# Copyright (c) 2009, Giampaolo Rodola'. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Linux platform implementation."""

from __future__ import division

import base64
import collections
import errno
import functools
import glob
import os
import re
import socket
import struct
import sys
import traceback
import warnings
from collections import defaultdict
from collections import namedtuple

from . import _common
from . import _psposix
from . import _psutil_linux as cext
from . import _psutil_posix as cext_posix
from ._common import NIC_DUPLEX_FULL
from ._common import NIC_DUPLEX_HALF
from ._common import NIC_DUPLEX_UNKNOWN
from ._common import AccessDenied
from ._common import NoSuchProcess
from ._common import ZombieProcess
from ._common import bcat
from ._common import cat
from ._common import debug
from ._common import decode
from ._common import get_procfs_path
from ._common import isfile_strict
from ._common import memoize
from ._common import memoize_when_activated
from ._common import open_binary
from ._common import open_text
from ._common import parse_environ_block
from ._common import path_exists_strict
from ._common import supports_ipv6
from ._common import usage_percent
from ._compat import PY3
from ._compat import FileNotFoundError
from ._compat import PermissionError
from ._compat import ProcessLookupError
from ._compat import b
from ._compat import basestring


if sys.version_info >= (3, 4):
    import enum
else:
    enum = None


__extra__all__ = [
    #
    'PROCFS_PATH',
    # io prio constants
    "IOPRIO_CLASS_NONE", "IOPRIO_CLASS_RT", "IOPRIO_CLASS_BE",
    "IOPRIO_CLASS_IDLE",
    # connection status constants
    "CONN_ESTABLISHED", "CONN_SYN_SENT", "CONN_SYN_RECV", "CONN_FIN_WAIT1",
    "CONN_FIN_WAIT2", "CONN_TIME_WAIT", "CONN_CLOSE", "CONN_CLOSE_WAIT",
    "CONN_LAST_ACK", "CONN_LISTEN", "CONN_CLOSING", ]


# =====================================================================
# --- globals
# =====================================================================


POWER_SUPPLY_PATH = "/sys/class/power_supply"
HAS_PROC_SMAPS = os.path.exists('/proc/%s/smaps' % os.getpid())
HAS_PROC_SMAPS_ROLLUP = os.path.exists('/proc/%s/smaps_rollup' % os.getpid())
HAS_PROC_IO_PRIORITY = hasattr(cext, "proc_ioprio_get")
HAS_CPU_AFFINITY = hasattr(cext, "proc_cpu_affinity_get")

# Number of clock ticks per second
CLOCK_TICKS = os.sysconf("SC_CLK_TCK")
PAGESIZE = cext_posix.getpagesize()
BOOT_TIME = None  # set later
LITTLE_ENDIAN = sys.byteorder == 'little'

# "man iostat" states that sectors are equivalent with blocks and have
# a size of 512 bytes. Despite this value can be queried at runtime
# via /sys/block/{DISK}/queue/hw_sector_size and results may vary
# between 1k, 2k, or 4k... 512 appears to be a magic constant used
# throughout Linux source code:
# * https://stackoverflow.com/a/38136179/376587
# * https://lists.gt.net/linux/kernel/2241060
# * https://github.com/giampaolo/psutil/issues/1305
# * https://github.com/torvalds/linux/blob/
#     4f671fe2f9523a1ea206f63fe60a7c7b3a56d5c7/include/linux/bio.h#L99
# * https://lkml.org/lkml/2015/8/17/234
DISK_SECTOR_SIZE = 512

if enum is None:
    AF_LINK = socket.AF_PACKET
else:
    AddressFamily = enum.IntEnum('AddressFamily',
                                 {'AF_LINK': int(socket.AF_PACKET)})
    AF_LINK = AddressFamily.AF_LINK

# ioprio_* constants http://linux.die.net/man/2/ioprio_get
if enum is None:
    IOPRIO_CLASS_NONE = 0
    IOPRIO_CLASS_RT = 1
    IOPRIO_CLASS_BE = 2
    IOPRIO_CLASS_IDLE = 3
else:
    class IOPriority(enum.IntEnum):
        IOPRIO_CLASS_NONE = 0
        IOPRIO_CLASS_RT = 1
        IOPRIO_CLASS_BE = 2
        IOPRIO_CLASS_IDLE = 3

    globals().update(IOPriority.__members__)

# See:
# https://github.com/torvalds/linux/blame/master/fs/proc/array.c
# ...and (TASK_* constants):
# https://github.com/torvalds/linux/blob/master/include/linux/sched.h
PROC_STATUSES = {
    "R": _common.STATUS_RUNNING,
    "S": _common.STATUS_SLEEPING,
    "D": _common.STATUS_DISK_SLEEP,
    "T": _common.STATUS_STOPPED,
    "t": _common.STATUS_TRACING_STOP,
    "Z": _common.STATUS_ZOMBIE,
    "X": _common.STATUS_DEAD,
    "x": _common.STATUS_DEAD,
    "K": _common.STATUS_WAKE_KILL,
    "W": _common.STATUS_WAKING,
    "I": _common.STATUS_IDLE,
    "P": _common.STATUS_PARKED,
}

# https://github.com/torvalds/linux/blob/master/include/net/tcp_states.h
TCP_STATUSES = {
    "01": _common.CONN_ESTABLISHED,
    "02": _common.CONN_SYN_SENT,
    "03": _common.CONN_SYN_RECV,
    "04": _common.CONN_FIN_WAIT1,
    "05": _common.CONN_FIN_WAIT2,
    "06": _common.CONN_TIME_WAIT,
    "07": _common.CONN_CLOSE,
    "08": _common.CONN_CLOSE_WAIT,
    "09": _common.CONN_LAST_ACK,
    "0A": _common.CONN_LISTEN,
    "0B": _common.CONN_CLOSING
}


# =====================================================================
# --- named tuples
# =====================================================================


# psutil.virtual_memory()
svmem = namedtuple(
    'svmem', ['total', 'available', 'percent', 'used', 'free',
              'active', 'inactive', 'buffers', 'cached', 'shared', 'slab'])
# psutil.disk_io_counters()
sdiskio = namedtuple(
    'sdiskio', ['read_count', 'write_count',
                'read_bytes', 'write_bytes',
                'read_time', 'write_time',
                'read_merged_count', 'write_merged_count',
                'busy_time'])
# psutil.Process().open_files()
popenfile = namedtuple(
    'popenfile', ['path', 'fd', 'position', 'mode', 'flags'])
# psutil.Process().memory_info()
pmem = namedtuple('pmem', 'rss vms shared text lib data dirty')
# psutil.Process().memory_full_info()
pfullmem = namedtuple('pfullmem', pmem._fields + ('uss', 'pss', 'swap'))
# psutil.Process().memory_maps(grouped=True)
pmmap_grouped = namedtuple(
    'pmmap_grouped',
    ['path', 'rss', 'size', 'pss', 'shared_clean', 'shared_dirty',
     'private_clean', 'private_dirty', 'referenced', 'anonymous', 'swap'])
# psutil.Process().memory_maps(grouped=False)
pmmap_ext = namedtuple(
    'pmmap_ext', 'addr perms ' + ' '.join(pmmap_grouped._fields))
# psutil.Process.io_counters()
pio = namedtuple('pio', ['read_count', 'write_count',
                         'read_bytes', 'write_bytes',
                         'read_chars', 'write_chars'])
# psutil.Process.cpu_times()
pcputimes = namedtuple('pcputimes',
                       ['user', 'system', 'children_user', 'children_system',
                        'iowait'])


# =====================================================================
# --- utils
# =====================================================================


def readlink(path):
    """Wrapper around os.readlink()."""
    assert isinstance(path, basestring), path
    path = os.readlink(path)
    # readlink() might return paths containing null bytes ('\x00')
    # resulting in "TypeError: must be encoded string without NULL
    # bytes, not str" errors when the string is passed to other
    # fs-related functions (os.*, open(), ...).
    # Apparently everything after '\x00' is garbage (we can have
    # ' (deleted)', 'new' and possibly others), see:
    # https://github.com/giampaolo/psutil/issues/717
    path = path.split('\x00')[0]
    # Certain paths have ' (deleted)' appended. Usually this is
    # bogus as the file actually exists. Even if it doesn't we
    # don't care.
    if path.endswith(' (deleted)') and not path_exists_strict(path):
        path = path[:-10]
    return path


def file_flags_to_mode(flags):
    """Convert file's open() flags into a readable string.
    Used by Process.open_files().
    """
    modes_map = {os.O_RDONLY: 'r', os.O_WRONLY: 'w', os.O_RDWR: 'w+'}
    mode = modes_map[flags & (os.O_RDONLY | os.O_WRONLY | os.O_RDWR)]
    if flags & os.O_APPEND:
        mode = mode.replace('w', 'a', 1)
    mode = mode.replace('w+', 'r+')
    # possible values: r, w, a, r+, a+
    return mode


def is_storage_device(name):
    """Return True if the given name refers to a root device (e.g.
    "sda", "nvme0n1") as opposed to a logical partition (e.g.  "sda1",
    "nvme0n1p1"). If name is a virtual device (e.g. "loop1", "ram")
    return True.
    """
    # Re-adapted from iostat source code, see:
    # https://github.com/sysstat/sysstat/blob/
    #     97912938cd476645b267280069e83b1c8dc0e1c7/common.c#L208
    # Some devices may have a slash in their name (e.g. cciss/c0d0...).
    name = name.replace('/', '!')
    including_virtual = True
    if including_virtual:
        path = "/sys/block/%s" % name
    else:
        path = "/sys/block/%s/device" % name
    return os.access(path, os.F_OK)


