A modern system requires a large amount of temporary files and directories. Some applications (and users) use the /tmp directory to store temporary data, while others use a more specific location for the task, such as daemon and user-specific volatile directories in /run. In this context, volatile means that the file system that stores these files only exists in memory. When the system restarts or loses power, all content in volatile storage will disappear.
To keep a system running smoothly, it's necessary for these directories and files to be created when they don't exist, as daemons and scripts may rely on them being there, and for old files to be deleted so they don't fill up disk space or provide incorrect information. CentOS/RHEL 7 and later versions include a new tool called systemd-tmpfiles, which provides a structured and configurable method for managing temporary files and directories. This service is run by a timer unit that queries the systemd's temporary daemon and runs it 15 minutes after the system startup and then every 24 hours from that moment.
The configuration files are located in different places and follow a hierarchical priority process, with the files having the following priority order.
1. /etc/tmpfiles.d/*.conf
2. /run/tmpfiles.d/*.conf
3. /usr/lib/tmpfiles.d/*.conf
The files in /usr/lib/tmpfiles.d/ are provided by relevant RPM packages and should not be edited.
The files under /run/tmpfiles.d/ are themselves volatile files, typically used by daemons to manage their own runtime temporary files.
The files in /etc/tmpfiles.d/ are intended for administrators to configure custom temporary locations and override default values provided by the vendor.
If a file in /run/tmpfiles.d/ has the same file name as a file in /usr/lib/tmpfiles.d/, then the file in /run/tmpfiles.d/ is used. If a file in /etc/tmpfiles.d/ has the same file name as a file in /run/tmpfiles.d/ or /usr/lib/tmpfiles.d/, then the file in /etc/tmpfiles.d/ is used.
1. /etc/tmpfiles.d/*.conf
2. /run/tmpfiles.d/*.conf
3. /usr/lib/tmpfiles.d/*.conf
The files in /usr/lib/tmpfiles.d/ are provided by relevant RPM packages and should not be edited.
The files under /run/tmpfiles.d/ are themselves volatile files, typically used by daemons to manage their own runtime temporary files.
The files in /etc/tmpfiles.d/ are intended for administrators to configure custom temporary locations and override default values provided by the vendor.
If a file in /run/tmpfiles.d/ has the same file name as a file in /usr/lib/tmpfiles.d/, then the file in /run/tmpfiles.d/ is used. If a file in /etc/tmpfiles.d/ has the same file name as a file in /run/tmpfiles.d/ or /usr/lib/tmpfiles.d/, then the file in /etc/tmpfiles.d/ is used.
