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diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst new file mode 100644 index 000000000000..38b606991065 --- /dev/null +++ b/Documentation/filesystems/proc.rst @@ -0,0 +1,2169 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +The /proc Filesystem +==================== + +===================== ======================================= ================ +/proc/sys Terrehon Bowden <terrehon@pacbell.net>, October 7 1999 + Bodo Bauer <bb@ricochet.net> +2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000 +move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009 +fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009 +===================== ======================================= ================ + + + +.. Table of Contents + + 0 Preface + 0.1 Introduction/Credits + 0.2 Legal Stuff + + 1 Collecting System Information + 1.1 Process-Specific Subdirectories + 1.2 Kernel data + 1.3 IDE devices in /proc/ide + 1.4 Networking info in /proc/net + 1.5 SCSI info + 1.6 Parallel port info in /proc/parport + 1.7 TTY info in /proc/tty + 1.8 Miscellaneous kernel statistics in /proc/stat + 1.9 Ext4 file system parameters + + 2 Modifying System Parameters + + 3 Per-Process Parameters + 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer + score + 3.2 /proc/<pid>/oom_score - Display current oom-killer score + 3.3 /proc/<pid>/io - Display the IO accounting fields + 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings + 3.5 /proc/<pid>/mountinfo - Information about mounts + 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm + 3.7 /proc/<pid>/task/<tid>/children - Information about task children + 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file + 3.9 /proc/<pid>/map_files - Information about memory mapped files + 3.10 /proc/<pid>/timerslack_ns - Task timerslack value + 3.11 /proc/<pid>/patch_state - Livepatch patch operation state + 3.12 /proc/<pid>/arch_status - Task architecture specific information + + 4 Configuring procfs + 4.1 Mount options + +Preface +======= + +0.1 Introduction/Credits +------------------------ + +This documentation is part of a soon (or so we hope) to be released book on +the SuSE Linux distribution. As there is no complete documentation for the +/proc file system and we've used many freely available sources to write these +chapters, it seems only fair to give the work back to the Linux community. +This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm +afraid it's still far from complete, but we hope it will be useful. As far as +we know, it is the first 'all-in-one' document about the /proc file system. It +is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, +SPARC, AXP, etc., features, you probably won't find what you are looking for. +It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But +additions and patches are welcome and will be added to this document if you +mail them to Bodo. + +We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of +other people for help compiling this documentation. We'd also like to extend a +special thank you to Andi Kleen for documentation, which we relied on heavily +to create this document, as well as the additional information he provided. +Thanks to everybody else who contributed source or docs to the Linux kernel +and helped create a great piece of software... :) + +If you have any comments, corrections or additions, please don't hesitate to +contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this +document. + +The latest version of this document is available online at +http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html + +If the above direction does not works for you, you could try the kernel +mailing list at linux-kernel@vger.kernel.org and/or try to reach me at +comandante@zaralinux.com. + +0.2 Legal Stuff +--------------- + +We don't guarantee the correctness of this document, and if you come to us +complaining about how you screwed up your system because of incorrect +documentation, we won't feel responsible... + +Chapter 1: Collecting System Information +======================================== + +In This Chapter +--------------- +* Investigating the properties of the pseudo file system /proc and its + ability to provide information on the running Linux system +* Examining /proc's structure +* Uncovering various information about the kernel and the processes running + on the system + +------------------------------------------------------------------------------ + +The proc file system acts as an interface to internal data structures in the +kernel. It can be used to obtain information about the system and to change +certain kernel parameters at runtime (sysctl). + +First, we'll take a look at the read-only parts of /proc. In Chapter 2, we +show you how you can use /proc/sys to change settings. + +1.1 Process-Specific Subdirectories +----------------------------------- + +The directory /proc contains (among other things) one subdirectory for each +process running on the system, which is named after the process ID (PID). + +The link self points to the process reading the file system. Each process +subdirectory has the entries listed in Table 1-1. + +Note that an open a file descriptor to /proc/<pid> or to any of its +contained files or subdirectories does not prevent <pid> being reused +for some other process in the event that <pid> exits. Operations on +open /proc/<pid> file descriptors corresponding to dead processes +never act on any new process that the kernel may, through chance, have +also assigned the process ID <pid>. Instead, operations on these FDs +usually fail with ESRCH. + +.. table:: Table 1-1: Process specific entries in /proc + + ============= =============================================================== + File Content + ============= =============================================================== + clear_refs Clears page referenced bits shown in smaps output + cmdline Command line arguments + cpu Current and last cpu in which it was executed (2.4)(smp) + cwd Link to the current working directory + environ Values of environment variables + exe Link to the executable of this process + fd Directory, which contains all file descriptors + maps Memory maps to executables and library files (2.4) + mem Memory held by this process + root Link to the root directory of this process + stat Process status + statm Process memory status information + status Process status in human readable form + wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function + symbol the task is blocked in - or "0" if not blocked. + pagemap Page table + stack Report full stack trace, enable via CONFIG_STACKTRACE + smaps An extension based on maps, showing the memory consumption of + each mapping and flags associated with it + smaps_rollup Accumulated smaps stats for all mappings of the process. This + can be derived from smaps, but is faster and more convenient + numa_maps An extension based on maps, showing the memory locality and + binding policy as well as mem usage (in pages) of each mapping. + ============= =============================================================== + +For example, to get the status information of a process, all you have to do is +read the file /proc/PID/status:: + + >cat /proc/self/status + Name: cat + State: R (running) + Tgid: 5452 + Pid: 5452 + PPid: 743 + TracerPid: 0 (2.4) + Uid: 501 501 501 501 + Gid: 100 100 100 100 + FDSize: 256 + Groups: 100 14 16 + VmPeak: 5004 kB + VmSize: 5004 kB + VmLck: 0 kB + VmHWM: 476 kB + VmRSS: 476 kB + RssAnon: 352 kB + RssFile: 120 kB + RssShmem: 4 kB + VmData: 156 kB + VmStk: 88 kB + VmExe: 68 kB + VmLib: 1412 kB + VmPTE: 20 kb + VmSwap: 0 kB + HugetlbPages: 0 kB + CoreDumping: 0 + THP_enabled: 1 + Threads: 1 + SigQ: 0/28578 + SigPnd: 0000000000000000 + ShdPnd: 0000000000000000 + SigBlk: 0000000000000000 + SigIgn: 0000000000000000 + SigCgt: 0000000000000000 + CapInh: 00000000fffffeff + CapPrm: 0000000000000000 + CapEff: 0000000000000000 + CapBnd: ffffffffffffffff + CapAmb: 0000000000000000 + NoNewPrivs: 0 + Seccomp: 0 + Speculation_Store_Bypass: thread vulnerable + voluntary_ctxt_switches: 0 + nonvoluntary_ctxt_switches: 1 + +This shows you nearly the same information you would get if you viewed it with +the ps command. In fact, ps uses the proc file system to obtain its +information. But you get a more detailed view of the process by reading the +file /proc/PID/status. It fields are described in table 1-2. + +The statm file contains more detailed information about the process +memory usage. Its seven fields are explained in Table 1-3. The stat file +contains details information about the process itself. Its fields are +explained in Table 1-4. + +(for SMP CONFIG users) + +For making accounting scalable, RSS related information are handled in an +asynchronous manner and the value may not be very precise. To see a precise +snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table. +It's slow but very precise. + +.. table:: Table 1-2: Contents of the status files (as of 4.19) + + ========================== =================================================== + Field Content + ========================== =================================================== + Name filename of the executable + Umask file mode creation mask + State state (R is running, S is sleeping, D is sleeping + in an uninterruptible wait, Z is zombie, + T is traced or stopped) + Tgid thread group ID + Ngid NUMA group ID (0 if none) + Pid process id + PPid process id of the parent process + TracerPid PID of process tracing this process (0 if not) + Uid Real, effective, saved set, and file system UIDs + Gid Real, effective, saved set, and file system GIDs + FDSize number of file descriptor slots currently allocated + Groups supplementary group list + NStgid descendant namespace thread group ID hierarchy + NSpid descendant namespace process ID hierarchy + NSpgid descendant namespace process group ID hierarchy + NSsid descendant namespace session ID hierarchy + VmPeak peak virtual memory size + VmSize total program size + VmLck locked memory size + VmPin pinned memory size + VmHWM peak resident set size ("high water mark") + VmRSS size of memory portions. It contains the three + following parts + (VmRSS = RssAnon + RssFile + RssShmem) + RssAnon size of resident anonymous memory + RssFile size of resident file mappings + RssShmem size of resident shmem memory (includes SysV shm, + mapping of tmpfs