2018--linux face question

1, Enterprise scene interview questions:
The difference between buffer and cache.

2, Enterprise scene interview questions:
The difference between Redhat and CentOS.

3, Enterprise scene interview questions:
Describes the features of RAID 0 1 5 10.

4, Enterprise scene interview questions:
32-bit and 64-bit systems, but not how to choose.

5, Enterprise scene interview questions:
The SSH service is not connected to how to troubleshoot.

6, Enterprise scene interview questions:
7 Types of Linux operating levels and their corresponding roles.

7, Enterprise scene interview questions:
The startup process of the Linux system from boot to login.

8, Enterprise scene interview questions:
A 100M (100000K) disk partition that writes 1K files or writes to 1M files, respectively, how many can be written.

9, Enterprise scene interview questions:
Enterprise Interview Question: If you write data to disk, no space left on device, through Df-h view disk space, found not full, the reason. What situations can cause this problem in an enterprise scenario?

Answer:
1 It is possible that the inode number has been exhausted.
2 Enterprise work in the mail temporary queue/var/spool/clientmquene It is very easy to get a large number of small files that cause no space left on device error. The Clientmquene directory is a temporary queue for sendmail messages only if the SendMail service is installed. centos5.8 default will be installed sendmail,centos6.6 default no sendmail, but there is postfix.

A solution for generating a large number of files under the Linux server/var/spool/clientmqueue directory
Today, you receive the Nagios alert message, where the disk partition space in one server exceeds 95%, log on to the server to view
[Email protected] ~]# df-h
Filesystem Size used Avail use% mounted on
/dev/sda5 19G 16G 2.8G 95%/var
To Directory/var to see which directory has the largest file size
[Email protected] var]# Du-sh *
Find is the/var/spool directory takes up a lot of space, go into the spool directory to continue to see the files that are found in the Clientmqueue directory many occupy most of the space.
Delete all Files
[Email protected] clientmqueue]# RM-RF *
Result returned-bash:/bin/rm:argument list too long
Swap command for Find. -print|xargs RM After a while, I finally deleted all the files.
But this approach is only a cure for the symptoms.
Why Var/spool/clientmqueue produce a large number of files, check the data is because cron execution will send the relevant results in mail to the execution of the user's account, but when the SendMail did not start all the letters will be temporarily present in this directory, This is the case at this point.
The root of the solution is to add >/dev/null to the cron task in the back 2>&1
For example
* * * * * */etc/init.d/snmp_cron.sh >/dev/null 2>&1

10, Enterprise scene interview questions:
The principle of file deletion under Linux:

Solution: In a Linux system, deleting a static file (no process call) (the directory is also a file) is conditional on all hard-link files associated with it being deleted (and also related to process occupancy).

11, Enterprise Scene interview questions:
Describe the differences between soft links and hard links under Linux:

Answer 2:

You can also draw directly:

Please describe the 12 steps of Linux system optimization.

1, login system.
2, prohibit SSH remote.
3, time synchronization.
4. Configure the Yum update source.
5, close SELinux and iptables.
6. Adjust the number of file descriptors.
7, scheduled automatic cleaning/var/spool/clientmquene/directory junk files.
8. Streamline boot-up service.
9, the Linux kernel parameter optimization/etc/sysctl.conf, the execution sysct-p takes effect.
10, change the character set, prevent garbled problem appears.
11. Lock critical system files.
12, clear/etc/issue, remove the system and kernel version before landing screen display.

Key features of the Linux system:
Basic ideas
The basic idea of Linux has two points: first, everything is a document; second, each software has a definite purpose. The first article in detail is that everything in the system boils down to a file, including commands, hardware and software devices, operating systems, processes, and so on for the operating system kernel, all of which are considered to have their own attributes or types of files. Linux is Unix-based, largely because of the similarity between the two basic ideas.
Completely free
Linux is a free operating system that can be obtained free of charge through the Internet or other channels, and can be arbitrarily modified by the source code. This is not what other operating systems can do. Because of this, countless programmers from all over the world are involved in the modification and writing of Linux, and programmers can change them according to their own interests and inspirations, which allows Linux to absorb the essence of countless programmers and grow.
Fully compatible with the POSIX1.0 standard
This makes it possible to run common DOS and Windows programs under Linux with the appropriate simulator. This lays the groundwork for users to go from Windows to Linux. When many users consider using Linux, they think about whether the programs that were common to windows before are working properly, which eliminates their doubts.
Multi-user, multi-tasking
Linux supports multiple users, each user has their own special rights to the file device, to ensure that the user does not affect each other. Multitasking is one of the most important features of computers now, and Linux allows multiple programs to run simultaneously and independently.
A good interface
Linux has both a character interface and a graphical interface. In the character interface, the user can use the keyboard to enter the appropriate instructions. It also provides a x-window system similar to the Windows graphical interface that allows users to manipulate it using the mouse. In the X-window environment, like in Windows, it can be said to be a Linux version of Windows.
Supports multiple platforms
Linux can run on a variety of hardware platforms, such as those with x86, 680x0, SPARC, and Alpha processors. In addition, Linux is an embedded operating system that can run on a handheld, set-top box, or game console. The Linux version 2.4 kernel, released in January 2001, has been able to fully support Intel's 64-bit chip architectures. Linux also supports multi-processor technology. Multiple processors work at the same time, which greatly improves system performance.

2018--linux face question