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 - Adjust the oom-killer score
37 3.2 /proc/<pid>/oom_score - Display current oom-killer score
38 3.3 /proc/<pid>/io - Display the IO accounting fields
39 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
40 3.5 /proc/<pid>/mountinfo - Information about mounts
43 ------------------------------------------------------------------------------
45 ------------------------------------------------------------------------------
47 0.1 Introduction/Credits
48 ------------------------
50 This documentation is part of a soon (or so we hope) to be released book on
51 the SuSE Linux distribution. As there is no complete documentation for the
52 /proc file system and we've used many freely available sources to write these
53 chapters, it seems only fair to give the work back to the Linux community.
54 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
55 afraid it's still far from complete, but we hope it will be useful. As far as
56 we know, it is the first 'all-in-one' document about the /proc file system. It
57 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
58 SPARC, AXP, etc., features, you probably won't find what you are looking for.
59 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
60 additions and patches are welcome and will be added to this document if you
63 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
64 other people for help compiling this documentation. We'd also like to extend a
65 special thank you to Andi Kleen for documentation, which we relied on heavily
66 to create this document, as well as the additional information he provided.
67 Thanks to everybody else who contributed source or docs to the Linux kernel
68 and helped create a great piece of software... :)
70 If you have any comments, corrections or additions, please don't hesitate to
71 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
74 The latest version of this document is available online at
75 http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
77 If the above direction does not works for you, ypu could try the kernel
78 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
79 comandante@zaralinux.com.
84 We don't guarantee the correctness of this document, and if you come to us
85 complaining about how you screwed up your system because of incorrect
86 documentation, we won't feel responsible...
88 ------------------------------------------------------------------------------
89 CHAPTER 1: COLLECTING SYSTEM INFORMATION
90 ------------------------------------------------------------------------------
92 ------------------------------------------------------------------------------
94 ------------------------------------------------------------------------------
95 * Investigating the properties of the pseudo file system /proc and its
96 ability to provide information on the running Linux system
97 * Examining /proc's structure
98 * Uncovering various information about the kernel and the processes running
100 ------------------------------------------------------------------------------
103 The proc file system acts as an interface to internal data structures in the
104 kernel. It can be used to obtain information about the system and to change
105 certain kernel parameters at runtime (sysctl).
107 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
108 show you how you can use /proc/sys to change settings.
110 1.1 Process-Specific Subdirectories
111 -----------------------------------
113 The directory /proc contains (among other things) one subdirectory for each
114 process running on the system, which is named after the process ID (PID).
116 The link self points to the process reading the file system. Each process
117 subdirectory has the entries listed in Table 1-1.
120 Table 1-1: Process specific entries in /proc
121 ..............................................................................
123 clear_refs Clears page referenced bits shown in smaps output
124 cmdline Command line arguments
125 cpu Current and last cpu in which it was executed (2.4)(smp)
126 cwd Link to the current working directory
127 environ Values of environment variables
128 exe Link to the executable of this process
129 fd Directory, which contains all file descriptors
130 maps Memory maps to executables and library files (2.4)
131 mem Memory held by this process
132 root Link to the root directory of this process
134 statm Process memory status information
135 status Process status in human readable form
136 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
137 stack Report full stack trace, enable via CONFIG_STACKTRACE
138 smaps a extension based on maps, showing the memory consumption of
140 ..............................................................................
142 For example, to get the status information of a process, all you have to do is
143 read the file /proc/PID/status:
145 >cat /proc/self/status
168 SigPnd: 0000000000000000
169 ShdPnd: 0000000000000000
170 SigBlk: 0000000000000000
171 SigIgn: 0000000000000000
172 SigCgt: 0000000000000000
173 CapInh: 00000000fffffeff
174 CapPrm: 0000000000000000
175 CapEff: 0000000000000000
176 CapBnd: ffffffffffffffff
177 voluntary_ctxt_switches: 0
178 nonvoluntary_ctxt_switches: 1
181 This shows you nearly the same information you would get if you viewed it with
182 the ps command. In fact, ps uses the proc file system to obtain its
183 information. But you get a more detailed view of the process by reading the
184 file /proc/PID/status. It fields are described in table 1-2.
186 The statm file contains more detailed information about the process
187 memory usage. Its seven fields are explained in Table 1-3. The stat file
188 contains details information about the process itself. Its fields are
189 explained in Table 1-4.
191 Table 1-2: Contents of the statm files (as of 2.6.30-rc7)
192 ..............................................................................
194 Name filename of the executable
195 State state (R is running, S is sleeping, D is sleeping
196 in an uninterruptible wait, Z is zombie,
197 T is traced or stopped)
200 PPid process id of the parent process
201 TracerPid PID of process tracing this process (0 if not)
202 Uid Real, effective, saved set, and file system UIDs
203 Gid Real, effective, saved set, and file system GIDs
204 FDSize number of file descriptor slots currently allocated
205 Groups supplementary group list
206 VmPeak peak virtual memory size
207 VmSize total program size
208 VmLck locked memory size
209 VmHWM peak resident set size ("high water mark")
210 VmRSS size of memory portions
211 VmData size of data, stack, and text segments
212 VmStk size of data, stack, and text segments
213 VmExe size of text segment
214 VmLib size of shared library code
215 VmPTE size of page table entries
216 Threads number of threads
217 SigQ number of signals queued/max. number for queue
218 SigPnd bitmap of pending signals for the thread
219 ShdPnd bitmap of shared pending signals for the process
220 SigBlk bitmap of blocked signals
221 SigIgn bitmap of ignored signals
222 SigCgt bitmap of catched signals
223 CapInh bitmap of inheritable capabilities
224 CapPrm bitmap of permitted capabilities
225 CapEff bitmap of effective capabilities
226 CapBnd bitmap of capabilities bounding set
227 Cpus_allowed mask of CPUs on which this process may run
228 Cpus_allowed_list Same as previous, but in "list format"
229 Mems_allowed mask of memory nodes allowed to this process
230 Mems_allowed_list Same as previous, but in "list format"
231 voluntary_ctxt_switches number of voluntary context switches
232 nonvoluntary_ctxt_switches number of non voluntary context switches
233 Stack usage: stack usage high water mark (round up to page size)
234 ..............................................................................
