Simple answer to the question of operation and dimension of Linux system

1. Brief introduction of commonly used high-availability technologies

Answer:

Keepalived:keepalived is a service software that ensures high availability of clusters to prevent single points of failure and is implemented using the VRRP protocol. The backup will take over Master's work and continue the service if the master proactively lowers its weight between master and backup, or if backup detects that master fails.

Haproxy:haproxy provides high availability, load balancing, and proxies based on TCP and HTTP applications, supporting virtual hosting, which is a free, fast, and reliable solution. Haproxy is especially useful for Web sites that are heavily loaded, and often require session-hold or seven-tier processing. The haproxy runs on the current hardware and can support tens of thousands of concurrent connections. and its operating mode makes it easy and safe to integrate into your current architecture, while protecting your Web server from being exposed to the web.

heartbeat+ DRBD:

Heartbeat (Linux-ha) Working principle: Heartbeat core consists of two parts, heartbeat monitoring part and the resource taking over part, heartbeat monitoring can be carried out through the network link and serial port, and support redundant links, they send each other a newspaper Greek tell each other their current state, If the message is not received by the other party within the specified time, then it is considered to be invalid, then the resource takeover module should be started to take over the resources or services running on the other host.

Distributed replicated block Device (DRBD) is a software-implemented, non-shared storage replication solution for mirrored block device content between servers.

Data mirroring: Real-time, transparent, synchronous (all servers are returned after success), asynchronous (returned after successful local server)

2. briefly describe the DNS parsing process

Answer:

1, enter the www.qq.com domain name in the browser, the operating system will first check their local hosts file whether there is this URL mapping relationship, if there is, first call this IP address mapping, complete the domain name resolution.

2, if the hosts do not have this domain name mapping, then find the local DNS resolver cache, whether there is this URL mapping relationship, if there is, direct return, complete the domain name resolution.

3, if the hosts and the local DNS resolver cache does not have the corresponding URL mapping relationship, first will find the TCP/IP parameters set in the preferred DNS server, where we call it a local DNS server, when the server receives the query, if the domain name to query, included in the Local Configuration zone resources, The parsing result is returned to the client and the domain name resolution is completed, which is authoritative.

4, if the domain name to be queried is not resolved by the local DNS server zone, but the server has cached this URL mapping relationship, call this IP address mapping, complete the domain name resolution, this resolution is not authoritative.

5, if the local DNS server local zone file and cache resolution are invalidated, according to the local DNS server settings (whether set forwarders) to query, if not in the forwarding mode, local DNS will send the request to 13 root DNS, the root DNS server receives the request will determine the domain name (. com) Who is authorized to administer and returns an IP that is responsible for the top-level domain name server. After the local DNS server receives the IP information, it will contact the server responsible for the. com domain. After the server that is responsible for the. com domain receives the request, if it cannot resolve itself, it will find a management. com domain's next-level DNS server address (qq.com) to the local DNS server. When the local DNS server receives this address, it will find the qq.com domain server, repeat the above action, query until the www.qq.com host is found.

6, if the use of a forwarding mode, this DNS server will forward the request to the first level of DNS server, from the previous level of the server to resolve, the previous level of the server if it can not resolve, or find root DNS or transfer requests to the upper ancestor, in this cycle. Whether the local DNS server uses either forwarding or root hints, the result is returned to the local DNS server, which is then returned to the client.

From the client to the local DNS server is a recursive query, and the DNS server is an interactive query between the iterative query.

3. Brief introduction of the server monitoring software you used, and briefly explain the characteristics of their respective, introduce the common monitoring indicators. View the status of your current Linux system, such as CPU usage, memory usage, load conditions, and more, to see the 5 most memory-intensive processes

Answer:

Nagios

The features that Nagios can monitor are:

1, monitoring network services (SMTP, POP3, HTTP, NNTP, ping, etc.);

2, monitor the host resources (processor load, disk utilization, etc.);

3, simple plug-in design allows users to easily expand their services to detect methods;

4, parallel service inspection mechanism;

