages: 49152 kB
885 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
886 bits and the kernel binary code)
887 MemFree: The sum of LowFree+HighFree
888 MemAvailable: An estimate of how much memory is available for starting new
889 applications, without swapping. Calculated from MemFree,
890 SReclaimable, the size of the file LRU lists, and the low
891 watermarks in each zone.
892 The estimate takes into account that the system needs some
893 page cache to function well, and that not all reclaimable
894 slab will be reclaimable, due to items being in use. The
895 impact of those factors will vary from system to system.
896 Buffers: Relatively temporary storage for raw disk blocks
897 shouldn't get tremendously large (20MB or so)
898 Cached: in-memory cache for files read from the disk (the
899 pagecache). Doesn't include SwapCached
900 SwapCached: Memory that once was swapped out, is swapped back in but
901 still also is in the swapfile (if memory is needed it
902 doesn't need to be swapped out AGAIN because it is already
903 in the swapfile. This saves I/O)
904 Active: Memory that has been used more recently and usually not
905 reclaimed unless absolutely necessary.
906 Inactive: Memory which has been less recently used. It is more
907 eligible to be reclaimed for other purposes
909 HighFree: Highmem is all memory above ~860MB of physical memory
910 Highmem areas are for use by userspace programs, or
911 for the pagecache. The kernel must use tricks to access
912 this memory, making it slower to access than lowmem.
914 LowFree: Lowmem is memory which can be used for everything that
915 highmem can be used for, but it is also available for the
916 kernel's use for its own data structures. Among many
917 other things, it is where everything from the Slab is
918 allocated. Bad things happen when you're out of lowmem.
919 SwapTotal: total amount of swap space available
920 SwapFree: Memory which has been evicted from RAM, and is temporarily
922 Dirty: Memory which is waiting to get written back to the disk
923 Writeback: Memory which is actively being written back to the disk
924 AnonPages: Non-file backed pages mapped into userspace page tables
925 HardwareCorrupted: The amount of RAM/memory in KB, the kernel identifies as
927 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
928 Mapped: files which have been mmaped, such as libraries
929 Shmem: Total memory used by shared memory (shmem) and tmpfs
930 ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
932 ShmemPmdMapped: Shared memory mapped into userspace with huge pages
933 Slab: in-kernel data structures cache
934 SReclaimable: Part of Slab, that might be reclaimed, such as caches
935 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
936 PageTables: amount of memory dedicated to the lowest level of page
938 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
940 Bounce: Memory used for block device "bounce buffers"
941 WritebackTmp: Memory used by FUSE for temporary writeback buffers
942 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
943 this is the total amount of memory currently available to
944 be allocated on the system. This limit is only adhered to
945 if strict overcommit accounting is enabled (mode 2 in
946 'vm.overcommit_memory').
947 The CommitLimit is calculated with the following formula:
948 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
949 overcommit_ratio / 100 + [total swap pages]
950 For example, on a system with 1G of physical RAM and 7G
951 of swap with a `vm.overcommit_ratio` of 30 it would
952 yield a CommitLimit of 7.3G.
953 For more details, see the memory overcommit documentation
954 in vm/overcommit-accounting.
955 Committed_AS: The amount of memory presently allocated on the system.
956 The committed memory is a sum of all of the memory which
957 has been allocated by processes, even if it has not been
958 "used" by them as of yet. A process which malloc()'s 1G
959 of memory, but only touches 300M of it will show up as
960 using 1G. This 1G is memory which has been "committed" to
961 by the VM and can be used at any time by the allocating
962 application. With strict overcommit enabled on the system
963 (mode 2 in 'vm.overcommit_memory'),allocations which would
964 exceed the CommitLimit (detailed above) will not be permitted.
965 This is useful if one needs to guarantee that processes will
966 not fail due to lack of memory once that memory has been
967 successfully allocated.
968 VmallocTotal: total size of vmalloc memory area
969 VmallocUsed: amount of vmalloc area which is used
970 VmallocChunk: largest contiguous block of vmalloc area which is free
971 Percpu: Memory allocated to the percpu allocator used to back percpu
972 allocations. This stat excludes the cost of metadata.
974 ..............................................................................