236 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
237 ..............................................................................
239 size total program size (pages) (same as VmSize in status)
240 resident size of memory portions (pages) (same as VmRSS in status)
241 shared number of pages that are shared (i.e. backed by a file)
242 trs number of pages that are 'code' (not including libs; broken,
243 includes data segment)
244 lrs number of pages of library (always 0 on 2.6)
245 drs number of pages of data/stack (including libs; broken,
246 includes library text)
247 dt number of dirty pages (always 0 on 2.6)
248 ..............................................................................
251 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
252 ..............................................................................
255 tcomm filename of the executable
256 state state (R is running, S is sleeping, D is sleeping in an
257 uninterruptible wait, Z is zombie, T is traced or stopped)
258 ppid process id of the parent process
259 pgrp pgrp of the process
261 tty_nr tty the process uses
262 tty_pgrp pgrp of the tty
264 min_flt number of minor faults
265 cmin_flt number of minor faults with child's
266 maj_flt number of major faults
267 cmaj_flt number of major faults with child's
268 utime user mode jiffies
269 stime kernel mode jiffies
270 cutime user mode jiffies with child's
271 cstime kernel mode jiffies with child's
272 priority priority level
274 num_threads number of threads
275 it_real_value (obsolete, always 0)
276 start_time time the process started after system boot
277 vsize virtual memory size
278 rss resident set memory size
279 rsslim current limit in bytes on the rss
280 start_code address above which program text can run
281 end_code address below which program text can run
282 start_stack address of the start of the stack
283 esp current value of ESP
284 eip current value of EIP
285 pending bitmap of pending signals
286 blocked bitmap of blocked signals
287 sigign bitmap of ignored signals
288 sigcatch bitmap of catched signals
289 wchan address where process went to sleep
292 exit_signal signal to send to parent thread on exit
293 task_cpu which CPU the task is scheduled on
294 rt_priority realtime priority
295 policy scheduling policy (man sched_setscheduler)
296 blkio_ticks time spent waiting for block IO
297 gtime guest time of the task in jiffies
298 cgtime guest time of the task children in jiffies
299 ..............................................................................
301 The /proc/PID/map file containing the currently mapped memory regions and
302 their access permissions.
306 address perms offset dev inode pathname
308 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
309 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
310 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
311 a7cb1000-a7cb2000 ---p 00000000 00:00 0
312 a7cb2000-a7eb2000 rw-p 00000000 00:00 0 [threadstack:001ff4b4]
313 a7eb2000-a7eb3000 ---p 00000000 00:00 0
314 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
315 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
316 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
317 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
318 a800b000-a800e000 rw-p 00000000 00:00 0
319 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
320 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
321 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
322 a8024000-a8027000 rw-p 00000000 00:00 0
323 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
324 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
325 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
326 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
327 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
329 where "address" is the address space in the process that it occupies, "perms"
330 is a set of permissions:
336 p = private (copy on write)
338 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
339 "inode" is the inode on that device. 0 indicates that no inode is associated
340 with the memory region, as the case would be with BSS (uninitialized data).
341 The "pathname" shows the name associated file for this mapping. If the mapping
342 is not associated with a file:
344 [heap] = the heap of the program
345 [stack] = the stack of the main process
346 [vdso] = the "virtual dynamic shared object",
347 the kernel system call handler
348 [threadstack:xxxxxxxx] = the stack of the thread, xxxxxxxx is the stack size
350 or if empty, the mapping is anonymous.
353 The /proc/PID/smaps is an extension based on maps, showing the memory
354 consumption for each of the process's mappings. For each of mappings there
355 is a series of lines such as the following:
357 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
370 The first of these lines shows the same information as is displayed for the
371 mapping in /proc/PID/maps. The remaining lines show the size of the mapping,
372 the amount of the mapping that is currently resident in RAM, the "proportional
373 set size” (divide each shared page by the number of processes sharing it), the
374 number of clean and dirty shared pages in the mapping, and the number of clean
375 and dirty private pages in the mapping. The "Referenced" indicates the amount
376 of memory currently marked as referenced or accessed.
378 This file is only present if the CONFIG_MMU kernel configuration option is
381 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
382 bits on both physical and virtual pages associated with a process.
