Ordinary Daemon

This is a simple UNIX daemon implemented in C that logs uptime and signal statistics to both a file and syslog.

Features

• Runs as a background daemon process.
• Handles the following signals:
• SIGUSR1 — increments an internal counter and triggers logging.
• SIGALRM — triggers logging and re-arms itself every 300 seconds.
• Logs:
• Time elapsed since the daemon started.
• PID of the daemon process.
• Number of SIGUSR1 signals received.
• Writes logs to:
• /tmp/ordinary_daemon.log (text file)
• System log (via syslog with facility LOG_USER).
• Detaches from the terminal, redirects standard streams to /dev/null.
• Double-fork daemonization to ensure it is fully detached from the controlling terminal.

How It Works

1. On startup, the process daemonizes itself:
   • Closes standard file descriptors.
   • Changes working directory to /.
   • Creates a new session (setsid()).
   • Forks twice to prevent acquiring a controlling terminal.
2. Opens /tmp/ordinary_daemon.log for writing.
3. Sets up signal handlers for SIGUSR1 and SIGALRM.
4. Starts a 300-second alarm to trigger periodic logging.
5. Waits in an infinite loop (pause()), writing logs when a signal is received.

Usage

Compile:

git clone https://git.scratko.xyz/typical-daemon-process
cd typical-daemon-process
gcc -o ordinary_daemon daemon.c

Run:

./ordinary_daemon

Send signals:

kill -USR1 <pid>  # increment counter and log immediately
kill -ALRM <pid>  # log immediately and restart 300s timer

View log file:

cat /tmp/ordinary_daemon.log

View syslog output (example for systemd-based systems):

journalctl -t "ordinary daemon"

Example Log Entry

time spent (in sec): 120.50 pid: 12345 SIGUSR1: 3