978 Provides information about vmalloced/vmaped areas. One line per area,
979 containing the virtual address range of the area, size in bytes,
980 caller information of the creator, and optional information depending
981 on the kind of area :
983 pages=nr number of pages
984 phys=addr if a physical address was specified
985 ioremap I/O mapping (ioremap() and friends)
986 vmalloc vmalloc() area
989 vpages buffer for pages pointers was vmalloced (huge area)
990 N<node>=nr (Only on NUMA kernels)
991 Number of pages allocated on memory node <node>
993 > cat /proc/vmallocinfo
994 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
995 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
996 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
997 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
998 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
999 phys=7fee8000 ioremap
1000 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
1001 phys=7fee7000 ioremap
1002 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
1003 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
1004 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1005 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
1006 pages=2 vmalloc N1=2
1007 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
1008 /0x130 [x_tables] pages=4 vmalloc N0=4
1009 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
1010 pages=14 vmalloc N2=14
1011 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
1012 pages=4 vmalloc N1=4
1013 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
1014 pages=2 vmalloc N1=2
1015 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
1016 pages=10 vmalloc N0=10
1018 ..............................................................................
1022 Provides counts of softirq handlers serviced since boot time, for each cpu.
1024 > cat /proc/softirqs
1027 TIMER: 27166 27120 27097 27034
1032 SCHED: 27035 26983 26971 26746
1034 RCU: 1678 1769 2178 2250
1037 1.3 IDE devices in /proc/ide
1038 ----------------------------
1040 The subdirectory /proc/ide contains information about all IDE devices of which
1041 the kernel is aware. There is one subdirectory for each IDE controller, the
1042 file drivers and a link for each IDE device, pointing to the device directory
1043 in the controller specific subtree.
1045 The file drivers contains general information about the drivers used for the
1048 > cat /proc/ide/drivers
1049 ide-cdrom version 4.53
1050 ide-disk version 1.08
1052 More detailed information can be found in the controller specific
1053 subdirectories. These are named ide0, ide1 and so on. Each of these
1054 directories contains the files shown in table 1-6.
1057 Table 1-6: IDE controller info in /proc/ide/ide?
1058 ..............................................................................
1060 channel IDE channel (0 or 1)
1061 config Configuration (only for PCI/IDE bridge)
1063 model Type/Chipset of IDE controller
1064 ..............................................................................
1066 Each device connected to a controller has a separate subdirectory in the
1067 controllers directory. The files listed in table 1-7 are contained in these
1071 Table 1-7: IDE device information
1072 ..............................................................................
1075 capacity Capacity of the medium (in 512Byte blocks)
1076 driver driver and version
1077 geometry physical and logical geometry
1078 identify device identify block
1080 model device identifier
1081 settings device setup
1082 smart_thresholds IDE disk management thresholds
1083 smart_values IDE disk management values
1084 ..............................................................................
1086 The most interesting file is settings. This file contains a nice overview of
1087 the drive parameters:
1089 # cat /proc/ide/ide0/hda/settings
1090 name value min max mode
1091 ---- ----- --- --- ----
1092 bios_cyl 526 0 65535 rw
1093 bios_head 255 0 255 rw
1094 bios_sect 63 0 63 rw
1095 breada_readahead 4 0 127 rw
1097 file_readahead 72 0 2097151 rw
1099 keepsettings 0 0 1 rw
1100 max_kb_per_request 122 1 127 rw
1104 pio_mode write-only 0 255 w
1110 1.4 Networking info in /proc/net
1111 --------------------------------
1113 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1114 additional values you get for IP version 6 if you configure the kernel to
1115 support this. Table 1-9 lists the files and their meaning.
1118 Table 1-8: IPv6 info in /proc/net
1119 ..............................................................................
1121 udp6 UDP sockets (IPv6)
1122 tcp6 TCP sockets (IPv6)
1123 raw6 Raw device statistics (IPv6)
1124 igmp6 IP multicast addresses, which this host joined (IPv6)
1125 if_inet6 List of IPv6 interface addresses
1126 ipv6_route Kernel routing table for IPv6
1127 rt6_stats Global IPv6 routing tables statistics
1128 sockstat6 Socket statistics (IPv6)
1129 snmp6 Snmp data (IPv6)
1130 ..............................................................................
1133 Table 1-9: Network info in /proc/net
1134 ..............................................................................