383 To clear the bits for all the pages associated with the process
384 > echo 1 > /proc/PID/clear_refs
386 To clear the bits for the anonymous pages associated with the process
387 > echo 2 > /proc/PID/clear_refs
389 To clear the bits for the file mapped pages associated with the process
390 > echo 3 > /proc/PID/clear_refs
391 Any other value written to /proc/PID/clear_refs will have no effect.
397 Similar to the process entries, the kernel data files give information about
398 the running kernel. The files used to obtain this information are contained in
399 /proc and are listed in Table 1-5. Not all of these will be present in your
400 system. It depends on the kernel configuration and the loaded modules, which
401 files are there, and which are missing.
403 Table 1-5: Kernel info in /proc
404 ..............................................................................
406 apm Advanced power management info
407 buddyinfo Kernel memory allocator information (see text) (2.5)
408 bus Directory containing bus specific information
409 cmdline Kernel command line
410 cpuinfo Info about the CPU
411 devices Available devices (block and character)
412 dma Used DMS channels
413 filesystems Supported filesystems
414 driver Various drivers grouped here, currently rtc (2.4)
415 execdomains Execdomains, related to security (2.4)
416 fb Frame Buffer devices (2.4)
417 fs File system parameters, currently nfs/exports (2.4)
418 ide Directory containing info about the IDE subsystem
419 interrupts Interrupt usage
420 iomem Memory map (2.4)
421 ioports I/O port usage
422 irq Masks for irq to cpu affinity (2.4)(smp?)
423 isapnp ISA PnP (Plug&Play) Info (2.4)
424 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
426 ksyms Kernel symbol table
427 loadavg Load average of last 1, 5 & 15 minutes
431 modules List of loaded modules
432 mounts Mounted filesystems
433 net Networking info (see text)
434 partitions Table of partitions known to the system
435 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
436 decoupled by lspci (2.4)
438 scsi SCSI info (see text)
439 slabinfo Slab pool info
440 softirqs softirq usage
441 stat Overall statistics
442 swaps Swap space utilization
444 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
445 tty Info of tty drivers
447 version Kernel version
448 video bttv info of video resources (2.4)
449 vmallocinfo Show vmalloced areas
450 ..............................................................................
452 You can, for example, check which interrupts are currently in use and what
453 they are used for by looking in the file /proc/interrupts:
455 > cat /proc/interrupts
457 0: 8728810 XT-PIC timer
458 1: 895 XT-PIC keyboard
460 3: 531695 XT-PIC aha152x
461 4: 2014133 XT-PIC serial
462 5: 44401 XT-PIC pcnet_cs
465 12: 182918 XT-PIC PS/2 Mouse
467 14: 1232265 XT-PIC ide0
471 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
472 output of a SMP machine):
474 > cat /proc/interrupts
477 0: 1243498 1214548 IO-APIC-edge timer
478 1: 8949 8958 IO-APIC-edge keyboard
479 2: 0 0 XT-PIC cascade
480 5: 11286 10161 IO-APIC-edge soundblaster
481 8: 1 0 IO-APIC-edge rtc
482 9: 27422 27407 IO-APIC-edge 3c503
483 12: 113645 113873 IO-APIC-edge PS/2 Mouse
485 14: 22491 24012 IO-APIC-edge ide0
486 15: 2183 2415 IO-APIC-edge ide1
487 17: 30564 30414 IO-APIC-level eth0
488 18: 177 164 IO-APIC-level bttv
493 NMI is incremented in this case because every timer interrupt generates a NMI
494 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
496 LOC is the local interrupt counter of the internal APIC of every CPU.
498 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
499 connects the CPUs in a SMP system. This means that an error has been detected,
500 the IO-APIC automatically retry the transmission, so it should not be a big
501 problem, but you should read the SMP-FAQ.
503 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
504 /proc/interrupts to display every IRQ vector in use by the system, not
505 just those considered 'most important'. The new vectors are:
507 THR -- interrupt raised when a machine check threshold counter
508 (typically counting ECC corrected errors of memory or cache) exceeds
509 a configurable threshold. Only available on some systems.
511 TRM -- a thermal event interrupt occurs when a temperature threshold
512 has been exceeded for the CPU. This interrupt may also be generated
513 when the temperature drops back to normal.
515 SPU -- a spurious interrupt is some interrupt that was raised then lowered
516 by some IO device before it could be fully processed by the APIC. Hence
517 the APIC sees the interrupt but does not know what device it came from.
518 For this case the APIC will generate the interrupt with a IRQ vector
519 of 0xff. This might also be generated by chipset bugs.
521 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
522 sent from one CPU to another per the needs of the OS. Typically,
523 their statistics are used by kernel developers and interested users to
524 determine the occurrence of interrupts of the given type.
526 The above IRQ vectors are displayed only when relevent. For example,
527 the threshold vector does not exist on x86_64 platforms. Others are
528 suppressed when the system is a uniprocessor. As of this writing, only
529 i386 and x86_64 platforms support the new IRQ vector displays.
531 Of some interest is the introduction of the /proc/irq directory to 2.4.
532 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
533 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
534 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
539 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
540 1 11 13 15 17 19 3 5 7 9 default_smp_affinity
544 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
545 IRQ, you can set it by doing:
547 > echo 1 > /proc/irq/10/smp_affinity
549 This means that only the first CPU will handle the IRQ, but you can also echo
550 5 which means that only the first and fourth CPU can handle the IRQ.
552 The contents of each smp_affinity file is the same by default:
554 > cat /proc/irq/0/smp_affinity
557 The default_smp_affinity mask applies to all non-active IRQs, which are the
558 IRQs which have not yet been allocated/activated, and hence which lack a
559 /proc/irq/[0-9]* directory.
