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 FDSize number of file descriptor slots currently allocated
229 Groups supplementary group list
230 NStgid descendant namespace thread group ID hierarchy
231 NSpid descendant namespace process ID hierarchy
232 NSpgid descendant namespace process group ID hierarchy
233 NSsid descendant namespace session ID hierarchy
234 VmPeak peak virtual memory size
235 VmSize total program size
236 VmLck locked memory size
237 VmHWM peak resident set size ("high water mark")
238 VmRSS size of memory portions. It contains the three
239 following parts (VmRSS = RssAnon + RssFile + RssShmem)
240 RssAnon size of resident anonymous memory
241 RssFile size of resident file mappings
242 RssShmem size of resident shmem memory (includes SysV shm,
243 mapping of tmpfs and shared anonymous mappings)
244 VmData size of private data segments
245 VmStk size of stack segments
246 VmExe size of text segment
247 VmLib size of shared library code
248 VmPTE size of page table entries
249 VmPMD size of second level page tables
250 VmSwap amount of swap used by anonymous private data
251 (shmem swap usage is not included)
252 HugetlbPages size of hugetlb memory portions
253 Threads number of threads
254 SigQ number of signals queued/max. number for queue
255 SigPnd bitmap of pending signals for the thread
256 ShdPnd bitmap of shared pending signals for the process
257 SigBlk bitmap of blocked signals
258 SigIgn bitmap of ignored signals
259 SigCgt bitmap of caught signals
260 CapInh bitmap of inheritable capabilities
261 CapPrm bitmap of permitted capabilities
262 CapEff bitmap of effective capabilities
263 CapBnd bitmap of capabilities bounding set
264 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
265 Cpus_allowed mask of CPUs on which this process may run
266 Cpus_allowed_list Same as previous, but in "list format"
267 Mems_allowed mask of memory nodes allowed to this process
268 Mems_allowed_list Same as previous, but in "list format"
269 voluntary_ctxt_switches number of voluntary context switches
270 nonvoluntary_ctxt_switches number of non voluntary context switches
271 ..............................................................................
273 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
274 ..............................................................................
276 size total program size (pages) (same as VmSize in status)
277 resident size of memory portions (pages) (same as VmRSS in status)
278 shared number of pages that are shared (i.e. backed by a file, same
279 as RssFile+RssShmem in status)
280 trs number of pages that are 'code' (not including libs; broken,
281 includes data segment)
282 lrs number of pages of library (always 0 on 2.6)
283 drs number of pages of data/stack (including libs; broken,
284 includes library text)
285 dt number of dirty pages (always 0 on 2.6)
286 ..............................................................................
289 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
290 ..............................................................................
293 tcomm filename of the executable
294 state state (R is running, S is sleeping, D is sleeping in an
295 uninterruptible wait, Z is zombie, T is traced or stopped)
296 ppid process id of the parent process
297 pgrp pgrp of the process
299 tty_nr tty the process uses
300 tty_pgrp pgrp of the tty
302 min_flt number of minor faults
303 cmin_flt number of minor faults with child's
304 maj_flt number of major faults
305 cmaj_flt number of major faults with child's
306 utime user mode jiffies
307 stime kernel mode jiffies
308 cutime user mode jiffies with child's
309 cstime kernel mode jiffies with child's
310 priority priority level
312 num_threads number of threads
313 it_real_value (obsolete, always 0)
314 start_time time the process started after system boot
315 vsize virtual memory size
316 rss resident set memory size
317 rsslim current limit in bytes on the rss
318 start_code address above which program text can run
319 end_code address below which program text can run
320 start_stack address of the start of the main process stack
321 esp current value of ESP
322 eip current value of EIP
323 pending bitmap of pending signals
324 blocked bitmap of blocked signals
325 sigign bitmap of ignored signals
326 sigcatch bitmap of caught signals
327 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead)
330 exit_signal signal to send to parent thread on exit
331 task_cpu which CPU the task is scheduled on
332 rt_priority realtime priority
333 policy scheduling policy (man sched_setscheduler)
334 blkio_ticks time spent waiting for block IO
335 gtime guest time of the task in jiffies
336 cgtime guest time of the task children in jiffies
337 start_data address above which program data+bss is placed
338 end_data address below which program data+bss is placed
339 start_brk address above which program heap can be expanded with brk()
340 arg_start address above which program command line is placed
341 arg_end address below which program command line is placed
342 env_start address above which program environment is placed
343 env_end address below which program environment is placed
344 exit_code the thread's exit_code in the form reported by the waitpid system call
345 ..............................................................................
347 The /proc/PID/maps file containing the currently mapped memory regions and
348 their access permissions.
352 address perms offset dev inode pathname
354 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
355 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
356 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
357 a7cb1000-a7cb2000 ---p 00000000 00:00 0
358 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
359 a7eb2000-a7eb3000 ---p 00000000 00:00 0
360 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
361 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
362 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
363 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
364 a800b000-a800e000 rw-p 00000000 00:00 0
365 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
366 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
367 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
368 a8024000-a8027000 rw-p 00000000 00:00 0
369 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
370 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
371 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
372 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
373 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
375 where "address" is the address space in the process that it occupies, "perms"
376 is a set of permissions:
382 p = private (copy on write)
384 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
385 "inode" is the inode on that device. 0 indicates that no inode is associated
386 with the memory region, as the case would be with BSS (uninitialized data).
387 The "pathname" shows the name associated file for this mapping. If the mapping
388 is not associated with a file:
390 [heap] = the heap of the program
391 [stack] = the stack of the main process
392 [vdso] = the "virtual dynamic shared object",
393 the kernel system call handler
395 or if empty, the mapping is anonymous.
397 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
398 of the individual tasks of a process. In this file you will see a mapping marked
399 as [stack] if that task sees it as a stack. Hence, for the example above, the
400 task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
402 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
403 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
404 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
405 a7cb1000-a7cb2000 ---p 00000000 00:00 0
406 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
407 a7eb2000-a7eb3000 ---p 00000000 00:00 0
408 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack]
409 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
410 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
411 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
412 a800b000-a800e000 rw-p 00000000 00:00 0
413 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
414 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
415 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
416 a8024000-a8027000 rw-p 00000000 00:00 0
417 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
418 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
419 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
420 aff35000-aff4a000 rw-p 00000000 00:00 0
421 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
423 The /proc/PID/smaps is an extension based on maps, showing the memory
424 consumption for each of the process's mappings. For each of mappings there
425 is a series of lines such as the following:
427 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
439 Private_Hugetlb: 0 kB
445 VmFlags: rd ex mr mw me dw
447 the first of these lines shows the same information as is displayed for the
448 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
449 (size), the amount of the mapping that is currently resident in RAM (RSS), the
450 process' proportional share of this mapping (PSS), the number of clean and
451 dirty private pages in the mapping.
