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
50 ------------------------------------------------------------------------------
52 ------------------------------------------------------------------------------
54 0.1 Introduction/Credits
55 ------------------------
57 This documentation is part of a soon (or so we hope) to be released book on
58 the SuSE Linux distribution. As there is no complete documentation for the
59 /proc file system and we've used many freely available sources to write these
60 chapters, it seems only fair to give the work back to the Linux community.
61 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
62 afraid it's still far from complete, but we hope it will be useful. As far as
63 we know, it is the first 'all-in-one' document about the /proc file system. It
64 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
65 SPARC, AXP, etc., features, you probably won't find what you are looking for.
66 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
67 additions and patches are welcome and will be added to this document if you
70 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
71 other people for help compiling this documentation. We'd also like to extend a
72 special thank you to Andi Kleen for documentation, which we relied on heavily
73 to create this document, as well as the additional information he provided.
74 Thanks to everybody else who contributed source or docs to the Linux kernel
75 and helped create a great piece of software... :)
77 If you have any comments, corrections or additions, please don't hesitate to
78 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
81 The latest version of this document is available online at
82 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
84 If the above direction does not works for you, you could try the kernel
85 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
86 comandante@zaralinux.com.
91 We don't guarantee the correctness of this document, and if you come to us
92 complaining about how you screwed up your system because of incorrect
93 documentation, we won't feel responsible...
95 ------------------------------------------------------------------------------
96 CHAPTER 1: COLLECTING SYSTEM INFORMATION
97 ------------------------------------------------------------------------------
99 ------------------------------------------------------------------------------
101 ------------------------------------------------------------------------------
102 * Investigating the properties of the pseudo file system /proc and its
103 ability to provide information on the running Linux system
104 * Examining /proc's structure
105 * Uncovering various information about the kernel and the processes running
107 ------------------------------------------------------------------------------
110 The proc file system acts as an interface to internal data structures in the
111 kernel. It can be used to obtain information about the system and to change
112 certain kernel parameters at runtime (sysctl).
114 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
115 show you how you can use /proc/sys to change settings.
117 1.1 Process-Specific Subdirectories
118 -----------------------------------
120 The directory /proc contains (among other things) one subdirectory for each
121 process running on the system, which is named after the process ID (PID).
123 The link self points to the process reading the file system. Each process
124 subdirectory has the entries listed in Table 1-1.
127 Table 1-1: Process specific entries in /proc
128 ..............................................................................
130 clear_refs Clears page referenced bits shown in smaps output
131 cmdline Command line arguments
132 cpu Current and last cpu in which it was executed (2.4)(smp)
133 cwd Link to the current working directory
134 environ Values of environment variables
135 exe Link to the executable of this process
136 fd Directory, which contains all file descriptors
137 maps Memory maps to executables and library files (2.4)
138 mem Memory held by this process
139 root Link to the root directory of this process
141 statm Process memory status information
142 status Process status in human readable form
143 wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
144 symbol the task is blocked in - or "0" if not blocked.
146 stack Report full stack trace, enable via CONFIG_STACKTRACE
147 smaps a extension based on maps, showing the memory consumption of
148 each mapping and flags associated with it
149 numa_maps an extension based on maps, showing the memory locality and
150 binding policy as well as mem usage (in pages) of each mapping.
151 ..............................................................................
153 For example, to get the status information of a process, all you have to do is
154 read the file /proc/PID/status:
156 >cat /proc/self/status
181 SigPnd: 0000000000000000
182 ShdPnd: 0000000000000000
183 SigBlk: 0000000000000000
184 SigIgn: 0000000000000000
185 SigCgt: 0000000000000000
186 CapInh: 00000000fffffeff
187 CapPrm: 0000000000000000
188 CapEff: 0000000000000000
189 CapBnd: ffffffffffffffff
191 voluntary_ctxt_switches: 0
192 nonvoluntary_ctxt_switches: 1
194 This shows you nearly the same information you would get if you viewed it with
195 the ps command. In fact, ps uses the proc file system to obtain its
196 information. But you get a more detailed view of the process by reading the
197 file /proc/PID/status. It fields are described in table 1-2.
199 The statm file contains more detailed information about the process
200 memory usage. Its seven fields are explained in Table 1-3. The stat file
201 contains details information about the process itself. Its fields are
202 explained in Table 1-4.
204 (for SMP CONFIG users)
205 For making accounting scalable, RSS related information are handled in an
206 asynchronous manner and the value may not be very precise. To see a precise
207 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
208 It's slow but very precise.
210 Table 1-2: Contents of the status files (as of 4.1)
211 ..............................................................................
213 Name filename of the executable
214 State state (R is running, S is sleeping, D is sleeping
215 in an uninterruptible wait, Z is zombie,
216 T is traced or stopped)
218 Ngid NUMA group ID (0 if none)
220 PPid process id of the parent process
221 TracerPid PID of process tracing this process (0 if not)
222 Uid Real, effective, saved set, and file system UIDs
223 Gid Real, effective, saved set, and file system GIDs
224 FDSize number of file descriptor slots currently allocated
225 Groups supplementary group list
226 NStgid descendant namespace thread group ID hierarchy
227 NSpid descendant namespace process ID hierarchy
228 NSpgid descendant namespace process group ID hierarchy
229 NSsid descendant namespace session ID hierarchy
230 VmPeak peak virtual memory size
231 VmSize total program size
232 VmLck locked memory size
233 VmHWM peak resident set size ("high water mark")
234 VmRSS size of memory portions
235 VmData size of data, stack, and text segments
236 VmStk size of data, stack, and text segments
237 VmExe size of text segment
238 VmLib size of shared library code
239 VmPTE size of page table entries
240 VmPMD size of second level page tables
241 VmSwap size of swap usage (the number of referred swapents)
242 HugetlbPages size of hugetlb memory portions
243 Threads number of threads
244 SigQ number of signals queued/max. number for queue
245 SigPnd bitmap of pending signals for the thread
246 ShdPnd bitmap of shared pending signals for the process
247 SigBlk bitmap of blocked signals
248 SigIgn bitmap of ignored signals
249 SigCgt bitmap of caught signals
250 CapInh bitmap of inheritable capabilities
251 CapPrm bitmap of permitted capabilities
252 CapEff bitmap of effective capabilities
253 CapBnd bitmap of capabilities bounding set
254 Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
255 Cpus_allowed mask of CPUs on which this process may run
256 Cpus_allowed_list Same as previous, but in "list format"
257 Mems_allowed mask of memory nodes allowed to this process
258 Mems_allowed_list Same as previous, but in "list format"
259 voluntary_ctxt_switches number of voluntary context switches
260 nonvoluntary_ctxt_switches number of non voluntary context switches
261 ..............................................................................
263 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
264 ..............................................................................
