What is linux service command

Linux service command

On Unix-like operating systems, the service command starts or stops a service by running an initialization script.

This page describes the Linux version of service.

Syntax

service runs an init script or upstart job in as predictable an environment as possible, removing most environment variables and with current working directory set to «/.«.

The SCRIPT parameter specifies an init script, located in /etc/init.d/SCRIPT, or the name of an upstart job in /etc/init. The existence of an upstart job of the same name as a script in /etc/init.d causes the upstart job to take precedence over the init.d script. The supported values of COMMAND depend on the invoked script, service passes COMMAND and OPTIONS to the init script unmodified. For upstart jobs, start, stop, and status are passed through to their upstart equivalents. Restart will call the upstart ‘stop‘ for the job, followed immediately by the ‘start‘, and will exit with the return code of the start command. All scripts should support at least the start and stop commands. As a special case, if COMMAND is —full-restart, the script is run twice, first with the stop command, then with the start command. This option has no effect on upstart jobs.

«service —status-all» runs all init scripts, in alphabetical order, with the status command. This option only calls status for sysvinit jobs, upstart jobs can be queried in a similar manner with ‘initctl list‘.

Related commands

init — The parent of all processes on the system.

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How to List All Running Services Under Systemd in Linux

A Linux systems provide a variety of system services (such as process management, login, syslog, cron, etc.) and network services (such as remote login, e-mail, printers, web hosting, data storage, file transfer, domain name resolution (using DNS), dynamic IP address assignment (using DHCP), and much more).

Technically, a service is a process or group of processes (commonly known as daemons) running continuously in the background, waiting for requests to come in (especially from clients).

Linux supports different ways to manage (start, stop, restart, enable auto-start at system boot, etc.) services, typically through a process or service manager. Most if not all modern Linux distributions now use the same process manager: systemd.

Systemd is a system and service manager for Linux; a drop-in replacement for the init process, which is compatible with SysV and LSB init scripts and the systemctl command is the primary tool to manage systemd.

In this guide, we will demonstrate how to list all running services under systemd in Linux.

Listing Running Services Under SystemD in Linux

When you run the systemctl command without any arguments, it will display a list of all loaded systemd units (read the systemd documentation for more information about systemd units) including services, showing their status (whether active or not).

To list all loaded services on your system (whether active; running, exited or failed, use the list-units subcommand and —type switch with a value of service.

List All Services Under Systemd

And to list all loaded but active services, both running and those that have exited, you can add the —state option with a value of active, as follows.

List All Active Running Services in Systemd

But to get a quick glance of all running services (i.e all loaded and actively running services), run the following command.

List Running Services in Systemd

If you frequently use the previous command, you can create an alias command in your

/.bashrc file as shown, to easily invoke it.

Then add the following line under the list of aliases as shown in the screenshot.

Create a Alias for Long Command

Save the changes in the file and close it. And from now onwards, use the “running_services” command to view a list of all loaded, actively running services on your server.

View All Running Services

Besides, an important aspect of services is the port they use. To determine the port a daemon process is listening on, you can use the netstat or ss tools as shown.

Where the flag -l means print all listening sockets, -t displays all TCP connections, -u shows all UDP connections, -n means print numeric port numbers (instead of application names) and -p means show application name.

The fifth column shows the socket: Local Address:Port. In this case, the process zabbix_agentd is listening on port 10050.

Determine Process Port

Also, if your server has a firewall service running, which controls how to block or allow traffic to or from selected services or ports, you can list services or ports that have been opened in the firewall, using the firewall-cmd or ufw command (depending on the Linux distributions you are using) as shown.

List Open Services and Ports on Firewall

That’s all for now! In this guide, we demonstrated how to view running services under systemd in Linux. We also covered how to check the port a service is listening on and how to view services or ports opened in the system firewall. Do you have any additions to make or questions? If yes, reach us using the comment form below.

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35 Linux Basic Commands Every User Should Know

When hearing about Linux, most people think of a complicated operating system that is only used by programmers. But it’s not as scary as it seems.

Linux is an entire family of open-source Unix operating systems, that are based on the Linux Kernel. This includes all of the most popular Linux based systems like Ubuntu, Fedora, Mint, Debian, and others. More accurately, they’re called distributions or distros.

Since Linux was first released in 1991, it has continued to gain popularity due to its open-source nature. People can freely modify and redistribute it under their own name.

When operating a Linux OS, you need to use a shell — an interface that gives you access to the operating system’s services. Most Linux distributions use a graphic user interface (GUI) as their shell, mainly to provide ease of use for their users.

That being said, it’s recommended to use a command-line interface (CLI) because it’s more powerful and effective. Tasks that require a multi-step process through GUI can be done in a matter of seconds by typing commands into the CLI.

So if you’re considering using Linux, learning basic command lines will go a long way. In this article, you’ll learn 35 basic Linux commands that will undoubtedly help you navigate through Linux as a newbie.

Linux Basic Commands

Before we go on to the list of commands, you need to open the command line first. If you are still unsure about the command-line interface, check out this CLI tutorial.