453 The "proportional set size" (PSS) of a process is the count of pages it has
454 in memory, where each page is divided by the number of processes sharing it.
455 So if a process has 1000 pages all to itself, and 1000 shared with one other
456 process, its PSS will be 1500.
457 Note that even a page which is part of a MAP_SHARED mapping, but has only
458 a single pte mapped, i.e. is currently used by only one process, is accounted
459 as private and not as shared.
460 "Referenced" indicates the amount of memory currently marked as referenced or
462 "Anonymous" shows the amount of memory that does not belong to any file. Even
463 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
464 and a page is modified, the file page is replaced by a private anonymous copy.
465 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
466 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
467 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
468 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
469 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
470 For shmem mappings, "Swap" includes also the size of the mapped (and not
471 replaced by copy-on-write) part of the underlying shmem object out on swap.
472 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
473 does not take into account swapped out page of underlying shmem objects.
474 "Locked" indicates whether the mapping is locked in memory or not.
476 "VmFlags" field deserves a separate description. This member represents the kernel
477 flags associated with the particular virtual memory area in two letter encoded
478 manner. The codes are the following:
487 gd - stack segment growns down
489 dw - disabled write to the mapped file
490 lo - pages are locked in memory
491 io - memory mapped I/O area
492 sr - sequential read advise provided
493 rr - random read advise provided
494 dc - do not copy area on fork
495 de - do not expand area on remapping
496 ac - area is accountable
497 nr - swap space is not reserved for the area
498 ht - area uses huge tlb pages
499 ar - architecture specific flag
500 dd - do not include area into core dump
503 hg - huge page advise flag
504 nh - no-huge page advise flag
505 mg - mergable advise flag
507 Note that there is no guarantee that every flag and associated mnemonic will
508 be present in all further kernel releases. Things get changed, the flags may
509 be vanished or the reverse -- new added.
511 This file is only present if the CONFIG_MMU kernel configuration option is
514 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
515 bits on both physical and virtual pages associated with a process, and the
516 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
517 To clear the bits for all the pages associated with the process
518 > echo 1 > /proc/PID/clear_refs
520 To clear the bits for the anonymous pages associated with the process
521 > echo 2 > /proc/PID/clear_refs
523 To clear the bits for the file mapped pages associated with the process
524 > echo 3 > /proc/PID/clear_refs
526 To clear the soft-dirty bit
527 > echo 4 > /proc/PID/clear_refs
529 To reset the peak resident set size ("high water mark") to the process's
531 > echo 5 > /proc/PID/clear_refs
533 Any other value written to /proc/PID/clear_refs will have no effect.
535 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
536 using /proc/kpageflags and number of times a page is mapped using
537 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
539 The /proc/pid/numa_maps is an extension based on maps, showing the memory
540 locality and binding policy, as well as the memory usage (in pages) of
541 each mapping. The output follows a general format where mapping details get
542 summarized separated by blank spaces, one mapping per each file line:
544 address policy mapping details
546 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
547 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
548 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
549 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
550 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
551 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
552 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
553 320698b000 default file=/lib64/libc-2.12.so
554 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
555 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
556 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
557 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
558 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
559 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
560 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
561 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
564 "address" is the starting address for the mapping;
565 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
566 "mapping details" summarizes mapping data such as mapping type, page usage counters,
567 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
568 size, in KB, that is backing the mapping up.
573 Similar to the process entries, the kernel data files give information about
574 the running kernel. The files used to obtain this information are contained in
575 /proc and are listed in Table 1-5. Not all of these will be present in your
576 system. It depends on the kernel configuration and the loaded modules, which
577 files are there, and which are missing.
579 Table 1-5: Kernel info in /proc
580 ..............................................................................
582 apm Advanced power management info
583 buddyinfo Kernel memory allocator information (see text) (2.5)
584 bus Directory containing bus specific information
585 cmdline Kernel command line
586 cpuinfo Info about the CPU
587 devices Available devices (block and character)
588 dma Used DMS channels
589 filesystems Supported filesystems
590 driver Various drivers grouped here, currently rtc (2.4)
591 execdomains Execdomains, related to security (2.4)
592 fb Frame Buffer devices (2.4)
593 fs File system parameters, currently nfs/exports (2.4)
594 ide Directory containing info about the IDE subsystem
595 interrupts Interrupt usage
596 iomem Memory map (2.4)
597 ioports I/O port usage
598 irq Masks for irq to cpu affinity (2.4)(smp?)
599 isapnp ISA PnP (Plug&Play) Info (2.4)
600 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
602 ksyms Kernel symbol table
603 loadavg Load average of last 1, 5 & 15 minutes
607 modules List of loaded modules
608 mounts Mounted filesystems
609 net Networking info (see text)
610 pagetypeinfo Additional page allocator information (see text) (2.5)
611 partitions Table of partitions known to the system
612 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
613 decoupled by lspci (2.4)
615 scsi SCSI info (see text)
616 slabinfo Slab pool info
617 softirqs softirq usage
618 stat Overall statistics
619 swaps Swap space utilization
621 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
622 tty Info of tty drivers
623 uptime Wall clock since boot, combined idle time of all cpus
624 version Kernel version
625 video bttv info of video resources (2.4)
626 vmallocinfo Show vmalloced areas
627 ..............................................................................
