运维同学看到一个系统的内存使用很高，但是通过其它命令却找不到相应的进程。让帮忙查看一下原因：
# free -m
total used free shared buff/cache available
Mem: 48120 14788 509 63 32823 32963
Swap: 8191 0 8191
free命令可以显示free、used物理内存，和swap内存，以及内核使用的buffers、caches。free显示的内容来自/proc/meminfo。
找了个手头的db服务器，给其分析了一下。执行不带任何参数的free命令，会显示以下类似内容：(这是低版本的linux)
# free -m
total used free shared buffers cached
Mem: 774027 740693 33333 1442 3258 169694
-/+ buffers/cache: 567741 206286
Swap: 65535 0 65535
第一行：
·total：总的内存大小。对应/proc/meminfo中的MemTotal ·used：使用的内存 ·free：未被使用的内存。对应/proc/meminfo中的MemFree ·shared：tmpfs使用的内存。对应/proc/meminfo中的Shmem ·buffers：内核buffers使用的内存。对应/proc/meminfo中的Buffers ·cached：page cache和slabs使用的内存。对应/proc/meminfo中的Cached和SReclaimable
第二行：
-/+ buffers/cache 的used、free值。
第三行：
swap内存的使用。/proc/meminfo中的SwapTotal、SwapFree
以这个低版本的linux为例，如何检查真正的空闲内存是多少呢？
根据上面的used和free两列，你可能会觉得空闲内存不多了(第一行显示空闲的内存只有33333MB)。可不要被第一行迷惑了。
其实，这里总内存是774027MB，进程使用了567741MB，空闲了206286MB。
所以可用的内存是206286MB，等于(cached+buffers+free)
linux的内存，大部分内存都是用于buffers和cache。Linux总是尝试通过将可用内存用于buffers（文件系统元数据）和cache（具有文件或块设备的实际内容的页面）来加速对磁盘的操作。这有助于系统运行得更快，因为磁盘信息已经在内存中，从而节省了I/O 操作。如果程序或应用程序（如 Oracle）需要空间，Linux将释放buffers和cache，为应用程序提供内存。
