Ubuntu displays "There is 1 zombie process" upon login
Solution 1:
There's nothing to worry about :
Zombie
On Unix operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. In the term's colorful metaphor, the child process has died but has not yet been reaped.
When a process ends, all of the memory and resources associated with it are deallocated so they can be used by other processes. However, the process's entry in the process table remains. The parent is sent a SIGCHLD signal indicating that a child has died; the handler for this signal will typically execute the wait system call, which reads the exit status and removes the zombie. The zombie's process ID and entry in the process table can then be reused. However, if a parent ignores the SIGCHLD, the zombie will be left in the process table. In some situations this may be desirable, for example if the parent creates another child process it ensures that it will not be allocated the same process ID.
Source : http://wiki.answers.com/Q/What_is_Zombie_Process_and_Orphan_Process
Solution 2:
I was able to end the zombie process following this tutorial - https://vitux.com/how-to-kill-zombie-processes-in-ubuntu-18-04/.
Basically:
1) Identify the zombie process:
ps axo stat,ppid,pid,comm | grep -w defunct
2) Kill the parent process:
sudo kill -9 <parent_process_number>
Ex:
Solution 3:
As explained in the accepted answer, you have a process that has completed execution but is still in process table: https://serverfault.com/a/390216/48449
This shouldn't cause harm if it's only one process, but still shouldn't happen. If there are too many and you don't reboot or restart the causing parent process that produces those, you could reach your maximum number of allowed processes and cause serious issues.
To find out if worry is appropriate and which other process the zombie belongs to, this works for me:
ps -elf --forest | grep -C5 '<[d]efunct>'
Increase the number of context lines if necessary to find out about the parent process, ideally fix that process to make it "reap" its ended subprocesses.