629 You can, for example, check which interrupts are currently in use and what
630 they are used for by looking in the file /proc/interrupts:
632 > cat /proc/interrupts
634 0: 8728810 XT-PIC timer
635 1: 895 XT-PIC keyboard
637 3: 531695 XT-PIC aha152x
638 4: 2014133 XT-PIC serial
639 5: 44401 XT-PIC pcnet_cs
642 12: 182918 XT-PIC PS/2 Mouse
644 14: 1232265 XT-PIC ide0
648 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
649 output of a SMP machine):
651 > cat /proc/interrupts
654 0: 1243498 1214548 IO-APIC-edge timer
655 1: 8949 8958 IO-APIC-edge keyboard
656 2: 0 0 XT-PIC cascade
657 5: 11286 10161 IO-APIC-edge soundblaster
658 8: 1 0 IO-APIC-edge rtc
659 9: 27422 27407 IO-APIC-edge 3c503
660 12: 113645 113873 IO-APIC-edge PS/2 Mouse
662 14: 22491 24012 IO-APIC-edge ide0
663 15: 2183 2415 IO-APIC-edge ide1
664 17: 30564 30414 IO-APIC-level eth0
665 18: 177 164 IO-APIC-level bttv
670 NMI is incremented in this case because every timer interrupt generates a NMI
671 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
673 LOC is the local interrupt counter of the internal APIC of every CPU.
675 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
676 connects the CPUs in a SMP system. This means that an error has been detected,
677 the IO-APIC automatically retry the transmission, so it should not be a big
678 problem, but you should read the SMP-FAQ.
680 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
681 /proc/interrupts to display every IRQ vector in use by the system, not
682 just those considered 'most important'. The new vectors are:
684 THR -- interrupt raised when a machine check threshold counter
685 (typically counting ECC corrected errors of memory or cache) exceeds
686 a configurable threshold. Only available on some systems.
688 TRM -- a thermal event interrupt occurs when a temperature threshold
689 has been exceeded for the CPU. This interrupt may also be generated
690 when the temperature drops back to normal.
692 SPU -- a spurious interrupt is some interrupt that was raised then lowered
693 by some IO device before it could be fully processed by the APIC. Hence
694 the APIC sees the interrupt but does not know what device it came from.
695 For this case the APIC will generate the interrupt with a IRQ vector
696 of 0xff. This might also be generated by chipset bugs.
698 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
699 sent from one CPU to another per the needs of the OS. Typically,
700 their statistics are used by kernel developers and interested users to
701 determine the occurrence of interrupts of the given type.
703 The above IRQ vectors are displayed only when relevant. For example,
704 the threshold vector does not exist on x86_64 platforms. Others are
705 suppressed when the system is a uniprocessor. As of this writing, only
706 i386 and x86_64 platforms support the new IRQ vector displays.
708 Of some interest is the introduction of the /proc/irq directory to 2.4.
709 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
710 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
711 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
716 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
717 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
721 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
722 IRQ, you can set it by doing:
724 > echo 1 > /proc/irq/10/smp_affinity
726 This means that only the first CPU will handle the IRQ, but you can also echo
727 5 which means that only the first and fourth CPU can handle the IRQ.
729 The contents of each smp_affinity file is the same by default:
731 > cat /proc/irq/0/smp_affinity
734 There is an alternate interface, smp_affinity_list which allows specifying
735 a cpu range instead of a bitmask:
737 > cat /proc/irq/0/smp_affinity_list
740 The default_smp_affinity mask applies to all non-active IRQs, which are the
741 IRQs which have not yet been allocated/activated, and hence which lack a
742 /proc/irq/[0-9]* directory.
744 The node file on an SMP system shows the node to which the device using the IRQ
745 reports itself as being attached. This hardware locality information does not
746 include information about any possible driver locality preference.
748 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
749 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
751 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
752 between all the CPUs which are allowed to handle it. As usual the kernel has
753 more info than you and does a better job than you, so the defaults are the
754 best choice for almost everyone. [Note this applies only to those IO-APIC's
755 that support "Round Robin" interrupt distribution.]
757 There are three more important subdirectories in /proc: net, scsi, and sys.
758 The general rule is that the contents, or even the existence of these
759 directories, depend on your kernel configuration. If SCSI is not enabled, the
760 directory scsi may not exist. The same is true with the net, which is there
761 only when networking support is present in the running kernel.
763 The slabinfo file gives information about memory usage at the slab level.
764 Linux uses slab pools for memory management above page level in version 2.2.
765 Commonly used objects have their own slab pool (such as network buffers,
766 directory cache, and so on).
768 ..............................................................................
770 > cat /proc/buddyinfo
772 Node 0, zone DMA 0 4 5 4 4 3 ...
773 Node 0, zone Normal 1 0 0 1 101 8 ...
774 Node 0, zone HighMem 2 0 0 1 1 0 ...
776 External fragmentation is a problem under some workloads, and buddyinfo is a
777 useful tool for helping diagnose these problems. Buddyinfo will give you a
778 clue as to how big an area you can safely allocate, or why a previous
781 Each column represents the number of pages of a certain order which are
782 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
783 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
784 available in ZONE_NORMAL, etc...
786 More information relevant to external fragmentation can be found in
789 > cat /proc/pagetypeinfo
793 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
794 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
795 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
796 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
797 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
798 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
799 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
800 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
801 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
802 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
803 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
805 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
806 Node 0, zone DMA 2 0 5 1 0
807 Node 0, zone DMA32 41 6 967 2 0
809 Fragmentation avoidance in the kernel works by grouping pages of different
810 migrate types into the same contiguous regions of memory called page blocks.
811 A page block is typically the size of the default hugepage size e.g. 2MB on
812 X86-64. By keeping pages grouped based on their ability to move, the kernel
813 can reclaim pages within a page block to satisfy a high-order allocation.
815 The pagetypinfo begins with information on the size of a page block. It
816 then gives the same type of information as buddyinfo except broken down
817 by migrate-type and finishes with details on how many page blocks of each
820 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
821 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
822 make an estimate of the likely number of huge pages that can be allocated
823 at a given point in time. All the "Movable" blocks should be allocatable
824 unless memory has been mlock()'d. Some of the Reclaimable blocks should
825 also be allocatable although a lot of filesystem metadata may have to be
826 reclaimed to achieve this.
828 ..............................................................................
832 Provides information about distribution and utilization of memory. This
833 varies by architecture and compile options. The following is from a
834 16GB PIII, which has highmem enabled. You may not have all of these fields.
838 MemTotal: 16344972 kB
840 MemAvailable: 14836172 kB
846 HighTotal: 15597528 kB
847 HighFree: 13629632 kB
858 SReclaimable: 159856 kB
859 SUnreclaim: 124508 kB
864 CommitLimit: 7669796 kB
865 Committed_AS: 100056 kB
866 VmallocTotal: 112216 kB
868 VmallocChunk: 111088 kB
869 AnonHugePages: 49152 kB
871 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
872 bits and the kernel binary code)
873 MemFree: The sum of LowFree+HighFree
874 MemAvailable: An estimate of how much memory is available for starting new
875 applications, without swapping. Calculated from MemFree,
876 SReclaimable, the size of the file LRU lists, and the low
877 watermarks in each zone.