1136 arp Kernel ARP table
1137 dev network devices with statistics
1138 dev_mcast the Layer2 multicast groups a device is listening too
1139 (interface index, label, number of references, number of bound
1141 dev_stat network device status
1142 ip_fwchains Firewall chain linkage
1143 ip_fwnames Firewall chain names
1144 ip_masq Directory containing the masquerading tables
1145 ip_masquerade Major masquerading table
1146 netstat Network statistics
1147 raw raw device statistics
1148 route Kernel routing table
1149 rpc Directory containing rpc info
1150 rt_cache Routing cache
1152 sockstat Socket statistics
1155 unix UNIX domain sockets
1156 wireless Wireless interface data (Wavelan etc)
1157 igmp IP multicast addresses, which this host joined
1158 psched Global packet scheduler parameters.
1159 netlink List of PF_NETLINK sockets
1160 ip_mr_vifs List of multicast virtual interfaces
1161 ip_mr_cache List of multicast routing cache
1162 ..............................................................................
1164 You can use this information to see which network devices are available in
1165 your system and how much traffic was routed over those devices:
1168 Inter-|Receive |[...
1169 face |bytes packets errs drop fifo frame compressed multicast|[...
1170 lo: 908188 5596 0 0 0 0 0 0 [...
1171 ppp0:15475140 20721 410 0 0 410 0 0 [...
1172 eth0: 614530 7085 0 0 0 0 0 1 [...
1175 ...] bytes packets errs drop fifo colls carrier compressed
1176 ...] 908188 5596 0 0 0 0 0 0
1177 ...] 1375103 17405 0 0 0 0 0 0
1178 ...] 1703981 5535 0 0 0 3 0 0
1180 In addition, each Channel Bond interface has its own directory. For
1181 example, the bond0 device will have a directory called /proc/net/bond0/.
1182 It will contain information that is specific to that bond, such as the
1183 current slaves of the bond, the link status of the slaves, and how
1184 many times the slaves link has failed.
1189 If you have a SCSI host adapter in your system, you'll find a subdirectory
1190 named after the driver for this adapter in /proc/scsi. You'll also see a list
1191 of all recognized SCSI devices in /proc/scsi:
1193 >cat /proc/scsi/scsi
1195 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1196 Vendor: IBM Model: DGHS09U Rev: 03E0
1197 Type: Direct-Access ANSI SCSI revision: 03
1198 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1199 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1200 Type: CD-ROM ANSI SCSI revision: 02
1203 The directory named after the driver has one file for each adapter found in
1204 the system. These files contain information about the controller, including
1205 the used IRQ and the IO address range. The amount of information shown is
1206 dependent on the adapter you use. The example shows the output for an Adaptec
1207 AHA-2940 SCSI adapter:
1209 > cat /proc/scsi/aic7xxx/0
1211 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1213 TCQ Enabled By Default : Disabled
1214 AIC7XXX_PROC_STATS : Disabled
1215 AIC7XXX_RESET_DELAY : 5
1216 Adapter Configuration:
1217 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1218 Ultra Wide Controller
1219 PCI MMAPed I/O Base: 0xeb001000
1220 Adapter SEEPROM Config: SEEPROM found and used.
1221 Adaptec SCSI BIOS: Enabled
1223 SCBs: Active 0, Max Active 2,
1224 Allocated 15, HW 16, Page 255
1226 BIOS Control Word: 0x18b6
1227 Adapter Control Word: 0x005b
1228 Extended Translation: Enabled
1229 Disconnect Enable Flags: 0xffff
1230 Ultra Enable Flags: 0x0001
1231 Tag Queue Enable Flags: 0x0000
1232 Ordered Queue Tag Flags: 0x0000
1233 Default Tag Queue Depth: 8
1234 Tagged Queue By Device array for aic7xxx host instance 0:
1235 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1236 Actual queue depth per device for aic7xxx host instance 0:
1237 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1240 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1241 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1242 Total transfers 160151 (74577 reads and 85574 writes)
1244 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1245 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1246 Total transfers 0 (0 reads and 0 writes)
1249 1.6 Parallel port info in /proc/parport
1250 ---------------------------------------
1252 The directory /proc/parport contains information about the parallel ports of
1253 your system. It has one subdirectory for each port, named after the port
1256 These directories contain the four files shown in Table 1-10.
1259 Table 1-10: Files in /proc/parport
1260 ..............................................................................