如果系统运行了一段时间，你通常会在第一行的"free"字段下看到的值很小。
为了提供说服力，在redhat官网找了以下的文档。
而对于新版本linux，看到的free结果是：
# free -m
total used free shared buff/cache available
Mem: 48120 14788 509 63 32823 32963
Swap: 8191 0 8191
新版本的linux，你可以通过available来查看真正的可用内存有多少。
如果想看看进程都使用了多少的内存，网上有个很好用的python脚本：
https://raw.githubusercontent.com/pixelb/ps_mem/master/ps_mem.py
贴一下脚本：
#!/usr/bin/env python
# Try to determine how much RAM is currently being used per program.
# Note per _program_, not per process. So for example this script
# will report RAM used by all httpd process together. In detail it reports:
# sum(private RAM for program processes) + sum(Shared RAM for program processes)
# The shared RAM is problematic to calculate, and this script automatically
# selects the most accurate method available for your kernel.
# Licence: LGPLv2
# Author: P@draigBrady.com
# Source: https://www.pixelbeat.org/scripts/ps_mem.py
# V1.0 06 Jul 2005 Initial release
# V1.1 11 Aug 2006 root permission required for accuracy
# V1.2 08 Nov 2006 Add total to output
# Use KiB,MiB,... for units rather than K,M,...
# V1.3 22 Nov 2006 Ignore shared col from /proc/$pid/statm for
# 2.6 kernels up to and including 2.6.9.
# There it represented the total file backed extent
# V1.4 23 Nov 2006 Remove total from output as it's meaningless
# (the shared values overlap with other programs).
# Display the shared column. This extra info is
# useful, especially as it overlaps between programs.
# V1.5 26 Mar 2007 Remove redundant recursion from human()
# V1.6 05 Jun 2007 Also report number of processes with a given name.
# Patch from riccardo.murri@gmail.com
# V1.7 20 Sep 2007 Use PSS from /proc/$pid/smaps if available, which
# fixes some over-estimation and allows totalling.
# Enumerate the PIDs directly rather than using ps,
# which fixes the possible race between reading
# RSS with ps, and shared memory with this program.
# Also we can show non truncated command names.
# V1.8 28 Sep 2007 More accurate matching for stats in /proc/$pid/smaps
# as otherwise could match libraries causing a crash.
# Patch from patrice.bouchand.fedora@gmail.com
# V1.9 20 Feb 2008 Fix invalid values reported when PSS is available.
# Reported by Andrey Borzenkov <arvidjaar@mail.ru>
# V3.13 17 Sep 2018
# https://github.com/pixelb/ps_mem/commits/master/ps_mem.py
# Notes:
#
# All interpreted programs where the interpreter is started
# by the shell or with env, will be merged to the interpreter
# (as that's what's given to exec). For e.g. all python programs
# starting with "#!/usr/bin/env python" will be grouped under python.
# You can change this by using the full command line but that will
# have the undesirable affect of splitting up programs started with
# differing parameters (for e.g. mingetty tty[1-6]).
#
# For 2.6 kernels up to and including 2.6.13 and later 2.4 redhat kernels
# (rmap vm without smaps) it can not be accurately determined how many pages
# are shared between processes in general or within a program in our case:
# http://lkml.org/lkml/2005/7/6/250
# A warning is printed if overestimation is possible.
# In addition for 2.6 kernels up to 2.6.9 inclusive, the shared
# value in /proc/$pid/statm is the total file-backed extent of a process.
# We ignore that, introducing more overestimation, again printing a warning.
# Since kernel 2.6.23-rc8-mm1 PSS is available in smaps, which allows
# us to calculate a more accurate value for the total RAM used by programs.
#
# Programs that use CLONE_VM without CLONE_THREAD are discounted by assuming
# they're the only programs that have the same /proc/$PID/smaps file for
# each instance. This will fail if there are multiple real instances of a
# program that then use CLONE_VM without CLONE_THREAD, or if a clone changes
# its memory map while we're checksumming each /proc/$PID/smaps.
#
# I don't take account of memory allocated for a program
# by other programs. For e.g. memory used in the X server for
# a program could be determined, but is not.
#
# FreeBSD is supported if linprocfs is mounted at /compat/linux/proc/
# FreeBSD 8.0 supports up to a level of Linux 2.6.16
import argparse
import errno
import os
import sys
import time
import io
# The following exits cleanly on Ctrl-C or EPIPE
# while treating other exceptions as before.
def std_exceptions(etype, value, tb):
sys.excepthook = sys.__excepthook__
if issubclass(etype, KeyboardInterrupt):
pass
elif issubclass(etype, IOError) and value.errno == errno.EPIPE:
pass
else:
sys.__excepthook__(etype, value, tb)
sys.excepthook = std_exceptions
#
# Define some global variables
#
PAGESIZE = os.sysconf("SC_PAGE_SIZE") / 1024 #KiB
our_pid = os.getpid()
have_pss = 0
have_swap_pss = 0
class Unbuffered(io.TextIOBase):
def __init__(self, stream):
super(Unbuffered, self).__init__()
self.stream = stream
def write(self, data):
self.stream.write(data)
self.stream.flush()
def close(self):
self.stream.close()
class Proc:
def __init__(self):
uname = os.uname()
if uname[0] == "FreeBSD":
self.proc = '/compat/linux/proc'
else:
self.proc = '/proc'
def path(self, *args):
return os.path.join(self.proc, *(str(a) for a in args))
def open(self, *args):
try:
if sys.version_info < (3,):
return open(self.path(*args))
else:
return open(self.path(*args), errors='ignore')
except (IOError, OSError):
if type(args[0]) is not int:
raise
val = sys.exc_info()[1]
if (val.errno == errno.ENOENT or # kernel thread or process gone
val.errno == errno.EPERM or
val.errno == errno.EACCES):
raise LookupError
raise
proc = Proc()
#
# Functions
#
def parse_options():
help_msg = 'Show program core memory usage.'