561 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
562 profiler. Default value is ffffffff (all cpus).
564 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
565 between all the CPUs which are allowed to handle it. As usual the kernel has
566 more info than you and does a better job than you, so the defaults are the
567 best choice for almost everyone.
569 There are three more important subdirectories in /proc: net, scsi, and sys.
570 The general rule is that the contents, or even the existence of these
571 directories, depend on your kernel configuration. If SCSI is not enabled, the
572 directory scsi may not exist. The same is true with the net, which is there
573 only when networking support is present in the running kernel.
575 The slabinfo file gives information about memory usage at the slab level.
576 Linux uses slab pools for memory management above page level in version 2.2.
577 Commonly used objects have their own slab pool (such as network buffers,
578 directory cache, and so on).
580 ..............................................................................
582 > cat /proc/buddyinfo
584 Node 0, zone DMA 0 4 5 4 4 3 ...
585 Node 0, zone Normal 1 0 0 1 101 8 ...
586 Node 0, zone HighMem 2 0 0 1 1 0 ...
588 Memory fragmentation is a problem under some workloads, and buddyinfo is a
589 useful tool for helping diagnose these problems. Buddyinfo will give you a
590 clue as to how big an area you can safely allocate, or why a previous
593 Each column represents the number of pages of a certain order which are
594 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
595 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
596 available in ZONE_NORMAL, etc...
598 ..............................................................................
602 Provides information about distribution and utilization of memory. This
603 varies by architecture and compile options. The following is from a
604 16GB PIII, which has highmem enabled. You may not have all of these fields.
609 MemTotal: 16344972 kB
616 HighTotal: 15597528 kB
617 HighFree: 13629632 kB
627 SReclaimable: 159856 kB
628 SUnreclaim: 124508 kB
633 CommitLimit: 7669796 kB
634 Committed_AS: 100056 kB
635 VmallocTotal: 112216 kB
637 VmallocChunk: 111088 kB
639 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
640 bits and the kernel binary code)
641 MemFree: The sum of LowFree+HighFree
642 Buffers: Relatively temporary storage for raw disk blocks
643 shouldn't get tremendously large (20MB or so)
644 Cached: in-memory cache for files read from the disk (the
645 pagecache). Doesn't include SwapCached
646 SwapCached: Memory that once was swapped out, is swapped back in but
647 still also is in the swapfile (if memory is needed it
648 doesn't need to be swapped out AGAIN because it is already
649 in the swapfile. This saves I/O)
650 Active: Memory that has been used more recently and usually not
651 reclaimed unless absolutely necessary.
652 Inactive: Memory which has been less recently used. It is more
653 eligible to be reclaimed for other purposes
655 HighFree: Highmem is all memory above ~860MB of physical memory
656 Highmem areas are for use by userspace programs, or
657 for the pagecache. The kernel must use tricks to access
658 this memory, making it slower to access than lowmem.
660 LowFree: Lowmem is memory which can be used for everything that
661 highmem can be used for, but it is also available for the
662 kernel's use for its own data structures. Among many
663 other things, it is where everything from the Slab is
664 allocated. Bad things happen when you're out of lowmem.
665 SwapTotal: total amount of swap space available
666 SwapFree: Memory which has been evicted from RAM, and is temporarily
668 Dirty: Memory which is waiting to get written back to the disk
669 Writeback: Memory which is actively being written back to the disk
670 AnonPages: Non-file backed pages mapped into userspace page tables
671 Mapped: files which have been mmaped, such as libraries
672 Slab: in-kernel data structures cache
673 SReclaimable: Part of Slab, that might be reclaimed, such as caches
674 SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
675 PageTables: amount of memory dedicated to the lowest level of page
677 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
679 Bounce: Memory used for block device "bounce buffers"
680 WritebackTmp: Memory used by FUSE for temporary writeback buffers
681 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
682 this is the total amount of memory currently available to
683 be allocated on the system. This limit is only adhered to
684 if strict overcommit accounting is enabled (mode 2 in
685 'vm.overcommit_memory').
686 The CommitLimit is calculated with the following formula:
687 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
688 For example, on a system with 1G of physical RAM and 7G
689 of swap with a `vm.overcommit_ratio` of 30 it would
690 yield a CommitLimit of 7.3G.
691 For more details, see the memory overcommit documentation
692 in vm/overcommit-accounting.
693 Committed_AS: The amount of memory presently allocated on the system.
694 The committed memory is a sum of all of the memory which
695 has been allocated by processes, even if it has not been
696 "used" by them as of yet. A process which malloc()'s 1G
697 of memory, but only touches 300M of it will only show up
698 as using 300M of memory even if it has the address space
699 allocated for the entire 1G. This 1G is memory which has
700 been "committed" to by the VM and can be used at any time
701 by the allocating application. With strict overcommit
702 enabled on the system (mode 2 in 'vm.overcommit_memory'),
703 allocations which would exceed the CommitLimit (detailed
704 above) will not be permitted. This is useful if one needs
705 to guarantee that processes will not fail due to lack of
706 memory once that memory has been successfully allocated.
707 VmallocTotal: total size of vmalloc memory area
708 VmallocUsed: amount of vmalloc area which is used
709 VmallocChunk: largest contiguous block of vmalloc area which is free
711 ..............................................................................
