A script on a schedule: environment, log, lock

Articles

• Bash scripts: running, variables, arguments — A script is a text file of shell commands: the #! line picks the interpreter, arguments arrive in $1, $2 and "$@".
• Exit codes: $?, && and || — An exit code is a number from 0 to 255 that a command reports: 0 means success, anything else a failure or a "no".
• flock — preventing a second run — flock holds a file lock while a command runs, so a second copy of the script waits for it or exits at once.
• journalctl — reading the systemd journal — Command for reading the systemd journal with service, time, and other filters.
• systemd — System and service manager that manages units and their dependencies.
• Cron — the task scheduler — Running tasks on a schedule: crontab syntax, classic cron and modern systemd timers.
• systemd timers — scheduled jobs — A systemd timer is a .timer unit that starts the service of the same name on a schedule; its output goes to the journal.