cesium webcam snapshot

Shell script-based routine that takes unique snapshots from live JPEG images published on the Web.

Prerequisities

• Shell - bash or Korn shell ksh (OpenBSD's default shell)
• curl

Installation

System user

useradd -c "Webcam routine" -b /var/webcam/ -d /var/webcam-snapshot/ -s /sbin/nologin _webcam
install -d -m 770 -o root -g _webcam /var/webcam-snapshot/

Clone & file copy

cd /tmp/
git clone https://github.com/cesiumcz/webcam-snapshot.git

Determine correct version bash/ksh:

mv snap.(bash|ksh) snap.sh

Install the script and set correct permissions

install -d -m 755 -o root -g _webcam /usr/local/webcam-snapshot/
install -m 754 -o root -g _webcam snap.sh /usr/local/webcam-snapshot/
rm -rf /tmp/webcam-snapshot/

Configuration

Camera list

vim /usr/local/webcam-snapshot/cameras.txt

For each webcam, insert a line according to the following syntax:

cam_name jpg_uri

• cam_name = unique string camera name. Use short and simple names.
• jpg_uri = URI to JPEG image

A line starting with # is ignored.

Example contents of cameras.txt

pec https://www.chmi.cz/files/portal/docs/meteo/kam/pecpodsnezkou.jpg
jizerka https://www.chmi.cz/files/portal/docs/meteo/kam/jizerka.jpg

Set proper permissions (cameras.txt is likely to contain credentials)

chown -R root:_webcam /usr/local/webcam-snapshot/
chmod 660 /usr/local/webcam-snapshot/cameras.txt

Cron

Invoke the script every minute between 6 to 18 hours:

crontab -e -u _webcam
* 6-18 * * * /usr/local/webcam-snapshot/snap.sh

Testing

su -l _webcam /usr/local/webcam-snapshot/snap.sh

Or alternative using doas command:

doas -u _webcam /usr/local/webcam-snapshot/snap.sh

Modus operandi

snap.sh does the following sequentially for each webcam:

• downloads current image into temporary location, if succeeds:
• checks if the new image differs from the last downloaded, if so:
• moves the second oldest image into final location

Directory structure

/tmp/webcam-snapshot/
|-- cam1
|   `-- 202401201023.jpg
`-- cam2
    `-- 202401201023.jpg

/var/webcam-snapshot/
|-- cam1
|   |-- 202401201020.jpg
|   `-- 202401201010.jpg
`-- cam2
    |-- 202401201020.jpg
    `-- 202401201010.jpg

Author

Matyáš Vohralík, 2024

License

BSD 3-Clause