715 Provides information about vmalloced/vmaped areas. One line per area,
716 containing the virtual address range of the area, size in bytes,
717 caller information of the creator, and optional information depending
718 on the kind of area :
720 pages=nr number of pages
721 phys=addr if a physical address was specified
722 ioremap I/O mapping (ioremap() and friends)
723 vmalloc vmalloc() area
726 vpages buffer for pages pointers was vmalloced (huge area)
727 N<node>=nr (Only on NUMA kernels)
728 Number of pages allocated on memory node <node>
730 > cat /proc/vmallocinfo
731 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
732 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
733 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
734 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
735 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
736 phys=7fee8000 ioremap
737 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
738 phys=7fee7000 ioremap
739 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
740 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
741 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
742 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
744 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
745 /0x130 [x_tables] pages=4 vmalloc N0=4
746 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
747 pages=14 vmalloc N2=14
748 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
750 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
752 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
753 pages=10 vmalloc N0=10
755 ..............................................................................
759 Provides counts of softirq handlers serviced since boot time, for each cpu.
764 TIMER: 27166 27120 27097 27034
769 SCHED: 27035 26983 26971 26746
771 RCU: 1678 1769 2178 2250
774 1.3 IDE devices in /proc/ide
775 ----------------------------
777 The subdirectory /proc/ide contains information about all IDE devices of which
778 the kernel is aware. There is one subdirectory for each IDE controller, the
779 file drivers and a link for each IDE device, pointing to the device directory
780 in the controller specific subtree.
782 The file drivers contains general information about the drivers used for the
785 > cat /proc/ide/drivers
786 ide-cdrom version 4.53
787 ide-disk version 1.08
789 More detailed information can be found in the controller specific
790 subdirectories. These are named ide0, ide1 and so on. Each of these
791 directories contains the files shown in table 1-6.
794 Table 1-6: IDE controller info in /proc/ide/ide?
795 ..............................................................................
797 channel IDE channel (0 or 1)
798 config Configuration (only for PCI/IDE bridge)
800 model Type/Chipset of IDE controller
801 ..............................................................................
803 Each device connected to a controller has a separate subdirectory in the
804 controllers directory. The files listed in table 1-7 are contained in these
808 Table 1-7: IDE device information
809 ..............................................................................
812 capacity Capacity of the medium (in 512Byte blocks)
813 driver driver and version
814 geometry physical and logical geometry
815 identify device identify block
817 model device identifier
818 settings device setup
819 smart_thresholds IDE disk management thresholds
820 smart_values IDE disk management values
821 ..............................................................................
823 The most interesting file is settings. This file contains a nice overview of
824 the drive parameters:
826 # cat /proc/ide/ide0/hda/settings
827 name value min max mode
828 ---- ----- --- --- ----
829 bios_cyl 526 0 65535 rw
830 bios_head 255 0 255 rw
832 breada_readahead 4 0 127 rw
834 file_readahead 72 0 2097151 rw
836 keepsettings 0 0 1 rw
837 max_kb_per_request 122 1 127 rw
841 pio_mode write-only 0 255 w
847 1.4 Networking info in /proc/net
848 --------------------------------
850 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
851 additional values you get for IP version 6 if you configure the kernel to
852 support this. Table 1-9 lists the files and their meaning.
855 Table 1-8: IPv6 info in /proc/net
856 ..............................................................................
858 udp6 UDP sockets (IPv6)
859 tcp6 TCP sockets (IPv6)
860 raw6 Raw device statistics (IPv6)
861 igmp6 IP multicast addresses, which this host joined (IPv6)
862 if_inet6 List of IPv6 interface addresses
863 ipv6_route Kernel routing table for IPv6
864 rt6_stats Global IPv6 routing tables statistics
865 sockstat6 Socket statistics (IPv6)
866 snmp6 Snmp data (IPv6)
867 ..............................................................................
870 Table 1-9: Network info in /proc/net
871 ..............................................................................
874 dev network devices with statistics
875 dev_mcast the Layer2 multicast groups a device is listening too
876 (interface index, label, number of references, number of bound
878 dev_stat network device status
879 ip_fwchains Firewall chain linkage
880 ip_fwnames Firewall chain names
881 ip_masq Directory containing the masquerading tables
882 ip_masquerade Major masquerading table
883 netstat Network statistics
884 raw raw device statistics
885 route Kernel routing table
886 rpc Directory containing rpc info
887 rt_cache Routing cache
889 sockstat Socket statistics
891 tr_rif Token ring RIF routing table
893 unix UNIX domain sockets
894 wireless Wireless interface data (Wavelan etc)
895 igmp IP multicast addresses, which this host joined
896 psched Global packet scheduler parameters.
897 netlink List of PF_NETLINK sockets
898 ip_mr_vifs List of multicast virtual interfaces
899 ip_mr_cache List of multicast routing cache
900 ..............................................................................
902 You can use this information to see which network devices are available in
903 your system and how much traffic was routed over those devices:
907 face |bytes packets errs drop fifo frame compressed multicast|[...
908 lo: 908188 5596 0 0 0 0 0 0 [...
909 ppp0:15475140 20721 410 0 0 410 0 0 [...
910 eth0: 614530 7085 0 0 0 0 0 1 [...
913 ...] bytes packets errs drop fifo colls carrier compressed
914 ...] 908188 5596 0 0 0 0 0 0
915 ...] 1375103 17405 0 0 0 0 0 0
916 ...] 1703981 5535 0 0 0 3 0 0
918 In addition, each Channel Bond interface has it's own directory. For
919 example, the bond0 device will have a directory called /proc/net/bond0/.
