Master Linux:คำสั่งสำคัญกว่า 50 คำสั่งเพื่อการจัดการระบบที่มีประสิทธิภาพ

เมื่อตั้งค่าตัวแปรสภาพแวดล้อมแล้ว จะสามารถเข้าถึงได้โดยกระบวนการหรือคำสั่งใดๆ ที่ทำงานอยู่ในเชลล์เดียวกัน

ตัวแปรสภาพแวดล้อมสามารถใช้เพื่อจัดเก็บข้อมูลได้หลากหลาย เช่น การตั้งค่าการกำหนดค่า การกำหนดค่าตามความชอบของผู้ใช้ หรือข้อมูลระบบ

นี่คือตัวอย่างการใช้ 2514 คำสั่ง:

root@ubuntu:~# export <variable name>=<value>

เรียนรู้เพิ่มเติมเกี่ยวกับ 2521 คำสั่ง

ข้ามกลับไปที่รายการคำสั่ง ↑

ไวยากรณ์พื้นฐานของ 2551 คำสั่งคือ:

root@ubuntu:~ ssh username@remote-server

คำสั่งนี้สร้าง 2562 การเชื่อมต่อกับ 2574 โดยใช้ 2586 account.

The 2590 command supports a wide range of options and configurations, including:

• Configuring authentication methods (password, public key, etc.)
• Configuring encryption algorithms
• Configuring compression
• Configuring port forwarding
• Configuring X11 forwarding
• Configuring SSH keys

The 2603 command in Linux

The 2610 command in Linux is used to manage system services, which are long-running processes that are started at boot time and run in the background. These services are responsible for providing various system functionalities, such as networking, database management, and user authentication.

The 2628 command is used to start, stop, restart, and check the status of these services. It is a front-end to the 2633 command, which is used to manage the 2647 service manager.

The basic syntax of the command is as below.

root@ubuntu:~ service ssh status
root@ubuntu:~ service ssh stop
root@ubuntu:~ service ssh start 

As you can see in the image, the 2657 server is running on our system.

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The 2662 , 2679 , and 2682 commands

The 2690 , 2700 , and 2715 commands are all used to manage processes in Linux.

The 2720 command is used to display information about the current running processes on the system. Here are some examples of using the 2733 command:

Display a list of all running processes:

root@ubuntu:~ ps -ef

Display a list of all processes for a specific process ID (PID):

root@ubuntu:~ ps -p PID

Let’s see all of this in action:

root@ubuntu:~ ps 
root@ubuntu:~ kill <process ID>
root@ubuntu:~ killall <process name>

For demonstration purposes, we will create a shell script with an infinite loop and will run it in the background.

With the use of the 2741 symbol, we can pass a process into the background. As you can see, a new bash process with PID 14490 is created.

Now, to kill a process with the 2755 command, you can type 2764 followed by the PID(Process Id) of the process.

But if you do not know the process ID and just want to kill the process with the name, you can make use of the killall command.

You will notice that PID 2779 stayed active. That is because, both times, we killed the sleep process.

Learn more about the 2783 command and the 2798 command.

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The 2806 and 2815 commands

When working with Linux, the 2828 and 2831 commands are very efficient utilities to mount filesystems and get details of the file system.

The 2844 command is used to display the amount of disk space used and available on the file systems, and the 2858 command is used to mount a file system or device to a specific directory.

When we say 2865 , it means that we’ll connect the device to a folder so we can access the files from our filesystem. The default syntax to mount a filesystem is below:

root@ubuntu:~ mount /dev/cdrom /mnt
root@ubuntu:~ df -h

In the above case, 2877 is the device that needs to be mounted. Usually, a mountable device is found inside the 2882 โฟลเดอร์ 2891 is the destination folder to which to mount the device. You can change it to any folder you want, but we have used 2907 as it’s the system’s default folder for mounting devices.

To see the mounted devices and get more information about them, we use the df command. Just typing 2917 will give us the data in bytes, which is not readable. So, we’ll use the 2923 parameter to make the data human-readable.

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The 2937 and 2948 commands

The 2950 and 2968 commands are used to modify file permissions and ownership in Linux.

The 2974 command is used to change the permissions of a file or directory, and the 2985 command is used to change the ownership of a file or directory

The default syntax for both the commands is 2996 and 3005

root@ubuntu:~ chmod +x loop.sh
root@ubuntu:~ chmod root:root loop.sh

In the above example, we’re adding executable permissions to the 3016 file with the 3021 คำสั่ง In addition, with the 3032 command, we’ve made it accessible only to the root user and users within the root group.