266 size total program size (pages) (same as VmSize in status)
267 resident size of memory portions (pages) (same as VmRSS in status)
268 shared number of pages that are shared (i.e. backed by a file)
269 trs number of pages that are 'code' (not including libs; broken,
270 includes data segment)
271 lrs number of pages of library (always 0 on 2.6)
272 drs number of pages of data/stack (including libs; broken,
273 includes library text)
274 dt number of dirty pages (always 0 on 2.6)
275 ..............................................................................
278 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
279 ..............................................................................
282 tcomm filename of the executable
283 state state (R is running, S is sleeping, D is sleeping in an
284 uninterruptible wait, Z is zombie, T is traced or stopped)
285 ppid process id of the parent process
286 pgrp pgrp of the process
288 tty_nr tty the process uses
289 tty_pgrp pgrp of the tty
291 min_flt number of minor faults
292 cmin_flt number of minor faults with child's
293 maj_flt number of major faults
294 cmaj_flt number of major faults with child's
295 utime user mode jiffies
296 stime kernel mode jiffies
297 cutime user mode jiffies with child's
298 cstime kernel mode jiffies with child's
299 priority priority level
301 num_threads number of threads
302 it_real_value (obsolete, always 0)
303 start_time time the process started after system boot
304 vsize virtual memory size
305 rss resident set memory size
306 rsslim current limit in bytes on the rss
307 start_code address above which program text can run
308 end_code address below which program text can run
309 start_stack address of the start of the main process stack
310 esp current value of ESP
311 eip current value of EIP
312 pending bitmap of pending signals
313 blocked bitmap of blocked signals
314 sigign bitmap of ignored signals
315 sigcatch bitmap of caught signals
316 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead)
319 exit_signal signal to send to parent thread on exit
320 task_cpu which CPU the task is scheduled on
321 rt_priority realtime priority
322 policy scheduling policy (man sched_setscheduler)
323 blkio_ticks time spent waiting for block IO
324 gtime guest time of the task in jiffies
325 cgtime guest time of the task children in jiffies
326 start_data address above which program data+bss is placed
327 end_data address below which program data+bss is placed
328 start_brk address above which program heap can be expanded with brk()
329 arg_start address above which program command line is placed
330 arg_end address below which program command line is placed
331 env_start address above which program environment is placed
332 env_end address below which program environment is placed
333 exit_code the thread's exit_code in the form reported by the waitpid system call
334 ..............................................................................
336 The /proc/PID/maps file containing the currently mapped memory regions and
337 their access permissions.
341 address perms offset dev inode pathname
343 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
344 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
345 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
346 a7cb1000-a7cb2000 ---p 00000000 00:00 0
347 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
348 a7eb2000-a7eb3000 ---p 00000000 00:00 0
349 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack:1001]
350 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
351 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
352 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
353 a800b000-a800e000 rw-p 00000000 00:00 0
354 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
355 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
356 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
357 a8024000-a8027000 rw-p 00000000 00:00 0
358 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
359 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
360 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
361 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
362 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
364 where "address" is the address space in the process that it occupies, "perms"
365 is a set of permissions:
371 p = private (copy on write)
373 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
374 "inode" is the inode on that device. 0 indicates that no inode is associated
375 with the memory region, as the case would be with BSS (uninitialized data).
376 The "pathname" shows the name associated file for this mapping. If the mapping
377 is not associated with a file:
379 [heap] = the heap of the program
380 [stack] = the stack of the main process
381 [stack:1001] = the stack of the thread with tid 1001
382 [vdso] = the "virtual dynamic shared object",
383 the kernel system call handler
385 or if empty, the mapping is anonymous.
387 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
388 of the individual tasks of a process. In this file you will see a mapping marked
389 as [stack] if that task sees it as a stack. This is a key difference from the
390 content of /proc/PID/maps, where you will see all mappings that are being used
391 as stack by all of those tasks. Hence, for the example above, the task-level
392 map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
394 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
395 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
396 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
397 a7cb1000-a7cb2000 ---p 00000000 00:00 0
398 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
399 a7eb2000-a7eb3000 ---p 00000000 00:00 0
400 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack]
401 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
402 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
403 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
404 a800b000-a800e000 rw-p 00000000 00:00 0
405 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
406 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
407 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
408 a8024000-a8027000 rw-p 00000000 00:00 0
409 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
410 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
411 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
412 aff35000-aff4a000 rw-p 00000000 00:00 0
413 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
415 The /proc/PID/smaps is an extension based on maps, showing the memory
416 consumption for each of the process's mappings. For each of mappings there
417 is a series of lines such as the following:
419 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
431 Private_Hugetlb: 0 kB
437 VmFlags: rd ex mr mw me dw
439 the first of these lines shows the same information as is displayed for the
440 mapping in /proc/PID/maps. The remaining lines show the size of the mapping
441 (size), the amount of the mapping that is currently resident in RAM (RSS), the
442 process' proportional share of this mapping (PSS), the number of clean and
443 dirty private pages in the mapping.
445 The "proportional set size" (PSS) of a process is the count of pages it has
446 in memory, where each page is divided by the number of processes sharing it.
447 So if a process has 1000 pages all to itself, and 1000 shared with one other
448 process, its PSS will be 1500.
449 Note that even a page which is part of a MAP_SHARED mapping, but has only
450 a single pte mapped, i.e. is currently used by only one process, is accounted
451 as private and not as shared.
452 "Referenced" indicates the amount of memory currently marked as referenced or
454 "Anonymous" shows the amount of memory that does not belong to any file. Even
455 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
456 and a page is modified, the file page is replaced by a private anonymous copy.
457 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
458 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
459 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
460 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
461 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
462 "SwapPss" shows proportional swap share of this mapping.
463 "Locked" indicates whether the mapping is locked in memory or not.
465 "VmFlags" field deserves a separate description. This member represents the kernel
466 flags associated with the particular virtual memory area in two letter encoded
467 manner. The codes are the following:
476 gd - stack segment growns down
478 dw - disabled write to the mapped file
479 lo - pages are locked in memory
480 io - memory mapped I/O area
481 sr - sequential read advise provided
482 rr - random read advise provided
483 dc - do not copy area on fork
484 de - do not expand area on remapping
485 ac - area is accountable
486 nr - swap space is not reserved for the area
487 ht - area uses huge tlb pages
488 ar - architecture specific flag
489 dd - do not include area into core dump
492 hg - huge page advise flag
493 nh - no-huge page advise flag
494 mg - mergable advise flag
496 Note that there is no guarantee that every flag and associated mnemonic will
497 be present in all further kernel releases. Things get changed, the flags may
498 be vanished or the reverse -- new added.
