Documentation/filesystems/proc.rst
.. SPDX-License-Identifier: GPL-2.0
===================== ======================================= ================ /proc/sys Terrehon Bowden [email protected], October 7 1999 Bodo Bauer [email protected] 2.4.x update Jorge Nerin [email protected] November 14 2000 move /proc/sys Shen Feng [email protected] April 1 2009 fixes/update part 1.1 Stefani Seibold [email protected] 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 3.13 /proc/<pid>/fd - List of symlinks to open files 3.14 /proc/<pid>/ksm_stat - Information about the process's ksm status.
4 Configuring procfs 4.1 Mount options
5 Filesystem behavior
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... :)
The latest version of this document is available online at https://www.kernel.org/doc/html/latest/filesystems/proc.html
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...
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.
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.
A process can read its own information from /proc/PID/* with no extra
permissions. When reading /proc/PID/* information for other processes, reading
process is required to have either CAP_SYS_PTRACE capability with
PTRACE_MODE_READ access permissions, or, alternatively, CAP_PERFMON
capability. This applies to all read-only information like maps, environ,
pagemap, etc. The only exception is mem file due to its read-write nature,
which requires CAP_SYS_PTRACE capabilities with more elevated
PTRACE_MODE_ATTACH permissions; CAP_PERFMON capability does not grant access
to /proc/PID/mem for other processes.
Note that an open 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 Kthread: 0 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 SpeculationIndirectBranch: conditional enabled 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 detailed 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 fields (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, or the tracer is outside of the current pid namespace) 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 Kthread kernel thread flag, 1 is yes, 0 is no 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 to disable THP completely, not just partially) 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 SpeculationIndirectBranch indirect branch speculation mode 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 fields (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 fields (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 [anon:<name>] a private anonymous mapping that has been named by userspace [anon_shmem:<name>] an anonymous shared memory mapping that has been named by userspace =================== ===========================================
or if empty, the mapping is anonymous.
Starting with 6.11 kernel, /proc/PID/maps provides an alternative
ioctl()-based API that gives ability to flexibly and efficiently query and
filter individual VMAs. This interface is binary and is meant for more
efficient and easy programmatic use. struct procmap_query, defined in
linux/fs.h UAPI header, serves as an input/output argument to the
PROCMAP_QUERY ioctl() command. See comments in linus/fs.h UAPI header for
details on query semantics, supported flags, data returned, and general API
usage information.
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
Pss_Dirty: 0 kB
Shared_Clean: 892 kB
Shared_Dirty: 0 kB
Private_Clean: 0 kB
Private_Dirty: 0 kB
Referenced: 892 kB
Anonymous: 0 kB
KSM: 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's 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. "Pss_Dirty" is the portion of PSS which consists of dirty pages. ("Pss_Clean" is not included, but it can be calculated by subtracting "Pss_Dirty" from "Pss".)
Traditionally, a page is accounted as "private" if it is mapped exactly once, and a page is accounted as "shared" when mapped multiple times, even when mapped in the same process multiple times. Note that this accounting is independent of MAP_SHARED.
In some kernel configurations, the semantics of pages part of a larger allocation (e.g., THP) can differ: a page is accounted as "private" if all pages part of the corresponding large allocation are certainly mapped in the same process, even if the page is mapped multiple times in that process. A page is accounted as "shared" if any page page of the larger allocation is maybe mapped in a different process. In some cases, a large allocation might be treated as "maybe mapped by multiple processes" even though this is no longer the case.
Some kernel configurations do not track the precise number of times a page part of a larger allocation is mapped. In this case, when calculating the PSS, the average number of mappings per page in this larger allocation might be used as an approximation for the number of mappings of a page. The PSS calculation will be imprecise in this case.
"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.
"KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages are not included, only actual KSM pages.
"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 amount of memory backed by transparent hugepage.
"ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by huge pages.
"Shared_Hugetlb" and "Private_Hugetlb" show the amounts 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 naturally aligned THP pages of any currently enabled size. 1 if true, 0 otherwise.
"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
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
sf synchronous page fault
ar architecture specific flag
wf wipe on fork
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 mergeable advise flag
bt arm64 BTI guarded page
mt arm64 MTE allocation tags are enabled
um userfaultfd missing tracking
uw userfaultfd wr-protect tracking
ui userfaultfd minor fault
ss shadow/guarded control stack page
sl sealed
lf lock on fault pages
dp always lazily freeable mapping
gu maybe contains guard regions (if not set, definitely doesn't)
== =============================================================
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:
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:
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.
Note that some kernel configurations do not track the precise number of times a page part of a larger allocation (e.g., THP) is mapped. In these configurations, "mapmax" might corresponds to the average number of mappings per page in such a larger allocation instead.
