Linux has become one of the most important operating systems for system administrators. As a system administrator, knowing Linux commands is essential to managing and maintaining a Linux system. In this article, we will introduce 10 must-know Linux commands for system administrators.

1. ls Command
The ls command is used to list files and directories in a directory. This command is often used to check the content of a directory, especially when you want to know if a file or directory exists or not. For example, typing "ls" will list all the files in the current directory.

2. chmod Command
The chmod command is used to change the permissions of files and directories. It is an important command for system administrators who need to manage file permissions. For example, typing "chmod 755 filename" will give the owner of the file read, write, and execute permissions, while others will only have read and execute permissions.

3. grep Command
The grep command is used to search for a specific string in a file. This command is very useful for system administrators who need to find specific information in a log file. For example, typing "grep error logfile" will find all the lines in the file that contain the word "error".

4. find Command
The find command is used to find files and directories based on a set of criteria. This command is very useful for system administrators who need to search for files that meet specific criteria. For example, typing "find / -name '* .txt'" will find all the files with the extension ".txt" in the root directory.

5. ps Command
The ps command is used to show the processes running on a Linux system. This command is very useful for system administrators who need to monitor system resources and identify processes that are using too much memory or CPU. For example, typing "ps -ef" will show all the processes running on the system.

6. ping Command
The ping command is used to test the connectivity between two hosts. This command is very useful for system administrators who need to troubleshoot network connectivity issues. For example, typing "ping google.com" will test the connection to the Google website.

7. top Command
The top command is used to view the resource usage of processes running on a Linux system. This command is very useful for system administrators who need to monitor system performance. For example, typing "top" will show the processes that are using the most CPU and memory.

8. df Command
The df command is used to show the disk space usage on a Linux system. This command is very useful for system administrators who need to monitor disk space usage and identify files that are taking up too much space. For example, typing "df -h" will show the disk space usage in a human-readable format.

9. free Command
The free command is used to show the memory usage on a Linux system. This command is very useful for system administrators who need to monitor system memory usage and identify processes that are using too much memory. For example, typing "free -m" will show the memory usage in megabytes.

10. ssh Command
The ssh command is used to connect to a remote Linux system using a secure shell protocol. This command is very useful for system administrators who need to manage and administer a Linux system remotely. For example, typing "ssh username@hostname" will connect to the remote system using the username and hostname.

In conclusion, these 10 must-know Linux commands are essential for system administrators who need to manage and maintain a Linux system. By mastering these commands, system administrators can efficiently manage and troubleshoot a Linux system.