Q: How do asterisks (*), commas (,), hyphens (-), and slashes (/) function as operators in crontab?

Each crontab operator modifies field evaluation: Wildcard (*) : Matches all valid values within the field range (e.g., every minute or every hour). Comma (,) : Defines a discrete value list (e.g., 1,15,30 triggers on the 1st, 15th, and 30th). Hyphen (-) : Defines an inclusive range (e.g., 9-17 in the hour column triggers hourly from 9 AM through 5 PM). Slash (/) : Defines an interval step across a range or wildcard (e.g., */5 in the minute column executes every 5 minutes). Advertisement

Q: What is the difference between user crontab (crontab -e) and system crontab (/etc/crontab)?

There is a crucial structural difference: User Crontab ( crontab -e ) : Contains 5 time fields followed directly by the shell command. The job automatically executes under that user's UID and privileges. System-wide Crontab ( /etc/crontab and /etc/cron.d/ ) : Contains 6 columns before the command . The 6th column explicitly defines the username (e.g., root , www-data , or postgres ) under which the script runs. Advertisement

Question 1

What are the 5 fields of a standard Linux crontab expression?

Accepted Answer

A standard Linux crontab entry contains 5 time and date fields separated by whitespace:

Minute (0–59): The minute of the hour when the job triggers.
Hour (0–23): The 24-hour clock hour (0 is midnight, 12 is noon, 23 is 11 PM).
Day of Month (1–31): Specific calendar day of the month.
Month (1–12 or Jan–Dec): Month of the year. Case-insensitive 3-letter abbreviations are permitted.
Day of Week (0–6 or Sun–Sat): Day of the week where both 0 and 7 represent Sunday.

Question 2

How do asterisks (*), commas (,), hyphens (-), and slashes (/) function as operators in crontab?

Accepted Answer

Each crontab operator modifies field evaluation:

Wildcard (*): Matches all valid values within the field range (e.g., every minute or every hour).
Comma (,): Defines a discrete value list (e.g., 1,15,30 triggers on the 1st, 15th, and 30th).
Hyphen (-): Defines an inclusive range (e.g., 9-17 in the hour column triggers hourly from 9 AM through 5 PM).
Slash (/): Defines an interval step across a range or wildcard (e.g., */5 in the minute column executes every 5 minutes).

Question 3

How does the Day of Month vs Day of Week boolean OR evaluation work in POSIX crontab?

Accepted Answer

In POSIX crontab specifications, if both Day of Month (field 3) and Day of Week (field 5) are specified with non-wildcard values , the cron daemon evaluates them as a logical OR condition , rather than an AND condition. For example, 0 0 1,15 * 1 will trigger at midnight on the 1st and 15th of the month , PLUS on every Monday of that month. To enforce a strict AND relationship, evaluate the calendar condition inside your shell script using [ $(date +\%u) -eq 1 ] . Advertisement

Question 4

What are the predefined crontab string macros (@reboot, @daily, @hourly, @weekly, @monthly, @yearly)?

Accepted Answer

Linux Vixie cron provides 8 intuitive string shortcuts that replace the 5 time fields:

@reboot: Runs once at system startup.
@hourly: Equivalent to 0 * * * * (top of every hour).
@daily / @midnight: Equivalent to 0 0 * * * (midnight every day).
@weekly: Equivalent to 0 0 * * 0 (Sunday midnight).
@monthly: Equivalent to 0 0 1 * * (first of every month at midnight).
@yearly / @annually: Equivalent to 0 0 1 1 * (Jan 1st at midnight).

Question 5

Can crontab schedules be configured down to seconds in standard Linux cron?

Accepted Answer

No. Standard Linux POSIX cron has a minimum resolution of one minute (60 seconds) . If sub-minute or high-frequency second-level execution is strictly required, use: Systemd Timers with AccuracySec=1s and OnUnitActiveSec=10s . Shell sleep loop in cron: * * * * * /path/script.sh; sleep 30; /path/script.sh . Dedicated daemon worker running under systemd or supervisor. Advertisement

Question 6

What is the difference between user crontab (crontab -e) and system crontab (/etc/crontab)?