920 It will contain information that is specific to that bond, such as the
921 current slaves of the bond, the link status of the slaves, and how
922 many times the slaves link has failed.
927 If you have a SCSI host adapter in your system, you'll find a subdirectory
928 named after the driver for this adapter in /proc/scsi. You'll also see a list
929 of all recognized SCSI devices in /proc/scsi:
933 Host: scsi0 Channel: 00 Id: 00 Lun: 00
934 Vendor: IBM Model: DGHS09U Rev: 03E0
935 Type: Direct-Access ANSI SCSI revision: 03
936 Host: scsi0 Channel: 00 Id: 06 Lun: 00
937 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
938 Type: CD-ROM ANSI SCSI revision: 02
941 The directory named after the driver has one file for each adapter found in
942 the system. These files contain information about the controller, including
943 the used IRQ and the IO address range. The amount of information shown is
944 dependent on the adapter you use. The example shows the output for an Adaptec
945 AHA-2940 SCSI adapter:
947 > cat /proc/scsi/aic7xxx/0
949 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
951 TCQ Enabled By Default : Disabled
952 AIC7XXX_PROC_STATS : Disabled
953 AIC7XXX_RESET_DELAY : 5
954 Adapter Configuration:
955 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
956 Ultra Wide Controller
957 PCI MMAPed I/O Base: 0xeb001000
958 Adapter SEEPROM Config: SEEPROM found and used.
959 Adaptec SCSI BIOS: Enabled
961 SCBs: Active 0, Max Active 2,
962 Allocated 15, HW 16, Page 255
964 BIOS Control Word: 0x18b6
965 Adapter Control Word: 0x005b
966 Extended Translation: Enabled
967 Disconnect Enable Flags: 0xffff
968 Ultra Enable Flags: 0x0001
969 Tag Queue Enable Flags: 0x0000
970 Ordered Queue Tag Flags: 0x0000
971 Default Tag Queue Depth: 8
972 Tagged Queue By Device array for aic7xxx host instance 0:
973 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
974 Actual queue depth per device for aic7xxx host instance 0:
975 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
978 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
979 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
980 Total transfers 160151 (74577 reads and 85574 writes)
982 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
983 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
984 Total transfers 0 (0 reads and 0 writes)
987 1.6 Parallel port info in /proc/parport
988 ---------------------------------------
990 The directory /proc/parport contains information about the parallel ports of
991 your system. It has one subdirectory for each port, named after the port
994 These directories contain the four files shown in Table 1-10.
997 Table 1-10: Files in /proc/parport
998 ..............................................................................
1000 autoprobe Any IEEE-1284 device ID information that has been acquired.
1001 devices list of the device drivers using that port. A + will appear by the
1002 name of the device currently using the port (it might not appear
1004 hardware Parallel port's base address, IRQ line and DMA channel.
1005 irq IRQ that parport is using for that port. This is in a separate
1006 file to allow you to alter it by writing a new value in (IRQ
1008 ..............................................................................
1010 1.7 TTY info in /proc/tty
1011 -------------------------
1013 Information about the available and actually used tty's can be found in the
1014 directory /proc/tty.You'll find entries for drivers and line disciplines in
1015 this directory, as shown in Table 1-11.
1018 Table 1-11: Files in /proc/tty
1019 ..............................................................................
1021 drivers list of drivers and their usage
1022 ldiscs registered line disciplines
1023 driver/serial usage statistic and status of single tty lines
1024 ..............................................................................
1026 To see which tty's are currently in use, you can simply look into the file
1029 > cat /proc/tty/drivers
1030 pty_slave /dev/pts 136 0-255 pty:slave
1031 pty_master /dev/ptm 128 0-255 pty:master
1032 pty_slave /dev/ttyp 3 0-255 pty:slave
1033 pty_master /dev/pty 2 0-255 pty:master
1034 serial /dev/cua 5 64-67 serial:callout
1035 serial /dev/ttyS 4 64-67 serial
1036 /dev/tty0 /dev/tty0 4 0 system:vtmaster
1037 /dev/ptmx /dev/ptmx 5 2 system
1038 /dev/console /dev/console 5 1 system:console
1039 /dev/tty /dev/tty 5 0 system:/dev/tty
1040 unknown /dev/tty 4 1-63 console
1043 1.8 Miscellaneous kernel statistics in /proc/stat
1044 -------------------------------------------------
1046 Various pieces of information about kernel activity are available in the
1047 /proc/stat file. All of the numbers reported in this file are aggregates
1048 since the system first booted. For a quick look, simply cat the file:
1051 cpu 2255 34 2290 22625563 6290 127 456 0 0
1052 cpu0 1132 34 1441 11311718 3675 127 438 0 0
1053 cpu1 1123 0 849 11313845 2614 0 18 0 0
1054 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1060 softirq 183433 0 21755 12 39 1137 231 21459 2263
1062 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1063 lines. These numbers identify the amount of time the CPU has spent performing
1064 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1065 second). The meanings of the columns are as follows, from left to right:
1067 - user: normal processes executing in user mode
1068 - nice: niced processes executing in user mode
1069 - system: processes executing in kernel mode
1070 - idle: twiddling thumbs
1071 - iowait: waiting for I/O to complete
1072 - irq: servicing interrupts
1073 - softirq: servicing softirqs
1074 - steal: involuntary wait
1075 - guest: running a guest
1077 The "intr" line gives counts of interrupts serviced since boot time, for each
1078 of the possible system interrupts. The first column is the total of all
1079 interrupts serviced; each subsequent column is the total for that particular
1082 The "ctxt" line gives the total number of context switches across all CPUs.
1084 The "btime" line gives the time at which the system booted, in seconds since
1087 The "processes" line gives the number of processes and threads created, which
1088 includes (but is not limited to) those created by calls to the fork() and
1089 clone() system calls.
