> ## Documentation Index > Fetch the complete documentation index at: https://help.freakhosting.com/llms.txt > Use this file to discover all available pages before exploring further. # How to Check Memory Usage on Linux (free Command Explained) > Check memory usage on Linux with free -h. The available column shows the RAM programs can still use; buff/cache is freed on demand. Find the biggest users. To check memory usage on Linux, run `free -h`. Read the **available** column: it is the kernel's estimate of how much RAM new programs can use without swapping. **buff/cache** is disk cache that Linux frees when programs need it, so low **free** is normal. To see which processes use the most RAM, run `ps -eo pid,user,rss,%mem,comm --sort=-rss | head`. | Difficulty | Time | Works on | Needs | | - | - | - | - | | Beginner | 5 minutes | Every Linux distribution (`free` is part of procps) | SSH access | ## Before you start * [Connect with SSH](https://help.freakhosting.com/portals/other/how-to-connect-to-a-linux-server-with-ssh.md). The commands here don't need `sudo`. * `free` reads `/proc/meminfo`, so it shows what the operating system sees. On a VPS that is the RAM in your plan, minus a little the kernel reserves. ## How to check memory usage with free ```bash theme={null} free -h ``` ```text theme={null} total used free shared buff/cache available Mem: 7.8Gi 1.1Gi 3.9Gi 58Mi 3.2Gi 6.8Gi Swap: 2.0Gi 0B 2.0Gi ``` `-h` prints human-readable units. Use `-m` for mebibytes or `-g` for gibibytes. ## What the free columns mean | Column | Meaning | | - | - | | `total` | Usable RAM (or swap) | | `used` | Memory in use, calculated as `total - available` | | `free` | Memory not used for anything, not even cache | | `shared` | Mostly `tmpfs` (RAM-backed file systems such as `/dev/shm`) | | `buff/cache` | Kernel buffers and page cache: recently read files kept in RAM to make the next read faster | | `available` | Estimate of RAM available for new programs without swapping. **This is the number to watch** | > [!NOTE] > > A server with little **free** memory and a large **buff/cache** is healthy. Linux uses spare RAM as cache and gives it back when a program needs it. You only have a memory problem when **available** is low. ## How to watch memory over time ```bash theme={null} free -h -s 2 # refresh every 2 seconds, Ctrl+C to stop vmstat 2 5 # 5 samples, 2 seconds apart ``` In `vmstat`, watch `si` and `so` (memory swapped in and out per second). Values above 0 on every line mean the server is short of RAM and using swap, which is much slower than memory. ## How to find which process uses the most memory ```bash theme={null} ps -eo pid,user,rss,%mem,comm --sort=-rss | head ``` ```text theme={null} PID USER RSS %MEM COMMAND 2038 mysql 105100 1.2 mariadbd 197 root 98824 1.2 dockerd 1185 www-data 65012 0.8 php-fpm8.3 ``` `RSS` (resident set size) is the physical RAM a process uses, in KiB. Several processes of the same program (PHP-FPM workers, Apache) share some memory, so adding their `RSS` values overstates the total. For an interactive view, open `htop` and press `M` to sort by memory. See [monitor resources with htop](https://help.freakhosting.com/portals/other/how-to-monitor-server-resources-with-htop.md). To see memory per service rather than per process: ```bash theme={null} systemctl status mariadb ``` The `Memory:` line shows what the whole service (all its processes) uses. Replace `mariadb` with your service name. ## How to check swap usage ```bash theme={null} swapon --show ``` ```text theme={null} NAME TYPE SIZE USED PRIO /swapfile file 2G 0B -2 ``` No output means the server has no swap. Swap gives the kernel room to move rarely used memory to disk instead of killing a process, but heavy swap use slows everything down. To add some, see [add swap space](https://help.freakhosting.com/portals/other/how-to-add-swap-space-on-linux.md). ## How to tell if the server ran out of memory When RAM and swap are both exhausted, the kernel's