@memoize
def set_scputimes_ntuple(procfs_path):
    """Set a namedtuple of variable fields depending on the CPU times
    available on this Linux kernel version which may be:
    (user, nice, system, idle, iowait, irq, softirq, [steal, [guest,
     [guest_nice]]])
    Used by cpu_times() function.
    """
    global scputimes
    with open_binary('%s/stat' % procfs_path) as f:
        values = f.readline().split()[1:]
    fields = ['user', 'nice', 'system', 'idle', 'iowait', 'irq', 'softirq']
    vlen = len(values)
    if vlen >= 8:
        # Linux >= 2.6.11
        fields.append('steal')
    if vlen >= 9:
        # Linux >= 2.6.24
        fields.append('guest')
    if vlen >= 10:
        # Linux >= 3.2.0
        fields.append('guest_nice')
    scputimes = namedtuple('scputimes', fields)


try:
    set_scputimes_ntuple("/proc")
except Exception:  # pragma: no cover
    # Don't want to crash at import time.
    traceback.print_exc()
    scputimes = namedtuple('scputimes', 'user system idle')(0.0, 0.0, 0.0)


# =====================================================================
# --- prlimit
# =====================================================================

# Backport of resource.prlimit() for Python 2. Originally this was done
# in C, but CentOS-6 which we use to create manylinux wheels is too old
# and does not support prlimit() syscall. As such the resulting wheel
# would not include prlimit(), even when installed on newer systems.
# This is the only part of psutil using ctypes.

prlimit = None
try:
    from resource import prlimit  # python >= 3.4
except ImportError:
    import ctypes

    libc = ctypes.CDLL(None, use_errno=True)

    if hasattr(libc, "prlimit"):

        def prlimit(pid, resource_, limits=None):
            class StructRlimit(ctypes.Structure):
                _fields_ = [('rlim_cur', ctypes.c_longlong),
                            ('rlim_max', ctypes.c_longlong)]

            current = StructRlimit()
            if limits is None:
                # get
                ret = libc.prlimit(pid, resource_, None, ctypes.byref(current))
            else:
                # set
                new = StructRlimit()
                new.rlim_cur = limits[0]
                new.rlim_max = limits[1]
                ret = libc.prlimit(
                    pid, resource_, ctypes.byref(new), ctypes.byref(current))

            if ret != 0:
                errno = ctypes.get_errno()
                raise OSError(errno, os.strerror(errno))
            return (current.rlim_cur, current.rlim_max)


if prlimit is not None:
    __extra__all__.extend(
        [x for x in dir(cext) if x.startswith('RLIM') and x.isupper()])


# =====================================================================
# --- system memory
# =====================================================================


def calculate_avail_vmem(mems):
    """Fallback for kernels < 3.14 where /proc/meminfo does not provide
    "MemAvailable:" column, see:
    https://blog.famzah.net/2014/09/24/
    This code reimplements the algorithm outlined here:
    https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/
        commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773

    XXX: on recent kernels this calculation differs by ~1.5% than
    "MemAvailable:" as it's calculated slightly differently, see:
    https://gitlab.com/procps-ng/procps/issues/42
    https://github.com/famzah/linux-memavailable-procfs/issues/2
    It is still way more realistic than doing (free + cached) though.
    """
    # Fallback for very old distros. According to
    # https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/
    #     commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773
    # ...long ago "avail" was calculated as (free + cached).
    # We might fallback in such cases:
    # "Active(file)" not available: 2.6.28 / Dec 2008
    # "Inactive(file)" not available: 2.6.28 / Dec 2008
    # "SReclaimable:" not available: 2.6.19 / Nov 2006
    # /proc/zoneinfo not available: 2.6.13 / Aug 2005
    free = mems[b'MemFree:']
    fallback = free + mems.get(b"Cached:", 0)
    try:
        lru_active_file = mems[b'Active(file):']
        lru_inactive_file = mems[b'Inactive(file):']
        slab_reclaimable = mems[b'SReclaimable:']
    except KeyError:
        return fallback
    try:
        f = open_binary('%s/zoneinfo' % get_procfs_path())
    except IOError:
        return fallback  # kernel 2.6.13

    watermark_low = 0
    with f:
        for line in f:
            line = line.strip()
            if line.startswith(b'low'):
                watermark_low += int(line.split()[1])
    watermark_low *= PAGESIZE

    avail = free - watermark_low
    pagecache = lru_active_file + lru_inactive_file
    pagecache -= min(pagecache / 2, watermark_low)
    avail += pagecache
    avail += slab_reclaimable - min(slab_reclaimable / 2.0, watermark_low)
    return int(avail)


def virtual_memory():
    """Report virtual memory stats.
    This implementation matches "free" and "vmstat -s" cmdline
    utility values and procps-ng-3.3.12 source was used as a reference
    (2016-09-18):
    https://gitlab.com/procps-ng/procps/blob/
        24fd2605c51fccc375ab0287cec33aa767f06718/proc/sysinfo.c
    For reference, procps-ng-3.3.10 is the version available on Ubuntu
    16.04.

    Note about "available" memory: up until psutil 4.3 it was
    calculated as "avail = (free + buffers + cached)". Now
    "MemAvailable:" column (kernel 3.14) from /proc/meminfo is used as
    it's more accurate.
    That matches "available" column in newer versions of "free".
    """
    missing_fields = []
    mems = {}
    with open_binary('%s/meminfo' % get_procfs_path()) as f:
        for line in f:
            fields = line.split()
            mems[fields[0]] = int(fields[1]) * 1024

    # /proc doc states that the available fields in /proc/meminfo vary
    # by architecture and compile options, but these 3 values are also
    # returned by sysinfo(2); as such we assume they are always there.
    total = mems[b'MemTotal:']
    free = mems[b'MemFree:']
    try:
        buffers = mems[b'Buffers:']
    except KeyError:
        # https://github.com/giampaolo/psutil/issues/1010
        buffers = 0
        missing_fields.append('buffers')
    try:
        cached = mems[b"Cached:"]
    except KeyError:
        cached = 0
        missing_fields.append('cached')
    else:
        # "free" cmdline utility sums reclaimable to cached.
        # Older versions of procps used to add slab memory instead.
        # This got changed in:
        # https://gitlab.com/procps-ng/procps/commit/
        #     05d751c4f076a2f0118b914c5e51cfbb4762ad8e
        cached += mems.get(b"SReclaimable:", 0)  # since kernel 2.6.19

    try:
        shared = mems[b'Shmem:']  # since kernel 2.6.32
    except KeyError:
        try:
            shared = mems[b'MemShared:']  # kernels 2.4
        except KeyError:
            shared = 0
            missing_fields.append('shared')

    try:
        active = mems[b"Active:"]
    except KeyError:
        active = 0
        missing_fields.append('active')

    try:
        inactive = mems[b"Inactive:"]
    except KeyError:
        try:
            inactive = \
                mems[b"Inact_dirty:"] + \
                mems[b"Inact_clean:"] + \
                mems[b"Inact_laundry:"]
        except KeyError:
            inactive = 0
            missing_fields.append('inactive')

    try:
        slab = mems[b"Slab:"]
    except KeyError:
        slab = 0

    used = total - free - cached - buffers
    if used < 0:
        # May be symptomatic of running within a LCX container where such
        # values will be dramatically distorted over those of the host.
        used = total - free

    # - starting from 4.4.0 we match free's "available" column.
    #   Before 4.4.0 we calculated it as (free + buffers + cached)
    #   which matched htop.
    # - free and htop available memory differs as per:
    #   http://askubuntu.com/a/369589
    #   http://unix.stackexchange.com/a/65852/168884
    # - MemAvailable has been introduced in kernel 3.14
    try:
        avail = mems[b'MemAvailable:']
    except KeyError:
        avail = calculate_avail_vmem(mems)

    if avail < 0:
        avail = 0
        missing_fields.append('available')

    # If avail is greater than total or our calculation overflows,
    # that's symptomatic of running within a LCX container where such
    # values will be dramatically distorted over those of the host.
    # https://gitlab.com/procps-ng/procps/blob/
    #     24fd2605c51fccc375ab0287cec33aa767f06718/proc/sysinfo.c#L764
    if avail > total:
        avail = free

    percent = usage_percent((total - avail), total, round_=1)

    # Warn about missing metrics which are set to 0.
    if missing_fields:
        msg = "%s memory stats couldn't be determined and %s set to 0" % (
            ", ".join(missing_fields),
            "was" if len(missing_fields) == 1 else "were")
        warnings.warn(msg, RuntimeWarning)

    return svmem(total, avail, percent, used, free,
                 active, inactive, buffers, cached, shared, slab)


def swap_memory():
    """Return swap memory metrics."""
    mems = {}
    with open_binary('%s/meminfo' % get_procfs_path()) as f:
        for line in f:
            fields = line.split()
            mems[fields[0]] = int(fields[1]) * 1024
    # We prefer /proc/meminfo over sysinfo() syscall so that
    # psutil.PROCFS_PATH can be used in order to allow retrieval
    # for linux containers, see:
    # https://github.com/giampaolo/psutil/issues/1015
    try:
        total = mems[b'SwapTotal:']
        free = mems[b'SwapFree:']
    except KeyError:
        _, _, _, _, total, free, unit_multiplier = cext.linux_sysinfo()
        total *= unit_multiplier
        free *= unit_multiplier

    used = total - free
    percent = usage_percent(used, total, round_=1)
    # get pgin/pgouts
    try:
        f = open_binary("%s/vmstat" % get_procfs_path())
    except IOError as err:
        # see https://github.com/giampaolo/psutil/issues/722
        msg = "'sin' and 'sout' swap memory stats couldn't " \
              "be determined and were set to 0 (%s)" % str(err)
        warnings.warn(msg, RuntimeWarning)
        sin = sout = 0
    else:
        with f:
            sin = sout = None
            for line in f:
                # values are expressed in 4 kilo bytes, we want
                # bytes instead
                if line.startswith(b'pswpin'):
                    sin = int(line.split(b' ')[1]) * 4 * 1024
                elif line.startswith(b'pswpout'):
                    sout = int(line.split(b' ')[1]) * 4 * 1024
                if sin is not None and sout is not None:
                    break
            else:
                # we might get here when dealing with exotic Linux
                # flavors, see:
                # https://github.com/giampaolo/psutil/issues/313
                msg = "'sin' and 'sout' swap memory stats couldn't " \
                      "be determined and were set to 0"
                warnings.warn(msg, RuntimeWarning)
                sin = sout = 0
    return _common.sswap(total, used, free, percent, sin, sout)