1262 autoprobe Any IEEE-1284 device ID information that has been acquired.
1263 devices list of the device drivers using that port. A + will appear by the
1264 name of the device currently using the port (it might not appear
1266 hardware Parallel port's base address, IRQ line and DMA channel.
1267 irq IRQ that parport is using for that port. This is in a separate
1268 file to allow you to alter it by writing a new value in (IRQ
1270 ..............................................................................
1272 1.7 TTY info in /proc/tty
1273 -------------------------
1275 Information about the available and actually used tty's can be found in the
1276 directory /proc/tty.You'll find entries for drivers and line disciplines in
1277 this directory, as shown in Table 1-11.
1280 Table 1-11: Files in /proc/tty
1281 ..............................................................................
1283 drivers list of drivers and their usage
1284 ldiscs registered line disciplines
1285 driver/serial usage statistic and status of single tty lines
1286 ..............................................................................
1288 To see which tty's are currently in use, you can simply look into the file
1291 > cat /proc/tty/drivers
1292 pty_slave /dev/pts 136 0-255 pty:slave
1293 pty_master /dev/ptm 128 0-255 pty:master
1294 pty_slave /dev/ttyp 3 0-255 pty:slave
1295 pty_master /dev/pty 2 0-255 pty:master
1296 serial /dev/cua 5 64-67 serial:callout
1297 serial /dev/ttyS 4 64-67 serial
1298 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1299 /dev/ptmx /dev/ptmx 5 2 system
1300 /dev/console /dev/console 5 1 system:console
1301 /dev/tty /dev/tty 5 0 system:/dev/tty
1302 unknown /dev/tty 4 1-63 console
1305 1.8 Miscellaneous kernel statistics in /proc/stat
1306 -------------------------------------------------
1308 Various pieces of information about kernel activity are available in the
1309 /proc/stat file. All of the numbers reported in this file are aggregates
1310 since the system first booted. For a quick look, simply cat the file:
1313 cpu 2255 34 2290 22625563 6290 127 456 0 0 0
1314 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1315 cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1316 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1322 softirq 183433 0 21755 12 39 1137 231 21459 2263
1324 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1325 lines. These numbers identify the amount of time the CPU has spent performing
1326 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1327 second). The meanings of the columns are as follows, from left to right:
1329 - user: normal processes executing in user mode
1330 - nice: niced processes executing in user mode
1331 - system: processes executing in kernel mode
1332 - idle: twiddling thumbs
1333 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
1334 are several problems:
1335 1. Cpu will not wait for I/O to complete, iowait is the time that a task is
1336 waiting for I/O to complete. When cpu goes into idle state for
1337 outstanding task io, another task will be scheduled on this CPU.
1338 2. In a multi-core CPU, the task waiting for I/O to complete is not running
1339 on any CPU, so the iowait of each CPU is difficult to calculate.
1340 3. The value of iowait field in /proc/stat will decrease in certain
1342 So, the iowait is not reliable by reading from /proc/stat.
1343 - irq: servicing interrupts
1344 - softirq: servicing softirqs
1345 - steal: involuntary wait
1346 - guest: running a normal guest
1347 - guest_nice: running a niced guest
1349 The "intr" line gives counts of interrupts serviced since boot time, for each
1350 of the possible system interrupts. The first column is the total of all
1351 interrupts serviced including unnumbered architecture specific interrupts;
1352 each subsequent column is the total for that particular numbered interrupt.
1353 Unnumbered interrupts are not shown, only summed into the total.
1355 The "ctxt" line gives the total number of context switches across all CPUs.
1357 The "btime" line gives the time at which the system booted, in seconds since
1360 The "processes" line gives the number of processes and threads created, which
1361 includes (but is not limited to) those created by calls to the fork() and
1362 clone() system calls.
1364 The "procs_running" line gives the total number of threads that are
1365 running or ready to run (i.e., the total number of runnable threads).
1367 The "procs_blocked" line gives the number of processes currently blocked,
1368 waiting for I/O to complete.
