21 Linux commands that interviewers often test

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find /var/mail/ -size +50M -exec rm {} ＼;

4. File permissions

Use " " to set permissions, use "-" to cancel

9. chmod command

• ##ls -lh show permissions
• chmod ugo rwx directory1 Sets the owner (u), group (g) and others (o) of the directory to read (r, 4), write (w, 2) and execute ( Permissions of
#10. chown command

##Change the owner of the file: chown user1 file1 Change the owner attribute of a file

chown -R user1 directory1 Change the owner attribute of a directory and change the attributes of all files in the directory at the same time

• chown user1:group1 file1 Change the owner and group attributes of a file

11. chgrp command

Change the user group to which the file belongs:

• chgrp group1 file1 Change the group of the file

##5. Text processing

12. The grep command

#analyzes the information in a line. If there is the information we need, the line will be displayed. Come out, this command is usually used together with the pipeline command to filter and process the output of some commands, etc.:

• grep Aug /var/log/messages in the file' Search for the keyword "Aug" in /var/log/messages'
• grep ^Aug /var/log/messages Search for the keyword "Aug" in the file '/var/log/messages' "Starting words
• grep [0-9] /var/log/messages Select all lines containing numbers in the '/var/log/messages' file
• grep Aug -R /var/log/* Search for the string "Aug" in the directory '/var/log' and subsequent directories
• sed 's/stringa1/stringa2/g' example.txt Replace "string1" in the example.txt file with "string2"
• sed '/^ $/d' example.txt Delete all blank lines from the example.txt file (search the public account Java Zhiyin, reply "2021", and give you a Java interview question guide)

13. paste command

• paste file1 file2 Merge the contents of two files or two columns
• paste -d ' ' file1 file2 Merge the contents of two files or two columns, using " " to distinguish

##14. sort command

• sort file1 file2 Sort the contents of two files
• sort file1 file2 | uniq takes out the union of two files (only one copy of duplicate lines is kept)
• sort file1 file2 | uniq -u deletes the intersection and leaves other lines
• sort file1 file2 | uniq -d removes the intersection of two files (leaving only files that exist in both files)

15. comm command

• comm -1 file1 file2 Compares the contents of two files and deletes only the contents contained in 'file1'
• comm -2 file1 file2 Compare the contents of two files and delete only the contents contained in 'file2'
• comm -3 file1 file2 Compare two Only the parts common to the two files are deleted from the file

6. Packing and compressing the file

16. The tar command

packages files. By default, it will not compress the files. If the corresponding parameters are specified, it will also Call the corresponding compression program (such as gzip and bzip, etc.) for compression and decompression:

• -c: Create a new packaging file
• -t: View the file names contained in the packaged file
• -x: Unpacking or decompression function, can be used with -C (capital) to specify the decompression directory, pay attention to -c ,-t,-x cannot appear in the same command at the same time
• -j: Compression/decompression through bzip2 support
• -z: Compress/decompress with gzip support
• -v: During the compression/decompression process, the file name being processed is displayed
• -f filename: filename is the file to be processed
• -C dir: Specify the compressed/decompressed directory dir
• Compression: tar -jcv -f filename.tar.bz2 The file to be processed Or directory name
• Query: tar -jtv -f filename.tar.bz2
• Decompression: tar -jxv -f filename.tar. bz2 -C Directory to be decompressed
• bunzip2 file1.bz2 Decompress a file called 'file1.bz2'
• bzip2 file1 Compress one A file called 'file1'
• gunzip file1.gz Decompress a file called 'file1.gz'
• gzip file1 Compress a file called ' file1' file
• gzip -9 file1 Maximum compression
• rar a file1.rar test_file Create a file called 'file1.rar' Package
• rar a file1.rar file1 file2 dir1 Compress 'file1', 'file2' and directory 'dir1' at the same time
• rar x file1 .rar Unzip the rar package
• zip file1.zip file1 Create a compressed package in zip format
• unzip file1.zip Unzip a compressed zip file Package
• zip -r file1.zip file1 file2 dir1 Compress several files and directories into a zip format compressed package

7. System and shutdown (system shutdown, restart and logout)

• shutdown -h now Shut down the system(1)
• init 0 Shut down the system(2)
• telinit 0 Shut down the system (3)
• shutdown -h hours:minutes & Shut down the system according to the scheduled time
• shutdown -c Cancel the shutdown according to the scheduled time System
• shutdown -r now Restart(1)
• reboot Restart(2)
• logout Logout
• time Measure the execution time of a command (i.e. program)

8. Process related The command

17 jps command

displays the current system The java process status and its id number:

• jps (Java Virtual Machine Process Status Tool) is a command provided by JDK 1.5 to display the pid of all current java processes. It is simple. Practical and very suitable for simply viewing some simple situations of the current java process on the linux/unix platform.

18 ps command

is used to change the Select the running status of the process and output it. The meaning of process:

• -A: All processes are displayed
• -a : All processes not related to the terminal
• -u : Processes related to the effective user
• #-x : Generally used with the a parameter, Can list more complete information
• -l: longer, list the PID information in more detail

ps aux # 查看系统所有的进程数据ps ax # 查看不与terminal有关的所有进程ps -lA # 查看系统所有的进程数据ps axjf # 查看连同一部分进程树状态

19 kill命令

用于向某个工作（%jobnumber）或者是某个PID（数字）传送一个信号，它通常与ps和jobs命令一起使用：

20 killall命令

（向一个命令启动的进程发送一个信号）

21 top命令

是Linux下常用的性能分析工具，能够实时显示系统中各个进程的资源占用状况，类似于Windows的任务管理器。

如何杀死进程：

• 图形化界面的方式
• kill -9 pid （-9表示强制关闭）
• killall -9 程序的名字
• pkill 程序的名字

查看进程端口号：

netstat -tunlp|grep 端口号

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