User data

Last update: September 26 2024

User data

User data — user configuration parameters of the server operating system. They are described as scripts in cloud-config format (text files with YAML syntax) or as a bash script. The scripts are automatically Base64 encoded, transferred to the server, and executed by the cloud-init agent when the operating system is first started. The use of user data helps automate server configuration.

Specify user data can be done at the operating system installation stage.

Read more about cloud-config and bash script formats in the instructions User data formats cloud-init documentation.

In scripts, you can pass both individual operating system configuration parameters and entire sequences of parameters. For example:

• time zone;
• create a directory and upload files to it;
• update repositories and install packages;
• place an SSH key on the server;
• configure the domain name resolver configuration file resolv.conf.

Check out the other examples in the manual Cloud config examples cloud-init documentation.

Specify user data⁠

You can only specify user data when installing the Linux operating system by auto-installation. The script text is added to the field User data.

After the automatic installation is complete, the text in the field User data can't be changed.

The maximum size of a script with data that is not Base64 encoded is 16 KB.

Examples of user data⁠

Set time zone⁠

Cloud-config

An example script for setting the Europe/Moscow time zone:

#cloud-config

timezone: Europe/Moscow

Bash script

An example script for setting the Europe/Moscow time zone:

#!/bin/bash

timedatectl set-timezone Europe/Moscow

Create a directory and upload files to it⁠

Cloud-config

An example script to create a directory and upload a file to it over the network:

#cloud-config

runcmd:
- mkdir /run/newdir
- [ wget, "http://example.com", -O, /run/newdir/index.html ]

Bash script

An example script to create a directory and upload a file to it over the network:

#!/bin/bash
mkdir /run/newdir
wget http://example.com -O /run/newdir/index.html

Update repositories and install packages⁠

Cloud-config

Sample script to install pwgen and pastebinit:

#cloud-config

package_update: true
packages:
- pwgen
- pastebinit

Bash script

Sample script to install pwgen and pastebinit:

#!/bin/bash
apt update
apt install pwgen pastebinit

Place the SSH key on the server⁠

Cloud-config

Sample script:

#cloud-config

ssh_authorized_keys:
 - ssh-rsa AAAAB3N…V7NZ user1@host
 - ssh-rsa AAAAB3N…NtHw== user2@server

Bash script

Sample script:

#!/bin/bash
echo "ssh-rsa AAAAB3N…V7NZ user1@host" >> /root/.ssh/authorized_keys
echo "ssh-rsa AAAAB3N…NtHw== user2@server" >> /root/.ssh/authorized_keys

Customize the configuration file⁠

Cloud-config

Sample script for the resolv.conf domain name resolver:

#cloud-config

manage_resolv_conf: true
resolv_conf:
 nameservers: ['4.4.4.4', '8.8.8.8']
 searchdomains:
   - foo.example.com
   - bar.example.com
 domain: example.com
 options:
   rotate: true
   timeout: 1

Bash script

Sample script for the resolv.conf domain name resolver:

#!/bin/bash
cat <<EOF > /etc/resolv.conf
domain example.com
nameserver 4.4.4.4
nameserver 8.8.8.8
search foo.example.com bar.example.com
options rotate
options timeout:1
EOF

Disable internet access⁠

Bash script

Sample script:

#!/bin/bash
ip addr show
public_interface=$(ip -4 addr show | awk '/inet/ && !/127.0.0.1/ && !/192\.0\.2\.0/ && !/10\./ && !/198\.(1[6-9]|2[0-9]|3[0-1])\./ && !/192\.168\./ {print $NF}')
if [ -n "$public_interface" ]; then
  ip link set down dev "$public_interface"
else
  echo "Public interface not found."
fi

Python script

Sample script:

#!/usr/bin/env python3
import subprocess
import re
import logging
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
def disable_public_interface():
  logging.info('Starting disable_public_interface function.')
  output = subprocess.check_output('ip -4 addr show', shell=True).decode('utf-8')
  interfaces = re.findall(r'^\d+: (\S+):.*?\n(?:.*\n)*?\s+inet (\d+\.\d+\.\d+\.\d+)/\d+', output, re.MULTILINE)
  public_interfaces = []
  for iface, ip in interfaces:
    if iface == 'lo':
      continue
    if re.match(r'^(127\.|10\.|198\.(1[6-9]|2[0-9]|3[0-1])\.|192\.168\.)', ip):
      continue
    public_interfaces.append(iface)
  for interface in public_interfaces:
    command = ['ip', 'link', 'set', 'dev', interface, 'down']
    try:
      subprocess.run(command, check=True)
      logging.info(f'Successfully disabled interface: {interface}')
    except subprocess.CalledProcessError as e:
      logging.error(f'Failed to disable interface: {interface}, error: {e}')
if __name__ == "__main__":
 logging.info('Script started.')
 disable_public_interface()
 lo gging.info('Script finished.')