1370 The "softirq" line gives counts of softirqs serviced since boot time, for each
1371 of the possible system softirqs. The first column is the total of all
1372 softirqs serviced; each subsequent column is the total for that particular
1376 1.9 Ext4 file system parameters
1377 -------------------------------
1379 Information about mounted ext4 file systems can be found in
1380 /proc/fs/ext4. Each mounted filesystem will have a directory in
1381 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1382 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1383 in Table 1-12, below.
1385 Table 1-12: Files in /proc/fs/ext4/<devname>
1386 ..............................................................................
1388 mb_groups details of multiblock allocator buddy cache of free blocks
1389 ..............................................................................
1393 Shows registered system console lines.
1395 To see which character device lines are currently used for the system console
1396 /dev/console, you may simply look into the file /proc/consoles:
1398 > cat /proc/consoles
1404 device name of the device
1405 operations R = can do read operations
1406 W = can do write operations
1408 flags E = it is enabled
1409 C = it is preferred console
1410 B = it is primary boot console
1411 p = it is used for printk buffer
1412 b = it is not a TTY but a Braille device
1413 a = it is safe to use when cpu is offline
1414 major:minor major and minor number of the device separated by a colon
1416 ------------------------------------------------------------------------------
1418 ------------------------------------------------------------------------------
1419 The /proc file system serves information about the running system. It not only
1420 allows access to process data but also allows you to request the kernel status
1421 by reading files in the hierarchy.
1423 The directory structure of /proc reflects the types of information and makes
1424 it easy, if not obvious, where to look for specific data.
1425 ------------------------------------------------------------------------------
1427 ------------------------------------------------------------------------------
1428 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1429 ------------------------------------------------------------------------------
1431 ------------------------------------------------------------------------------
1433 ------------------------------------------------------------------------------
1434 * Modifying kernel parameters by writing into files found in /proc/sys
1435 * Exploring the files which modify certain parameters
1436 * Review of the /proc/sys file tree
1437 ------------------------------------------------------------------------------
1440 A very interesting part of /proc is the directory /proc/sys. This is not only
1441 a source of information, it also allows you to change parameters within the
1442 kernel. Be very careful when attempting this. You can optimize your system,
1443 but you can also cause it to crash. Never alter kernel parameters on a
1444 production system. Set up a development machine and test to make sure that
1445 everything works the way you want it to. You may have no alternative but to
1446 reboot the machine once an error has been made.
1448 To change a value, simply echo the new value into the file. An example is
1449 given below in the section on the file system data. You need to be root to do
1450 this. You can create your own boot script to perform this every time your
1453 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1454 general things in the operation of the Linux kernel. Since some of the files
1455 can inadvertently disrupt your system, it is advisable to read both
1456 documentation and source before actually making adjustments. In any case, be
1457 very careful when writing to any of these files. The entries in /proc may
1458 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1459 review the kernel documentation in the directory /usr/src/linux/Documentation.
1460 This chapter is heavily based on the documentation included in the pre 2.2
1461 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1463 Please see: Documentation/sysctl/ directory for descriptions of these
1466 ------------------------------------------------------------------------------
1468 ------------------------------------------------------------------------------
1469 Certain aspects of kernel behavior can be modified at runtime, without the
1470 need to recompile the kernel, or even to reboot the system. The files in the
1471 /proc/sys tree can not only be read, but also modified. You can use the echo
1472 command to write value into these files, thereby changing the default settings
1474 ------------------------------------------------------------------------------
1476 ------------------------------------------------------------------------------
1477 CHAPTER 3: PER-PROCESS PARAMETERS
1478 ------------------------------------------------------------------------------
1480 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1481 --------------------------------------------------------------------------------
1483 These file can be used to adjust the badness heuristic used to select which
1484 process gets killed in out of memory conditions.
1486 The badness heuristic assigns a value to each candidate task ranging from 0
1487 (never kill) to 1000 (always kill) to determine which process is targeted. The
1488 units are roughly a proportion along that range of allowed memory the process
1489 may allocate from based on an estimation of its current memory and swap use.
1490 For example, if a task is using all allowed memory, its badness score will be
1491 1000. If it is using half of its allowed memory, its score will be 500.
1493 There is an additional factor included in the badness score: the current memory
1494 and swap usage is discounted by 3% for root processes.
