Killing processes in linux by name

Убиваем процессы в Linux — команды ps, kill и killall

Под процессом мы будем понимать запущенную в системе копию программы. Например, если вы открыли три окна калькулятора (например, gcalctool), это значит, что вы запустили три процесса.

Находим PID зависшего процесса

Каждый процесс в Linux имеет свой идентификатор, называемый PID. Перед тем, как выполнить остановку процесса, нужно определить его PID. Для этого воспользуемся командами ps и grep. Команда ps предназначена для вывода списка активных процессов в системе и информации о них. Команда grep запускается одновременно с ps (в канале) и будет выполнять поиск по результатам команды ps. Вывести список всех процессов можно, выполнив в командной строке:

Но, как правило, список очень большой и найти процесс, который мы хотим «убить», бывает не так просто. Здесь на помощь приходит команда grep. Например, чтобы найти информацию о процессе с именем gcalctool выполните команду:

Команда grep выполнит поиск по результатам команды ps и на экран будут выведены только те строки, которые содержат строку (слово) gcalctool. Здесь есть одна интересная деталь, например, если у вас не запущено приложение gcalctool, то после выполнения ps axu | grep gcalctool вы получите:

То есть мы получили сам процесс grep, так как в качестве параметра команде мы указали слово gcalctool, и grep нашел сам себя в выводе команды ps.

Если процесс gcalctool запущен, то мы получим:

Здесь нас интересует строка: «yuriy 25609 7.6 0.4 500840 17964 ? Sl 10:20 0:00 gcalctool». Число 25609 и есть идентификатор (PID) процесса gcalctool.

Есть еще один более простой способ узнать PID процесса — это команда pidof, которая принимает в качестве параметра название процесса и выводит его PID. Пример выполнения команды pidof:

«Убиваем» процесс командой kill

Когда известен PID процесса, мы можем убить его командой kill. Команда kill принимает в качестве параметра PID процесса. Например, убьем процесс с номером 25609:

Вообще команда kill предназначена для посылки сигнала процессу. По умолчанию, если мы не указываем какой сигнал посылать, посылается сигнал SIGTERM (от слова termination — завершение). SIGTERM указывает процессу на то, что необходимо завершиться. Каждый сигнал имеет свой номер. SIGTERM имеет номер 15. Список всех сигналов (и их номеров), которые может послать команда kill, можно вывести, выполнив kill -l. Чтобы послать сигнал SIGKILL (он имеет номер 9) процессу 25609, выполните в командой строке:

Сигнал SIGTERM может и не остановить процесс (например, при перехвате или блокировке сигнала), SIGKILL же выполняет уничтожение процесса всегда, так как его нельзя перехватить или проигнорировать.

Убиваем процессы командой killall

Команда killall в Linux предназначена для «убийства» всех процессов, имеющих одно и то же имя. Это удобно, так как нам не нужно знать PID процесса. Например, мы хотим закрыть все процессы с именем gcalctool. Выполните в терминале:

Команда killall, также как и kill, по умолчанию шлет сигнал SIGTERM. Чтобы послать другой сигнал нужно воспользоваться опцией -s. Например:

Заключение

Некоторые процессы не удается остановить под обычным пользователем. Например, если процесс был запущен от имени пользователя root или от имени другого пользователя системы, то команды kill и killall нужно выполнять от имени суперпользователя, добавляя sudo (в Ubuntu):

Бывают ситуации, когда вы работаете в графическом интерфейсе (например, GNOME) и вам не удается открыть эмулятор терминала, чтобы остановить зависший процесс. Тогда можно переключиться на виртуальную консоль клавишами Ctrl+Alt+F1, залогиниться в ней и выполнять команды уже из нее. А потом перейти обратно, нажав Ctrl+Alt+F7.

Справку по использованию любой команды можно получить командой man:

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How to Kill Linux Process Using Kill, Pkill and Killall

Linux Operating System comes with a kill command to terminate a process. The command makes it possible to continue running the server without the need to reboot after a major change/update. Here comes the great power of Linux and this is one of the reasons, why Linux is running on 96.4% of servers, on the planet.

Kill command sends a signal, a specified signal to a currently running process. The kill command can be executed in a number of ways, directly or from a shell script.

Using kill command from /usr/bin provide you some extra feature to kill a process by process name using pkill.

Kill Command Usage

The common syntax for kill command is:

For a kill command a Signal Name could be:

Clearly from the behavior above, SIGTERM is the default and safest way to kill a process. SIGHUP is a less secure way of killing a process than SIGTERM. SIGKILL is the most unsafe way among the above three, to kill a process that terminates a process without saving.