5, with the ability to define the hierarchical structure of the network, with the "parent" host definition to express the relationship between the network host, this relationship can be used to identify and clarify the host outage or unreachable state;

6, when the service or host problems arise and resolve the alarm sent to the contact person (via email, SMS, user-defined mode);

7, can define some processing procedures, so that it can be in service or host failure to play a preventive role;

8, automatic log scrolling function;

9, can support and implement redundant monitoring of the host;

10, the optional web interface for viewing the current network status, notification and fault history, log files and so on;

11, can be viewed through the mobile phone system monitoring information;

12, can specify the custom event processing controller;

To view the status of the current system: top

View the top 5 processes that occupy the largest memory, and then press the M (uppercase) key. Method Two: Ps-aux | Sort-k4nr | Head-5

4. Use the Windows Service Management command to turn on the BEASD service and view the number of connections currently established, with a default port of

Answer:

Start service: net start BEASD

If the service is forbidden to start, use this command: sc config beasd=demand (manual) |auto (Auto) |disabled (disabled); SC start BEASD

5. briefly describe the boot sequence of Linux systems, query program RunLevel and modify RunLevel.

Answer:

Post power-on self-test-"MBR boot-" grub--"Loading kernel-" Start the init process-"read/etc/inittab file,/etc/init/*.conf file--" Use/etc/rc.d/ Rc.sysinit init Script-"Execute/ETC/RC.D/RC script (load/etc/rc3.d/all scripts)-" Execute/etc/rc.d/rc.local--"execute/bin/login Login Program

Query program Run Level: RunLevel

Modify RunLevel: init [0123456]

6. Describe the differences between soft links and hard links.

Answer:

Soft link refers to the creation of a new file, the block is stored in the file name of the link is pointed, the inode of the soft link with the source file of the inode, the source files are deleted, then rebuilt, changed the inode, the soft link file is still valid.

The hard link is to create a new file name that points its inode to the inode of the source file, so the hard-link inode and source files are the same, and the source files are deleted after the hard link can still be valid.

7. Host A needs to transmit a copy of 100G data to Host B, which transmission optimization can be done?

Answer:

1. Data packaging compression

2. Data fragmentation, synchronous transmission

3. Increase transmission bandwidth, network port aggregation

8. Describe the working mode and scheduling algorithm of LVS, and recommend architecture of large concurrent environment.

Answer:

Operating mode: Nat,tunnel,dr,fullnat

Algorithm	Description
Rr	Polling schedule (Round-robin), which assigns the request to a different RS node in turn, that is, the request is divided across the RS node. This algorithm is simple to answer, but only suitable for the RS node processing performance is not small difference situation
Wrr	Weighted polling Schedule (Weighted Round-robin) It assigns tasks according to the weights of the different RS nodes. RS with higher weights will take precedence over the task, and the number of connections allocated will be greater than RS nodes with lower weights. RS of the same weighted value get the same number of connections.
Dh	Destination Address hash dispatch (Destination Hashing) find a static hash table with the destination address as the keyword to obtain the required RS
Sh	Source Address Hash Dispatch (source Hashing) finds a static hash table with the source address as a keyword to obtain the required RS
Lc	The minimum number of connections is dispatched (Least-connection), and the Ipvs table stores all active connections. Send a new connection request to the smallest current number of connections RS
Wlc	Weighted minimum number of connections scheduling (Weighted least-connection) assume that the weights of each RS is WI (I=1..N), the current number of TCP connections is Ti (I=1..N), and then select Ti/wi as the smallest RS as the next assigned RS
Lblc	Address-based minimum number of connections dispatch (Locality-based least-connection), the request from the same destination address is assigned to the same RS node, if this server is full load, assigned to the minimum number of connections RS, and it for the next assignment is the first consideration
Lblcr	The minimum number of connections is scheduled based on the address band repetition (locality-based least-connection with Replication), for a certain destination address, corresponding to an RS subset. For this address request, assign it the minimum number of sub-set connections RS; If all servers in the subset are full, select a smaller number of servers from the cluster, add it to this subset, and assign connections; If no modification is made within a certain time, the node with the largest subset of the sub-set is removed
Sed	Shortest expected delay (shortest expected delay scheduling SED) Based on the WLC algorithm. Example: The ABC three machines weigh 123 respectively, and the number of connections is 123. Then if a new request comes in using the WLC algorithm, it may be assigned to any of the ABC's. This is done after using the SED algorithm: A (+)/1 B (1+2)/2 C (1+3)/3 According to the result of the operation, the connection is given C
NQ	Minimum queue scheduling (never queue scheduling NQ) No queues are required. If the number of connections to RS = 0 is allocated directly to the past, no further SED operations are required

