Help Center/ Cloud Container Engine/ User Guide/ Nodes/ Node O&M/ Optimizing Node System Parameters/ Changing the Maximum Number of File Handles
Updated on 2026-06-16 GMT+08:00
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Changing the Maximum Number of File Handles

The maximum number of file handles is the maximum number of files that can be opened simultaneously. In Linux, there are two file handle limits. System-level: the maximum number of files that can be opened by all user processes at the same time. User-level: the maximum number of files that can be opened by a single user process. Containers have a third limit: the maximum number of file handles for a single process in the container.

  • Commands for modifying node system parameters are valid only when public images are used. For private images, the commands in this section are for reference only.
  • Directly logging in to a node to modify system parameters may cause changes to be lost during subsequent node reset or upgrade, affecting running services. Fully evaluate the risks before proceeding. Use a pre-installation script or post-installation script to modify the node parameters instead.

Changing the System-Level File Handle Limit

  1. Log in to the node and check the /etc/sysctl.conf file. 

    cat /etc/sysctl.conf

  2. Modify the fs.file-max parameter. fs.file-max=1048576 indicates the kernel parameter name and recommended value.

    • If fs.file-max is already set in sysctl.conf, run the following command to change the value: 
      sed -i "s/fs.file-max=[0-9]*$/fs.file-max=1048576/g" /etc/sysctl.conf && sysctl -p
    • If fs.file-max is not set in the sysctl.conf file, run the following command to add it: 
      echo fs.file-max=1048576 >> /etc/sysctl.conf && sysctl -p

  3. Check whether the returned value matches your configuration. If it does, the change is successful. 

    sysctl fs.file-max

    Information similar to the following is displayed:

    fs.file-max = 1048576

Changing the Single-Process File Handle Limit

  1. Log in to the node and view the /etc/security/limits.conf file. 

    cat /etc/security/limits.conf

    The maximum number of file handles for a single process of a node is specified by the following parameters:

    ...
root soft nofile 65535
root hard nofile 65535
* soft nofile 65535
* hard nofile 65535

  2. Run the sed command to change the maximum number of file handles. In the command, 65535 is the recommended maximum number of file handles. The /etc/security/limits.conf file on the EulerOS 2.3 node does not contain the default configuration related to nofile. Therefore, you cannot run the sed command to modify the configuration. 

    sed -i "s/nofile.[0-9]*$/nofile 65535/g" /etc/security/limits.conf

  3. Log in to the node again and check whether the modification is successful. If the returned value matches your configuration, the modification is successful. 

    ulimit -n

    Information similar to the following is displayed:

    65535

Changing the File Handle Limit for a Single Container Process

  1. Log in to the node and check the maximum number of file handles for a single container process.

    • CentOS/EulerOS:
      • Docker nodes: 
        cat /usr/lib/systemd/system/docker.service
      • containerd nodes: 
        cat /usr/lib/systemd/system/containerd.service
    • Ubuntu:
      • Docker nodes: 
        cat /lib/systemd/system/docker.service
      • containerd nodes: 
        cat /lib/systemd/system/containerd.service

    Parameter settings:

    ...
LimitNOFILE=1048576
LimitNPROC=1048576
...
    • LimitNOFILE specifies the maximum number of file handles a single process can open. When set to infinity, the effective limit is 1,048,576 file handles per container process.
    • LimitNPROC specifies the maximum number of processes a single user can run. If it is set to infinity, there is no limit on the number of processes.

  2. Modify both parameters. In the following command, 1048576 is the recommended maximum.

    Changing the maximum number of file handles of a container will restart the docker/containerd process.

