Linux port already used

How do I check if a port is in use on Linux?

I am a new Linux system user. I need to find out which process is listening on a port on Linux using the command line. How do you find out which process is listening on a port on Linux operating systems?

A network port in Linux is nothing but a number that identifies one side of a connection between two systems. All networked devices use port numbers to determine to which process a message should be delivered. The domain name and IP address are like a street address, and port numbers are like room numbers.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	Linux
Est. reading time	2 minutes

Popular port numbers in Linux

• HTTP – TCP 80
• HTTPS – TCP 443
• POP3 – TCP 110
• SMTP – TCP 25
• SSH – TCP 22
• DNS/DOMAIN – TCP/UDP 53

Use the cat command or grep command/egrep command to query port numbers as follows:
cat /etc/services
grep -w 80 /etc/services
egrep -w ’53/(tcp|udp)’ /etc/services

How to check if a port is in use on Linux

The procedure is as follows:

1. Open the terminal application on Linux.
2. Type any one of the following command to check if a port is in use on Linux
   sudo lsof -i -P -n | grep LISTEN
   sudo netstat -tulpn | grep LISTEN
   sudo netstat -tulpn | grep :443
   sudo ss -tulpn | grep LISTEN
   sudo ss -tulpn | grep ‘:22’
3. Search for the TCP or UDP port description in /etc/services file on Linux:
   grep -E -w ‘PORT_NUMBER_HERE/(tcp|udp)’ /etc/services

Let us see some examples and sample commands in details.

How can you find out which process is listening on a port on Linux

Type the ss command or netstat command to see if a TCP port 443 is in use on Linux?
sudo netstat -tulpn | grep :443
sudo ss -tulpn | grep :443
If a port is open, you should see the output as follows:

The port 443 is in use and opened by nginx service. Where,

• -t : Display TCP sockets/port
• -u : Show UDP sockets/port
• -l : See only listening sockets i.e. open port
• -p : Also display process name that opened port/socket
• -n : View addresses and port numbers in numerical format. Do not use DNS to resolve names.

Getting a list of all open port in production

Simply run:
sudo lsof -i -P -n | grep LISTEN
sudo ss -tulpn
sudo netstat -tulpn
Sample outputs:

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How to check if port is in use on Linux or Unix

H ow do I determine if a port is in use under Linux or Unix-like system? How can I verify which ports are listening on Linux server? How do I check if port is in use on Linux operating system using the CLI?

It is important you verify which ports are listening on the server’s network interfaces. You need to pay attention to open ports to detect an intrusion. Apart from an intrusion, for troubleshooting purposes, it may be necessary to check if a port is already in use by a different application on your servers. For example, you may install Apache and Nginx server on the same system. So it is necessary to know if Apache or Nginx is using TCP port # 80/443. This quick tutorial provides steps to use the netstat, nmap and lsof command to check the ports in use and view the application that is utilizing the port.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	lsof, ss, and netstat on Linux
Est. reading time	3 minutes

How to check if port is in use in

To check the listening ports and applications on Linux:

1. Open a terminal application i.e. shell prompt.
2. Run any one of the following command on Linux to see open ports:
   sudo lsof -i -P -n | grep LISTEN
   sudo netstat -tulpn | grep LISTEN
   sudo ss -tulpn | grep LISTEN
   sudo lsof -i:22 ## see a specific port such as 22 ##
   sudo nmap -sTU -O IP-address-Here
3. For the latest version of Linux use the ss command. For example, ss -tulw

Let us see commands and its output in details.

Option #1: lsof command

The syntax is:
$ sudo lsof -i -P -n
$ sudo lsof -i -P -n | grep LISTEN
$ doas lsof -i -P -n | grep LISTEN ### [OpenBSD] ###
Sample outputs:

Fig.01: Check the listening ports and applications with lsof command

Option #2: netstat command

You can check the listening ports and applications with netstat as follows.

