10 Advanced Linux Commands Every System Administrator Should Know

What Is Linux?

Linux is a popular open-source operating system that is based on the Unix operating system. It is widely used on servers, desktop computers, and other devices, and is known for its stability, security, and flexibility. Linux is developed and maintained by a global community of volunteers, and it is distributed under a variety of open-source licenses.

What is a Shell?

A shell is a command-line interface (CLI) that allows users to interact with the operating system. It provides a way to enter commands and execute programs, as well as access various features and functions of the operating system. The shell is an important component of Linux and other Unix-like operating systems, and there are many different shells available, each with its own set of features and capabilities.

Some common shells used on Linux systems include the Bourne shell (sh), the C shell (csh), and the Bourne Again shell (bash). The bash shell is the most widely used shell on Linux systems and is the default shell on many Linux distributions. It provides a range of features and tools for interacting with the operating system and is highly customizable.

The 10 Best Linux Commands That You Should Know

In this blog, we will take a look at the 10 best Linux commands that you should know, along with examples and explanations of how to use them.

1. grep

grep is a command-line utility that searches for lines in a file or input stream that match a given pattern. It is commonly used to search through logs, configuration files, and other types of text-based data.

Here is an example of how grep can be used to search for a specific string in a file:

grep "ERROR" /var/log/syslog

This command will search through the syslog file located in the /var/log directory for any lines that contain the string "ERROR".

grep has a number of options that can be used to modify its behavior. For example, the -v option can be used to invert the search, so that only lines that do not match the pattern are returned. The -i option can be used to perform a case-insensitive search, and the -n option can be used to include the line numbers in the output.

2. sed

sed is a command-line utility that is used to perform text transformations on an input stream. It is commonly used to manipulate files and streams of data, such as log files or the output of other commands.

Here is an example of how sed can be used to replace all occurrences of a specific string in a file:

sed "s/OLD_STRING/NEW_STRING/g" input.txt > output.txt

This command will take the input.txt file as input and replace all occurrences of "OLD_STRING" with "NEW_STRING", writing the result to the output.txt file.

sed has a number of powerful features, including the ability to use regular expressions to match patterns, and the ability to specify different actions to take based on the contents of a line. It can also be used in conjunction with other commands, such as grep, to perform more complex transformations.

3. awk

awk is a command-line utility that is used to process and analyze text-based data. It is particularly useful for extracting information from structured data, such as tab-separated or comma-separated values (TSV or CSV).

Here is an example of how awk can be used to extract the third field from each line of a TSV file:

awk -F'\t' '{print $3}' input.tsv

This command will take the input.tsv file as input and print the third field from each line, using the tab character (\t) as the field delimiter.

awk has a powerful programming language built into it, which allows you to specify complex processing rules and perform calculations on the input data. It is a versatile tool that is well worth learning if you need to work with structured data on the command line.

4. find

find is a command-line utility that is used to search for files and directories based on a set of criteria. It can be used to locate specific files by name, size, or other attributes, and can also be used to perform actions on the files that it finds.

Here is an example of how find can be used to search for all files with a specific extension in the current directory and its subdirectories:

find . -name "*.txt"

This command will search for all files with a .txt extension in the current directory (.) and its subdirectories, and will print the names of the files that it finds.

find has a number of options that can be used to refine the search criteria, such as -type to specify the type of file (e.g., f for regular files, d for directories), and -size to specify the size of the file in bytes. It can also be used in combination with other commands, such as xargs or grep, to perform more complex tasks.

5. tar

tar is a command-line utility that is used to create, extract, and manipulate archive files. It is commonly used to package files and directories for distribution or backup, and is capable of handling a wide variety of compression formats.

Here is an example of how tar can be used to create a compressed archive of a directory:

tar -czvf archive.tar.gz /path/to/directory

This command will create a gzip-compressed tar archive called archive.tar.gz of the contents of the /path/to/directory directory. The -c option tells tar to create an archive, the -z option specifies that the archive should be compressed with gzip, the -v option enables verbose output, and the -f option specifies the name of the archive file.

tar has a number of options that can be used to customize the behavior of the command, such as -x to extract an archive, -t to list the contents of an archive, and -u to update an existing archive with new or modified files.