and shared anonymous mappings) + VmData size of private data segments + VmStk size of stack segments + VmExe size of text segment + VmLib size of shared library code + VmPTE size of page table entries + VmSwap amount of swap used by anonymous private data + (shmem swap usage is not included) + HugetlbPages size of hugetlb memory portions + CoreDumping process's memory is currently being dumped + (killing the process may lead to a corrupted core) + THP_enabled process is allowed to use THP (returns 0 when + PR_SET_THP_DISABLE is set on the process + Threads number of threads + SigQ number of signals queued/max. number for queue + SigPnd bitmap of pending signals for the thread + ShdPnd bitmap of shared pending signals for the process + SigBlk bitmap of blocked signals + SigIgn bitmap of ignored signals + SigCgt bitmap of caught signals + CapInh bitmap of inheritable capabilities + CapPrm bitmap of permitted capabilities + CapEff bitmap of effective capabilities + CapBnd bitmap of capabilities bounding set + CapAmb bitmap of ambient capabilities + NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...) + Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...) + Speculation_Store_Bypass speculative store bypass mitigation status + Cpus_allowed mask of CPUs on which this process may run + Cpus_allowed_list Same as previous, but in "list format" + Mems_allowed mask of memory nodes allowed to this process + Mems_allowed_list Same as previous, but in "list format" + voluntary_ctxt_switches number of voluntary context switches + nonvoluntary_ctxt_switches number of non voluntary context switches + ========================== =================================================== + + +.. table:: Table 1-3: Contents of the statm files (as of 2.6.8-rc3) + + ======== =============================== ============================== + Field Content + ======== =============================== ============================== + size total program size (pages) (same as VmSize in status) + resident size of memory portions (pages) (same as VmRSS in status) + shared number of pages that are shared (i.e. backed by a file, same + as RssFile+RssShmem in status) + trs number of pages that are 'code' (not including libs; broken, + includes data segment) + lrs number of pages of library (always 0 on 2.6) + drs number of pages of data/stack (including libs; broken, + includes library text) + dt number of dirty pages (always 0 on 2.6) + ======== =============================== ============================== + + +.. table:: Table 1-4: Contents of the stat files (as of 2.6.30-rc7) + + ============= =============================================================== + Field Content + ============= =============================================================== + pid process id + tcomm filename of the executable + state state (R is running, S is sleeping, D is sleeping in an + uninterruptible wait, Z is zombie, T is traced or stopped) + ppid process id of the parent process + pgrp pgrp of the process + sid session id + tty_nr tty the process uses + tty_pgrp pgrp of the tty + flags task flags + min_flt number of minor faults + cmin_flt number of minor faults with child's + maj_flt number of major faults + cmaj_flt number of major faults with child's + utime user mode jiffies + stime kernel mode jiffies + cutime user mode jiffies with child's + cstime kernel mode jiffies with child's + priority priority level + nice nice level + num_threads number of threads + it_real_value (obsolete, always 0) + start_time time the process started after system boot + vsize virtual memory size + rss resident set memory size + rsslim current limit in bytes on the rss + start_code address above which program text can run + end_code address below which program text can run + start_stack address of the start of the main process stack + esp current value of ESP + eip current value of EIP + pending bitmap of pending signals + blocked bitmap of blocked signals + sigign bitmap of ignored signals + sigcatch bitmap of caught signals + 0 (place holder, used to be the wchan address, + use /proc/PID/wchan instead) + 0 (place holder) + 0 (place holder) + exit_signal signal to send to parent thread on exit + task_cpu which CPU the task is scheduled on + rt_priority realtime priority + policy scheduling policy (man sched_setscheduler) + blkio_ticks time spent waiting for block IO + gtime guest time of the task in jiffies + cgtime guest time of the task children in jiffies + start_data address above which program data+bss is placed + end_data address below which program data+bss is placed + start_brk address above which program heap can be expanded with brk() + arg_start address above which program command line is placed + arg_end address below which program command line is placed + env_start address above which program environment is placed + env_end address below which program environment is placed + exit_code the thread's exit_code in the form reported by the waitpid + system call + ============= =============================================================== + +The /proc/PID/maps file contains the currently mapped memory regions and +their access permissions. + +The format is:: + + address perms offset dev inode pathname + + 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test + 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test + 0804a000-0806b000 rw-p 00000000 00:00 0 [heap] + a7cb1000-a7cb2000 ---p 00000000 00:00 0 + a7cb2000-a7eb2000 rw-p 00000000 00:00 0 + a7eb2000-a7eb3000 ---p 00000000 00:00 0 + a7eb3000-a7ed5000 rw-p 00000000 00:00 0 + a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 + a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 + a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 + a800b000-a800e000 rw-p 00000000 00:00 0 + a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 + a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 + a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 + a8024000-a8027000 rw-p 00000000 00:00 0 + a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 + a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 + a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 + aff35000-aff4a000 rw-p 00000000 00:00 0 [stack] + ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] + +where "address" is the address space in the process that it occupies, "perms" +is a set of permissions:: + + r = read + w = write + x = execute + s = shared + p = private (copy on write) + +"offset" is the offset into the mapping, "dev" is the device (major:minor), and +"inode" is the inode on that device. 0 indicates that no inode is associated +with the memory region, as the case would be with BSS (uninitialized data). +The "pathname" shows the name associated file for this mapping. If the mapping +is not associated with a file: + + ======= ==================================== + [heap] the heap of the program + [stack] the stack of the main process + [vdso] the "virtual dynamic shared object", + the kernel system call handler + ======= ==================================== + + or if empty, the mapping is anonymous. + +The /proc/PID/smaps is an extension based on maps, showing the memory +consumption for each of the process's mappings. For each mapping (aka Virtual +Memory Area, or VMA) there is a series of lines such as the following:: + + 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash + + Size: 1084 kB + KernelPageSize: 4 kB + MMUPageSize: 4 kB + Rss: 892 kB + Pss: 374 kB + Shared_Clean: 892 kB + Shared_Dirty: 0 kB + Private_Clean: 0 kB + Private_Dirty: 0 kB + Referenced: 892 kB + Anonymous: 0 kB + LazyFree: 0 kB + AnonHugePages: 0 kB + ShmemPmdMapped: 0 kB + Shared_Hugetlb: 0 kB + Private_Hugetlb: 0 kB + Swap: 0 kB + SwapPss: 0 kB + KernelPageSize: 4 kB + MMUPageSize: 4 kB + Locked: 0 kB + THPeligible: 0 + VmFlags: rd ex mr mw me dw + +The first of these lines shows the same information as is displayed for the +mapping in /proc/PID/maps. Following lines show the size of the mapping +(size); the size of each page allocated when backing a VMA (KernelPageSize), +which is usually the same as the size in the page table entries; the page size +used by the MMU when backing a VMA (in most cases, the same as KernelPageSize); +the amount of the mapping that is currently resident in RAM (RSS); the +process' proportional share of this mapping (PSS); and the number of clean and +dirty shared and private pages in the mapping. + +The "proportional set size" (PSS) of a process is the count of pages it has +in memory, where each page is divided by the number of processes sharing it. +So if a process has 1000 pages all to itself, and 1000 shared with one other +process, its PSS will be 1500. + +Note that even a page which is part of a MAP_SHARED mapping, but has only +a single pte mapped, i.e. is currently used by only one process, is accounted +as private and not as shared. + +"Referenced" indicates the amount of memory currently marked as referenced or +accessed. + +"Anonymous" shows the amount of memory that does not belong to any file. Even +a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE +and a page is modified, the file page is replaced by a private anonymous copy. + +"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE). +The memory isn't freed immediately with madvise(). It's freed in memory +pressure if the memory is clean. Please note that the printed value might +be lower than the real value due to optimizations used in the current +implementation. If this is not desirable please file a bug report. + +"AnonHugePages" shows the ammount of memory backed by transparent hugepage. + +"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by +huge pages. + +"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by +hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical +reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field. + +"Swap" shows how much would-be-anonymous memory is also used, but out on swap. + +For shmem mappings, "Swap" includes also the size of the mapped (and not +replaced by copy-on-write) part of the underlying shmem object out on swap. +"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this +does not take into account swapped out page of underlying shmem objects. +"Locked" indicates whether the mapping is locked in memory or not. +"THPeligible" indicates whether the mapping is eligible for allocating THP +pages - 1 if true, 0 otherwise. It just shows the current