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System Information

Understanding your system's hardware and software configuration

Commands
    uname -a # Displays kernel version and system architecture.
    lscpu  # Provides detailed information about the CPU.
    lsblk # Lists all available block devices.
    lsusb # Shows USB devices connected to the system.

CPU and Memory Diagnostics

Monitoring CPU and memory usage helps in identifying performance bottlenecks.

htop is an interactive system monitor process viewer and process manager. It is designed as an alternative to the Unix program top. It shows a frequently updated list of the processes running on a computer, normally ordered by the amount of CPU usage.

    htop

 vmstat -s Provides a detailed breakdown of memory usage and other related metrics since the last system boot. 

    vmstat -s        
       980492 K total memory
       480208 K used memory
       132040 K active memory
       582364 K inactive memory
        67924 K free memory
        21724 K buffer memory
       410636 K swap cache
            0 K total swap
            0 K used swap
            0 K free swap

 free -h Displays memory usage in "human-readable" format

    free -h
               total        used        free      shared  buff/cache   available
Mem:           7.7G        1.9G        3.9G        487M        1.9G        5.0G
Swap:          2.0G          0B        2.0G


Disk Usage and Health

Keeping track of disk usage and health is crucial for preventing data loss and ensuring efficient storage management.

df -h # Shows disk space usage in "human-readable" format

   df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3.8G     0  3.8G   0% /dev
tmpfs           783M  1.7M  781M   1% /run
/dev/sda2       233G   25G  197G  12% /
tmpfs           3.9G   39M  3.8G   1% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           783M   80K  783M   1% /run/user/1000

du -sh /path/to/directory  Displays the size of a specific directory.

Commands
   du -sh /path/to/directory 
1.1G    /path/to/director

    iostat # Reports CPU and I/O statistics.

fdisk -l  # List all partitions

Commands
   fdisk -l
Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors
Disk model: QEMU HARDDISK    
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: XXXXXX-XXX-XXX-XXXX-XXXXXXXXXX

Device     Start      End  Sectors Size Type
/dev/sda1   2048     4095     2048   1M BIOS boot
/dev/sda2   4096 41940607 41936512  20G Linux filesystem


Process and Service Management

Managing processes and services is essential for maintaining system stability.

ps aux # Lists all running processes

Commands
ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.0 168800 10944 ?        Ss   Jun12   0:02 /sbin/init
root         2  0.0  0.0      0     0 ?        S    Jun12   0:00 [kthreadd]
root         3  0.0  0.0      0     0 ?        I<   Jun12   0:00 [rcu_gp]
root         4  0.0  0.0      0     0 ?        I<   Jun12   0:00 [rcu_par_gp]
...
    journalctl -u service_name # Views logs for a specific service.
    kill -9 process_id # Forces termination of a process.
    nice and renice # Adjusts process priority.

systemctl status service_name # Checks the status of a service

Commands
     systemctl status apache2
● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2024-05-29 16:06:04 UTC; 2 weeks 5 days ago
       Docs: https://httpd.apache.org/docs/2.4/
    Process: 1000205 ExecReload=/usr/sbin/apachectl graceful (code=exited, status=0/SUCCESS)
   Main PID: 40385 (apache2)
      Tasks: 55 (limit: 1013)
     Memory: 8.8M
        CPU: 1min 55.654s
     CGroup: /system.slice/apache2.service
             ├─  40385 /usr/sbin/apache2 -k start
             ├─1000209 /usr/sbin/apache2 -k start
             └─1000210 /usr/sbin/apache2 -k start

ps aux # Lists all running processes

Commands
    ps aux # Lists all running processes.
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.0 168800 10944 ?        Ss   Jun12   0:02 /sbin/init
root         2  0.0  0.0      0     0 ?        S    Jun12   0:00 [kthreadd]
root         3  0.0  0.0      0     0 ?        I<   Jun12   0:00 [rcu_gp]
root         4  0.0  0.0      0     0 ?        I<   Jun12   0:00 [rcu_par_gp]
...
   

 kill -9 process_id(PID) # Forces termination of a process.


Logs and Monitoring

Analyzing logs and monitoring system activities can help in identifying issues and tracking system performance.

Commands
    dmesg # Prints kernel ring buffer messages.
    journalctl # Views systemd logs.
    journalctl -u service_name # Views logs for a specific service.
    tail -f /var/log/syslog # Continuously displays system log updates.
    sar # Collects, reports, and saves system activity information (requires sysstat).
    uptime # Shows how long the system has been running and load averages.
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