1. Overview of Linux

1.1 Why do testers learn linux

For software testers, any product we test is based on an operating system. For example, the QQ software we use every day, it has versions for windows, ios, Android, Mac OS, etc. It is necessary to install QQ on each platform to conduct corresponding tests. Therefore, proficiency in using these operating systems and mastering the basic knowledge of a series of operating systems should be the basic skills that every test engineer must master.

At present, the mainstream operating systems in the market include windows, unix, linux, etc., and linux, as the operating system used for the background server deployment of many software applications, is also the most widely used server-side operating system. Proficient in the use of linux systems, such words often appear in test job requirements and job seekers' skill descriptions. In this group of testers, those who can really use the Linux operating system proficiently, even if they are only familiar with common commands, are relatively rare! Therefore , testers learn linux , not only can they improve the depth of testing , but also can increase their core competitiveness , broaden their skill stacks , and improve their testing capabilities at a deeper level

What can testers do to learn linux? As a beginner, building a test environment should be the primary purpose of learning.

1.2 What is linux

Linux is an open source, free operating system. Its stability, security, and multi-concurrency processing have been recognized by the industry. At present, many neutral, large and even giant projects are using Linux.

Linux kernel: redhat, red flag linux, ubuntu, suse, fedora,

Their kernels are all the same (linux is actually a general term)

The Linux operating system has many advantages: free open source, multi-threading, multi-user support, good security, superior memory and file management, embedded system suitable for small kernel programs, etc.

The disadvantage of linux is that it uses command line operation, so the operation is relatively difficult, but it is this kind of character-level command line operation, which will occupy less system resources and reduce the possibility of being attacked and making mistakes.

1.3 Differences between linux and Windows

1.4 How to learn linux

A tester's learning of linux is not necessarily very systematic, because proficient in linux is the job responsibility of the operation and maintenance personnel. As a tester, the primary purpose of learning should be to be proficient in using common commands and proficient in building a test environment. Therefore, keep practicing the commands. You should type each common command several times to verify the feedback after entering the command. Finally, practice makes perfect, and you can slowly remember the common commands.

So, how to learn linux? One word: practice!

2. Getting started with linux

2.1 Files, Directories

13.2.2 linux files

All contents of linux are stored in the form of files, including hardware (everything is a file), and linux does not distinguish file types by extension.

There are many basic types of linux, the common ones are as follows:

2.3 linux directory

The Linux file system adopts a hierarchical tree-like directory structure. The top level of this structure is the root directory "/", and then other directories are created under this directory.

In the linux system, all files and directories start with the root directory /, the directories starting with / become absolute directories, and those that do not start with the root directory / are called relative directories.

The linux system file directory is organized as follows

2.4 Common shortcut keys

3. Common commands

After users log in to Linux, they can enter commands behind the Linux command prompt to interact with the system.

As follows:

[root@localhost~]#

in:

root: the currently logged in user

localhost:hostname

~: the current directory, ~ represents the home directory

#: The prompt of the super user, if it is a normal user, the prompt is $

linux command format: command [options] [parameters]

For example: cp dir1 dir2, cp is the copy command, dir1 and dir2 are parameters, which means to copy dir1 to dir2

Notice:

Individual command usage does not follow this format

When there are multiple commands, they can be written together

Simplified and full options, such as -a equals -all

Linux is strictly case-sensitive, and general commands are all lowercase without special instructions.

There are spaces between linux commands and parameters, please do not crowd them all together like English letters

The following is a detailed description of the most frequently used and commonly used commands in Linux.

4. Disk Management

4.1 cd

cd , change directory (chang directory)

The cd command allows the login user to switch between different directories

Syntax: cd [target directory]

The following are some commonly used directory switching

Difference between relative path and absolute path

cd relative path: as long as the beginning is not / is a relative path, it will refer to the current directory and search through the relative path

cd absolute path: An absolute path is a file or directory name starting with the root directory /. For example: /home/data/package, it will start from the root directory (that is, the top-level directory /), and perform recursive search level by level. The absolute path e method is used through the cd command. As long as the path is correct, it can be located in any directory. Enter the specified directory.

4.2 ls

ls, list directory contents

Syntax: ls [target directory]

The ls command lists directory contents, including the names of files and subdirectories

The habit of using at work is generally to switch to a certain directory with the cd command, and directly enter ls to view the contents of the current directory, which is similar to opening a certain folder on the Windows system.

Another common way of writing is ll, ll is the abbreviation of ls -l, which can list the contents of the directory in a list format, such as:

The description of each property of the package below:

The first 10 characters of each line can determine the type of the file and the permissions of different users on the file

The first character indicates the type: file (-), directory (d), link (l)

The rest of the characters are in groups of 3 (rwx), read (r), write (w), execute (x)

The first group of rwx: file owner permissions are read, write and execute

The second group of rx: the permissions of users in the same group as the file owner are read and execute, no write permissions

The third group rx: the permissions of other users who are not in the same group as the file owner are read and execute, no write permissions

Read, write, and execute are represented by numbers as r=4, w=2, x=1 respectively.

rwx =4+2+1=7

rx=4+0+1=5

rx=4+0+1=5

So the permissions of the file for different users can be represented by the value 755

4.3 pwd

pwd, print working directory

Execute the pwd command to obtain the absolute path of the current working directory.

4.4 mkdir

mkdir, make directory

-p: Create a directory recursively, that is, if the upper-level directory of the directory is not created, the upper-level directory will be created together.