1496 The amount of "allowed" memory depends on the context in which the oom killer
1497 was called. If it is due to the memory assigned to the allocating task's cpuset
1498 being exhausted, the allowed memory represents the set of mems assigned to that
1499 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1500 memory represents the set of mempolicy nodes. If it is due to a memory
1501 limit (or swap limit) being reached, the allowed memory is that configured
1502 limit. Finally, if it is due to the entire system being out of memory, the
1503 allowed memory represents all allocatable resources.
1505 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1506 is used to determine which task to kill. Acceptable values range from -1000
1507 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1508 polarize the preference for oom killing either by always preferring a certain
1509 task or completely disabling it. The lowest possible value, -1000, is
1510 equivalent to disabling oom killing entirely for that task since it will always
1511 report a badness score of 0.
1513 Consequently, it is very simple for userspace to define the amount of memory to
1514 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1515 example, is roughly equivalent to allowing the remainder of tasks sharing the
1516 same system, cpuset, mempolicy, or memory controller resources to use at least
1517 50% more memory. A value of -500, on the other hand, would be roughly
1518 equivalent to discounting 50% of the task's allowed memory from being considered
1519 as scoring against the task.
1521 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1522 be used to tune the badness score. Its acceptable values range from -16
1523 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1524 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1525 scaled linearly with /proc/<pid>/oom_score_adj.
1527 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1528 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1529 requires CAP_SYS_RESOURCE.
1531 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1532 generation children with separate address spaces instead, if possible. This
1533 avoids servers and important system daemons from being killed and loses the
1534 minimal amount of work.
1537 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1538 -------------------------------------------------------------
1540 This file can be used to check the current score used by the oom-killer is for
1541 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1542 process should be killed in an out-of-memory situation.
1545 3.3 /proc/<pid>/io - Display the IO accounting fields
1546 -------------------------------------------------------
1548 This file contains IO statistics for each running process
1553 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1556 test:/tmp # cat /proc/3828/io
1562 write_bytes: 323932160
1563 cancelled_write_bytes: 0
1572 I/O counter: chars read
1573 The number of bytes which this task has caused to be read from storage. This
1574 is simply the sum of bytes which this process passed to read() and pread().
1575 It includes things like tty IO and it is unaffected by whether or not actual
1576 physical disk IO was required (the read might have been satisfied from
1583 I/O counter: chars written
1584 The number of bytes which this task has caused, or shall cause to be written
1585 to disk. Similar caveats apply here as with rchar.
1591 I/O counter: read syscalls
1592 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1599 I/O counter: write syscalls
1600 Attempt to count the number of write I/O operations, i.e. syscalls like
1601 write() and pwrite().
1607 I/O counter: bytes read
1608 Attempt to count the number of bytes which this process really did cause to
1609 be fetched from the storage layer. Done at the submit_bio() level, so it is
1610 accurate for block-backed filesystems. <please add status regarding NFS and
1611 CIFS at a later time>
1617 I/O counter: bytes written
1618 Attempt to count the number of bytes which this process caused to be sent to
1619 the storage layer. This is done at page-dirtying time.
1622 cancelled_write_bytes
1623 ---------------------
1625 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1626 then deletes the file, it will in fact perform no writeout. But it will have
1627 been accounted as having caused 1MB of write.
1628 In other words: The number of bytes which this process caused to not happen,
1629 by truncating pagecache. A task can cause "negative" IO too. If this task
1630 truncates some dirty pagecache, some IO which another task has been accounted
1631 for (in its write_bytes) will not be happening. We _could_ just subtract that
1632 from the truncating task's write_bytes, but there is information loss in doing
1639 At its current implementation state, this is a bit racy on 32-bit machines: if
1640 process A reads process B's /proc/pid/io while process B is updating one of
1641 those 64-bit counters, process A could see an intermediate result.
1644 More information about this can be found within the taskstats documentation in
1645 Documentation/accounting.
1647 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1648 ---------------------------------------------------------------
1649 When a process is dumped, all anonymous memory is written to a core file as
1650 long as the size of the core file isn't limited. But sometimes we don't want
1651 to dump some memory segments, for example, huge shared memory or DAX.
1652 Conversely, sometimes we want to save file-backed memory segments into a core
1653 file, not only the individual files.