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 ============ =============================================================== allocinfo Memory allocations profiling information apm Advanced power management info bootconfig Kernel command line obtained from boot config, and, if there were kernel parameters from the boot loader, a "# Parameters from bootloader:" line followed by a line containing those parameters prefixed by "# ". (5.5) buddyinfo Kernel memory allocator information (see text) (2.5) bus Directory containing bus specific information cmdline Kernel command line, both from bootloader and embedded in the kernel image 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; number of processes currently runnable (running or on ready queue); total number of processes in system; last pid created. All fields are separated by one space except "number of processes currently runnable" and "total number of processes in system", which are separated by a slash ('/'). Example: 0.61 0.61 0.55 3/828 22084 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 2^0PAGE_SIZE available in ZONE_DMA, 4 chunks of 2^1PAGE_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.
allocinfo
Provides information about memory allocations at all locations in the code
base. Each allocation in the code is identified by its source file, line
number, module (if originates from a loadable module) and the function calling
the allocation. The number of bytes allocated and number of calls at each
location are reported. The first line indicates the version of the file, the
second line is the header listing fields in the file.
If file version is 2.0 or higher then each line may contain additional
<key>:<value> pairs representing extra information about the call site.
For example if the counters are not accurate, the line will be appended with
"accurate:no" pair.
Supported markers in v2:
accurate:no
Absolute values of the counters in this line are not accurate
because of the failure to allocate memory to track some of the
allocations made at this location. Deltas in these counters are
accurate, therefore counters can be used to track allocation size
and count changes.
Example output.
::
> tail -n +3 /proc/allocinfo | sort -rn
127664128 31168 mm/page_ext.c:270 func:alloc_page_ext
56373248 4737 mm/slub.c:2259 func:alloc_slab_page
14880768 3633 mm/readahead.c:247 func:page_cache_ra_unbounded
14417920 3520 mm/mm_init.c:2530 func:alloc_large_system_hash
13377536 234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
11718656 2861 mm/filemap.c:1919 func:__filemap_get_folio
9192960 2800 kernel/fork.c:307 func:alloc_thread_stack_node
4206592 4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
4136960 1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
3940352 962 mm/memory.c:4214 func:alloc_anon_folio
2894464 22613 fs/kernfs/dir.c:615 func:__kernfs_new_node
...
meminfo
~~~~~~~
Provides information about distribution and utilization of memory. This
varies by architecture and compile options. Some of the counters reported
here overlap. The memory reported by the non overlapping counters may not
add up to the overall memory usage and the difference for some workloads
can be substantial. In many cases there are other means to find out
additional memory using subsystem specific interfaces, for instance
/proc/net/sockstat for TCP memory allocations.
Example output. You may not have all of these fields.
::
> cat /proc/meminfo
MemTotal: 32858820 kB
MemFree: 21001236 kB
MemAvailable: 27214312 kB
Buffers: 581092 kB
Cached: 5587612 kB
SwapCached: 0 kB
Active: 3237152 kB
Inactive: 7586256 kB
Active(anon): 94064 kB
Inactive(anon): 4570616 kB
Active(file): 3143088 kB
Inactive(file): 3015640 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Zswap: 1904 kB
Zswapped: 7792 kB
Dirty: 12 kB
Writeback: 0 kB
AnonPages: 4654780 kB
Mapped: 266244 kB
Shmem: 9976 kB
KReclaimable: 517708 kB
Slab: 660044 kB
SReclaimable: 517708 kB
SUnreclaim: 142336 kB
KernelStack: 11168 kB
PageTables: 20540 kB
SecPageTables: 0 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 16429408 kB
Committed_AS: 7715148 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 40444 kB
VmallocChunk: 0 kB
Percpu: 29312 kB
EarlyMemtestBad: 0 kB
HardwareCorrupted: 0 kB
AnonHugePages: 4149248 kB
ShmemHugePages: 0 kB
ShmemPmdMapped: 0 kB
FileHugePages: 0 kB
FilePmdMapped: 0 kB
CmaTotal: 0 kB
CmaFree: 0 kB
Unaccepted: 0 kB
Balloon: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 0 kB
DirectMap4k: 401152 kB
DirectMap2M: 10008576 kB
DirectMap1G: 24117248 kB
MemTotal
Total usable RAM (i.e. physical RAM minus a few reserved
bits and the kernel binary code)
MemFree
Total free RAM. On highmem systems, 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) as well as tmpfs & shmem.
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
Unevictable
Memory allocated for userspace which cannot be reclaimed, such
as mlocked pages, ramfs backing pages, secret memfd pages etc.
