/dev/shm vs /tmp: When to Use Each

👤 Diwas Poudel    🕒 06 May 2023    📁 TECH

If you have ever used Linux, you might have stumbled across a folder called /dev/shm. Similarly, there is another one called /tmp. If you have ever wondered what those folders are for and what can be done with them, I am here to help. Let’s get right into it.

What are these folders?

Let’s start with /dev/shm. This is a temporary file system. This folder is used as a mounted RAM disk usually. This means that the files stored in this folder will be deleted as soon as the system reboots. ‘shm’ is an abbreviation for Shared Memory. Here is an image of the contents of my /dev/shm folder. 

/dev/shm content
fig. /dev/shm content

The /tmp folder is also common for temporary file storage. However, unlike the /dev/shm folder, this isn’t dedicated to the RAM. It is accessible to all the users in the system and can be backed by a hard disk or other storage media. This means that the files stored here aren’t going to get purged after a reboot. 

tmp contents
fig. tmp contents

Now that we have a basic understanding of the folders, let’s get to the differences. 

The Differences and Use Cases

The main differences between the /dev/shm folder and the /tmp folder are in the way they store temporary data and in their presence after a system reboot.

The files and directories stored in /dev/shm are kept in memory. The data is lost when the system is shut down or restarted. /dev/shm is ideal for applications that require high-speed access to temporary data, such as scratch space for processing or inter-process communication, but its contents are not persistent after a reboot.

On the other hand, the /tmp folder is a standard directory that can be backed by the hard disk or other storage media. Files stored in /tmp can persist after a system reboot, although the directory's contents are generally cleared during system startup.

Another difference between /dev/shm and /tmp is their intended use cases. /dev/shm is typically used for storing data that needs to be accessed quickly and frequently, whereas /tmp is used for storing temporary files that may not be accessed as frequently and are generally not as critical.

Overall, the choice between using /dev/shm and /tmp will depend on the specific use case and requirements of the application or system. If you need high-speed access to temporary data and do not require persistence after a reboot, /dev/shm may be a better choice. If you need to store temporary files that may need to survive a system reboot, /tmp would be the more appropriate choice.

It's important to remember that /dev/shm is a shared memory area that allows different processes to access the same files, which is useful for programs that need data sharing between processes. However, using shared memory requires caution because, if not used appropriately, it might lead to race conditions.

/dev/shm vs /tmp in tabular format

  /dev/shm /tmp
Storage RAM Hard Disk or RAM
Performance Faster Slower
Persistence Volatile Non Volatile
Use Case Used for frequently accessing small files, sharing data between processes Used for infrequently accessing for large files, temporary files, installation files, logs
Security Less Secure More Secure
Shared Memory Yes No


Both /dev/shm/ and /tmp/ are used for temporary file storage, but some differences can affect when and how you should use them.

/dev/shm/ uses RAM for storage. It is typically mounted automatically on most Linux distributions and intended for applications requiring high-speed access to temporary data. Since the data is it is stored in RAM, it can be faster than accessing files on disk. However, it also means that the storage is volatile, meaning that the data is lost when the system is shut down or restarted. On the other hand, /tmp is a directory typically used for storing temporary files that are not critical and can be deleted without harm. It is mounted on the root filesystem and can be configured to use disk space. Since it is not dedicated solely to RAM, /tmp/ may be slower, but can survive a system reboot.

In conclusion, if you want to use the fast, RAM-based directory, use the /dev/shm filesystem. On the other hand, if you want a more persistent directory then you will be better off using the /tmp directory.