1655 /proc/<pid>/coredump_filter allows you to customize which memory segments
1656 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1657 of memory types. If a bit of the bitmask is set, memory segments of the
1658 corresponding memory type are dumped, otherwise they are not dumped.
1660 The following 9 memory types are supported:
1661 - (bit 0) anonymous private memory
1662 - (bit 1) anonymous shared memory
1663 - (bit 2) file-backed private memory
1664 - (bit 3) file-backed shared memory
1665 - (bit 4) ELF header pages in file-backed private memory areas (it is
1666 effective only if the bit 2 is cleared)
1667 - (bit 5) hugetlb private memory
1668 - (bit 6) hugetlb shared memory
1669 - (bit 7) DAX private memory
1670 - (bit 8) DAX shared memory
1672 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1673 are always dumped regardless of the bitmask status.
1675 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1676 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1678 The default value of coredump_filter is 0x33; this means all anonymous memory
1679 segments, ELF header pages and hugetlb private memory are dumped.
1681 If you don't want to dump all shared memory segments attached to pid 1234,
1682 write 0x31 to the process's proc file.
1684 $ echo 0x31 > /proc/1234/coredump_filter
1686 When a new process is created, the process inherits the bitmask status from its
1687 parent. It is useful to set up coredump_filter before the program runs.
1690 $ echo 0x7 > /proc/self/coredump_filter
1693 3.5 /proc/<pid>/mountinfo - Information about mounts
1694 --------------------------------------------------------
1696 This file contains lines of the form:
1698 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1699 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1701 (1) mount ID: unique identifier of the mount (may be reused after umount)
1702 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1703 (3) major:minor: value of st_dev for files on filesystem
1704 (4) root: root of the mount within the filesystem
1705 (5) mount point: mount point relative to the process's root
1706 (6) mount options: per mount options
1707 (7) optional fields: zero or more fields of the form "tag[:value]"
1708 (8) separator: marks the end of the optional fields
1709 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1710 (10) mount source: filesystem specific information or "none"
1711 (11) super options: per super block options
1713 Parsers should ignore all unrecognised optional fields. Currently the
1714 possible optional fields are:
1716 shared:X mount is shared in peer group X
1717 master:X mount is slave to peer group X
1718 propagate_from:X mount is slave and receives propagation from peer group X (*)
1719 unbindable mount is unbindable
1721 (*) X is the closest dominant peer group under the process's root. If
1722 X is the immediate master of the mount, or if there's no dominant peer
1723 group under the same root, then only the "master:X" field is present
1724 and not the "propagate_from:X" field.
1726 For more information on mount propagation see:
1728 Documentation/filesystems/sharedsubtree.txt
1731 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1732 --------------------------------------------------------
1733 These files provide a method to access a tasks comm value. It also allows for
1734 a task to set its own or one of its thread siblings comm value. The comm value
1735 is limited in size compared to the cmdline value, so writing anything longer
1736 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1740 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1741 -------------------------------------------------------------------------
1742 This file provides a fast way to retrieve first level children pids
1743 of a task pointed by <pid>/<tid> pair. The format is a space separated
1746 Note the "first level" here -- if a child has own children they will
1747 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1748 to obtain the descendants.
1750 Since this interface is intended to be fast and cheap it doesn't
1751 guarantee to provide precise results and some children might be
1752 skipped, especially if they've exited right after we printed their
1753 pids, so one need to either stop or freeze processes being inspected
1754 if precise results are needed.
1757 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1758 ---------------------------------------------------------------
1759 This file provides information associated with an opened file. The regular
1760 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1761 represents the current offset of the opened file in decimal form [see lseek(2)
1762 for details], 'flags' denotes the octal O_xxx mask the file has been
1763 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1764 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1773 All locks associated with a file descriptor are shown in its fdinfo too.
1775 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1777 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1778 pair provide additional information particular to the objects they represent.
1787 where 'eventfd-count' is hex value of a counter.
1794 sigmask: 0000000000000200
1796 where 'sigmask' is hex value of the signal mask associated
1804 tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1806 where 'tfd' is a target file descriptor number in decimal form,
1807 'events' is events mask being watched and the 'data' is data
1808 associated with a target [see epoll(7) for more details].
1810 The 'pos' is current offset of the target file in decimal form
1811 [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1812 where target file resides, all in hex format.
