Linux system administrator Interview 50 questions

2. What does the command nslookup do?

4. Nslookup is a command-line tool that monitors whether DNS servers in a network can correctly implement domain name resolution.

6. How do you show the process with the highest CPU usage?

8. Top-c Sort by CPU

10. What if I check the open ports on Linux and screen out unused ports?

12. Natstat-ltup view open up those ports, not the firewall shield off

14. What is Linux? How does it differ from UNIX?

16. Linux is a free-to-use and free-to-propagate Unix-like operating system, a POSIX and Unix-based multiuser, multitasking, multi-threaded and multi-CPU operating system. It can run major UNIX tools software, applications, and network protocols. It supports 32-bit and 64-bit hardware. Linux inherits the design idea of Unix as the core of network, and is a stable multi-user network operating system. The biggest difference between Linux and Unix is that the former is free software that develops source code, and the latter is the traditional commercial software that protects the source code from intellectual property. This should be their biggest difference, this difference manifests in the user to the former has the very high autonomy, but to the latter can only go passively adapts, this difference also manifests in the former development is in a completely open environment, but the latter development is in a black box completely, Only the relevant developer is able to access the prototype of the product.

    Difference

18. Describe the UNIX system startup process in detail?

19.  1   user power on the computer.  2   The computer automatically executes the ROM boot program.  3   The boot area of the first hard drive is transferred into memory and executed. The boot area of the hard drive contains partition information and drivers for the hard drive.  4   The bootstrap program on the active partition of the hard disk is transferred into memory and executed. The bootstrap program is located in block No. 0 on the active partition.  5 /boot into memory and executes.  6 /unix into memory and executes.  7   detects and configures memory and hardware devices.  

    Process

21. How to modify file permissions, how to create a read-only file?

23.  + filename

25. Details of the sudo command, what are the drawbacks of this?

26. 1, sudo is like a yellow jacket, running in the Linux/unix environment is privileged, such as: run some commands such as MOUNT,HALT,SU, or edit some system configuration files,/etc/mtab,/etc/samba/smb.conf and so on. This reduces the number of logins and administration time of the root user, and also improves system security. 2, sudo faithful log: What you have done. And configuration are saved in/etc/under the sudoers. 3, the user with the sudo command, you must enter the password to continue to execute, for a certain period of time, such as 5 minutes without any custom-made, you must retype the password to make a difference. This feature is also a feature of time stamping or entry volume. 4, common sudo commands and their meanings: sudo-h Help lists the methods used to exit. sudo-V Version Displays the release information and exits. sudo-the list lists the commands that the current user can execute.  　　This option is available only to users in Sudoers. sudo-U username|#uid User executes the command as the specified user.    　　The following users are other than root, which can be either a user name or a #uid. sudo-K Kill clears the time on the "entry volume" and re-enters the password the next time you use sudo. sudo-K sure kill with-K is similar, but it also rips the "entry volume", which is to delete the timestamp file. sudo-B Command Background executes the specified commands in the background. sudo-P prompt Command Prompt can change the prompt to ask for a password, where%u will be substituted for the user account name,%h Displays the host name.  　　Very user-friendly design. sudo-The e file edit is not an execution command, but a modification of the files, equivalent to the command sudoedit. There are also some infrequently used parameters in the manual page sudo (8) can be found in the. 5, about configuring Sudo. Configuration sudo must be edited by/etc/sudoers file, and only Superuser can modify it, and must also use Visudo editing. There are two reasons for using Visudo, one is that it prevents two users from modifying it at the same time, and the other is that it can perform a limited syntax check. So, even if you are only a superuser, you'd better use Visudo to check the syntax. 

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28. What is the difference between UDP and TCP?

30. TCP) Transmission Control Protocol, which is a general agreement for reliable data transmission. (UDP) User Datagram Protocol, which is a non-connection oriented protocol. Using this protocol does not require two applications to establish a connection first. The UDP protocol does not provide error recovery and cannot provide data retransmission, so the protocol transmits data with poor security.

32. Describes the order in which Linux machines are started.

34. Start the first step-- load BIOS boot Step two -- read MBR boot step three --bootLoader start step Fourth -- load kernel boot fifth step -- 　User layer init According to Inittab file to set RunLevel start sixth --init Process Execution rc.sysinit start Seventh step -- start kernel module Start eighth step -- execute different running level of the script program Start Nineth Step --execute/etc/rc.d/rc.local start Tenth step --Execute/bin/login program, enter login status

36. Design a 3-tier Web application.

38. The persistence layer (data access layer), the business logic layer, the presentation layer and the expression layer adopt the MVC architecture pattern, differentiate into the model, the view, the control three parts

40. Outlines how you can import Internet traffic into a subnet.

42. Nat principle

44. Do you know anything about virtualization? Does it use?

46. Virtualization refers to virtualizing a computer into multiple logical computers through virtualization technology.

48. What is the difference between different levels of RAID? What level of RAID will you use for the Web server and database server?

