When automating infrastructure tasks, we often need to wait for a host to become available before proceeding with subsequent operations. The standard ping command in Linux doesn't have a built-in "ping until available" feature, but we can implement this logic in a bash script.

Here's a simple yet effective approach using a while loop:

while ! ping -c 1 target_host &> /dev/null
do
    echo "Host unreachable - retrying in 2 seconds..."
    sleep 2
done
echo "Host is now reachable!"

For production scripts, we should add a timeout mechanism to prevent infinite loops:

MAX_ATTEMPTS=30
ATTEMPT=0

while ! ping -c 1 -W 1 target_host &> /dev/null
do
    ATTEMPT=$((ATTEMPT+1))
    echo "Attempt $ATTEMPT/$MAX_ATTEMPTS - host not responding"
    
    if [ $ATTEMPT -eq $MAX_ATTEMPTS ]; then
        echo "Maximum attempts reached - aborting"
        exit 1
    fi
    
    sleep 2
done
echo "Host is now reachable!"

Sometimes you need to wait for DNS resolution first. This modified version checks both DNS and ping:

while ! getent hosts target_host > /dev/null 2>&1 || \
      ! ping -c 1 -W 1 target_host > /dev/null 2>&1
do
    sleep 1
done

For more robust checking of specific services (not just ICMP), consider using nc (netcat):

until nc -zv target_host 22 2>/dev/null
do
    sleep 1
done
echo "SSH port is now open"

Always include proper error handling in your scripts:

ping_host() {
    local host=$1
    local max_attempts=${2:-30}
    
    for ((i=1; i<=max_attempts; i++)); do
        if ping -c 1 -W 1 "$host" &> /dev/null; then
            echo "Host $host is reachable"
            return 0
        fi
        sleep 1
    done
    
    echo "ERROR: Host $host not reachable after $max_attempts attempts" >&2
    return 1
}

# Usage example:
ping_host "example.com" || exit 1

When automating processes in Linux, we often need to wait for a host to become available before proceeding with subsequent operations. A common scenario is waiting for a server to finish booting before running configuration scripts or deployment processes.

The simplest approach uses a while loop with ping:

while ! ping -c 1 hostname &> /dev/null
do
    echo "Host not available, waiting..."
    sleep 1
done
echo "Host is now reachable!"

For production scripts, we should add a timeout to prevent infinite waiting:

#!/bin/bash

HOST="example.com"
TIMEOUT=60
INTERVAL=1
COUNT=0

while ! ping -c 1 $HOST &> /dev/null
do
    sleep $INTERVAL
    COUNT=$((COUNT+1))
    echo "Waiting for $HOST to become reachable ($COUNT seconds elapsed)..."
    
    if [ $COUNT -ge $TIMEOUT ]; then
        echo "Timeout reached while waiting for $HOST"
        exit 1
    fi
done

echo "$HOST is now reachable"
# Continue with your script here

For enterprise environments, consider this more robust version with error handling:

#!/bin/bash

set -euo pipefail

TARGET_HOST=${1:-localhost}
MAX_ATTEMPTS=120
SLEEP_INTERVAL=5

wait_for_host() {
    local attempts=0
    until ping -c 1 -W 1 "$TARGET_HOST" &> /dev/null; do
        attempts=$((attempts + 1))
        if [ $attempts -ge $MAX_ATTEMPTS ]; then
            echo "Error: $TARGET_HOST not reachable after $MAX_ATTEMPTS attempts" >&2
            return 1
        fi
        sleep $SLEEP_INTERVAL
    done
    echo "$TARGET_HOST is now reachable"
}

if wait_for_host; then
    # Proceed with your operations
    echo "Starting main operations..."
else
    exit 1
fi

For more sophisticated host availability checks, consider these alternatives:

# Using nc (netcat) for port checking
until nc -zv hostname 22 &> /dev/null; do sleep 1; done

# Using curl for web services
until curl --silent --fail http://hostname/ &> /dev/null; do sleep 1; done

When working with systemd services, you can use ExecStartPre to implement host waiting:

[Unit]
Description=My Service
After=network.target

[Service]
ExecStartPre=/bin/bash -c 'until ping -c 1 hostname; do sleep 1; done'
ExecStart=/path/to/your/script
Restart=on-failure

[Install]
WantedBy=multi-user.target