500 This file is only present if the CONFIG_MMU kernel configuration option is
503 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
504 bits on both physical and virtual pages associated with a process, and the
505 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
506 To clear the bits for all the pages associated with the process
507 > echo 1 > /proc/PID/clear_refs
509 To clear the bits for the anonymous pages associated with the process
510 > echo 2 > /proc/PID/clear_refs
512 To clear the bits for the file mapped pages associated with the process
513 > echo 3 > /proc/PID/clear_refs
515 To clear the soft-dirty bit
516 > echo 4 > /proc/PID/clear_refs
518 To reset the peak resident set size ("high water mark") to the process's
520 > echo 5 > /proc/PID/clear_refs
522 Any other value written to /proc/PID/clear_refs will have no effect.
524 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
525 using /proc/kpageflags and number of times a page is mapped using
526 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
528 The /proc/pid/numa_maps is an extension based on maps, showing the memory
529 locality and binding policy, as well as the memory usage (in pages) of
530 each mapping. The output follows a general format where mapping details get
531 summarized separated by blank spaces, one mapping per each file line:
533 address policy mapping details
535 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
536 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
537 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
538 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
539 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
540 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
541 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
542 320698b000 default file=/lib64/libc-2.12.so
543 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
544 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
545 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
546 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
547 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
548 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
549 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
550 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
553 "address" is the starting address for the mapping;
554 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
555 "mapping details" summarizes mapping data such as mapping type, page usage counters,
556 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
557 size, in KB, that is backing the mapping up.
562 Similar to the process entries, the kernel data files give information about
563 the running kernel. The files used to obtain this information are contained in
564 /proc and are listed in Table 1-5. Not all of these will be present in your
565 system. It depends on the kernel configuration and the loaded modules, which
566 files are there, and which are missing.
568 Table 1-5: Kernel info in /proc
569 ..............................................................................
571 apm Advanced power management info
572 buddyinfo Kernel memory allocator information (see text) (2.5)
573 bus Directory containing bus specific information
574 cmdline Kernel command line
575 cpuinfo Info about the CPU
576 devices Available devices (block and character)
577 dma Used DMS channels
578 filesystems Supported filesystems
579 driver Various drivers grouped here, currently rtc (2.4)
580 execdomains Execdomains, related to security (2.4)
581 fb Frame Buffer devices (2.4)
582 fs File system parameters, currently nfs/exports (2.4)
583 ide Directory containing info about the IDE subsystem
584 interrupts Interrupt usage
585 iomem Memory map (2.4)
586 ioports I/O port usage
587 irq Masks for irq to cpu affinity (2.4)(smp?)
588 isapnp ISA PnP (Plug&Play) Info (2.4)
589 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
591 ksyms Kernel symbol table
592 loadavg Load average of last 1, 5 & 15 minutes
596 modules List of loaded modules
597 mounts Mounted filesystems
598 net Networking info (see text)
599 pagetypeinfo Additional page allocator information (see text) (2.5)
600 partitions Table of partitions known to the system
601 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
602 decoupled by lspci (2.4)
604 scsi SCSI info (see text)
605 slabinfo Slab pool info
606 softirqs softirq usage
607 stat Overall statistics
608 swaps Swap space utilization
610 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
611 tty Info of tty drivers
612 uptime Wall clock since boot, combined idle time of all cpus
613 version Kernel version
614 video bttv info of video resources (2.4)
615 vmallocinfo Show vmalloced areas
616 ..............................................................................
618 You can, for example, check which interrupts are currently in use and what
619 they are used for by looking in the file /proc/interrupts:
621 > cat /proc/interrupts
623 0: 8728810 XT-PIC timer
624 1: 895 XT-PIC keyboard
626 3: 531695 XT-PIC aha152x
627 4: 2014133 XT-PIC serial
628 5: 44401 XT-PIC pcnet_cs
631 12: 182918 XT-PIC PS/2 Mouse
633 14: 1232265 XT-PIC ide0
637 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
638 output of a SMP machine):
640 > cat /proc/interrupts
643 0: 1243498 1214548 IO-APIC-edge timer
644 1: 8949 8958 IO-APIC-edge keyboard
645 2: 0 0 XT-PIC cascade
646 5: 11286 10161 IO-APIC-edge soundblaster
647 8: 1 0 IO-APIC-edge rtc
648 9: 27422 27407 IO-APIC-edge 3c503
649 12: 113645 113873 IO-APIC-edge PS/2 Mouse
651 14: 22491 24012 IO-APIC-edge ide0
652 15: 2183 2415 IO-APIC-edge ide1
653 17: 30564 30414 IO-APIC-level eth0
654 18: 177 164 IO-APIC-level bttv
659 NMI is incremented in this case because every timer interrupt generates a NMI
660 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
662 LOC is the local interrupt counter of the internal APIC of every CPU.
664 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
665 connects the CPUs in a SMP system. This means that an error has been detected,
666 the IO-APIC automatically retry the transmission, so it should not be a big
667 problem, but you should read the SMP-FAQ.
669 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
670 /proc/interrupts to display every IRQ vector in use by the system, not
671 just those considered 'most important'. The new vectors are:
673 THR -- interrupt raised when a machine check threshold counter
674 (typically counting ECC corrected errors of memory or cache) exceeds
675 a configurable threshold. Only available on some systems.
677 TRM -- a thermal event interrupt occurs when a temperature threshold
678 has been exceeded for the CPU. This interrupt may also be generated
679 when the temperature drops back to normal.
681 SPU -- a spurious interrupt is some interrupt that was raised then lowered
682 by some IO device before it could be fully processed by the APIC. Hence
683 the APIC sees the interrupt but does not know what device it came from.
684 For this case the APIC will generate the interrupt with a IRQ vector
685 of 0xff. This might also be generated by chipset bugs.
687 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
688 sent from one CPU to another per the needs of the OS. Typically,
689 their statistics are used by kernel developers and interested users to
690 determine the occurrence of interrupts of the given type.
692 The above IRQ vectors are displayed only when relevant. For example,
693 the threshold vector does not exist on x86_64 platforms. Others are
694 suppressed when the system is a uniprocessor. As of this writing, only
695 i386 and x86_64 platforms support the new IRQ vector displays.
697 Of some interest is the introduction of the /proc/irq directory to 2.4.
698 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
699 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
700 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
705 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
706 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
710 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
711 IRQ, you can set it by doing:
713 > echo 1 > /proc/irq/10/smp_affinity
715 This means that only the first CPU will handle the IRQ, but you can also echo
716 5 which means that only the first and fourth CPU can handle the IRQ.
718 The contents of each smp_affinity file is the same by default:
720 > cat /proc/irq/0/smp_affinity
723 There is an alternate interface, smp_affinity_list which allows specifying
724 a cpu range instead of a bitmask:
726 > cat /proc/irq/0/smp_affinity_list
729 The default_smp_affinity mask applies to all non-active IRQs, which are the
730 IRQs which have not yet been allocated/activated, and hence which lack a
731 /proc/irq/[0-9]* directory.
733 The node file on an SMP system shows the node to which the device using the IRQ
734 reports itself as being attached. This hardware locality information does not
735 include information about any possible driver locality preference.
737 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
738 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
740 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
741 between all the CPUs which are allowed to handle it. As usual the kernel has
742 more info than you and does a better job than you, so the defaults are the
743 best choice for almost everyone. [Note this applies only to those IO-APIC's
744 that support "Round Robin" interrupt distribution.]
