Read the synopsis for the specific upgrade release at https://community.ui.com/releases.

Obtain the URL from the Download Links.

• Example, https://dl.ui.com/unifi/6.0.36/unifi_sysvinit_all.deb.

ssh ubnt@192.168.1.10
ubnt@192.168.1.10's password: 

cd /tmp
 
ls -l
 
rm unifi_sysvinit_all.deb
 
wget https://dl.ui.com/unifi/6.0.36/unifi_sysvinit_all.deb
 
sudo dpkg -i unifi_sysvinit_all.deb
 
rm unifi_sysvinit_all.deb 

unifi-os shell
 
rm /tmp/unifi_sysvinit_all.deb &> /dev/null; curl -o "/tmp/unifi_sysvinit_all.deb" https://dl.ui.com/unifi/6.0.36/unifi_sysvinit_all.deb && dpkg -i /tmp/unifi_sysvinit_all.deb && rm /tmp/unifi_sysvinit_all.deb

#!/bin/bash
 
https_url='https://dl.ui.com'
package_name='unifi_sysvinit_all.deb'
upgrade_log="${HOME}/ssh_upgrade.log"
 
# CLI opts
checksum=''
version=''
 
function cleanup
{
  echo "$(timestamp) Removing temp directory ${output_dir}" | tee -a "${upgrade_log}"
  rm -rf "${output_dir}"
}
 
function timestamp
{
  local __tstamp=$1
  local mytstamp=$(date '+%Y-%m-%d %H:%M:%S')
  if [[ "$__tstamp" ]]
  then
    eval $__tstamp="'${mytstamp}'"
  else
    echo "${mytstamp}"
  fi
}
 
function usage
{
  echo "Usage: $0 [-v <version>] [-c <sha256 checksum>]" 1>&2
  exit 1
}
 
# Get command line args
while getopts ":c:v:" opt
do
  case "${opt}" in
    c)
      checksum="${OPTARG}"
      ;;
    v)
      version="${OPTARG}"
      ;;
    *)
      usage
      ;;
  esac
done
shift $((OPTIND-1))
 
# Make sure required args are passed
if [ -z "${version}" ] || [ -z "${checksum}" ]
then
  usage
fi
 
# Make sure checksum looks like a sha256 hash
if ! [[ ${checksum} =~ ^[0-9a-f]{64}$ ]]
then  
  echo "$(timestamp) Error: checksum must be a sha256 hash string" | tee -a "${upgrade_log}"
  exit 1
fi
 
# Get currently installed unifi package version
current_ver=$(dpkg -s unifi | grep '^Version:' | grep -o -E '[0-9]+\.[0-9]+\.[0-9]+')
target_ver=$(echo "${version}" | grep -o -E '[0-9]+\.[0-9]+\.[0-9]+')
 
# Don't bother upgrading to same version as installed
if [ "${current_ver}" = "${target_ver}" ]
then
  echo "$(timestamp) Error: Current controller version and target controller version are the same (${current_ver})" | tee -a "${upgrade_log}"
  exit 1
fi
 
# Create a temp dir to store downloads
if ! output_dir=$(mktemp -d -t unifi_${version}_$(date +%Y-%m-%d-%H-%M-%S)_XXXXXXXXXX)
then
  echo "$(timestamp) Error: Failed to create output directory" | tee -a "${upgrade_log}"
  exit 1
fi
trap cleanup 0
 
# Download package
echo "$(timestamp) Downloading ${https_url}/unifi/${version}/${package_name}" | tee -a "${upgrade_log}"
cd "${output_dir}" && wget -O "${output_dir}/${package_name}" "${https_url}/unifi/${version}/${package_name}"
retval=$?
if [[ ! ${retval} -eq 0 ]]
then
  echo "$(timestamp) Error: wget exited with error ${retval}" | tee -a "${upgrade_log}"
  exit 1
fi
 
# Verify package checksum
echo "${checksum} ${output_dir}/${package_name}" > "${output_dir}/${package_name}.sha256"
if [ -f "${output_dir}/${package_name}.sha256" ]
then
  echo "$(timestamp) Checking downloaded file integrity..." | tee -a "${upgrade_log}"
  if ! shasum -c "${output_dir}/${package_name}.sha256" -a 256 -s
  then
    echo "$(timestamp) Error: File failed integrity check" | tee -a "${upgrade_log}"
    exit 1
  else
    echo "$(timestamp) File passed integrity check, performing package update" | tee -a "${upgrade_log}"
    dpkg --debug=1 --install "${output_dir}/${package_name}" | tee -a "${upgrade_log}"
  fi
else
  echo "$(timestamp) Error: Cannot verify downloaded file integrity (missing checksum)" | tee -a "${upgrade_log}"
  exit 1
fi
 
echo "$(timestamp) Done." | tee -a "${upgrade_log}"
exit 0

Run it as:

./ssh_upgrade.sh -v 6.0.26-dfb550c0bf -c b4496144e3a9feb4a6779622611407b59d5cd48b8379c0c81525776aa068ffb0

https://help.ui.com/hc/en-us/articles/216655518-UniFi-UDM-UCK-How-to-Change-the-Controller-Version-Using-SSH-

https://help.ui.com/hc/en-us/articles/216655518