Accepted Answer

There is a crucial structural difference:

User Crontab (crontab -e): Contains 5 time fields followed directly by the shell command. The job automatically executes under that user's UID and privileges.
System-wide Crontab (/etc/crontab and /etc/cron.d/): Contains 6 columns before the command. The 6th column explicitly defines the username (e.g., root, www-data, or postgres) under which the script runs.

Question 7

How do 0 and 7 both represent Sunday in Linux crontab?

Accepted Answer

The POSIX standard assigns 0 as Sunday (0=Sun, 1=Mon, 2=Tue, 3=Wed, 4=Thu, 5=Fri, 6=Sat). However, to maintain compatibility with Unix BSD conventions and user intuition (where 7 represents the 7th day of the week), modern cron implementations (including Vixie cron and Cronie ) treat both 0 and 7 as valid synonyms for Sunday . Advertisement

Question 8

Can month and day-of-week names be used instead of numbers (e.g., JAN, MON)?

Accepted Answer

Yes. Standard Vixie cron supports case-insensitive three-letter English abbreviations : Months : JAN , FEB , MAR , APR , MAY , JUN , JUL , AUG , SEP , OCT , NOV , DEC . Days of Week : SUN , MON , TUE , WED , THU , FRI , SAT . Note: Ranges or steps cannot be combined with names on older POSIX systems (e.g., MON-FRI works, but MON/2 is invalid). Advertisement

Question 9

Why does my script work when run manually in the terminal, but fails when executed by crontab?

Accepted Answer

This is the #1 most common crontab failure . It is almost always caused by one of three differences: Stripped Environment PATH : Cron provides only PATH=/usr/bin:/bin . Utilities located in /usr/local/bin , /opt , or ~/.cargo/bin cannot be found unless referenced by absolute path. Non-Interactive Shell : Cron does not load ~/.bashrc , ~/.bash_profile , or environment aliases. Different Working Directory : Cron executes commands with $HOME as current working directory , causing relative file paths (e.g., ./config.json ) to fail. Advertisement

Question 10

How do I inspect crontab execution logs on Ubuntu/Debian vs RHEL/CentOS/Rocky Linux?

Accepted Answer

Log locations depend on the Linux distribution: Ubuntu / Debian : Cron outputs to syslog. Filter with: grep CRON /var/log/syslog

Question 11

Why is the cron daemon not executing any jobs even though crontab -l lists them?

Accepted Answer

Verify these 4 critical checklist items:

Missing Trailing Newline: Vixie cron strictly requires a trailing newline character at the end of the crontab file. If the last line does not end with an Enter/Newline, cron ignores the line completely.
Service Stopped: Ensure the service is active with systemctl status cron (Debian/Ubuntu) or systemctl status crond (RHEL).
User Account Locked: If the user password expired or shell is set to /usr/sbin/nologin, cron may refuse to spawn sessions depending on PAM settings.
Access Restrictions: Check if the user is listed in /etc/cron.deny or excluded from /etc/cron.allow.

Question 12

Why do scripts requiring executable permissions fail in cron (chmod +x)?

Accepted Answer

When crontab triggers a script directly (e.g., /opt/backup.sh ), the Linux kernel requires the file to have the executable bit (+x) set. Fix this by running: chmod +x /opt/backup.sh

Question 13

How do I verify whether the cron or crond system service is actively running?

Accepted Answer

Check service status with systemctl: systemctl is-active cron || systemctl is-active crond

Question 14

Why do scripts with relative paths fail when executed under cron?

Accepted Answer

When cron launches a job, it sets the process current working directory (CWD) to the executing user home directory ($HOME), NOT the directory where the script resides.

If your script references ./data/input.csv, it will look in /home/username/data/input.csv instead of /opt/app/data/input.csv.

Solution: Either use absolute paths everywhere, change directories at the start of your script with cd "$(dirname "$0")", or change directory in your crontab line: cd /opt/app && ./run.sh.

Question 15

What causes "No space left on device" errors during crontab editing or execution?

Accepted Answer

When editing a crontab with crontab -e , a temporary file is created in /tmp . If /tmp has filled up with logs or uncollected temp files, crontab aborts with No space left on device . Another common culprit is inode exhaustion (check with df -i /tmp ), where small temp files consume all available filesystem index nodes. Advertisement

Question 16

How do I recover a mistakenly deleted user crontab (crontab -r accidental wipe)?

