How to monitor resource usage on a Linux server

    Monitoring resource usage on a Linux server is crucial for maintaining performance and troubleshooting issues. Various tools are available to help you track CPU, memory, disk, and network usage. Below are some common methods and commands to monitor system resources.

    1. Check CPU Usage

    Using top

    The top command provides a dynamic, real-time view of system processes, including CPU usage.

    $ top

    You will see a list of running processes, and at the top of the screen, you’ll find CPU usage details under the “%CPU” column. The CPU usage is broken down into user processes, system processes, and idle time.

    Example output:

    top - 15:25:01 up 3 days,  4:14,  1 user,  load average: 0.13, 0.12, 0.10
    Tasks: 204 total,   1 running, 203 sleeping,   0 stopped,   0 zombie
%Cpu(s):  5.2 us,  2.1 sy,  0.0 ni, 92.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  8032.8 total,  3094.0 free,  1634.4 used,  4304.4 buff/cache
MiB Swap:  2048.0 total,  2048.0 free,     0.0 used.  6112.8 avail Mem

    2. Monitor Memory Usage

    Using free

    The free command shows memory usage, including total, used, and free memory, as well as swap usage.

    $ free -h

    The -h flag displays the information in a human-readable format.

    Example output:

                  total        used        free      shared  buff/cache   available
    Mem:           7.8Gi       1.6Gi       3.0Gi       155Mi       3.2Gi       5.7Gi
Swap:          2.0Gi          0B       2.0Gi

    3. Disk Usage

    Using df

    The df command shows the amount of disk space used and available on all mounted filesystems.

    $ df -h

    The -h flag ensures the output is human-readable (e.g., in GiB or MiB).

    Example output:

    Filesystem      Size  Used Avail Use% Mounted on
    /dev/sda1        50G   30G   18G  63% /
tmpfs            16G  1.6G   15G  10% /dev/shm
/dev/sdb1       100G   25G   70G  27% /data

    4. Monitor Network Usage

    Using iftop

    The iftop command shows network usage for the active connections in real-time.

    $ sudo iftop

    This will display a list of active network connections and show their incoming and outgoing bandwidth.

    Example output:

    TX:             15.3 KB  22.1 KB        Total  60.1 KB
    RX:             10.1 KB  12.3 KB
                             
   IP address       Port  Pkts In Pkts Out  Total In  Total Out
   192.168.1.2      22    200    150        25.5 KB   13.4 KB
   192.168.1.5      80    85     120        5.2 KB    9.1 KB

    Using netstat

    netstat shows network connections, routing tables, and interface statistics.

    $ netstat -tuln

    This displays listening ports and the corresponding services using them.

    Example output:

    Proto Recv-Q Send-Q Local Address           Foreign Address         State
    tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN
tcp6       0      0 :::80                   :::*                    LISTEN

    5. Check System Load

    Using uptime

    The uptime command provides a quick overview of the system’s load averages over 1, 5, and 15 minutes.

    $ uptime

    Example output:

    15:30:02 up 3 days,  4:21,  1 user,  load average: 0.10, 0.12, 0.08

    6. Monitor Process Usage

    Using ps

    The ps command allows you to check the resource usage of specific processes.

    $ ps aux --sort=-%cpu | head

    This command sorts processes by CPU usage and shows the top processes.

    Example output:

    USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
    root      1123 10.5  3.1 112340 31092 ?        S    15:10   0:12 /usr/bin/python3
user      2345  7.8  1.8  82344 18640 ?        S    15:15   0:09 /usr/bin/nginx

    7. Advanced Monitoring Tools

    Using htop

    htop is an interactive process viewer that provides a more user-friendly way to monitor system resources.

    $ sudo htop

    It allows you to sort processes by CPU, memory usage, and more, with a visually appealing display.

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