What is the dev shm?
You can check disk partition in linux by the “df” command, the “/dev/shm” can be found.
Now, let’s have a look at the screenshot. The size is 2G, the size is set half of the main memory.
Don’t worry. It is not actually assigned half of the main memory. It is only assigned to memory when data save to that space.
The “/dev/shm” is the Virtual Memory FileSystem. It can access all of from the Linux Processes.
And You will see the “tmpfs”. It’s a filesystem. simply, H\W memory can use a like disk.
There is something similar. It’s a Ramdisk. The Ramdisk and the “tmpfs” are the same as to save them in memory.
The difference is, the Ramdisk has a limit of space. But the “tmpfs” is If other processes are located in the memory When the sum of the processes used memory size and the “/dev/shm (tmpfs)” size over the memory size.
The Linux will be using a swap partition. You know, When the swap partition is using, the system is slow down.
What should We check before using?
As mentioned above, The “/dev/shm” can access all of the processes. Because. We should be careful about file and directory permission.
We do better make a personal directory.
And the “/dev/shm” is a memory, and the memory is volatile. Because, When rebooting the system, all data will be deleted in the space.
Where should we use it?
In application. Sometimes we use a temporary file. In this situation easily change the path to the “/dev/shm”, we will get fast I/O, or We might be used for storage of batch process.