A "camera not found" message can be due many different things. Here are some steps to try:

1. If this is a new RPi camera, make sure the ribbon cable is installed correctly. This is an easy mistake to make since the cable will go in backwards. See the camera documentation for details on how to correctly plug the camera in.
2. If you have access to another Pi, try plugging the camera in it to see if it works.
3. Check for the correct camera driver.
   On Bullseye, execute:

   libcamera-hello

   If you get an error like this:

   terminate called after throwing an instance of 'std::runtime_error'
     	what():  failed to import fd 22

   run sudo raspi-config, navigate to Advanced Options and enable Glamor graphic acceleration. Then reboot your Pi. Now, try libcamera-hello again. You should get a Hello world! message in a new window.
   This is not needed on Bookworm.
4. Check for under voltage (Bullseye and Bookworm only)
   Execute:

   libcamera-hello

   If you get an error that contains

   Unable to request 0 buffers: Device or resource busy

   your Pi may be under voltaged.
   • If you have another power supply try it.
   • Using sudo, add over_voltage=4 to /boot/config.txt then reboot your Pi. If you are still having the problem, add arm_freq=700 to /boot/config.txt then reboot your Pi. Note that this decreases the speed of your Pi so should be a last resort.
     See more information.

This issue is normally resolved by upgrading the firmware on your Pi by doing the following:

sudo apt update 
sudo apt full-upgrade
sudo shutdown -r now

When a Linux command (for example, date) completes, it has an exit code, also called a "return code" or "RETCODE". By convention, a code of 0 means the command was successful and a non-zero code means there was some problem. The developer of the command specifies what each non-zero code means. When Allsky commands detect an issue, like a required file is not found, they print an error message then exit with a non-zero code.

An exit code of 137 usually means the command was forcefully killed by an outside source, often the Linux kernel. When this happens to an Allsky command, the log file will usually contain a message with Killed in it, and often with RETCODE=137 in it.

If you are using a RPi camera and get a notification message saying ERROR See /var/log/allsky.log for details and the log file contains entries similar to these:

Jan 20 18:45:50 allsky allsky.sh[4480]: /home/pi/allsky/allsky.sh: line 372:
     4562 Killed "${ALLSKY_HOME}/${CAPTURE}" "${ARGUMENTS[@]}"
Jan 20 18:45:50 allsky allsky.sh[4480]: 'capture_RPi' exited with RETCODE=137

The installation of Allsky checked if additional swap space was needed, and if so, prompted you to add it. If you are seeing this problem you either didn't add swap space, or additional space is needed.

This problem happens more often on Pi's with small amounts of memory such as the Pi Zero 2 with only 512 MB. It's less likely (although still possible) on a Pi 4 with 4 or 8 GB of memory.