878 The estimate takes into account that the system needs some
879 page cache to function well, and that not all reclaimable
880 slab will be reclaimable, due to items being in use. The
881 impact of those factors will vary from system to system.
882 Buffers: Relatively temporary storage for raw disk blocks
883 shouldn't get tremendously large (20MB or so)
884 Cached: in-memory cache for files read from the disk (the
885 pagecache). Doesn't include SwapCached
886 SwapCached: Memory that once was swapped out, is swapped back in but
887 still also is in the swapfile (if memory is needed it
888 doesn't need to be swapped out AGAIN because it is already
889 in the swapfile. This saves I/O)
890 Active: Memory that has been used more recently and usually not
891 reclaimed unless absolutely necessary.
892 Inactive: Memory which has been less recently used. It is more
893 eligible to be reclaimed for other purposes
895 HighFree: Highmem is all memory above ~860MB of physical memory
896 Highmem areas are for use by userspace programs, or
897 for the pagecache. The kernel must use tricks to access
898 this memory, making it slower to access than lowmem.
900 LowFree: Lowmem is memory which can be used for everything that
901 highmem can be used for, but it is also available for the
902 kernel's use for its own data structures. Among many
903 other things, it is where everything from the Slab is
904 allocated. Bad things happen when you're out of lowmem.
905 SwapTotal: total amount of swap space available
906 SwapFree: Memory which has been evicted from RAM, and is temporarily
908 Dirty: Memory which is waiting to get written back to the disk
909 Writeback: Memory which is actively being written back to the disk
910 AnonPages: Non-file backed pages mapped into userspace page tables
911 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
912 Mapped: files which have been mmaped, such as libraries
913 Shmem: Total memory used by shared memory (shmem) and tmpfs
914 Slab: in-kernel data structures cache
915 SReclaimable: Part of Slab, that might be reclaimed, such as caches
916 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
917 PageTables: amount of memory dedicated to the lowest level of page
919 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
921 Bounce: Memory used for block device "bounce buffers"
922 WritebackTmp: Memory used by FUSE for temporary writeback buffers
923 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
924 this is the total amount of memory currently available to
925 be allocated on the system. This limit is only adhered to
926 if strict overcommit accounting is enabled (mode 2 in
927 'vm.overcommit_memory').
928 The CommitLimit is calculated with the following formula:
929 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
930 overcommit_ratio / 100 + [total swap pages]
931 For example, on a system with 1G of physical RAM and 7G
932 of swap with a `vm.overcommit_ratio` of 30 it would
933 yield a CommitLimit of 7.3G.
934 For more details, see the memory overcommit documentation
935 in vm/overcommit-accounting.
936 Committed_AS: The amount of memory presently allocated on the system.
937 The committed memory is a sum of all of the memory which
938 has been allocated by processes, even if it has not been
939 "used" by them as of yet. A process which malloc()'s 1G
940 of memory, but only touches 300M of it will show up as
941 using 1G. This 1G is memory which has been "committed" to
942 by the VM and can be used at any time by the allocating
943 application. With strict overcommit enabled on the system
944 (mode 2 in 'vm.overcommit_memory'),allocations which would
945 exceed the CommitLimit (detailed above) will not be permitted.
946 This is useful if one needs to guarantee that processes will
947 not fail due to lack of memory once that memory has been
948 successfully allocated.
949 VmallocTotal: total size of vmalloc memory area
950 VmallocUsed: amount of vmalloc area which is used
951 VmallocChunk: largest contiguous block of vmalloc area which is free
953 ..............................................................................
957 Provides information about vmalloced/vmaped areas. One line per area,
958 containing the virtual address range of the area, size in bytes,
959 caller information of the creator, and optional information depending
960 on the kind of area :
962 pages=nr number of pages
963 phys=addr if a physical address was specified
964 ioremap I/O mapping (ioremap() and friends)
965 vmalloc vmalloc() area
968 vpages buffer for pages pointers was vmalloced (huge area)
969 N<node>=nr (Only on NUMA kernels)
970 Number of pages allocated on memory node <node>
972 > cat /proc/vmallocinfo
973 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
974 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
975 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
976 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
977 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
978 phys=7fee8000 ioremap
979 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
980 phys=7fee7000 ioremap
981 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
982 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
983 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
984 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
986 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
987 /0x130 [x_tables] pages=4 vmalloc N0=4
988 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
989 pages=14 vmalloc N2=14
990 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
992 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
994 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
995 pages=10 vmalloc N0=10
997 ..............................................................................
1001 Provides counts of softirq handlers serviced since boot time, for each cpu.
1003 > cat /proc/softirqs
1006 TIMER: 27166 27120 27097 27034
1011 SCHED: 27035 26983 26971 26746
1013 RCU: 1678 1769 2178 2250
1016 1.3 IDE devices in /proc/ide
1017 ----------------------------
1019 The subdirectory /proc/ide contains information about all IDE devices of which
1020 the kernel is aware. There is one subdirectory for each IDE controller, the
1021 file drivers and a link for each IDE device, pointing to the device directory
1022 in the controller specific subtree.
1024 The file drivers contains general information about the drivers used for the
1027 > cat /proc/ide/drivers
1028 ide-cdrom version 4.53
1029 ide-disk version 1.08
1031 More detailed information can be found in the controller specific
1032 subdirectories. These are named ide0, ide1 and so on. Each of these
1033 directories contains the files shown in table 1-6.
1036 Table 1-6: IDE controller info in /proc/ide/ide?
1037 ..............................................................................
1039 channel IDE channel (0 or 1)
1040 config Configuration (only for PCI/IDE bridge)
1042 model Type/Chipset of IDE controller
1043 ..............................................................................
1045 Each device connected to a controller has a separate subdirectory in the
1046 controllers directory. The files listed in table 1-7 are contained in these
1050 Table 1-7: IDE device information
1051 ..............................................................................
1054 capacity Capacity of the medium (in 512Byte blocks)
1055 driver driver and version
1056 geometry physical and logical geometry
1057 identify device identify block
1059 model device identifier
1060 settings device setup
1061 smart_thresholds IDE disk management thresholds
1062 smart_values IDE disk management values
1063 ..............................................................................