status. + +"VmFlags" field deserves a separate description. This member represents the +kernel flags associated with the particular virtual memory area in two letter +encoded manner. The codes are the following: + + == ======================================= + rd readable + wr writeable + ex executable + sh shared + mr may read + mw may write + me may execute + ms may share + gd stack segment growns down + pf pure PFN range + dw disabled write to the mapped file + lo pages are locked in memory + io memory mapped I/O area + sr sequential read advise provided + rr random read advise provided + dc do not copy area on fork + de do not expand area on remapping + ac area is accountable + nr swap space is not reserved for the area + ht area uses huge tlb pages + ar architecture specific flag + dd do not include area into core dump + sd soft dirty flag + mm mixed map area + hg huge page advise flag + nh no huge page advise flag + mg mergable advise flag + == ======================================= + +Note that there is no guarantee that every flag and associated mnemonic will +be present in all further kernel releases. Things get changed, the flags may +be vanished or the reverse -- new added. Interpretation of their meaning +might change in future as well. So each consumer of these flags has to +follow each specific kernel version for the exact semantic. + +This file is only present if the CONFIG_MMU kernel configuration option is +enabled. + +Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent +output can be achieved only in the single read call). + +This typically manifests when doing partial reads of these files while the +memory map is being modified. Despite the races, we do provide the following +guarantees: + +1) The mapped addresses never go backwards, which implies no two + regions will ever overlap. +2) If there is something at a given vaddr during the entirety of the + life of the smaps/maps walk, there will be some output for it. + +The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps, +but their values are the sums of the corresponding values for all mappings of +the process. Additionally, it contains these fields: + +- Pss_Anon +- Pss_File +- Pss_Shmem + +They represent the proportional shares of anonymous, file, and shmem pages, as +described for smaps above. These fields are omitted in smaps since each +mapping identifies the type (anon, file, or shmem) of all pages it contains. +Thus all information in smaps_rollup can be derived from smaps, but at a +significantly higher cost. + +The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG +bits on both physical and virtual pages associated with a process, and the +soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst +for details). +To clear the bits for all the pages associated with the process:: + + > echo 1 > /proc/PID/clear_refs + +To clear the bits for the anonymous pages associated with the process:: + + > echo 2 > /proc/PID/clear_refs + +To clear the bits for the file mapped pages associated with the process:: + + > echo 3 > /proc/PID/clear_refs + +To clear the soft-dirty bit:: + + > echo 4 > /proc/PID/clear_refs + +To reset the peak resident set size ("high water mark") to the process's +current value:: + + > echo 5 > /proc/PID/clear_refs + +Any other value written to /proc/PID/clear_refs will have no effect. + +The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags +using /proc/kpageflags and number of times a page is mapped using +/proc/kpagecount. For detailed explanation, see +Documentation/admin-guide/mm/pagemap.rst. + +The /proc/pid/numa_maps is an extension based on maps, showing the memory +locality and binding policy, as well as the memory usage (in pages) of +each mapping. The output follows a general format where mapping details get +summarized separated by blank spaces, one mapping per each file line:: + + address policy mapping details + + 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4 + 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4 + 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4 + 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 + 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 + 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4 + 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4 + 320698b000 default file=/lib64/libc-2.12.so + 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4 + 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4 + 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4 + 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4 + 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4 + 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048 + 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4 + 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4 + +Where: + +"address" is the starting address for the mapping; + +"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst); + +"mapping details" summarizes mapping data such as mapping type, page usage counters, +node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page +size, in KB, that is backing the mapping up. + +1.2 Kernel data +--------------- + +Similar to the process entries, the kernel data files give information about +the running kernel. The files used to obtain this information are contained in +/proc and are listed in Table 1-5. Not all of these will be present in your +system. It depends on the kernel configuration and the loaded modules, which +files are there, and which are missing. + +.. table:: Table 1-5: Kernel info in /proc + + ============ =============================================================== + File Content + ============ =============================================================== + apm Advanced power management info + buddyinfo Kernel memory allocator information (see text) (2.5) + bus Directory containing bus specific information + cmdline Kernel command line + cpuinfo Info about the CPU + devices Available devices (block and character) + dma Used DMS channels + filesystems Supported filesystems + driver Various drivers grouped here, currently rtc (2.4) + execdomains Execdomains, related to security (2.4) + fb Frame Buffer devices (2.4) + fs File system parameters, currently nfs/exports (2.4) + ide Directory containing info about the IDE subsystem + interrupts Interrupt usage + iomem Memory map (2.4) + ioports I/O port usage + irq Masks for irq to cpu affinity (2.4)(smp?) + isapnp ISA PnP (Plug&Play) Info (2.4) + kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) + kmsg Kernel messages + ksyms Kernel symbol table + loadavg Load average of last 1, 5 & 15 minutes + locks Kernel locks + meminfo Memory info + misc Miscellaneous + modules List of loaded modules + mounts Mounted filesystems + net Networking info (see text) + pagetypeinfo Additional page allocator information (see text) (2.5) + partitions Table of partitions known to the system + pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, + decoupled by lspci (2.4) + rtc Real time clock + scsi SCSI info (see text) + slabinfo Slab pool info + softirqs softirq usage + stat Overall statistics + swaps Swap space utilization + sys See chapter 2 + sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) + tty Info of tty drivers + uptime Wall clock since boot, combined idle time of all cpus + version Kernel version + video bttv info of video resources (2.4) + vmallocinfo Show vmalloced areas + ============ =============================================================== + +You can, for example, check which interrupts are currently in use and what +they are used for by looking in the file /proc/interrupts:: + + > cat /proc/interrupts + CPU0 + 0: 8728810 XT-PIC timer + 1: 895 XT-PIC keyboard + 2: 0 XT-PIC cascade + 3: 531695 XT-PIC aha152x + 4: 2014133 XT-PIC serial + 5: 44401 XT-PIC pcnet_cs + 8: 2 XT-PIC rtc + 11: 8 XT-PIC i82365 + 12: 182918 XT-PIC PS/2 Mouse + 13: 1 XT-PIC fpu + 14: 1232265 XT-PIC ide0 + 15: 7 XT-PIC ide1 + NMI: 0 + +In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the +output of a SMP machine):: + + > cat /proc/interrupts + + CPU0 CPU1 + 0: 1243498 1214548 IO-APIC-edge timer + 1: 8949 8958 IO-APIC-edge keyboard + 2: 0 0 XT-PIC cascade + 5: 11286 10161 IO-APIC-edge soundblaster + 8: 1 0 IO-APIC-edge rtc + 9: 27422 27407 IO-APIC-edge 3c503 + 12: 113645 113873 IO-APIC-edge PS/2 Mouse + 13: 0 0 XT-PIC fpu + 14: 22491 24012 IO-APIC-edge ide0 + 15: 2183 2415 IO-APIC-edge ide1 + 17: 30564 30414 IO-APIC-level eth0 + 18: 177 164 IO-APIC-level bttv + NMI: 2457961 2457959 + LOC: 2457882 2457881 + ERR: 2155 + +NMI is incremented in this case because every timer interrupt generates a NMI +(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. + +LOC is the local interrupt counter of the internal APIC of every CPU. + +ERR is incremented in the case of errors in the IO-APIC bus (the bus that +connects the CPUs in a SMP system. This means that an error has been detected, +the IO-APIC automatically retry the transmission, so it should not be a big +problem, but you should read the SMP-FAQ. + +In 2.6.2* /proc/interrupts was expanded again. This time the goal was for +/proc/interrupts to display every IRQ vector in use by the system, not +just those considered 'most important'. The new vectors are: + +THR + interrupt raised when a machine check threshold counter + (typically counting ECC corrected errors of memory or cache) exceeds + a configurable threshold. Only available on some systems. + +TRM + a thermal event interrupt occurs when a temperature threshold + has been exceeded for the CPU. This interrupt may also be generated + when the temperature drops back to normal. + +SPU + a spurious interrupt is some interrupt that was raised then lowered + by some IO device before it could be fully processed by the APIC. Hence + the APIC sees the interrupt but does not know what device it came from. + For this case the APIC will generate the interrupt with a IRQ vector + of 0xff. This might also be generated by chipset bugs. + +RES, CAL, TLB] + rescheduling, call and TLB flush interrupts are + sent from one CPU to another per the needs of the OS. Typically, + their statistics are used by kernel developers and interested users to + determine the occurrence of interrupts of the given type. + +The above IRQ vectors are displayed only when relevant. For example, +the threshold vector does not exist on x86_64 platforms. Others are +suppressed when the system is