Understanding your system's hardware and software configuration
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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.
uptime # Shows how long the system has been running and load averages.Load average reflects the average number of processes waiting to run or use CPU resources over different time intervals, typically 1, 5, and 15 minutes. |
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CPU and Memory Diagnostics
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Monitoring CPU and memory usage helps in identifying performance bottlenecks.
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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.
Installation: on Ubuntu or Debian-based systems via command apt install htop or sudo yum install htop on CentOS
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htop |
vmstat -s # Provides a detailed breakdown of memory usage and other related metrics since the last system boot.
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mpstat
Linux 5.15.0-112-generic (testhost) 06/21/24 _x86_64_ (1 CPU)
10:37:12 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
10:37:12 all 1.68 0.11 1.38 0.14 0.00 0.04 1.16 0.00 0.00 95.49 |
Keeping track of disk usage and health is crucial for preventing data loss and ensuring efficient storage management.
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iostat
Linux 5.15.0-112-generic (testhost) 06/21/24 _x86_64_ (1 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
1.68 0.11 1.41 0.14 1.16 95.50 |
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Process and Service Management |
Managing processes and services is essential for maintaining system stability.
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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
├─1000209 /usr/sbin/apache2 -k start
/apache2 -k start
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systemctl restart service_name # Restarts a service.If a service is not behaving correctly, stopped responding, restarting it can often resolve the issue without needing a full system reboot. Also, when you modify a service config file, using systemctl restart applies the changes immediately. |
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systemctl restart service_name # Restarts a service.
systemctl enable service_name # Enables a service to start at boot.
kill -9 process_id(PID) # Forces termination of a process.
#(No output unless there is an error, the process is terminated forcefully) |
Analyzing logs and monitoring system activities can help in identifying issues and tracking system performance.
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tail /var/log/syslog # Shows the last part of the logs, where problems usually liejournalctl -f # will show you the latest system logs and keep updating the display with new log entries as they are created, which is useful for monitoring live system activity. |
Essential Linux Log Files:
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/var/log/auth.log or /var/log/secure - Stores authentication logs, including both successful and failed logins and authentication methods. Debian/Ubuntu information is stored in /var/log/auth.log, while Redhat/CentrOS is stored in /var/log/secure.
4. Application Logs: (examples):
/var/log/apache2/ - Apache HTTP server logs (access, error).
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/var/log/yum.log - Red Hat-based systems store the yum and dnf package manager logs, file provides information about the results of a specific command, such as any errors or warnings that were generated. For example, if a package update fails
6. Event Logs:
var/log/wtmp - Records of user logins and logouts.
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