As you will notice, the 3043 part is now changed to 3059 which is the new user who has full file ownership.

Learn more about the Linux file Permissions and using the 3062 command.

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The 3071 and 3085 commands

The 3095 and 3106 commands manage network interfaces and trace the route of network packets in Linux.

The 3114 command will give you the list of all the network interfaces along with the IP addresses, MAC addresses and other information about the interface.

root@ubuntu:~ ifconfig

There are multiple parameters that can be used, but we’ll work with the basic command here.

The 3129 command is used to trace the route of network packets and determine the path they take to reach a specific destination.

When working with 3132 , you can simply specify the IP address, hostname, or domain name of the endpoint.

root@ubuntu:~ traceroute <destination address>

Now, obviously, 3141 is just one hop (the network interface itself). You can try this same command with any other domain name or IP address to see all the routers your data packets pass through to reach the destination.

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The 3157 command in Linux

If you want to download a file from within the terminal, the 3164 command is one of the handiest command-line utilities available. It is one of the important Linux commands you should know when working with source files.

When you specify the link for download, it has to directly be a link to the file. If the file cannot be accessed by the 3174 command, it will simply download the webpage in HTML format instead of the actual file that you wanted.

Let’s try an example. The basic syntax of the 3188 command is :

root@ubuntu:~ wget <link to file>

Or,

root@ubuntu:~ wget -c <link to file>

The 3194 argument allows us to resume an interrupted download.

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The 3205 and 3217 commands

The 3227 and 3233 commands are used to manage firewalls in Linux.

UFW and IPTables are firewall interfaces for the Linux Kernel’s netfilter firewall. IPTables directly passes firewall rules to Netfilter while UFW configures the rules in IPTables, which then sends those rules to Netfilter.

Why do we need UFW when we have IPTables? Because IPTables is pretty difficult for a newbie. UFW makes things extremely easy. See the below example where we are trying to allow port 80 for our webserver.

root@ubuntu:~# iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
root@ubuntu:~# ufw allow 80

I’m sure you now know why UFW was created! Look at how easy the syntax becomes. Both these firewalls are very comprehensive and can allow you to create any kind of configuration required for your network. Learn at least the basics of UFW or IPTables firewall, as these are the Linux commands you must know.

Learn more about managing firewall with 3246 and managing firewall with 3251 .

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Package Managers in Linux

Different Linux distributions use different package managers. Since we’re working on a Ubuntu server, we have the 3261 package manager. But for someone working on a Fedora, Red Hat, Arch, or Centos machine, the package manager will be different.

Below are the commands on how to use these package managers on different Linux distributions.

• Debian and Debian-based distros - 3276
• Arch and Arch-based distros - 3288
• Red Hat and Red Hat-based distros - 3290
• Fedora and CentOS - 3306

Getting yourself well versed with the package manager of your distribution will make things much easier for you in the long run. So even if you have a GUI based package management tool installed, try an make use of the CLI based tool before you move on to the GUI utility. Add these to your list of Linux commands you must know.

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The 3319 command in Linux

“With great power, comes great responsibility” _

This is the quote displayed when a sudo-enabled user(sudoer) first uses the 3325 command to escalate privileges. This command is equivalent to logging in as 3330 (based on what permissions you have as a sudoer).

non-root-user@ubuntu:~# sudo <command you want to run>
Password: 

Just add the command 3344 before any command that you need to run with escalated privileges, and that’s it. It’s very simple to use, but can also be an added security risk if a malicious user gains access to a sudoer.

Learn more about how to create a new 3359 user and how to edit sudoers file.

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The 3364 command in Linux

Have you ever wanted to view the calendar in the terminal? There apparently are people who want it to happen, and well, here it is.

The 3376 command displays a well-presented calendar on the terminal. Just enter the command 3385 on your terminal prompt.

root@ubuntu:~# cal
root@ubuntu:~# cal March 2024

Although we don’t need it often, it’s a great addition! It’s an amazing option for terminal fans.

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The 3398 command

Do you have some commands that you run very frequently while using the terminal? It could be 3405 or 3419 , or it could be something longer like 3426 .

This is one of the productivity-boosting Linux commands you must know.

If you know a command that you run very often, it’s time to create an 3438 .

What’s an alias? In simple terms, it’s another name for a command that you’ve defined.

root@ubuntu:~# alias lsl="ls -l"
OR
root@ubuntu:~# alias rmd="rm -r"

Now, every time you enter 3449 or 3459 in the terminal, you’ll receive the output that you’d have received if you had used the full commands.