Although the steps may differ depending on the distribution that you’re using, you can usually find the command line in the Utilities section.

Here is a list of basic Linux commands:

1. pwd command

Use the pwd command to find out the path of the current working directory (folder) you’re in. The command will return an absolute (full) path, which is basically a path of all the directories that starts with a forward slash (/). An example of an absolute path is /home/username.

2. cd command

To navigate through the Linux files and directories, use the cd command. It requires either the full path or the name of the directory, depending on the current working directory that you’re in.

Let’s say you’re in /home/username/Documents and you want to go to Photos, a subdirectory of Documents. To do so, simply type the following command: cd Photos.

Another scenario is if you want to switch to a completely new directory, for example,/home/username/Movies. In this case, you have to type cd followed by the directory’s absolute path: cd /home/username/Movies.

There are some shortcuts to help you navigate quickly:

• cd .. (with two dots) to move one directory up
• cd to go straight to the home folder
• cd- (with a hyphen) to move to your previous directory

On a side note, Linux’s shell is case sensitive. So, you have to type the name’s directory exactly as it is.

3. ls command

The ls command is used to view the contents of a directory. By default, this command will display the contents of your current working directory.

If you want to see the content of other directories, type ls and then the directory’s path. For example, enter ls /home/username/Documents to view the content of Documents.

There are variations you can use with the ls command:

• ls -R will list all the files in the sub-directories as well
• ls -a will show the hidden files
• ls -al will list the files and directories with detailed information like the permissions, size, owner, etc.

4. cat command

cat (short for concatenate) is one of the most frequently used commands in Linux. It is used to list the contents of a file on the standard output (sdout). To run this command, type cat followed by the file’s name and its extension. For instance: cat file.txt.

Here are other ways to use the cat command:

• cat > filename creates a new file
• cat filename1 filename2>filename3 joins two files (1 and 2) and stores the output of them in a new file (3)
• to convert a file to upper or lower case use, cat filename | tr a-z A-Z >output.txt

5. cp command

Use the cp command to copy files from the current directory to a different directory. For instance, the command cp scenery.jpg /home/username/Pictures would create a copy of scenery.jpg (from your current directory) into the Pictures directory.

6. mv command

The primary use of the mv command is to move files, although it can also be used to rename files.

The arguments in mv are similar to the cp command. You need to type mv, the file’s name, and the destination’s directory. For example: mv file.txt /home/username/Documents.

To rename files, the Linux command is mv oldname.ext newname.ext

7. mkdir command

Use mkdir command to make a new directory — if you type mkdir Music it will create a directory called Music.

There are extra mkdir commands as well:

• To generate a new directory inside another directory, use this Linux basic command mkdir Music/Newfile
• use the p (parents) option to create a directory in between two existing directories. For example, mkdir -p Music/2020/Newfile will create the new “2020” file.

8. rmdir command

If you need to delete a directory, use the rmdir command. However, rmdir only allows you to delete empty directories.

9. rm command

The rm command is used to delete directories and the contents within them. If you only want to delete the directory — as an alternative to rmdir — use rm -r.

Note: Be very careful with this command and double-check which directory you are in. This will delete everything and there is no undo.

10. touch command

The touch command allows you to create a blank new file through the Linux command line. As an example, enter touch /home/username/Documents/Web.html to create an HTML file entitled Web under the Documents directory.

11. locate command

You can use this command to locate a file, just like the search command in Windows. What’s more, using the -i argument along with this command will make it case-insensitive, so you can search for a file even if you don’t remember its exact name.

To search for a file that contains two or more words, use an asterisk (*). For example, locate -i school*note command will search for any file that contains the word “school” and “note”, whether it is uppercase or lowercase.

12. find command

Similar to the locate command, using find also searches for files and directories. The difference is, you use the find command to locate files within a given directory.

As an example, find /home/ -name notes.txt command will search for a file called notes.txt within the home directory and its subdirectories.

Other variations when using the find are:

• To find files in the current directory use, find . -name notes.txt
• To look for directories use, / -type d -name notes. txt

13. grep command

Another basic Linux command that is undoubtedly helpful for everyday use is grep. It lets you search through all the text in a given file.

To illustrate, grep blue notepad.txt will search for the word blue in the notepad file. Lines that contain the searched word will be displayed fully.

14. sudo command

Short for “SuperUser Do”, this command enables you to perform tasks that require administrative or root permissions. However, it is not advisable to use this command for daily use because it might be easy for an error to occur if you did something wrong.

15. df command

Use df command to get a report on the system’s disk space usage, shown in percentage and KBs. If you want to see the report in megabytes, type df -m.

16. du command

If you want to check how much space a file or a directory takes, the du (Disk Usage) command is the answer. However, the disk usage summary will show disk block numbers instead of the usual size format. If you want to see it in bytes, kilobytes, and megabytes, add the -h argument to the command line.

