How to adjust the limits system parameters of Linux instances -

Introduction

The /etc/security/limits.conf configuration file of the Linux can be used to limit system resources. You can use the configuration file to limit the number of files, threads, memory, and other resource usage to improve system stability. The nofile parameter indicates the maximum number of files opened by all users in the system. The value /proc/sys/fs/nr_open parameter indicates the maximum number of files that a single process can allocate to the system. If the value of the nofile parameter in the system exceeds the value of the nr_opn parameter, the instance may not be connected remotely. This article describes how to modify the value of the limits.conf parameter in the nofile configuration file.

Background

Alibaba Cloud reminds you that:

Before you perform operations that may cause risks, such as modifying instance configurations or data, we recommend that you check the disaster recovery and fault tolerance capabilities of the instances to ensure data security.

You can modify the configurations and data of instances including but not limited to Elastic Compute Service (ECS) and Relational Database Service (RDS) instances. Before the modification, we recommend that you create snapshots or enable RDS log backup.

If you have authorized or submitted sensitive information such as the logon account and password in the Alibaba Cloud Management Console, we recommend that you modify such information in a timely manner.

Detach the system disk of the abnormal ECS instance and attach the disk as a data disk to a normal ECS instance. For more information, seehow to log on to an abnormal system disk by attaching a data disk to an ECS instance. For more information, see Step 1 to step 4.
Log on to a normal ECS instance and run the following command to edit the configuration file /etc/security/limits.conf.
```
vim /etc/security/limits.conf
```
In the configuration file section, find the root soft nofile and root hard nofile parameters and set them to the following values: After the settings are complete, press Shift+: Key, then Enter the wq, and finally Press the Enter key to save and exit.
```
root soft nofile 65535
root hard nofile 65535
```
Note:
- soft nofile: The Warning value of the number of files opened by the user. It is recommended that you modify it to the default value of 65535. If you understand the role of this system parameter, you can also modify it to the expected value according to your needs. For more information about this parameter, see more information.
- hard nofile: the actual threshold of the number of files opened by users. If the number of files opened by users exceeds this parameter value, an error is reported. We recommend that you change the default value to 65535. If you understand the function of this system parameter, you can change it to the expected value according to your needs. For more information about this parameter, see more information.
- This method takes effect permanently after you set parameters. If you need to temporarily set the nofile parameter, you can use the uitit-n}#nofile] command to set the nofile parameter.
See step 5 "how to log on to an abnormal system disk by using an ECS instance as a data disk to restore the system disk of an abnormal ECS instance."
Remotely log on to the repaired ECS instance and make sure that it is working properly again.

References

Notes for soft nofile
The value of softnofile cannot be greater than the value of hardnofile.
hard nofile notes
The hardnofile value cannot be greater than the value of /proc/sys/fs/nr_open parameter. If the value of the nofile parameter is greater than the value of the nr_open parameter, the user may fail to log on to the instance.
In addition to resource parameter configurations, the Linux of a kernel parameter also determines the performance of the server to a certain extent. For more information about kernel parameter, see Introduction to common kernel network parameters of Linux instances and FAQ.

Application scope

Elastic Compute Service