1091 The "procs_running" line gives the number of processes currently running on
1094 The "procs_blocked" line gives the number of processes currently blocked,
1095 waiting for I/O to complete.
1097 The "softirq" line gives counts of softirqs serviced since boot time, for each
1098 of the possible system softirqs. The first column is the total of all
1099 softirqs serviced; each subsequent column is the total for that particular
1103 1.9 Ext4 file system parameters
1104 ------------------------------
1106 Information about mounted ext4 file systems can be found in
1107 /proc/fs/ext4. Each mounted filesystem will have a directory in
1108 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1109 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1110 in Table 1-12, below.
1112 Table 1-12: Files in /proc/fs/ext4/<devname>
1113 ..............................................................................
1115 mb_groups details of multiblock allocator buddy cache of free blocks
1116 ..............................................................................
1119 ------------------------------------------------------------------------------
1121 ------------------------------------------------------------------------------
1122 The /proc file system serves information about the running system. It not only
1123 allows access to process data but also allows you to request the kernel status
1124 by reading files in the hierarchy.
1126 The directory structure of /proc reflects the types of information and makes
1127 it easy, if not obvious, where to look for specific data.
1128 ------------------------------------------------------------------------------
1130 ------------------------------------------------------------------------------
1131 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1132 ------------------------------------------------------------------------------
1134 ------------------------------------------------------------------------------
1136 ------------------------------------------------------------------------------
1137 * Modifying kernel parameters by writing into files found in /proc/sys
1138 * Exploring the files which modify certain parameters
1139 * Review of the /proc/sys file tree
1140 ------------------------------------------------------------------------------
1143 A very interesting part of /proc is the directory /proc/sys. This is not only
1144 a source of information, it also allows you to change parameters within the
1145 kernel. Be very careful when attempting this. You can optimize your system,
1146 but you can also cause it to crash. Never alter kernel parameters on a
1147 production system. Set up a development machine and test to make sure that
1148 everything works the way you want it to. You may have no alternative but to
1149 reboot the machine once an error has been made.
1151 To change a value, simply echo the new value into the file. An example is
1152 given below in the section on the file system data. You need to be root to do
1153 this. You can create your own boot script to perform this every time your
1156 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1157 general things in the operation of the Linux kernel. Since some of the files
1158 can inadvertently disrupt your system, it is advisable to read both
1159 documentation and source before actually making adjustments. In any case, be
1160 very careful when writing to any of these files. The entries in /proc may
1161 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1162 review the kernel documentation in the directory /usr/src/linux/Documentation.
1163 This chapter is heavily based on the documentation included in the pre 2.2
1164 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1166 Please see: Documentation/sysctls/ directory for descriptions of these
1169 ------------------------------------------------------------------------------
1171 ------------------------------------------------------------------------------
1172 Certain aspects of kernel behavior can be modified at runtime, without the
1173 need to recompile the kernel, or even to reboot the system. The files in the
1174 /proc/sys tree can not only be read, but also modified. You can use the echo
1175 command to write value into these files, thereby changing the default settings
1177 ------------------------------------------------------------------------------
1179 ------------------------------------------------------------------------------
1180 CHAPTER 3: PER-PROCESS PARAMETERS
1181 ------------------------------------------------------------------------------
1183 3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
1184 ------------------------------------------------------
1186 This file can be used to adjust the score used to select which processes
1187 should be killed in an out-of-memory situation. Giving it a high score will
1188 increase the likelihood of this process being killed by the oom-killer. Valid
1189 values are in the range -16 to +15, plus the special value -17, which disables
1190 oom-killing altogether for this process.
1192 The process to be killed in an out-of-memory situation is selected among all others
1193 based on its badness score. This value equals the original memory size of the process
1194 and is then updated according to its CPU time (utime + stime) and the
1195 run time (uptime - start time). The longer it runs the smaller is the score.
1196 Badness score is divided by the square root of the CPU time and then by
1197 the double square root of the run time.
1199 Swapped out tasks are killed first. Half of each child's memory size is added to
1200 the parent's score if they do not share the same memory. Thus forking servers
1201 are the prime candidates to be killed. Having only one 'hungry' child will make
1202 parent less preferable than the child.
1204 /proc/<pid>/oom_score shows process' current badness score.
1206 The following heuristics are then applied:
1207 * if the task was reniced, its score doubles
1208 * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
1209 or CAP_SYS_RAWIO) have their score divided by 4
1210 * if oom condition happened in one cpuset and checked process does not belong
1211 to it, its score is divided by 8
1212 * the resulting score is multiplied by two to the power of oom_adj, i.e.
1213 points <<= oom_adj when it is positive and
1214 points >>= -(oom_adj) otherwise
1216 The task with the highest badness score is then selected and its children
1217 are killed, process itself will be killed in an OOM situation when it does
1218 not have children or some of them disabled oom like described above.