746 There are three more important subdirectories in /proc: net, scsi, and sys.
747 The general rule is that the contents, or even the existence of these
748 directories, depend on your kernel configuration. If SCSI is not enabled, the
749 directory scsi may not exist. The same is true with the net, which is there
750 only when networking support is present in the running kernel.
752 The slabinfo file gives information about memory usage at the slab level.
753 Linux uses slab pools for memory management above page level in version 2.2.
754 Commonly used objects have their own slab pool (such as network buffers,
755 directory cache, and so on).
757 ..............................................................................
759 > cat /proc/buddyinfo
761 Node 0, zone DMA 0 4 5 4 4 3 ...
762 Node 0, zone Normal 1 0 0 1 101 8 ...
763 Node 0, zone HighMem 2 0 0 1 1 0 ...
765 External fragmentation is a problem under some workloads, and buddyinfo is a
766 useful tool for helping diagnose these problems. Buddyinfo will give you a
767 clue as to how big an area you can safely allocate, or why a previous
770 Each column represents the number of pages of a certain order which are
771 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
772 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
773 available in ZONE_NORMAL, etc...
775 More information relevant to external fragmentation can be found in
778 > cat /proc/pagetypeinfo
782 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
783 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
784 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
785 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
786 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
787 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
788 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
789 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
790 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
791 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
792 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
794 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
795 Node 0, zone DMA 2 0 5 1 0
796 Node 0, zone DMA32 41 6 967 2 0
798 Fragmentation avoidance in the kernel works by grouping pages of different
799 migrate types into the same contiguous regions of memory called page blocks.
800 A page block is typically the size of the default hugepage size e.g. 2MB on
801 X86-64. By keeping pages grouped based on their ability to move, the kernel
802 can reclaim pages within a page block to satisfy a high-order allocation.
804 The pagetypinfo begins with information on the size of a page block. It
805 then gives the same type of information as buddyinfo except broken down
806 by migrate-type and finishes with details on how many page blocks of each
809 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
810 from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
811 make an estimate of the likely number of huge pages that can be allocated
812 at a given point in time. All the "Movable" blocks should be allocatable
813 unless memory has been mlock()'d. Some of the Reclaimable blocks should
814 also be allocatable although a lot of filesystem metadata may have to be
815 reclaimed to achieve this.
817 ..............................................................................
821 Provides information about distribution and utilization of memory. This
822 varies by architecture and compile options. The following is from a
823 16GB PIII, which has highmem enabled. You may not have all of these fields.
827 MemTotal: 16344972 kB
829 MemAvailable: 14836172 kB
835 HighTotal: 15597528 kB
836 HighFree: 13629632 kB
846 SReclaimable: 159856 kB
847 SUnreclaim: 124508 kB
852 CommitLimit: 7669796 kB
853 Committed_AS: 100056 kB
854 VmallocTotal: 112216 kB
856 VmallocChunk: 111088 kB
857 AnonHugePages: 49152 kB
859 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
860 bits and the kernel binary code)
861 MemFree: The sum of LowFree+HighFree
862 MemAvailable: An estimate of how much memory is available for starting new
863 applications, without swapping. Calculated from MemFree,
864 SReclaimable, the size of the file LRU lists, and the low
865 watermarks in each zone.
866 The estimate takes into account that the system needs some
867 page cache to function well, and that not all reclaimable
868 slab will be reclaimable, due to items being in use. The
869 impact of those factors will vary from system to system.
870 Buffers: Relatively temporary storage for raw disk blocks
871 shouldn't get tremendously large (20MB or so)
872 Cached: in-memory cache for files read from the disk (the
873 pagecache). Doesn't include SwapCached
874 SwapCached: Memory that once was swapped out, is swapped back in but
875 still also is in the swapfile (if memory is needed it
876 doesn't need to be swapped out AGAIN because it is already
877 in the swapfile. This saves I/O)
878 Active: Memory that has been used more recently and usually not
879 reclaimed unless absolutely necessary.
880 Inactive: Memory which has been less recently used. It is more
881 eligible to be reclaimed for other purposes
883 HighFree: Highmem is all memory above ~860MB of physical memory
884 Highmem areas are for use by userspace programs, or
885 for the pagecache. The kernel must use tricks to access
886 this memory, making it slower to access than lowmem.
888 LowFree: Lowmem is memory which can be used for everything that
889 highmem can be used for, but it is also available for the
890 kernel's use for its own data structures. Among many
891 other things, it is where everything from the Slab is
892 allocated. Bad things happen when you're out of lowmem.
893 SwapTotal: total amount of swap space available
894 SwapFree: Memory which has been evicted from RAM, and is temporarily
896 Dirty: Memory which is waiting to get written back to the disk
897 Writeback: Memory which is actively being written back to the disk
898 AnonPages: Non-file backed pages mapped into userspace page tables
899 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
900 Mapped: files which have been mmaped, such as libraries
901 Slab: in-kernel data structures cache
902 SReclaimable: Part of Slab, that might be reclaimed, such as caches
903 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
904 PageTables: amount of memory dedicated to the lowest level of page
906 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
908 Bounce: Memory used for block device "bounce buffers"
909 WritebackTmp: Memory used by FUSE for temporary writeback buffers
910 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
911 this is the total amount of memory currently available to
912 be allocated on the system. This limit is only adhered to
913 if strict overcommit accounting is enabled (mode 2 in
914 'vm.overcommit_memory').
915 The CommitLimit is calculated with the following formula:
916 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
917 overcommit_ratio / 100 + [total swap pages]
918 For example, on a system with 1G of physical RAM and 7G
919 of swap with a `vm.overcommit_ratio` of 30 it would
920 yield a CommitLimit of 7.3G.
921 For more details, see the memory overcommit documentation
922 in vm/overcommit-accounting.
923 Committed_AS: The amount of memory presently allocated on the system.
924 The committed memory is a sum of all of the memory which
925 has been allocated by processes, even if it has not been
926 "used" by them as of yet. A process which malloc()'s 1G
927 of memory, but only touches 300M of it will show up as
928 using 1G. This 1G is memory which has been "committed" to
929 by the VM and can be used at any time by the allocating
930 application. With strict overcommit enabled on the system
931 (mode 2 in 'vm.overcommit_memory'),allocations which would
932 exceed the CommitLimit (detailed above) will not be permitted.
933 This is useful if one needs to guarantee that processes will
934 not fail due to lack of memory once that memory has been
935 successfully allocated.
936 VmallocTotal: total size of vmalloc memory area
937 VmallocUsed: amount of vmalloc area which is used
938 VmallocChunk: largest contiguous block of vmalloc area which is free
940 ..............................................................................
