Some useful /proc information I can use to check the state of the system.

get_ip.cpp

// This program simply gets the ip for the specified interface.

#include <iostream>
#include <sys/ioctl.h>
#include <net/if.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

using namespace std;

int main(int argc, char** argv)
{
    if (argc < 2)
    {
        cerr << "Usage: " << argv[0] << " IFACE" << endl;
        return 0;
    }

    const char* iface_name = argv[1];

    int sock;
    struct  sockaddr_in soc_addr;
    struct ifreq ifr;

    if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
    {
        cerr << "Failed to create socket for " << iface_name << endl;
        return 1;
    }

    strncpy(ifr.ifr_name, iface_name, IF_NAMESIZE);
    ifr.ifr_name[IFNAMSIZ-1]='\0';

    if (ioctl(sock, SIOCGIFADDR, &ifr) < 0)
    {
        cerr << "Failed to get ip of " << iface_name << endl;
        return 1;
    }

    memcpy(&soc_addr, &ifr.ifr_addr, sizeof(soc_addr));
    cout << inet_ntoa(soc_addr.sin_addr) << endl;
    close(sock);

    return 0;
}

note.md

1. /proc/net/dev records the recv/send bytes and packet number through all the interfaces. The number is accumulated from the booting up, so you can subtract the number from the last check.

2. /proc/stat contains information about CPU usage. For cpu0 usage in 20s, you can do the following:

   cpu0_line=$(cat /proc/stat | grep cpu0)
   cpu0_total1=$(echo $cpu0_line | awk '{print $2 + $3 + $4 + $5 + $6 + $7 + $8}')
   cpu0_used1=$(echo $cpu0_line | awk '{print $2 + $3 + $4 + $7 + $8}')
   sleep 20
   # calculate again
   cpu0_line=$(cat /proc/stat | grep cpu0)
   cpu0_total2=$(echo $cpu0_line | awk '{print $2 + $3 + $4 + $5 + $6 + $7 + $8}')
   cpu0_used2=$(echo $cpu0_line | awk '{print $2 + $3 + $4 + $7 + $8}')
      
   cpu0_usage_rate=$(python -c "print ($cpu0_used2 - $cpu0_used1) * 100.0 / ($cpu0_total2 - $cpu0_total1)")

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