Elastic Compute Service:Configure a custom Linux image

Prerequisites

The image must meet the following requirements:

• The first partition (typically /dev/sda1 or /dev/vda1) has write permissions.

• The first partition uses FAT32, EXT2, EXT3, EXT4, or UFS as its file system.

  Note

  Run blkid /dev/sdXn to check the file system type. Replace /dev/sdXn with the actual first partition path, such as /dev/sda1.

• The image virtual size exceeds 5 GiB.

  Note

  Run df -h /dev/sdXn to check the partition space. Replace /dev/sdXn with the actual first partition path, such as /dev/sda1.

Procedure

1. Log on to the source virtual machine as the root user.

2. Create a directory named aliyun_custom_image in the root directory of the first partition.

   mkdir /aliyun_custom_image

   On first boot, Alibaba Cloud writes instance information, such as the hostname, root user password, and DNS server addresses, to the os.conf file in the aliyun_custom_image directory. The system creates os.conf automatically if it does not exist.

   Sample os.conf content:

   hostname=<yourHostName>
   password=<yourPassword>
   eth0_ip_addr=10.0.0.2
   eth0_mac_addr=00:xx:xx:xx:xx:23
   eth0_netmask=255.255.255.0
   eth0_gateway=10.0.0.1
   eth0_route="0.0.0.0/0 10.0.0.1"
   dns_nameserver="7.7.X.X 8.8.8.8"

   Parameters in the sample:

   Parameter	Description
   hostname	The instance hostname.
   password	The password of the root user.
   eth0_ip_addr	The IP address of the eth0 NIC.
   eth0_mac_addr	The MAC address of the eth0 NIC.
   eth0_netmask	The subnet mask of the eth0 NIC.
   eth0_gateway	The default gateway IP address of eth0.
   eth0_route	Internal routes for eth0. Space-separated.
   dns_nameserver	DNS server addresses. Space-separated.

3. Create a parsing script, such as a service file named customized-config.service, to read and apply system configurations from the os.conf file.

   This script runs on first boot to configure the hostname, root user password, DNS server addresses, and network settings.

   Sample script:

   #!/bin/bash
   
   ### BEGIN INIT INFO
   # Provides:          os-conf
   # Required-Start:    $local_fs $network $named $remote_fs
   # Required-Stop:
   # Should-Stop:
   # Default-Start:     2 3 4 5
   # Default-Stop:      0 1 6
   # Short-Description: The initial os-conf job, config the system.
   ### END INIT INFO
   
   first_partition_dir='/boot/'
   os_conf_dir=${first_partition_dir}/aliyun_custom_image
   os_conf_file=${os_conf_dir}/os.conf
   
   load_os_conf() {
       if [[ -f $os_conf_file ]]; then
           . $os_conf_file
           return 0
       else
           return 1
       fi
   }
   
   cleanup() {
       # ensure $os_conf_file is deleted, to avoid repeating config system
       rm $os_conf_file >& /dev/null
       # ensure $os_conf_dir exists
       mkdir -p $os_conf_dir
   }
   
   config_password() {
       if [[ -n $password ]]; then
           password=$(echo $password | base64 -d)
           if [[ $? == 0 && -n $password ]]; then
               echo "root:$password" | chpasswd
           fi
       fi
   }
   
   config_hostname() {
       if [[ -n $hostname ]]; then
           sed -i "s/^HOSTNAME=.*/HOSTNAME=$hostname/" /etc/sysconfig/network
           hostname $hostname
       fi
   }
   
   config_dns() {
       if [[ -n $dns_nameserver ]]; then
           dns_conf=/etc/resolv.conf
           sed -i '/^nameserver.*/d' $dns_conf
           for i in $dns_nameserver; do
               echo "nameserver $i" >> $dns_conf
           done
       fi
   }
   
   is_classic_network() {
       # vpc: eth0
       # classic: eth0 eth1
       grep -q 'eth1' $os_conf_file
   }
   
   config_network() {
       /etc/init.d/network stop
       config_interface eth0 ${eth0_ip_addr} ${eth0_netmask} ${eth0_mac_addr}
       config_route eth0 "${eth0_route}"
       if is_classic_network ; then
           config_interface eth1 ${eth1_ip_addr} ${eth1_netmask} ${eth1_mac_addr}
           config_route eth1 "${eth1_route}"
       fi
       /etc/init.d/network start
   }
   
   config_interface() {
       local interface=$1
       local ip=$2
       local netmask=$3
       local mac=$4
       interface_cfg="/etc/sysconfig/network-scripts/ifcfg-${interface}"
       cat << EOF > $interface_cfg
   DEVICE=$interface
   IPADDR=$ip
   NETMASK=$netmask
   HWADDR=$mac
   ONBOOT=yes
   BOOTPROTO=static
   EOF
   }
   
   config_default_gateway() {
       local gateway=$1
       sed -i "s/^GATEWAY=.*/GATEWAY=$gateway/" /etc/sysconfig/network
   }
   
   config_route() {
       local interface=$1
       local route="$2"
       route_conf=/etc/sysconfig/network-scripts/route-${interface}
       > $route_conf
       echo $route | sed 's/;/\n/' | \
           while read line; do
               dst=$(echo $line | awk '{print $1}')
               gw=$(echo $line | awk '{print $2}')
               if ! grep -q "$dst" $route_conf 2> /dev/null; then
                   echo "$dst via $gw dev $interface" >> $route_conf
               fi
               if [[ "$dst" == "0.0.0.0/0" ]]; then
                   config_default_gateway $gw
               fi
           done
   }
   
   ################## sysvinit service portal ####################
   
   start() {
       if load_os_conf ; then
           config_password
           config_network
           config_hostname
           config_dns
           cleanup
           return 0
       else
           echo "not load $os_conf_file"
           return 0
       fi
   }
   
   RETVAL=0
   
   case "$1" in
       start)
           start
           RETVAL=$?
       ;;
       *)
           echo "Usage: $0 {start}"
           RETVAL=3
       ;;
   esac
   
   exit $RETVAL

4. Enable the script to run on system startup.

   The following commands are for Ubuntu. Adjust for your operating system.

   sudo systemctl daemon-reload
   sudo systemctl enable customized-config.service

   Note

   Custom images created from a Customized Linux instance inherit this startup script. Alibaba Cloud applies os.conf settings only on first boot.

References

After configuration, select Customized Linux as the OS Version when you import the custom image.