Accepted Answer

Running crontab -r removes the user crontab without confirmation. To recover: Check System Logs : Cron logs previously executed commands in /var/log/syslog or /var/log/cron . Search with: grep -i "CRON.*(username)" /var/log/syslog

Question 17

Why does editing /etc/crontab directly not trigger jobs without valid file permissions?

Accepted Answer

Files located in /etc/cron.d/ and /etc/crontab must adhere to strict Linux security policies: Must be owned by root:root . Must NOT be group-writable or world-writable (permissions must be 0644 or 0600 ). Must NOT be executable. Filenames in /etc/cron.d/ must consist only of alphanumeric characters, hyphens, and underscores (no dots or tildes). Advertisement

Question 18

How do I simulate the exact non-interactive cron environment to reproduce script failures?

Accepted Answer

To reproduce a cron bug in your terminal, use env -i to strip all interactive variables and run with minimal PATH: env -i HOME="$HOME" SHELL=/bin/sh PATH=/usr/bin:/bin /bin/sh -c "/path/to/my-script.sh"

Question 19

Why does cron use a minimal $PATH (/usr/bin:/bin) and how do I declare custom PATH variables?

Accepted Answer

Cron executes with a stripped-down POSIX path (typically /usr/bin:/bin) to ensure security and predictable execution across system users.

To include additional tool paths like /usr/local/bin, /usr/local/go/bin, or custom user paths, define PATH at the top of your crontab:

SHELL=/bin/bash PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin # Jobs now inherit the full PATH above: 0 2 * * * backup-tool --sync

Question 20

Why does not cron execute .bashrc, .bash_profile, or /etc/profile by default?

Accepted Answer

Cron spawns tasks as a non-interactive, non-login shell . According to GNU Bash specifications, login files ( /etc/profile , ~/.bash_profile ) are only read for login sessions, and ~/.bashrc is only read for interactive shells. Cron deliberately bypasses them to avoid terminal prompt codes, color codes, and unwanted side effects. Advertisement

Question 21

How do I specify a custom shell (e.g., /bin/bash or /bin/zsh) in a crontab file using SHELL=?

Accepted Answer

By default, cron invokes commands using /bin/sh (which is Dash on Ubuntu or a minimal POSIX shell).

To use modern Bash syntax (like process substitution <() or array variables), place SHELL=/bin/bash at the very top of your crontab file:

SHELL=/bin/bash 0 * * * * [[ -f /tmp/lock ]] || /usr/local/bin/worker.sh

Question 22

How do I pass custom environment variables (e.g., DB_PASSWORD, NODE_ENV) to cron jobs?

Accepted Answer

You can declare environment variables in 3 verified ways: Crontab Header Declarations : NODE_ENV=production APP_SECRET=xyz987 0 4 * * * /usr/bin/node /opt/app/index.js

Question 23

How do I set the working directory for a cron task using the cd command?

Accepted Answer

Use the logical AND operator ( && ) to navigate into the destination directory before launching the script: 0 1 * * * cd /var/www/myproject && ./manage.py generate_reports

Question 24

Why do Python scripts inside virtual environments (venv or conda) fail in crontab?

Accepted Answer

Cron does not know about your active virtual environment. If you run python3 script.py, it will execute with the system Python interpreter and fail with ModuleNotFoundError.

Fix: Always call the Python binary located inside your virtual environment bin folder:

0 3 * * * /home/deploy/app/venv/bin/python /home/deploy/app/sync.py

Question 25

How do I source an environment configuration file (like .env) inside a crontab command?

Accepted Answer

Use the POSIX dot ( . ) or source command before executing your script: 0 * * * * . /opt/app/env.sh && /opt/app/sync.sh

Question 26

Why do GUI applications or notify-send fail when executed from a crontab?

Accepted Answer

Cron operates in a background session without an attached X11 or Wayland graphical display server or D-Bus message session bus.

To send desktop notifications or launch GUI utilities, export DISPLAY and DBUS_SESSION_BUS_ADDRESS:

0 12 * * * DISPLAY=:0 DBUS_SESSION_BUS_ADDRESS="unix:path=/run/user/$(id -u)/bus" notify-send "Lunch Time"

Question 27

How do I redirect crontab standard output and error output to a persistent log file?

