A network scan --NMAP
NMAP port scanning is a powerful class security assessment tool.
Designed to detect a number of huge number of network hosts, support multiple technologies ping scan, multi-port detection, OS recognition.
Use NMAP regularly scan the internal network, the network can identify uncontrolled application services, promptly shut down unsafe services, reducing the security risks
-sS, TCP SYN scan (half-open scanning): issue SYN packets only to the target, if the received SYN / ACK response
should pack it that the target port is listening, and disconnect immediately; otherwise think the goal did not open port .
-sT, TCP connect scan: This is the complete TCP scan mode, used to establish a TCP connection, as if
the work is considered the target port is listening service, or that the target port is not open.
-sF, TCP FIN scanning: open ports ignore this data packet, closed port will respond RST data
packet. Many firewalls only a simple SYN packet filtering, while ignoring other forms of TCP *** package.
This type of scanning may be indirectly detectable firewall robustness.
-sU, UDP scan: UDP probe target hosts which provide the service, UDP scanning speed will be slower.
-sP, ICMP scanning: similar to ping testing, to quickly determine the target host is alive, do not do other scans.
-P0, skip the ping test: in this way that all target host is alive, and when they do not respond to ICMP
request, can be avoided by using this method can not ping give up scanning.
1. In the warehouse yum install nmap
2. Check the external tcp service
3. Replace the HTTPD service to view its TCP ports and services
4. Detection of UDP port and service
The detection target host site information
Detailed block with two .inode
Operating system file data in addition to the actual content, usually contain a lot of attributes, such as the Linux operating system file permissions (rwx) and file attributes (owner, group, time parameters, etc.). These two parts will usually file system content are stored in the inode and block.
1. to experiment a bit with the stat command
2. Time to experiment a bit to see the property ctime atime mtime
3. We take a closer look inode 
little experiment to see all the available inode nodes and node 
4. Delete the inode
