Drop-in Files for systemd

As an alternative to adding applications to the barrier file, you can use drop-in files to configure the secfs-fs-barrier.service file for dependency management using systemd. This eliminates the need to modify the service file for configuring dependencies.

All drop-in directory files with the suffix .conf are merged in alphanumeric order and parsed after the main unit file has been parsed. Each drop-in file must contain appropriate section headers. Systemd reads the .conf files in the following order.

1. The instance .d/ subdirectory

2. The template .d/ subdirectory

The drop-in .d/ directories for system services can be placed in the following directories:

• /etc/systemd/system

• /usr/lib/systemd/system (Ubuntu only)

• /run/systemd/system

Drop-in files in /etc/ take precedence over those in the /run/ directory which, in turn, take precedence over those in the /usr/lib/ directory. Drop-in files in any of those directories take precedence over unit files wherever they are located. Multiple drop-in files with different names are applied in lexicographic order, regardless of which directories they reside in.

Following is an example of a drop-in file (dependencies.conf) for the secfs-fs-barrier.service:

cat /usr/lib/systemd/system/sec-fs-barrier.service.d/dependencies.conf
[Unit]
Before=mfetpd.service mfeespd.service

The above example displays a drop-in file which adds two McAfee related services in the Before= clause of the secfs-fs-barrier.service file without modifying the service file itself. Eventually, systemd detects the drop-in files and links them to the secfs-fs-barrier.service file.