# =====================================================================
# --- CPU
# =====================================================================


def cpu_times():
    """Return a named tuple representing the following system-wide
    CPU times:
    (user, nice, system, idle, iowait, irq, softirq [steal, [guest,
     [guest_nice]]])
    Last 3 fields may not be available on all Linux kernel versions.
    """
    procfs_path = get_procfs_path()
    set_scputimes_ntuple(procfs_path)
    with open_binary('%s/stat' % procfs_path) as f:
        values = f.readline().split()
    fields = values[1:len(scputimes._fields) + 1]
    fields = [float(x) / CLOCK_TICKS for x in fields]
    return scputimes(*fields)


def per_cpu_times():
    """Return a list of namedtuple representing the CPU times
    for every CPU available on the system.
    """
    procfs_path = get_procfs_path()
    set_scputimes_ntuple(procfs_path)
    cpus = []
    with open_binary('%s/stat' % procfs_path) as f:
        # get rid of the first line which refers to system wide CPU stats
        f.readline()
        for line in f:
            if line.startswith(b'cpu'):
                values = line.split()
                fields = values[1:len(scputimes._fields) + 1]
                fields = [float(x) / CLOCK_TICKS for x in fields]
                entry = scputimes(*fields)
                cpus.append(entry)
        return cpus


def cpu_count_logical():
    """Return the number of logical CPUs in the system."""
    try:
        return os.sysconf("SC_NPROCESSORS_ONLN")
    except ValueError:
        # as a second fallback we try to parse /proc/cpuinfo
        num = 0
        with open_binary('%s/cpuinfo' % get_procfs_path()) as f:
            for line in f:
                if line.lower().startswith(b'processor'):
                    num += 1

        # unknown format (e.g. amrel/sparc architectures), see:
        # https://github.com/giampaolo/psutil/issues/200
        # try to parse /proc/stat as a last resort
        if num == 0:
            search = re.compile(r'cpu\d')
            with open_text('%s/stat' % get_procfs_path()) as f:
                for line in f:
                    line = line.split(' ')[0]
                    if search.match(line):
                        num += 1

        if num == 0:
            # mimic os.cpu_count()
            return None
        return num


def cpu_count_cores():
    """Return the number of CPU cores in the system."""
    # Method #1
    ls = set()
    # These 2 files are the same but */core_cpus_list is newer while
    # */thread_siblings_list is deprecated and may disappear in the future.
    # https://www.kernel.org/doc/Documentation/admin-guide/cputopology.rst
    # https://github.com/giampaolo/psutil/pull/1727#issuecomment-707624964
    # https://lkml.org/lkml/2019/2/26/41
    p1 = "/sys/devices/system/cpu/cpu[0-9]*/topology/core_cpus_list"
    p2 = "/sys/devices/system/cpu/cpu[0-9]*/topology/thread_siblings_list"
    for path in glob.glob(p1) or glob.glob(p2):
        with open_binary(path) as f:
            ls.add(f.read().strip())
    result = len(ls)
    if result != 0:
        return result

    # Method #2
    mapping = {}
    current_info = {}
    with open_binary('%s/cpuinfo' % get_procfs_path()) as f:
        for line in f:
            line = line.strip().lower()
            if not line:
                # new section
                try:
                    mapping[current_info[b'physical id']] = \
                        current_info[b'cpu cores']
                except KeyError:
                    pass
                current_info = {}
            else:
                # ongoing section
                if line.startswith((b'physical id', b'cpu cores')):
                    key, value = line.split(b'\t:', 1)
                    current_info[key] = int(value)

    result = sum(mapping.values())
    return result or None  # mimic os.cpu_count()


def cpu_stats():
    """Return various CPU stats as a named tuple."""
    with open_binary('%s/stat' % get_procfs_path()) as f:
        ctx_switches = None
        interrupts = None
        soft_interrupts = None
        for line in f:
            if line.startswith(b'ctxt'):
                ctx_switches = int(line.split()[1])
            elif line.startswith(b'intr'):
                interrupts = int(line.split()[1])
            elif line.startswith(b'softirq'):
                soft_interrupts = int(line.split()[1])
            if ctx_switches is not None and soft_interrupts is not None \
                    and interrupts is not None:
                break
    syscalls = 0
    return _common.scpustats(
        ctx_switches, interrupts, soft_interrupts, syscalls)


def _cpu_get_cpuinfo_freq():
    """Return current CPU frequency from cpuinfo if available.
    """
    ret = []
    with open_binary('%s/cpuinfo' % get_procfs_path()) as f:
        for line in f:
            if line.lower().startswith(b'cpu mhz'):
                ret.append(float(line.split(b':', 1)[1]))
    return ret


if os.path.exists("/sys/devices/system/cpu/cpufreq/policy0") or \
        os.path.exists("/sys/devices/system/cpu/cpu0/cpufreq"):
    def cpu_freq():
        """Return frequency metrics for all CPUs.
        Contrarily to other OSes, Linux updates these values in
        real-time.
        """
        cpuinfo_freqs = _cpu_get_cpuinfo_freq()
        paths = \
            glob.glob("/sys/devices/system/cpu/cpufreq/policy[0-9]*") or \
            glob.glob("/sys/devices/system/cpu/cpu[0-9]*/cpufreq")
        paths.sort(key=lambda x: int(re.search(r"[0-9]+", x).group()))
        ret = []
        pjoin = os.path.join
        for i, path in enumerate(paths):
            if len(paths) == len(cpuinfo_freqs):
                # take cached value from cpuinfo if available, see:
                # https://github.com/giampaolo/psutil/issues/1851
                curr = cpuinfo_freqs[i] * 1000
            else:
                curr = bcat(pjoin(path, "scaling_cur_freq"), fallback=None)
            if curr is None:
                # Likely an old RedHat, see:
                # https://github.com/giampaolo/psutil/issues/1071
                curr = bcat(pjoin(path, "cpuinfo_cur_freq"), fallback=None)
                if curr is None:
                    raise NotImplementedError(
                        "can't find current frequency file")
            curr = int(curr) / 1000
            max_ = int(bcat(pjoin(path, "scaling_max_freq"))) / 1000
            min_ = int(bcat(pjoin(path, "scaling_min_freq"))) / 1000
            ret.append(_common.scpufreq(curr, min_, max_))
        return ret

else:
    def cpu_freq():
        """Alternate implementation using /proc/cpuinfo.
        min and max frequencies are not available and are set to None.
        """
        return [_common.scpufreq(x, 0., 0.) for x in _cpu_get_cpuinfo_freq()]


# =====================================================================
# --- network
# =====================================================================


net_if_addrs = cext_posix.net_if_addrs


class _Ipv6UnsupportedError(Exception):
    pass


class Connections:
    """A wrapper on top of /proc/net/* files, retrieving per-process
    and system-wide open connections (TCP, UDP, UNIX) similarly to
    "netstat -an".

    Note: in case of UNIX sockets we're only able to determine the
    local endpoint/path, not the one it's connected to.
    According to [1] it would be possible but not easily.

    [1] http://serverfault.com/a/417946
    """

    def __init__(self):
        # The string represents the basename of the corresponding
        # /proc/net/{proto_name} file.
        tcp4 = ("tcp", socket.AF_INET, socket.SOCK_STREAM)
        tcp6 = ("tcp6", socket.AF_INET6, socket.SOCK_STREAM)
        udp4 = ("udp", socket.AF_INET, socket.SOCK_DGRAM)
        udp6 = ("udp6", socket.AF_INET6, socket.SOCK_DGRAM)
        unix = ("unix", socket.AF_UNIX, None)
        self.tmap = {
            "all": (tcp4, tcp6, udp4, udp6, unix),
            "tcp": (tcp4, tcp6),
            "tcp4": (tcp4,),
            "tcp6": (tcp6,),
            "udp": (udp4, udp6),
            "udp4": (udp4,),
            "udp6": (udp6,),
            "unix": (unix,),
            "inet": (tcp4, tcp6, udp4, udp6),
            "inet4": (tcp4, udp4),
            "inet6": (tcp6, udp6),
        }
        self._procfs_path = None

    def get_proc_inodes(self, pid):
        inodes = defaultdict(list)
        for fd in os.listdir("%s/%s/fd" % (self._procfs_path, pid)):
            try:
                inode = readlink("%s/%s/fd/%s" % (self._procfs_path, pid, fd))
            except (FileNotFoundError, ProcessLookupError):
                # ENOENT == file which is gone in the meantime;
                # os.stat('/proc/%s' % self.pid) will be done later
                # to force NSP (if it's the case)
                continue
            except OSError as err:
                if err.errno == errno.EINVAL:
                    # not a link
                    continue
                if err.errno == errno.ENAMETOOLONG:
                    # file name too long
                    debug(err)
                    continue
                raise
            else:
                if inode.startswith('socket:['):
                    # the process is using a socket
                    inode = inode[8:][:-1]
                    inodes[inode].append((pid, int(fd)))
        return inodes

    def get_all_inodes(self):
        inodes = {}
        for pid in pids():
            try:
                inodes.update(self.get_proc_inodes(pid))
            except (FileNotFoundError, ProcessLookupError, PermissionError):
                # os.listdir() is gonna raise a lot of access denied
                # exceptions in case of unprivileged user; that's fine
                # as we'll just end up returning a connection with PID
                # and fd set to None anyway.
                # Both netstat -an and lsof does the same so it's
                # unlikely we can do any better.
                # ENOENT just means a PID disappeared on us.
                continue
        return inodes

    @staticmethod
    def decode_address(addr, family):
        """Accept an "ip:port" address as displayed in /proc/net/*
        and convert it into a human readable form, like:

        "0500000A:0016" -> ("10.0.0.5", 22)
        "0000000000000000FFFF00000100007F:9E49" -> ("::ffff:127.0.0.1", 40521)

        The IP address portion is a little or big endian four-byte
        hexadecimal number; that is, the least significant byte is listed
        first, so we need to reverse the order of the bytes to convert it
        to an IP address.
        The port is represented as a two-byte hexadecimal number.

