How To Check Memory Usage By User In Linux?

Published September 3, 2024

Problem: Monitoring Memory Usage per User

Linux systems often need to track memory use for each user. This information helps system administrators find users who use a lot of resources and improve system performance. Checking memory usage by user in Linux helps manage resources well and prevent memory-related problems.

Methods to Check Memory Usage by User

Using the Command Line Interface

Linux has command-line tools to check memory usage by user:

PS command with AWK: This combination gathers memory usage information for each user. PS provides process data, while AWK processes and formats the output.
Top command: This system monitor shows system processes, including memory usage. You can configure it to show user-specific information.
Free command: While not showing per-user data, Free provides an overview of system memory usage, which can be useful with other tools.

Tip: Using PS with AWK

To check memory usage by user with PS and AWK, use this command:

ps aux | awk '{print $1, $4}' | sort | uniq -c | sort -n

This command lists users, their memory usage percentage, and the number of processes.

Using System Monitoring Tools

For a more user-friendly approach, you can use system monitoring tools:

htop: An interactive process viewer that shows processes and their resource usage, including memory. You can sort and filter by user.
glances: A cross-platform monitoring tool that shows system resources. It can display per-user memory usage in an easy-to-read format.
nmon: This tool offers system performance statistics, including memory usage. You can configure it to show user-specific data.

These methods and tools provide ways to monitor memory usage by user in Linux, suiting different needs and preferences.

Step-by-Step Guide: PS Command with AWK

Preparing the Command

The PS and AWK combination is a useful way to check memory usage by user in Linux. This method uses PS to gather process information and AWK to process and format the output.

Here's the command we'll use:

ps hax -o rss,user | awk '{a[$2]+=$1;}END{for(i in a)print i" "int(a[i]/1024+0.5);}' | sort -rnk2

Let's break down the parts:

ps hax -o rss,user: This runs PS to show the Resident Set Size (RSS) and username for each process.
awk '{a[$2]+=$1;}END{for(i in a)print i" "int(a[i]/1024+0.5);}': AWK adds up the RSS for each user and converts it to megabytes.
sort -rnk2: This sorts the output by memory usage in descending order.

Tip: Understanding RSS

RSS (Resident Set Size) represents the portion of a process's memory that is held in RAM. It's a good indicator of the actual physical memory used by a process, making it useful for tracking memory usage per user.

Executing the Command

To run this command:

Open a terminal on your Linux system.
Copy and paste the command.
Press Enter to execute it.

The output will look like this:

mysql 1566
joshua 1186
tomcat 353
root 28
wwwrun 12

This shows each user and their total memory usage in megabytes, sorted from highest to lowest.

Customizing the Output

You can change the command to modify the output:

To sort by username instead of memory usage, change sort -rnk2 to sort -k1.
To filter for a specific user, add | grep username at the end of the command.

For a more readable output, use this version:

echo "USER RSS PROCS" ; echo "-------------------- -------- -----" ; ps hax -o rss,user | awk '{rss[$2]+=$1;procs[$2]+=1;}END{for(user in rss) printf "%-20s %8.0f %5.0f\n", user, rss[user]/1024, procs[user];}' | sort -rnk2

This command adds headers and shows the number of processes for each user.

By using these PS and AWK commands, you can get a clear view of memory usage by user on your Linux system.

Alternative Solution: Using Top Command

Configuring Top for User-Specific Memory Usage

The Top command is a tool for checking memory usage by user in Linux. Here's how to use it:

Launch Top:
1. Open a terminal window.
2. Type top and press Enter.
3. The Top interface will show real-time system information.
Customize the display:
1. Press 'f' to enter the field management screen.
2. Use arrow keys to move to 'USER' and press space to select it.
3. Press 'q' to return to the main display.
4. Press 'u' and enter a username to filter processes for a specific user.
5. Use '<' and '>' keys to sort columns. Sort by '%MEM' to see high memory users.

Tip: Refresh Rate Adjustment

To adjust the refresh rate of Top, use the 's' command followed by the number of seconds. For example, 's 5' will refresh the display every 5 seconds, allowing for more stable observation of memory usage trends.

Reading and Analyzing Top Output

Understand memory metrics:
1. '%MEM': Shows the percentage of physical memory used by each process.
2. 'RES': Displays the resident memory size (non-swapped physical memory) in KB.
3. 'VIRT': Indicates the total amount of virtual memory used by the process.
Identify high-memory users:
1. Look at the '%MEM' column to spot processes using a lot of memory.
2. Check the 'USER' column to see which user owns these high-memory processes.
3. Use the 'k' command followed by the Process ID (PID) to terminate a process if needed.

Top provides a dynamic view of system resource usage, making it easier to spot memory-intensive processes and the users running them. This real-time monitoring can help identify memory issues as they occur.

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