4.5 rmdir

Delete empty directories, this command is rarely used in actual operation, we generally use rm

Note that the rmdir command can only delete empty directories. If you want to delete all files in the directory, you can use: rm -rf path

4.6 df

df, displays information about the disk, such as file system usage

df [-ahikHTm] [directory or filename]

-a : list all filesystems

-k: Display each file system in KB

-m: Display each file system in MB

-h: Display in GB, MB, KB, etc. formats

-H: replace the calculation method of M=1024K with M=1000K

-T: List along with the partition's filesystem name (eg ext3)

-i: Display the number of inodes instead of the hard disk capacity

df [path], see which partition a directory is in, and display other information

Note that the two commands df and du are not frequently used by testers.

4.7 du

du, displays the size of a directory or file, and the du command displays the disk space occupied by the specified directory or file

Syntax: du [-ahskm] [file or directory name]

-a : List all file and directory sizes

-h: Display in human-readable capacity format (G/M)

-s: show the total, do not list the capacity occupied by each directory

-k: display capacity in KB

-m: List capacity display in MB

5. File Management

5.1 touch

touch, change the file or directory time, can also create an empty document

touch [-acdmt] filename

-a : modify access time

-c : modify time without creating file

-d: You can follow the date, or you can use --date="date or time"

-m: modify mtime

-t: Time can be followed by time, the format is [YYMMDDhhmm]

5.2 cp

cp copy command

The cp command is used to copy files or directories. The parameter must specify two or more files or directories, and the last path must be an existing directory. The previously specified file or directory can be copied to this directory.

Common parameters:

-a This option is usually used when copying directories. It preserves links, file attributes, and recursively copies directories.

-p copies the contents of the source file, and copies the modification time and access rights to the new file

-r If the given source file is a directory file, then cp will recursively copy all subdirectories and files in the directory. At this point the target file must be a directory name

Such as: cp -r dir1 dir2 dir3, recursively copy, copy dir1 and dir2 to the dir3 directory

5.3 mv

mv , move and rename

The mv command can move files or directories, and can also change file or directory names

grammar:

mv [source file or directory] [destination file or directory]

Such as mv dir1 dir2: move dir1 to the dir2 directory

mv /home/hello /home/world; rename the hello file in the /home directory to world

5.4rm

rm , delete files and directories

The rm command can delete a file or directory, use the parameter "-r" to delete the directory, otherwise the default is to delete the file

rm -rf * , delete everything, including directories and files

where -r means recursion and -f means force

5.5 cat

cat , display the contents of the file, and print the contents of the file to the standard output device

Syntax: cat fileName

Common parameters:

-n : Number the number of lines of output

5.6 head

View the first N lines of a plain text document and write to standard output

head -n 20 View the first 20 lines of a text file

5.7 tail

View the last N lines of a plain text document and write to standard output

tail -n 20 View the last 20 lines of a text document

tail -f error.log is constantly refreshed to view changes in file content in real time

5.8 more, less

more , display file content with pagination

Syntax: more fileName

The more command is similar to cat. It is displayed one page at a time, which is easy to read. Press the space bar to turn to the next page, and press the b key (or ctrl + pag up to turn up) to turn forward one page.

more + 10 fileName : display the content of fileName from line 10

less , display file content with pagination

less is similar to more, use less to browse files at will

5.9 echo

echo: output string

Syntax: echo [-ne] [string] or echo [--help][--version]

echo will send the input string to standard output

6. System Settings

6.1 alias

alias: some commands are very long, or the name seems awkward, you can give the command an alias

Command: alias: Display all aliases currently defined by the system

【Case】 alias cp = 'cp -i'

[Case] ​​alias li = 'ls -l -color=tty'

Users can use alias , the alias of a custom command. If only alias is entered, all current alias settings will be listed. The validity of the alias is only based on the operation of the login. To set the alias automatically every time you log in, you can set the alias of the command in /etc/profile or your own ~/.bashrc.

Also, if you want a valid alias for every user, add the line alias la = 'ls -al' to the end of /etc/bashrc

bashrc is a configuration file for environment variables. The difference between /etc/bashrc and ~/.bashrc is that one is set for the whole system and the other is set for a single user. If you want to give an alias that takes effect for every user, please put alias la = 'ls -al' line is added to the end of /etc/bashrc, bashrc is a configuration file for environment variables. The difference between /etc/bashrc and ~/.bashrc is that one is set for the whole system and the other is set for single-user use

Execution order of commands:

1: Execute commands with absolute and relative paths

2: Execute alias

3: Execute Bash's internal commands

4: Execute to find the first command according to the directory defined by the $PATH environment variable

6.2 aliases

unalias: remove alias

Syntax: unalias alias

6.3 export

export, set and display environment variables

The export command can add, modify and delete environment variables

export -p : List all environment variables assigned to the program by the shell.

6.4 man

man [command] , help, similar to help in dos; man is actually manual (operation instructions),

man's level:

1: View the help for the command

2: View help for functions that can be called by the kernel

3: View help for functions and function libraries

4: View special files for help, mainly files in the /dev directory

5: View the help of the configuration file

6: View the game's help

7: View help for other miscellaneous items

8: View help for commands available to system administrators

9: View and kernel related files for help

See what level of help the command has:

man -f command, equivalent to whats command

eg: man -5 passwd

man -4 null

man -8 ifconfig

View all help related to commands

man -k command, equivalent to apropos command