        Reference:
        http://linuxdevcenter.com/pub/a/linux/2000/11/16/LinuxAdmin.html
        """
        ip, port = addr.split(':')
        port = int(port, 16)
        # this usually refers to a local socket in listen mode with
        # no end-points connected
        if not port:
            return ()
        if PY3:
            ip = ip.encode('ascii')
        if family == socket.AF_INET:
            # see: https://github.com/giampaolo/psutil/issues/201
            if LITTLE_ENDIAN:
                ip = socket.inet_ntop(family, base64.b16decode(ip)[::-1])
            else:
                ip = socket.inet_ntop(family, base64.b16decode(ip))
        else:  # IPv6
            ip = base64.b16decode(ip)
            try:
                # see: https://github.com/giampaolo/psutil/issues/201
                if LITTLE_ENDIAN:
                    ip = socket.inet_ntop(
                        socket.AF_INET6,
                        struct.pack('>4I', *struct.unpack('<4I', ip)))
                else:
                    ip = socket.inet_ntop(
                        socket.AF_INET6,
                        struct.pack('<4I', *struct.unpack('<4I', ip)))
            except ValueError:
                # see: https://github.com/giampaolo/psutil/issues/623
                if not supports_ipv6():
                    raise _Ipv6UnsupportedError
                else:
                    raise
        return _common.addr(ip, port)

    @staticmethod
    def process_inet(file, family, type_, inodes, filter_pid=None):
        """Parse /proc/net/tcp* and /proc/net/udp* files."""
        if file.endswith('6') and not os.path.exists(file):
            # IPv6 not supported
            return
        with open_text(file) as f:
            f.readline()  # skip the first line
            for lineno, line in enumerate(f, 1):
                try:
                    _, laddr, raddr, status, _, _, _, _, _, inode = \
                        line.split()[:10]
                except ValueError:
                    raise RuntimeError(
                        "error while parsing %s; malformed line %s %r" % (
                            file, lineno, line))
                if inode in inodes:
                    # # We assume inet sockets are unique, so we error
                    # # out if there are multiple references to the
                    # # same inode. We won't do this for UNIX sockets.
                    # if len(inodes[inode]) > 1 and family != socket.AF_UNIX:
                    #     raise ValueError("ambiguous inode with multiple "
                    #                      "PIDs references")
                    pid, fd = inodes[inode][0]
                else:
                    pid, fd = None, -1
                if filter_pid is not None and filter_pid != pid:
                    continue
                else:
                    if type_ == socket.SOCK_STREAM:
                        status = TCP_STATUSES[status]
                    else:
                        status = _common.CONN_NONE
                    try:
                        laddr = Connections.decode_address(laddr, family)
                        raddr = Connections.decode_address(raddr, family)
                    except _Ipv6UnsupportedError:
                        continue
                    yield (fd, family, type_, laddr, raddr, status, pid)

    @staticmethod
    def process_unix(file, family, inodes, filter_pid=None):
        """Parse /proc/net/unix files."""
        with open_text(file) as f:
            f.readline()  # skip the first line
            for line in f:
                tokens = line.split()
                try:
                    _, _, _, _, type_, _, inode = tokens[0:7]
                except ValueError:
                    if ' ' not in line:
                        # see: https://github.com/giampaolo/psutil/issues/766
                        continue
                    raise RuntimeError(
                        "error while parsing %s; malformed line %r" % (
                            file, line))
                if inode in inodes:
                    # With UNIX sockets we can have a single inode
                    # referencing many file descriptors.
                    pairs = inodes[inode]
                else:
                    pairs = [(None, -1)]
                for pid, fd in pairs:
                    if filter_pid is not None and filter_pid != pid:
                        continue
                    else:
                        if len(tokens) == 8:
                            path = tokens[-1]
                        else:
                            path = ""
                        type_ = _common.socktype_to_enum(int(type_))
                        # XXX: determining the remote endpoint of a
                        # UNIX socket on Linux is not possible, see:
                        # https://serverfault.com/questions/252723/
                        raddr = ""
                        status = _common.CONN_NONE
                        yield (fd, family, type_, path, raddr, status, pid)

    def retrieve(self, kind, pid=None):
        if kind not in self.tmap:
            raise ValueError("invalid %r kind argument; choose between %s"
                             % (kind, ', '.join([repr(x) for x in self.tmap])))
        self._procfs_path = get_procfs_path()
        if pid is not None:
            inodes = self.get_proc_inodes(pid)
            if not inodes:
                # no connections for this process
                return []
        else:
            inodes = self.get_all_inodes()
        ret = set()
        for proto_name, family, type_ in self.tmap[kind]:
            path = "%s/net/%s" % (self._procfs_path, proto_name)
            if family in (socket.AF_INET, socket.AF_INET6):
                ls = self.process_inet(
                    path, family, type_, inodes, filter_pid=pid)
            else:
                ls = self.process_unix(
                    path, family, inodes, filter_pid=pid)
            for fd, family, type_, laddr, raddr, status, bound_pid in ls:
                if pid:
                    conn = _common.pconn(fd, family, type_, laddr, raddr,
                                         status)
                else:
                    conn = _common.sconn(fd, family, type_, laddr, raddr,
                                         status, bound_pid)
                ret.add(conn)
        return list(ret)


_connections = Connections()


def net_connections(kind='inet'):
    """Return system-wide open connections."""
    return _connections.retrieve(kind)


def net_io_counters():
    """Return network I/O statistics for every network interface
    installed on the system as a dict of raw tuples.
    """
    with open_text("%s/net/dev" % get_procfs_path()) as f:
        lines = f.readlines()
    retdict = {}
    for line in lines[2:]:
        colon = line.rfind(':')
        assert colon > 0, repr(line)
        name = line[:colon].strip()
        fields = line[colon + 1:].strip().split()

        # in
        (bytes_recv,
         packets_recv,
         errin,
         dropin,
         fifoin,  # unused
         framein,  # unused
         compressedin,  # unused
         multicastin,  # unused
         # out
         bytes_sent,
         packets_sent,
         errout,
         dropout,
         fifoout,  # unused
         collisionsout,  # unused
         carrierout,  # unused
         compressedout) = map(int, fields)

        retdict[name] = (bytes_sent, bytes_recv, packets_sent, packets_recv,
                         errin, errout, dropin, dropout)
    return retdict


def net_if_stats():
    """Get NIC stats (isup, duplex, speed, mtu)."""
    duplex_map = {cext.DUPLEX_FULL: NIC_DUPLEX_FULL,
                  cext.DUPLEX_HALF: NIC_DUPLEX_HALF,
                  cext.DUPLEX_UNKNOWN: NIC_DUPLEX_UNKNOWN}
    names = net_io_counters().keys()
    ret = {}
    for name in names:
        try:
            mtu = cext_posix.net_if_mtu(name)
            flags = cext_posix.net_if_flags(name)
            duplex, speed = cext.net_if_duplex_speed(name)
        except OSError as err:
            # https://github.com/giampaolo/psutil/issues/1279
            if err.errno != errno.ENODEV:
                raise
            else:
                debug(err)
        else:
            output_flags = ','.join(flags)
            isup = 'running' in flags
            ret[name] = _common.snicstats(isup, duplex_map[duplex], speed, mtu,
                                          output_flags)
    return ret


# =====================================================================
# --- disks
# =====================================================================


disk_usage = _psposix.disk_usage


def disk_io_counters(perdisk=False):
    """Return disk I/O statistics for every disk installed on the
    system as a dict of raw tuples.
    """
    def read_procfs():
        # OK, this is a bit confusing. The format of /proc/diskstats can
        # have 3 variations.
        # On Linux 2.4 each line has always 15 fields, e.g.:
        # "3     0   8 hda 8 8 8 8 8 8 8 8 8 8 8"
        # On Linux 2.6+ each line *usually* has 14 fields, and the disk
        # name is in another position, like this:
        # "3    0   hda 8 8 8 8 8 8 8 8 8 8 8"
        # ...unless (Linux 2.6) the line refers to a partition instead
        # of a disk, in which case the line has less fields (7):
        # "3    1   hda1 8 8 8 8"
        # 4.18+ has 4 fields added:
        # "3    0   hda 8 8 8 8 8 8 8 8 8 8 8 0 0 0 0"
        # 5.5 has 2 more fields.
        # See:
        # https://www.kernel.org/doc/Documentation/iostats.txt
        # https://www.kernel.org/doc/Documentation/ABI/testing/procfs-diskstats
        with open_text("%s/diskstats" % get_procfs_path()) as f:
            lines = f.readlines()
        for line in lines:
            fields = line.split()
            flen = len(fields)
            if flen == 15:
                # Linux 2.4
                name = fields[3]
                reads = int(fields[2])
                (reads_merged, rbytes, rtime, writes, writes_merged,
                    wbytes, wtime, _, busy_time, _) = map(int, fields[4:14])
            elif flen == 14 or flen >= 18:
                # Linux 2.6+, line referring to a disk
                name = fields[2]
                (reads, reads_merged, rbytes, rtime, writes, writes_merged,
                    wbytes, wtime, _, busy_time, _) = map(int, fields[3:14])
            elif flen == 7:
                # Linux 2.6+, line referring to a partition
                name = fields[2]
                reads, rbytes, writes, wbytes = map(int, fields[3:])
                rtime = wtime = reads_merged = writes_merged = busy_time = 0
            else:
                raise ValueError("not sure how to interpret line %r" % line)
            yield (name, reads, writes, rbytes, wbytes, rtime, wtime,
                   reads_merged, writes_merged, busy_time)