Mlocked
Memory locked with mlock().
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
Zswap
Memory consumed by the zswap backend (compressed size)
Zswapped
Amount of anonymous memory stored in zswap (original size)
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. Note that
some kernel configurations might consider all pages part of a
larger allocation (e.g., THP) as "mapped", as soon as a single
page is mapped.
Mapped
files which have been mmapped, such as libraries. Note that some
kernel configurations might consider all pages part of a larger
allocation (e.g., THP) as "mapped", as soon as a single page is
mapped.
Shmem
Total memory used by shared memory (shmem) and tmpfs
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
KernelStack
Memory consumed by the kernel stacks of all tasks
PageTables
Memory consumed by userspace page tables
SecPageTables
Memory consumed by secondary page tables, this currently includes
KVM mmu and IOMMU allocations on x86 and arm64.
NFS_Unstable
Always zero. Previously counted pages which had been written to
the server, but has not been committed to stable storage.
Bounce
Always zero. Previously memory used for block device
"bounce buffers".
WritebackTmp
Always zero. Previously 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 mm/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 virtual address space
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.
EarlyMemtestBad
The amount of RAM/memory in kB, that was identified as corrupted
by early memtest. If memtest was not run, this field will not
be displayed at all. Size is never rounded down to 0 kB.
That means if 0 kB is reported, you can safely assume
there was at least one pass of memtest and none of the passes
found a single faulty byte of RAM.
HardwareCorrupted
The amount of RAM/memory in KB, the kernel identifies as
corrupted.
AnonHugePages
Non-file backed huge pages mapped into userspace page tables
ShmemHugePages
Memory used by shared memory (shmem) and tmpfs allocated
with huge pages
ShmemPmdMapped
Shared memory mapped into userspace with huge pages
FileHugePages
Memory used for filesystem data (page cache) allocated
with huge pages
FilePmdMapped
Page cache mapped into userspace with huge pages
CmaTotal
Memory reserved for the Contiguous Memory Allocator (CMA)
CmaFree
Free remaining memory in the CMA reserves
Unaccepted
Memory that has not been accepted by the guest
Balloon
Memory returned to Host by VM Balloon Drivers
HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
See Documentation/admin-guide/mm/hugetlbpage.rst.
DirectMap4k, DirectMap2M, DirectMap1G
Breakdown of page table sizes used in the kernel's
identity mapping of RAM
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 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
softnet_stat Per-CPU incoming packets queues statistics of online CPUs
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.
1.4 SCSI info
-------------
If you have a SCSI or ATA 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)
1.5 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).
========= ====================================================================
1.6 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
1.7 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 237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0
cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0
cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0
cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0
cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0
intr 8688370575 8 3373 0 0 0 0 0 0 1 40791 0 0 353317 0 0 0 0 224789828 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 190974333 41958554 123983334 43 0 224593 0 0 0 <more 0's deleted>
ctxt 22848221062
btime 1605316999
processes 746787147
procs_running 2
procs_blocked 0
softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354
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 I/O, 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.
1.8 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/sda9 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
============== ==========================================================
1.9 /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.
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 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 files can be used to adjust the badness heuristic used to select which
process gets killed in out of memory (oom) 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.
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.
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 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.
Please note that the exported value includes oom_score_adj so it is
effectively in range [0,2000].
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.
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:
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
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) (n…m) (m+1)(m+2) (m+3) (m+4)
(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
(n…m) optional fields: zero or more fields of the form "tag[:value]"
(m+1) separator: marks the end of the optional fields
(m+2) filesystem type: name of filesystem of the form "type[.subtype]"
(m+3) mount source: filesystem specific information or "none"
(m+4) 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.rst
These files provide a method to access a task's 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, including the NUL terminator) will result in a truncated comm value.
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 its 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 needs to either stop or freeze processes being inspected if precise results are needed.
This file provides information associated with an opened file. The regular files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'. 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]. 'ino' represents the inode number of the file.
A typical output is::
pos: 0
flags: 0100002
mnt_id: 19
ino: 63107
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
ino: 63107
eventfd-count: 5a
where 'eventfd-count' is hex value of a counter.
Signalfd files
::
pos: 0
flags: 04002
mnt_id: 9
ino: 63107
sigmask: 0000000000000200
where 'sigmask' is hex value of the signal mask associated with a file.
Epoll files
::
pos: 0
flags: 02
mnt_id: 9
ino: 63107
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
mnt_id: 9
ino: 63107
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, i.e. 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
ino: 63107
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' and '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 are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask' 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
ino: 63107
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 expiration.
'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.