1065 The most interesting file is settings. This file contains a nice overview of
1066 the drive parameters:
1068 # cat /proc/ide/ide0/hda/settings
1069 name value min max mode
1070 ---- ----- --- --- ----
1071 bios_cyl 526 0 65535 rw
1072 bios_head 255 0 255 rw
1073 bios_sect 63 0 63 rw
1074 breada_readahead 4 0 127 rw
1076 file_readahead 72 0 2097151 rw
1078 keepsettings 0 0 1 rw
1079 max_kb_per_request 122 1 127 rw
1083 pio_mode write-only 0 255 w
1089 1.4 Networking info in /proc/net
1090 --------------------------------
1092 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1093 additional values you get for IP version 6 if you configure the kernel to
1094 support this. Table 1-9 lists the files and their meaning.
1097 Table 1-8: IPv6 info in /proc/net
1098 ..............................................................................
1100 udp6 UDP sockets (IPv6)
1101 tcp6 TCP sockets (IPv6)
1102 raw6 Raw device statistics (IPv6)
1103 igmp6 IP multicast addresses, which this host joined (IPv6)
1104 if_inet6 List of IPv6 interface addresses
1105 ipv6_route Kernel routing table for IPv6
1106 rt6_stats Global IPv6 routing tables statistics
1107 sockstat6 Socket statistics (IPv6)
1108 snmp6 Snmp data (IPv6)
1109 ..............................................................................
1112 Table 1-9: Network info in /proc/net
1113 ..............................................................................
1115 arp Kernel ARP table
1116 dev network devices with statistics
1117 dev_mcast the Layer2 multicast groups a device is listening too
1118 (interface index, label, number of references, number of bound
1120 dev_stat network device status
1121 ip_fwchains Firewall chain linkage
1122 ip_fwnames Firewall chain names
1123 ip_masq Directory containing the masquerading tables
1124 ip_masquerade Major masquerading table
1125 netstat Network statistics
1126 raw raw device statistics
1127 route Kernel routing table
1128 rpc Directory containing rpc info
1129 rt_cache Routing cache
1131 sockstat Socket statistics
1134 unix UNIX domain sockets
1135 wireless Wireless interface data (Wavelan etc)
1136 igmp IP multicast addresses, which this host joined
1137 psched Global packet scheduler parameters.
1138 netlink List of PF_NETLINK sockets
1139 ip_mr_vifs List of multicast virtual interfaces
1140 ip_mr_cache List of multicast routing cache
1141 ..............................................................................
1143 You can use this information to see which network devices are available in
1144 your system and how much traffic was routed over those devices:
1147 Inter-|Receive |[...
1148 face |bytes packets errs drop fifo frame compressed multicast|[...
1149 lo: 908188 5596 0 0 0 0 0 0 [...
1150 ppp0:15475140 20721 410 0 0 410 0 0 [...
1151 eth0: 614530 7085 0 0 0 0 0 1 [...
1154 ...] bytes packets errs drop fifo colls carrier compressed
1155 ...] 908188 5596 0 0 0 0 0 0
1156 ...] 1375103 17405 0 0 0 0 0 0
1157 ...] 1703981 5535 0 0 0 3 0 0
1159 In addition, each Channel Bond interface has its own directory. For
1160 example, the bond0 device will have a directory called /proc/net/bond0/.
1161 It will contain information that is specific to that bond, such as the
1162 current slaves of the bond, the link status of the slaves, and how
1163 many times the slaves link has failed.
1168 If you have a SCSI host adapter in your system, you'll find a subdirectory
1169 named after the driver for this adapter in /proc/scsi. You'll also see a list
1170 of all recognized SCSI devices in /proc/scsi:
1172 >cat /proc/scsi/scsi
1174 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1175 Vendor: IBM Model: DGHS09U Rev: 03E0
1176 Type: Direct-Access ANSI SCSI revision: 03
1177 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1178 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1179 Type: CD-ROM ANSI SCSI revision: 02
1182 The directory named after the driver has one file for each adapter found in
1183 the system. These files contain information about the controller, including
1184 the used IRQ and the IO address range. The amount of information shown is
1185 dependent on the adapter you use. The example shows the output for an Adaptec
1186 AHA-2940 SCSI adapter:
1188 > cat /proc/scsi/aic7xxx/0
1190 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1192 TCQ Enabled By Default : Disabled
1193 AIC7XXX_PROC_STATS : Disabled
1194 AIC7XXX_RESET_DELAY : 5
1195 Adapter Configuration:
1196 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1197 Ultra Wide Controller
1198 PCI MMAPed I/O Base: 0xeb001000
1199 Adapter SEEPROM Config: SEEPROM found and used.
1200 Adaptec SCSI BIOS: Enabled
1202 SCBs: Active 0, Max Active 2,
1203 Allocated 15, HW 16, Page 255
1205 BIOS Control Word: 0x18b6
1206 Adapter Control Word: 0x005b
1207 Extended Translation: Enabled
1208 Disconnect Enable Flags: 0xffff
1209 Ultra Enable Flags: 0x0001
1210 Tag Queue Enable Flags: 0x0000
1211 Ordered Queue Tag Flags: 0x0000
1212 Default Tag Queue Depth: 8
1213 Tagged Queue By Device array for aic7xxx host instance 0:
1214 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1215 Actual queue depth per device for aic7xxx host instance 0:
1216 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1219 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1220 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1221 Total transfers 160151 (74577 reads and 85574 writes)
1223 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1224 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1225 Total transfers 0 (0 reads and 0 writes)
1228 1.6 Parallel port info in /proc/parport
1229 ---------------------------------------
1231 The directory /proc/parport contains information about the parallel ports of
1232 your system. It has one subdirectory for each port, named after the port
1235 These directories contain the four files shown in Table 1-10.
1238 Table 1-10: Files in /proc/parport
1239 ..............................................................................
1241 autoprobe Any IEEE-1284 device ID information that has been acquired.
1242 devices list of the device drivers using that port. A + will appear by the
1243 name of the device currently using the port (it might not appear
1245 hardware Parallel port's base address, IRQ line and DMA channel.
1246 irq IRQ that parport is using for that port. This is in a separate
1247 file to allow you to alter it by writing a new value in (IRQ
1249 ..............................................................................
1251 1.7 TTY info in /proc/tty
1252 -------------------------
1254 Information about the available and actually used tty's can be found in the
1255 directory /proc/tty.You'll find entries for drivers and line disciplines in
1256 this directory, as shown in Table 1-11.
