2-Phases Backup with Unison

backup.prf

# Unison preferences file (Fast backup)

root = /home/xxxx/your-folder
root = ssh://target.host/your-folder

auto = true
batch = true

prefer = newer

ignore = Name venv
ignore = Name node_modules
ignore = Name .DS_Store

# Fast backup is fast, usually takes seconds. But may miss some file
fastcheck = true

backup_full.prf

# Unison preferences file (Full backup)

include backup

# Full backup is slow, usually takes minutes. But must be correct
fastcheck=false

backup_with_unison

#!/usr/bin/env bash

fast_backup_name="${1:-backup}"
slow_backup_name=("${2:-backup_full}")
unison_args=("${@:3}")

fast_backup_interval=600 # 10 mins for fast backup
slow_backup_interval=86400 # 1 day for slow backup

next_backup_type='Fast'

get_time() {
    date '+%s'
}

get_backup_name() {
    local backup_type="${1:-$next_backup_type}"
    if [[ "$backup_type" == 'Slow' ]]; then
        echo "$slow_backup_name"
    else
        echo "$fast_backup_name"
    fi
}

get_last_time_path() {
    local backup_type="${1:-$next_backup_type}"
    echo "$backup_path/.LastBackupTime.$backup_type.$host_name"
}

get_last_time() {
    local last_time="$(
        cat "$(get_last_time_path "$1")" 2>/dev/null \
        | sed -n 2p
    )"
    [[ -z "$last_time" ]] && echo "0" || echo "$last_time"
}

backup_path=$(
    cat ~/".unison/$(get_backup_name Fast).prf" \
    | grep 'root = ' \
    | head -1 \
    | awk -F' = ' '{print $2}'
)

min_wait_time=0
host_name=$(hostname)

while true; do
    now_time=$(get_time)

    fast_used_time=$(( "$now_time" - "$(get_last_time Fast)" ))
    fast_diff_time=$(( "$fast_backup_interval" - "$fast_used_time" ))

    slow_used_time=$(( "$now_time" - "$(get_last_time Slow)" ))
    slow_diff_time=$(( "$slow_backup_interval" - "$slow_used_time" ))

    # Take smaller between fast_diff_time and slow_diff_time
    diff_time=$(( "$fast_diff_time" < "$slow_diff_time" ? "$fast_diff_time" : "$slow_diff_time" ))
    next_backup_type=$([[ "$fast_diff_time" -lt "$slow_diff_time" ]] && echo "Fast" || echo "Slow")

    # At least 180 seconds until next backup
    sleep_time=$(( "$diff_time" > "$min_wait_time" ? "$diff_time" : "$min_wait_time" ))

    echo "Now sleep for $sleep_time seconds to run $next_backup_type backup type..."
    sleep "$sleep_time"

    yes '.' | tr -d '\n' | head -c $(tput cols)
    start_time=$(get_time)
    start_time_human=$(date '+%Y-%m-%d %H:%M:%S %Z %z')
    echo "Date: $start_time_human"
    echo "Type: $next_backup_type"
    echo

    old_time=$(cat "$(get_last_time_path)")

    echo -e "$start_time_human\n$start_time" > "$(get_last_time_path)"

    # The "meat"
    unison "$(get_backup_name)" "${unison_args[@]}"

    if [[ $? -ne 0 ]]; then
        # Restore the time if backup failed
        echo "$old_time" > "$(get_last_time_path)"
    fi

    now_time=$(get_time)
    used_time=$(( "$now_time" - "$start_time" ))

    echo
    echo "Used $used_time seconds."

    min_wait_time=180

done