On 22/06/2019 09:56, Markus Robert Kessler wrote:
> - I switched to crontab-based reboots because the same machine (RPi Zero
> Wifi) is used for taking photos on demand. Therefore I ssh into it and
> start a script which accesses a USB webcam via fswebcam and transfers the
> photos to a webserver.
> This works fine, but from time to time fswebcam suddenly is no longer
> able to get data from the webcam for some reason. In this case even a
> "USB reset" does not work. So the machine has to be rebooted anyway.

This suggests to me that the webcam may be very close to the maximum
current available from the Zero's USB port. If it has been currently
limited the voltage will drop and many devices will no longer respond
until the power is cycled. A USB deivce drawing too much current may
also cause the WiFi to drop out on the Pi.

The solution would be to either attach the webcam through an externally
powered USB hub, or replace it with a Raspberrp Pi camera, which are
lower power.

> B.t.w., I already tried to put the line "fsck -p /dev/mmcblk0p1" into /
> etc/rc.local to reset file system's "dirty bit" to prevent it from
> demanding for a filesystem check. This seems to have no effect.

A fsck will be performed on system startup, long before anything in
/etc/rc.local gets run. I know you can force an fsck on boot using
/boot/cmdline.txt but I don't think you can prevent one.

> So, RPi or the OS, seems to make changes to the filesystem / MBR or what
> else, which cannot be recovered by RPi itself, but a "normal" Linux
> machine can handle this without even alerting about any trouble.

If this is happening the card needs to be replaced. If it wasn't a Zero
I'd suggest booting from a USB stick for better reliability, but as an
SD card is the only option, a high endurance version is probably worthwhile.

---druck

--- SoupGate-Win32 v1.05