a uniprocessor. As of this writing, only +i386 and x86_64 platforms support the new IRQ vector displays. + +Of some interest is the introduction of the /proc/irq directory to 2.4. +It could be used to set IRQ to CPU affinity, this means that you can "hook" an +IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the +irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and +prof_cpu_mask. + +For example:: + + > ls /proc/irq/ + 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask + 1 11 13 15 17 19 3 5 7 9 default_smp_affinity + > ls /proc/irq/0/ + smp_affinity + +smp_affinity is a bitmask, in which you can specify which CPUs can handle the +IRQ, you can set it by doing:: + + > echo 1 > /proc/irq/10/smp_affinity + +This means that only the first CPU will handle the IRQ, but you can also echo +5 which means that only the first and third CPU can handle the IRQ. + +The contents of each smp_affinity file is the same by default:: + + > cat /proc/irq/0/smp_affinity + ffffffff + +There is an alternate interface, smp_affinity_list which allows specifying +a cpu range instead of a bitmask:: + + > cat /proc/irq/0/smp_affinity_list + 1024-1031 + +The default_smp_affinity mask applies to all non-active IRQs, which are the +IRQs which have not yet been allocated/activated, and hence which lack a +/proc/irq/[0-9]* directory. + +The node file on an SMP system shows the node to which the device using the IRQ +reports itself as being attached. This hardware locality information does not +include information about any possible driver locality preference. + +prof_cpu_mask specifies which CPUs are to be profiled by the system wide +profiler. Default value is ffffffff (all cpus if there are only 32 of them). + +The way IRQs are routed is handled by the IO-APIC, and it's Round Robin +between all the CPUs which are allowed to handle it. As usual the kernel has +more info than you and does a better job than you, so the defaults are the +best choice for almost everyone. [Note this applies only to those IO-APIC's +that support "Round Robin" interrupt distribution.] + +There are three more important subdirectories in /proc: net, scsi, and sys. +The general rule is that the contents, or even the existence of these +directories, depend on your kernel configuration. If SCSI is not enabled, the +directory scsi may not exist. The same is true with the net, which is there +only when networking support is present in the running kernel. + +The slabinfo file gives information about memory usage at the slab level. +Linux uses slab pools for memory management above page level in version 2.2. +Commonly used objects have their own slab pool (such as network buffers, +directory cache, and so on). + +:: + + > cat /proc/buddyinfo + + Node 0, zone DMA 0 4 5 4 4 3 ... + Node 0, zone Normal 1 0 0 1 101 8 ... + Node 0, zone HighMem 2 0 0 1 1 0 ... + +External fragmentation is a problem under some workloads, and buddyinfo is a +useful tool for helping diagnose these problems. Buddyinfo will give you a +clue as to how big an area you can safely allocate, or why a previous +allocation failed. + +Each column represents the number of pages of a certain order which are +available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in +ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE +available in ZONE_NORMAL, etc... + +More information relevant to external fragmentation can be found in +pagetypeinfo:: + + > cat /proc/pagetypeinfo + Page block order: 9 + Pages per block: 512 + + Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 + Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0 + Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0 + Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2 + Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0 + Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0 + Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9 + Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0 + Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452 + Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0 + Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0 + + Number of blocks type Unmovable Reclaimable Movable Reserve Isolate + Node 0, zone DMA 2 0 5 1 0 + Node 0, zone DMA32 41 6 967 2 0 + +Fragmentation avoidance in the kernel works by grouping pages of different +migrate types into the same contiguous regions of memory called page blocks. +A page block is typically the size of the default hugepage size e.g. 2MB on +X86-64. By keeping pages grouped based on their ability to move, the kernel +can reclaim pages within a page block to satisfy a high-order allocation. + +The pagetypinfo begins with information on the size of a page block. It +then gives the same type of information as buddyinfo except broken down +by migrate-type and finishes with details on how many page blocks of each +type exist. + +If min_free_kbytes has been tuned correctly (recommendations made by hugeadm +from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can +make an estimate of the likely number of huge pages that can be allocated +at a given point in time. All the "Movable" blocks should be allocatable +unless memory has been mlock()'d. Some of the Reclaimable blocks should +also be allocatable although a lot of filesystem metadata may have to be +reclaimed to achieve this. + + +meminfo +~~~~~~~ + +Provides information about distribution and utilization of memory. This +varies by architecture and compile options. The following is from a +16GB PIII, which has highmem enabled. You may not have all of these fields. + +:: + + > cat /proc/meminfo + + MemTotal: 16344972 kB + MemFree: 13634064 kB + MemAvailable: 14836172 kB + Buffers: 3656 kB + Cached: 1195708 kB + SwapCached: 0 kB + Active: 891636 kB + Inactive: 1077224 kB + HighTotal: 15597528 kB + HighFree: 13629632 kB + LowTotal: 747444 kB + LowFree: 4432 kB + SwapTotal: 0 kB + SwapFree: 0 kB + Dirty: 968 kB + Writeback: 0 kB + AnonPages: 861800 kB + Mapped: 280372 kB + Shmem: 644 kB + KReclaimable: 168048 kB + Slab: 284364 kB + SReclaimable: 159856 kB + SUnreclaim: 124508 kB + PageTables: 24448 kB + NFS_Unstable: 0 kB + Bounce: 0 kB + WritebackTmp: 0 kB + CommitLimit: 7669796 kB + Committed_AS: 100056 kB + VmallocTotal: 112216 kB + VmallocUsed: 428 kB + VmallocChunk: 111088 kB + Percpu: 62080 kB + HardwareCorrupted: 0 kB + AnonHugePages: 49152 kB + ShmemHugePages: 0 kB + ShmemPmdMapped: 0 kB + +MemTotal + Total usable ram (i.e. physical ram minus a few reserved + bits and the kernel binary code) +MemFree + The sum of LowFree+HighFree +MemAvailable + An estimate of how much memory is available for starting new + applications, without swapping. Calculated from MemFree, + SReclaimable, the size of the file LRU lists, and the low + watermarks in each zone. + The estimate takes into account that the system needs some + page cache to function well, and that not all reclaimable + slab will be reclaimable, due to items being in use. The + impact of those factors will vary from system to system. +Buffers + Relatively temporary storage for raw disk blocks + shouldn't get tremendously large (20MB or so) +Cached + in-memory cache for files read from the disk (the + pagecache). Doesn't include SwapCached +SwapCached + Memory that once was swapped out, is swapped back in but + still also is in the swapfile (if memory is needed it + doesn't need to be swapped out AGAIN because it is already + in the swapfile. This saves I/O) +Active + Memory that has been used more recently and usually not + reclaimed unless absolutely necessary. +Inactive + Memory which has been less recently used. It is more + eligible to be reclaimed for other purposes +HighTotal, HighFree + Highmem is all memory above ~860MB of physical memory + Highmem areas are for use by userspace programs, or + for the pagecache. The kernel must use tricks to access + this memory, making it slower to access than lowmem. +LowTotal, LowFree + Lowmem is memory which can be used for everything that + highmem can be used for, but it is also available for the + kernel's use for its own data structures. Among many + other things, it is where everything from the Slab is + allocated. Bad things happen when you're out of lowmem. +SwapTotal + total amount of swap space available +SwapFree + Memory which has been evicted from RAM, and is temporarily + on the disk +Dirty + Memory which is waiting to get written back to the disk +Writeback + Memory which is actively being written back to the disk +AnonPages + Non-file backed pages mapped into userspace page tables +HardwareCorrupted + The amount of RAM/memory in KB, the kernel identifies as + corrupted. +AnonHugePages + Non-file backed huge pages mapped into userspace page tables +Mapped + files which have been mmaped, such as libraries +Shmem + Total memory used by shared memory (shmem) and tmpfs +ShmemHugePages + Memory used by shared memory (shmem) and tmpfs allocated + with huge pages +ShmemPmdMapped + Shared memory mapped into userspace with huge pages +KReclaimable + Kernel allocations that the kernel will attempt to reclaim + under memory pressure. Includes SReclaimable (below), and other + direct allocations with a shrinker. +Slab + in-kernel data structures cache +SReclaimable + Part of Slab, that might be reclaimed, such as caches +SUnreclaim + Part of Slab, that cannot be reclaimed on memory pressure +PageTables + amount of memory dedicated to the lowest level of page + tables. +NFS_Unstable + NFS pages sent to the server, but not yet committed to stable + storage +Bounce + Memory used for block device "bounce buffers" +WritebackTmp + Memory used by FUSE for temporary writeback buffers +CommitLimit + Based on the overcommit ratio ('vm.overcommit_ratio'), + this is the total amount of memory currently available to + be allocated on the system. This limit is only adhered to + if strict overcommit accounting is enabled (mode 2 in + 'vm.overcommit_memory'). + + The CommitLimit is calculated with the following formula:: + + CommitLimit = ([total RAM pages] - [total huge TLB pages]) * + overcommit_ratio / 100 + [total swap pages] + + For example, on a system with 1G of physical RAM and 7G + of swap with a `vm.overcommit_ratio` of 30 it would + yield a CommitLimit of 7.3G. + + For more details, see the memory overcommit documentation + in vm/overcommit-accounting. +Committed_AS + The amount of memory presently allocated on the system. + The committed memory is a sum of all of the