A zombie process in Linux is a process that has finished executing, but its entry in the process table has not yet been removed. This can happen if the parent process of the child process terminates before the child process has a chance to exit.
Zombie processes do not consume any CPU resources, but they do consume a small amount of memory for their entry in the process table. If there are a large number of zombie processes on a system, it can eventually lead to problems, such as a shortage of process IDs.
Zombie processes are typically removed from the system when their parent process collects their exit status using the wait() system call. However, if the parent process terminates before it has a chance to collect the child process’s exit status, the child process will remain a zombie process.
If you find that you have many zombie processes on your system, you can remove them using the kill -9 signal. However, this should only be done as a last resort, as it can potentially cause data loss.
Here is an example of how to remove a zombie process using the kill -9 signal:
kill -9 <pid>
where <pid> is the process ID of the zombie process.
Finding Zombie process
There are two common ways to find zombie processes in Linux:
- Using the
pscommand:
The ps command can be used to list all processes running on the system. To list zombie processes, you can use the following command:
ps aux | grep Z
This will list all processes with a status of Z, which indicates that they are zombie processes.
- Using the
topcommand:
The top command provides a real-time view of system processes. To view zombie processes, you can use the following command:
top -b1 -n1 | grep Z
This will display a list of all processes, sorted by CPU usage, with a status of Z.
Once you have identified the zombie processes, you can remove them using the kill command.
To kill a zombie process, you can use the following command:
kill -9 <pid>
where <pid> is the process ID of the zombie process.
Here is an example of how to kill a zombie process using the kill -9 signal:
kill -9 1234
This will kill the zombie process with the process ID 1234.
If you are not sure whether or not a process is a zombie process, you can check the STATE column in the output of the ps or top commands. A zombie process will have a state of Z.
It is important to note that the Zombie process in Linux are not typically a serious problem. However, if you find that you have many zombie processes on your system, it is essential to investigate the cause and take steps to prevent them from accumulating in the future.