Daemon Tools Serial Number
Hedgeworth Hennigan
I have just set up a new home server (a review of which will be coming soon) and have been installing various programs that I want to run on it. A number of these are servers, such as sshd, apache, samba etc. All of these have fairly easy installs under Debian and will automatically run at startup, and can be controlled by /etc/init.d scripts.
At this point I should mention that I have only been using daemontools for a few hours, so I could be completely wrong about anything I say below. These instructions will be for Debian, but should be fairly easily to use with other distros (the only bit that will be significantly different is exactly how to install it with the package manager). Anyway, proceed at your own risk!
- Finished!That should be all you need to get the service running. You should probably restart the machine now as that will ensure that all of the daemontools monitoring services have started correctly. Once the machine has started the new service should have started running. If it crashes or ends for some reason it will restart after one second. Any new services you add (which you can do exactly as above) should start within five seconds. You can use the svc command to control the services you have created (see man svc for details)
This post originally appeared on Robin's Blog.
I downloaded Daemon tools from the official site (the first one that comes up in google, its www.daemon-tools.cc/eng/downloads) and when I clicked the download link Norton said that the site I was downloading the exe from was a known malicious site (something like soft24.com). It was talking about the mirror that was actually serving the file.
Unfortunately anti-virus software is not the smartest piece of software out there, and is really an annoyance to most Super Users. Although anti-virus software is necessary for keeping your PC safe, the user must realize that all "threats" it detects may not really be a threat. Daemon tools is a safe piece of software and is used by many.
A DaemonSet ensures that all (or some) Nodes run a copy of a Pod. As nodes are added to thecluster, Pods are added to them. As nodes are removed from the cluster, those Pods are garbagecollected. Deleting a DaemonSet will clean up the Pods it created.
In a simple case, one DaemonSet, covering all nodes, would be used for each type of daemon.A more complex setup might use multiple DaemonSets for a single type of daemon, but withdifferent flags and/or different memory and cpu requests for different hardware types.
As with all other Kubernetes config, a DaemonSet needs apiVersion, kind, and metadata fields. Forgeneral information about working with config files, seerunning stateless applicationsand object management using kubectl.
You must specify a pod selector that matches the labels of the.spec.template.Also, once a DaemonSet is created,its .spec.selector can not be mutated. Mutating the pod selector can lead to theunintentional orphaning of Pods, and it was found to be confusing to users.
If you specify a .spec.template.spec.nodeSelector, then the DaemonSet controller willcreate Pods on nodes which match that node selector.Likewise if you specify a .spec.template.spec.affinity,then DaemonSet controller will create Pods on nodes which match thatnode affinity.If you do not specify either, then the DaemonSet controller will create Pods on all nodes.
A DaemonSet can be used to ensure that all eligible nodes run a copy of a Pod.The DaemonSet controller creates a Pod for each eligible node and adds thespec.affinity.nodeAffinity field of the Pod to match the target host. Afterthe Pod is created, the default scheduler typically takes over and then bindsthe Pod to the target host by setting the .spec.nodeName field. If the newPod cannot fit on the node, the default scheduler may preempt (evict) some ofthe existing Pods based on thepriorityof the new Pod.
The original node affinity specified at the.spec.template.spec.affinity.nodeAffinity field (if specified) is taken intoconsideration by the DaemonSet controller when evaluating the eligible nodes,but is replaced on the created Pod with the node affinity that matches the nameof the eligible node.
If you use a DaemonSet to provide an important node-level function, such ascluster networking, it ishelpful that Kubernetes places DaemonSet Pods on nodes before they are ready.For example, without that special toleration, you could end up in a deadlocksituation where the node is not marked as ready because the network plugin isnot running there, and at the same time the network plugin is not running onthat node because the node is not yet ready.
You can modify the Pods that a DaemonSet creates. However, Pods do not allow allfields to be updated. Also, the DaemonSet controller will use the original template the nexttime a node (even with the same name) is created.
You can delete a DaemonSet. If you specify --cascade=orphan with kubectl, then the Podswill be left on the nodes. If you subsequently create a new DaemonSet with the same selector,the new DaemonSet adopts the existing Pods. If any Pods need replacing the DaemonSet replacesthem according to its updateStrategy.
