19 commands commonly used under CentOS

People who have played Linux will know that there are really a lot of commands in Linux, but people who have played Linux have never bothered by the fact that Linux commands are so many, because we only need to master the commands we use most often. Of course you can also use to find the man, he will help you solve a lot of problems. However, everyone's purpose of playing Linux is different, so the commands they often use are very big, and I mainly use Linux for C + + and shell programs, so common commands can be different from a person who manages Linux systems. Because do not want in use is always East search, so summarize here, convenient for later view.

Not much, let's talk about my most commonly used Linux commands.

1. CD command

This is a very basic, is also a common need to use the command, it is used to switch the current directory, its parameters are to switch to the path of the directory, can be an absolute path, can also be a relative path. Such as:

• Cd/root/docements # Switch to directory/root/docements

• cd./path # Switch to the path directory in the current directory, "." Represents the current directory

• Cd.. /PATH # Switch to the path directory in the upper directory, "..." Represents a previous level of directory

2. ls command

This is a very useful view of the file and directory commands, List of meaning, it has a lot of parameters, the following list some of my commonly used parameters, as follows:

• -L: Lists Long data strings, including file attributes and permission data, etc.

• -A: Lists all the files, together with hidden files (files that begin with.) (common)

• -D: Lists only the directory itself, not the file data for the directory

• -H: List the file capacity in a more readable way (GB,KB, etc.)

• -R: Listed along with the contents of the subdirectory (recursively listed), equal to all files in that directory will be displayed

• Note: These parameters can also be used in combination, the following two examples:

• Ls-l #以长数据串的形式列出当前目录下的数据文件和目录

• LS-LR #以长数据串的形式列出当前目录下的所有文件

3. grep command

This command is often used to parse a row of information, if there is information we need, the row is displayed, the command is usually used with the pipeline command, for the output of some commands to filter processing, etc., its simple syntax is

grep [-ACINV] [--color=auto] ' Find string ' filename

Its common parameters are as follows:

• -A: Find data in a binary file as a text file

• -C: Calculate the number of times to find ' find string '

• -I: Ignore case differences, that is, case is considered the same

• -V: Reverse selection, which shows the line without the ' Find string ' content

For example:

# Take out the file/etc/man.config contains the MANPATH line and add the Found keyword color  grep–color=auto ' MANPATH '/etc/man.config  # put LS- The output of L contains the letter file (case-insensitive) content output  ls-l | grep-i file  

4. Find command

Find is a very powerful search-based command, relatively speaking, its use is relatively complex, parameters are also more, so here will be to classify them, its basic syntax is as follows:

Find [PATH] [option] [action]

Time-related parameters:

• -mtime N: = n is a number, meaning a file that has been changed in "One Day" before the nth day;

• -mtime +n: Lists the file names that were changed before n days (excluding the N-day itself);

• -mtime-n: Lists filenames that have been changed within n days (including n days themselves);

• -newer file: List file names that are newer than file

For example:

Find/root-mtime 0 # Find files that have changed within the current directory today

Parameters related to user or user group name:

• -user Name: List files with file owner name

• -group Name: List files that belong to the user group named name

• -uid N: List file owner as User ID n

• -gid N: Lists files that belong to the user group whose user group ID is n

For example:

Find/home/ljianhui-user Ljianhui # Find the owner-Ljianhui file in the directory/home/ljianhui

Parameters related to file permissions and names:

• -name FileName: Find the file named filename

• -size [+-]size: Find a file larger than size (+) or small (-)

• -tpye Type: Find file type of file, the value of type is mainly: General file (f), device file (b, c), directory (d), connection file (L), socket (s), FIFO pipeline file (p);

• -perm mode: Find file permissions just equal to the mode file, mode is represented by a number, such as 0755;

• -perm-mode: Find file permissions must all include the mode permission of the file, mode is represented by a number

• -perm +mode: Find file Permissions file that contains the permissions of either mode, mode is represented by a number

For example:

Find/-name passwd # Lookup file named passwd file Find  .-perm 0755 # 0755 file to find file permissions in the current directory  