In order to kill a process, we need to know the Process ID of a process. A Process is an instance of a program. Every time a program starts, automatically a unique PID is generated for that process.

Every Process in Linux has a pid. The first process that starts when Linux System is booted is the – init process, hence it is assigned a value of ‘1‘ in most cases.

Init is the master process and can not be killed this way, which ensures that the master process doesn’t get killed accidentally. Init decides and allows itself to be killed, where kill is merely a request for a shutdown.

List All Running Linux Processes

To know all the processes and correspondingly their assigned pid, run the following ps command.

Sample Output

How about Customising the above output using syntax as ‘pidof process‘.

Sample Output

Another way to achieve the above goal is to follow the below syntax.

Sample Output

How to Kill a Process in Linux

Before we step ahead and execute a kill command, some important points to be noted:

• A user can kill all his processes.
• A user can not kill another user’s process.
• A user can not kill processes the System is using.
• A root user can kill System-level-process and the process of any user.

Another way to perform the same function is to execute the ‘pgrep‘ command.

Sample Output

To kill the above process PID, use the kill command as shown.

The above command will kill the process having pid=3139, where PID is a Numerical Value of the process.

Another way to perform the same function can be rewritten as.

Similarly ‘kill -9 PID‘ is similar to ‘kill -SIGKILL PID‘ and vice-versa.

How to Kill a Process in Linux Using Process Name

You must be aware of the process name, before killing and entering a wrong process name may screw you.

Kill more than one process at a time.

What if a process has too many instances and a number of child processes, we have a command ‘killall‘ or pkill. These two are the only commands of this family, which takes process name as argument in-place of process number.

Syntax:

To kill all mysql instances along with child processes, use the command as follow.

You can always verify the status of the process if it is running or not, using any of the below commands.

That’s all for now, from my side. I will soon be here again with another Interesting and Informative topic. Till Then, stay tuned, connected to Tecmint, and healthy. Don’t forget to give your valuable feedback in the comment section.

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How to Kill a Process in Linux

In an operating system, there are many programs, which may be either run by an user or by the OS itself (such as system services). Such programs which are running on the system are called “processes”. Usually, a process terminates on its own when they’re done with their task, or when you ask them to quit by pressing a keyboard shortcut or clicking on the “Close” button.

However, sometimes a process can hang up or consume a lot of CPU or RAM. In this situation, you would want to manually “kill” the process. In this article, we will look at various tools you can use to kill processes on a Linux system.

Locating the process to kill

In order to kill a process, you should first locate the details of the process. You can do this through three commands — top , ps , pidof and pgrep . Depending upon the situation, you can use one of these commands for this purpose.

As we will see later in this article, you can kill a process by its name or its process ID (PID). The PID is a number that uniquely identifies a process. Killing by the process ID is useful when you want to kill only a specific process. On the other hand, killing by the process name is useful when you want to kill all running instances of a particular program.

Locating the process with the top command

We will first look at the top command. Fire up the top command by typing:

You will get an interactive interface, as shown below. You can browse through this list to find the name or the PID of the process you want to kill.

To browse through this list, you can use the up/down keys. Additionally, the top command also has ways to filter processes by CPU usage, user and process names, which you can read about in this guide.

The leftmost column contains the PID of the process, and the right side contains the program name. As an example, in the above screenshot we have the vnstatd process running with a process ID of 263.

Locating the process with ps and grep commands

Another way to get a list of process is by running:

In the above command, we have used the flags aux which have the following meanings:

• a : Show processes for all users
• u : Display the user who is using the process
• x : Show all processes. (Without this, ps won’t show processes running in a GUI environment.)

The output of the command is similar to that of top . The PID is available in second column from the left, and the process name is available on the rightmost column.

The advantage of using ps is that you can easily filter this list with the grep command. For example, to find a process associated with the term “vnstat”, you can use:

Here, we got two results — the vnstatd process, as well as the grep process. Since we were searching for all instances of the term “vnstat”, and we were also running grep with “vnstat” as its argument, we got grep as well in the results.

Thus, even when there are no “vnstat” related processes running, we would get one entry showing the grep process:

So, even though we got a result, there are no processes that are of interest to us.

Finding the PID with pidof and pgrep

The top and ps / grep combination allows us to search for processes. On the other hand, if you know the exact name of a process, you can use pidof to find its PID.