    def read_sysfs():
        for block in os.listdir('/sys/block'):
            for root, _, files in os.walk(os.path.join('/sys/block', block)):
                if 'stat' not in files:
                    continue
                with open_text(os.path.join(root, 'stat')) as f:
                    fields = f.read().strip().split()
                name = os.path.basename(root)
                (reads, reads_merged, rbytes, rtime, writes, writes_merged,
                    wbytes, wtime, _, busy_time) = map(int, fields[:10])
                yield (name, reads, writes, rbytes, wbytes, rtime,
                       wtime, reads_merged, writes_merged, busy_time)

    if os.path.exists('%s/diskstats' % get_procfs_path()):
        gen = read_procfs()
    elif os.path.exists('/sys/block'):
        gen = read_sysfs()
    else:
        raise NotImplementedError(
            "%s/diskstats nor /sys/block filesystem are available on this "
            "system" % get_procfs_path())

    retdict = {}
    for entry in gen:
        (name, reads, writes, rbytes, wbytes, rtime, wtime, reads_merged,
            writes_merged, busy_time) = entry
        if not perdisk and not is_storage_device(name):
            # perdisk=False means we want to calculate totals so we skip
            # partitions (e.g. 'sda1', 'nvme0n1p1') and only include
            # base disk devices (e.g. 'sda', 'nvme0n1'). Base disks
            # include a total of all their partitions + some extra size
            # of their own:
            #     $ cat /proc/diskstats
            #     259       0 sda 10485760 ...
            #     259       1 sda1 5186039 ...
            #     259       1 sda2 5082039 ...
            # See:
            # https://github.com/giampaolo/psutil/pull/1313
            continue

        rbytes *= DISK_SECTOR_SIZE
        wbytes *= DISK_SECTOR_SIZE
        retdict[name] = (reads, writes, rbytes, wbytes, rtime, wtime,
                         reads_merged, writes_merged, busy_time)

    return retdict


class RootFsDeviceFinder:
    """disk_partitions() may return partitions with device == "/dev/root"
    or "rootfs". This container class uses different strategies to try to
    obtain the real device path. Resources:
    https://bootlin.com/blog/find-root-device/
    https://www.systutorials.com/how-to-find-the-disk-where-root-is-on-in-bash-on-linux/
    """
    __slots__ = ['major', 'minor']

    def __init__(self):
        dev = os.stat("/").st_dev
        self.major = os.major(dev)
        self.minor = os.minor(dev)

    def ask_proc_partitions(self):
        with open_text("%s/partitions" % get_procfs_path()) as f:
            for line in f.readlines()[2:]:
                fields = line.split()
                if len(fields) < 4:  # just for extra safety
                    continue
                major = int(fields[0]) if fields[0].isdigit() else None
                minor = int(fields[1]) if fields[1].isdigit() else None
                name = fields[3]
                if major == self.major and minor == self.minor:
                    if name:  # just for extra safety
                        return "/dev/%s" % name

    def ask_sys_dev_block(self):
        path = "/sys/dev/block/%s:%s/uevent" % (self.major, self.minor)
        with open_text(path) as f:
            for line in f:
                if line.startswith("DEVNAME="):
                    name = line.strip().rpartition("DEVNAME=")[2]
                    if name:  # just for extra safety
                        return "/dev/%s" % name

    def ask_sys_class_block(self):
        needle = "%s:%s" % (self.major, self.minor)
        files = glob.iglob("/sys/class/block/*/dev")
        for file in files:
            try:
                f = open_text(file)
            except FileNotFoundError:  # race condition
                continue
            else:
                with f:
                    data = f.read().strip()
                    if data == needle:
                        name = os.path.basename(os.path.dirname(file))
                        return "/dev/%s" % name

    def find(self):
        path = None
        if path is None:
            try:
                path = self.ask_proc_partitions()
            except (IOError, OSError) as err:
                debug(err)
        if path is None:
            try:
                path = self.ask_sys_dev_block()
            except (IOError, OSError) as err:
                debug(err)
        if path is None:
            try:
                path = self.ask_sys_class_block()
            except (IOError, OSError) as err:
                debug(err)
        # We use exists() because the "/dev/*" part of the path is hard
        # coded, so we want to be sure.
        if path is not None and os.path.exists(path):
            return path


def disk_partitions(all=False):
    """Return mounted disk partitions as a list of namedtuples."""
    fstypes = set()
    procfs_path = get_procfs_path()
    with open_text("%s/filesystems" % procfs_path) as f:
        for line in f:
            line = line.strip()
            if not line.startswith("nodev"):
                fstypes.add(line.strip())
            else:
                # ignore all lines starting with "nodev" except "nodev zfs"
                fstype = line.split("\t")[1]
                if fstype == "zfs":
                    fstypes.add("zfs")

    # See: https://github.com/giampaolo/psutil/issues/1307
    if procfs_path == "/proc" and os.path.isfile('/etc/mtab'):
        mounts_path = os.path.realpath("/etc/mtab")
    else:
        mounts_path = os.path.realpath("%s/self/mounts" % procfs_path)

    retlist = []
    partitions = cext.disk_partitions(mounts_path)
    for partition in partitions:
        device, mountpoint, fstype, opts = partition
        if device == 'none':
            device = ''
        if device in ("/dev/root", "rootfs"):
            device = RootFsDeviceFinder().find() or device
        if not all:
            if device == '' or fstype not in fstypes:
                continue
        maxfile = maxpath = None  # set later
        ntuple = _common.sdiskpart(device, mountpoint, fstype, opts,
                                   maxfile, maxpath)
        retlist.append(ntuple)

    return retlist


# =====================================================================
# --- sensors
# =====================================================================


def sensors_temperatures():
    """Return hardware (CPU and others) temperatures as a dict
    including hardware name, label, current, max and critical
    temperatures.

    Implementation notes:
    - /sys/class/hwmon looks like the most recent interface to
      retrieve this info, and this implementation relies on it
      only (old distros will probably use something else)
    - lm-sensors on Ubuntu 16.04 relies on /sys/class/hwmon
    - /sys/class/thermal/thermal_zone* is another one but it's more
      difficult to parse
    """
    ret = collections.defaultdict(list)
    basenames = glob.glob('/sys/class/hwmon/hwmon*/temp*_*')
    # CentOS has an intermediate /device directory:
    # https://github.com/giampaolo/psutil/issues/971
    # https://github.com/nicolargo/glances/issues/1060
    basenames.extend(glob.glob('/sys/class/hwmon/hwmon*/device/temp*_*'))
    basenames = sorted(set([x.split('_')[0] for x in basenames]))

    # Only add the coretemp hwmon entries if they're not already in
    # /sys/class/hwmon/
    # https://github.com/giampaolo/psutil/issues/1708
    # https://github.com/giampaolo/psutil/pull/1648
    basenames2 = glob.glob(
        '/sys/devices/platform/coretemp.*/hwmon/hwmon*/temp*_*')
    repl = re.compile('/sys/devices/platform/coretemp.*/hwmon/')
    for name in basenames2:
        altname = repl.sub('/sys/class/hwmon/', name)
        if altname not in basenames:
            basenames.append(name)

    for base in basenames:
        try:
            path = base + '_input'
            current = float(bcat(path)) / 1000.0
            path = os.path.join(os.path.dirname(base), 'name')
            unit_name = cat(path).strip()
        except (IOError, OSError, ValueError):
            # A lot of things can go wrong here, so let's just skip the
            # whole entry. Sure thing is Linux's /sys/class/hwmon really
            # is a stinky broken mess.
            # https://github.com/giampaolo/psutil/issues/1009
            # https://github.com/giampaolo/psutil/issues/1101
            # https://github.com/giampaolo/psutil/issues/1129
            # https://github.com/giampaolo/psutil/issues/1245
            # https://github.com/giampaolo/psutil/issues/1323
            continue

        high = bcat(base + '_max', fallback=None)
        critical = bcat(base + '_crit', fallback=None)
        label = cat(base + '_label', fallback='').strip()

        if high is not None:
            try:
                high = float(high) / 1000.0
            except ValueError:
                high = None
        if critical is not None:
            try:
                critical = float(critical) / 1000.0
            except ValueError:
                critical = None

        ret[unit_name].append((label, current, high, critical))

    # Indication that no sensors were detected in /sys/class/hwmon/
    if not basenames:
        basenames = glob.glob('/sys/class/thermal/thermal_zone*')
        basenames = sorted(set(basenames))

        for base in basenames:
            try:
                path = os.path.join(base, 'temp')
                current = float(bcat(path)) / 1000.0
                path = os.path.join(base, 'type')
                unit_name = cat(path).strip()
            except (IOError, OSError, ValueError) as err:
                debug(err)
                continue

            trip_paths = glob.glob(base + '/trip_point*')
            trip_points = set(['_'.join(
                os.path.basename(p).split('_')[0:3]) for p in trip_paths])
            critical = None
            high = None
            for trip_point in trip_points:
                path = os.path.join(base, trip_point + "_type")
                trip_type = cat(path, fallback='').strip()
                if trip_type == 'critical':
                    critical = bcat(os.path.join(base, trip_point + "_temp"),
                                    fallback=None)
                elif trip_type == 'high':
                    high = bcat(os.path.join(base, trip_point + "_temp"),
                                fallback=None)

                if high is not None:
                    try:
                        high = float(high) / 1000.0
                    except ValueError:
                        high = None
                if critical is not None:
                    try:
                        critical = float(critical) / 1000.0
                    except ValueError:
                        critical = None

            ret[unit_name].append(('', current, high, critical))

    return dict(ret)


def sensors_fans():
    """Return hardware fans info (for CPU and other peripherals) as a
    dict including hardware label and current speed.

