Linux一些陌生命令和概念总结

netstat — print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
ip — show / manipulate routing, devices, policy routing and tunnels.
ss — another utility to investigate sockets.

Filesystem — a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device(s) which contain it.
Inode — an Index Node, is a structure which store all the information about a file system object (file, directory, etc.) except data content and file name.
Block — a minimum chunk of disk space which can be allocated. It usually defaults to 4096 bytes, or 4 Kilobytes.
Journal — a structure which allows the filesystem track of what was written and when. This allows to quickly understand what was not properly written in case of power outage or similar problem.

tune2fs — print out and change file system parameters.

 1: sudo iptables-save
 2: sudo iptables -t filter -A INPUT -i lo -j ACCEPT
 3: sudo iptables -t filter -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
 4: sudo iptables -t filter -P INPUT DROP
 5: sudo iptables -nt filter -L --line-numbers
 6: ping -c 2 -W 1 10.0.2.2
 7: sudo iptables -t filter -A INPUT --match state --state ESTABLISHED -j ACCEPT
 8: sudo iptables -nt filter -L --line-numbers
 9: ping -c 2 -W 1 10.0.2.2
10: sudo modprobe ipt_LOG
11: sudo iptables -nt raw -L --line-numbers
12: sudo iptables -t raw -A PREROUTING -p udp -m udp --dport 1024 -j TRACE
13: sudo iptables -t raw -A OUTPUT -p udp -m udp --sport 1024 -j TRACE
14: sudo tail -n0 -f /var/log/kern.log | cut -c52-300 &
15: nc -ulp 1024 &
16: echo 'Hello there!' | nc -u localhost 1000
17: <CTRL+C>
18: fg
19: <CTRL+C>
20: fg
21: <CTRL+C>

uptime — how long the system has been running.
free — display amount of free and used memory in the system.
vmstat — information about processes, memory, paging, block IO, traps, disks and cpu activity.