1816 For inotify files the format is the following
1820 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1822 where 'wd' is a watch descriptor in decimal form, ie a target file
1823 descriptor number, 'ino' and 'sdev' are inode and device where the
1824 target file resides and the 'mask' is the mask of events, all in hex
1825 form [see inotify(7) for more details].
1827 If the kernel was built with exportfs support, the path to the target
1828 file is encoded as a file handle. The file handle is provided by three
1829 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1832 If the kernel is built without exportfs support the file handle won't be
1835 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1837 For fanotify files the format is
1842 fanotify flags:10 event-flags:0
1843 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1844 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1846 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1847 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1848 flags associated with mark which are tracked separately from events
1849 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1850 mask and 'ignored_mask' is the mask of events which are to be ignored.
1851 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1852 does provide information about flags and mask used in fanotify_mark
1853 call [see fsnotify manpage for details].
1855 While the first three lines are mandatory and always printed, the rest is
1856 optional and may be omitted if no marks created yet.
1867 it_value: (0, 49406829)
1870 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1871 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1872 flags in octal form been used to setup the timer [see timerfd_settime(2) for
1873 details]. 'it_value' is remaining time until the timer exiration.
1874 'it_interval' is the interval for the timer. Note the timer might be set up
1875 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1876 still exhibits timer's remaining time.
1878 3.9 /proc/<pid>/map_files - Information about memory mapped files
1879 ---------------------------------------------------------------------
1880 This directory contains symbolic links which represent memory mapped files
1881 the process is maintaining. Example output:
1883 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1884 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1885 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1887 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1888 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1890 The name of a link represents the virtual memory bounds of a mapping, i.e.
1891 vm_area_struct::vm_start-vm_area_struct::vm_end.
1893 The main purpose of the map_files is to retrieve a set of memory mapped
1894 files in a fast way instead of parsing /proc/<pid>/maps or
1895 /proc/<pid>/smaps, both of which contain many more records. At the same
1896 time one can open(2) mappings from the listings of two processes and
1897 comparing their inode numbers to figure out which anonymous memory areas
1898 are actually shared.
1900 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
1901 ---------------------------------------------------------
1902 This file provides the value of the task's timerslack value in nanoseconds.
1903 This value specifies a amount of time that normal timers may be deferred
1904 in order to coalesce timers and avoid unnecessary wakeups.
1906 This allows a task's interactivity vs power consumption trade off to be
1909 Writing 0 to the file will set the tasks timerslack to the default value.
1911 Valid values are from 0 - ULLONG_MAX
1913 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1914 permissions on the task specified to change its timerslack_ns value.
1916 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
1917 -----------------------------------------------------------------
1918 When CONFIG_LIVEPATCH is enabled, this file displays the value of the
1919 patch state for the task.
1921 A value of '-1' indicates that no patch is in transition.
1923 A value of '0' indicates that a patch is in transition and the task is
1924 unpatched. If the patch is being enabled, then the task hasn't been
1925 patched yet. If the patch is being disabled, then the task has already
1928 A value of '1' indicates that a patch is in transition and the task is
1929 patched. If the patch is being enabled, then the task has already been
1930 patched. If the patch is being disabled, then the task hasn't been
1934 ------------------------------------------------------------------------------
1936 ------------------------------------------------------------------------------
1939 ---------------------
1941 The following mount options are supported:
1943 hidepid= Set /proc/<pid>/ access mode.
1944 gid= Set the group authorized to learn processes information.
1946 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1949 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1950 own. Sensitive files like cmdline, sched*, status are now protected against
1951 other users. This makes it impossible to learn whether any user runs
1952 specific program (given the program doesn't reveal itself by its behaviour).
1953 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1954 poorly written programs passing sensitive information via program arguments are
1955 now protected against local eavesdroppers.
1957 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1958 users. It doesn't mean that it hides a fact whether a process with a specific
1959 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1960 but it hides process' uid and gid, which may be learned by stat()'ing
1961 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1962 information about running processes, whether some daemon runs with elevated
1963 privileges, whether other user runs some sensitive program, whether other users
1964 run any program at all, etc.
1966 gid= defines a group authorized to learn processes information otherwise
1967 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1968 information about processes information, just add identd to this group.
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