System Commands

Process monitoring and management commands

# Show all processes
ps aux

# Show processes in tree format
ps auxf

# Show processes for current user
ps -u $USER

# Show processes with custom format
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu

# Show processes by specific user
ps -u root

# Show processes with full command line
ps -ef

# Show processes with threads
ps -eLf

System monitoring and performance analysis

# Interactive system monitor
top

# Show top processes by CPU
top -o %CPU

# Show top processes by memory
top -o %MEM

# Run top in batch mode
top -b -n 1

# Alternative to top (if available)
htop

# Show system load
uptime

# Show system information
uname -a

Disk space monitoring and analysis

# Show disk space usage
df -h

# Show disk usage for specific directory
du -h /path/to/directory

# Show disk usage summary
du -sh /path/to/directory

# Show disk usage for all directories
du -h --max-depth=1

# Show largest directories
du -h | sort -hr | head -10

# Show inode usage
df -i

# Show filesystem type
df -T

Memory usage monitoring and analysis

# Show memory usage
free -h

# Show memory usage in MB
free -m

# Show memory usage continuously
free -h -s 5

# Show memory usage in GB
free -g

# Show detailed memory info
cat /proc/meminfo

System service management and control

# List all services
systemctl list-units --type=service

# Start a service
systemctl start service_name

# Stop a service
systemctl stop service_name

# Restart a service
systemctl restart service_name

# Enable service at boot
systemctl enable service_name

# Disable service at boot
systemctl disable service_name

# Check service status
systemctl status service_name

# Show service logs
journalctl -u service_name

Scheduled task management and automation

# List current user's crontab
crontab -l

# Edit current user's crontab
crontab -e

# List root's crontab
sudo crontab -l

# Remove current user's crontab
crontab -r

# Crontab format examples:
# * * * * * command
# 0 2 * * * /path/to/backup.sh
# */15 * * * * /path/to/monitor.sh
# 0 0 1 * * /path/to/monthly.sh

Process termination and signal management

# Kill process by PID
kill 1234

# Force kill process
kill -9 1234

# Kill process by name
killall process_name

# Kill all processes by name
killall -9 process_name

# Send signal to process
kill -HUP 1234

# List available signals
kill -l

# Kill processes by pattern
pkill -f "pattern"

Filesystem mounting and unmounting operations

# List mounted filesystems
mount

# Mount a filesystem
mount /dev/sdb1 /mnt/backup

# Mount with specific options
mount -t ext4 -o rw /dev/sdb1 /mnt/backup

# Unmount filesystem
umount /mnt/backup

# Force unmount
umount -f /mnt/backup

# Show mount options
mount -o remount,rw /mnt/backup

# Mount network filesystem
mount -t nfs server:/path /mnt/nfs