Disk / Memory / CPU Troubleshooting

This page gives the fastest commands for capacity and performance issues. Each command includes a short one-line explanation for quick lookup.

Disk

Command	What it does	Example
`df -h`	Shows free and used disk space on filesystems.	`df -h`
`du -sh /var/log/*`	Shows sizes of log directories.	`du -sh /var/log/*`
`find /var/log -type f -size +100M`	Finds very large log files.	`find /var/log -type f -size +100M`
`iostat -xz 1 3`	Shows disk IO utilization and wait stats.	`iostat -xz 1 3`
`lsof \| grep deleted`	Finds deleted files still held open by processes.	`lsof \| grep deleted`

Use cases: disk full, growing logs, deleted-but-still-open files, slow storage, container volume issues.

Command	What it does	Example
`free -h`	Shows RAM and swap usage in human-readable form.	`free -h`
`vmstat 1 5`	Shows memory, CPU and IO activity over time.	`vmstat 1 5`
`top`	Shows live process and memory usage.	`top`
`ps aux --sort=-%mem \| head`	Shows the highest memory-using processes.	`ps aux --sort=-%mem \| head`
`pmap -x PID \| tail -20`	Shows detailed memory map for a process.	`pmap -x PID \| tail -20`

Use cases: RAM pressure, swap activity, large Java process, leak suspicion, runaway cache.

Command	What it does	Example
`top`	Shows live CPU usage by process.	`top`
`htop`	Shows a more readable live CPU view.	`htop`
`mpstat -P ALL 1 3`	Shows CPU usage per core.	`mpstat -P ALL 1 3`
`ps aux --sort=-%cpu \| head`	Shows the highest CPU-using processes.	`ps aux --sort=-%cpu \| head`
`uptime`	Shows system load averages and uptime.	`uptime`

Use cases: high CPU, one hot core, thread contention, busy container, load spikes.