out-of-memory (OOM) killer ends a process. Check the kernel log: ```bash theme={null} sudo journalctl -k | grep -i -E "out of memory|oom-kill" ``` A line such as `Out of memory: Killed process 2038 (mariadbd)` names the victim. Fixes are in [fix out of memory killed processes](https://help.freakhosting.com/portals/other/how-to-fix-out-of-memory-killed-processes.md). ## What to do if memory is low **1. Find the biggest user** Run the `ps` command above or `htop`, sorted by memory. **2. Restart or tune it** A leak often clears after `sudo systemctl restart name`. For databases, PHP-FPM and Java game servers, lower their memory settings (buffer pool, `pm.max_children`, `-Xmx`). **3. Cap it** Stop one program taking all the RAM with a `MemoryMax=` limit. See [limit CPU and memory for a process](https://help.freakhosting.com/portals/other/how-to-limit-cpu-and-memory-for-a-process.md). **4. Add swap or RAM** Add a swap file as a safety net, or move to a plan with more memory. > [!WARNING] > > You may find advice to run `echo 3 > /proc/sys/vm/drop_caches` to "free memory". It only empties the cache, which the kernel would free anyway when needed, and it makes the server slower until the cache refills. Don't add it to cron. ## Frequently asked questions ### Why is my free memory so low when nothing is running? Linux fills spare RAM with file cache. Check **available**, not **free**. If **available** is high, you have plenty of memory. ### What is the difference between free and available memory? **free** is RAM holding nothing at all. **available** adds the cache and other memory the kernel can reclaim, so it shows the real room for new programs. ### Why does my VPS show slightly less RAM than my plan? The kernel reserves some memory for itself at boot, so `total` is a little lower than the installed RAM. That is normal on every Linux server. ### How do I see memory usage in MB? Run `free -m`. For gigabytes use `free -g` (rounded down) or `free -h`. ## Related guides > [card] [VPS and dedicated server guides](https://help.freakhosting.com/portals/other/vps-and-dedicated-server-guides.md) > > Every server guide in one place. > [card] [Fix out of memory errors](https://help.freakhosting.com/portals/other/how-to-fix-out-of-memory-killed-processes.md) > > When the OOM killer strikes. > [card] [Add swap space](https://help.freakhosting.com/portals/other/how-to-add-swap-space-on-linux.md) > > Create a swap file safely. > [card] [Monitor resources with htop](https://help.freakhosting.com/portals/other/how-to-monitor-server-resources-with-htop.md) > > Live view of every process. > [card] [Limit CPU and memory](https://help.freakhosting.com/portals/other/how-to-limit-cpu-and-memory-for-a-process.md) > > systemd MemoryMax and CPUQuota. > [card] [VPS Panel resource graphs](https://help.freakhosting.com/portals/vps-panel/how-to-monitor-vps-resource-usage.md) > > Memory use over time. *** > [!NOTE] > > **Checked against the [free(1)](https://man7.org/linux/man-pages/man1/free.1.html), [ps(1)](https://man7.org/linux/man-pages/man1/ps.1.html) and [vmstat(8)](https://man7.org/linux/man-pages/man8/vmstat.8.html) manuals and the [Linux kernel /proc/sys/vm documentation](https://docs.kernel.org/admin-guide/sysctl/vm.html)** on 4 November 2026; commands tested on Ubuntu 24.04 LTS. Commands can differ on other distributions or releases. > [!NOTE] > > ### Need Extra Help? > > If you encounter any issues, our support team is ready to assist: > > * **Live Chat:** Quick assistance via our website. > * **Support Ticket:** [Open a Ticket](https://freakhosting.com/clientarea/submitticket.php) > * **Discord:** [Join our Community](https://discord.gg/freakhosting) > * **Email:** [support@freakhosting.com](mailto:support@freakhosting.com) > [!TIP] > > ### Save on Your Hosting > > Ready to upgrade your hosting? Use code **KB20** at checkout for **20% off** your first order! *** **Last Updated:** November 2026 This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.