initial commit, actually done already

.gitignore

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+.idea/

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.31)
+project(cputild C)
+
+set(CMAKE_C_STANDARD 11)
+
+add_executable(cputild main.c)

cputild.service

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+[Unit]
+Description=Simple daemon that will continuously write the cpu usage to /tmp/cputild
+After=network.target
+
+[Service]
+Type=simple
+ExecStart=/usr/local/cputild
+ExecStop=kill -INT $MAIN_PID
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target

main.c

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+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <time.h>
+#include <signal.h>
+
+
+#define STAT_FILE "/proc/stat"
+#define OUT_FILE "/tmp/cputild"
+
+volatile int running = 1;
+
+void signal_handler_sigint(const int _signal) {
+    assert(_signal == SIGINT && "ERROR: Signal except SIGINT received by the SIGINT handler");
+
+    printf("hello there\n");
+    running = 0;
+}
+
+int main(void) {
+    // register the SIGINT handler
+    signal(SIGINT, signal_handler_sigint);
+
+    FILE *out_file = fopen(OUT_FILE, "w");
+    FILE *stat_file = fopen(STAT_FILE, "r");
+
+    uint64_t total_jiffies_active = 0;
+    uint64_t total_jiffies_idle = 0;
+
+    size_t line_len = 1024;
+    char *line_buffer = (char*)malloc(line_len);
+
+    while (running) {
+        struct timespec now;
+        struct timespec request;
+        struct timespec remain;
+
+        request.tv_sec = 1;
+        request.tv_nsec = 0;
+        nanosleep(&request, &remain);
+        clock_gettime(CLOCK_REALTIME, &now);
+
+        fflush(stat_file);
+        fseek(stat_file, 0, SEEK_SET);
+        const ssize_t read = getline(&line_buffer, &line_len, stat_file);
+        if (read == -1) {
+            printf("Failed to read the stat file!\n");
+            exit(1);
+        }
+
+        uint64_t user, user_nice, system, idle, iowait, irq, softirq, steal, guest, guest_nice;
+        const int n_read = sscanf(line_buffer, "cpu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu", &user, &user_nice, &system, &idle, &iowait, &irq, &softirq, &steal, &guest, &guest_nice); // NOLINT(*-err34-c)
+        if (n_read != 10) {
+            printf("Failed to read the stat file: Invalid format?\n");
+            exit(1);
+        }
+
+        const uint64_t current_total_jiffies_active = user + user_nice + system + irq + softirq + guest + guest_nice;
+        const uint64_t current_total_jiffies_idle = iowait + idle;
+
+        const uint64_t delta_jiffies_active = current_total_jiffies_active - total_jiffies_active;
+        const uint64_t delta_jiffies_idle = current_total_jiffies_idle - total_jiffies_idle;
+
+        const double utilization = (double)(delta_jiffies_active) / (double)(delta_jiffies_idle + delta_jiffies_active);
+
+        total_jiffies_active = current_total_jiffies_active;
+        total_jiffies_idle = current_total_jiffies_idle;
+
+        fseek(out_file, 0, SEEK_SET);
+        fprintf(out_file, "Custom CPU: %.02f", utilization * 100);
+        fflush(out_file);
+    }
+
+    free(line_buffer);
+
+    printf("Terminating...\n");
+    return 0;
+}