Accepted Answer

Append both standard output (stdout, fd 1) and standard error (stderr, fd 2) using >> log.txt 2>&1 : 0 2 * * * /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1

Question 28

How do I discard all crontab output to prevent spam and disk filling (> /dev/null 2>&1)?

Accepted Answer

Redirect stdout to the null character special device /dev/null , and point stderr (fd 2) to stdout (fd 1): */10 * * * * /usr/local/bin/ping-service.sh > /dev/null 2>&1

Question 29

What is the critical difference between >> log.txt 2>&1 and 2>&1 >> log.txt?

Accepted Answer

Order of redirection operators in Bash matters critically:

>> log.txt 2>&1 (CORRECT): First opens log.txt for stdout, then duplicates file descriptor 1 onto 2. Both stdout and stderr write to the log file.
2>&1 >> log.txt (INCORRECT): Duplicates descriptor 1 (which still points to the console) onto 2, then redirects stdout to log.txt. Errors still print to console / get emailed!

Question 30

How do I configure email alerts for failed cron jobs using MAILTO=?

Accepted Answer

Declare MAILTO in your crontab header: MAILTO="devops-alerts@mycompany.com" 0 4 * * * /opt/scripts/database-backup.sh

Question 31

How do I append timestamps to every line of crontab log output?

Accepted Answer

Pipe your output through ts (from moreutils ) or use an inline awk command: # Using moreutils ts: 0 * * * * /opt/app/job.sh 2>&1 | ts '[%Y-%m-%d %H:%M:%S]' >> /var/log/job.log # Using awk: 0 * * * * /opt/app/job.sh 2>&1 | awk '{ print strftime("[%Y-%m-%d %H:%M:%S]"), $0 }' >> /var/log/job.log

Question 32

How do I prevent massive log file growth generated by cron jobs (logrotate)?

Accepted Answer

Never let cron append to an unmanaged log file indefinitely. Create a logrotate definition in /etc/logrotate.d/cronjobs:

/var/log/cronjobs/*.log { daily missingok rotate 14 compress delaycompress notifempty create 0640 root adm }

Question 33

How does cron handle percent signs (%) in command strings, and why must they be escaped?

Accepted Answer

In crontab specifications, the percent sign (%) is a special delimiter representing a newline, with all following text routed to the command standard input. If you use date +%Y-%m-%d , cron will fail with a syntax error. You must escape every percent sign with a backslash : date +\%Y-\%m-\%d . Advertisement

Question 34

How do I prevent long-running cron jobs from overlapping if a previous instance is still running?

Accepted Answer

If a job scheduled every 5 minutes takes 12 minutes to process data, multiple instances will run concurrently, leading to CPU contention, race conditions, and database deadlocks.

Use flock (file lock) to ensure only one instance executes at any time.

Storage Architecture Tip: When scheduling heavy automated backup tasks, snapshot rotations, or deduplication passes on VMware Cloud Foundation hyperconverged infrastructure, calculate available headroom, raw-to-usable capacity, and slack space using the VCF & vSAN Capacity Calculator & Sizer.

Question 35

How do I use flock to create non-blocking file locks for crontab commands?

Accepted Answer

Wrap your command with flock -n /path/to/lockfile command : */5 * * * * /usr/bin/flock -n /tmp/backup.lock /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1

Question 36

What is the difference between flock -n (non-blocking) and flock -x (exclusive lock)?

Accepted Answer

Locking modes serve different operational requirements:

flock -n (Non-blocking): Fails immediately if locked. Best for periodic jobs (e.g. every 5 min) where skipped runs are preferred over queued pile-ups.
flock -x (Exclusive / Blocking): Waits patiently until the previous job finishes and releases the lock file descriptor before starting.

Question 37

How do utilities like run-one and lockrun compare to flock?

Accepted Answer

Alternative process singletons include:

run-one: Standard on Ubuntu. Automatically generates lock keys based on the command hash (no manual lockfile path needed): run-one /opt/backup.sh.
lockrun: Lightweight C utility that manages PID tracking and lock files across legacy Unix distributions.

Question 38

How do I enforce execution timeouts on cron jobs to prevent runaway processes (timeout)?

Accepted Answer

Use the GNU coreutils timeout command to terminate tasks that exceed an SLA threshold: 0 * * * * /usr/bin/timeout -k 15s 2h /opt/sync-job.sh

Question 39

What happens if a server shuts down or is asleep when a cron job was scheduled to trigger?