17. head command

The head command is used to view the first lines of any text file. By default, it will show the first ten lines, but you can change this number to your liking. For example, if you only want to show the first five lines, type head -n 5 filename.ext.

18. tail command

This one has a similar function to the head command, but instead of showing the first lines, the tail command will display the last ten lines of a text file. For example, tail -n filename.ext.

19. diff command

Short for difference, the diff command compares the contents of two files line by line. After analyzing the files, it will output the lines that do not match. Programmers often use this command when they need to make program alterations instead of rewriting the entire source code.

The simplest form of this command is diff file1.ext file2.ext

20. tar command

The tar command is the most used command to archive multiple files into a tarball — a common Linux file format that is similar to zip format, with compression being optional.

This command is quite complex with a long list of functions such as adding new files into an existing archive, listing the content of an archive, extracting the content from an archive, and many more. Check out some practical examples to know more about other functions.

21. chmod command

chmod is another Linux command, used to change the read, write, and execute permissions of files and directories. As this command is rather complicated, you can read the full tutorial in order to execute it properly.

22. chown command

In Linux, all files are owned by a specific user. The chown command enables you to change or transfer the ownership of a file to the specified username. For instance, chown linuxuser2 file.ext will make linuxuser2 as the owner of the file.ext.

23. jobs command

jobs command will display all current jobs along with their statuses. A job is basically a process that is started by the shell.

24. kill command

If you have an unresponsive program, you can terminate it manually by using the kill command. It will send a certain signal to the misbehaving app and instructs the app to terminate itself.

There is a total of sixty-four signals that you can use, but people usually only use two signals:

• SIGTERM (15) — requests a program to stop running and gives it some time to save all of its progress. If you don’t specify the signal when entering the kill command, this signal will be used.
• SIGKILL (9) — forces programs to stop immediately. Unsaved progress will be lost.

Besides knowing the signals, you also need to know the process identification number (PID) of the program you want to kill. If you don’t know the PID, simply run the command ps ux.

After knowing what signal you want to use and the PID of the program, enter the following syntax:

kill [signal option] PID.

25. ping command

Use the ping command to check your connectivity status to a server. For example, by simply entering ping google.com, the command will check whether you’re able to connect to Google and also measure the response time.

26. wget command

The Linux command line is super useful — you can even download files from the internet with the help of the wget command. To do so, simply type wget followed by the download link.

27. uname command

The uname command, short for Unix Name, will print detailed information about your Linux system like the machine name, operating system, kernel, and so on.

28. top command

As a terminal equivalent to Task Manager in Windows, the top command will display a list of running processes and how much CPU each process uses. It’s very useful to monitor system resource usage, especially knowing which process needs to be terminated because it consumes too many resources.

29. history command

When you’ve been using Linux for a certain period of time, you’ll quickly notice that you can run hundreds of commands every day. As such, running history command is particularly useful if you want to review the commands you’ve entered before.

30. man command

Confused about the function of certain Linux commands? Don’t worry, you can easily learn how to use them right from Linux’s shell by using the man command. For instance, entering man tail will show the manual instruction of the tail command.

31. echo command

This command is used to move some data into a file. For example, if you want to add the text, “Hello, my name is John” into a file called name.txt, you would type echo Hello, my name is John >> name.txt

32. zip, unzip command

Use the zip command to compress your files into a zip archive, and use the unzip command to extract the zipped files from a zip archive.

33. hostname command

If you want to know the name of your host/network simply type hostname. Adding a -i to the end will display the IP address of your network.

34. useradd, userdel command

Since Linux is a multi-user system, this means more than one person can interact with the same system at the same time. useradd is used to create a new user, while passwd is adding a password to that user’s account. To add a new person named John type, useradd John and then to add his password type, passwd 123456789.

To remove a user is very similar to adding a new user. To delete the users account type, userdel UserName

Bonus Tips and Tricks

Use the clear command to clean out the terminal if it is getting cluttered with too many past commands.

Try the TAB button to autofill what you are typing. For example, if you need to type Documents, begin to type a command (let’s go with cd Docu, then hit the TAB key) and the terminal will fill in the rest, showing you cd Documents.

Ctrl+C and Ctrl+Z are used to stop any command that is currently working. Ctrl+C will stop and terminate the command, while Ctrl+Z will simply pause the command.

If you accidental freeze your terminal by using Ctrl+S, simply undo this with the unfreeze Ctrl+Q.

Ctrl+A moves you to the beginning of the line while Ctrl+E moves you to the end.

You can run multiple commands in one single command by using the “;” to separate them. For example Command1; Command2; Command3. Or use && if you only want the next command to run when the first one is successful.

To Sum Up

Basic Linux commands help users execute tasks easily and effectively. It might take a while to remember some of the basic commands, but nothing is impossible with lots of practice.

In the end, knowing and mastering these basic Linux commands will be undoubtedly beneficial for you. Good luck!

Artūras is an experienced technical content writer. Bringing in a lot of knowledge about WordPress and web hosting to the team, he strives to write pristine content about any IT related subject. He also loves dogs.

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