Using pidof is pretty straightforward. To get the PIDs of a process with the exact name of “nginx”, use:

If there are processes with the exact name of “nginx”, you will get a list of PIDs, as shown below. If there are none, you will get nothing as the output.

If you don’t know the full name, you can use pgrep instead of pidof . As an example, to search for all processes that contain “ngin” somewhere in their name, run:

This will match processes with the exact name of “nginx”, as well as any other process that matches the same criteria. For our system, notice that we get all the PIDs that belonged to “nginx” in the above screenshot.

The pidof and pkill commands give you far less information. As we shall see in the next section, there are some circumstances in which you can’t kill a process. The output of top and ps contain additional information that help you determine if you can really kill a process.

What processes can you kill?

Now that we have located the process, it is time to kill it. However, before we learn how to do so, there are a few things you need to know.

If you are a normal user, you can kill your own processes, but not those that belong to other users. Both top and ps show the user under which a process is running. In the case of top , the second column contains the username. With ps aux , the first column contains the username.

However, a root user can kill all processes. You can either add sudo before any command to run it as root, or obtain a root shell by typing su , and then execute the command.

In Linux, when a process is killed, a “terminating signal” is delivered to the process. Although there are many different types of signals, we mostly deal with the “SIGTERM” and “SIGKILL” signals. They have a numeric value of 15 and 9 respectively. By default, all the process killing commands use “SIGTERM”, which allows the program to run some code before it exits, thus allowing it to terminate “gracefully”. If you want to terminate the process forcibly, you can use “SIGKILL” instead.

The Linux kernel maintains some information related to the state of a process. When a process terminates, the kernel must keep the information around, so that the parent process can find out if the child process was able to complete its tasks and whether it terminated on its own, or it was killed. Until the parent has done so, these “zombie” processes will appear in the list of processes. You can’t kill such a process because it’s just an entry in the list of all processes, and it doesn’t have an actual process associated with it.

When a process performs input/output operations (such as reading from or writing to disks), it is said to be in a state of “uninterruptible sleep”. You can’t kill a process while it is in this state.

You can tell if a process is in the “zombie”(Z) or “uninterruptible sleep”(D) state by looking at the 8th column of the top / ps output.

Killing a process

There are various commands you can use to kill a process — kill , killall , pkill and top . We will begin from the simplest one: the killall command.

Killing processes with the killall command

The killall command is one of the easiest ways to kill a process. If you know the exact name of a process, and you know that it’s not running as another user and it is not in the Z or D states, then you can use this command directly; there’s no need to manually locate the process as we described above.

By default, For example, to kill a process named “firefox”, run:

To forcibly kill the process with SIGKILL, run:

You can also use -SIGKILL instead of -9 .

If you want to kill processes interactively, you can use -i like so:

If you want to kill a process running as a different user, you can use sudo :

You can also kill a process that has been running for a certain period of time with the -o and -y flags. So, if you want to kill a process that has been running for more than 30 minutes, use:

If you want to kill a process that has been running for less than 30 minutes, use:

Similarly, use the following abbreviations for the respective units of time:

s	seconds
m	minutes
h	hours
d	days
w	weeks
M	months
y	years

Killing processes with the pkill command

Sometimes, you only know part of a program’s name. Just like pgrep , pkill allows you to kill processes based on partial matches. For example, if you want to kill all processes containing the name apache in the name, run:

If you want to use a SIGKILL instead of a SIGTERM, use:

Again, you can also use -SIGKILL instead of -9 .

Killing processes with the kill command

Using the kill command is straightforward. Once you have found out the PID of the process that you want to kill, you can terminate it using the kill command. For example, if you want to kill a process having a PID of 1234, then use the following command:

As we mentioned previously, the default is to use a SIGTERM. To use a SIGKILL, use -9 or -SIGKILL as we have seen before:

Killing processes with the top command

It is very easy to kill processes using the top command. First, search for the process that you want to kill and note the PID. Then, press k while top is running (this is case sensitive). It will prompt you to enter the PID of the process that you want to kill.

After you enter the PID, press enter. Now it will ask which signal you want to use to kill the process. If you want to use SIGTERM(15), then simply press enter as it is the default signal. If you want to use SIGKILL(9), then type 9 and press enter.

If you leave the process ID blank and hit enter directly, it will terminate the topmost process in the list. You can scroll using the arrow keys, and change the process you want to kill in this way.

Conclusion

In this post, we saw the various ways to kill processes in Linux. Learning these commands is essential for proper system administration and management. If you want to explore more of those commands, have a look at their respective man pages.

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