Recommended for large concurrency environments: Dr Mode, RR scheduling algorithm.

9. Describe the TCP three handshake process?

Answer:

sed changes all "/opt/tmp" in file Test.txt to "/root/tmp" and removes all empty lines.

Answer:

Sed-i ' s#/opt/tmp #/root/tmp #g ' test.txt|sed-i '/^\s*$/d '

192.168.16.3 This Windows Server folder to the Linux local/mnt/server directory, the Windows account is: Administrator, password: 123456

Answer:

1. First share the directory server that needs to be mounted under Windows.

2, make sure that Linux and Windows are in the same LAN.

3. Create a directory/mnt/server below Linux that needs to be mounted.

4. Mount using the Mount command.

Mount command: mount-t cifs-o username=administrator,password=123456//192.168.16.3/server/mnt/server

Write a firewall configuration script that allows only remote hosts to access the local port 80. (Linux iptables)

Answer:

#!/bin/bash# This  isa server firewall#updated by YEHAIFENG#QQ:769358362#defineVarIPT=/sbin/iptables #Remove any existing rules$ipt-F$ipt-X$ipt-z#settingdefaultFirewallpolicy$ipt--Policy OUTPUT Accept$ipt--Policy FORWARD Drop$ipt-P INPUT DROP #setting forLoopbackInterface$IPT-A input-i lo-J Accept$ipt-A Output-o lo-J ACCEPT #accept thePort Only$ipt-A Input-p TCP--dport the-J ACCEPT #save iptables/etc/init.d/iptables Save

Write a shell script to transfer files from the/logs directory 3 days ago to the/tmp directory.

Answer:

#!/bin/bash#This was3 from/logs to/tmp#updated by YEHAIFENG#QQ:  769358362#define varfile_from=/logsfile_to=/Tmpday_ago= 3 CD $FILE _from  for  in ' Find $FILE _from-type f-mtime +3'   do              /bin/mv $FILE _from/$ File $FILE _to/$file    Done

Daily 1:00 backup the log files of the previous day in the/var/log directory and place them in the Btslog directory of the current directory, and delete the log backup file 15 days ago, using the shell script. (The log format is: BTSVR.LOG.2016-01-01, the package backup file format is: btsvr.log.2016-01-01.tar.gz)

Answer:

Cat bak_logs.sh#!/bin/bash# This  isTo backup logs#updated by YEHAIFENG#QQ:769358362 #defineVarYesterday= ' Date +%f-d'-1 Day'' Log_dir=/var/Logbak_dir=/var/log/Btsloglog_file=btsvr.log CD $LOG _dir/if[-F $LOG _dir/$LOG _file. $YESTERDAY]; Then{tar zcf $LOG _dir/$LOG _file. $YESTERDAY. tar.gz$log_dir/$LOG _file. $YESTERDAY/BIN/MV $LOG _dir/$LOG _file $YESTERDAY. tar.gz/bak_dir/}Elseecho "The file isNot exist. " Fi

Use a timed task to execute the script 1 points per day: 0001 * * */bin/bash bak_logs.sh

Write a script for nginx log statistics, get the top 10 IP access (nginx log path:/nginx/default/access.log)

Answer:

cat bak_logs.sh#!/bin/bash# This was to the backup logs#updated by YEHAIFENG#QQ:  769358362#define varlog_file=/nginx/default/'  {Print $} '/application/nginx/logs/access.log |sort|uniq-c|sort-r|head->/tmp//tmp/ Ip_max.txt

Simple answer to the question of operation and dimension of Linux system