操作系统信息：

# cat /etc/redhat-release 
Red Hat Enterprise Linux Server release 7.5 (Maipo)

runcluvfy检查结果：

Starting check for /dev/shm mounted as temporary file system ...
ERROR: 
PRVE-0426 : The size of in-memory file system mounted as /dev/shm is "1000" megabytes which is less than the required size of "2048" megabytes on node ""
PRVE-0426 : The size of in-memory file system mounted as /dev/shm is "995" megabytes which is less than the required size of "2048" megabytes on node ""
Check for /dev/shm mounted as temporary file system failed

当前配置：
[root@prodb1 ~]# df -h

Filesystem           Size  Used Avail Use% Mounted on
devtmpfs             975M     0  975M   0% /dev
tmpfs                995M     0  995M   0% /dev/shm
tmpfs                995M  8.7M  986M   1% /run
tmpfs                995M     0  995M   0% /sys/fs/cgroup
/dev/mapper/ol-root   22G  3.9G   19G  18% /
/dev/sda1           1014M  158M  857M  16% /boot
tmpfs                199M     0  199M   0% /run/user/0
tmpfs                199M     0  199M   0% /run/user/1002

当前shm大小 为995m。
检查fstab
[root@prodb1 ~]# cat /etc/fstab

# /etc/fstab
# Created by anaconda on Wed Jan 30 13:44:53 2019
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/ol-root     /                       xfs     defaults        0 0
UUID=266095fc-dca4-4fce-a808-a10628d642d3 /boot                   xfs     defaults        0 0
/dev/mapper/ol-swap     swap                    swap    defaults        0 0

fstab没有了shm的配置，配置信息写入了以下文件：

# ll /usr/lib/dracut/modules.d/99base/init.sh 
-rwxr-xr-x. 1 root root 11467 4月  11 2018 /usr/lib/dracut/modules.d/99base/init.sh

    62  if ! ismounted /dev/shm; then
    63      mkdir -m 0755 /dev/shm
    64      mount -t tmpfs -o mode=1777,nosuid,nodev,strictatime tmpfs /dev/shm >/dev/null 
    65  fi

修改64行，保证下次重启依然有效：

mount -t tmpfs -o mode=1777,nosuid,nodev,strictatime,size=2G tmpfs /dev/shm >/dev/null 

修改当前设置：

#fsuser -km /dev/shm
#umount /dev/shm
#mount -t tmpfs -o mode=1777,nosuid,nodev,strictatime,size=2G tmpfs /dev/shm

参考：Linux OL7/RHEL7: PRVE-0421 : No entry exists in /etc/fstab for mounting /dev/shm (文档 ID 2065603.1)