On Debian (or any Linux system) without sudo or root access, you can use cgroups (Control Groups) to monitor and trigger actions based on memory usage without polling. However, creating and managing cgroups typically requires root privileges.

Alternative: systemd User Service with Memory Limit

If your user has a systemd user instance (common on modern Debian), you can create a user service that runs your command when memory usage exceeds a threshold. This approach uses systemd's built-in memory monitoring and does not require polling.

Steps:

1. Create a user service file (e.g., ~/.config/systemd/user/memory-watch.service):

   ini
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   [Unit]
   Description=Run command when memory usage exceeds threshold
   
   [Service]
   Type=oneshot
   ExecStart=/path/to/your/command
   MemoryHigh=80%  # Adjust threshold as needed
   MemoryMax=90%    # Hard limit (optional)

   • MemoryHigh: Triggers throttling or actions when memory usage exceeds this percentage.
   • MemoryMax: Hard limit (optional, but useful for testing).

2. Create a companion .path or .timer unit (if you want to trigger on specific events or intervals, but this is not polling).

3. Enable and start the service:

   bash
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   systemctl --user enable memory-watch.service
   systemctl --user start memory-watch.service

   • This will run your command once when the memory threshold is crossed.

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Pure User-Space Solution: inotify + /proc (No Polling)

If you cannot use systemd, you can use inotify to monitor /proc/self/status or /proc/meminfo for changes. However, this is not event-driven for memory thresholds—it only detects file changes, not specific values.

Example (Bash + inotifywait):

bash
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while inotifywait -q -e modify /proc/meminfo; do
    # Parse /proc/meminfo for MemAvailable or your metric
    mem_available=$(grep MemAvailable /proc/meminfo | awk '{print $2}')
    if [ "$mem_available" -lt YOUR_THRESHOLD ]; then
        /path/to/your/command
    fi
done

• Limitation: This still involves reading /proc/meminfo on every change, which is not true event-driven but avoids active polling loops.

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Best Approach Without Root: systemd User Service

• Pros: No polling, uses kernel-level memory tracking.
• Cons: Requires systemd user instance (enabled by default on Debian with loginctl enable-linger).

Verify systemd user instance:

bash
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loginctl show-user $(whoami) | grep Linger

If Linger=no, enable it:

bash
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loginctl enable-linger $(whoami)

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Final Recommendation

Use systemd user service with MemoryHigh if available. It is the only non-polling, non-root solution for this use case on Debian. If systemd is not an option, you must use a lightweight polling script (e.g., watch or cron).