    • CentOS/EulerOS:
      • Docker nodes: 
        sed -i "s/LimitNOFILE=[0-9a-Z]*$/LimitNOFILE=1048576/g" /usr/lib/systemd/system/docker.service;sed -i "s/LimitNPROC=[0-9a-Z]*$/LimitNPROC=1048576/g" /usr/lib/systemd/system/docker.service && systemctl daemon-reload && systemctl restart docker
      • containerd nodes: 
        sed -i "s/LimitNOFILE=[0-9a-Z]*$/LimitNOFILE=1048576/g" /usr/lib/systemd/system/containerd.service;sed -i "s/LimitNPROC=[0-9a-Z]*$/LimitNPROC=1048576/g" /usr/lib/systemd/system/containerd.service && systemctl daemon-reload && systemctl restart containerd
    • Ubuntu:
      • Docker nodes: 
        sed -i "s/LimitNOFILE=[0-9a-Z]*$/LimitNOFILE=1048576/g" /lib/systemd/system/docker.service;sed -i "s/LimitNPROC=[0-9a-Z]*$/LimitNPROC=1048576/g" /lib/systemd/system/docker.service && systemctl daemon-reload && systemctl restart docker
      • containerd nodes: 
        sed -i "s/LimitNOFILE=[0-9a-Z]*$/LimitNOFILE=1048576/g" /usr/lib/systemd/system/containerd.service;sed -i "s/LimitNPROC=[0-9a-Z]*$/LimitNPROC=1048576/g" /usr/lib/systemd/system/containerd.service && systemctl daemon-reload && systemctl restart containerd

  3. Check the maximum number of file handles of a single process in the container. If the returned value is the same as the modified value, the modification is successful.

    • Docker nodes: 
      cat /proc/`pidof dockerd`/limits | grep files

      Information similar to the following is displayed:

      Max open files            1048576              1048576              files
    • containerd nodes: 
      cat /proc/`pidof containerd`/limits | grep files

      Information similar to the following is displayed:

      Max open files            1048576              1048576              files

Automatically Configuring the Maximum Number of File Handles When Creating a Node or Node Pool

You can set the script to be executed after a node or node pool is created. When creating a node or node pool, you can use the script to configure the maximum number of file handles.

  1. Confirm the OS of the node or node pool to be created, for example, CentOS 7.6.
  2. Before applying the script, manually test the commands on nodes in the same cluster running the same OS.

  3. When creating a node or node pool, choose Advanced Settings > Post-installation script to add the commands. The commands must be verified as executable before configuration.

    • Change the maximum number of system-level file handles on a node.
      • Log in to the node and check the /etc/sysctl.conf file. If the value of fs.file-max has been set in the file, run the following command to change it: 
        sed -i "s/fs.file-max=[0-9]*$/fs.file-max=1048576/g" /etc/sysctl.conf && sysctl -p
      • Log in to the node and check the /etc/sysctl.conf file. If the value of fs.file-max is not set in the file, run the following command to add it: 
        echo fs.file-max=1048576 >> /etc/sysctl.conf && sysctl -p

      In this command, fs.file-max=1048576 indicates the kernel parameter name and recommended value.

    • Run the following command to change the maximum number of file handles for a single process on a node: 
      sed -i "s/nofile.[0-9]*$/nofile 65535/g" /etc/security/limits.conf

      In the preceding command, 65535 is the recommended maximum number of file handles.

    • Change the maximum number of file handles for a single process of a container.
      • CentOS/EulerOS: 
        sed -i "s/LimitNOFILE=[0-9a-Z]*$/LimitNOFILE=1048576/g" /usr/lib/systemd/system/docker.service;sed -i "s/LimitNPROC=[0-9a-Z]*$/LimitNPROC=1048576/g" /usr/lib/systemd/system/docker.service && systemctl daemon-reload && systemctl restart docker
      • Ubuntu: 
        sed -i "s/LimitNOFILE=[0-9a-Z]*$/LimitNOFILE=1048576/g" /lib/systemd/system/docker.service;sed -i "s/LimitNPROC=[0-9a-Z]*$/LimitNPROC=1048576/g" /lib/systemd/system/docker.service && systemctl daemon-reload && systemctl restart docker

      In the preceding command, 1048576 is the recommended maximum number of file handles.

    The command in the following figure is used only as an example. Change it as needed.

  4. After node creation, log in to the node and verify that the parameter was modified successfully.
Parent Topic: Optimizing Node System Parameters