Process Killer Download
Cassi Sturgul
When targeting processes with the --process argument, you can pass a regular expression, which matches processes in the same way that pgrep(1) does, or you can pass a specific Process ID (PID). When passing a regular expression, Gremlin will only match on the process name (arg0) unless --full is also supplied.
PID 1 is most commonly reserved for the init process. On hosts, Process Killer does not work for PID 1. Instead, you should use a Shutdown experiment. On container-based systems (e.g. Kubernetes), you can terminate PID 1, which has the same effect as running a Shutdown experiment.
The only exception is if you want to repeatedly terminate a container process, which is only possible with Process Killer. In that case, you would need to run Process Killer on the container host, ensure that the Gremlin agent is deployed with hostPID set to true, and select the container process from the host.
The Web Host Manager (WHM) has a number of ways that you can manage the health of your hosting server. The Background Process Killer option provided in the System Health section of the WHM allow yous to take action if there is a specific process that could leave your server vulnerable to attack. This article will describe the use of the Background Process Killer. Stopping the processes is important as they can often lead to denial-of-service attacks. If necessary, you can also create trusted users that can run these processes.
That concludes the tutorials for using the Background Process killer. You should be able to select the process that you do not want running on the server, or add/remove users that have been trusted to run those processes. Learn how to monitor and trace processes in the Process Manager.
This article describes a quick way to find easy exploitable process killer drivers. There are many ways to identify and exploit process killer drivers. This article is not exhaustive and presents only one (easy) method.
Finally, the driver executes the function in its code related to the IOCTL, which in our case is a process termination function. The PID is retrieved by the function code using a buffer that contains the data (PID in our case) provided via the DeviceIoControl() function.
The script checks all the imported functions for each driver in the json file. If a driver has in its imported functions Nt/ZwOpenProcess AND Nt/ZwTerminateProcess then it will be selected as a potential process killer drivers.
Still, you can also use the kernel function PsLookupProcessByProcessId() to retrieve a pointer to the EPROCESS structure of a running process using its PID (documentation here). EPROCESS is a data structure representing the process object in the kernel (documentation here).
The "OOM Killer" or "Out of Memory Killer" is a process that the Linux kernel employs when the system is critically low on memory. This situation occurs because processes on the server are consuming a large amount of memory, and the system requires more memory for its own processes and to allocate to other processes. When a process starts it requests a block of memory from the kernel. This initial request is usually a large request that the process will not immediately or indeed ever use all of. The kernel, aware of this tendency for processes to request redundant memory, over allocates the system memory. This means that when the system has, for example, 8GB of RAM the kernel may allocate 8.5GB to processes. This maximises the use of system memory by ensuring that the memory that is allocated to processes is being actively used.
Normally, this situation does not cause a problem. However, if enough processes begin to use all of their requested memory blocks then there will not be enough physical memory to support them all. This means that the running processes require more memory than is physically available. This situation is critical and must be resolved immediately.
The OOM Killer works by reviewing all running processes and assigning them a badness score. The process that has the highest score is the one that is killed. The OOM Killer assigns a badness score based on a number of criteria. The principle of which are as follows are as follows:
The above listed criteria mean that when selecting a process to kill the OOM Killer will choose a process using lots of memory and has lots of child processes and which are not system processes. An application such as Apache, MySQL, Nginx, Clamd (ClamAV), or a mail server will make an good candidate. However, as this situation usually occurs on a busy web servers Apache or MySQL will be the largest in-memory, non-system processes and consequently gets killed.
It must be remembered that although the Web Server or DB Server are very important to you, when the kernel calls the OOM Killer the situation is critical. If memory is not freed by killing a process the server will crash very shortly afterwards. Continuing normal operations at this juncture is impossible.
The easiest way to find if the OOM Killer was invoked and potentially the reason that a website went offline or similar, is to check the system logs. Whenever the OOM Killer is invoked it will write a great deal of information to the system log including which process was killed and why. You can run the following commands;
The first step that should be taken to reduce memory usage to stop any processes running that are not needed. For example if the server is not shared and FTP is only occasionally used then this process can be initiated prior to uploading and terminated afterwards.
Choosing alternative applications or tweaking configuration will only produce limited results. Increasing the available RAM to an amount sufficient to support the needed processes is always the best solution.
The Out Of Memory Killer or OOM Killer is a process that the linux kernel employs when the system is critically low on memory. Thissituation occurs because the linux kernel has over allocated memory to its processes.
When a process starts it requests a block of memory from the kernel. This initial request is usually a large request that the processwill not immediately or indeed ever use all of. The kernel, aware of this tendency for processes to request redundant memory, overallocates the system memory. This means that when the system has, for example, 2GB of RAM the kernel may allocate 2.5GB to processes.
Normally, this situation does not cause a problem. However, if enough processes begin to use all of their requested memory blocksthen there will not be enough physical memory to support them all. This means that the running processes require more memory thanis physically available. This situation is critical and must be resolved immediately.
This article describes the Linux out-of-memory (OOM) killer and how to find out why it killed a particular process. It also provides methods for configuring the OOM killer to better suit the needs of many different environments.
When a server that's supporting a database or an application server goes down, it's often a race to get critical services back up and running especially if it is an important production system. When attempting to determine the root cause after the initial triage, it's often a mystery as to why the application or database suddenly stopped functioning. In certain situations, the root cause of the issue can be traced to the system running low on memory and killing an important process in order to remain operational.
The Linux kernel allocates memory upon the demand of the applications running on the system. Because many applications allocate their memory up front and often don't utilize the memory allocated, the kernel was designed with the ability to over-commit memory to make memory usage more efficient. This over-commit model allows the kernel to allocate more memory than it actually has physically available. If a process actually utilizes the memory it was allocated, the kernel then provides these resources to the application. When too many applications start utilizing the memory they were allocated, the over-commit model sometimes becomes problematic and the kernel must start killing processes in order to stay operational. The mechanism the kernel uses to recover memory on the system is referred to as the out-of-memory killer or OOM killer for short.
When troubleshooting an issue where an application has been killed by the OOM killer, there are several clues that might shed light on how and why the process was killed. In the following example, we are going to take a look at our syslog to see whether we can locate the source of our problem. The oracle process was killed by the OOM killer because of an out-of-memory condition. The capital K in Killed indicates that the process was killed with a -9 signal, and this is usually a good sign that the OOM killer might be the culprit.
We can also examine the status of low and high memory usage on a system. It's important to note that these values are real time and change depending on the system workload; therefore, these should be watched frequently before memory pressure occurs. Looking at these values after a process was killed won't be very insightful and, thus, can't really help in investigating OOM issues.
There are a number of other tools available for monitoring memory and system performance for investigating issues of this nature. Tools such as sar (System Activity Reporter) and dtrace (Dynamic Tracing) are quite useful for collecting specific data about system performance over time. For even more visibility, the dtrace stability and data stability probes even have a trigger for OOM conditions that will fire if the kernel kills a process due to an OOM condition. More information about dtrace and sar is included in the "See Also" section of this article.
The OOM killer on Linux has several configuration options that allow developers some choice as to the behavior the system will exhibit when it is faced with an out-of-memory condition. These settings and choices vary depending on the environment and applications that the system has configured on it.
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