    Implementation notes:
    - /sys/class/hwmon looks like the most recent interface to
      retrieve this info, and this implementation relies on it
      only (old distros will probably use something else)
    - lm-sensors on Ubuntu 16.04 relies on /sys/class/hwmon
    """
    ret = collections.defaultdict(list)
    basenames = glob.glob('/sys/class/hwmon/hwmon*/fan*_*')
    if not basenames:
        # CentOS has an intermediate /device directory:
        # https://github.com/giampaolo/psutil/issues/971
        basenames = glob.glob('/sys/class/hwmon/hwmon*/device/fan*_*')

    basenames = sorted(set([x.split('_')[0] for x in basenames]))
    for base in basenames:
        try:
            current = int(bcat(base + '_input'))
        except (IOError, OSError) as err:
            debug(err)
            continue
        unit_name = cat(os.path.join(os.path.dirname(base), 'name')).strip()
        label = cat(base + '_label', fallback='').strip()
        ret[unit_name].append(_common.sfan(label, current))

    return dict(ret)


def sensors_battery():
    """Return battery information.
    Implementation note: it appears /sys/class/power_supply/BAT0/
    directory structure may vary and provide files with the same
    meaning but under different names, see:
    https://github.com/giampaolo/psutil/issues/966
    """
    null = object()

    def multi_bcat(*paths):
        """Attempt to read the content of multiple files which may
        not exist. If none of them exist return None.
        """
        for path in paths:
            ret = bcat(path, fallback=null)
            if ret != null:
                try:
                    return int(ret)
                except ValueError:
                    return ret.strip()
        return None

    bats = [x for x in os.listdir(POWER_SUPPLY_PATH) if x.startswith('BAT') or
            'battery' in x.lower()]
    if not bats:
        return None
    # Get the first available battery. Usually this is "BAT0", except
    # some rare exceptions:
    # https://github.com/giampaolo/psutil/issues/1238
    root = os.path.join(POWER_SUPPLY_PATH, sorted(bats)[0])

    # Base metrics.
    energy_now = multi_bcat(
        root + "/energy_now",
        root + "/charge_now")
    power_now = multi_bcat(
        root + "/power_now",
        root + "/current_now")
    energy_full = multi_bcat(
        root + "/energy_full",
        root + "/charge_full")
    time_to_empty = multi_bcat(root + "/time_to_empty_now")

    # Percent. If we have energy_full the percentage will be more
    # accurate compared to reading /capacity file (float vs. int).
    if energy_full is not None and energy_now is not None:
        try:
            percent = 100.0 * energy_now / energy_full
        except ZeroDivisionError:
            percent = 0.0
    else:
        percent = int(cat(root + "/capacity", fallback=-1))
        if percent == -1:
            return None

    # Is AC power cable plugged in?
    # Note: AC0 is not always available and sometimes (e.g. CentOS7)
    # it's called "AC".
    power_plugged = None
    online = multi_bcat(
        os.path.join(POWER_SUPPLY_PATH, "AC0/online"),
        os.path.join(POWER_SUPPLY_PATH, "AC/online"))
    if online is not None:
        power_plugged = online == 1
    else:
        status = cat(root + "/status", fallback="").strip().lower()
        if status == "discharging":
            power_plugged = False
        elif status in ("charging", "full"):
            power_plugged = True

    # Seconds left.
    # Note to self: we may also calculate the charging ETA as per:
    # https://github.com/thialfihar/dotfiles/blob/
    #     013937745fd9050c30146290e8f963d65c0179e6/bin/battery.py#L55
    if power_plugged:
        secsleft = _common.POWER_TIME_UNLIMITED
    elif energy_now is not None and power_now is not None:
        try:
            secsleft = int(energy_now / power_now * 3600)
        except ZeroDivisionError:
            secsleft = _common.POWER_TIME_UNKNOWN
    elif time_to_empty is not None:
        secsleft = int(time_to_empty * 60)
        if secsleft < 0:
            secsleft = _common.POWER_TIME_UNKNOWN
    else:
        secsleft = _common.POWER_TIME_UNKNOWN

    return _common.sbattery(percent, secsleft, power_plugged)


# =====================================================================
# --- other system functions
# =====================================================================


def users():
    """Return currently connected users as a list of namedtuples."""
    retlist = []
    rawlist = cext.users()
    for item in rawlist:
        user, tty, hostname, tstamp, user_process, pid = item
        # note: the underlying C function includes entries about
        # system boot, run level and others.  We might want
        # to use them in the future.
        if not user_process:
            continue
        if hostname in (':0.0', ':0'):
            hostname = 'localhost'
        nt = _common.suser(user, tty or None, hostname, tstamp, pid)
        retlist.append(nt)
    return retlist


def boot_time():
    """Return the system boot time expressed in seconds since the epoch."""
    global BOOT_TIME
    path = '%s/stat' % get_procfs_path()
    with open_binary(path) as f:
        for line in f:
            if line.startswith(b'btime'):
                ret = float(line.strip().split()[1])
                BOOT_TIME = ret
                return ret
        raise RuntimeError(
            "line 'btime' not found in %s" % path)


# =====================================================================
# --- processes
# =====================================================================


def pids():
    """Returns a list of PIDs currently running on the system."""
    return [int(x) for x in os.listdir(b(get_procfs_path())) if x.isdigit()]


def pid_exists(pid):
    """Check for the existence of a unix PID. Linux TIDs are not
    supported (always return False).
    """
    if not _psposix.pid_exists(pid):
        return False
    else:
        # Linux's apparently does not distinguish between PIDs and TIDs
        # (thread IDs).
        # listdir("/proc") won't show any TID (only PIDs) but
        # os.stat("/proc/{tid}") will succeed if {tid} exists.
        # os.kill() can also be passed a TID. This is quite confusing.
        # In here we want to enforce this distinction and support PIDs
        # only, see:
        # https://github.com/giampaolo/psutil/issues/687
        try:
            # Note: already checked that this is faster than using a
            # regular expr. Also (a lot) faster than doing
            # 'return pid in pids()'
            path = "%s/%s/status" % (get_procfs_path(), pid)
            with open_binary(path) as f:
                for line in f:
                    if line.startswith(b"Tgid:"):
                        tgid = int(line.split()[1])
                        # If tgid and pid are the same then we're
                        # dealing with a process PID.
                        return tgid == pid
                raise ValueError("'Tgid' line not found in %s" % path)
        except (EnvironmentError, ValueError):
            return pid in pids()


def ppid_map():
    """Obtain a {pid: ppid, ...} dict for all running processes in
    one shot. Used to speed up Process.children().
    """
    ret = {}
    procfs_path = get_procfs_path()
    for pid in pids():
        try:
            with open_binary("%s/%s/stat" % (procfs_path, pid)) as f:
                data = f.read()
        except (FileNotFoundError, ProcessLookupError):
            # Note: we should be able to access /stat for all processes
            # aka it's unlikely we'll bump into EPERM, which is good.
            pass
        else:
            rpar = data.rfind(b')')
            dset = data[rpar + 2:].split()
            ppid = int(dset[1])
            ret[pid] = ppid
    return ret


def wrap_exceptions(fun):
    """Decorator which translates bare OSError and IOError exceptions
    into NoSuchProcess and AccessDenied.
    """
    @functools.wraps(fun)
    def wrapper(self, *args, **kwargs):
        try:
            return fun(self, *args, **kwargs)
        except PermissionError:
            raise AccessDenied(self.pid, self._name)
        except ProcessLookupError:
            raise NoSuchProcess(self.pid, self._name)
        except FileNotFoundError:
            if not os.path.exists("%s/%s" % (self._procfs_path, self.pid)):
                raise NoSuchProcess(self.pid, self._name)
            # Note: zombies will keep existing under /proc until they're
            # gone so there's no way to distinguish them in here.
            raise
    return wrapper


class Process(object):
    """Linux process implementation."""

    __slots__ = ["pid", "_name", "_ppid", "_procfs_path", "_cache"]

    def __init__(self, pid):
        self.pid = pid
        self._name = None
        self._ppid = None
        self._procfs_path = get_procfs_path()

    def _assert_alive(self):
        """Raise NSP if the process disappeared on us."""
        # For those C function who do not raise NSP, possibly returning
        # incorrect or incomplete result.
        os.stat('%s/%s' % (self._procfs_path, self.pid))

    @wrap_exceptions
    @memoize_when_activated
    def _parse_stat_file(self):
        """Parse /proc/{pid}/stat file and return a dict with various
        process info.
        Using "man proc" as a reference: where "man proc" refers to
        position N always subtract 3 (e.g ppid position 4 in
        'man proc' == position 1 in here).
        The return value is cached in case oneshot() ctx manager is
        in use.
        """
        data = bcat("%s/%s/stat" % (self._procfs_path, self.pid))
        # Process name is between parentheses. It can contain spaces and
        # other parentheses. This is taken into account by looking for
        # the first occurrence of "(" and the last occurrence of ")".
        rpar = data.rfind(b')')
        name = data[data.find(b'(') + 1:rpar]
        fields = data[rpar + 2:].split()

        ret = {}
        ret['name'] = name
        ret['status'] = fields[0]
        ret['ppid'] = fields[1]
        ret['ttynr'] = fields[4]
        ret['utime'] = fields[11]
        ret['stime'] = fields[12]
        ret['children_utime'] = fields[13]
        ret['children_stime'] = fields[14]
        ret['create_time'] = fields[19]
        ret['cpu_num'] = fields[36]
        ret['blkio_ticks'] = fields[39]  # aka 'delayacct_blkio_ticks'

        return ret

    @wrap_exceptions
    @memoize_when_activated
    def _read_status_file(self):
        """Read /proc/{pid}/stat file and return its content.
        The return value is cached in case oneshot() ctx manager is
        in use.
        """
        with open_binary("%s/%s/status" % (self._procfs_path, self.pid)) as f:
            return f.read()

