Short Answer
To check RAM usage in Linux, use the following command:
free -h
It shows total, used, and available memory in a human-readable format.
You can also use:
top
or
htop
to view real-time memory usage by processes.
Now let’s understand these commands in detail and explore all the reliable ways to monitor memory usage in Linux from basic terminal commands to advanced tools.
Why Check RAM Usage in Linux?
Monitoring RAM (Random Access Memory) usage helps you:
- Detect memory-hungry processes
- Identify performance bottlenecks
- Optimize applications and servers
- Prevent system slowdowns or crashes
Whether you’re running Ubuntu, Fedora, CentOS, or Debian — knowing how to check RAM usage is a fundamental Linux skill.
Check RAM Usage Using the free Command
The free command is the simplest and most widely used way to check memory usage in Linux.
Command:
free -h
Example Output:
total used free shared buff/cache available
Mem: 7.7G 2.9G 1.8G 210M 3.0G 4.2G
Swap: 2.0G 0B 2.0G
Explanation:
- total → Total physical RAM available
- used → Memory currently in use
- free → Completely unused memory
- buff/cache → Memory used by kernel buffers and cache
- available → Memory available for new processes
The -h flag displays data in a human-readable format (like MB or GB).
Without -h, it shows memory in kilobytes.
Check RAM Usage in Real-Time Using top
The top command gives a live view of system performance — including CPU and memory usage.
Command:
top
Example Output:
MiB Mem : 7849.3 total, 1823.6 free, 2890.2 used, 3135.5 buff/cache
MiB Swap: 2048.0 total, 2048.0 free, 0.0 used.
In top, memory usage is shown near the top of the output.
Press q to quit.
Use htop for an Easier, Colorful View (Recommended)
htop is an improved version of top with an interactive, color-coded interface.
Install it first (if not already installed):
For Ubuntu/Debian:
sudo apt install htop
For Fedora:
sudo dnf install htop
For CentOS:
sudo yum install htop
Run it:
htop
You’ll see:
- Total, used, and available memory bars
- CPU and swap usage
- Per-process memory usage
- Search and sort options
You can scroll or kill processes right from within the tool — making it much easier for live system monitoring.
Check RAM Usage with /proc/meminfo
If you prefer raw data directly from the kernel, check this file:
cat /proc/meminfo
Example Output:
MemTotal: 8029384 kB
MemFree: 1925432 kB
MemAvailable: 4312872 kB
Buffers: 230764 kB
Cached: 2789236 kB
SwapTotal: 2097148 kB
SwapFree: 2097148 kB
This shows detailed memory statistics including:
- Total physical RAM (
MemTotal) - Free memory (
MemFree) - Cached data (
Cached) - Swap memory usage (
SwapTotal,SwapFree)
You can combine it with grep to simplify:
grep MemTotal /proc/meminfo
grep MemFree /proc/meminfo
Check RAM Usage with vmstat
vmstat (Virtual Memory Statistics) shows memory, CPU, and process info in one place.
Command:
vmstat -s
Example Output:
8029384 K total memory
2890232 K used memory
1925432 K active memory
4312872 K free memory
230764 K buffer memory
2789236 K cache memory
You can also use:
vmstat 2
This updates every 2 seconds — great for tracking changes over time.
If vmstat is missing, install it via:
sudo apt install procps
Using sar Command (System Activity Report)
sar is part of the sysstat package and is useful for tracking historical RAM usage.
Install it:
For Ubuntu/Debian:
sudo apt install sysstat
For Fedora/CentOS:
sudo dnf install sysstat
Command:
sar -r 2 5
This checks memory usage every 2 seconds for 5 intervals.
Output includes:
- Used and free memory
- Buffer/cache statistics
- Swap usage
This is especially helpful for server administrators analyzing performance over time.
Check Memory Usage by Process with ps
To see how much memory each process consumes:
ps aux --sort=-%mem | head
Output Example:
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
mysql 1321 3.2 20.4 1802432 825432 ? Ssl 09:12 1:05 mysqld
firefox 2543 4.5 12.7 2809036 513784 ? Sl 09:15 2:14 firefox
Here:
- %MEM → Percentage of RAM used
- VSZ → Virtual memory size
- RSS → Resident set size (actual physical RAM used)
Use this to find which applications are using the most memory.
Check Total RAM Installed
To see total physical memory:
grep MemTotal /proc/meminfo
or
sudo dmidecode -t memory | grep -i size
The second command gives hardware-level details about your RAM modules (like total size and slots used).
Check Swap Memory Usage
Swap memory acts as virtual memory when physical RAM is full.
Command:
swapon --show
Example:
NAME TYPE SIZE USED PRIO
/swapfile file 2G 0B -2
To check it with free:
free -h
Look under the Swap row.
Combine Commands for Quick Monitoring
Here’s a quick one-liner to see total, used, and free memory together:
free -h && vmstat -s | grep "total memory"
Or a continuous live feed (every 2 seconds):
watch -n 2 free -h
This automatically refreshes memory data every few seconds — great for monitoring in real-time.
Monitor Memory Graphically (GUI Tools)
If you’re using a desktop environment, you can check memory usage without touching the terminal.
For Ubuntu:
Open System Monitor → Resources tab
You’ll see live graphs for Memory and Swap usage.
For KDE (Plasma):
Open KSysGuard or System Monitor → Memory section.
These tools visualize memory usage with graphs and history — useful for beginners and developers.
Example: Diagnosing High Memory Usage
Let’s say your Linux system feels slow. Here’s how you can troubleshoot:
- Check overall memory
free -h - List top memory-consuming processes
ps aux --sort=-%mem | head - Monitor real-time usage
htop - Check swap usage
swapon --show
If swap usage is high and free memory is low, your system is running out of RAM.
In that case, consider:
- Closing heavy processes
- Adding more physical RAM
- Increasing swap space
Common Commands Summary
| Task | Command |
|---|---|
| Check total RAM usage | free -h |
| Real-time memory monitoring | top or htop |
| Detailed memory info | cat /proc/meminfo |
| Per-process RAM usage | `ps aux –sort=-%mem |
| Memory stats summary | vmstat -s |
| Historical memory tracking | sar -r 2 5 |
| Check total installed RAM | grep MemTotal /proc/meminfo |
| Check swap memory | swapon --show |
Pro Tip: Combine Tools for Deeper Insight
Use htop for live monitoring, free -h for quick snapshots, and /proc/meminfo when you need technical breakdowns.
For production servers, tools like Grafana, Prometheus, or Glances can provide real-time dashboards for memory and CPU tracking.
Wrap Up
Checking RAM usage in Linux is simple once you know the right tools.
If you just need a quick overview:
free -h
If you want a live and colorful view:
htop
And if you need raw technical data:
cat /proc/meminfo
Whether you’re managing a local system or a large-scale server, these commands will help you keep performance under control and troubleshoot memory issues quickly.