1220 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1221 -------------------------------------------------------------
1223 This file can be used to check the current score used by the oom-killer is for
1224 any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
1225 process should be killed in an out-of-memory situation.
1228 3.3 /proc/<pid>/io - Display the IO accounting fields
1229 -------------------------------------------------------
1231 This file contains IO statistics for each running process
1236 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1239 test:/tmp # cat /proc/3828/io
1245 write_bytes: 323932160
1246 cancelled_write_bytes: 0
1255 I/O counter: chars read
1256 The number of bytes which this task has caused to be read from storage. This
1257 is simply the sum of bytes which this process passed to read() and pread().
1258 It includes things like tty IO and it is unaffected by whether or not actual
1259 physical disk IO was required (the read might have been satisfied from
1266 I/O counter: chars written
1267 The number of bytes which this task has caused, or shall cause to be written
1268 to disk. Similar caveats apply here as with rchar.
1274 I/O counter: read syscalls
1275 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1282 I/O counter: write syscalls
1283 Attempt to count the number of write I/O operations, i.e. syscalls like
1284 write() and pwrite().
1290 I/O counter: bytes read
1291 Attempt to count the number of bytes which this process really did cause to
1292 be fetched from the storage layer. Done at the submit_bio() level, so it is
1293 accurate for block-backed filesystems. <please add status regarding NFS and
1294 CIFS at a later time>
1300 I/O counter: bytes written
1301 Attempt to count the number of bytes which this process caused to be sent to
1302 the storage layer. This is done at page-dirtying time.
1305 cancelled_write_bytes
1306 ---------------------
1308 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1309 then deletes the file, it will in fact perform no writeout. But it will have
1310 been accounted as having caused 1MB of write.
1311 In other words: The number of bytes which this process caused to not happen,
1312 by truncating pagecache. A task can cause "negative" IO too. If this task
1313 truncates some dirty pagecache, some IO which another task has been accounted
1314 for (in it's write_bytes) will not be happening. We _could_ just subtract that
1315 from the truncating task's write_bytes, but there is information loss in doing
1322 At its current implementation state, this is a bit racy on 32-bit machines: if
1323 process A reads process B's /proc/pid/io while process B is updating one of
1324 those 64-bit counters, process A could see an intermediate result.
1327 More information about this can be found within the taskstats documentation in
1328 Documentation/accounting.
1330 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1331 ---------------------------------------------------------------
1332 When a process is dumped, all anonymous memory is written to a core file as
1333 long as the size of the core file isn't limited. But sometimes we don't want
1334 to dump some memory segments, for example, huge shared memory. Conversely,
1335 sometimes we want to save file-backed memory segments into a core file, not
1336 only the individual files.
1338 /proc/<pid>/coredump_filter allows you to customize which memory segments
1339 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1340 of memory types. If a bit of the bitmask is set, memory segments of the
1341 corresponding memory type are dumped, otherwise they are not dumped.
1343 The following 7 memory types are supported:
1344 - (bit 0) anonymous private memory
1345 - (bit 1) anonymous shared memory
1346 - (bit 2) file-backed private memory
1347 - (bit 3) file-backed shared memory
1348 - (bit 4) ELF header pages in file-backed private memory areas (it is
1349 effective only if the bit 2 is cleared)
1350 - (bit 5) hugetlb private memory
1351 - (bit 6) hugetlb shared memory
1353 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1354 are always dumped regardless of the bitmask status.
1356 Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1357 effected by bit 5-6.
1359 Default value of coredump_filter is 0x23; this means all anonymous memory
1360 segments and hugetlb private memory are dumped.
1362 If you don't want to dump all shared memory segments attached to pid 1234,
1363 write 0x21 to the process's proc file.
1365 $ echo 0x21 > /proc/1234/coredump_filter
1367 When a new process is created, the process inherits the bitmask status from its
1368 parent. It is useful to set up coredump_filter before the program runs.
1371 $ echo 0x7 > /proc/self/coredump_filter
1374 3.5 /proc/<pid>/mountinfo - Information about mounts
1375 --------------------------------------------------------
1377 This file contains lines of the form:
1379 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1380 (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
1382 (1) mount ID: unique identifier of the mount (may be reused after umount)
1383 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1384 (3) major:minor: value of st_dev for files on filesystem
1385 (4) root: root of the mount within the filesystem
1386 (5) mount point: mount point relative to the process's root
1387 (6) mount options: per mount options
1388 (7) optional fields: zero or more fields of the form "tag[:value]"
1389 (8) separator: marks the end of the optional fields
1390 (9) filesystem type: name of filesystem of the form "type[.subtype]"
1391 (10) mount source: filesystem specific information or "none"
1392 (11) super options: per super block options
1394 Parsers should ignore all unrecognised optional fields. Currently the
1395 possible optional fields are:
1397 shared:X mount is shared in peer group X
1398 master:X mount is slave to peer group X
1399 propagate_from:X mount is slave and receives propagation from peer group X (*)
1400 unbindable mount is unbindable
1402 (*) X is the closest dominant peer group under the process's root. If
1403 X is the immediate master of the mount, or if there's no dominant peer
1404 group under the same root, then only the "master:X" field is present
1405 and not the "propagate_from:X" field.
1407 For more information on mount propagation see:
1409 Documentation/filesystems/sharedsubtree.txt
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