Shared memory in linux

Linux and Unix-Like Red Hat
1

Hello, I am using Linux os.

[tom@tattu ~]$ df -k /dev/shm
Filesystem           1K-blocks      Used Available Use% Mounted on
tmpfs                  2023256   1065000    958256  53% /dev/shm
[tom@tattu ~]$

Based on my google this, it is shared memory. What is this shared memory and where exactly it is used? Can you please help me to understand more about this?

2

Shared memory is physical memory that is used by two or more different processes at the same time.

Ex: shared libraries. This is code that gets loaded into memory, and all processes running on the system see it an use it at the same time.

3

Thanks....

4

shared memory isn't quite the same thing as /dev/shm. shared mem can be done many ways actually. /dev/shm is essentially a RAM disk.

5

shm/shmfs is the filesystem used by used for temporary storage as tmpfs .
/dev/shm is the physicaly shared memory from RAM which is used to speed up execution in Linux/unix . i.e. if a programme is having a portion of memory that can be shared to another programme if permitted .

We can increase our /dev/shm if we have enough RAM , for better performance .

6

Program code ends up cached in RAM anyway. Shared libraries end up in shared memory anyway. You might want to rethink your strategy for improving performance.

/dev/shm is often used to explicitly create memory blocks for processes to share between them but in the end is just a ramdisk, no more, no less.