I am looking to speed up the boot time on my Raspberry pi and systemd-random-seed is taking 20s (old Pi 1). From what I've read up this is waiting to collect entropy to generate a system random seed. I don't care whatsoever about security and I'm wondering if there is some way to hard-code this, disable it, or otherwise make it not take so ridiculously long to boot?

I tried just running systemctl disable systemd-random-seed to see what would happen and it still ran at boot, so evidently it's being started by another service or something.

I also tried adding random.trust_cpu=on to cmdline.txt based on something I read, but it seems to have done nothing.

I'm completely new to Linux and raspberry if that wasn't already obvious, so sorry if it's a dumb question a requires a dumb answer... I attempted to look through the man page and it's completely over my head (wasn't sure how to translate that into the boot process).

  • On what are you basing this conclusion? systemd services start asynchronously, so even if you think something is causing "slow" boot (which 20s isn't - my Pi4 takes 30sec) removing it is unlikely to make a significant difference.
    – Milliways
    Nov 27, 2021 at 4:01
  • Incidentally WHY are you rebooting - I only reboot if updating firmware, other that that my Pi run 24/7?
    – Milliways
    Nov 27, 2021 at 4:02
  • 1
    @Milliways I ran systemd-analyze plot and this service was by far the slowest. So far as I know that is the best way to time boot services... As to WHY, I am working on a camera controller and I want it to boot as quickly as possible because this is a set-up I will be carrying on film sets (not sitting at home or in a server room or something).
    – Spencer
    Nov 27, 2021 at 4:10
  • @Milliways This guy got his boot time down to 3-4 seconds ;) himeshp.blogspot.com/2018/08/fast-boot-with-raspberry-pi.html
    – Spencer
    Nov 27, 2021 at 4:19

1 Answer 1


Many over the years have tried to minimise boot times, and it can be done.

The best start is systemd-analyze critical-chain. Optimising anything not on the critical-chain won't help. Disabling networking is often successful.

  • So this means that it isn't taking any time? Why is it that when I run this the critical chain starts @31.6s - is there nothing I can do about the time before second 31?
    – Spencer
    Nov 27, 2021 at 4:36
  • Also, and I do realize this is a bit off topic, can I disable systemd-timesyncd? According to my critical chain it is taking 2.3s and I don't particularly care about time...
    – Spencer
    Nov 27, 2021 at 4:40
  • Everything takes time, but most run asynchronously. This is obviously limited on a single CPU system.systemd-timesyncd synchronises the clock. It is not needed, and will do nothing unless you have a network and you will still have clock - it just won't show the real time. systemd-analyze time shows kernel & userspace time.
    – Milliways
    Nov 27, 2021 at 4:55
  • Ok so just to wrap this up because it isn't totally clear to me yet, it was totally false to think that systemd-random-seed was slowing my boot times? I tried systemd-analyze time and yes it shows 4s for kernel and 30s for userspace but that doesn't really help me much except to tell me that userspace is where I need to focus. But what is taking so long in userspace, that isn't in the critical chain? (which only showed about 5 seconds worth of time)
    – Spencer
    Nov 27, 2021 at 5:04
  • I suggest you read man systemd-analyze and look at blame. This is complex, and I don't understand all of it. I am afraid I can't offer any concrete help for your specific problem, other than disabling everything you don't need.
    – Milliways
    Nov 27, 2021 at 5:22

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