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The ACT LED on my Raspberry Pi 3 B+ is flashing three times very quickly after boot. I am not able to connect via ssh (the error message is "Connection Refused" – despite ssh being enabled), but I am able to ping it. It's connected via Wifi, so I guess the OS is loaded, otherwise it wouldn't show up on the network.

What does the quick flashing mean?

The Pi was running fine for a few weeks now. After a reboot, the problem above occured.

  • Have you enabled SSH? Be aware that it's not on by default, which would explain your connections being refused if you didn't do this. – Aurora0001 Apr 9 '18 at 15:54
  • Possible duplicate of What do system LEDs signify? – Fabian Apr 9 '18 at 15:56
  • quote from What do system LEDs signify?: 3 flashes: loader.bin not found??? Although the os is loading, if it hadn't, it wouldn't say connection refused. So that means you probably just have to enable ssh by adding a file ssh to the boot partition on the sd card. – scitronboy Apr 9 '18 at 16:16
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    It happened after a reboot, the Pi was running for a few weeks already. SSH is enabled. – Unkn0wn Apr 9 '18 at 17:52
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Looks like my RootFS actually got corrupt. A lot of files in /bin and /etc were missing (e.g. passwd files + its backups and shadows), which rendered the whole system useless. The only thing I could do was reinstall the whole OS. I still do not know what those three flashes mean. I've had a problem with the loader.bin once, which resulted in a slow blinking. This time it was very fast.

  • Flashes of the ACT light also mean that the "disk" (SD card) is being accessed. It is possible, I suppose, that the flashes you were seeing were normal disk access flashes before the corruption caused the boot process to hang – perhaps loader.bin is there and loads but was corrupted and didn't execute correctly. Did you notice if loader.bin was still there? – dlu Apr 10 '18 at 12:22
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So, if nothing has changed, but something has changed it must be magic – or DHCP (which some would argue is the same thing). But seriously, from what you've described it sounds like the Pi's IP address may have changed and there is a machine (hence the connection refused rather than a timeout) at the Pi's old address that is not running sshd.

The reason that this has happened may be related to the three flashes of the ACT LED – according to @Dmitry Grigoryev's answer to What do system LEDs signify? the three flashes means that loader.bin wasn't found – meaning that the SD card may have been corrupted.

UPDATE: based on the OP's answer, stating that the SD card had been corrupted and that the flashes were faster than the Pi's diagnostic flashes, it is possible that the Pi was able to boot normally (and that what appeared to be three flashes of the ACT light were normal card access flashes during boot). However due to the corruption of the memory card the ssh daemon was not running and thus the connection was refused. This would be the likely explanation if you know that there wasn't another device responding the the ping. You could check that with arp -a which would let you see the MAC address of the device at the IP addresess responding to the ping.

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    In case of missing loader.bin the OP wouldn't be able to ping the RPi for sure. Either the OP mistakes ACT flashing due to normal booting process with flashing due to early boot problems, or they ping a different device thinking it's their RPi. – Dmitry Grigoryev Apr 10 '18 at 8:20
  • I would lean towards the later, a different device is responding to the ping, but it could also be the former and an inability to laugh 'sshd'. – dlu Apr 10 '18 at 12:35

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