944 Provides information about vmalloced/vmaped areas. One line per area,
945 containing the virtual address range of the area, size in bytes,
946 caller information of the creator, and optional information depending
947 on the kind of area :
949 pages=nr number of pages
950 phys=addr if a physical address was specified
951 ioremap I/O mapping (ioremap() and friends)
952 vmalloc vmalloc() area
955 vpages buffer for pages pointers was vmalloced (huge area)
956 N<node>=nr (Only on NUMA kernels)
957 Number of pages allocated on memory node <node>
959 > cat /proc/vmallocinfo
960 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
961 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
962 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
963 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
964 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
965 phys=7fee8000 ioremap
966 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
967 phys=7fee7000 ioremap
968 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
969 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
970 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
971 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
973 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
974 /0x130 [x_tables] pages=4 vmalloc N0=4
975 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
976 pages=14 vmalloc N2=14
977 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
979 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
981 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
982 pages=10 vmalloc N0=10
984 ..............................................................................
988 Provides counts of softirq handlers serviced since boot time, for each cpu.
993 TIMER: 27166 27120 27097 27034
998 SCHED: 27035 26983 26971 26746
1000 RCU: 1678 1769 2178 2250
1003 1.3 IDE devices in /proc/ide
1004 ----------------------------
1006 The subdirectory /proc/ide contains information about all IDE devices of which
1007 the kernel is aware. There is one subdirectory for each IDE controller, the
1008 file drivers and a link for each IDE device, pointing to the device directory
1009 in the controller specific subtree.
1011 The file drivers contains general information about the drivers used for the
1014 > cat /proc/ide/drivers
1015 ide-cdrom version 4.53
1016 ide-disk version 1.08
1018 More detailed information can be found in the controller specific
1019 subdirectories. These are named ide0, ide1 and so on. Each of these
1020 directories contains the files shown in table 1-6.
1023 Table 1-6: IDE controller info in /proc/ide/ide?
1024 ..............................................................................
1026 channel IDE channel (0 or 1)
1027 config Configuration (only for PCI/IDE bridge)
1029 model Type/Chipset of IDE controller
1030 ..............................................................................
1032 Each device connected to a controller has a separate subdirectory in the
1033 controllers directory. The files listed in table 1-7 are contained in these
1037 Table 1-7: IDE device information
1038 ..............................................................................
1041 capacity Capacity of the medium (in 512Byte blocks)
1042 driver driver and version
1043 geometry physical and logical geometry
1044 identify device identify block
1046 model device identifier
1047 settings device setup
1048 smart_thresholds IDE disk management thresholds
1049 smart_values IDE disk management values
1050 ..............................................................................
1052 The most interesting file is settings. This file contains a nice overview of
1053 the drive parameters:
1055 # cat /proc/ide/ide0/hda/settings
1056 name value min max mode
1057 ---- ----- --- --- ----
1058 bios_cyl 526 0 65535 rw
1059 bios_head 255 0 255 rw
1060 bios_sect 63 0 63 rw
1061 breada_readahead 4 0 127 rw
1063 file_readahead 72 0 2097151 rw
1065 keepsettings 0 0 1 rw
1066 max_kb_per_request 122 1 127 rw
1070 pio_mode write-only 0 255 w
1076 1.4 Networking info in /proc/net
1077 --------------------------------
1079 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1080 additional values you get for IP version 6 if you configure the kernel to
1081 support this. Table 1-9 lists the files and their meaning.
1084 Table 1-8: IPv6 info in /proc/net
1085 ..............................................................................
1087 udp6 UDP sockets (IPv6)
1088 tcp6 TCP sockets (IPv6)
1089 raw6 Raw device statistics (IPv6)
1090 igmp6 IP multicast addresses, which this host joined (IPv6)
1091 if_inet6 List of IPv6 interface addresses
1092 ipv6_route Kernel routing table for IPv6
1093 rt6_stats Global IPv6 routing tables statistics
1094 sockstat6 Socket statistics (IPv6)
1095 snmp6 Snmp data (IPv6)
1096 ..............................................................................
1099 Table 1-9: Network info in /proc/net
1100 ..............................................................................
1102 arp Kernel ARP table
1103 dev network devices with statistics
1104 dev_mcast the Layer2 multicast groups a device is listening too
1105 (interface index, label, number of references, number of bound
1107 dev_stat network device status
1108 ip_fwchains Firewall chain linkage
1109 ip_fwnames Firewall chain names
1110 ip_masq Directory containing the masquerading tables
1111 ip_masquerade Major masquerading table
1112 netstat Network statistics
1113 raw raw device statistics
1114 route Kernel routing table
1115 rpc Directory containing rpc info
1116 rt_cache Routing cache
1118 sockstat Socket statistics
1121 unix UNIX domain sockets
1122 wireless Wireless interface data (Wavelan etc)
1123 igmp IP multicast addresses, which this host joined
1124 psched Global packet scheduler parameters.
1125 netlink List of PF_NETLINK sockets
1126 ip_mr_vifs List of multicast virtual interfaces
1127 ip_mr_cache List of multicast routing cache
1128 ..............................................................................
1130 You can use this information to see which network devices are available in
1131 your system and how much traffic was routed over those devices:
1134 Inter-|Receive |[...
1135 face |bytes packets errs drop fifo frame compressed multicast|[...
1136 lo: 908188 5596 0 0 0 0 0 0 [...
1137 ppp0:15475140 20721 410 0 0 410 0 0 [...
1138 eth0: 614530 7085 0 0 0 0 0 1 [...
1141 ...] bytes packets errs drop fifo colls carrier compressed
1142 ...] 908188 5596 0 0 0 0 0 0
1143 ...] 1375103 17405 0 0 0 0 0 0
1144 ...] 1703981 5535 0 0 0 3 0 0
1146 In addition, each Channel Bond interface has its own directory. For
1147 example, the bond0 device will have a directory called /proc/net/bond0/.
1148 It will contain information that is specific to that bond, such as the
1149 current slaves of the bond, the link status of the slaves, and how
1150 many times the slaves link has failed.
1155 If you have a SCSI host adapter in your system, you'll find a subdirectory
1156 named after the driver for this adapter in /proc/scsi. You'll also see a list
1157 of all recognized SCSI devices in /proc/scsi:
1159 >cat /proc/scsi/scsi
1161 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1162 Vendor: IBM Model: DGHS09U Rev: 03E0
1163 Type: Direct-Access ANSI SCSI revision: 03
1164 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1165 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1166 Type: CD-ROM ANSI SCSI revision: 02
1169 The directory named after the driver has one file for each adapter found in
1170 the system. These files contain information about the controller, including
1171 the used IRQ and the IO address range. The amount of information shown is
1172 dependent on the adapter you use. The example shows the output for an Adaptec
1173 AHA-2940 SCSI adapter:
1175 > cat /proc/scsi/aic7xxx/0
1177 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1179 TCQ Enabled By Default : Disabled
1180 AIC7XXX_PROC_STATS : Disabled
1181 AIC7XXX_RESET_DELAY : 5
1182 Adapter Configuration:
1183 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1184 Ultra Wide Controller
