Troubleshoot high memory usage on Linux instances - - Alibaba Cloud Documentation Center

Symptoms

High memory usage on a Linux instance can cause the following symptoms:

The system is sluggish, service response times increase, and application performance degrades.
In the ECS console, you notice high memory usage on the instance. A memory usage percentage greater than 80% is generally considered high.
You receive an alert that memory usage has exceeded the configured threshold.

Possible causes

Common causes of high memory usage include:

Abnormal processes or services are consuming a large amount of memory.
The workload from your applications is too high, and the instance's physical memory is insufficient for the workload.

Procedure

Check memory usage with top

Follow these steps to resolve the high memory usage.

Connect to the ECS instance. For more information, see Connect to a Linux instance by using an SSH key pair.

Identify the processes that are consuming a large amount of memory.

Run the following command to view CPU, memory, and other resource usage by process.

top

Note

You can press the lowercase letter q to exit the top command.

Press M to sort processes by their memory usage. The following example shows that the process with PID 13183 is consuming the most memory.

The following tables describe the system summary and process metric fields.

Fields in the system information summary and process list

Fields in the system information summary

Field (row)	Description
top	General system information. The current time. up: the system uptime. user: the number of active users. load average: the average run queue length over the previous 1, 5, and 15 minutes.
Tasks	Process statistics by state. total: the total number of processes. running: the number of running processes. sleeping: the number of sleeping processes. stopped: the number of stopped processes. zombie: the number of zombie processes.
%Cpu(s)	CPU utilization breakdown. us: the percentage of CPU time spent running user processes. sy: the percentage of CPU time spent running kernel processes. ni: the percentage of CPU time spent running user processes prioritized by using the nice command. id: the percentage of time for which the CPU remains idle. wa: the percentage of CPU time spent waiting for I/O. hi: the percentage of CPU time spent servicing hardware interrupts. si: the percentage of CPU time spent servicing software interrupts. st: the steal time.
MiB Mem	Memory usage statistics. total: total physical memory. free: available memory. used: used memory. buff/cache: memory used for kernel cache and buffers.
MiB Swap	Swap usage statistics. total: total swap space. free: available swap space. used: used swap space. avail Mem: estimated available memory for starting new applications.

Fields in the process list

Field (column)	Description
PID	The PID.
USER	The username of the process owner.
PR	The scheduling priority of the process. A smaller value indicates a higher priority.
NI	The priority specified by the nice command for the process.
VIRT	The amount of virtual memory used by the process.
RES	The amount of physical memory used by the process.
SHR	The amount of shared memory used by the process.
S	Process status. R: running S: sleeping Z: zombie D: uninterruptible sleep T: traced or stopped
%CPU	CPU usage percentage of the process.
%MEM	Physical memory usage percentage of the process.
TIME+	Total CPU time used by the process.
COMMAND	Command that started the process.

Resolve high memory usage

The following table lists common causes of high memory usage and how to resolve them.

Problem description	Cause	Solution
A process consumes excessive memory over an extended period.	An abnormal program or process is consuming excessive memory.	Use the `top` utility to find the PID of the memory-intensive program and terminate the process using one of the following methods: Warning Before you terminate a process, make sure that you understand what the process does to prevent unplanned service interruptions. Run the `sudo kill -15 <PID>` command to terminate the process. Terminate the process in the interactive mode of the `top` command. For more information, see Terminate a process by PID. If you suspect the process is malicious, perform virus detection and removal.
A normal process consumes a large amount of memory for an extended period.	The process is legitimate but consumes excessive memory during operation.	If the instance is experiencing a memory bottleneck, choose a strategy based on your business needs. Change the instance type. For more information, see Change the instance type. Optimize your application.
A process experiences occasional, brief memory spikes.	Traffic spikes or scheduled tasks cause a short-term memory surge.	Workaround: You can configure a swap partition to mitigate this issue. For more information, see How do I configure a swap partition for a Linux instance?. Solution: Change the instance type. For more information, see Change the instance type.
No single program or process is consuming a large amount of memory, but the overall memory usage is high.	The memory required for normal operation on the instance exceeds the configured memory size of the instance.	If the instance has a memory bottleneck, change the instance type. For more information, see Change the instance type.

References

For information about how to troubleshoot and resolve high memory usage on Windows instances, see Troubleshoot and resolve high memory usage on Windows instances.
If you need to collect memory metrics in advance for anomaly analysis, you can use the atop utility. For more information, see Monitor Linux system metrics with atop.