5. CP command

This command is used to copy the file, copy the meaning, it can also copy multiple files to a directory at one time, its common parameters are as follows:

• -A: Copy the attributes of the file together

• -P: Copied along with the properties of the file, not by default, similar to-a, often used for backup

• -I: If the target file already exists, the action will be asked before overwriting

• -R: Recursive continuous Replication for directory replication behavior

• -U: The destination file is copied when it differs from the source file

For example:

Cp-a file1 file2 #连同文件的所有特性把文件file1复制成文件file2  cp file1 file2 file3 dir #把文件file1, file2, file3 copy to directory dir  

6. MV Command

This command is used to move a file, directory, or rename, and its common parameters are as follows:

• -f:force mandatory Meaning, if the target file already exists, will not ask and directly overwrite

• -I: If the target file already exists, you will be asked to overwrite

• -U: Updates if the target file already exists and is newer than the target file

Note: This command can move a file or multiple files one folder at a time, but the last target file must be "directory".

For example:

MV File1 file2 file3 dir # move the file file1, File2, file3 to the directory dir in  mv file1 file2 # Rename the file file1 to File2  

7. RM command

This command is used to delete files or directories, between remove, and its common parameters are as follows:

• -F: Force means ignoring files that do not exist and warning messages are not present

• -I: Interactive mode, ask the user whether to operate before deleting

• -R: Recursive delete, most commonly used for directory deletion, it is a very dangerous parameter

For example:

Rm-i File # To delete files, ask if you want to do this before deleting  rm-fr dir # forces all files in directory dir to be deleted  

8. PS command

This command is used to select and output the process run at a point in time, and its common parameters are as follows:

• -A: All processes are displayed

• -A: All processes not related to terminal

• -U: Related processes for effective users

• -X: Generally used in conjunction with a parameter to list more complete information

• -L: Longer, the PID information is listed in more detail

In fact, we just need to remember the general use of PS command parameter collocation can be, they are not many, as follows:

PS aux # View system All process data  PS Ax # View all processes not related to terminal  Ps-la # View system All process data  PS AXJF # View together with part of the process tree status  

9. Kill command

This command is used to send a signal to a job (%jobnumber) or to a PID (number), which is typically used with the PS and jobs commands, with the following basic syntax:

Kill-signal PID

The commonly used parameters of signal are as follows (note: The first digit is the signal's code name, can be used to replace the corresponding signal):

• View Plaincopyprint?

• 1:sighup, start the terminated process

• 2:sigint, equivalent to input CTRL + C, interrupts the process of a program

• 9:sigkill, forcing the interruption of a process

• 15:sigterm to terminate the process with normal end-of-process mode

• 17:sigstop, which is equivalent to input CTRL + Z, pauses a process

For example:

# at the end of the normal process to finally the first background work, you can use the Jobs command to view the background of the first worker process  kill-sigterm%1  # re-change process ID PID process, PID can be filtered with the PS command via the pipe command plus grep command to get  kill-sighup pid  

10. Killall command

This command is used to send a signal to a process initiated by a command whose general syntax is as follows:

Killall [-iie] [command name]

It has the following parameters:

• -I: interactive meaning, if need to delete, will ask the user

• -E: Indicates that command name is followed by the same, but command name cannot exceed 15 characters

• -I: Command name ignores case

Example: Killall-sighup syslogd # reboot SYSLOGD

11. File command

This command is used to determine the basic data of files after the file command, because the type of the file under Linux is not the suffix of the future, so this command is very useful for us, its usage is very simple, the basic syntax is as follows:

View Plaincopyprint?

