Basic System Info Commands

• uptime → time, uptime, users, load average
• hostname → current hostname
• ip hostname → show IP & hostname
• uname -a → current OS and kernel info
• which command → path to a command

• cal → calendar for current month/year

  • cal 2025 → full year
• bc → basic calculator

System Monitoring

• systemctl → interact with systemd system manager
• ps → view current processes
• top → dynamic view of process usage

Systemctl Usage

• systemctl start|stop|status servicename.service → manage service state
• systemctl enable servicename.service → start service at boot
• systemctl restart|reload servicename → restart or reload service
• systemctl list-units --all → list all units

• To add a service:

  • Create a unit file in /etc/systemd/system/servicename.service

Process Management

• Start a process in the background:

  • Ctrl + Z then jobs → suspend and background
  • bg → continue in background
  • fg → bring back to foreground

• Run process detached from terminal:

  • nohup process & → keep running after logout
  • nohup process > /dev/null 2>&1 & → suppress all logs/output

Killing and Prioritizing

• pkill name → kill process by name

• nice → start process with a priority (range -20 to 19)

  • lower = higher priority
  • nice -20 top

Jobs Monitoring

• jobs → list background/foreground job states

ps Command

• ps → Current shell process status
• ps -E → All running processes
• ps aux → All in BSD style with details
• ps -EF → Running process with details
• ps -u root → Processes of specific user
• ps -EF | grep ? → Find process by pattern

top Command

• top -u username → Show only that user's processes
• top +d c → Absolute path
• top +d k → Kill by PID
• top +d M or +d P → Sort by memory or process usage

kill Commands

• kill -l → List all signals
• kill PID → Default terminate
• kill -1 → Restart
• kill -2 → Equivalent to Ctrl+C
• kill -9 → Force kill
• kill -15 → Graceful kill
• killall → Kill all processes by name
• pkill → Kill by process name