[CentOS] CentOS 7, memory hungry (2.5GB) without user and heavy services running

Hello,

The last weekend, the VM with CentOS 7
(kernel-3.10.0-327.28.2.el7.x86_64) was running with 2.5GB of used memory,
but without users connected, and heavy services running. Three minutes
after reboot, the o.s. is running with 114MB used. ¿Why the 62% of memory
is used if the o.s. does not have an intensive load?


top sorted by memory:

top - 12:55:34 up 8 days, 21:41,  1 user,  load average: 0.16, 0.74, 0.49
Tasks:  90 total,   1 running,  89 sleeping,   0 stopped,   0 zombie
%Cpu0  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,
0.0 st
KiB Mem :  3882816 total,   310948 free,  2639892 used,   931976 buff/cache
KiB Swap:  7815164 total,  7815164 free,        0 used.   825004 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
  579 root      20   0  323592  23168   6232 S  0.0  0.6   0:30.07 firewalld
 1110 root      20   0  553052  18264   5624 S  0.0  0.5   3:29.65 tuned
  720 polkitd   20   0  530364  10900   4736 S  0.0  0.3   0:12.84 polkitd
  587 root      20   0  250252   8060   4800 S  0.7  0.2  20:48.88 vmtoolsd
  692 root      20   0  436892   7988   6156 S  0.0  0.2   0:12.36
NetworkManager
    1 root      20   0  273832   7128   3820 S  0.0  0.2   2:20.92 systemd
  577 root      20   0  210456   5488   3708 S  0.0  0.1   0:03.85 abrtd
26833 root      20   0  143008   5436   4148 S  0.0  0.1   0:13.47 sshd
  487 root      20   0   46424   5112   2652 S  0.0  0.1   0:02.26
systemd-udevd
  592 root      20   0  207976   4480   3124 S  0.0  0.1   0:02.31
abrt-watch-log
 1806 postfix   20   0   93512   4088   3028 S  0.0  0.1   0:02.80 qmgr
  470 root      20   0  129132   3956   2456 S  0.0  0.1   0:00.02 lvmetad
  580 root      20   0  445712   3888   3156 S  0.0  0.1   1:00.74 rsyslogd
26950 postfix   20   0   93328   3848   2840 S  0.0  0.1   0:00.11 pickup
 1112 root      20   0   82560   3544   2688 S  0.0  0.1   1:02.99 sshd
26837 root      20   0  116160   2976   1732 S  0.0  0.1   0:01.94 bash
  719 root      20   0   53064   2644   2052 S  0.0  0.1   0:00.25
wpa_supplicant
26783 root      20   0  178108   2448   1520 S  0.0  0.1   0:00.07 crond
  578 root      20   0  130060   2184   1672 S  0.0  0.1   0:00.66 smartd
 1801 root      20   0   93224   2168   1116 S  0.0  0.1   0:11.25 master
27041 root      20   0  157688   2128   1448 R  1.4  0.1   0:00.51 top
  581 dbus      20   0   37112   2116   1392 S  0.0  0.1   0:28.27
dbus-daemon
26968 root      20   0   36820   2076   1812 S  0.0  0.1   0:00.69
systemd-journal
  608 chrony    20   0  115844   1860   1448 S  0.0  0.0   0:14.59 chronyd
  586 root      20   0   26448   1700   1348 S  0.0  0.0   0:46.24
systemd-logind
  615 root      20   0  126336   1680   1028 S  0.0  0.0   0:21.39 crond
  555 root      16  -4  116724   1604   1208 S  0.0  0.0   0:33.97 auditd
26787 root      20   0  113120   1404   1220 S  0.0  0.0   0:00.05
freshclam-sleep
  620 root      20   0   25964    952    752 S  0.0  0.0   0:00.62 atd
18160 root      20   0  110036    816    692 S  0.0  0.0   0:00.18 agetty
  601 libstor+  20   0    8532    780    632 S  0.0  0.0   0:10.61 lsmd
26792 root      20   0  107896    620    528 S  0.0  0.0   0:00.00 sleep
    2 root      20   0       0      0      0 S  0.0  0.0   0:00.24 kthreadd
    3 root      20   0       0      0      0 S  0.0  0.0   0:06.40
ksoftirqd/0


# netstat -nao
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address
State       Timer
tcp        0      0 127.0.0.1:10025         0.0.0.0:*
LISTEN      off (0.00/0/0)
tcp        0      0 0.0.0.0:22              0.0.0.0:*
LISTEN      off (0.00/0/0)
tcp        0      0 127.0.0.1:25            0.0.0.0:*
LISTEN      off (0.00/0/0)
tcp        0     64 ip.ad.dr.ess:22         my.ip.by.myisp:50470
ESTABLISHED on (0.26/0/0)
tcp6       0      0 :::22                   :::*
LISTEN      off (0.00/0/0)
tcp6       0      0 ::1:25                  :::*
LISTEN      off (0.00/0/0)
udp        0      0 127.0.0.1:323           0.0.0.0:*
off (0.00/0/0)
udp6       0      0 ::1:323
:::*                                off (0.00/0/0)
raw6       0      0 :::58                   :::*
7           off (0.00/0/0)
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     9979
/run/lvm/lvmpolld.socket
unix  2      [ ACC ]     STREAM     LISTENING     9988
/run/lvm/lvmetad.socket
unix  2      [ ]         DGRAM                    6664
/run/systemd/notify
unix  2      [ ACC ]     STREAM     LISTENING     17787    private/tlsmgr
unix  2      [ ACC ]     STREAM     LISTENING     17790    private/rewrite
unix  2      [ ACC ]     STREAM     LISTENING     17793    private/bounce
unix  2      [ ACC ]     STREAM     LISTENING     6676
/run/systemd/journal/stdout
unix  2      [ ACC ]     STREAM     LISTENING     17796    private/defer
unix  2      [ ACC ]     STREAM     LISTENING     17799    private/trace
unix  5      [ ]         DGRAM                    6679
/run/systemd/journal/socket
unix  2      [ ACC ]     STREAM     LISTENING     17802    private/verify
unix  11     [ ]         DGRAM                    6681     /dev/log
unix  2      [ ACC ]     STREAM     LISTENING     17805    public/flush
unix  2      [ ACC ]     STREAM     LISTENING     17808    private/proxymap
unix  2      [ ACC ]     STREAM     LISTENING     17811
private/proxywrite
unix  2      [ ACC ]     STREAM     LISTENING     17814    private/smtp