Ubuntu Memory Optimization: Clearing Cache, Optimizing Swap, and Utilizing zRAM

By 佐川 直弘 | Naohiro Sagawa (運営者)

※記事内に広告を含みます。Amazonアソシエイトとして適格販売により収入を得ています。　

1. Introduction

Ubuntu is a popular open-source Linux distribution used by many users. However, as the system runs for an extended period, memory may gradually become insufficient. This is caused by caches and unnecessary processes occupying memory.

In this article, we will explain specific methods to free up memory and improve system performance in Ubuntu. Aimed at beginners and intermediate users, we provide practical solutions using actual command examples and scripts. If you have basic knowledge of Ubuntu operations, you can easily follow along.

Benefits of Reading This Article

• Understand how memory works.
• Learn specific methods to free up memory in Ubuntu.
• Gain optimization tips to enhance system performance.

2. Basics of Ubuntu Memory Management

Types and Roles of Memory

Ubuntu’s memory management consists of three main components:

1. RAM (Physical Memory)
   This is where programs and data are temporarily stored. Having sufficient RAM is crucial as it directly affects system speed.
2. Cache Memory
   Stores temporary data to speed up the reuse of programs and files. While increasing cache can improve performance, excessive cache accumulation may lead to memory shortages.
3. Swap Space
   A storage area used temporarily when RAM is insufficient. However, since HDDs and SSDs are slower than RAM, excessive reliance on swap can degrade performance.

How to Check Current Memory Usage

To check memory usage, use the following command:

free -h Command

free -h

This command displays memory usage in a human-readable format.

Example Output:

              total        used        free      shared  buff/cache   available
Mem:           7.7G        2.5G        1.8G        1.2G        3.4G        4.0G
Swap:          2.0G          0B        2.0G

• total: Total memory
• used: Used memory
• free: Available memory
• buff/cache: Memory used for caching
• available: Memory actually available for use

htop Tool

For real-time memory usage monitoring, htop is a useful tool.

1. Installation:

   sudo apt install htop

2. Execution:

   htop

This tool provides a colorful interface displaying CPU and memory usage in real time.

3. Specific Methods for Freeing Up Memory

3.1 Clearing Page Cache

What is Page Cache?

Page cache temporarily stores files and data in memory for faster access. While it is a useful feature, if memory becomes insufficient, clearing the cache can free up resources.

How to Clear Page Cache

To clear the cache, follow these steps:

1. Cache Clearing Command
   Use the following command to clear the cache.

   sudo sync && sudo sysctl -w vm.drop_caches=3

• sync: Synchronizes data that needs to be written to disk.
• sysctl -w vm.drop_caches=3: Clears the page cache.

1. Verification
   Check memory status before and after clearing the cache using free -h.

Precautions

• Clearing the cache may temporarily slow down the system.
• Caches are managed automatically, so frequent manual clearing is unnecessary.

3.2 Optimizing Swap Space

What is Swap?

Swap space is a temporary storage area on the disk used when RAM is full. Since disks are slower than RAM, excessive use of swap can degrade performance.

Checking Swap Space

To check the current swap space, use the following command:

swapon --show

Adding Swap Space

If your system lacks sufficient swap space, you can create a swap file.

1. Create a Swap File

   sudo fallocate -l 1G /swapfile

This command creates a 1GB swap file.

2. Set Permissions

   sudo chmod 600 /swapfile

3. Enable Swap

   sudo mkswap /swapfile
   sudo swapon /swapfile

4. Verification
   Run swapon --show again to confirm the new swap space is active.

Freeing Up Swap

To clear swap and move data back to RAM, use the following command:

sudo swapoff -a && sudo swapon -a

This helps free up swap space and improve performance.

3.3 Terminating Unnecessary Processes

What are Unnecessary Processes?

Processes consuming large amounts of memory but not currently needed should be identified and terminated to free up memory.

How to Check Running Processes

You can use either htop or ps aux to find processes consuming the most memory.

1. ps aux Command

   ps aux --sort=-%mem | head

This command lists the top memory-consuming processes.

2. htop Command

• htop provides an interactive way to monitor and easily terminate processes.

How to Kill a Process

After identifying the Process ID (PID), use the following command:

sudo kill -9 <PID>

4. Using Automated Memory Management Tools

4.1 Setting Up zRAM

What is zRAM?

zRAM is a technique that uses compressed memory to virtually increase RAM. It is faster than disk-based swap and helps efficiently resolve memory shortages.

Installing and Configuring zRAM

1. Install zRAM
   Ubuntu provides an official zRAM configuration tool.

   sudo apt install zram-config

2. Check zRAM Status
   Once installed, zRAM is automatically enabled. Verify using:

   swapon --show

If /dev/zram0 appears in the output, zRAM is active.

4.2 Creating an Automatic Memory Cleanup Script

Simple Script

You can create a shell script to automate memory cleanup.

1. Script Content

   #!/bin/bash
   sync && echo 3 > /proc/sys/vm/drop_caches
   echo "Memory cleared: $(date)"

2. Save the Script
   Save the file as memory_cleanup.sh.

   nano ~/memory_cleanup.sh

3. Make the Script Executable

   chmod +x ~/memory_cleanup.sh

4. Run the Script

   sudo ~/memory_cleanup.sh

5. Important Considerations

5.1 Understanding Cache Deletion Effects

• Clearing cache may temporarily slow down the system.
• For database servers or environments with frequent file access, clearing cache can be counterproductive.

5.2 Managing Swap Space

• Frequent swap usage increases disk I/O and lowers system responsiveness.

6. FAQ

Q1. Do I need to free up memory frequently?

A: No, Ubuntu automatically manages memory, and manual intervention is usually unnecessary.

Q2. Does clearing cache slow down my system?

A: It may temporarily slow down as the system reloads data.

Q3. Will increasing swap improve performance?

A: It prevents crashes but may slow performance due to disk access.

7. Conclusion

We covered various ways to free up memory in Ubuntu. Understanding memory management and using proper tools can significantly improve system performance.

• Learned how memory works
• Implemented cache clearing and swap optimization
• Utilized zRAM and automation scripts

By monitoring your system and applying these techniques, you can maintain optimal performance in Ubuntu.