memory which + has been allocated by processes, even if it has not been + "used" by them as of yet. A process which malloc()'s 1G + of memory, but only touches 300M of it will show up as + using 1G. This 1G is memory which has been "committed" to + by the VM and can be used at any time by the allocating + application. With strict overcommit enabled on the system + (mode 2 in 'vm.overcommit_memory'),allocations which would + exceed the CommitLimit (detailed above) will not be permitted. + This is useful if one needs to guarantee that processes will + not fail due to lack of memory once that memory has been + successfully allocated. +VmallocTotal + total size of vmalloc memory area +VmallocUsed + amount of vmalloc area which is used +VmallocChunk + largest contiguous block of vmalloc area which is free +Percpu + Memory allocated to the percpu allocator used to back percpu + allocations. This stat excludes the cost of metadata. + +vmallocinfo +~~~~~~~~~~~ + +Provides information about vmalloced/vmaped areas. One line per area, +containing the virtual address range of the area, size in bytes, +caller information of the creator, and optional information depending +on the kind of area : + + ========== =================================================== + pages=nr number of pages + phys=addr if a physical address was specified + ioremap I/O mapping (ioremap() and friends) + vmalloc vmalloc() area + vmap vmap()ed pages + user VM_USERMAP area + vpages buffer for pages pointers was vmalloced (huge area) + N<node>=nr (Only on NUMA kernels) + Number of pages allocated on memory node <node> + ========== =================================================== + +:: + + > cat /proc/vmallocinfo + 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... + /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 + 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... + /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 + 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... + phys=7fee8000 ioremap + 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... + phys=7fee7000 ioremap + 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 + 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... + /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 + 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... + pages=2 vmalloc N1=2 + 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... + /0x130 [x_tables] pages=4 vmalloc N0=4 + 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... + pages=14 vmalloc N2=14 + 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... + pages=4 vmalloc N1=4 + 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... + pages=2 vmalloc N1=2 + 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... + pages=10 vmalloc N0=10 + + +softirqs +~~~~~~~~ + +Provides counts of softirq handlers serviced since boot time, for each cpu. + +:: + + > cat /proc/softirqs + CPU0 CPU1 CPU2 CPU3 + HI: 0 0 0 0 + TIMER: 27166 27120 27097 27034 + NET_TX: 0 0 0 17 + NET_RX: 42 0 0 39 + BLOCK: 0 0 107 1121 + TASKLET: 0 0 0 290 + SCHED: 27035 26983 26971 26746 + HRTIMER: 0 0 0 0 + RCU: 1678 1769 2178 2250 + + +1.3 IDE devices in /proc/ide +---------------------------- + +The subdirectory /proc/ide contains information about all IDE devices of which +the kernel is aware. There is one subdirectory for each IDE controller, the +file drivers and a link for each IDE device, pointing to the device directory +in the controller specific subtree. + +The file drivers contains general information about the drivers used for the +IDE devices:: + + > cat /proc/ide/drivers + ide-cdrom version 4.53 + ide-disk version 1.08 + +More detailed information can be found in the controller specific +subdirectories. These are named ide0, ide1 and so on. Each of these +directories contains the files shown in table 1-6. + + +.. table:: Table 1-6: IDE controller info in /proc/ide/ide? + + ======= ======================================= + File Content + ======= ======================================= + channel IDE channel (0 or 1) + config Configuration (only for PCI/IDE bridge) + mate Mate name + model Type/Chipset of IDE controller + ======= ======================================= + +Each device connected to a controller has a separate subdirectory in the +controllers directory. The files listed in table 1-7 are contained in these +directories. + + +.. table:: Table 1-7: IDE device information + + ================ ========================================== + File Content + ================ ========================================== + cache The cache + capacity Capacity of the medium (in 512Byte blocks) + driver driver and version + geometry physical and logical geometry + identify device identify block + media media type + model device identifier + settings device setup + smart_thresholds IDE disk management thresholds + smart_values IDE disk management values + ================ ========================================== + +The most interesting file is ``settings``. This file contains a nice +overview of the drive parameters:: + + # cat /proc/ide/ide0/hda/settings + name value min max mode + ---- ----- --- --- ---- + bios_cyl 526 0 65535 rw + bios_head 255 0 255 rw + bios_sect 63 0 63 rw + breada_readahead 4 0 127 rw + bswap 0 0 1 r + file_readahead 72 0 2097151 rw + io_32bit 0 0 3 rw + keepsettings 0 0 1 rw + max_kb_per_request 122 1 127 rw + multcount 0 0 8 rw + nice1 1 0 1 rw + nowerr 0 0 1 rw + pio_mode write-only 0 255 w + slow 0 0 1 rw + unmaskirq 0 0 1 rw + using_dma 0 0 1 rw + + +1.4 Networking info in /proc/net +-------------------------------- + +The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the +additional values you get for IP version 6 if you configure the kernel to +support this. Table 1-9 lists the files and their meaning. + + +.. table:: Table 1-8: IPv6 info in /proc/net + + ========== ===================================================== + File Content + ========== ===================================================== + udp6 UDP sockets (IPv6) + tcp6 TCP sockets (IPv6) + raw6 Raw device statistics (IPv6) + igmp6 IP multicast addresses, which this host joined (IPv6) + if_inet6 List of IPv6 interface addresses + ipv6_route Kernel routing table for IPv6 + rt6_stats Global IPv6 routing tables statistics + sockstat6 Socket statistics (IPv6) + snmp6 Snmp data (IPv6) + ========== ===================================================== + +.. table:: Table 1-9: Network info in /proc/net + + ============= ================================================================ + File Content + ============= ================================================================ + arp Kernel ARP table + dev network devices with statistics + dev_mcast the Layer2 multicast groups a device is listening too + (interface index, label, number of references, number of bound + addresses). + dev_stat network device status + ip_fwchains Firewall chain linkage + ip_fwnames Firewall chain names + ip_masq Directory containing the masquerading tables + ip_masquerade Major masquerading table + netstat Network statistics + raw raw device statistics + route Kernel routing table + rpc Directory containing rpc info + rt_cache Routing cache + snmp SNMP data + sockstat Socket statistics + tcp TCP sockets + udp UDP sockets + unix UNIX domain sockets + wireless Wireless interface data (Wavelan etc) + igmp IP multicast addresses, which this host joined + psched Global packet scheduler parameters. + netlink List of PF_NETLINK sockets + ip_mr_vifs List of multicast virtual interfaces + ip_mr_cache List of multicast routing cache + ============= ================================================================ + +You can use this information to see which network devices are available in +your system and how much traffic was routed over those devices:: + + > cat /proc/net/dev + Inter-|Receive |[... + face |bytes packets errs drop fifo frame compressed multicast|[... + lo: 908188 5596 0 0 0 0 0 0 [... + ppp0:15475140 20721 410 0 0 410 0 0 [... + eth0: 614530 7085 0 0 0 0 0 1 [... + + ...] Transmit + ...] bytes packets errs drop fifo colls carrier compressed + ...] 908188 5596 0 0 0 0 0 0 + ...] 1375103 17405 0 0 0 0 0 0 + ...] 1703981 5535 0 0 0 3 0 0 + +In addition, each Channel Bond interface has its own directory. For +example, the bond0 device will have a directory called /proc/net/bond0/. +It will contain information that is specific to that bond, such as the +current slaves of the bond, the link status of the slaves, and how +many times the slaves link has failed. + +1.5 SCSI info +------------- + +If you have a SCSI host adapter in your system, you'll find a subdirectory +named after the driver for this adapter in /proc/scsi. You'll also see a list +of all recognized SCSI devices in /proc/scsi:: + + >cat /proc/scsi/scsi + Attached devices: + Host: scsi0 Channel: 00 Id: 00 Lun: 00 + Vendor: IBM Model: DGHS09U Rev: 03E0 + Type: Direct-Access ANSI SCSI revision: 03 + Host: scsi0 Channel: 00 Id: 06 Lun: 00 + Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 + Type: CD-ROM ANSI SCSI revision: 02 + + +The directory named after the driver has one file for each adapter found in +the system. These files contain information about the controller, including +the used IRQ and the IO address range. The amount of information shown is +dependent on the adapter you use. The example shows the output for an Adaptec +AHA-2940 SCSI adapter:: + + > cat /proc/scsi/aic7xxx/0 + + Adaptec AIC7xxx driver version: 5.1.19/3.2.4 + Compile Options: + TCQ Enabled By Default : Disabled + AIC7XXX_PROC_STATS : Disabled + AIC7XXX_RESET_DELAY : 5 + Adapter Configuration: + SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter + Ultra Wide Controller + PCI MMAPed I/O Base: 0xeb001000 + Adapter SEEPROM Config: SEEPROM found and used. + Adaptec SCSI BIOS: Enabled + IRQ: 10 + SCBs: Active 0, Max Active 2, + Allocated 15, HW 16, Page 255 + Interrupts: 160328 + BIOS Control Word: 0x18b6 + Adapter Control Word: 0x005b + Extended Translation: Enabled + Disconnect Enable Flags: 0xffff + Ultra Enable Flags: 0x0001 + Tag Queue Enable Flags: 0x0000 + Ordered Queue Tag Flags: 0x0000 + Default Tag Queue Depth: 8 + Tagged Queue By Device array for aic7xxx host instance 0: + {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} + Actual queue depth per device for aic7xxx host instance 0: + {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} + Statistics: + (scsi0:0:0:0) + Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 + Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) + Total transfers 160151 (74577 reads and 85574 writes) + (scsi0:0:6:0) + Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 + Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) + Total transfers 0 (0 reads and 0 writes) + + +1.6 Parallel port info in /proc/parport +--------------------------------------- + +The directory /proc/parport contains information about the parallel ports of +your system. It has one subdirectory for each port, named after the port +number (0,1,2,...). + +These directories contain the four files shown in Table 1-10. + + +.. table:: Table 1-10: Files in /proc/parport + + ========= ==================================================================== + File Content + ========= ==================================================================== + autoprobe Any IEEE-1284 device ID information that has been acquired. + devices list of the device drivers using that port. A + will appear by the + name of the device currently using the port (it might not appear + against any). + hardware Parallel port's base address, IRQ line and DMA channel. + irq IRQ that parport is using for that port. This is in a separate + file to allow you to alter it by writing a new value in (IRQ + number or none). + ========= ==================================================================== + +1.7 TTY info in /proc/tty +------------------------- + +Information about the available and actually used tty's can be found in the +directory /proc/tty.You'll find entries for drivers and line disciplines in +this directory, as shown in Table 1-11. + + +.. table:: Table 1-11: Files in /proc/tty + + ============= ============================================== + File Content + ============= ============================================== + drivers list of drivers and their usage + ldiscs registered line disciplines + driver/serial usage statistic and status of single tty lines + ============= ============================================== + +To see which tty's are currently in use, you can simply look into the file +/proc/tty/drivers:: + + > cat /proc/tty/drivers + pty_slave /dev/pts 136 0-255 pty:slave + pty_master /dev/ptm 128 0-255 pty:master + pty_slave /dev/ttyp 3 0-255 pty:slave + pty_master /dev/pty 2 0-255 pty:master + serial /dev/cua 5 64-67 serial:callout + serial /dev/ttyS 4 64-67 serial + /dev/tty0 /dev/tty0 4 0 system:vtmaster + /dev/ptmx /dev/ptmx 5 2 system + /dev/console /dev/console 5 1 system:console + /dev/tty /dev/tty 5 0 system:/dev/tty + unknown /dev/tty 4 1-63 console + + +1.8 Miscellaneous kernel statistics in /proc/stat +------------------------------------------------- + +Various pieces of information about kernel activity are available in the +/proc/stat file. All of the numbers reported in this file are aggregates +since the system first booted. For a quick look, simply cat the file:: + + > cat /proc/stat + cpu 2255 34 2290 22625563 6290 127 456 0 0 0 + cpu0 1132 34 1441 11311718 3675 127 438 0 0 0 + cpu1 1123 0 849 11313845 2614 0 18 0 0 0 + intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] + ctxt 1990473 + btime 1062191376 + processes 2915 + procs_running 1 + procs_blocked 0 + softirq 183433 0 21755 12 39 1137 231 21459 2263 + +The very first "cpu" line aggregates the numbers in all of the other "cpuN" +lines. These numbers identify the amount of time the CPU has spent performing +different kinds of work. Time units are in USER_HZ (typically hundredths of a +second). The meanings of the columns are as follows, from left to right: + +- user: normal processes executing in user mode +- nice: niced processes executing in user mode +- system: processes executing in kernel mode +- idle: twiddling thumbs +- iowait: In a word, iowait stands for waiting for I/O to complete. But there + are several problems: + + 1. Cpu will not wait for I/O to complete, iowait is the time that a task is + waiting for I/O to complete. When cpu goes into idle state for + outstanding task io, another task will be scheduled on this CPU. + 2. In a multi-core CPU, the task waiting for I/O to complete is not running + on any CPU, so the iowait of each CPU is difficult to calculate. + 3. The value of iowait field in /proc/stat will decrease in certain + conditions. + + So, the iowait is not reliable by reading from /proc/stat. +- irq: servicing interrupts +- softirq: servicing softirqs +- steal: involuntary wait +- guest: running a normal guest +- guest_nice: running a niced guest + +The "intr" line gives counts of interrupts serviced since boot time, for each +of the possible system interrupts. The first column is the total of all +interrupts serviced including unnumbered architecture specific interrupts; +each subsequent column is the total for that particular numbered interrupt. +Unnumbered interrupts are not shown, only summed into the total. + +The "ctxt" line gives the total number of context switches across all CPUs. + +The "btime" line gives the time at which the system booted, in seconds since +the Unix epoch. + +The "processes" line gives the number of processes and threads created, which +includes (but is not limited to) those created by calls to the fork() and +clone() system calls. + +The "procs_running" line gives the total number of threads that are +running or ready to run (i.e., the total number of runnable threads). + +The "procs_blocked" line gives the number of processes currently blocked, +waiting for I/O to complete. + +The "softirq" line gives counts of softirqs serviced since boot time, for each +of the possible system softirqs. The first column is the total of all +softirqs serviced; each subsequent column is the total for that particular +softirq. + + +1.9 Ext4 file system parameters +------------------------------- + +Information about mounted ext4 file systems can be found in +/proc/fs/ext4. Each mounted filesystem will have a directory in +/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or +/proc/fs/ext4/dm-0). The files in each per-device directory are shown +in Table 1-12, below. + +.. table:: Table 1-12: Files in /proc/fs/ext4/<devname> + + ============== ========================================================== + File Content + mb_groups details of multiblock allocator buddy cache of free blocks + ============== ========================================================== + +2.0 /proc/consoles +------------------ +Shows registered system console lines. + +To see which character device lines are currently used for the system console +/dev/console, you may simply look into the file /proc/consoles:: + + > cat /proc/consoles + tty0 -WU (ECp) 4:7 + ttyS0 -W- (Ep) 4:64 + +The columns are: + ++--------------------+-------------------------------------------------------+ +| device | name of the device | ++====================+=======================================================+ +| operations | * R = can do read operations | +| | * W = can do write operations | +| | * U = can do unblank | ++--------------------+-------------------------------------------------------+ +| flags | * E = it is enabled | +| | * C = it is preferred console | +| | * B = it is primary boot console | +| | * p = it is used for printk buffer | +| | * b = it is not a TTY but a Braille device | +| | * a = it is safe to use when cpu is offline | ++--------------------+-------------------------------------------------------+ +| major:minor | major and minor number of the device separated by a | +| | colon | ++--------------------+-------------------------------------------------------+ + +Summary +------- + +The /proc file system serves information about the running system. It not only +allows access to process data but also allows you to request the kernel status +by reading files in the hierarchy. + +The directory structure of /proc reflects the types of information and makes +it easy, if not obvious, where to look for specific data. + +Chapter 2: Modifying System Parameters +====================================== + +In This Chapter +--------------- + +* Modifying kernel parameters by writing into files found in /proc/sys +* Exploring the files which modify certain parameters +* Review of the /proc/sys file tree + +------------------------------------------------------------------------------ + +A very interesting part of /proc is the directory /proc/sys. This is not only +a source of information, it also allows you to change parameters within the +kernel. Be very careful when attempting this. You can optimize your system, +but you can also cause it to crash. Never alter kernel parameters on a +production system. Set up a development machine and test to make sure that +everything works the way you want it to. You may have no alternative but to +reboot the machine once an error has been made. + +To change a value, simply echo the new value into the file. An example is +given below in the section on the file system data. You need to be root to do +this. You can create your own boot script to perform this every time your +system boots. + +The files in /proc/sys can be used to fine tune and monitor miscellaneous and +general things in the operation of the Linux kernel. Since some of the files +can inadvertently disrupt your system, it is advisable to read both +documentation and source before actually making adjustments. In any case, be +very careful when writing to any of these files. The entries in /proc may +change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt +review the kernel documentation in the directory /usr/src/linux/Documentation. +This chapter is heavily based on the documentation included in the pre 2.2 +kernels, and became part of it in version 2.2.1 of the Linux kernel. + +Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these +entries. + +Summary +------- + +Certain aspects of kernel behavior can be modified at runtime, without the +need to recompile the kernel, or even to reboot the system. The files in the +/proc/sys tree can not only be read, but also modified. You can use the echo +command to write value into these files, thereby changing the default settings +of the kernel. + + +Chapter 3: Per-process Parameters +================================= + +3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score +-------------------------------------------------------------------------------- + +These file can be used to adjust the badness heuristic