DMA Buffer files
::
pos: 0
flags: 04002
mnt_id: 9
ino: 63107
size: 32768
count: 2
exp_name: system-heap
where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
VFIO Device files
::
pos: 0
flags: 02000002
mnt_id: 17
ino: 5122
vfio-device-syspath: /sys/devices/pci0000:e0/0000:e0:01.1/0000:e1:00.0/0000:e2:05.0/0000:e8:00.0
where 'vfio-device-syspath' is the sysfs path corresponding to the VFIO device
file.
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 an 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 tradeoff to be
adjusted.
Writing 0 to the file will set the task's 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.
This directory contains symbolic links which represent open files the process is maintaining. Example output::
lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]' lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]' lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]'
When CONFIG_KSM is enabled, each process has this file which displays the information of ksm merging status.
Example
::
/ # cat /proc/self/ksm_stat
ksm_rmap_items 0
ksm_zero_pages 0
ksm_merging_pages 0
ksm_process_profit 0
ksm_merge_any: no
ksm_mergeable: no
Description
ksm_rmap_items ^^^^^^^^^^^^^^
The number of ksm_rmap_item structures in use. The structure ksm_rmap_item stores the reverse mapping information for virtual addresses. KSM will generate a ksm_rmap_item for each ksm-scanned page of the process.
ksm_zero_pages ^^^^^^^^^^^^^^
When /sys/kernel/mm/ksm/use_zero_pages is enabled, it represent how many empty pages are merged with kernel zero pages by KSM.
ksm_merging_pages ^^^^^^^^^^^^^^^^^
It represents how many pages of this process are involved in KSM merging (not including ksm_zero_pages). It is the same with what /proc/<pid>/ksm_merging_pages shows.
ksm_process_profit ^^^^^^^^^^^^^^^^^^
The profit that KSM brings (Saved bytes). KSM can save memory by merging identical pages, but also can consume additional memory, because it needs to generate a number of rmap_items to save each scanned page's brief rmap information. Some of these pages may be merged, but some may not be abled to be merged after being checked several times, which are unprofitable memory consumed.
ksm_merge_any ^^^^^^^^^^^^^
It specifies whether the process's 'mm is added by prctl() into the candidate list of KSM or not, and if KSM scanning is fully enabled at process level.
ksm_mergeable ^^^^^^^^^^^^^
It specifies whether any VMAs of the process''s mms are currently applicable to KSM.
More information about KSM can be found in Documentation/admin-guide/mm/ksm.rst.
The following mount options are supported:
========= ========================================================
hidepid= Set /proc/<pid>/ access mode.
gid= Set the group authorized to learn processes information.
subset= Show only the specified subset of procfs.
pidns= Specify a the namespace used by this procfs.
========= ========================================================
hidepid=off or hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories (default).
hidepid=noaccess or 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=invisible or 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 $PID"), but it hides process's uid and gid, which may be learned by stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering information about running processes, whether some daemon runs with elevated privileges, whether other user runs some sensitive program, whether other users run any program at all, etc.
hidepid=ptraceable or hidepid=4 means that procfs should only contain /proc/<pid>/ directories that the caller can ptrace.
gid= defines a group authorized to learn processes information otherwise prohibited by hidepid=. If you use some daemon like identd which needs to learn information about processes information, just add identd to this group.
subset=pid hides all top level files and directories in the procfs that are not related to tasks.
pidns= specifies a pid namespace (either as a string path to something like
/proc/$pid/ns/pid, or a file descriptor when using FSCONFIG_SET_FD) that
will be used by the procfs instance when translating pids. By default, procfs
will use the calling process's active pid namespace. Note that the pid
namespace of an existing procfs instance cannot be modified (attempting to do
so will give an -EBUSY error).
Originally, before the advent of pid namespace, procfs was a global file system. It means that there was only one procfs instance in the system.
When pid namespace was added, a separate procfs instance was mounted in each pid namespace. So, procfs mount options are global among all mountpoints within the same namespace::
# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=2 0 0
# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
+++ exited with 0 +++
# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=2 0 0
proc /tmp/proc proc rw,relatime,hidepid=2 0 0
and only after remounting procfs mount options will change at all mountpoints::
# mount -o remount,hidepid=1 -t proc proc /tmp/proc
# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=1 0 0
proc /tmp/proc proc rw,relatime,hidepid=1 0 0
This behavior is different from the behavior of other filesystems.
The new procfs behavior is more like other filesystems. Each procfs mount creates a new procfs instance. Mount options affect own procfs instance. It means that it became possible to have several procfs instances displaying tasks with different filtering options in one pid namespace::
# mount -o hidepid=invisible -t proc proc /proc
# mount -o hidepid=noaccess -t proc proc /tmp/proc
# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=invisible 0 0
proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0