1185 PCI MMAPed I/O Base: 0xeb001000
1186 Adapter SEEPROM Config: SEEPROM found and used.
1187 Adaptec SCSI BIOS: Enabled
1189 SCBs: Active 0, Max Active 2,
1190 Allocated 15, HW 16, Page 255
1192 BIOS Control Word: 0x18b6
1193 Adapter Control Word: 0x005b
1194 Extended Translation: Enabled
1195 Disconnect Enable Flags: 0xffff
1196 Ultra Enable Flags: 0x0001
1197 Tag Queue Enable Flags: 0x0000
1198 Ordered Queue Tag Flags: 0x0000
1199 Default Tag Queue Depth: 8
1200 Tagged Queue By Device array for aic7xxx host instance 0:
1201 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1202 Actual queue depth per device for aic7xxx host instance 0:
1203 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1206 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1207 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1208 Total transfers 160151 (74577 reads and 85574 writes)
1210 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1211 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1212 Total transfers 0 (0 reads and 0 writes)
1215 1.6 Parallel port info in /proc/parport
1216 ---------------------------------------
1218 The directory /proc/parport contains information about the parallel ports of
1219 your system. It has one subdirectory for each port, named after the port
1222 These directories contain the four files shown in Table 1-10.
1225 Table 1-10: Files in /proc/parport
1226 ..............................................................................
1228 autoprobe Any IEEE-1284 device ID information that has been acquired.
1229 devices list of the device drivers using that port. A + will appear by the
1230 name of the device currently using the port (it might not appear
1232 hardware Parallel port's base address, IRQ line and DMA channel.
1233 irq IRQ that parport is using for that port. This is in a separate
1234 file to allow you to alter it by writing a new value in (IRQ
1236 ..............................................................................
1238 1.7 TTY info in /proc/tty
1239 -------------------------
1241 Information about the available and actually used tty's can be found in the
1242 directory /proc/tty.You'll find entries for drivers and line disciplines in
1243 this directory, as shown in Table 1-11.
1246 Table 1-11: Files in /proc/tty
1247 ..............................................................................
1249 drivers list of drivers and their usage
1250 ldiscs registered line disciplines
1251 driver/serial usage statistic and status of single tty lines
1252 ..............................................................................
1254 To see which tty's are currently in use, you can simply look into the file
1257 > cat /proc/tty/drivers
1258 pty_slave /dev/pts 136 0-255 pty:slave
1259 pty_master /dev/ptm 128 0-255 pty:master
1260 pty_slave /dev/ttyp 3 0-255 pty:slave
1261 pty_master /dev/pty 2 0-255 pty:master
1262 serial /dev/cua 5 64-67 serial:callout
1263 serial /dev/ttyS 4 64-67 serial
1264 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1265 /dev/ptmx /dev/ptmx 5 2 system
1266 /dev/console /dev/console 5 1 system:console
1267 /dev/tty /dev/tty 5 0 system:/dev/tty
1268 unknown /dev/tty 4 1-63 console
1271 1.8 Miscellaneous kernel statistics in /proc/stat
1272 -------------------------------------------------
1274 Various pieces of information about kernel activity are available in the
1275 /proc/stat file. All of the numbers reported in this file are aggregates
1276 since the system first booted. For a quick look, simply cat the file:
1279 cpu 2255 34 2290 22625563 6290 127 456 0 0 0
1280 cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1281 cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1282 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1288 softirq 183433 0 21755 12 39 1137 231 21459 2263
1290 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1291 lines. These numbers identify the amount of time the CPU has spent performing
1292 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1293 second). The meanings of the columns are as follows, from left to right:
1295 - user: normal processes executing in user mode
1296 - nice: niced processes executing in user mode
1297 - system: processes executing in kernel mode
1298 - idle: twiddling thumbs
1299 - iowait: waiting for I/O to complete
1300 - irq: servicing interrupts
1301 - softirq: servicing softirqs
1302 - steal: involuntary wait
1303 - guest: running a normal guest
1304 - guest_nice: running a niced guest
1306 The "intr" line gives counts of interrupts serviced since boot time, for each
1307 of the possible system interrupts. The first column is the total of all
1308 interrupts serviced including unnumbered architecture specific interrupts;
1309 each subsequent column is the total for that particular numbered interrupt.
1310 Unnumbered interrupts are not shown, only summed into the total.
1312 The "ctxt" line gives the total number of context switches across all CPUs.
1314 The "btime" line gives the time at which the system booted, in seconds since
1317 The "processes" line gives the number of processes and threads created, which
1318 includes (but is not limited to) those created by calls to the fork() and
1319 clone() system calls.
1321 The "procs_running" line gives the total number of threads that are
1322 running or ready to run (i.e., the total number of runnable threads).
1324 The "procs_blocked" line gives the number of processes currently blocked,
1325 waiting for I/O to complete.
1327 The "softirq" line gives counts of softirqs serviced since boot time, for each
1328 of the possible system softirqs. The first column is the total of all
1329 softirqs serviced; each subsequent column is the total for that particular
1333 1.9 Ext4 file system parameters
1334 -------------------------------
1336 Information about mounted ext4 file systems can be found in
1337 /proc/fs/ext4. Each mounted filesystem will have a directory in
1338 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1339 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1340 in Table 1-12, below.
1342 Table 1-12: Files in /proc/fs/ext4/<devname>
1343 ..............................................................................
1345 mb_groups details of multiblock allocator buddy cache of free blocks
1346 ..............................................................................
1350 Shows registered system console lines.
1352 To see which character device lines are currently used for the system console
1353 /dev/console, you may simply look into the file /proc/consoles:
1355 > cat /proc/consoles
1361 device name of the device
1362 operations R = can do read operations
1363 W = can do write operations
1365 flags E = it is enabled
1366 C = it is preferred console
1367 B = it is primary boot console
1368 p = it is used for printk buffer
1369 b = it is not a TTY but a Braille device
1370 a = it is safe to use when cpu is offline
1371 major:minor major and minor number of the device separated by a colon
1373 ------------------------------------------------------------------------------
1375 ------------------------------------------------------------------------------
1376 The /proc file system serves information about the running system. It not only
1377 allows access to process data but also allows you to request the kernel status
1378 by reading files in the hierarchy.
1380 The directory structure of /proc reflects the types of information and makes
1381 it easy, if not obvious, where to look for specific data.
1382 ------------------------------------------------------------------------------
1384 ------------------------------------------------------------------------------
1385 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1386 ------------------------------------------------------------------------------
1388 ------------------------------------------------------------------------------
1390 ------------------------------------------------------------------------------
1391 * Modifying kernel parameters by writing into files found in /proc/sys
1392 * Exploring the files which modify certain parameters
1393 * Review of the /proc/sys file tree
1394 ------------------------------------------------------------------------------
1397 A very interesting part of /proc is the directory /proc/sys. This is not only
1398 a source of information, it also allows you to change parameters within the
1399 kernel. Be very careful when attempting this. You can optimize your system,
1400 but you can also cause it to crash. Never alter kernel parameters on a
1401 production system. Set up a development machine and test to make sure that
1402 everything works the way you want it to. You may have no alternative but to
1403 reboot the machine once an error has been made.