File filename

For example: file./test

12. Tar command

This command is used to package the file, which is not compressed by default and, if specified, it also invokes the appropriate compression program (such as Gzip and bzip) for compression and decompression. Its common parameters are as follows:

• -C: New package file

• -T: See what file names are included in the contents of the packaged files

• -X: Unpacking or decompression function, can be used with-C (uppercase) to specify the extracted directory, note-c,-t,-x cannot appear in the same command

• -J: Compression/decompression via BZIP2 support

• -Z: Compression/decompression with GZIP support

• -V: Displays the file name being processed during the compression/decompression process

• -F filename:filename for files to be processed

• -C dir: Specify a directory for compression/decompression dir

The above commentary may have knocked you out of the way, but usually we just need to remember the following three commands:

• Compression: TAR-JCV filename.tar.bz2 The name of the file or directory to be processed

• Enquiry: Tar-jtv-f filename.tar.bz2

• Unzip: Tar-jxv-f filename.tar.bz2-c to extract the directory

Note: The file name is not set to end in the suffix tar.bz2, this is mainly to illustrate the use of the compression program for BZIP2

13. Cat Commands

This command is used to view the contents of a text file, followed by the name of the file to be viewed, and is typically used in conjunction with more and less to allow you to view the data one page at a time.

Example: Cat text | Less # View the contents of the text file

# Note: This command can also use less text instead

14. CHGRP command

This command is used to change the user group to which the file belongs, it is very simple to use, its basic usage is as follows:

CHGRP [-R] Dirname/filename

-R: Recursive persistent changes to all files and subdirectories

For example: Chgrp users-r./dir # Recursively modifies the user group for all files and subdirectories under the Dir directory to users

15. Chown Command

This command is used to change the owner of the file, using the same method as the CHGRP command, except that the modified file attributes are different and are no longer detailed

16. chmod command

This command is used to change the permissions of a file, as follows:

chmod [-r] XYZ file or directory

-R: Continuous change of recursion, that is, all files under subdirectories are changed

At the same time, chmod can also use the U (user), G (group), O (Other), a (all) and + (join),-(delete), = (set) with the rwx to make changes to the permissions of the file.

For example:

chmod 0755 File # change files permissions to-rxwr-xr-x  chmod g+w File # To add user group writable permissions to files ' permissions  

17. Vim Command

This command is primarily used for text editing, which takes one or more file names as parameters, opens if the file exists, and creates a file with the file name if it does not exist. Vim is a very useful text editor, it has a lot of very useful commands, here no longer say. You can download a detailed description of VIM's common operations from here.

18. GCC command

For a person who developed a C program with Linux, this command is very important, it is used to compile the C language source program files, compiled into an executable program, because many parameters of g++ and it very similar, so here only the parameters of the GCC, its common parameters are as follows:

• -o:output, used to specify the file name to generate an executable file

• -C: Used to generate a target file (. o) from the source file and prevent the compiler from creating a complete program

• -I: Increase the path of the search header file at compile time

• -L: Increase the path of the search static connection library at compile time

• -S: Generate assembly code files for source files

• -LM: A library of libraries named LIBM.A in the directory that represents the standard library

• -lpthread: Connecting NPTL-Implemented lines libraries

• -std=: Used to specify the version of the C language to use

For example:

# The source file test.c compiled into executable program test  gcc-o test test.c-lm-std=c99 #把源文件test according to C99 Standard  . c to the corresponding assembler source file Test.s  gcc-s TEST.c  

19. Time command

This command is used to measure the execution time of a command (that is, a program). It's very simple to use, just like you would normally enter a command, but add a time to the front of the command, for example:

Time./process

Time PS aux

After the program or command has finished running, it outputs three times at the end, respectively:

• User: CPU time, the user CPU time that the command executes, that is, the command executes the sum of time in the user state;

• System: CPU time, the system CPU time that the command executes, that is, the command executes the sum of time in the kernel mentality;

• Real: The actual time, from the command line to start execution to the end of the elapsed time;

Note: The sum of CPU time and system CPU time is CPU time, that is, the total amount of time the command consumes CPU execution. The actual time is greater than the CPU time, because Linux is a multitasking operating system, often when executing a command, the system also handles other tasks. Another problem to be aware of is that even though the same command is executed every time, the time spent is not the same, and the time spent is related to the operation of the system.

19 commands commonly used under CentOS