Linux Operations engineer face test seventh set

1. Explanation of top command and Vmstat command

The top command is a real-time monitoring of the current system's overall process state and the process state of each program, Vmstat can show the status of the server at a given time interval, including the server CPU utilization, memory usage, virtual memory exchange situation, IO Read and write situation. One of its main uses is to view virtual memory conditions.

"Comment" Vmstat if directly use, is now the current moment of the server state value, generally speaking vmstat are paired with time and collection times use, such as #vmstat 2 5, is every two seconds to collect the server state, a total of 5. If it is #vmstat 2, it is always in the collection.

2. What is the common port for VPN? What is the default port for MySQL? What is the default port for Oracle? What are the common ports for NFS? What is the common port for FTP?

The LLTP VPN port is typically 1723; The default port for MySQL is 3306;oracle's default port is 123 (UDP) and the common port for 1521;nfs is the port 21 and 20 for FTP.

3, Linux How to check the user log log

Less/var/log/secure

"Comment" Check the system of the various administrator login command There are many, such as last,last-x this display more full point, or use who/var/log/wtmp, but who/var/log/wtmp not last look comfortable,/var/log/ Mtmp is a garbled file, open with the cat command is not understood.

4, the server between how to achieve no password login? Lists the operation steps.

Assume that server A and Server B are present, where Server A's server name is a, the corresponding IP address is 192.168.1.10, and the name of Server B is B, and its IP address is 192.168.1.20.

1) First #yum install-y on two machines openssh-clients

2) then on the respective server/etc/sysconfig/network on the hostname corresponding to fill a and B, and then on the respective server put/etc/hosts, a and B server name and IP address are added to the end of the file, as follows

A 192.168.1.10

B 192.168.1.20

3) on a server, #ssh-keygen, and then return all the way. This is also true for Server B.

4) on a server, #ssh-copy-id-i. ssh/id_rsa.pub [Email protected], enter the root password of the B server one time. b also divert, ssh-copy-id-i ssh/id_rsa.pub [email protected], also enter the root password of a server in the middle.

5) Done, now the AB between the landing has no longer need password.

5. A simple description of the seven levels of the OSI reference Model

Physical layer: Network cable, optical cable, copper wire These things can be seen by the naked eye.

Data Link layer: frame, MAC address

Network layer: Packet, IP address

Transport layer: TCP protocol, UDP protocol

Session Layer: Establish session, maintain session

Presentation layer: Complete data conversion, formatting, and text compression.

Application Layer: Specific services

6, the design of a PV 20 million site architecture

http://blog.liuts.com/post/234/

7. Briefly describe the three-time handshake process of TCP protocol

First handshake: The client sends a SYN packet to the server and enters the syn_send state;

Second handshake: The server receives the packet, confirms that it returns an ACK to the client (and a SYN, at which point the server is in the SYN_RECV State;

Third handshake: After the client receives the Syn+ack returned by the server and sends an ACK to the server, the link state of the server and client is established

This article is from "Life is waiting for Gordo" blog, please make sure to keep this source http://chenx1242.blog.51cto.com/10430133/1744394

Linux Operations engineer face test seventh set