Cron Jobs & Task Scheduling ⏰

# A cron line has FIVE time fields, then the command to run.
# Read them left to right:
#
#   ┌───────────── minute        (0 - 59)
#   │ ┌─────────── hour          (0 - 23)
#   │ │ ┌───────── day of month  (1 - 31)
#   │ │ │ ┌─────── month         (1 - 12)
#   │ │ │ │ ┌───── day of week    (0 - 6, Sunday = 0)
#   │ │ │ │ │
#   * * * * *  command to run

# * means "every".  */5 means "every 5th".  1-5 is a range.  1,15 is a list.

* * * * *      echo "runs every minute"
*/5 * * * *    echo "runs every 5 minutes"
0 * * * *      echo "runs at minute 0 of every hour"
0 9 * * 1-5    echo "runs at 09:00, Monday to Friday"
30 2 * * 0     echo "runs at 02:30 every Sunday"
0 0 1 * *      echo "runs at midnight on the 1st of each month"

# Cron does not "print" anything itself — it just launches the command
# at the scheduled time. The five fields above decide WHEN.
#
# Quick reads of the lines above:
#   * * * * *     -> every minute
#   */5 * * * *   -> every 5 minutes
#   0 * * * *     -> top of every hour
#   0 9 * * 1-5   -> weekdays at 9 AM
#   30 2 * * 0    -> Sundays at 2:30 AM
#   0 0 1 * *     -> first day of every month, midnight

# Open YOUR personal crontab in an editor:
crontab -e

# ...then add lines like these. ALWAYS use absolute paths in cron —
# cron runs with a bare environment, so "php" or "./script.php" may not resolve.

# Run a PHP CLI script every night at 02:30, logging everything to a file.
# >> appends stdout to the log;  2>&1 sends stderr (errors) to the same place.
30 2 * * * /usr/bin/php /var/www/app/backup.php >> /var/log/app/backup.log 2>&1

# Every 5 minutes, but never let two copies overlap (see flock below).
*/5 * * * * /usr/bin/flock -n /tmp/poll.lock /usr/bin/php /var/www/app/poll.php >> /var/log/app/poll.log 2>&1

# Set PATH and MAILTO at the top of the crontab if your scripts need them:
# PATH=/usr/local/bin:/usr/bin:/bin
# MAILTO=ops@example.com

# Other useful commands:
crontab -l      # list the current user's jobs
crontab -r      # remove ALL jobs for the user (careful!)

# crontab -e opens vi/nano; saving installs the schedule immediately.
# crontab -l then shows what is installed:

30 2 * * * /usr/bin/php /var/www/app/backup.php >> /var/log/app/backup.log 2>&1
*/5 * * * * /usr/bin/flock -n /tmp/poll.lock /usr/bin/php /var/www/app/poll.php >> /var/log/app/poll.log 2>&1

# After 02:30, tail the log to confirm it ran:
#   $ tail -n 2 /var/log/app/backup.log
#   [2026-06-16 02:30:01] Backup started
#   [2026-06-16 02:30:04] Backup OK: 45MB written

<?php
// backup.php — a PHP script meant to be run from the COMMAND LINE by cron,
// not requested through a browser. Run it yourself with:  php backup.php
//
// php_sapi_name() tells you HOW PHP was started. From cron it is "cli".
if (php_sapi_name() !== 'cli') {
    exit("Run this from the command line, not the web.\n");
}

// A timestamped logger so every line in the log file is traceable.
function logLine(string $msg): void {
    $stamp = date('Y-m-d H:i:s');     // e.g. 2026-06-16 02:30:01
    echo "[{$stamp}] {$msg}\n";       // cron redirects this echo into the log file
}

logLine('Backup started');

// Do the real work. Pretend we copied the database to a file.
$bytes  = 47185920;                    // 45 MB, as bytes
$sizeMb = round($bytes / 1024 / 1024); // -> 45

logLine("Backup OK: {$sizeMb}MB written");

// Exit code 0 = success. Cron records a non-zero code as a failed run.
exit(0);

[2026-06-16 02:30:01] Backup started
[2026-06-16 02:30:04] Backup OK: 45MB written

<?php
// poll.php — runs every 5 minutes from cron. But what if one run takes
// 7 minutes? Without protection, a second copy starts on top of the first.
//
// A file LOCK fixes this: the first run grabs the lock; later runs that
// can't grab it simply exit. (You can also do this in the cron line with
// the 'flock' command — both approaches are shown in this lesson.)

$lockFile = '/tmp/poll.lock';
$handle   = fopen($lockFile, 'c');                 // open (create if missing)

// LOCK_EX = exclusive lock, LOCK_NB = non-blocking (don't wait — fail fast).
if (!flock($handle, LOCK_EX | LOCK_NB)) {
    echo "Another run is still going — skipping this one.\n";
    exit(0);                                        // not an error, just busy
}

echo "Lock acquired — doing the work...\n";
// ... real work happens here ...
echo "Work done.\n";

flock($handle, LOCK_UN);                            // release the lock
fclose($handle);

Lock acquired — doing the work...
Work done.

# If a second copy starts while the first still holds the lock, it prints:
#   Another run is still going — skipping this one.

# 🎯 YOUR TURN — write ONE cron line.
# Goal: run  /usr/bin/php /var/www/app/report.php  every weekday at 6:45 AM,
# appending all output (and errors) to /var/log/app/report.log
#
# Fill in each ___ . Remember the field order:
#   minute hour day-of-month month day-of-week  command

# 1) minute  -> 45
# 2) hour    -> 6  (24-hour clock)
# 3) dom     -> *  (any day of month)
# 4) month   -> *  (any month)
# 5) dow     -> 1-5 (Monday through Friday)

___ ___ * * ___ /usr/bin/php /var/www/app/report.php >> /var/log/app/report.log 2>&1

# 👉 replace the three ___ with  45  ,  6  , and  1-5
# ✅ Expected line:
#    45 6 * * 1-5 /usr/bin/php /var/www/app/report.php >> /var/log/app/report.log 2>&1

45 6 * * 1-5 /usr/bin/php /var/www/app/report.php >> /var/log/app/report.log 2>&1

<?php
// 🎯 YOUR TURN — make this cron script log WITH timestamps.
// Fill in each ___ , then run it with:  php cleanup.php

function logLine(string $msg): void {
    $stamp = ___;                 // 👉 use date('Y-m-d H:i:s') for the timestamp
    echo "[{$stamp}] {$msg}\n";   // cron will redirect this into the log file
}

___("Cleanup started");           // 👉 call your logLine() function
$deleted = 12;                    // pretend we removed 12 stale files
___("Removed {$deleted} files");  // 👉 log the result the same way

// ✅ Expected output (timestamp will differ):
//    [2026-06-16 03:00:00] Cleanup started
//    [2026-06-16 03:00:00] Removed 12 files

[2026-06-16 03:00:00] Cleanup started
[2026-06-16 03:00:00] Removed 12 files

<?php
// In Laravel you define schedules in code (routes/console.php or a Schedule
// class), so timing lives in version control — not a crontab nobody can find.

use Illuminate\Support\Facades\Schedule;

// Run an Artisan command on weekdays at 06:45, without overlapping runs.
Schedule::command('report:send')
    ->weekdaysAt('06:45')
    ->withoutOverlapping()           // built-in flock-style guard
    ->appendOutputTo('/var/log/app/report.log');

// You only need ONE real cron line on the server for ALL of the above:
//   * * * * * cd /var/www/app && php artisan schedule:run >> /dev/null 2>&1