parser = argparse.ArgumentParser(prog='ps_mem', description=help_msg)
parser.add_argument('--version', action='version', version='3.13')
parser.add_argument(
'-s', '--split-args',
action='store_true',
help='Show and separate by, all command line arguments',
)
parser.add_argument(
'-t', '--total',
dest='only_total',
action='store_true',
help='Show only the total value',
)
parser.add_argument(
'-d', '--discriminate-by-pid',
action='store_true',
help='Show by process rather than by program',
)
parser.add_argument(
'-S', '--swap',
dest='show_swap',
action='store_true',
help='Show swap information',
)
parser.add_argument(
'-p',
dest='pids',
metavar='<pid>[,pid2,...pidN]',
help='Only show memory usage PIDs in the specified list',
)
parser.add_argument(
'-w',
dest='watch',
metavar='<N>',
type=int,
help='Measure and show process memory every N seconds',
)
args = parser.parse_args()
args.pids_to_show = []
if args.pids:
try:
args.pids_to_show = [int(x) for x in args.pids.split(',')]
except ValueError:
parser.error('Invalid PID(s): %s' % args.pids)
if args.watch is not None:
if args.watch <= 0:
parser.error('Seconds must be positive! (%s)' % args.watch)
return (
args.split_args,
args.pids_to_show,
args.watch,
args.only_total,
args.discriminate_by_pid,
args.show_swap,
)
# (major,minor,release)
def kernel_ver():
kv = proc.open('sys/kernel/osrelease').readline().split(".")[:3]
last = len(kv)
if last == 2:
kv.append('0')
last -= 1
while last > 0:
for char in "-_":
kv[last] = kv[last].split(char)[0]
try:
int(kv[last])
except:
kv[last] = 0
last -= 1
return (int(kv[0]), int(kv[1]), int(kv[2]))
#return Private,Shared,Swap(Pss),unique_id
#Note shared is always a subset of rss (trs is not always)
def getMemStats(pid):
global have_pss
global have_swap_pss
mem_id = pid #unique
Private_lines = []
Shared_lines = []
Private_huge_lines = []
Shared_huge_lines = []
Pss_lines = []
Rss = (int(proc.open(pid, 'statm').readline().split()[1])
* PAGESIZE)
Swap_lines = []
Swap_pss_lines = []
Swap = 0
if os.path.exists(proc.path(pid, 'smaps')): # stat
smaps = 'smaps'
if os.path.exists(proc.path(pid, 'smaps_rollup')):
smaps = 'smaps_rollup' # faster to process
lines = proc.open(pid, smaps).readlines() # open
# Note we checksum smaps as maps is usually but
# not always different for separate processes.
mem_id = hash(''.join(lines))
for line in lines:
# {Private,Shared}_Hugetlb is not included in Pss (why?)
# so we need to account for separately.
if line.startswith("Private_Hugetlb:"):
Private_huge_lines.append(line)
elif line.startswith("Shared_Hugetlb:"):
Shared_huge_lines.append(line)
elif line.startswith("Shared"):
Shared_lines.append(line)
elif line.startswith("Private"):
Private_lines.append(line)
elif line.startswith("Pss:"):
have_pss = 1
Pss_lines.append(line)
elif line.startswith("Swap:"):
Swap_lines.append(line)
elif line.startswith("SwapPss:"):
have_swap_pss = 1
Swap_pss_lines.append(line)
Shared = sum([int(line.split()[1]) for line in Shared_lines])
Private = sum([int(line.split()[1]) for line in Private_lines])
Shared_huge = sum([int(line.split()[1]) for line in Shared_huge_lines])
Private_huge = sum([int(line.split()[1]) for line in Private_huge_lines])
#Note Shared + Private = Rss above
#The Rss in smaps includes video card mem etc.
if have_pss:
pss_adjust = 0.5 # add 0.5KiB as this avg error due to truncation
Pss = sum([float(line.split()[1])+pss_adjust for line in Pss_lines])
Shared = Pss - Private
Private += Private_huge # Add after as PSS doesn't a/c for huge pages
if have_swap_pss:
# The kernel supports SwapPss, that shows proportional swap share.
# Note that Swap - SwapPss is not Private Swap.
Swap = sum([int(line.split()[1]) for line in Swap_pss_lines])
else:
# Note that Swap = Private swap + Shared swap.
Swap = sum([int(line.split()[1]) for line in Swap_lines])
elif (2,6,1) <= kernel_ver() <= (2,6,9):
Shared = 0 #lots of overestimation, but what can we do?