used to select which +process gets killed in out of memory conditions. + +The badness heuristic assigns a value to each candidate task ranging from 0 +(never kill) to 1000 (always kill) to determine which process is targeted. The +units are roughly a proportion along that range of allowed memory the process +may allocate from based on an estimation of its current memory and swap use. +For example, if a task is using all allowed memory, its badness score will be +1000. If it is using half of its allowed memory, its score will be 500. + +There is an additional factor included in the badness score: the current memory +and swap usage is discounted by 3% for root processes. + +The amount of "allowed" memory depends on the context in which the oom killer +was called. If it is due to the memory assigned to the allocating task's cpuset +being exhausted, the allowed memory represents the set of mems assigned to that +cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed +memory represents the set of mempolicy nodes. If it is due to a memory +limit (or swap limit) being reached, the allowed memory is that configured +limit. Finally, if it is due to the entire system being out of memory, the +allowed memory represents all allocatable resources. + +The value of /proc/<pid>/oom_score_adj is added to the badness score before it +is used to determine which task to kill. Acceptable values range from -1000 +(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to +polarize the preference for oom killing either by always preferring a certain +task or completely disabling it. The lowest possible value, -1000, is +equivalent to disabling oom killing entirely for that task since it will always +report a badness score of 0. + +Consequently, it is very simple for userspace to define the amount of memory to +consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for +example, is roughly equivalent to allowing the remainder of tasks sharing the +same system, cpuset, mempolicy, or memory controller resources to use at least +50% more memory. A value of -500, on the other hand, would be roughly +equivalent to discounting 50% of the task's allowed memory from being considered +as scoring against the task. + +For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also +be used to tune the badness score. Its acceptable values range from -16 +(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17 +(OOM_DISABLE) to disable oom killing entirely for that task. Its value is +scaled linearly with /proc/<pid>/oom_score_adj. + +The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last +value set by a CAP_SYS_RESOURCE process. To reduce the value any lower +requires CAP_SYS_RESOURCE. + +Caveat: when a parent task is selected, the oom killer will sacrifice any first +generation children with separate address spaces instead, if possible. This +avoids servers and important system daemons from being killed and loses the +minimal amount of work. + + +3.2 /proc/<pid>/oom_score - Display current oom-killer score +------------------------------------------------------------- + +This file can be used to check the current score used by the oom-killer is for +any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which +process should be killed in an out-of-memory situation. + + +3.3 /proc/<pid>/io - Display the IO accounting fields +------------------------------------------------------- + +This file contains IO statistics for each running process + +Example +~~~~~~~ + +:: + + test:/tmp # dd if=/dev/zero of=/tmp/test.dat & + [1] 3828 + + test:/tmp # cat /proc/3828/io + rchar: 323934931 + wchar: 323929600 + syscr: 632687 + syscw: 632675 + read_bytes: 0 + write_bytes: 323932160 + cancelled_write_bytes: 0 + + +Description +~~~~~~~~~~~ + +rchar +^^^^^ + +I/O counter: chars read +The number of bytes which this task has caused to be read from storage. This +is simply the sum of bytes which this process passed to read() and pread(). +It includes things like tty IO and it is unaffected by whether or not actual +physical disk IO was required (the read might have been satisfied from +pagecache) + + +wchar +^^^^^ + +I/O counter: chars written +The number of bytes which this task has caused, or shall cause to be written +to disk. Similar caveats apply here as with rchar. + + +syscr +^^^^^ + +I/O counter: read syscalls +Attempt to count the number of read I/O operations, i.e. syscalls like read() +and pread(). + + +syscw +^^^^^ + +I/O counter: write syscalls +Attempt to count the number of write I/O operations, i.e. syscalls like +write() and pwrite(). + + +read_bytes +^^^^^^^^^^ + +I/O counter: bytes read +Attempt to count the number of bytes which this process really did cause to +be fetched from the storage layer. Done at the submit_bio() level, so it is +accurate for block-backed filesystems. <please add status regarding NFS and +CIFS at a later time> + + +write_bytes +^^^^^^^^^^^ + +I/O counter: bytes written +Attempt to count the number of bytes which this process caused to be sent to +the storage layer. This is done at page-dirtying time. + + +cancelled_write_bytes +^^^^^^^^^^^^^^^^^^^^^ + +The big inaccuracy here is truncate. If a process writes 1MB to a file and +then deletes the file, it will in fact perform no writeout. But it will have +been accounted as having caused 1MB of write. +In other words: The number of bytes which this process caused to not happen, +by truncating pagecache. A task can cause "negative" IO too. If this task +truncates some dirty pagecache, some IO which another task has been accounted +for (in its write_bytes) will not be happening. We _could_ just subtract that +from the truncating task's write_bytes, but there is information loss in doing +that. + + +.. Note:: + + At its current implementation state, this is a bit racy on 32-bit machines: + if process A reads process B's /proc/pid/io while process B is updating one + of those 64-bit counters, process A could see an intermediate result. + + +More information about this can be found within the taskstats documentation in +Documentation/accounting. + +3.4 /proc/<pid>/coredump_filter - Core dump filtering settings +--------------------------------------------------------------- +When a process is dumped, all anonymous memory is written to a core file as +long as the size of the core file isn't limited. But sometimes we don't want +to dump some memory segments, for example, huge shared memory or DAX. +Conversely, sometimes we want to save file-backed memory segments into a core +file, not only the individual files. + +/proc/<pid>/coredump_filter allows you to customize which memory segments +will be dumped when the <pid> process is dumped. coredump_filter is a bitmask +of memory types. If a bit of the bitmask is set, memory segments of the +corresponding memory type are dumped, otherwise they are not dumped. + +The following 9 memory types are supported: + + - (bit 0) anonymous private memory + - (bit 1) anonymous shared memory + - (bit 2) file-backed private memory + - (bit 3) file-backed shared memory + - (bit 4) ELF header pages in file-backed private memory areas (it is + effective only if the bit 2 is cleared) + - (bit 5) hugetlb private memory + - (bit 6) hugetlb shared memory + - (bit 7) DAX private memory + - (bit 8) DAX shared memory + + Note that MMIO pages such as frame buffer are never dumped and vDSO pages + are always dumped regardless of the bitmask status. + + Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is + only affected by bit 5-6, and DAX is only affected by bits 7-8. + +The default value of coredump_filter is 0x33; this means all anonymous memory +segments, ELF header pages and hugetlb private memory are dumped. + +If you don't want to dump all shared memory segments attached to pid 1234, +write 0x31 to the process's proc file:: + + $ echo 0x31 > /proc/1234/coredump_filter + +When a new process is created, the process inherits the bitmask status from its +parent. It is useful to set up coredump_filter before the program runs. +For example:: + + $ echo 0x7 > /proc/self/coredump_filter + $ ./some_program + +3.5 /proc/<pid>/mountinfo - Information about mounts +-------------------------------------------------------- + +This file contains lines of the form:: + + 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue + (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11) + + (1) mount ID: unique identifier of the mount (may be reused after umount) + (2) parent ID: ID of parent (or of self for the top of the mount tree) + (3) major:minor: value of st_dev for files on filesystem + (4) root: root of the mount within the filesystem + (5) mount point: mount point relative to the process's root + (6) mount options: per mount options + (7) optional fields: zero or more fields of the form "tag[:value]" + (8) separator: marks the end of the optional fields + (9) filesystem type: name of filesystem of the form "type[.subtype]" + (10) mount source: filesystem specific information or "none" + (11) super options: per super block options + +Parsers should ignore all unrecognised optional fields. Currently the +possible optional fields are: + +================ ============================================================== +shared:X mount is shared in peer group X +master:X mount is slave to peer group X +propagate_from:X mount is slave and receives propagation from peer group X [#]_ +unbindable mount is unbindable +================ ============================================================== + +.. [#] X is the closest dominant peer group under the process's root. If + X is the immediate master of the mount, or if there's no dominant peer + group under the same root, then only the "master:X" field is present + and not the "propagate_from:X" field. + +For more information on mount propagation see: + + Documentation/filesystems/sharedsubtree.txt + + +3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm +-------------------------------------------------------- +These files provide a method to access a tasks comm value. It also allows for +a task to set its own or one of its thread siblings comm value. The comm value +is limited in size compared to the cmdline value, so writing anything longer +then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated +comm value. + + +3.7 /proc/<pid>/task/<tid>/children - Information about task children +------------------------------------------------------------------------- +This file