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Exploring /run on Linux | Network World

If you haven’t been paying close attention, you might not have noticed a small but significant change in how Linux systems work with respect to runtime data. A re-arrangement of how and where it’s accessible in the file system started taking hold about eight years ago. And while this change might not have been big enough of a splash to wet your socks, it provides some additional consistency in the Linux file system and is worthy of some exploration.

To get started, cd your way over to /run. If you use df to check it out, you’ll see something like this:

$ df -k .
Filesystem     1K-blocks  Used Available Use% Mounted on
tmpfs             609984  2604    607380   1% /run

Identified as a “tmpfs” (temporary file system), we know that the files and directories in /run are not stored on disk but only in volatile memory. They represent data kept in memory (or disk-based swap) that takes on the appearance of a mounted file system to allow it to be more accessible and easier to manage.

/run is home to a wide assortment of data. For example, if you take a look at /run/user, you will notice a group of directories with numeric names.

$ ls /run/user
1000  1002  121

A long file listing will clarify the significance of these numbers.

$ ls -l
total 0
drwx------ 5 shs  shs  120 Jun 16 12:44 1000
drwx------ 5 dory dory 120 Jun 16 16:14 1002
drwx------ 8 gdm  gdm  220 Jun 14 12:18 121

This allows us to see that each directory is related to a user who is currently logged in or to the display manager, gdm. The numbers represent their UIDs. The content of each of these directories are files that are used by running processes.

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