Shared_huge = 0
Private = Rss
else:
Shared = int(proc.open(pid, 'statm').readline().split()[2])
Shared *= PAGESIZE
Shared_huge = 0
Private = Rss - Shared
return (Private, Shared, Shared_huge, Swap, mem_id)
def getCmdName(pid, split_args, discriminate_by_pid, exe_only=False):
cmdline = proc.open(pid, 'cmdline').read().split("\0")
while cmdline[-1] == '' and len(cmdline) > 1:
cmdline = cmdline[:-1]
path = proc.path(pid, 'exe')
try:
path = os.readlink(path)
# Some symlink targets were seen to contain NULs on RHEL 5 at least
# https://github.com/pixelb/scripts/pull/10, so take string up to NUL
path = path.split('\0')[0]
except OSError:
val = sys.exc_info()[1]
if (val.errno == errno.ENOENT or # either kernel thread or process gone
val.errno == errno.EPERM or
val.errno == errno.EACCES):
raise LookupError
raise
if split_args:
return ' '.join(cmdline).replace('\n', ' ')
if path.endswith(" (deleted)"):
path = path[:-10]
if os.path.exists(path):
path += " [updated]"
else:
#The path could be have prelink stuff so try cmdline
#which might have the full path present. This helped for:
#/usr/libexec/notification-area-applet.#prelink#.fX7LCT (deleted)
if os.path.exists(cmdline[0]):
path = cmdline[0] + " [updated]"
else:
path += " [deleted]"
exe = os.path.basename(path)
if exe_only: return exe
proc_status = proc.open(pid, 'status').readlines()
cmd = proc_status[0][6:-1]
if exe.startswith(cmd):
cmd = exe #show non truncated version
#Note because we show the non truncated name
#one can have separated programs as follows:
#584.0 KiB + 1.0 MiB = 1.6 MiB mozilla-thunder (exe -> bash)
# 56.0 MiB + 22.2 MiB = 78.2 MiB mozilla-thunderbird-bin
else:
#Lookup the parent's exe and use that if matching
#which will merge "Web Content" with "firefox" for example
ppid = 0
for l in range(10):
ps_line = proc_status[l]
if ps_line.startswith('PPid:'):
ppid = int(ps_line[6:-1])
break
if ppid:
try:
p_exe = getCmdName(ppid, False, False, exe_only=True)
except LookupError:
pass
else:
if exe == p_exe:
cmd = exe
if sys.version_info >= (3,):
cmd = cmd.encode(errors='replace').decode()
if discriminate_by_pid:
cmd = '%s [%d]' % (cmd, pid)
return cmd
#The following matches "du -h" output
#see also human.py
def human(num, power="Ki", units=None):
if units is None:
powers = ["Ki", "Mi", "Gi", "Ti"]
while num >= 1000: #4 digits
num /= 1024.0
power = powers[powers.index(power)+1]
return "%.1f %sB" % (num, power)
else:
return "%.f" % ((num * 1024) / units)
def cmd_with_count(cmd, count):
if count > 1:
return "%s (%u)" % (cmd, count)
else:
return cmd
#Warn of possible inaccuracies
#RAM:
#2 = accurate & can total
#1 = accurate only considering each process in isolation
#0 = some shared mem not reported
#-1= all shared mem not reported
#SWAP:
#2 = accurate & can total
#1 = accurate only considering each process in isolation
#-1= not available
def val_accuracy(show_swap):
"""http://wiki.apache.org/spamassassin/TopSharedMemoryBug"""
kv = kernel_ver()
pid = os.getpid()