The examples here are for really small commands that you can still type by hand every time. But in some situations where a command has too many arguments that you need to type, it’s best to create a shorthand version of the same.

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The 3461 command in Linux

This command was created to convert and copy files from multiple file system formats. In the current day, the command is simply used to create bootable USB for Linux but there still are some things important you can do with the command.

The 3474 command in Linux is a versatile command used for low-level copying and conversion of data. It stands for “data-description” or “data definition,” and it can be used to copy and convert data between different file formats and storage devices.

For example, if we wanted to back up the entire hard drive as is to another drive, we would use the 3487 command.

root@ubuntu:~# dd if=/dev/sdb of=/dev/sda

The if and of arguments stand for input file and output file .

It’s a powerful and flexible tool, but it can also be dangerous if not used carefully. Always double-check your syntax and make sure you know what the command will do before executing it.

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The 3498 and 3509 commands

The 3510 and 3525 commands are used in Linux to search for information about programs and files.

The 3534 command locates the binary, source, and manual pages for a specific command or program, and the 3540 command displays a short description of a command or program.

root@ubuntu:~# whereis sudo
sudo: /usr/bin/sudo /usr/lib/sudo /usr/share/man/man8/sudo.8.gz

The 3550 command gives us an explanation of what a command actually is.

root@ubuntu:~# whatis sudo
sudo (8) - execute a command as another user

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The 3566 command in Linux

A few sections earlier, we talked about the 3578 คำสั่ง You observed that the 3581 command will output the active processes and end itself.

The 3593 command is like a CLI version of the task manager in Windows.

The 3601 command in Linux is a system monitoring tool that displays real-time information about system processes and resource usage. It provides a dynamic, real-time view of system activity, including CPU usage, memory usage, and process information.

หมายเหตุ: Here are some examples of using the 3617 command:

• Sort processes by memory usage:

root@ubuntu:~# top -o MEM

This will sort the process list by memory usage, with the most memory-intensive processes at the top.

• Display detailed information about a specific process:

root@ubuntu:~# top -p PID

Replace 3626 with the ID of the process you want to inspect.

• Display a summary of system resource usage:

root@ubuntu:~# top -n 1

This will display a single summary screen of system resource usage.

It’s a powerful and flexible tool for monitoring system activity and troubleshooting performance issues.

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The 3636 and 3646 commands

The 3657 and 3664 commands are used in Linux to manage user accounts.

The 3675 or 3686 commands are the exact same commands where 3690 is just a symbolic link to the 3705 คำสั่ง This command allows us to create a new user in Linux.

root@ubuntu:~# useradd JournalDev -d /home/JD

The above command will create a new user named 3715 with the home directory as 3728 .

The 3736 command, on the other hand, is used to modify existing users. You can modify any value of the user including the groups, the permissions, etc.

For example, if you want to add more groups to the user, you can type in:

root@ubuntu:~# usermod JournalDev -a -G sudo, audio, mysql

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The 3746 command in Linux

Now that you know how to create new users, let’s also set the password for them. The 3755 command lets you set the password for your own account, or if you have the permissions, set the password for other accounts.

Here are some examples of using the 3760 command:

• Change the password for the current user:

  root@ubuntu:~# passwd
  

This will prompt you to enter a new password for the current user.

• Change the password for a specific user:

  root@ubuntu:~# passwd username
  

Replace 3775 with the name of the user whose password you want to change.

• Force a user to change their password at the next login:

  root@ubuntu:~# passwd -f username
  

• Set an expiration date for a user’s password:

  root@ubuntu:~# passwd -e -n days -w warndays username
  

Replace 3781 with the number of days before the password expires and 3791 with the number of days before the password expires that the user will be warned.

These are just a few examples of using the 3807 command in Linux. By understanding how to use this command effectively, you can manage user accounts and ensure that your system is secure.

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Common Errors and Debugging

When working with Linux commands, you may encounter various errors and issues. Here are some common problems and how to resolve them:

1. Fixing “command not found” errors

If you receive a 3815 error, it means that the command you are trying to run is not recognized by the system. This can happen for several reasons:

1. The command is not installed on your system. You can install it using your package manager (e.g., 3829 , 3837 , 3845 ).

