Daily Driver

systemctl

Usage       : systemctl start nginx
Example     : systemctl enable ssh
Description : Manage systemd services and units.
Takeaway    : Use for starting, stopping, enabling, or disabling services on modern Linux systems.

service

Usage       : service apache2 restart
Example     : Restart Apache service.
Description : Manage services (SysV init style).
Takeaway    : Use for legacy service management (pre-systemd).

crontab

Usage       : crontab -e
Example     : 0 2 * * * /usr/bin/backup.sh
Description : Schedule recurring tasks.
Takeaway    : Use for automating repetitive jobs.

cron

Usage       : systemctl status cron
Example     : Ensure cron service is running.
Description : Cron daemon for scheduled jobs.
Takeaway    : Use to manage background scheduling service.

alias

Usage       : alias ll='ls -la'
Example     : Simplify frequent commands.
Description : Create command shortcuts.
Takeaway    : Use for productivity and customization.

unalias

Usage       : unalias ll
Example     : Disable alias temporarily.
Description : Remove command aliases.
Takeaway    : Use to manage or reset aliases.

export

Usage       : export PATH=$PATH:/opt/bin
Example     : Add custom path.
Description : Set environment variables.
Takeaway    : Use for configuring environment variables.

env

Usage       : env VAR=value command
Example     : env DEBUG=1 ./app
Description : Run commands with custom environment.
Takeaway    : Use for temporary environment changes.

set / unset

Usage       : set VAR=value / unset VAR
Example     : unset HISTFILE
Description : Manage shell variables.
Takeaway    : Use for shell-level variable control.

Time Management

clock

Usage       : clock -s
Example     : Set system time.
Description : Display/set system clock.
Takeaway    : Legacy tool, replaced by timedatectl.

zdump

Usage       : zdump Asia/Kolkata
Example     : Display timezone data.
Description : Show timezone info.
Takeaway    : Use for timezone debugging.

rdate

Usage       : rdate time.server.com
Example     : Sync with NTP server.
Description : Sync time with remote server.
Takeaway    : Use for manual time sync.

Disk Quotas

quota / edquota

Usage       : quota -u user / edquota user
Example     : Set quota limits.
Description : Manage user disk quotas.
Takeaway    : Use for storage management.

repquota

Usage       : repquota /home
Example     : Show quota report.
Description : Report quota usage.
Takeaway    : Use for monitoring quota usage.

Advanced System Tools

chroot

Usage       : chroot /mnt /bin/bash
Example     : Enter rescue environment.
Description : Run process in isolated root.
Takeaway    : Use for recovery or sandboxing.

lspci

Usage       : lspci
Example     : Identify graphics card.
Description : List PCI devices.
Takeaway    : Use for hardware inspection.

Miscellaneous & Legacy

lilo

Usage       : lilo
Example     : Update boot loader.
Description : Legacy Linux boot loader.
Takeaway    : Use for legacy boot systems.