swap_accuracy = -1
if kv[:2] == (2,4):
if proc.open('meminfo').read().find("Inact_") == -1:
return 1, swap_accuracy
return 0, swap_accuracy
elif kv[:2] == (2,6):
if os.path.exists(proc.path(pid, 'smaps')):
swap_accuracy = 1
if proc.open(pid, 'smaps').read().find("Pss:")!=-1:
return 2, swap_accuracy
else:
return 1, swap_accuracy
if (2,6,1) <= kv <= (2,6,9):
return -1, swap_accuracy
return 0, swap_accuracy
elif kv[0] > 2 and os.path.exists(proc.path(pid, 'smaps')):
swap_accuracy = 1
if show_swap and proc.open(pid, 'smaps').read().find("SwapPss:")!=-1:
swap_accuracy = 2
return 2, swap_accuracy
else:
return 1, swap_accuracy
def show_val_accuracy( ram_inacc, swap_inacc, only_total, show_swap ):
level = ("Warning","Error")[only_total]
# Only show significant warnings
if not show_swap:
swap_inacc = 2
elif only_total:
ram_inacc = 2
if ram_inacc == -1:
sys.stderr.write(
"%s: Shared memory is not reported by this system.\n" % level
)
sys.stderr.write(
"Values reported will be too large, and totals are not reported\n"
)
elif ram_inacc == 0:
sys.stderr.write(
"%s: Shared memory is not reported accurately by this system.\n" % level
)
sys.stderr.write(
"Values reported could be too large, and totals are not reported\n"
)
elif ram_inacc == 1:
sys.stderr.write(
"%s: Shared memory is slightly over-estimated by this system\n"
"for each program, so totals are not reported.\n" % level
)
if swap_inacc == -1:
sys.stderr.write(
"%s: Swap is not reported by this system.\n" % level
)
elif swap_inacc == 1:
sys.stderr.write(
"%s: Swap is over-estimated by this system for each program,\n"
"so totals are not reported.\n" % level
)
sys.stderr.close()
if only_total:
if show_swap:
accuracy = swap_inacc
else:
accuracy = ram_inacc
if accuracy != 2:
sys.exit(1)
def get_memory_usage(pids_to_show, split_args, discriminate_by_pid,
include_self=False, only_self=False):
cmds = {}
shareds = {}
shared_huges = {}
mem_ids = {}
count = {}
swaps = {}
for pid in os.listdir(proc.path('')):
if not pid.isdigit():
continue
pid = int(pid)
# Some filters
if only_self and pid != our_pid:
continue
if pid == our_pid and not include_self:
continue
if pids_to_show and pid not in pids_to_show:
continue
try:
cmd = getCmdName(pid, split_args, discriminate_by_pid)
except LookupError:
#operation not permitted
#kernel threads don't have exe links or
#process gone
continue
try:
private, shared, shared_huge, swap, mem_id = getMemStats(pid)
except RuntimeError:
continue #process gone
if shareds.get(cmd):
if have_pss: #add shared portion of PSS together
shareds[cmd] += shared
elif shareds[cmd] < shared: #just take largest shared val
shareds[cmd] = shared
else:
shareds[cmd] = shared
if shared_huges.get(cmd):
if shared_huges[cmd] < shared_huge: #just take largest shared_huge
shared_huges[cmd] = shared_huge
else:
shared_huges[cmd] = shared_huge
cmds[cmd] = cmds.setdefault(cmd, 0) + private
if cmd in count:
count[cmd] += 1
else:
count[cmd] = 1
mem_ids.setdefault(cmd, {}).update({mem_id: None})