    @wrap_exceptions
    @memoize_when_activated
    def _read_smaps_file(self):
        with open_binary("%s/%s/smaps" % (self._procfs_path, self.pid)) as f:
            return f.read().strip()

    def oneshot_enter(self):
        self._parse_stat_file.cache_activate(self)
        self._read_status_file.cache_activate(self)
        self._read_smaps_file.cache_activate(self)

    def oneshot_exit(self):
        self._parse_stat_file.cache_deactivate(self)
        self._read_status_file.cache_deactivate(self)
        self._read_smaps_file.cache_deactivate(self)

    @wrap_exceptions
    def name(self):
        name = self._parse_stat_file()['name']
        if PY3:
            name = decode(name)
        # XXX - gets changed later and probably needs refactoring
        return name

    def exe(self):
        try:
            return readlink("%s/%s/exe" % (self._procfs_path, self.pid))
        except (FileNotFoundError, ProcessLookupError):
            # no such file error; might be raised also if the
            # path actually exists for system processes with
            # low pids (about 0-20)
            if os.path.lexists("%s/%s" % (self._procfs_path, self.pid)):
                return ""
            else:
                if not pid_exists(self.pid):
                    raise NoSuchProcess(self.pid, self._name)
                else:
                    raise ZombieProcess(self.pid, self._name, self._ppid)
        except PermissionError:
            raise AccessDenied(self.pid, self._name)

    @wrap_exceptions
    def cmdline(self):
        with open_text("%s/%s/cmdline" % (self._procfs_path, self.pid)) as f:
            data = f.read()
        if not data:
            # may happen in case of zombie process
            return []
        # 'man proc' states that args are separated by null bytes '\0'
        # and last char is supposed to be a null byte. Nevertheless
        # some processes may change their cmdline after being started
        # (via setproctitle() or similar), they are usually not
        # compliant with this rule and use spaces instead. Google
        # Chrome process is an example. See:
        # https://github.com/giampaolo/psutil/issues/1179
        sep = '\x00' if data.endswith('\x00') else ' '
        if data.endswith(sep):
            data = data[:-1]
        cmdline = data.split(sep)
        # Sometimes last char is a null byte '\0' but the args are
        # separated by spaces, see: https://github.com/giampaolo/psutil/
        # issues/1179#issuecomment-552984549
        if sep == '\x00' and len(cmdline) == 1 and ' ' in data:
            cmdline = data.split(' ')
        return cmdline

    @wrap_exceptions
    def environ(self):
        with open_text("%s/%s/environ" % (self._procfs_path, self.pid)) as f:
            data = f.read()
        return parse_environ_block(data)

    @wrap_exceptions
    def terminal(self):
        tty_nr = int(self._parse_stat_file()['ttynr'])
        tmap = _psposix.get_terminal_map()
        try:
            return tmap[tty_nr]
        except KeyError:
            return None

    # May not be available on old kernels.
    if os.path.exists('/proc/%s/io' % os.getpid()):
        @wrap_exceptions
        def io_counters(self):
            fname = "%s/%s/io" % (self._procfs_path, self.pid)
            fields = {}
            with open_binary(fname) as f:
                for line in f:
                    # https://github.com/giampaolo/psutil/issues/1004
                    line = line.strip()
                    if line:
                        try:
                            name, value = line.split(b': ')
                        except ValueError:
                            # https://github.com/giampaolo/psutil/issues/1004
                            continue
                        else:
                            fields[name] = int(value)
            if not fields:
                raise RuntimeError("%s file was empty" % fname)
            try:
                return pio(
                    fields[b'syscr'],  # read syscalls
                    fields[b'syscw'],  # write syscalls
                    fields[b'read_bytes'],  # read bytes
                    fields[b'write_bytes'],  # write bytes
                    fields[b'rchar'],  # read chars
                    fields[b'wchar'],  # write chars
                )
            except KeyError as err:
                raise ValueError("%r field was not found in %s; found fields "
                                 "are %r" % (err[0], fname, fields))

    @wrap_exceptions
    def cpu_times(self):
        values = self._parse_stat_file()
        utime = float(values['utime']) / CLOCK_TICKS
        stime = float(values['stime']) / CLOCK_TICKS
        children_utime = float(values['children_utime']) / CLOCK_TICKS
        children_stime = float(values['children_stime']) / CLOCK_TICKS
        iowait = float(values['blkio_ticks']) / CLOCK_TICKS
        return pcputimes(utime, stime, children_utime, children_stime, iowait)

    @wrap_exceptions
    def cpu_num(self):
        """What CPU the process is on."""
        return int(self._parse_stat_file()['cpu_num'])

    @wrap_exceptions
    def wait(self, timeout=None):
        return _psposix.wait_pid(self.pid, timeout, self._name)

    @wrap_exceptions
    def create_time(self):
        ctime = float(self._parse_stat_file()['create_time'])
        # According to documentation, starttime is in field 21 and the
        # unit is jiffies (clock ticks).
        # We first divide it for clock ticks and then add uptime returning
        # seconds since the epoch.
        # Also use cached value if available.
        bt = BOOT_TIME or boot_time()
        return (ctime / CLOCK_TICKS) + bt

    @wrap_exceptions
    def memory_info(self):
        #  ============================================================
        # | FIELD  | DESCRIPTION                         | AKA  | TOP  |
        #  ============================================================
        # | rss    | resident set size                   |      | RES  |
        # | vms    | total program size                  | size | VIRT |
        # | shared | shared pages (from shared mappings) |      | SHR  |
        # | text   | text ('code')                       | trs  | CODE |
        # | lib    | library (unused in Linux 2.6)       | lrs  |      |
        # | data   | data + stack                        | drs  | DATA |
        # | dirty  | dirty pages (unused in Linux 2.6)   | dt   |      |
        #  ============================================================
        with open_binary("%s/%s/statm" % (self._procfs_path, self.pid)) as f:
            vms, rss, shared, text, lib, data, dirty = \
                [int(x) * PAGESIZE for x in f.readline().split()[:7]]
        return pmem(rss, vms, shared, text, lib, data, dirty)

    if HAS_PROC_SMAPS_ROLLUP or HAS_PROC_SMAPS:

        @wrap_exceptions
        def _parse_smaps_rollup(self):
            # /proc/pid/smaps_rollup was added to Linux in 2017. Faster
            # than /proc/pid/smaps. It reports higher PSS than */smaps
            # (from 1k up to 200k higher; tested against all processes).
            uss = pss = swap = 0
            try:
                with open_binary("{}/{}/smaps_rollup".format(
                        self._procfs_path, self.pid)) as f:
                    for line in f:
                        if line.startswith(b"Private_"):
                            # Private_Clean, Private_Dirty, Private_Hugetlb
                            uss += int(line.split()[1]) * 1024
                        elif line.startswith(b"Pss:"):
                            pss = int(line.split()[1]) * 1024
                        elif line.startswith(b"Swap:"):
                            swap = int(line.split()[1]) * 1024
            except ProcessLookupError:  # happens on readline()
                if not pid_exists(self.pid):
                    raise NoSuchProcess(self.pid, self._name)
                else:
                    raise ZombieProcess(self.pid, self._name, self._ppid)
            return (uss, pss, swap)

        @wrap_exceptions
        def _parse_smaps(
                self,
                # Gets Private_Clean, Private_Dirty, Private_Hugetlb.
                _private_re=re.compile(br"\nPrivate.*:\s+(\d+)"),
                _pss_re=re.compile(br"\nPss\:\s+(\d+)"),
                _swap_re=re.compile(br"\nSwap\:\s+(\d+)")):
            # /proc/pid/smaps does not exist on kernels < 2.6.14 or if
            # CONFIG_MMU kernel configuration option is not enabled.

            # Note: using 3 regexes is faster than reading the file
            # line by line.
            # XXX: on Python 3 the 2 regexes are 30% slower than on
            # Python 2 though. Figure out why.
            #
            # You might be tempted to calculate USS by subtracting
            # the "shared" value from the "resident" value in
            # /proc/<pid>/statm. But at least on Linux, statm's "shared"
            # value actually counts pages backed by files, which has
            # little to do with whether the pages are actually shared.
            # /proc/self/smaps on the other hand appears to give us the
            # correct information.
            smaps_data = self._read_smaps_file()
            # Note: smaps file can be empty for certain processes.
            # The code below will not crash though and will result to 0.
            uss = sum(map(int, _private_re.findall(smaps_data))) * 1024
            pss = sum(map(int, _pss_re.findall(smaps_data))) * 1024
            swap = sum(map(int, _swap_re.findall(smaps_data))) * 1024
            return (uss, pss, swap)

        def memory_full_info(self):
            if HAS_PROC_SMAPS_ROLLUP:  # faster
                uss, pss, swap = self._parse_smaps_rollup()
            else:
                uss, pss, swap = self._parse_smaps()
            basic_mem = self.memory_info()
            return pfullmem(*basic_mem + (uss, pss, swap))

    else:
        memory_full_info = memory_info

    if HAS_PROC_SMAPS:

        @wrap_exceptions
        def memory_maps(self):
            """Return process's mapped memory regions as a list of named
            tuples. Fields are explained in 'man proc'; here is an updated
            (Apr 2012) version: http://goo.gl/fmebo

