How to Check CPU, RAM & Disk Usage on a Linux Server
server is slowhigh CPUdisk fullWhen a server feels slow or a game lags, the first job is to see what's using the resources. These four commands tell you in seconds.
CPU & memory in real time: top / htop
top is on every server; htop is the friendlier colour version (install it if you can). Both show a live list of processes sorted by CPU, so you can spot the hog:
top # press 'M' to sort by memory, 'P' by CPU, 'q' to quit
htop # nicer UI; arrow keys + F9 to kill a processMemory at a glance: free
free -h shows total, used and available RAM in human-readable units:
free -h
# total used free available
# Mem: 7.7Gi 3.1Gi 1.2Gi 4.3GiLinux uses spare RAM for cache, so "free" looks low on a healthy server. The "available" column is the real figure — that's how much your apps can still use.
Disk space: df & du
df -h shows how full each disk is. If one is at 100%, that alone can crash services:
df -h # usage per filesystem
du -sh /home/* | sort -h # which folders are biggestDisk I/O: is the disk the bottleneck?
High %wa (I/O wait) in top means processes are waiting on the disk — a classic cause of lag on slow storage. iostat (from sysstat) shows per-disk activity.
Quick triage order
htop/top— what's using the CPU?free -h— is RAM exhausted (low "available")?df -h— is a disk full?- High
%wain top — is storage the bottleneck?
Slow server? top, free, df — in that order. Ninety seconds tells you whether it's CPU, RAM or disk.
NVMe-backed game servers
Slow disks cause lag. Our servers run on fast NVMe with high-clock CPUs — so resources are never the bottleneck.
Frequently asked questions
Why is my "free" memory so low on Linux?
Linux deliberately uses unused RAM as disk cache to speed things up. That memory is instantly reclaimable, so look at the "available" column in free -h, not "free".
How do I find what's using all my CPU?
Run htop (or top and press P). The process at the top of the list is your biggest CPU user. For game servers it's usually the game process itself when full.
What does high I/O wait mean?
A high %wa value means the CPU is idle but waiting for the disk. It points to slow storage or too much disk activity — a common cause of lag that more CPU won't fix. NVMe storage solves most of it.
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