linux下修改/dev/shm tmpfs文件系统大小

默认系统就会加载/dev/shm ，它就是所谓的tmpfs，有人说跟ramdisk（虚拟磁盘），但不一样。象虚拟磁盘一
样，tmpfs 可以使用您的 RAM，但它也可以使用您的交换分区来存储。而且传统的虚拟磁盘是个块设备，并需要
一个 mkfs 之类的命令才能真正地使用它，tmpfs 是一个文件系统，而不是块设备；您只是安装它，它就可以使
用了。
tmpfs有以下优势：

1.动态文件系统的大小。
2.tmpfs 的另一个主要的好处是它闪电般的速度。因为典型的 tmpfs 文件系统会完全驻留在 RAM 中，读写几乎
可以是瞬间的。
3.tmpfs 数据在重新启动之后不会保留，因为虚拟内存本质上就是易失的。所以有必要做一些脚本做诸如加载，
绑定的操作。
通常使用/dev/shm作共享内存（shm_open，shm_unlink)。 /dev/shm是个临时文档系统（tmpfs），能够
从/etc/fstab中mount。因此，支持标准的参数例如"size"，能够用来增加或减少在/dev/shm上的tmpfs大小.（默认的，他的大小是系统RAM的一半）

调整/dev/shm的大小

1)查看大小

df -h /dev/shm

2)修改大小

vi /etc/fstab

tmpfs /dev/shm tmpfs defaults,size=4096M 0 0

3)重新挂载

umount /dev/shm

mount /dev/shm

4)查看修改后的大小

df -h /dev/shm
5)不重起修改tmpfs大小 mount -o remount,size=38g /dev/shm

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