[systemd-devel] Loading systemd units files at startup

[Eswaran Vinothkumar (BEG-PT/PJ-IOT1)]

Hello systemd developers,

Currently, I am working on a task to reduce the boot time of an embedded product. systemd is used as the init system. I have a couple of questions, could you please clarify?


1.   From the systemd-analyze plot, I am seeing that it takes around 2 seconds to load the systemd unit files. Is there any way to reduce this time? I read a blog about systemd-readahead and systemd-replay services used in such cases to reduce the loading time, but it also have mentioned that the services are not maintained in the latest systemd versions. Is it advisable to use such services?


2.   There are some systemd services which are used mostly for debugging purposes, so I tried to mask those services. My question is if the service is masked , do the service files gets loaded during the systemd initialization? I have masked around 5 services but I am not seeing any reduction in the systemd unit files loading time though there is a considerable reduction in the overall boot time.


3.       I have read that the preferred way to have the mount points is to write in /etc/fstab. This will create a *.mount file using systemd_fstab_generator. I am seeing that in the project for the debugfs there is a systemd mount file defined in  /lib/systemd/system/ and also an option present in /etc/fstab ('debugfs  /sys/kernel/debug  debugfs noauto 0 0').


Which file has precedence when the system is  initialized?

/lib/systemd/system/sys-kernel-debug.mount
or
/run/systemd/generator/sys-kernel-debug.mount

Mit freundlichen Grüßen / Best regards
Vinothkumar Eswaran


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