PERFORMANCE MONITORING AND STATISTICS
# Display and manage the top processes
top
# Interactive process viewer (top alternative)
htop
# Display processor related statistics
mpstat 1
# Display virtual memory statistics
vmstat 1
# Display I/O statistics
iostat 1
# Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.)
tail 100 /var/log/messages
# Capture and display all packets on interface eth0
tcpdump -i eth0
# Monitor all traffic on port 80 ( HTTP )
tcpdump -i eth0 'port 80'
# List all open files on the system
lsof
# List files opened by user
lsof -u user
# Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
free -h
# Execute "df -h", showing periodic updates
watch df -h