# Swap (overcounting for now...)
swaps[cmd] = swaps.setdefault(cmd, 0) + swap
# Total swaped mem for each program
total_swap = 0
# Add shared mem for each program
total = 0
for cmd in cmds:
cmd_count = count[cmd]
if len(mem_ids[cmd]) == 1 and cmd_count > 1:
# Assume this program is using CLONE_VM without CLONE_THREAD
# so only account for one of the processes
cmds[cmd] /= cmd_count
if have_pss:
shareds[cmd] /= cmd_count
# overestimation possible if shared_huges shared across commands
shareds[cmd] += shared_huges[cmd]
cmds[cmd] = cmds[cmd] + shareds[cmd]
total += cmds[cmd] # valid if PSS available
total_swap += swaps[cmd]
sorted_cmds = sorted(cmds.items(), key=lambda x:x[1])
sorted_cmds = [x for x in sorted_cmds if x[1]]
return sorted_cmds, shareds, count, total, swaps, total_swap
def print_header(show_swap, discriminate_by_pid):
output_string = " Private + Shared = RAM used"
if show_swap:
output_string += " Swap used"
output_string += "\tProgram"
if discriminate_by_pid:
output_string += "[pid]"
output_string += "\n\n"
sys.stdout.write(output_string)
def print_memory_usage(sorted_cmds, shareds, count, total, swaps, total_swap,
show_swap):
for cmd in sorted_cmds:
output_string = "%9s + %9s = %9s"
output_data = (human(cmd[1]-shareds[cmd[0]]),
human(shareds[cmd[0]]), human(cmd[1]))
if show_swap:
output_string += " %9s"
output_data += (human(swaps[cmd[0]]),)
output_string += "\t%s\n"
output_data += (cmd_with_count(cmd[0], count[cmd[0]]),)
sys.stdout.write(output_string % output_data)
# Only show totals if appropriate
if have_swap_pss and show_swap: # kernel will have_pss
sys.stdout.write("%s\n%s%9s%s%9s\n%s\n" %
("-" * 45, " " * 24, human(total), " " * 3,
human(total_swap), "=" * 45))
elif have_pss:
sys.stdout.write("%s\n%s%9s\n%s\n" %
("-" * 33, " " * 24, human(total), "=" * 33))
def verify_environment(pids_to_show):
if os.geteuid() != 0 and not pids_to_show:
sys.stderr.write("Sorry, root permission required, or specify pids with -p\n")
sys.stderr.close()
sys.exit(1)
try:
kernel_ver()
except (IOError, OSError):
val = sys.exc_info()[1]
if val.errno == errno.ENOENT:
sys.stderr.write(
"Couldn't access " + proc.path('') + "\n"
"Only GNU/Linux and FreeBSD (with linprocfs) are supported\n")
sys.exit(2)
else:
raise
def main():
# Force the stdout and stderr streams to be unbuffered
sys.stdout = Unbuffered(sys.stdout)
sys.stderr = Unbuffered(sys.stderr)
split_args, pids_to_show, watch, only_total, discriminate_by_pid, \
show_swap = parse_options()
verify_environment(pids_to_show)
if not only_total:
print_header(show_swap, discriminate_by_pid)
if watch is not None:
try:
sorted_cmds = True
while sorted_cmds:
sorted_cmds, shareds, count, total, swaps, total_swap = \
get_memory_usage(pids_to_show, split_args,
discriminate_by_pid)
if only_total and show_swap and have_swap_pss:
sys.stdout.write(human(total_swap, units=1)+'\n')
elif only_total and not show_swap and have_pss:
sys.stdout.write(human(total, units=1)+'\n')
elif not only_total:
print_memory_usage(sorted_cmds, shareds, count, total,
swaps, total_swap, show_swap)
sys.stdout.flush()
time.sleep(watch)
else:
sys.stdout.write('Process does not exist anymore.\n')
except KeyboardInterrupt:
pass
else:
# This is the default behavior
sorted_cmds, shareds, count, total, swaps, total_swap = \
get_memory_usage(pids_to_show, split_args,
discriminate_by_pid)
if only_total and show_swap and have_swap_pss:
sys.stdout.write(human(total_swap, units=1)+'\n')
elif only_total and not show_swap and have_pss:
sys.stdout.write(human(total, units=1)+'\n')
elif not only_total:
print_memory_usage(sorted_cmds, shareds, count, total, swaps,
total_swap, show_swap)
# We must close explicitly, so that any EPIPE exception
# is handled by our excepthook, rather than the default
# one which is reenabled after this script finishes.
sys.stdout.close()
ram_accuracy, swap_accuracy = val_accuracy( show_swap )
show_val_accuracy( ram_accuracy, swap_accuracy, only_total, show_swap )
if __name__ == '__main__': main()