Linux netstat syntax

Run netstat command along with grep command to filter out port in LISTEN state:
$ netstat -tulpn | grep LISTEN
The netstat command deprecated for some time on Linux. Therefore, you need to use the ss command as follows:
sudo ss -tulw
sudo ss -tulwn
sudo ss -tulwn | grep LISTEN

Where, ss command options are as follows:

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• -t : Show only TCP sockets on Linux
• -u : Display only UDP sockets on Linux
• -l : Show listening sockets. For example, TCP port 22 is opened by SSHD server.
• -p : List process name that opened sockets
• -n : Don’t resolve service names i.e. don’t use DNS

FreeBSD/MacOS X netstat syntax

$ netstat -anp tcp | grep LISTEN
$ netstat -anp udp | grep LISTEN

OpenBSD netstat syntax

$ netstat -na -f inet | grep LISTEN
$ netstat -nat | grep LISTEN

Option #3: nmap command

The syntax is:
$ sudo nmap -sT -O localhost
$ sudo nmap -sU -O 192.168.2.13 ##[ list open UDP ports ]##
$ sudo nmap -sT -O 192.168.2.13 ##[ list open TCP ports ]##
Sample outputs:

Fig.02: Determines which ports are listening for TCP connections using nmap

A note about Windows users

You can check port usage from Windows operating system using following command:
netstat -bano | more
netstat -bano | grep LISTENING
netstat -bano | findstr /R /C:»[LISTEING]»

Conclusion

This page explained command to determining if a port is in use on Linux or Unix-like server. For more information see the nmap command and lsof command page online here

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Ошибка сервера Django: порт уже используется

Перезапуск сервера Django отображает следующую ошибку:

Эта проблема возникает именно в Ubuntu, а не в других операционных системах. Как я могу освободить порт для перезагрузки сервера?

Более простое решение просто введите sudo fuser -k 8000/tcp .
Это должно убить все процессы, связанные с портом 8000.

Для пользователей osx вы можете использовать sudo lsof -t -i tcp:8000 | xargs kill -9

Он покажет что-то вроде этого.

Теперь просто закройте порт, в котором запущен Django/python, убив связанный с ним процесс.

Теперь запустите приложение Django.

Мы не используем эту команду Потому что он закрывает все вкладки… Вы должны использовать

ps -ef | grep python (показать весь процесс с id)

kill -9 11633
(11633 – это идентификатор процесса для: -/bin/python manage.py runningerver)

Это расширение на ответ Мунира. Я добавил bash script, который охватывает это для вас. Просто запустите ./scripts/runserver.sh вместо ./manage.py runserver , и он будет работать точно так же.

По умолчанию команда runserver запускает сервер разработки с внутреннего IP-адреса на порту 8000.

Если вы хотите изменить порт сервера, передайте его в качестве аргумента командной строки. Например, эта команда запускает сервер на порту 8080:

ps aux | grep manage

ubuntu 3438 127.0.0 2.3 40256 14064 pts/0 T 06:47 0:00 python manage.py runningerver

Кажется, что IDE, VSCode, Puppeteer, nodemon, express и т.д. Вызывают эту проблему, вы запустили процесс в фоновом режиме или просто закрыли область отладки [браузер, терминал и т.д.] Или что-то еще, во всяком случае, я ответил на тот же вопрос раньше, вот ты это ссылка

Для меня это происходит потому, что мой запрос API в Postman перехватывается точкой останова отладчика в моем приложении… оставляя запрос зависшим. Если я отменю запрос в Postman перед тем, как убить сервер приложений, ошибка не возникнет.

→ Так что попробуйте отменить любые открытые запросы, которые вы делаете в других программах.

В macOS я использовал sudo lsof -t -i tcp:8000 | xargs kill -9 sudo lsof -t -i tcp:8000 | xargs kill -9 когда я забываю отменить открытый запрос http для решения error = That port is already in use. Это также завершает закрытие моего приложения Почтальон, поэтому мое первое решение лучше.