It is certainly possible to run daemon processes by directly starting them on a node (e.g. usinginit, upstartd, or systemd). This is perfectly fine. However, there are several advantages torunning such processes via a DaemonSet:
It is possible to create Pods directly which specify a particular node to run on. However,a DaemonSet replaces Pods that are deleted or terminated for any reason, such as in the case ofnode failure or disruptive node maintenance, such as a kernel upgrade. For this reason, you shoulduse a DaemonSet rather than creating individual Pods.
It is possible to create Pods by writing a file to a certain directory watched by Kubelet. Theseare called static pods.Unlike DaemonSet, static Pods cannot be managed with kubectlor other Kubernetes API clients. Static Pods do not depend on the apiserver, making them usefulin cluster bootstrapping cases. Also, static Pods may be deprecated in the future.
Use a Deployment for stateless services, like frontends, where scaling up and down thenumber of replicas and rolling out updates are more important than controlling exactly which hostthe Pod runs on. Use a DaemonSet when it is important that a copy of a Pod always run onall or certain hosts, if the DaemonSet provides node-level functionality that allows other Pods to run correctly on that particular node.
Daemontools-encore is a backwards compatible, enhanced version of Daniel J. Bernstein's daemontools package, written by Bruce Guenter. A summary of the features that have been added to daemontools-encore is available here. The last release of daemontools-encore was in 2014 (as of 2021-11).
Bernstein daemontools and daemontools-encore implement process supervision: programs that run as long-lived processes, such as a server program, can be supervised by being run as a child process of a supervisor. The supervisor can detect if the process, also called the service or the daemon in this context, has unexpectedly terminated, e.g. because it exited with an error status or was killed by a signal, and automatically restart it. The supervisor also provides a reliable interface for controlling both the supervised process and itself, to send signals to the process, and to query status information about it.
All this is based on standard POSIX features: a process reliably knows its child's process ID (PID), because it is the return value of the fork() call that creates it, knows when its child terminates, because it is notified with a SIGCHLD signal, and can obtain exit status information when it happens using the wait() or waitpid() calls.
The program that implements the supervisor features in Bernstein daemontools and daemontools-encore is supervise. Supervision for a single process is configured using a service directory (or servicedir). A servicedir is an ordinary directory containing at least one executable file named run. It can also contain an optional, regular file named down. The (absolute or relative to the working directory) pathname of this directory is then passed as an argument to supervise. This however is not supposed to be done directly by the user, but to happen indirectly as a consequence of running svscan.
When supervise is invoked, it changes its working directory to the specifed servicedir, and executes the contained run file as a child process, unless there is also a down file, or, for daemontools-encore only, a start file (see the start, stop and notify files, and the daemontools-encore extended service state). Daemontools-encore's supervise also makes the child process the leader of a new session using the POSIX setsid() call, unless the servicedir contains a regular file named no-setsid. In that case, the child process will run in supervise's session instead. Making the child process a session leader with Bernstein daemontools requires using the pgrphack program inside run (see supervised process execution state changes). If supervise is invoked with a servicedir that contains a down file, the run file won't be executed, but the service can be started later with the svc program (see controlling supervised processes). The contents of the down and no-setsid files are ignored, so they are usually empty.
run can have any file format that the kernel knows how to execute, but is usually a shell script that performs some sort of initialization, and then calls the real program intended to be supervised, using the shell's exec builtin utility. This allows the program to run without creating a new process, so it will have the same PID as the run script, and from there on become the supervised process. supervise waits for 1 second between two child process spawns, so that it does not loop too quickly if the process exits immediately. The daemontools-encore version of supervise also has special behaviour when it receives a signal: if it receives a SIGTERM signal, it behaves as if an svc -dx command naming the corresponding servicedir had been used (see controlling supervised processes), if it receives a SIGTSTP signal, it sends a SIGSTOP signal to the supervised process, as if an svc -p command naming the corresponding servicedir had been used, and if it receives a SIGCONT signal, it sends a SIGCONT signal to the supervised process, as if an svc -c command naming the corresponding servicedir had been used.
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