Accepted Answer

Traditional cron does NOT queue or replay missed jobs . If the server was powered off at 02:00 AM, the 2:00 AM cron job is permanently skipped until the next calendar match. To execute missed jobs after system resume or reboot, use anacron (which checks daily/weekly/monthly timestamps on boot) or systemd timers with Persistent=true . Advertisement

Question 40

How do /etc/cron.allow and /etc/cron.deny control user access to crontab?

Accepted Answer

Access control follows this strict priority:

If /etc/cron.allow exists, ONLY users listed inside can use crontab. /etc/cron.deny is ignored.
If /etc/cron.allow does NOT exist, users listed in /etc/cron.deny are blocked from using crontab.
If neither file exists, access depends on distribution configuration (usually only root or all users can execute).

Question 41

What is the default access behavior if neither /etc/cron.allow nor /etc/cron.deny exists?

Accepted Answer

On most Linux distributions (Ubuntu, Debian, RHEL, CentOS), if neither file exists, all system users are permitted to create and edit personal crontabs, provided their user account has a valid shell and is not locked in /etc/shadow.

Question 42

How does crontab execute tasks as different users (root vs non-root vs service accounts)?

Accepted Answer

Execution privileges follow user identity:

To edit a specific user crontab as root: sudo crontab -u www-data -e.
In system crontabs (/etc/crontab and /etc/cron.d/), declare the user in column 6: 0 3 * * * www-data /var/www/script.sh.
Security Best Practice: Never run web syncs, scraping, or database maintenance as root. Always use dedicated low-privilege service accounts.

Question 43

How do SELinux and AppArmor enforce security policies on crontab executions?

Accepted Answer

On systems with SELinux (RHEL/Rocky/Fedora), cron tasks execute in the crond_t security context domain.

If your script tries to write to non-standard directories or connect to arbitrary network ports, SELinux may block it with an AVC denial (check with audit2why < /var/log/audit/audit.log). Label your script files with bin_t or adjust SELinux booleans accordingly.

Question 44

Can a non-root user view or edit another user crontab?

Accepted Answer

No. User crontabs are stored in /var/spool/cron/crontabs/ with permissions 0600 or 0400 owned by the respective user. The crontab binary itself is setuid or setgid, strictly enforcing that unprivileged users cannot read or modify schedules belonging to other users. Advertisement

Question 45

How does a Kubernetes CronJob resource compare to standard Linux crontab?

Accepted Answer

A Kubernetes CronJob uses standard crontab 5-field syntax, but executes within containerized pods across a distributed cluster: concurrencyPolicy : Supports Allow , Forbid (like flock), or Replace . startingDeadlineSeconds : Tolerates cluster scheduling delays. successfulJobsHistoryLimit : Keeps past pod run logs for audit and telemetry. Advertisement

Question 46

How do I run scheduled tasks inside a Docker container using cron?

Accepted Answer

In containerized architectures, running cron requires running the daemon in the foreground: # In Dockerfile: RUN apt-get update && apt-get install -y cron COPY my-crontab /etc/cron.d/my-crontab RUN chmod 0644 /etc/cron.d/my-crontab && crontab /etc/cron.d/my-crontab CMD ["cron", "-f"]

Question 47

What are the key differences between systemd timers (.timer units) and traditional cron?

Accepted Answer

Modern Linux distributions recommend systemd timers over cron for complex workloads: Precision : Timers support microsecond and second resolution. Missed Execution Catchup : Persistent=true automatically runs tasks missed during downtime. Cgroup Isolation : Memory, CPU, and I/O bandwidth limits can be enforced directly in the service unit. Unified Logging : All stdout/stderr is indexed in journalctl . Advertisement

Question 48

What are the pros and cons of using centralized workflow schedulers (Airflow, Celery) vs Cron?

Accepted Answer

Architectural comparison: Cron : Lightweight, zero external dependencies, native to all Linux hosts. Disadvantages: Single point of failure, no native retry graphs, no centralized UI dashboard. Airflow / Celery : Provides DAG dependency graphs, automatic retries with backoff, distributed execution pools, and visual dashboards. Disadvantages: Substantial infrastructure overhead and complexity. Advertisement

Question 49

Interview Question: How does the Linux cron daemon work internally under the hood (polling vs inotify)?

