20 most used Linux commands to troubleshoot issues

Using the below commands effectively allows for comprehensive troubleshooting and monitoring of a Linux system, helping to quickly identify and resolve issues.

System Performance and Resource Usage

top: Provides a dynamic, real-time view of the system’s processes. Useful for checking CPU and memory usage.
```
top
```
htop: An enhanced version of top, with a more user-friendly interface (if installed).
```
htop
```
free -m: Displays memory usage, with -m showing the information in megabytes.
```
free -m
```
vmstat: Reports virtual memory statistics.
```
vmstat 5
```
iostat: Provides CPU and I/O statistics. Useful for diagnosing disk performance issues.
```
iostat
```

Disk Usage and Space

df -h: Shows disk space usage in a human-readable format.
```
df -h
```
du -sh *: Displays the disk usage of files and directories in the current directory, summarized and human-readable.
```
du -sh *
```

Network

ping: Checks the network connectivity between the host and a target IP or domain.
```
ping google.com
```
netstat -tuln: Lists all listening ports and their respective services.
```
netstat -tuln
```
ss -tuln: A modern replacement for netstat, displaying listening sockets.
```
ss -tuln
```
traceroute: Traces the route packets take to a network host.
```
traceroute google.com
```
ifconfig or ip addr: Displays network interfaces and their configurations.
```
ifconfig
ip addr
```

Processes and Services

ps aux: Lists all running processes with detailed information.
```
ps aux
```
systemctl status <service>: Checks the status of a specific service.
```
systemctl status apache2
```
journalctl -xe: Views system logs, particularly useful for diagnosing issues with services managed by systemd.
```
journalctl -xe
```

Logs and Files

tail -f /var/log/syslog: Monitors the system log file in real-time.
```
tail -f /var/log/syslog
```
dmesg: Displays kernel-related messages.
```
dmesg
```

System Information

uname -a: Displays detailed information about the system, including the kernel version.
```
uname -a
```
uptime: Shows how long the system has been running, along with the load average.
```
uptime
```
lsof: Lists open files and the processes that opened them. Useful for troubleshooting issues related to files and directories.
```
lsof
```