Cron job spec to run Polkadot nodes in a crontab for a few mins every hour, enough to keep them synced.

polkadot-sync-cron

# create these functions in some bash file to be imported in the crontab
# crontab in macos is weird and cannot load normal zsh functions.
# cat ~/.shell_functions

function base_run_chain() {
        chain=$1
        port=$2
        sync=$3
        polkadot --chain $chain \
                --sync $sync \
                --database paritydb \
                --blocks-pruning 256 \
                --state-pruning 256 \
                --base-path ~/chains-data \
                --rpc-max-request-size 1000000 \
                --rpc-max-response-size 1000000 \
                --rpc-port $port
}

function run_chain() {
  base_run_chain $1 $2 "fast-unsafe"
}

function warp_chain() {
  base_run_chain $1 $2 "warp"
}

# ---------------------------------
# create file update-chians.sh somehwere with this content 
# cat ~/update-chains.sh

#! /bin/bash
source ~/.shell_functions
export -f run_chain
export -f base_run_chain
PATH=$PATH:where-you-have-polkadot-binaries

timeout $1m bash -c 'run_chain "$@"' _ polkadot 9999
timeout $1m bash -c 'run_chain "$@"' _ kusama 9998
timeout $1m bash -c 'run_chain "$@"' _ westend 9997

# ---------------------------------
# finally, in `crontab -e`, put: 
1 * * * * ~/update-chains.sh 3 2>&1 | while read line; do echo "$(date) == $line"; done > ~/cron.log