{"id":256,"date":"2018-10-17T06:38:37","date_gmt":"2018-10-17T06:38:37","guid":{"rendered":"http:\/\/www.appservgrid.com\/paw92\/index.php\/2018\/10\/17\/what-is-dev-shm-in-linux\/"},"modified":"2018-10-17T06:38:37","modified_gmt":"2018-10-17T06:38:37","slug":"what-is-dev-shm-in-linux","status":"publish","type":"post","link":"https:\/\/www.appservgrid.com\/paw92\/index.php\/2018\/10\/17\/what-is-dev-shm-in-linux\/","title":{"rendered":"What Is \/dev\/shm in linux?"},"content":{"rendered":"


<\/b> <\/p>\n

\nShared (Virtual) Memory (SHM)<\/p>\n


<\/b> <\/p>\n

\nShared memory is a way to shared state between process.<\/p>\n

Shared memory, as its name implies, is a method to \u201cshare\u201d data between processes. <\/p>\n

\nBoth processes define the same memory area as \u201cshared\u201d, and they can then exchange <\/p>\n

\ninformation simply by writing into it. This (used to be, and still is somewhat) faster than <\/p>\n

\nthe alternative of sending network or pipe-based messages between processes.<\/p>\n

If you see the memory as a mean of storing data, a file on a file system can be seen as <\/p>\n

\nshared memory (ie shared file).<\/p>\n

It is difficult to account for shared memory. Does it belong to one process? Both? Neither?<\/p>\n

\n If we naively sum the memory belonging to multiple processes, we grossly \u201cover-count\u201d.<\/p>\n

As the name implies, the Shared (Virtual) Memory refers to virtual memory that are shared<\/p>\n

\n by more than one process and then can be used by multiple programs simultaneously.<\/p>\n

Although virtual memory allows processes to have separate (virtual) address spaces, there <\/p>\n

\nare times when you need processes to share memory.<\/p>\n

Shared memory (SHM) is another method of interprocess communication (IPC) <\/p>\n

\nwhereby several processes share a single chunk of memory to communicate.<\/p>\n

Shared memory provides the fastest way for processes to pass large amounts of data<\/p>\n

\n to one another.<\/p>\n


<\/b> <\/p>\n

\n\/dev\/shm is nothing but implementation of traditional shared memory concept. It is an<\/p>\n

\n efficient means of passing data between programs. One program will create a memory <\/p>\n

\nportion, which other processes (if permitted) can access. This will result into speeding up <\/p>\n

\nthings on Linux.<\/p>\n


<\/b> <\/p>\n

\nshm \/ shmfs is also known as tmpfs, which is a common name for a temporary file storage <\/p>\n

\nfacility on many Unix-like operating systems. It is intended to appear as a mounted <\/p>\n

\nfile system, but one which uses virtual memory instead of a persistent storage device.<\/p>\n

\nIf you type mount command you will see \/dev\/shm as a tempfs file system. Therefore, <\/p>\n

\nit is a file system, which keeps all files in virtual memory. Everything in tmpfs is temporary<\/p>\n

\n in the sense that no files will be created on your hard drive. If you unmount a tmpfs instance, everything stored therein is lost. By default almost all Linux distros configured to use \/dev\/shm.<\/p>\n

\nDifference between tmpfs and swap<\/h3>\n