1259 Table 1-11: Files in /proc/tty
1260 ..............................................................................
1262 drivers list of drivers and their usage
1263 ldiscs registered line disciplines
1264 driver/serial usage statistic and status of single tty lines
1265 ..............................................................................
1267 To see which tty's are currently in use, you can simply look into the file
1270 > cat /proc/tty/drivers
1271 pty_slave /dev/pts 136 0-255 pty:slave
1272 pty_master /dev/ptm 128 0-255 pty:master
1273 pty_slave /dev/ttyp 3 0-255 pty:slave
1274 pty_master /dev/pty 2 0-255 pty:master
1275 serial /dev/cua 5 64-67 serial:callout
1276 serial /dev/ttyS 4 64-67 serial
1277 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1278 /dev/ptmx /dev/ptmx 5 2 system
1279 /dev/console /dev/console 5 1 system:console
1280 /dev/tty /dev/tty 5 0 system:/dev/tty
1281 unknown /dev/tty 4 1-63 console
1284 1.8 Miscellaneous kernel statistics in /proc/stat
1285 -------------------------------------------------
1287 Various pieces of information about kernel activity are available in the
1288 /proc/stat file. All of the numbers reported in this file are aggregates
1289 since the system first booted. For a quick look, simply cat the file:
1292 cpu 2255 34 2290 22625563 6290 127 456 0 0 0
1293 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1294 cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1295 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1301 softirq 183433 0 21755 12 39 1137 231 21459 2263
1303 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1304 lines. These numbers identify the amount of time the CPU has spent performing
1305 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1306 second). The meanings of the columns are as follows, from left to right:
1308 - user: normal processes executing in user mode
1309 - nice: niced processes executing in user mode
1310 - system: processes executing in kernel mode
1311 - idle: twiddling thumbs
1312 - iowait: waiting for I/O to complete
1313 - irq: servicing interrupts
1314 - softirq: servicing softirqs
1315 - steal: involuntary wait
1316 - guest: running a normal guest
1317 - guest_nice: running a niced guest
1319 The "intr" line gives counts of interrupts serviced since boot time, for each
1320 of the possible system interrupts. The first column is the total of all
1321 interrupts serviced including unnumbered architecture specific interrupts;
1322 each subsequent column is the total for that particular numbered interrupt.
1323 Unnumbered interrupts are not shown, only summed into the total.
1325 The "ctxt" line gives the total number of context switches across all CPUs.
1327 The "btime" line gives the time at which the system booted, in seconds since
1330 The "processes" line gives the number of processes and threads created, which
1331 includes (but is not limited to) those created by calls to the fork() and
1332 clone() system calls.
1334 The "procs_running" line gives the total number of threads that are
1335 running or ready to run (i.e., the total number of runnable threads).
1337 The "procs_blocked" line gives the number of processes currently blocked,
1338 waiting for I/O to complete.
1340 The "softirq" line gives counts of softirqs serviced since boot time, for each
1341 of the possible system softirqs. The first column is the total of all
1342 softirqs serviced; each subsequent column is the total for that particular
1346 1.9 Ext4 file system parameters
1347 -------------------------------
1349 Information about mounted ext4 file systems can be found in
1350 /proc/fs/ext4. Each mounted filesystem will have a directory in
1351 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1352 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1353 in Table 1-12, below.
1355 Table 1-12: Files in /proc/fs/ext4/<devname>
1356 ..............................................................................
1358 mb_groups details of multiblock allocator buddy cache of free blocks
1359 ..............................................................................
1363 Shows registered system console lines.
1365 To see which character device lines are currently used for the system console
1366 /dev/console, you may simply look into the file /proc/consoles:
1368 > cat /proc/consoles
1374 device name of the device
1375 operations R = can do read operations
1376 W = can do write operations
1378 flags E = it is enabled
1379 C = it is preferred console
1380 B = it is primary boot console
1381 p = it is used for printk buffer
1382 b = it is not a TTY but a Braille device
1383 a = it is safe to use when cpu is offline
1384 major:minor major and minor number of the device separated by a colon
1386 ------------------------------------------------------------------------------
1388 ------------------------------------------------------------------------------
1389 The /proc file system serves information about the running system. It not only
1390 allows access to process data but also allows you to request the kernel status
1391 by reading files in the hierarchy.
1393 The directory structure of /proc reflects the types of information and makes
1394 it easy, if not obvious, where to look for specific data.
1395 ------------------------------------------------------------------------------
1397 ------------------------------------------------------------------------------
1398 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1399 ------------------------------------------------------------------------------
1401 ------------------------------------------------------------------------------
1403 ------------------------------------------------------------------------------
1404 * Modifying kernel parameters by writing into files found in /proc/sys
1405 * Exploring the files which modify certain parameters
1406 * Review of the /proc/sys file tree
1407 ------------------------------------------------------------------------------
1410 A very interesting part of /proc is the directory /proc/sys. This is not only
1411 a source of information, it also allows you to change parameters within the
1412 kernel. Be very careful when attempting this. You can optimize your system,
1413 but you can also cause it to crash. Never alter kernel parameters on a
1414 production system. Set up a development machine and test to make sure that
1415 everything works the way you want it to. You may have no alternative but to
1416 reboot the machine once an error has been made.
1418 To change a value, simply echo the new value into the file. An example is
1419 given below in the section on the file system data. You need to be root to do
1420 this. You can create your own boot script to perform this every time your
1423 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1424 general things in the operation of the Linux kernel. Since some of the files
1425 can inadvertently disrupt your system, it is advisable to read both
1426 documentation and source before actually making adjustments. In any case, be
1427 very careful when writing to any of these files. The entries in /proc may
1428 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1429 review the kernel documentation in the directory /usr/src/linux/Documentation.
1430 This chapter is heavily based on the documentation included in the pre 2.2
1431 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1433 Please see: Documentation/sysctl/ directory for descriptions of these
1436 ------------------------------------------------------------------------------
1438 ------------------------------------------------------------------------------
1439 Certain aspects of kernel behavior can be modified at runtime, without the
1440 need to recompile the kernel, or even to reboot the system. The files in the
1441 /proc/sys tree can not only be read, but also modified. You can use the echo
1442 command to write value into these files, thereby changing the default settings
1444 ------------------------------------------------------------------------------
1446 ------------------------------------------------------------------------------
1447 CHAPTER 3: PER-PROCESS PARAMETERS
1448 ------------------------------------------------------------------------------
1450 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1451 --------------------------------------------------------------------------------
1453 These file can be used to adjust the badness heuristic used to select which
1454 process gets killed in out of memory conditions.
