How to Delete a User in Linux When the System Says Its Currently Used in a Process

How can I delete a user in linux when the system says its currently used in a process

First use pkill or kill -9 <pid> to kill the process.

Then use following userdel command to delete user,

userdel -f cafe_fixer

According to userdel man page:

-f, --force

This option forces the removal of the user account, even if the user
is still logged in. It also forces userdel to remove the user's home
directory and mail spool, even if another user uses the same home
directory or if the mail spool is not owned by the specified user. If
USERGROUPS_ENAB is defined to yes in /etc/login.defs and if a group
exists with the same name as the deleted user, then this group will be
removed, even if it is still the primary group of another user.

Edit 1:

Note: This option (i.e. --force) is dangerous and may leave your system in an inconsistent state.

Edit 2:

In spite of the description about some files, this key allows removing the user while it is in use. Don't forget to chdir / before, because this command will also remove home directory.

Killing process of a user before deleting

man ps mentions the U flag to ps to filter by effective user ID. -o defines the output, so you can just get the process IDs. Since ps also prints "PID" as column header, you need to discard the first line of the ps output.

for pid in `ps U "$name" -o pid | head -n -1` 
do
    sudo kill -KILL $pid
done

should do the trick.

How do I kill all a user's processes using their UID

Use pkill -U UID or pkill -u UID or username instead of UID. Sometimes skill -u USERNAME may work, another tool is killall -u USERNAME.

Skill was a linux-specific and is now outdated, and pkill is more portable (Linux, Solaris, BSD).

pkill allow both numberic and symbolic UIDs, effective and real http://man7.org/linux/man-pages/man1/pkill.1.html

pkill - ... signal processes based on name and other attributes

    -u, --euid euid,...
         Only match processes whose effective user ID is listed.
         Either the numerical or symbolical value may be used.
    -U, --uid uid,...
         Only match processes whose real user ID is listed.  Either the
         numerical or symbolical value may be used.

Man page of skill says is it allowed only to use username, not user id: http://man7.org/linux/man-pages/man1/skill.1.html

skill, snice ... These tools are obsolete and unportable. The command syntax is poorly defined. Consider using the killall, pkill

  -u, --user user
         The next expression is a username.

killall is not marked as outdated in Linux, but it also will not work with numberic UID; only username: http://man7.org/linux/man-pages/man1/killall.1.html

killall - kill processes by name

   -u, --user
         Kill only processes the specified user owns.  Command names
         are optional.

I think, any utility used to find process in Linux/Solaris style /proc (procfs) will use full list of processes (doing some readdir of /proc). I think, they will iterate over /proc digital subfolders and check every found process for match.

To get list of users, use getpwent (it will get one user per call).

skill (procps & procps-ng) and killall (psmisc) tools both uses getpwnam library call to parse argument of -u option, and only username will be parsed. pkill (procps & procps-ng) uses both atol and getpwnam to parse -u/-U argument and allow both numeric and textual user specifier.

How to kill a process running on particular port in Linux?

Use the command

 sudo netstat -plten |grep java

used grep java as tomcat uses java as their processes.

It will show the list of processes with port number and process id

tcp6       0      0 :::8080                 :::*                    LISTEN      
1000       30070621    16085/java

the number before /java is a process id. Now use kill command to kill the process

kill -9 16085

-9 implies the process will be killed forcefully.

How to kill all processes with a given partial name?

Use pkill -f, which matches the pattern for any part of the command line

pkill -f my_pattern

Just in case it doesn't work, try to use this one as well:

pkill -9 -f my_pattern

Find and kill a process in one line using bash and regex

In bash, you should be able to do:

kill $(ps aux | grep '[p]ython csp_build.py' | awk '{print $2}')

Details on its workings are as follows:

• The ps gives you the list of all the processes.
• The grep filters that based on your search string, [p] is a trick to stop you picking up the actual grep process itself.
• The awk just gives you the second field of each line, which is the PID.
• The $(x) construct means to execute x then take its output and put it on the command line. The output of that ps pipeline inside that construct above is the list of process IDs so you end up with a command like kill 1234 1122 7654.

Here's a transcript showing it in action:

pax> sleep 3600 &
[1] 2225
pax> sleep 3600 &
[2] 2226
pax> sleep 3600 &
[3] 2227
pax> sleep 3600 &
[4] 2228
pax> sleep 3600 &
[5] 2229
pax> kill $(ps aux | grep '[s]leep' | awk '{print $2}')
[5]+  Terminated              sleep 3600
[1]   Terminated              sleep 3600
[2]   Terminated              sleep 3600
[3]-  Terminated              sleep 3600
[4]+  Terminated              sleep 3600

and you can see it terminating all the sleepers.

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Explaining the grep '[p]ython csp_build.py' bit in a bit more detail:

When you do sleep 3600 & followed by ps -ef | grep sleep, you tend to get two processes with sleep in it, the sleep 3600 and the grep sleep (because they both have sleep in them, that's not rocket science).

However, ps -ef | grep '[s]leep' won't create a process with sleep in it, it instead creates grep '[s]leep' and here's the tricky bit: the grep doesn't find it because it's looking for the regular expression "any character from the character class [s] (which is s) followed by leep.

In other words, it's looking for sleep but the grep process is grep '[s]leep' which doesn't have sleep in it.

When I was shown this (by someone here on SO), I immediately started using it because

• it's one less process than adding | grep -v grep; and
• it's elegant and sneaky, a rare combination :-)

How to unmount a busy device

YES!! There is a way to detach a busy device immediately - even if it is busy and cannot be unmounted forcefully. You may cleanup all later:

umount -l /PATH/OF/BUSY-DEVICE
umount -f /PATH/OF/BUSY-NFS (NETWORK-FILE-SYSTEM)

NOTE/CAUTION

1. These commands can disrupt a running process, cause data loss OR corrupt open files. Programs accessing target DEVICE/NFS files may throw errors OR could not work properly after force unmount.
2. Do not execute above umount commands when inside mounted path (Folder/Drive/Device) itself. First, you may use pwd command to validate your current directory path (which should not be the mounted path), then use cd command to get out of the mounted path - to unmount it later using above commands.

Shell script to capture Process ID and kill it if exist

Actually the easiest way to do that would be to pass kill arguments like below:

ps -ef | grep your_process_name | grep -v grep | awk '{print $2}' | xargs kill

Hope it helps.

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