Accepted Answer

Internal Architecture: Upon launch, the crond daemon scans /var/spool/cron and /etc/cron.d/ , building an in-memory linked list of scheduled jobs. The daemon then calculates the exact number of seconds remaining until the start of the next minute and calls sleep() or nanosleep() . At second 00, the daemon wakes up, checks the current system calendar time against the compiled schedules, forks worker processes to execute matching commands, and returns to sleep. Modern implementations use inotify on spool directories to instantly reload modified crontab files without requiring a service restart. Advertisement

Question 50

Interview Question: How does cron behave during Daylight Saving Time (DST) shifts (spring forward & fall back)?

Accepted Answer

DST transitions create temporal anomalies:

Spring Forward (Clock jumps 02:00 -> 03:00): Jobs scheduled between 02:00 and 02:59 would normally be skipped because that clock time never occurs. Vixie cron compensates by executing them immediately after the transition.
Fall Back (Clock rolls 03:00 -> 02:00): Jobs scheduled between 02:00 and 02:59 could trigger twice. Vixie cron tracks previous execution timestamps to prevent duplicate runs.
DevOps Golden Rule: Always configure production Linux servers to UTC timezone to completely eliminate DST ambiguity!

Timezone Tool Tip: To convert, plan, and verify cron job schedules across multi-region cloud infrastructures (UTC, EST, PST, GMT, CET, IST, JST), use the official vNetes Global Timezone Converter & Scheduler.

Question 51

Interview Question: How would you design a distributed, fault-tolerant cron architecture across multiple cloud servers?

Accepted Answer

To avoid single-point-of-failure (SPOF) and duplicate executions across multi-node server clusters:

Distributed Lock Manager: Use Redis (Redlock) or Consul/ZooKeeper session locks before acquiring job execution rights.
Queue / Worker Architecture: A high-availability scheduler (like AWS EventBridge or temporal.io) pushes trigger messages into a reliable queue (SQS, RabbitMQ, Kafka), and a pool of stateless workers consumes and processes them.
Idempotent Task Design: Ensure all scheduled scripts are inherently idempotent so accidental re-execution produces identical results without corrupting state.

Daemon / Scheduler Engine	Resident Memory (RSS)	Subprocess Fork Latency	Polling Sleep Accuracy	Spool Reload Mechanism	Missed Job Catch-Up
Vixie Cron 3.0pl1 (Debian / Ubuntu)	1.18 MB RSS	1.84 ms (clone syscall)	60s tick (nanosleep)	`inotify` + 60s fallback stat	Dropped silently
Cronie 1.6.1+ (RHEL / Rocky / Fedora)	1.72 MB RSS	2.12 ms (fork/execve)	60s boundary align	`inotify` event loop (realtime)	`anacron` handoff
BusyBox crond (Alpine Linux / Containers)	480 KB RSS	0.92 ms (vfork/exec)	60s sleep loop	Periodic directory polling	Dropped
systemd.timer (Modern Linux Core)	0 MB (Integrated in PID 1)	1.10 ms (cgroup spawn)	1 ms (timerfd_create)	`systemctl daemon-reload`	`Persistent=true`

Position (Attribute)	Entity Target	Value Domain	Allowed Operators	POSIX Standard	POSIX Specification Caveat
Field 1 (01)	Minute	0 – 59	* , - /	Mandatory	Step syntax `*/N` is an extension supported in Vixie cron & cronie.
Field 2 (02)	Hour	0 – 23	* , - /	Mandatory	24-hour notation. `0` = Midnight, `12` = Noon, `23` = 11 PM.
Field 3 (03)	Day of Month (DoM)	1 – 31	* , - /	Mandatory	Evaluates with boolean OR against Day of Week if both are non-wildcards.
Field 4 (04)	Month	1 – 12 (or Jan–Dec)	* , - /	Mandatory	Names are case-insensitive 3-letter strings without ranges in pure POSIX.
Field 5 (05)	Day of Week (DoW)	0 – 6 (or Sun–Sat, 7=Sun)	* , - /	Mandatory	POSIX specifies `0=Sun`; Linux cron accepts both `0` and `7` for Sunday.
Trailing Field	Command String	Executable CLI command	Shell pipes, redirection	Mandatory	Unescaped `%` characters are translated into newlines and piped to stdin.

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