60 essential Linux commands 2/3

[javajolt]

21. cut command

The cut command selects specific sections from a file and prints them as a Terminal output. The syntax looks like this:

cut options file

Unlike other Linux utilities, the cut command’s options are mandatory for file sectioning. Here are some of the flags:

   • -f – selects a specific row field.

   • -b – cuts the line by a specified byte size.

   • -c – sections the line using a specified character.

   • -d – separates lines based on delimiters.

You can combine multiple options for a more specific output. For example, this command extracts the third to fifth field from a comma-separated list:

cut -d',' -f3-5 list.txt

22. diff command

The diff command compares two files and prints their differences. Here’s the syntax

diff file_name1 file_name2

By default, the diff command only shows the differences between the two files. To print all the content and highlight the discrepancies, enable the context format using the -c option. You can also ignore case sensitivity by adding -i.

For example, run the following to show only the differences between 1.txt and 2.txt:

diff -c 1.txt 2.txt

23. tee command

The tee command outputs another command’s results to both the Terminal and a file. It’s helpful if you want to use the data for further processing or backups. Here’s the syntax:

command | tee [options] file_name

If the specified file doesn’t exist, tee will create it. Be careful when using this command since it will overwrite the existing content. To preserve and append existing data, add the -a option.

For example, we will save the ping command’s output as new entries in the test_network.txt file

ping 8.8.8.8 | tee -a test_network.txt

24. locate command

The locate command searches for a file and prints its location path. Here’s the syntax:

locate [options] [keyword]

If you use the -r option to search files using regular expressions, omit the [keyword] argument. The locate command is case-sensitive by default, but you can turn off this behavior using the -i flag.

Note that locate will look for files from its database. While this behavior speeds up the search process, you must wait for the list to refresh before finding newly created items.

Alternatively, enter the following to reload the data manually:

updatedb

25. find command

The find command searches for a file within a specific directory. Here’s the syntax

find [path] [options] expression

If you don’t specify the path, the find command will search your current working directory. To find files using their name, add the -name option followed by the keyword.

You can specify the type of item you are looking for using the -type flag. The –type f option will search files only, while -type d will find directories. For example, we will check file.txt in path/to/folder:

find path/to/folder -type f -name "file"

Unlike locate, the find command searches through folders in real time. While it slows down the process, you can look for new items immediately without waiting for the system database to refresh.

26. sudo command

superuser do or sudo enables non-root users who are part of the sudo group to execute administrative commands. Simply add it at the beginning of another utility like so:

sudo [options] your_command

For example, enter the following to open a file using nano as an administrator:

sudo nano file.txt

The Terminal will prompt you to enter the user’s password before executing the command. By default, you must reenter it after five minutes of inactivity.

Typically, you don’t add any option to sudo, but you can check them by entering:

sudo --help

27. su and whoami commands

The su command lets you switch to another user in the Terminal session. The syntax looks as follows:

su [options] [username]

If you don’t specify any option or username, this command will switch you to the root user. In this case, you must enter the password before changing the account.

You can check the currently logged-in user from the Linux command-line shell. Alternatively, use the whoami command:

whoami

28. chmod command

Chmod lets you change the permissions of files or directories. The basic syntax looks as follows:

chmod [options] [permission] [file_or_directory]

In Linux, there are three folder and file permissions – read (r), write (w), and execute (x). You can assign them to three parties – the owner, a group, or other accounts belonging to neither category. Consider this example:

chmod -rwx---r-– file1.txt

The spot after the first hyphen (–) specifies the permission for the owner of file1.txt. In the previous example, we grant them the rwx privilege.

The next spot is for groups. Since we won’t grant them any privilege, we put three hyphens to indicate emptiness. The last slot is for other users who only have read or r permission.

29. chown command

The chown command lets you change the ownership of files, directories, or symbolic links. Here’s the syntax:

chown [options] newowner:newgroup file1 file2

If you want to assign a user as the new owner of an item, leave the group name empty. For example, we will make admin-vps the owner of file1.txt:

chown admin-vps file1.txt

Conversely, omit the username to make all group members the owner. Remember to write the colons ( like so:

chown :newgroup file1.txt

30. useradd, passwd, and userdel command

Use the useradd command to create a new account in your Linux system. The syntax is as follows:

useradd [options] new_username

By default, the useradd command doesn’t prompt you to give the new user a password. You can add or change it manually later with the passwd command:

passwd new_username

To remove a user, use the userdel command followed by the account name like the syntax in the example:

userdel new_username

Since managing other users requires a superuser privilege, run these commands as root or with the sudo prefix.



31. df command

The df command checks your Linux system’s disk usage, displaying the used space in percentage and kilobyte (KB). The syntax looks like this:

df [options] [file system]

Note that the df command operates at the file system level. If you don’t specify one, the utility will display all the active file systems.



32. du command

To check the size of a directory and its content, use the du command. Here’s the syntax:

du [directory]

The command will check your working directory if you don’t specify a path or folder. By default, it breaks down each subfolder’s disk usage, but you can add the -s option to summarize the total usage in one output.

You can also use the -M option to change the information from KB to MB.

33. top command

The top command displays all running processes in your system and their hardware consumption. The syntax looks like this:

top [options]

The top command has various options. For example, -p lets you check a specific process by specifying its ID. Meanwhile, add the -d flag to change the delay between screen updates.

34. htop command

Like top, the htop command lets you display and manage processes in your Linux server. It also shares the same syntax:

htop [options]

htop has options similar to top, but you can add additional ones. For example, -C enables the monochrome mode, while –-tree shows processes in a hierarchical view.



35. ps command

The ps command summarizes the status of all running processes in your Linux system at a specific time. Unlike top and htop, it doesn’t update the information automatically. Here’s the syntax:

ps [options]

You can print a more detailed report by adding other options. For example, use -A to list all processes in your system, -r to check only the running ones, or -u username to query those associated with a particular account.

36. uname command

The unix name or uname command displays detailed information about your Linux machine, including hardware, name, and operating system kernel. Its basic syntax looks as follows:

uname [options]

Without any option, the command will print your system’s kernel name. To check all information about your machine, add the -a option.

37. hostname command

Use the hostname command to check your VPS hostname and other related information. Here is the syntax:

hostname [options]

If you leave the option empty, the command will print your hostname. Add -i to check your server’s IP address, -a to print the hostname alias, and -A to output the system’s fully qualified domain name (FQDN).

38. time command

The time command measures the execution time of commands or scripts to gain insights into your system performance. The basic syntax looks as follows:

time command_or_script

You can measure a series of commands by separating them using double ampersands (&&) or semicolons (;) like so:

time command; command; command

39. systemctl command

The systemctl command is used to manage services in your Linux system. Here’s the basic syntax:

systemctl subcommand [service_name][options]

The subcommands represent your task, like listing, restarting, terminating, or enabling the services. For example, we will list Linux services using this:

sudo systemctl list-unit-files --type service --all

Note that this command might not work with older distributions since they use another service manager.



40. watch command

The watch command lets you continuously run a utility at a specific interval to monitor changes in the output. Here’s the basic syntax:

watch [options] command_name

By default, watch will run your command every two seconds, but you can change the interval using the -n option followed by the delay. If you want to highlight changes in the output, add the -d flag

source