1405 To change a value, simply echo the new value into the file. An example is
1406 given below in the section on the file system data. You need to be root to do
1407 this. You can create your own boot script to perform this every time your
1410 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1411 general things in the operation of the Linux kernel. Since some of the files
1412 can inadvertently disrupt your system, it is advisable to read both
1413 documentation and source before actually making adjustments. In any case, be
1414 very careful when writing to any of these files. The entries in /proc may
1415 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1416 review the kernel documentation in the directory /usr/src/linux/Documentation.
1417 This chapter is heavily based on the documentation included in the pre 2.2
1418 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1420 Please see: Documentation/sysctl/ directory for descriptions of these
1423 ------------------------------------------------------------------------------
1425 ------------------------------------------------------------------------------
1426 Certain aspects of kernel behavior can be modified at runtime, without the
1427 need to recompile the kernel, or even to reboot the system. The files in the
1428 /proc/sys tree can not only be read, but also modified. You can use the echo
1429 command to write value into these files, thereby changing the default settings
1431 ------------------------------------------------------------------------------
1433 ------------------------------------------------------------------------------
1434 CHAPTER 3: PER-PROCESS PARAMETERS
1435 ------------------------------------------------------------------------------
1437 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1438 --------------------------------------------------------------------------------
1440 These file can be used to adjust the badness heuristic used to select which
1441 process gets killed in out of memory conditions.
1443 The badness heuristic assigns a value to each candidate task ranging from 0
1444 (never kill) to 1000 (always kill) to determine which process is targeted. The
1445 units are roughly a proportion along that range of allowed memory the process
1446 may allocate from based on an estimation of its current memory and swap use.
1447 For example, if a task is using all allowed memory, its badness score will be
1448 1000. If it is using half of its allowed memory, its score will be 500.
1450 There is an additional factor included in the badness score: the current memory
1451 and swap usage is discounted by 3% for root processes.
1453 The amount of "allowed" memory depends on the context in which the oom killer
1454 was called. If it is due to the memory assigned to the allocating task's cpuset
1455 being exhausted, the allowed memory represents the set of mems assigned to that
1456 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1457 memory represents the set of mempolicy nodes. If it is due to a memory
1458 limit (or swap limit) being reached, the allowed memory is that configured
1459 limit. Finally, if it is due to the entire system being out of memory, the
1460 allowed memory represents all allocatable resources.
1462 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1463 is used to determine which task to kill. Acceptable values range from -1000
1464 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to
1465 polarize the preference for oom killing either by always preferring a certain
1466 task or completely disabling it. The lowest possible value, -1000, is
1467 equivalent to disabling oom killing entirely for that task since it will always
1468 report a badness score of 0.
1470 Consequently, it is very simple for userspace to define the amount of memory to
1471 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1472 example, is roughly equivalent to allowing the remainder of tasks sharing the
1473 same system, cpuset, mempolicy, or memory controller resources to use at least
1474 50% more memory. A value of -500, on the other hand, would be roughly
1475 equivalent to discounting 50% of the task's allowed memory from being considered
1476 as scoring against the task.
1478 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1479 be used to tune the badness score. Its acceptable values range from -16
1480 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1481 (OOM_DISABLE) to disable oom killing entirely for that task. Its value is
1482 scaled linearly with /proc/<pid>/oom_score_adj.
1484 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1485 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1486 requires CAP_SYS_RESOURCE.
1488 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1489 generation children with separate address spaces instead, if possible. This
1490 avoids servers and important system daemons from being killed and loses the
1491 minimal amount of work.
1494 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1495 -------------------------------------------------------------
1497 This file can be used to check the current score used by the oom-killer is for
1498 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1499 process should be killed in an out-of-memory situation.
1502 3.3 /proc/<pid>/io - Display the IO accounting fields
1503 -------------------------------------------------------
1505 This file contains IO statistics for each running process
1510 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1513 test:/tmp # cat /proc/3828/io
1519 write_bytes: 323932160
1520 cancelled_write_bytes: 0
1529 I/O counter: chars read
1530 The number of bytes which this task has caused to be read from storage. This
1531 is simply the sum of bytes which this process passed to read() and pread().
1532 It includes things like tty IO and it is unaffected by whether or not actual
1533 physical disk IO was required (the read might have been satisfied from
1540 I/O counter: chars written
1541 The number of bytes which this task has caused, or shall cause to be written
1542 to disk. Similar caveats apply here as with rchar.
1548 I/O counter: read syscalls
1549 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1556 I/O counter: write syscalls
1557 Attempt to count the number of write I/O operations, i.e. syscalls like
1558 write() and pwrite().
1564 I/O counter: bytes read
1565 Attempt to count the number of bytes which this process really did cause to
1566 be fetched from the storage layer. Done at the submit_bio() level, so it is
1567 accurate for block-backed filesystems. <please add status regarding NFS and
1568 CIFS at a later time>
1574 I/O counter: bytes written
1575 Attempt to count the number of bytes which this process caused to be sent to
1576 the storage layer. This is done at page-dirtying time.
1579 cancelled_write_bytes
1580 ---------------------
1582 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1583 then deletes the file, it will in fact perform no writeout. But it will have
1584 been accounted as having caused 1MB of write.
1585 In other words: The number of bytes which this process caused to not happen,
1586 by truncating pagecache. A task can cause "negative" IO too. If this task
1587 truncates some dirty pagecache, some IO which another task has been accounted
1588 for (in its write_bytes) will not be happening. We _could_ just subtract that
1589 from the truncating task's write_bytes, but there is information loss in doing
1596 At its current implementation state, this is a bit racy on 32-bit machines: if
1597 process A reads process B's /proc/pid/io while process B is updating one of
1598 those 64-bit counters, process A could see an intermediate result.
1601 More information about this can be found within the taskstats documentation in
1602 Documentation/accounting.
1604 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1605 ---------------------------------------------------------------
1606 When a process is dumped, all anonymous memory is written to a core file as
1607 long as the size of the core file isn't limited. But sometimes we don't want
1608 to dump some memory segments, for example, huge shared memory or DAX.
1609 Conversely, sometimes we want to save file-backed memory segments into a core
1610 file, not only the individual files.
1612 /proc/<pid>/coredump_filter allows you to customize which memory segments
1613 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1614 of memory types. If a bit of the bitmask is set, memory segments of the
1615 corresponding memory type are dumped, otherwise they are not dumped.
1617 The following 9 memory types are supported:
1618 - (bit 0) anonymous private memory
1619 - (bit 1) anonymous shared memory
1620 - (bit 2) file-backed private memory
1621 - (bit 3) file-backed shared memory
1622 - (bit 4) ELF header pages in file-backed private memory areas (it is
1623 effective only if the bit 2 is cleared)
1624 - (bit 5) hugetlb private memory
1625 - (bit 6) hugetlb shared memory
1626 - (bit 7) DAX private memory
1627 - (bit 8) DAX shared memory
1629 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1630 are always dumped regardless of the bitmask status.