6. ssh

ssh is a command-line utility that is used to securely connect to a remote machine over a network. It is commonly used to remotely administer servers, or to securely transfer files between systems.

Here is an example of how ssh can be used to connect to a remote machine:

ssh user@remote.example.com

This command will connect to the machine at remote.example.com as the user user. Once connected, you will be able to enter commands on the remote machine as if you were sitting at the console.

ssh has a number of options that can be used to customize the behavior of the command, such as -p to specify a different port number, -i to specify the path to an identity file (for key-based authentication), and -L to forward a local port to a port on the remote machine.

7. rsync

rsync is a command-line utility that is used to efficiently synchronize files and directories between two locations. It is commonly used to backup or transfer data between systems, and is particularly useful for transferring large amounts of data over a network, as it only transfers the parts of files that have changed.

Here is an example of how rsync can be used to synchronize the contents of a local directory with a remote directory:

rsync -avz /local/directory user@remote.example.com:/remote/directory

This command will synchronize the contents of the /local/directory directory on the local machine with the /remote/directory directory on the remote.example.com machine. The -a option tells rsync to preserve the attributes of the files and directories, the -v option enables verbose output, the -z option enables compression to reduce the amount of data transferred over the network, and the -e option specifies the ssh command to use to connect to the remote machine.

rsync has a number of options that can be used to customize its behavior, such as --exclude to specify patterns of files to exclude from the transfer, and --delete to delete files in the destination that are no longer present in the source.

8. chmod

chmod is a command-line utility that is used to change the permissions of files and directories. In Linux, permissions are used to control who is allowed to access and modify files and directories.

Here is an example of how chmod can be used to give read and execute permissions to all users for a file:

chmod a+rx file.txt

This command will add read (r) and execute (x) permissions to all users (a) for the file.txt file. The + operator adds the specified permissions, and the - operator removes them.

chmod can also be used to specify permissions using octal notation, which represents the permissions for each class of users (owner, group, and others) as a three-digit octal number. For example, the permissions rwxr-xr-x can be represented as 755.

9. ln

ln is a command-line utility that is used to create links between files and directories. In Linux, a link is a reference to a file or directory that is stored in a different location. There are two types of links: hard links and symbolic links.

A hard link is a direct link to a file or directory that is stored on the same filesystem. It is essentially an additional name for the same file or directory, and changes to the file or directory through one link will be reflected through all of the other links.

A symbolic link is a special type of file that contains a reference to another file or directory. It is essentially a shortcut to the target file or directory, and changes to the target file or directory will be reflected through the symbolic link.

Here is an example of how ln can be used to create a hard link to a file:

ln file.txt hardlink.txt

This command will create a hard link called hardlink.txt to the file.txt file. Changes to file.txt will be reflected through hardlink.txt, and deleting file.txt will not affect hardlink.txt, as it is a separate link to the same file.

Here is an example of how ln can be used to create a symbolic link to a file:

ln -s file.txt symlink.txt

This command will create a symbolic link called symlink.txt to the file.txt file. Changes to file.txt will be reflected through symlink.txt, and deleting file.txt will cause symlink.txt to become broken, as it is only a reference to the target file.

ln has a number of options that can be used to customize its behavior, such as -f to force the creation of a link, even if a file with the same name already exists, and -T to treat the target as a file, even if it is a symbolic link.

10. df

df is a command-line utility that is used to display information about the filesystems on a system. It can be used to show the available and used space on each filesystem, as well as the percentage of the filesystem that is used.

Here is an example of how df can be used to display information about the filesystems on a system:

df -h

This command will display information about the filesystems on the system in human-readable form (-h). The output will include the filesystem type, the total size of the filesystem, the amount of used space, the amount of available space, the percentage of the filesystem that is used, and the mount point for each filesystem.

df has a number of options that can be used to customize its behavior, such as -a to include filesystems of all types, -i to display information about the number of inodes on the filesystem, and -T to display the filesystem type for each filesystem.