            /proc/{PID}/smaps does not exist on kernels < 2.6.14 or if
            CONFIG_MMU kernel configuration option is not enabled.
            """
            def get_blocks(lines, current_block):
                data = {}
                for line in lines:
                    fields = line.split(None, 5)
                    if not fields[0].endswith(b':'):
                        # new block section
                        yield (current_block.pop(), data)
                        current_block.append(line)
                    else:
                        try:
                            data[fields[0]] = int(fields[1]) * 1024
                        except ValueError:
                            if fields[0].startswith(b'VmFlags:'):
                                # see issue #369
                                continue
                            else:
                                raise ValueError("don't know how to inte"
                                                 "rpret line %r" % line)
                yield (current_block.pop(), data)

            data = self._read_smaps_file()
            # Note: smaps file can be empty for certain processes.
            if not data:
                return []
            lines = data.split(b'\n')
            ls = []
            first_line = lines.pop(0)
            current_block = [first_line]
            for header, data in get_blocks(lines, current_block):
                hfields = header.split(None, 5)
                try:
                    addr, perms, offset, dev, inode, path = hfields
                except ValueError:
                    addr, perms, offset, dev, inode, path = \
                        hfields + ['']
                if not path:
                    path = '[anon]'
                else:
                    if PY3:
                        path = decode(path)
                    path = path.strip()
                    if (path.endswith(' (deleted)') and not
                            path_exists_strict(path)):
                        path = path[:-10]
                ls.append((
                    decode(addr), decode(perms), path,
                    data.get(b'Rss:', 0),
                    data.get(b'Size:', 0),
                    data.get(b'Pss:', 0),
                    data.get(b'Shared_Clean:', 0),
                    data.get(b'Shared_Dirty:', 0),
                    data.get(b'Private_Clean:', 0),
                    data.get(b'Private_Dirty:', 0),
                    data.get(b'Referenced:', 0),
                    data.get(b'Anonymous:', 0),
                    data.get(b'Swap:', 0)
                ))
            return ls

    @wrap_exceptions
    def cwd(self):
        try:
            return readlink("%s/%s/cwd" % (self._procfs_path, self.pid))
        except (FileNotFoundError, ProcessLookupError):
            # https://github.com/giampaolo/psutil/issues/986
            if not pid_exists(self.pid):
                raise NoSuchProcess(self.pid, self._name)
            else:
                raise ZombieProcess(self.pid, self._name, self._ppid)

    @wrap_exceptions
    def num_ctx_switches(self,
                         _ctxsw_re=re.compile(br'ctxt_switches:\t(\d+)')):
        data = self._read_status_file()
        ctxsw = _ctxsw_re.findall(data)
        if not ctxsw:
            raise NotImplementedError(
                "'voluntary_ctxt_switches' and 'nonvoluntary_ctxt_switches'"
                "lines were not found in %s/%s/status; the kernel is "
                "probably older than 2.6.23" % (
                    self._procfs_path, self.pid))
        else:
            return _common.pctxsw(int(ctxsw[0]), int(ctxsw[1]))

    @wrap_exceptions
    def num_threads(self, _num_threads_re=re.compile(br'Threads:\t(\d+)')):
        # Note: on Python 3 using a re is faster than iterating over file
        # line by line. On Python 2 is the exact opposite, and iterating
        # over a file on Python 3 is slower than on Python 2.
        data = self._read_status_file()
        return int(_num_threads_re.findall(data)[0])

    @wrap_exceptions
    def threads(self):
        thread_ids = os.listdir("%s/%s/task" % (self._procfs_path, self.pid))
        thread_ids.sort()
        retlist = []
        hit_enoent = False
        for thread_id in thread_ids:
            fname = "%s/%s/task/%s/stat" % (
                self._procfs_path, self.pid, thread_id)
            try:
                with open_binary(fname) as f:
                    st = f.read().strip()
            except (FileNotFoundError, ProcessLookupError):
                # no such file or directory or no such process;
                # it means thread disappeared on us
                hit_enoent = True
                continue
            # ignore the first two values ("pid (exe)")
            st = st[st.find(b')') + 2:]
            values = st.split(b' ')
            utime = float(values[11]) / CLOCK_TICKS
            stime = float(values[12]) / CLOCK_TICKS
            ntuple = _common.pthread(int(thread_id), utime, stime)
            retlist.append(ntuple)
        if hit_enoent:
            self._assert_alive()
        return retlist

    @wrap_exceptions
    def nice_get(self):
        # with open_text('%s/%s/stat' % (self._procfs_path, self.pid)) as f:
        #   data = f.read()
        #   return int(data.split()[18])

        # Use C implementation
        return cext_posix.getpriority(self.pid)

    @wrap_exceptions
    def nice_set(self, value):
        return cext_posix.setpriority(self.pid, value)

    # starting from CentOS 6.
    if HAS_CPU_AFFINITY:

        @wrap_exceptions
        def cpu_affinity_get(self):
            return cext.proc_cpu_affinity_get(self.pid)

        def _get_eligible_cpus(
                self, _re=re.compile(br"Cpus_allowed_list:\t(\d+)-(\d+)")):
            # See: https://github.com/giampaolo/psutil/issues/956
            data = self._read_status_file()
            match = _re.findall(data)
            if match:
                return list(range(int(match[0][0]), int(match[0][1]) + 1))
            else:
                return list(range(len(per_cpu_times())))

        @wrap_exceptions
        def cpu_affinity_set(self, cpus):
            try:
                cext.proc_cpu_affinity_set(self.pid, cpus)
            except (OSError, ValueError) as err:
                if isinstance(err, ValueError) or err.errno == errno.EINVAL:
                    eligible_cpus = self._get_eligible_cpus()
                    all_cpus = tuple(range(len(per_cpu_times())))
                    for cpu in cpus:
                        if cpu not in all_cpus:
                            raise ValueError(
                                "invalid CPU number %r; choose between %s" % (
                                    cpu, eligible_cpus))
                        if cpu not in eligible_cpus:
                            raise ValueError(
                                "CPU number %r is not eligible; choose "
                                "between %s" % (cpu, eligible_cpus))
                raise

    # only starting from kernel 2.6.13
    if HAS_PROC_IO_PRIORITY:

        @wrap_exceptions
        def ionice_get(self):
            ioclass, value = cext.proc_ioprio_get(self.pid)
            if enum is not None:
                ioclass = IOPriority(ioclass)
            return _common.pionice(ioclass, value)

        @wrap_exceptions
        def ionice_set(self, ioclass, value):
            if value is None:
                value = 0
            if value and ioclass in (IOPRIO_CLASS_IDLE, IOPRIO_CLASS_NONE):
                raise ValueError("%r ioclass accepts no value" % ioclass)
            if value < 0 or value > 7:
                raise ValueError("value not in 0-7 range")
            return cext.proc_ioprio_set(self.pid, ioclass, value)

    if prlimit is not None:

        @wrap_exceptions
        def rlimit(self, resource_, limits=None):
            # If pid is 0 prlimit() applies to the calling process and
            # we don't want that. We should never get here though as
            # PID 0 is not supported on Linux.
            if self.pid == 0:
                raise ValueError("can't use prlimit() against PID 0 process")
            try:
                if limits is None:
                    # get
                    return prlimit(self.pid, resource_)
                else:
                    # set
                    if len(limits) != 2:
                        raise ValueError(
                            "second argument must be a (soft, hard) tuple, "
                            "got %s" % repr(limits))
                    prlimit(self.pid, resource_, limits)
            except OSError as err:
                if err.errno == errno.ENOSYS and pid_exists(self.pid):
                    # I saw this happening on Travis:
                    # https://travis-ci.org/giampaolo/psutil/jobs/51368273
                    raise ZombieProcess(self.pid, self._name, self._ppid)
                else:
                    raise

    @wrap_exceptions
    def status(self):
        letter = self._parse_stat_file()['status']
        if PY3:
            letter = letter.decode()
        # XXX is '?' legit? (we're not supposed to return it anyway)
        return PROC_STATUSES.get(letter, '?')

    @wrap_exceptions
    def open_files(self):
        retlist = []
        files = os.listdir("%s/%s/fd" % (self._procfs_path, self.pid))
        hit_enoent = False
        for fd in files:
            file = "%s/%s/fd/%s" % (self._procfs_path, self.pid, fd)
            try:
                path = readlink(file)
            except (FileNotFoundError, ProcessLookupError):
                # ENOENT == file which is gone in the meantime
                hit_enoent = True
                continue
            except OSError as err:
                if err.errno == errno.EINVAL:
                    # not a link
                    continue
                if err.errno == errno.ENAMETOOLONG:
                    # file name too long
                    debug(err)
                    continue
                raise
            else:
                # If path is not an absolute there's no way to tell
                # whether it's a regular file or not, so we skip it.
                # A regular file is always supposed to be have an
                # absolute path though.
                if path.startswith('/') and isfile_strict(path):
                    # Get file position and flags.
                    file = "%s/%s/fdinfo/%s" % (
                        self._procfs_path, self.pid, fd)
                    try:
                        with open_binary(file) as f:
                            pos = int(f.readline().split()[1])
                            flags = int(f.readline().split()[1], 8)
                    except (FileNotFoundError, ProcessLookupError):
                        # fd gone in the meantime; process may
                        # still be alive
                        hit_enoent = True
                    else:
                        mode = file_flags_to_mode(flags)
                        ntuple = popenfile(
                            path, int(fd), int(pos), mode, flags)
                        retlist.append(ntuple)
        if hit_enoent:
            self._assert_alive()
        return retlist

    @wrap_exceptions
    def connections(self, kind='inet'):
        ret = _connections.retrieve(kind, self.pid)
        self._assert_alive()
        return ret

    @wrap_exceptions
    def num_fds(self):
        return len(os.listdir("%s/%s/fd" % (self._procfs_path, self.pid)))

    @wrap_exceptions
    def ppid(self):
        return int(self._parse_stat_file()['ppid'])

    @wrap_exceptions
    def uids(self, _uids_re=re.compile(br'Uid:\t(\d+)\t(\d+)\t(\d+)')):
        data = self._read_status_file()
        real, effective, saved = _uids_re.findall(data)[0]
        return _common.puids(int(real), int(effective), int(saved))

    @wrap_exceptions
    def gids(self, _gids_re=re.compile(br'Gid:\t(\d+)\t(\d+)\t(\d+)')):
        data = self._read_status_file()
        real, effective, saved = _gids_re.findall(data)[0]
        return _common.pgids(int(real), int(effective), int(saved))