50. If it is a cache service database, RAID0 if it is a storage database, RAID10,RAID5

52. Say some recent developments in the open source community.

54. Do you contribute to open source projects?

56. What is the difference between a system engineer and a system administrator? Explain it?

58. Different levels, different wages

60. List some of the unethical behavior of system experts.

62. How large is the swap partition for Linux systems in general?

66. What does a directory with no name represent in a Linux system?

70. How do I list all the files in a directory, including hidden files?

72. LS-ladhtree

74. How do I add a new system user with no login privileges?

76. Useradd user-s/sbin/nologin,

78. Describe what a hard link is? What happens if a hard link is deleted?

82. What happens to the system administrator executing this command: chmod 444 chmod?

84. File Change Permissions

86. How do I find a common IP and private IP for a Linux system?

88. How do I send an attachment with bash?

90. Name some Linux distributions that are used on the server.

92. Redhat, CentOS, Ubuntu, Debian, son

94. Describe the easiest way to reinstall Grub on Linux?

96. Yum-y Install Grub

98. What are records, NS Records, PTR records, CNAME records, and MX records?

100.     A address this record lists the IP addresses for a specific host name. This is an important record for name resolution.
     　　PTR records are often used for reverse address resolution CNAME Standard name This record specifies the alias of the standard hostname.　　MX Mail Exchanger This record lists the hosts responsible for receiving e-mail messages sent to the domain. NS Name server This record specifies the name server that is responsible for the given zone.

102. What is a zombie process? What can be done to cause a zombie process?

104. The ⒈ parent process waits for the child process to end through functions such as wait and waitpid, which causes the parent process to hang. ⒉ If the parent process is busy, you can use the signal function to install handler for SIGCHLD, because when the child process finishes, the parent process receives the signal and the wait recycle can be called in handler. ⒊ If the parent process does not care about when the child process ends, the kernel can be notified with signal (Sigchld,sig_ign), and the end of the child process is not interested, and the kernel recycles and no longer sends a signal to the parent process when the subprocess ends. ⒋ also has a few tricks, that is, fork two times, the parent process fork a child process, and then continue to work, the child process fork a grandchild process exit, then the Sun process is init takeover, after the sun process, init will be recycled. But the recycling of the child process has to be done by itself.

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106. When do we choose to use a script instead of a compiled program?

108. Small program

110. How do I create a simple master-slave cluster?

114. What happens when you delete a file link's source file?

118. How does the FTP server restrict access to IP?

122. Describe the directory structure of Linux, what is placed in the/usr/local folder?

124. Self-installing software catalog files

126. What is Git? Explain the structure and how it works?

128. Reference Blog http://www.nowamagic.net/academy/detail/48160210

130. How do you send an e-mail to 100 people at 12 o'clock noon?

132. Describes the ZFS file system.

134. The English name of the ZFS file system is the Zettabyte. File system, also known as the dynamic filesystem, which is the first 128-bit file system. Originally a file system developed by Sun for the Solaris 10 operating system

136. How do I modify the default runlevel of a Linux system?

138. How do I modify kernel parameters for Linux?

140. Describes the difference between SSH and telnet.

142. SSH is encrypted and SSL-based. Telnet is a plaintext transmission, the data sent by the listener does not need to decrypt to see the content.

144. How do you virtualize a Linux physical machine?

146. Tell me some weird linux commands.

148. Explains how HTTPS works.

150. http://blog.csdn.net/sean_cd/article/details/6966130

     How HTTPS works

152. Do you know Tor browser? Explain how it works.

154. How do I trigger a forced system check the next time I start the machine?

156. What backup technology do you like?

158. Master-slave replication tape drive scripting network backup

160. Explains some of the swap partitions.

162. Explain the ping death attack.

164. 65500 Target ip-t (65500 indicates the maximum data length,-t means to ping the destination address continuously) to achieve this. The UNIX system also has a similar situation.

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166. How you sniff the contents of IP packets.

168. Wireshark Grab Bag Analysis

170. How does the OSI hierarchy ensure that packets arrive at the correct address?

Linux system administrator Interview 50 questions