provides a fast way to retrieve first level children pids +of a task pointed by <pid>/<tid> pair. The format is a space separated +stream of pids. + +Note the "first level" here -- if a child has own children they will +not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children +to obtain the descendants. + +Since this interface is intended to be fast and cheap it doesn't +guarantee to provide precise results and some children might be +skipped, especially if they've exited right after we printed their +pids, so one need to either stop or freeze processes being inspected +if precise results are needed. + + +3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file +--------------------------------------------------------------- +This file provides information associated with an opened file. The regular +files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos' +represents the current offset of the opened file in decimal form [see lseek(2) +for details], 'flags' denotes the octal O_xxx mask the file has been +created with [see open(2) for details] and 'mnt_id' represents mount ID of +the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo +for details]. + +A typical output is:: + + pos: 0 + flags: 0100002 + mnt_id: 19 + +All locks associated with a file descriptor are shown in its fdinfo too:: + + lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF + +The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags +pair provide additional information particular to the objects they represent. + +Eventfd files +~~~~~~~~~~~~~ + +:: + + pos: 0 + flags: 04002 + mnt_id: 9 + eventfd-count: 5a + +where 'eventfd-count' is hex value of a counter. + +Signalfd files +~~~~~~~~~~~~~~ + +:: + + pos: 0 + flags: 04002 + mnt_id: 9 + sigmask: 0000000000000200 + +where 'sigmask' is hex value of the signal mask associated +with a file. + +Epoll files +~~~~~~~~~~~ + +:: + + pos: 0 + flags: 02 + mnt_id: 9 + tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 + +where 'tfd' is a target file descriptor number in decimal form, +'events' is events mask being watched and the 'data' is data +associated with a target [see epoll(7) for more details]. + +The 'pos' is current offset of the target file in decimal form +[see lseek(2)], 'ino' and 'sdev' are inode and device numbers +where target file resides, all in hex format. + +Fsnotify files +~~~~~~~~~~~~~~ +For inotify files the format is the following:: + + pos: 0 + flags: 02000000 + inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d + +where 'wd' is a watch descriptor in decimal form, ie a target file +descriptor number, 'ino' and 'sdev' are inode and device where the +target file resides and the 'mask' is the mask of events, all in hex +form [see inotify(7) for more details]. + +If the kernel was built with exportfs support, the path to the target +file is encoded as a file handle. The file handle is provided by three +fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex +format. + +If the kernel is built without exportfs support the file handle won't be +printed out. + +If there is no inotify mark attached yet the 'inotify' line will be omitted. + +For fanotify files the format is:: + + pos: 0 + flags: 02 + mnt_id: 9 + fanotify flags:10 event-flags:0 + fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003 + fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4 + +where fanotify 'flags' and 'event-flags' are values used in fanotify_init +call, 'mnt_id' is the mount point identifier, 'mflags' is the value of +flags associated with mark which are tracked separately from events +mask. 'ino', 'sdev' are target inode and device, 'mask' is the events +mask and 'ignored_mask' is the mask of events which are to be ignored. +All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask' +does provide information about flags and mask used in fanotify_mark +call [see fsnotify manpage for details]. + +While the first three lines are mandatory and always printed, the rest is +optional and may be omitted if no marks created yet. + +Timerfd files +~~~~~~~~~~~~~ + +:: + + pos: 0 + flags: 02 + mnt_id: 9 + clockid: 0 + ticks: 0 + settime flags: 01 + it_value: (0, 49406829) + it_interval: (1, 0) + +where 'clockid' is the clock type and 'ticks' is the number of the timer expirations +that have occurred [see timerfd_create(2) for details]. 'settime flags' are +flags in octal form been used to setup the timer [see timerfd_settime(2) for +details]. 'it_value' is remaining time until the timer exiration. +'it_interval' is the interval for the timer. Note the timer might be set up +with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value' +still exhibits timer's remaining time. + +3.9 /proc/<pid>/map_files - Information about memory mapped files +--------------------------------------------------------------------- +This directory contains symbolic links which represent memory mapped files +the process is maintaining. Example output:: + + | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so + | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so + | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so + | ... + | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1 + | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls + +The name of a link represents the virtual memory bounds of a mapping, i.e. +vm_area_struct::vm_start-vm_area_struct::vm_end. + +The main purpose of the map_files is to retrieve a set of memory mapped +files in a fast way instead of parsing /proc/<pid>/maps or +/proc/<pid>/smaps, both of which contain many more records. At the same +time one can open(2) mappings from the listings of two processes and +comparing their inode numbers to figure out which anonymous memory areas +are actually shared. + +3.10 /proc/<pid>/timerslack_ns - Task timerslack value +--------------------------------------------------------- +This file provides the value of the task's timerslack value in nanoseconds. +This value specifies a amount of time that normal timers may be deferred +in order to coalesce timers and avoid unnecessary wakeups. + +This allows a task's interactivity vs power consumption trade off to be +adjusted. + +Writing 0 to the file will set the tasks timerslack to the default value. + +Valid values are from 0 - ULLONG_MAX + +An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level +permissions on the task specified to change its timerslack_ns value. + +3.11 /proc/<pid>/patch_state - Livepatch patch operation state +----------------------------------------------------------------- +When CONFIG_LIVEPATCH is enabled, this file displays the value of the +patch state for the task. + +A value of '-1' indicates that no patch is in transition. + +A value of '0' indicates that a patch is in transition and the task is +unpatched. If the patch is being enabled, then the task hasn't been +patched yet. If the patch is being disabled, then the task has already +been unpatched. + +A value of '1' indicates that a patch is in transition and the task is +patched. If the patch is being enabled, then the task has already been +patched. If the patch is being disabled, then the task hasn't been +unpatched yet. + +3.12 /proc/<pid>/arch_status - task architecture specific status +------------------------------------------------------------------- +When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the +architecture specific status of the task. + +Example +~~~~~~~ + +:: + + $ cat /proc/6753/arch_status + AVX512_elapsed_ms: 8 + +Description +~~~~~~~~~~~ + +x86 specific entries: +~~~~~~~~~~~~~~~~~~~~~ + +AVX512_elapsed_ms: +^^^^^^^^^^^^^^^^^^ + + If AVX512 is supported on the machine, this entry shows the milliseconds + elapsed since the last time AVX512 usage was recorded. The recording + happens on a best effort basis when a task is scheduled out. This means + that the value depends on two factors: + + 1) The time which the task spent on the CPU without being scheduled + out. With CPU isolation and a single runnable task this can take + several seconds. + + 2) The time since the task was scheduled out last. Depending on the + reason for being scheduled out (time slice exhausted, syscall ...) + this can be arbitrary long time. + + As a consequence the value cannot be considered precise and authoritative + information. The application which uses this information has to be aware + of the overall scenario on the system in order to determine whether a + task is a real AVX512 user or not. Precise information can be obtained + with performance counters. + + A special value of '-1' indicates that no AVX512 usage was recorded, thus + the task is unlikely an AVX512 user, but depends on the workload and the + scheduling scenario, it also could be a false negative mentioned above. + +Configuring procfs +------------------ + +4.1 Mount options +--------------------- + +The following mount options are supported: + + ========= ======================================================== + hidepid= Set /proc/<pid>/ access mode. + gid= Set the group authorized to learn processes information. + ========= ======================================================== + +hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories +(default). + +hidepid=1 means users may not access any /proc/<pid>/ directories but their +own. Sensitive files like cmdline, sched*, status are now protected against +other users. This makes it impossible to learn whether any user runs +specific program (given the program doesn't reveal itself by its behaviour). +As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users, +poorly written programs passing sensitive information via program arguments are +now protected against local eavesdroppers. + +hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other +users. It doesn't mean that it hides a fact whether a process with a specific +pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), +but it hides process' uid and gid, which may be learned by stat()'ing +/proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering +information about running processes, whether some daemon runs with elevated +privileges, whether other user runs some sensitive program, whether other users +run any program at all, etc. + +gid= defines a group authorized to learn processes information otherwise +prohibited by hidepid=. If you use some daemon like identd which needs to learn +information about processes information, just add identd to this group. |