本文最后更新于 2020 年 6 月 21 日，文章已超过 6 个月！内容可能已失效，请自行测试 ~

由于Centos系统为 kdump 服务预留了一部分内存导致服务器内存显示不足实际购买 4G

[root@VM_0_9_centos ~]# free -m

total used free shared buff/cache available

Mem: 3789 898 102 35 2788 2540

Swap: 0 0 0

停止kdump服务

停止并禁止自启动

[root@VM_0_9_centos ~]# systemctl stop kdump.service

[root@VM_0_9_centos ~]# systemctl disable kdump.service

修改grub文件

将crashkernel=auto修改为crashkernel=0

[root@VM_0_9_centos ~]# vim /etc/default/grub

GRUB_TIMEOUT=5

GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"

GRUB_DEFAULT=saved

GRUB_DISABLE_SUBMENU=true

GRUB_TERMINAL="serial console"

GRUB_TERMINAL_OUTPUT="serial console"

GRUB_CMDLINE_LINUX="crashkernel=0 console=ttyS0 console=tty0 panic=5 net.ifnames=0 biosdevname=0"

GRUB_DISABLE_RECOVERY="true"

GRUB_SERIAL_COMMAND="serial --speed=9600 --unit=0 --word=8 --parity=no --stop=1"

生成配置并重启

重启前注意无其他正在进行的工作，以免造成数据丢失

[root@VM_0_9_centos ~]# grub2-mkconfig -o /boot/grub2/grub.cfg

[root@VM_0_9_centos ~]# reboot

验证

减少了161MB内存

[root@nginx-server logs]# free -m

total used free shared buff/cache available

Mem: 3950 898 2502 32 550 2792

Swap: 0 0 0

其他

查看底层硬件信息，可以看到这台轻量云 2G 内存的服务器是分配足了 2048M 内存的。

[root@VM_0_9_centos ~]# dmidecode |egrep "Maximum|Size"

Runtime Size: 96 kB

ROM Size: 64 kB

Maximum Capacity: 4 GB

Size: 4096 MB

Range Size: 3584 MB

Range Size: 512 MB

Range Size: 3584 MB

Range Size: 512 MB

Reserving

[root@VM_0_9_centos ~]# dmesg | grep -i memory

[ 0.000000] Base memory trampoline at [ffff9f7000099000] 99000 size 24576

[ 0.000000] Early memory node ranges

[ 0.000000] PM: Registered nosave memory: [mem 0x0009f000-0x0009ffff]

[ 0.000000] PM: Registered nosave memory: [mem 0x000a0000-0x000effff]

[ 0.000000] PM: Registered nosave memory: [mem 0x000f0000-0x000fffff]

[ 0.000000] PM: Registered nosave memory: [mem 0xdfffe000-0xdfffffff]

[ 0.000000] PM: Registered nosave memory: [mem 0xe0000000-0xfeffbfff]

[ 0.000000] PM: Registered nosave memory: [mem 0xfeffc000-0xfeffffff]

[ 0.000000] PM: Registered nosave memory: [mem 0xff000000-0xfffbffff]

[ 0.000000] PM: Registered nosave memory: [mem 0xfffc0000-0xffffffff]

[ 0.000000] Memory: 4024148k/4718592k available (7664k kernel code, 524688k absent, 169756k reserved, 6055k data, 1876k init)

[ 0.000000] please try 'cgroup_disable=memory' option if you don't want memory cgroups

[ 0.024204] Initializing cgroup subsys memory

[ 0.556576] Freeing initrd memory: 18236k freed

[ 0.699529] Non-volatile memory driver v1.3

[ 0.702670] crash memory driver: version 1.1

[ 0.840195] Freeing unused kernel memory: 1876k freed

[ 0.845600] Freeing unused kernel memory: 516k freed

[ 0.848671] Freeing unused kernel memory: 600k freed

[ 1.579629] [TTM] Zone kernel: Available graphics memory: 2022702 kiB