   If you see:

   bash: xyz: command not found
   

   Use:

   which xyz
   

   If the command isn’t installed, try installing:

   apt-get install <package-name>
   

2. The command is not in your system’s PATH. You can add the directory containing the command to your PATH.

   export PATH=$PATH:/path/to/command
   

3. You made a typo. Double-check the command for any spelling errors.

2. Resolving permission issues with sudo

If you encounter permission issues, you can use 3858 to run the command with superuser privileges. ตัวอย่างเช่น:

sudo command_name

3. Handling File Conflicts

File conflicts can occur when multiple users or processes attempt to modify the same file simultaneously. Here are some ways to handle file conflicts:

1. Use Version Control Systems (VCS): Tools like Git can help manage file conflicts by allowing users to merge changes and resolve conflicts manually.

   git merge <branch_name>
   

   If there are conflicts, Git will prompt you to resolve them. Open the conflicting files, make the necessary changes, and then commit the resolved files.

   git add <resolved_file>
   git commit -m "Resolved merge conflict"
   

2. Locking Mechanisms: Implement file locking to prevent multiple processes from writing to the same file simultaneously. Use 3860 in Linux to create a lock on a file.

   flock -x <file> -c "<command>"
   

3. Atomic Operations: Use atomic operations to ensure that file writes are completed in a single step, reducing the risk of conflicts.

   mv temp_file target_file
   

   Or, Use 3877 with 3887 (force) or 3894 with 3904 (interactive):

   mv -f file1 file2
   cp -i file1 file2
   

4. Debugging Performance Bottlenecks

Performance bottlenecks can significantly impact the efficiency of your system. Here are some steps to debug and resolve them:

1. Identify the Bottleneck: Use tools like 3919 , 3921 , 3933 , and 3949 to monitor system performance and identify the resource causing the bottleneck (CPU, memory, disk I/O, etc.).

   top
   

2. Analyze Logs: Check system and application logs for any errors or warnings that might indicate performance issues.

   tail -f /var/log/syslog
   

3. Optimize Code: Review and optimize your code to improve performance. Look for inefficient algorithms, unnecessary computations, and memory leaks.

4. Profile Your Application: Use profiling tools like 3953 , 3969 , or 3973 to analyze your application’s performance and identify slow functions or memory issues.

   gprof <executable> gmon.out
   

5. Scale Resources: If the bottleneck is due to resource limitations, consider scaling up your hardware or using load balancing to distribute the load across multiple servers.

FAQs

1. What are the most used Linux commands?

The most used Linux commands include 3987 , 3999 , 4007 , 4016 , 4025 , 4039 , 4048 , 4052 , 4069 , 4071 , 4082 , 4092 , 4104 , 4117 , 4127 , 4132 , 4142 , 4154 , 4168 , 4175 , 4180 , 4193 , 4209 , 4211 , 4224 , 4236 , 4244 , 4250 , 4269 , 4279 , and 4289 .

2. How do I list all available commands in Linux?

You can list all available commands in Linux by using the 4290 คำสั่ง This will display a list of all commands that are available on your system.

3. How do I find a file in Linux?

You can find a file in Linux using the 4307 คำสั่ง The basic syntax is 4316 , where 4327 is the directory where you want to start searching, and 4333 is the name of the file you’re looking for. For example, 4348 .

4. How do I kill a process in Linux?

You can kill a process in Linux using the 4355 คำสั่ง First, you need to find the process ID (PID) of the process you want to kill using the 4368 or 4379 คำสั่ง Then, use the 4380 command followed by the PID. For example, 4398 , where 4403 is the PID of the process.

5. What is the difference between 4418 and 4424 ?

The 4431 command is used to copy files or directories, while the 4440 command is used to move or rename files or directories. 4458 creates a duplicate of the original file, leaving the original intact, whereas 4462 moves the file to a new location, removing it from the original location.

6. How do I check my Linux system’s memory usage?

You can check your Linux system’s memory usage using the 4470 คำสั่ง This command displays the total amount of free and used physical and swap memory in the system. For example, 4488 will display the memory usage in a human-readable format.

บทสรุป

In this tutorial, you explored over 50 essential Linux commands covering file and directory management, process control, user permissions, networking, text processing, and shell utilities. You also worked through real-world examples, troubleshooting patterns, and comparisons between related commands.

You can now navigate the Linux filesystem, manage processes, configure permissions, and troubleshoot common issues from the command line. These commands form the foundation of effective Linux system administration and scripting.

To go deeper on specific topics, explore these tutorials:

• The grep Command in Linux/Unix
• The ls Command in Linux/Unix
• Process Management in Linux
• The ps Command in Linux
• An Introduction to the Linux Terminal

This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License.