1456 The badness heuristic assigns a value to each candidate task ranging from 0
1457 (never kill) to 1000 (always kill) to determine which process is targeted. The
1458 units are roughly a proportion along that range of allowed memory the process
1459 may allocate from based on an estimation of its current memory and swap use.
1460 For example, if a task is using all allowed memory, its badness score will be
1461 1000. If it is using half of its allowed memory, its score will be 500.
1463 There is an additional factor included in the badness score: the current memory
1464 and swap usage is discounted by 3% for root processes.
1466 The amount of "allowed" memory depends on the context in which the oom killer
1467 was called. If it is due to the memory assigned to the allocating task's cpuset
1468 being exhausted, the allowed memory represents the set of mems assigned to that
1469 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1470 memory represents the set of mempolicy nodes. If it is due to a memory
1471 limit (or swap limit) being reached, the allowed memory is that configured
1472 limit. Finally, if it is due to the entire system being out of memory, the
1473 allowed memory represents all allocatable resources.
1475 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1476 is used to determine which task to kill. Acceptable values range from -1000
1477 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1478 polarize the preference for oom killing either by always preferring a certain
1479 task or completely disabling it. The lowest possible value, -1000, is
1480 equivalent to disabling oom killing entirely for that task since it will always
1481 report a badness score of 0.
1483 Consequently, it is very simple for userspace to define the amount of memory to
1484 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1485 example, is roughly equivalent to allowing the remainder of tasks sharing the
1486 same system, cpuset, mempolicy, or memory controller resources to use at least
1487 50% more memory. A value of -500, on the other hand, would be roughly
1488 equivalent to discounting 50% of the task's allowed memory from being considered
1489 as scoring against the task.
1491 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1492 be used to tune the badness score. Its acceptable values range from -16
1493 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1494 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1495 scaled linearly with /proc/<pid>/oom_score_adj.
1497 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1498 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1499 requires CAP_SYS_RESOURCE.
1501 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1502 generation children with separate address spaces instead, if possible. This
1503 avoids servers and important system daemons from being killed and loses the
1504 minimal amount of work.
1507 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1508 -------------------------------------------------------------
1510 This file can be used to check the current score used by the oom-killer is for
1511 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1512 process should be killed in an out-of-memory situation.
1515 3.3 /proc/<pid>/io - Display the IO accounting fields
1516 -------------------------------------------------------
1518 This file contains IO statistics for each running process
1523 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1526 test:/tmp # cat /proc/3828/io
1532 write_bytes: 323932160
1533 cancelled_write_bytes: 0
1542 I/O counter: chars read
1543 The number of bytes which this task has caused to be read from storage. This
1544 is simply the sum of bytes which this process passed to read() and pread().
1545 It includes things like tty IO and it is unaffected by whether or not actual
1546 physical disk IO was required (the read might have been satisfied from
1553 I/O counter: chars written
1554 The number of bytes which this task has caused, or shall cause to be written
1555 to disk. Similar caveats apply here as with rchar.
1561 I/O counter: read syscalls
1562 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1569 I/O counter: write syscalls
1570 Attempt to count the number of write I/O operations, i.e. syscalls like
1571 write() and pwrite().
1577 I/O counter: bytes read
1578 Attempt to count the number of bytes which this process really did cause to
1579 be fetched from the storage layer. Done at the submit_bio() level, so it is
1580 accurate for block-backed filesystems. <please add status regarding NFS and
1581 CIFS at a later time>
1587 I/O counter: bytes written
1588 Attempt to count the number of bytes which this process caused to be sent to
1589 the storage layer. This is done at page-dirtying time.
1592 cancelled_write_bytes
1593 ---------------------
1595 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1596 then deletes the file, it will in fact perform no writeout. But it will have
1597 been accounted as having caused 1MB of write.
1598 In other words: The number of bytes which this process caused to not happen,
1599 by truncating pagecache. A task can cause "negative" IO too. If this task
1600 truncates some dirty pagecache, some IO which another task has been accounted
1601 for (in its write_bytes) will not be happening. We _could_ just subtract that
1602 from the truncating task's write_bytes, but there is information loss in doing
1609 At its current implementation state, this is a bit racy on 32-bit machines: if
1610 process A reads process B's /proc/pid/io while process B is updating one of
1611 those 64-bit counters, process A could see an intermediate result.
1614 More information about this can be found within the taskstats documentation in
1615 Documentation/accounting.
1617 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1618 ---------------------------------------------------------------
1619 When a process is dumped, all anonymous memory is written to a core file as
1620 long as the size of the core file isn't limited. But sometimes we don't want
1621 to dump some memory segments, for example, huge shared memory or DAX.
1622 Conversely, sometimes we want to save file-backed memory segments into a core
1623 file, not only the individual files.
1625 /proc/<pid>/coredump_filter allows you to customize which memory segments
1626 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1627 of memory types. If a bit of the bitmask is set, memory segments of the
1628 corresponding memory type are dumped, otherwise they are not dumped.
1630 The following 9 memory types are supported:
1631 - (bit 0) anonymous private memory
1632 - (bit 1) anonymous shared memory
1633 - (bit 2) file-backed private memory
1634 - (bit 3) file-backed shared memory
1635 - (bit 4) ELF header pages in file-backed private memory areas (it is
1636 effective only if the bit 2 is cleared)
1637 - (bit 5) hugetlb private memory
1638 - (bit 6) hugetlb shared memory
1639 - (bit 7) DAX private memory
1640 - (bit 8) DAX shared memory
1642 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1643 are always dumped regardless of the bitmask status.
1645 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1646 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1648 The default value of coredump_filter is 0x33; this means all anonymous memory
1649 segments, ELF header pages and hugetlb private memory are dumped.
1651 If you don't want to dump all shared memory segments attached to pid 1234,
1652 write 0x31 to the process's proc file.
1654 $ echo 0x31 > /proc/1234/coredump_filter
1656 When a new process is created, the process inherits the bitmask status from its
1657 parent. It is useful to set up coredump_filter before the program runs.
