Tuning network performance for your Linux environment

Before you use real-time runtime metrics collection, ensure that your Linux® environment can handle the data flow from real-time runtime metrics collection.

About this task

You can take the following actions to ensure that network performance on your Linux environment performs optimally.

Avoid Domain Name System (DNS) delays. This problem can manifest on z/TPF as a timeout condition on your first message analysis tool collection and potentially succeed on following collections.
Avoid overruns on the Linux socket receive buffer. This problem can occur on the z/TPF system in the form of a timeout condition on real-time runtime metrics collection data types.

Procedure

To avoid DNS delays, verify that your DNS settings list your preferred local DNS servers before public DNS servers.
1. View the contents of the file: /etc/resolv.conf
2. If your preferred local DNS servers are not listed first, modify the contents of the file to list your preferred local DNS servers first and save the file.
To prevent Linux socket receive buffer overruns, verify that the current receive buffer allocation of your socket is at least 4 MB or greater.
- If you use Docker, take any of the following actions:
  - If you want to change the value of the socket buffer temporarily, enter the following command:
```
sudo sysctl -w net.core.rmem_max=maxval
```
    maxval
    
    The socket buffer value that you want to set, for example, 4136960.
  - If you have permissions to update the sysctl system configuration files, complete the following steps:
    1. Change the value of the socket buffer by entering one of the following commands depending on the kind of system configuration file that you have:
      - sudo echo 'net.core.rmem_max=maxval' > /etc/sysctl.d/filename.conf
        
        maxval
        
        The socket buffer value that you want to set, for example, 4136960.
        
        filename.conf
        
        The name of the system configuration file, for example, 01-rmem_max.conf.
      - sudo echo 'net.core.rmem_max=maxval' > filename.conf
        
        maxval
        
        The socket buffer value that you want to set, for example, 4136960.
        
        filename.conf
        
        The name of the system configuration file, for example, 90-override.conf.
    2. Ensure that the system is updated with your change by entering the following command:
```
sudo sysctl --system
```
    3. Verify that the socket buffer value is updated by entering the following command:
```
sysctl net.core.rmem_max
```
      If the value is not updated, take the following action.
  - If the socket buffer value was not updated after taking the previous step and you have limited access to the sysctl system configuration files, complete the following steps:
    1. Move to the directory where the system configuration files are by entering the following command:
```
cd /etc/sysctl.d
```
    2. Take any of the following actions:
      - If a default system configuration file exists, modify the file by using your editing tool.
      - If a default system configuration file does not exist, create a new system configuration file. For example, enter the following command:
        touch filename.conf
        
        filename.conf
        
        The name of the system configuration file, for example, 90-override.conf or 01-rmem_max.conf.
    3. Change the value of the socket buffer by taking one of the following actions:
      - Enter the following command:
        sudo echo 'net.core.rmem_max= maxval' > /etc/sysctl.d/filename.conf
        
        maxval
        
        The value of the socket buffer that you want to set, for example, 4136960.
        
        filename.conf
        
        The name of the system configuration file, for example, 01-rmem_max.conf.
      - Manually edit the configuration file by adding the following line in your configuration file:
        net.core.rmem_max=maxval
        
        maxval
        
        The value of the socket buffer that you want to set, for example, 4123456.
    4. Verify that the socket buffer value is updated by entering the following command:
```
sysctl net.core.rmem_max
```
- If you use another system type that is not Docker, complete the following steps:
  1. Navigate to the directory where the system configuration files are by entering the following command. Ensure that you locate the correct system configuration file that your environment uses.
```
cd /etc/sysctl
```
  2. Edit the system configuration file to update the value of the socket buffer to 4 MB or larger.
  3. Verify that the socket buffer value is updated.
  4. If the socket buffer value is not updated, contact your IT manager regarding allocating resources.