Linux kill, killall, kill-9

1) how to view the process:

PS-EF or PS aux

Root 15087 0.0 0.0 0 0? S [kworker/]
Root 15219 0.0 0.0 0 0? S [kworker/1:0]
Root 15460 0.0 0.0 0 0? S [kworker/]
Homer 15572 23.0 5.8 791472 119788? SL/usr/lib/Firefox
Homer 15590 0.1 0.1 273796 3132? SL/usr/lib/at-spi2-core/AT-SPI-bus-Launcher
Homer 15620 0.0 0.0 22360 1268 pts/0 r + PS aux

2) Kill-9

Kill-S 9 15572

Among them,-S 9 sets the signal sent to the process to be 9, that is, force and terminate the process as soon as possible. 15572 is the PID of Firefox found by PS above.

It's easy, but there is a problem. It doesn't matter if the process is small, and if there are too many processes, it will feel painful, whether it's PS-EF or PS-Aux, every time I find the PID of the process to be killed in a large string of process information, I have spent all my eyes.

Usage Details:

Kill-9, this powerful and dangerous Command forces the process to terminate suddenly at runtime, and the process cannot be self-cleaned after it ends. The hazard is that the system resources cannot be released normally. It is generally not recommended unless other methods are ineffective.
When using this command, you must use PS-Ef to confirm that no zombie process is left. Only the parent process can be terminated to eliminate zombie processes. If the zombie process is adopted by init, the problem will be serious. Killing the INIT process means shutting down the system.
If there is a zombie process in the system, and its parent process is INIT, And the zombie process occupies a large amount of system resources, you need to restart the machine at some time to clear the process.

2.1) Improvement 1 -- grep

Pass the PS query result to grep through a pipeline to find the process that contains a specific string. The pipe operator "|" is used to separate two commands. The output of the command on the left of the pipe operator is used as the input of the command on the right of the pipe operator.

Example: Homer @ Ubuntu :~ $ PS-Aux | grep Firefox

Homer 15572 1.7 5.0 808644 103260? SL/usr/lib/Firefox
Homer 15735 0.0 0.0 13584 920 pts/0 S + grep -- color = auto Firefox

Find the Firefox process PID and enter: Kill-S 9 15572

2.2) Improvement 2 -- pgrep

Pgrep P indicates that this command is specially used for process query grep.

Example: Homer @ Ubuntu :~ $ Pgrep Firefox
15572

2.3) Improvement 3 -- pidof

Pidof command, indicating PID of XX, literally translated as XX PID

Example: Homer @ Ubuntu :~ $ Pidof Firefox
15572

2.4) improvement 4 -- grep + awk

Grep Firefox lists Firefox process information, and awk takes the second field, that is, PID

Example: Homer @ Ubuntu :~ $ PS-Ef | grep Firefox | grep-V grep | awk '{print $2 }'
15572

2.5) Improvement 5 -- kill + xargs

There are several ways to kill a process:

A)PS-Ef | grep Firefox | grep-V grep | awk '{print $2}' |XargsKill-S 9

B)PgrepFirefox | xargs kill-S 9

C)PidofFirefox | xargs kill-S 9

Or

D) Kill-s 9'PS-Ef | grep Firefox | grep-V grep | awk '{print $2 }''

E) Kill-s 9'PgrepFirefox'

F) Kill-s 9'PidofFirefox'

2.6) Improvement 6 -- pkill

Pkill is similar to pgrep, and pkill indicates pgrep + kill

Example: pkill Firefox

3) killall

Killall command to kill all processes in the same process group. It allows you to specify the name of the process to be terminated, rather than the PID.

Killall and pkill are similar. However, if the process name is incomplete, killall reports an error. Pkill or pgrep can terminate a process as long as a part of the process name is given.

Homer @ Ubuntu :~ $ Killall firefo
Firefo: No process found
Homer @ Ubuntu :~ $ Killall Firefox
Homer @ Ubuntu :~ $ Killall-9 Firefox

4) Kill

The safest way to kill a process is to simply use the kill command without a modifier or a flag.
Example: # Kill-PID
Note: For standard kill commands, the default signal (signal) number is 15, which can usually achieve the goal of terminating problematic processes and Releasing Process resources to the system. However, if a child process is started and only the parent process is killed, the child process is still running and consumes resources. To prevent these so-called "zombie processes", ensure that all child processes are killed before the parent process is killed.