1660 $ echo 0x7 > /proc/self/coredump_filter
1663 3.5 /proc/<pid>/mountinfo - Information about mounts
1664 --------------------------------------------------------
1666 This file contains lines of the form:
1668 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1669 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1671 (1) mount ID: unique identifier of the mount (may be reused after umount)
1672 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1673 (3) major:minor: value of st_dev for files on filesystem
1674 (4) root: root of the mount within the filesystem
1675 (5) mount point: mount point relative to the process's root
1676 (6) mount options: per mount options
1677 (7) optional fields: zero or more fields of the form "tag[:value]"
1678 (8) separator: marks the end of the optional fields
1679 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1680 (10) mount source: filesystem specific information or "none"
1681 (11) super options: per super block options
1683 Parsers should ignore all unrecognised optional fields. Currently the
1684 possible optional fields are:
1686 shared:X mount is shared in peer group X
1687 master:X mount is slave to peer group X
1688 propagate_from:X mount is slave and receives propagation from peer group X (*)
1689 unbindable mount is unbindable
1691 (*) X is the closest dominant peer group under the process's root. If
1692 X is the immediate master of the mount, or if there's no dominant peer
1693 group under the same root, then only the "master:X" field is present
1694 and not the "propagate_from:X" field.
1696 For more information on mount propagation see:
1698 Documentation/filesystems/sharedsubtree.txt
1701 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1702 --------------------------------------------------------
1703 These files provide a method to access a tasks comm value. It also allows for
1704 a task to set its own or one of its thread siblings comm value. The comm value
1705 is limited in size compared to the cmdline value, so writing anything longer
1706 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1710 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1711 -------------------------------------------------------------------------
1712 This file provides a fast way to retrieve first level children pids
1713 of a task pointed by <pid>/<tid> pair. The format is a space separated
1716 Note the "first level" here -- if a child has own children they will
1717 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1718 to obtain the descendants.
1720 Since this interface is intended to be fast and cheap it doesn't
1721 guarantee to provide precise results and some children might be
1722 skipped, especially if they've exited right after we printed their
1723 pids, so one need to either stop or freeze processes being inspected
1724 if precise results are needed.
1727 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1728 ---------------------------------------------------------------
1729 This file provides information associated with an opened file. The regular
1730 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1731 represents the current offset of the opened file in decimal form [see lseek(2)
1732 for details], 'flags' denotes the octal O_xxx mask the file has been
1733 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1734 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1743 All locks associated with a file descriptor are shown in its fdinfo too.
1745 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1747 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1748 pair provide additional information particular to the objects they represent.
1757 where 'eventfd-count' is hex value of a counter.
1764 sigmask: 0000000000000200
1766 where 'sigmask' is hex value of the signal mask associated
1774 tfd: 5 events: 1d data: ffffffffffffffff
1776 where 'tfd' is a target file descriptor number in decimal form,
1777 'events' is events mask being watched and the 'data' is data
1778 associated with a target [see epoll(7) for more details].
1782 For inotify files the format is the following
1786 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1788 where 'wd' is a watch descriptor in decimal form, ie a target file
1789 descriptor number, 'ino' and 'sdev' are inode and device where the
1790 target file resides and the 'mask' is the mask of events, all in hex
1791 form [see inotify(7) for more details].
1793 If the kernel was built with exportfs support, the path to the target
1794 file is encoded as a file handle. The file handle is provided by three
1795 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1798 If the kernel is built without exportfs support the file handle won't be
1801 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1803 For fanotify files the format is
1808 fanotify flags:10 event-flags:0
1809 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1810 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1812 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1813 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1814 flags associated with mark which are tracked separately from events
1815 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1816 mask and 'ignored_mask' is the mask of events which are to be ignored.
1817 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1818 does provide information about flags and mask used in fanotify_mark
1819 call [see fsnotify manpage for details].
1821 While the first three lines are mandatory and always printed, the rest is
1822 optional and may be omitted if no marks created yet.
1833 it_value: (0, 49406829)
1836 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1837 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1838 flags in octal form been used to setup the timer [see timerfd_settime(2) for
1839 details]. 'it_value' is remaining time until the timer exiration.
1840 'it_interval' is the interval for the timer. Note the timer might be set up
1841 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1842 still exhibits timer's remaining time.
1844 3.9 /proc/<pid>/map_files - Information about memory mapped files
1845 ---------------------------------------------------------------------
1846 This directory contains symbolic links which represent memory mapped files
1847 the process is maintaining. Example output:
1849 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1850 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1851 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1853 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1854 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1856 The name of a link represents the virtual memory bounds of a mapping, i.e.
1857 vm_area_struct::vm_start-vm_area_struct::vm_end.
1859 The main purpose of the map_files is to retrieve a set of memory mapped
1860 files in a fast way instead of parsing /proc/<pid>/maps or
1861 /proc/<pid>/smaps, both of which contain many more records. At the same
1862 time one can open(2) mappings from the listings of two processes and
1863 comparing their inode numbers to figure out which anonymous memory areas
1864 are actually shared.
1866 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
1867 ---------------------------------------------------------
1868 This file provides the value of the task's timerslack value in nanoseconds.
1869 This value specifies a amount of time that normal timers may be deferred
1870 in order to coalesce timers and avoid unnecessary wakeups.
1872 This allows a task's interactivity vs power consumption trade off to be
1875 Writing 0 to the file will set the tasks timerslack to the default value.
1877 Valid values are from 0 - ULLONG_MAX
1879 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1880 permissions on the task specified to change its timerslack_ns value.
1883 ------------------------------------------------------------------------------
1885 ------------------------------------------------------------------------------
1888 ---------------------
1890 The following mount options are supported:
1892 hidepid= Set /proc/<pid>/ access mode.
1893 gid= Set the group authorized to learn processes information.
1895 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1898 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1899 own. Sensitive files like cmdline, sched*, status are now protected against
1900 other users. This makes it impossible to learn whether any user runs
1901 specific program (given the program doesn't reveal itself by its behaviour).
1902 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1903 poorly written programs passing sensitive information via program arguments are
1904 now protected against local eavesdroppers.
1906 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1907 users. It doesn't mean that it hides a fact whether a process with a specific
1908 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1909 but it hides process' uid and gid, which may be learned by stat()'ing
1910 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1911 information about running processes, whether some daemon runs with elevated
1912 privileges, whether other user runs some sensitive program, whether other users
1913 run any program at all, etc.
1915 gid= defines a group authorized to learn processes information otherwise
1916 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1917 information about processes information, just add identd to this group.
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