Linux common commands
foreword
This blog will summarize the basic operating instructions of Linux based on the existing knowledge. Because my understanding of Linux is still at a relatively shallow level, this blog is only a summary of the most basic instructions of Linux. The following blogs are only for personal use. A summary of the learning process, it would be a great honor to be of help to all bloggers.
Basic instructions for directory or file operations
ls command
Function: For a directory, the subdirectories and files under the directory will be listed; for files, the file name and other related information will be listed
Syntax: ls [option] [directory or file]
Common options:
- ls -a : list all files in the directory
- ls -d : display the directory as a file
- ls -k : Indicates the file size in k bytes
- ls -l : list detailed information about files
- ls -r : Reverse the directory display
- ls -t : display in chronological order
- ls -R: List all files in subdirectories
example:
pwd command
Function: Display the current directory of the user
Syntax: pwd
cd command
Function: Switch the working directory, switch the current working directory to the specified directory
Syntax: cd directory name
Common options:
- cd . . : Return to the previous directory
- cd ~ : return to the user directory
- cd - : Return to the last visited directory
In the Linux system, the directory root files on the disk are formed into a directory tree, and each node is a directory or file
touch command
Syntax: touch [option] File
function: The touch command parameter can change the date and time of the document or directory, or create a new file
example
mkdir command
Syntax: mkdir[options] dirname(directory name)
Function: Create a directory named "dirname" under the current directory
Example
rm command
Function: Delete file or directory
Syntax: rm [option] [directory name/file name]
Common options:
- rm -f : force deletion, even if the file is read-only, it will be deleted directly
- rm -i : Ask for confirmation one by one before deleting
- rm -r : delete the directory and all files under it
Example:
ps: When performing a delete operation, try not to use the forced delete command, and carefully confirm the file name before proceeding
cp command
Function: copy file or directory
Syntax : cp[option] source file or directory name target file or directory name
Explanation: cp command is used to copy files or directories, if more than two files or directories are specified in one command at the same time, it will be Different results are produced depending on whether the last destination is an existing directory. If it is an existing directory, all previous directories and files will be copied to this directory. If not, an error message will be reported.
Common options:
- cp -f or -force: Forcibly copy files or directories, regardless of whether the destination directory or file already exists
- cp -i or -interactive: ask user before overwriting files
- cp -r : Recursive processing, processing files and subdirectories under the specified directory together, if the form of the source file or directory does not belong to a directory or a symbolic link, it will be treated as an ordinary file
Example:
mv command
Function: Move directory or file
Syntax: mv [options] source file or directory target file or directory
Common options:
- mv -f : Mandatory overwriting, if the target file already exists, directly overwrite without asking
- mv -i : If the target file already exists, ask if you want to overwrite it
Example:
man
Function: View the documentation of a command
Syntax: man [option] command
Common options:
- man -k : search the online help by keyword
- man num can only be found on page num
- man man can view several chapters and meanings in the man manual
Basic commands for file operations
vi command
Function: Default text editor on Linux
Syntax: vi filename
Operation instructions inside the text editor:
In view mode:
i: Enter edit mode (start editing from the cursor position)
o: Enter edit mode (start editing from a new line
j/k: The function is the same as the up and down arrows, switch lines
/search Content: Search after pressing Enter, press n after searching to switch to the next matching string, shift+n to return to the previous
gg: switch to the beginning of the entire document
shift+g: switch to the end of the entire document
dd: delete The line where the cursor is
located After completing all operations, enter:
w: write (save the modified document)
q: exit
!: force
wq: exit after writing
! q: force exit without writing,
and finally press enter to execute
in edit mode:
esc: switch back In view mode
, except the esc key, other keys will be edited as text content in edit mode
cat command
Function: Display file content (print output)
Syntax: cat [options] filename
Common options:
cat -n: number all lines of output
Example:
less instruction
Function: View the content of the file, even if all the content of the file will not be loaded into the memory immediately, you can also search
Syntax: less [parameter] file name
Commonly used options:
j/k/arrow keys: scroll up and down the screen
less -N: display the number of each line
n: repeat the previous search
q: exit
head command
**Function:** Used to display the beginning of the document to the standard output, the default head command prints the first 10 lines of the corresponding file
Syntax: head [option] file name
Common options:
- head -n+lines: how many lines before the custom display
Example:
tail command
Function: Used to display the content at the end of the specified file
Syntax: tail [options] [parameters] filename
Common options:
- -f read in a loop
- How many lines after -n+line number display
Example:
pipeline
Pipes are an old way of "interprocess communication". You can use | as a pipe symbol in Linux commands.
Syntax: Command 1 | Command 2
Function: Use the output of the previous command as the input of the next command
Example:
output line 15 in the test.txt file
redirect
In Linux, the startup of each process will be accompanied by the opening of these three IOs by default, that is, standard output, standard input, and standard error, which will correspond to the three devices of the monitor, keyboard, and monitor respectively. In Linux, many commands will
be The default output is to the standard output, that is, it is displayed on the monitor. For example: cat test.txt
We can use the > symbol to write the content that should be output to the standard output to the specified file. This operation is called redirection
Redirection can be broken down into three types
1. Standard input redirection: <
2. Standard output redirection >
3. Standard error redirection: 2 >
Therefore, in the previous example in the introduction pipeline, it is also possible to output the 15th line of the test.txt file. In the above,
first write the output of the first 15 lines of test.txt to a temporary file temp (if the current directory cannot find The file will automatically create one), and then output the last line of tmep
Process, network, system statistics related instructions
View process pid
Find by port number:
netstat -anp | grep port number
Example:
Find by process name:
ps -ef | grep process name
ps aux | grep process name
Example:
Linux users and permissions
Linux users
There are two types of users under Linux: super user (root) and ordinary user
- Super User: Can perform anything under Linux system
- Ordinary users: limited things to do under the Linux system
Related commands:
useradd username——create a new user
password password—set password
su -username——switch to a user, and switch system environment variables will also switch to the specified user
User permissions to access files
Basic authority
i read (r/4): Read has the authority to read the content of the file for the file; for the directory, it has the authority to browse the directory information write
(w/2): Write has the authority for the file The authority to modify the content of the file; for the directory, it has the authority to delete the files in the mobile directory
Execute (x/1): execute For the file, it has the authority to execute the file; for the directory, it has the authority to enter the directory
"-" Indicates that it does not have this permission
chmod: command
Function: Set the access permission of the file
Syntax: chmod [option] permission file name
Common options:
- R -> : recursively modify the permissions of directory files
The relevant format for permissions:
- +: increase permissions
- -: Cancel permission
- =: grant permission
User symbol:
- u: owner
- g: same group as the owner
- o: other users
- a: all users
ll: View the permissions and accessible users of files in the current directory