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Linux Find Out Which Process Is Listening Upon a Port

Linux Find Out Which Process Is Listening Upon a Port

You can the following programs to find out about port numbers and its associated process:

1. netstat command or ss command – a command-line tool that displays network connections, routing tables, and a number of network interface statistics.
2. fuser command – a command line tool to identify processes using files or sockets.
3. lsof command – a command line tool to list open files under Linux / UNIX to report a list of all open files and the processes that opened them.
4. /proc/$pid/ file system – Under Linux /proc includes a directory for each running process (including kernel processes) at /proc/PID, containing information about that process, notably including the processes name that opened port.

You must run above command(s) as the root user.

Linux netstat command find out which process is listing upon a port

Type the following command:
# netstat -tulpn
Sample outputs:

TCP port 3306 was opened by mysqld process having PID # 1138. You can verify this using /proc, enter:
# ls -l /proc/1138/exe
Sample outputs:

You can use grep command or egrep command to filter out information:
# netstat -tulpn | grep :80
Sample outputs:

A note about ss command

Some Linux distro considered the nestat command as deprecated and therefore should be phased out in favor of more modern replacements such as ss command. The syntax is:
$ sudo ss -tulpn
$ sudo ss -tulpn | grep :3306

Click to enlarge image

Video demo

fuser command

Find out the processes PID that opened tcp port 7000, enter:
# fuser 7000/tcp
Sample outputs:

Finally, find out process name associated with PID # 3813, enter:
# ls -l /proc/3813/exe
Sample outputs:

/usr/bin/transmission is a bittorrent client, enter:
# man transmission
OR
# whatis transmission
Sample outputs:

Find Out Current Working Directory Of a Process

To find out current working directory of a process called bittorrent or pid 3813, enter:
# ls -l /proc/3813/cwd
Sample outputs:

OR use pwdx command, enter:
# pwdx 3813
Sample outputs:

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Find Out Owner Of a Process on Linux

Use the following command to find out the owner of a process PID called 3813:
# ps aux | grep 3813
OR
# ps aux | grep ‘[3]813’
Sample outputs:

OR try the following ps command:
# ps -eo pid,user,group,args,etime,lstart | grep ‘[3]813’
Sample outputs:

Another option is /proc/$PID/environ, enter:
# cat /proc/3813/environ
OR
# grep —color -w -a USER /proc/3813/environ
Sample outputs (note –colour option):

Fig.01: grep output

lsof Command Example

Type the command as follows:

Now, you get more information about pid # 1607 or 1616 and so on:
# ps aux | grep ‘[1]616’
Sample outputs:
www-data 1616 0.0 0.0 35816 3880 ? S 10:20 0:00 /usr/sbin/apache2 -k start
I recommend the following command to grab info about pid # 1616:
# ps -eo pid,user,group,args,etime,lstart | grep ‘[1]616’
Sample outputs:

• 1616 : PID
• www-date : User name (owner – EUID)
• www-date : Group name (group – EGID)
• /usr/sbin/apache2 -k start : The command name and its args
• 03:16:22 : Elapsed time since the process was started, in the form [[dd-]hh:]mm:ss.
• Fri Oct 29 10:20:17 2010 : Time the command started.

Help: I Discover an Open Port Which I Don’t Recognize At All

The file /etc/services is used to map port numbers and protocols to service names. Try matching port numbers:
$ grep port /etc/services
$ grep 443 /etc/services
Sample outputs:

Check For rootkit

I strongly recommend that you find out which processes are really running, especially servers connected to the high speed Internet access. You can look for rootkit which is a program designed to take fundamental control (in Linux / UNIX terms “root” access, in Windows terms “Administrator” access) of a computer system, without authorization by the system’s owners and legitimate managers. See how to detecting / checking rootkits under Linux.

Keep an Eye On Your Bandwidth Graphs

Usually, rooted servers are used to send a large number of spam or malware or DoS style attacks on other computers.

Conlcusion

You learned various Linux commands to find information about running process and their ports. See the following man pages for more information:
$ man ps
$ man grep
$ man lsof
$ man netstat
$ man fuser

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