5) Kill-l

Example: Kill-l PID

-L option to tell the kill command to end the process as if the user who started the process had logged out. When this option is used, the kill command also tries to kill the left child process. But this command is not always successful-you may still need to manually kill the child process and then kill the parent process.

6) kill-HUP

Sometimes you only want to simply stop and restart the process.
Example: # kill-HUP PID
This command causes Linux to shut down the slow execution process and then restart immediately. This command is convenient when you configure the application. You can execute this command when you need to restart the process after modifying the configuration file.

Appendix: various signals and their usage

Signal	Description	Signal Number on Linux x86
SIGABRT	Process aborted	6
Sigalrm	Signal raisedAlarm	14
Sigbus	Bus Error: "Access to undefined portion of Memory Object"	7
Sigchld	Child process terminated, stopped (or continued *)	17
Sigcont	Continue if stopped	18
Sigfpe	Floating Point exception: "erroneous arithmetic operation"	8
Sighup	Hangup	1
Sigill	Illegal instruction	4
SIGINT	Interrupt	2
Sigkill	Kill (terminate immediately)	9
Sigpipe	Write to pipe with no one reading	13
Sigquit	Quit and dump Core	3
SIGSEGV	Segmentation Violation	11
Sigstop	Stop executing temporarily	19
Sigterm	Termination (request to terminate)	15
Sigtstp	Terminal stop signal	20
Sigttin	Background process attempting to read from tty ("in ")	21
Sigttou	Background process attempting to write to TTY ("out ")	22
SIGUSR1	User-Defined 1	10
Sigusr2	User-Defined 2	12
Sigpoll	Pollable event	29
Sigprof	Profiling timer expired	27
Sigsys	Bad syscall	31
Sigtrap	Trace/breakpoint trap	5
Sigurg	Urgent Data available on socket	23
Sigvtalrm	Signal raised by timer counting virtual time: "virtual timer expired"	26
Sigxcpu	CPU time limit exceeded	24
Sigxfsz	File size limit exceeded	25

Grep globalhandlerexceptionresolver.-NR -- exclude-Dir = ". SVN" -- Binary-files = without-match

Reference recommendations:

N methods to kill processes in Linux

How to kill processes in Linux (kill, killall)

Killing processes in Linux, using Fuser, kill, and pkill commands

Appendix: various signals and their usage

Signal	Description	Signal Number on Linux x86
SIGABRT	Process aborted	6
Sigalrm	Signal raisedAlarm	14
Sigbus	Bus Error: "Access to undefined portion of Memory Object"	7
Sigchld	Child process terminated, stopped (or continued *)	17
Sigcont	Continue if stopped	18
Sigfpe	Floating Point exception: "erroneous arithmetic operation"	8
Sighup	Hangup	1
Sigill	Illegal instruction	4
SIGINT	Interrupt	2
Sigkill	Kill (terminate immediately)	9
Sigpipe	Write to pipe with no one reading	13
Sigquit	Quit and dump Core	3
SIGSEGV	Segmentation Violation	11
Sigstop	Stop executing temporarily	19
Sigterm	Termination (request to terminate)	15
Sigtstp	Terminal stop signal	20
Sigttin	Background process attempting to read from tty ("in ")	21
Sigttou	Background process attempting to write to TTY ("out ")	22
SIGUSR1	User-Defined 1	10
Sigusr2	User-Defined 2	12
Sigpoll	Pollable event	29
Sigprof	Profiling timer expired	27
Sigsys	Bad syscall	31
Sigtrap	Trace/breakpoint trap	5
Sigurg	Urgent Data available on socket	23
Sigvtalrm	Signal raised by timer counting virtual time: "virtual timer expired"	26
Sigxcpu	CPU time limit exceeded	24
Sigxfsz	File size limit exceeded	25