Use a named constant rather than a magic number.

void do_dmesg() {

    printf("------ KERNEL LOG (dmesg) ------\n");

    int size = klogctl(10, NULL, 0); /* Get size of kernel buffer */

    /* Get size of kernel buffer */

    int size = klogctl(KLOG_SIZE_BUFFER, NULL, 0);

    if (size <= 0) {

        printf("Unexpected klogctl return value: %d\n\n", size);

        return;