1632 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1633 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1635 The default value of coredump_filter is 0x33; this means all anonymous memory
1636 segments, ELF header pages and hugetlb private memory are dumped.
1638 If you don't want to dump all shared memory segments attached to pid 1234,
1639 write 0x31 to the process's proc file.
1641 $ echo 0x31 > /proc/1234/coredump_filter
1643 When a new process is created, the process inherits the bitmask status from its
1644 parent. It is useful to set up coredump_filter before the program runs.
1647 $ echo 0x7 > /proc/self/coredump_filter
1650 3.5 /proc/<pid>/mountinfo - Information about mounts
1651 --------------------------------------------------------
1653 This file contains lines of the form:
1655 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1656 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1658 (1) mount ID: unique identifier of the mount (may be reused after umount)
1659 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1660 (3) major:minor: value of st_dev for files on filesystem
1661 (4) root: root of the mount within the filesystem
1662 (5) mount point: mount point relative to the process's root
1663 (6) mount options: per mount options
1664 (7) optional fields: zero or more fields of the form "tag[:value]"
1665 (8) separator: marks the end of the optional fields
1666 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1667 (10) mount source: filesystem specific information or "none"
1668 (11) super options: per super block options
1670 Parsers should ignore all unrecognised optional fields. Currently the
1671 possible optional fields are:
1673 shared:X mount is shared in peer group X
1674 master:X mount is slave to peer group X
1675 propagate_from:X mount is slave and receives propagation from peer group X (*)
1676 unbindable mount is unbindable
1678 (*) X is the closest dominant peer group under the process's root. If
1679 X is the immediate master of the mount, or if there's no dominant peer
1680 group under the same root, then only the "master:X" field is present
1681 and not the "propagate_from:X" field.
1683 For more information on mount propagation see:
1685 Documentation/filesystems/sharedsubtree.txt
1688 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1689 --------------------------------------------------------
1690 These files provide a method to access a tasks comm value. It also allows for
1691 a task to set its own or one of its thread siblings comm value. The comm value
1692 is limited in size compared to the cmdline value, so writing anything longer
1693 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1697 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1698 -------------------------------------------------------------------------
1699 This file provides a fast way to retrieve first level children pids
1700 of a task pointed by <pid>/<tid> pair. The format is a space separated
1703 Note the "first level" here -- if a child has own children they will
1704 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1705 to obtain the descendants.
1707 Since this interface is intended to be fast and cheap it doesn't
1708 guarantee to provide precise results and some children might be
1709 skipped, especially if they've exited right after we printed their
1710 pids, so one need to either stop or freeze processes being inspected
1711 if precise results are needed.
1714 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1715 ---------------------------------------------------------------
1716 This file provides information associated with an opened file. The regular
1717 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1718 represents the current offset of the opened file in decimal form [see lseek(2)
1719 for details], 'flags' denotes the octal O_xxx mask the file has been
1720 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1721 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1730 All locks associated with a file descriptor are shown in its fdinfo too.
1732 lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF
1734 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1735 pair provide additional information particular to the objects they represent.
1744 where 'eventfd-count' is hex value of a counter.
1751 sigmask: 0000000000000200
1753 where 'sigmask' is hex value of the signal mask associated
1761 tfd: 5 events: 1d data: ffffffffffffffff
1763 where 'tfd' is a target file descriptor number in decimal form,
1764 'events' is events mask being watched and the 'data' is data
1765 associated with a target [see epoll(7) for more details].
1769 For inotify files the format is the following
1773 inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1775 where 'wd' is a watch descriptor in decimal form, ie a target file
1776 descriptor number, 'ino' and 'sdev' are inode and device where the
1777 target file resides and the 'mask' is the mask of events, all in hex
1778 form [see inotify(7) for more details].
1780 If the kernel was built with exportfs support, the path to the target
1781 file is encoded as a file handle. The file handle is provided by three
1782 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1785 If the kernel is built without exportfs support the file handle won't be
1788 If there is no inotify mark attached yet the 'inotify' line will be omitted.
1790 For fanotify files the format is
1795 fanotify flags:10 event-flags:0
1796 fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1797 fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1799 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1800 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1801 flags associated with mark which are tracked separately from events
1802 mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1803 mask and 'ignored_mask' is the mask of events which are to be ignored.
1804 All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1805 does provide information about flags and mask used in fanotify_mark
1806 call [see fsnotify manpage for details].
1808 While the first three lines are mandatory and always printed, the rest is
1809 optional and may be omitted if no marks created yet.
1820 it_value: (0, 49406829)
1823 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1824 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1825 flags in octal form been used to setup the timer [see timerfd_settime(2) for
1826 details]. 'it_value' is remaining time until the timer exiration.
1827 'it_interval' is the interval for the timer. Note the timer might be set up
1828 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1829 still exhibits timer's remaining time.
1831 3.9 /proc/<pid>/map_files - Information about memory mapped files
1832 ---------------------------------------------------------------------
1833 This directory contains symbolic links which represent memory mapped files
1834 the process is maintaining. Example output:
1836 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1837 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1838 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1840 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1841 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1843 The name of a link represents the virtual memory bounds of a mapping, i.e.
1844 vm_area_struct::vm_start-vm_area_struct::vm_end.
1846 The main purpose of the map_files is to retrieve a set of memory mapped
1847 files in a fast way instead of parsing /proc/<pid>/maps or
1848 /proc/<pid>/smaps, both of which contain many more records. At the same
1849 time one can open(2) mappings from the listings of two processes and
1850 comparing their inode numbers to figure out which anonymous memory areas
1851 are actually shared.
1853 ------------------------------------------------------------------------------
1855 ------------------------------------------------------------------------------
1858 ---------------------
1860 The following mount options are supported:
1862 hidepid= Set /proc/<pid>/ access mode.
1863 gid= Set the group authorized to learn processes information.
1865 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1868 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1869 own. Sensitive files like cmdline, sched*, status are now protected against
1870 other users. This makes it impossible to learn whether any user runs
1871 specific program (given the program doesn't reveal itself by its behaviour).
1872 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1873 poorly written programs passing sensitive information via program arguments are
1874 now protected against local eavesdroppers.
1876 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1877 users. It doesn't mean that it hides a fact whether a process with a specific
1878 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1879 but it hides process' uid and gid, which may be learned by stat()'ing
1880 /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
1881 information about running processes, whether some daemon runs with elevated
1882 privileges, whether other user runs some sensitive program, whether other users
1883 run any program at all, etc.
1885 gid= defines a group authorized to learn processes information otherwise
1886 prohibited by hidepid=. If you use some daemon like identd which needs to learn
1887 information about processes information, just add identd to this group.
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