What system is the father of almost all modern multiuser systems

Wenjie Wang Software defined network SDN is a new network architecture in which the control function is decoupled from the data forwarding plane, that is attracting wide attentions from both research and industry sectors. However, SDN still faces the energy waste problem as do traditional networks. At present, research on energy saving in SDN is mainly focused on the static optimization of the network with zero load when new traffic arrives, changing the transmission path of the uncompleted traffic which arrived before the optimization, possibly resulting in route oscillation and other deleterious effects. To avoid this, a dynamical energy saving optimization scheme in which the paths of the uncompleted flows will not be changed when new traffic arrives is designed.

What system is the father of almost all modern multiuser systems

Distributors ponder a systemd change Did you know? Please help out by buying a subscription and keeping LWN on the net. By Jonathan Corbet June 7, Linux users tend to pride themselves on their position at the leading edge of a fast-moving development community.

But, in truth, much of what we do is rooted in many decades of Unix tradition, and we tend to get grumpy when young developers show up and start changing things around. A recent change of default in systemd represents such a change and the kind of response that it brings out; as a result, Linux distributors are going to have to make a decision on whether they should preserve the way things have always worked or make a change that, while potentially disruptive to users, is arguably a step toward more predictable, controllable, and secure behavior.

Killing processes on logout Systemd makes extensive use of control groups to manage processes on the system; because control groups contain processes and any subprocesses they may create, systemd has a clear view of the full set of processes that belong to each service or session.

That allows it to, for example, kill all of the processes belonging to a given service, regardless of whether those processes were started directly by systemd. When it comes to user sessions, systemd or, rather, the logind component has, for some time, had the ability to kill all of a user's running processes when that user logs out.

That capability is controlled by the KillUserProcesses configuration option to logind; by default in older systemd releases, that option was set to "no".

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The systemd release announcement included, among many other changes, the news that the default had been changed to "yes," so that, absent other measures, users cannot leave processes running after they log out of the system.

This change quickly found its way into the faster-moving development distributions; the unhappy cries from users were not far behind.

The problem, from the point of view of these users, is that systemd 's behavior represents a significant change in how Linux systems work, and that this change will surprise people in unpleasant ways.

Prior to this change, processes could easily be made to persist after the user logs out; it was just a matter of blocking the SIGHUP signal that is delivered when the controlling terminal goes away.

In the new scheme of things, life is not so simple. Thus, programs that have traditionally set themselves up to survive a logout screen and tmux are often-cited examples can no longer do so and will not be able to perform their intended function.

There are ways around this problem, of course. One is for the program to tell systemd directly that it needs to persist.

That involves accepting the systemd library as a dependency. Not all projects are willing to add this kind of systemd-specific code; see this tmux tracker entryfor example.

So it may be some time before even the programs that are explicitly intended to run after logout are able to work transparently in this manner. Beyond that, most programs are not designed for this kind of persistence, but can be used that way anyway; it is not uncommon to place a long-running task in the background and expect it to complete after logging out.

What system is the father of almost all modern multiuser systems

In the new systemd world, these programs need to be run with the systemd-run command. Creating a version of nohup that invokes systemd-run should not be a hard thing for a distributor to do, so there should be relatively little disruption in cases where users explicitly ask for persistence already.

The only remaining snag is that the user account must have "lingering" enabled for persistence requests to actually be honored. This is done with the "loginctl enable-linger" command, but is turned off by default.

Enabling lingering can be configured as an unprivileged operation, or it can be restricted to system administrators. In the end, the ability to run processes that persist after logout has not gone away, but the way things behave by default has changed. There may be some truth to that, but it also appears that all desktop environments have at least some problems with unwanted persistent processes.

Such processes don't just clog the system; they can also delay the availability of the console for another login or slow down the shutdown process. It is easy to say that such programs should simply be fixed, but, in the real world, sometimes one has to stop playing whack-a-mole and just pave the field instead.

Beyond that, systemd creator Lennart Poettering sees process persistence as a security issue. Allowing somebody to log into a machine should not imply allowing that user to run code when they are not logged in; that is a separate decision that should be reserved for the administrator.

Even if the change creates some trouble, he believes that somebody needs to do it: In my view it was actually quite strange of UNIX that it by default let arbitrary user code stay around unrestricted after logout. It has been discussed for ages now among many OS people, that this should possible but certainly not be the default, but nobody dared so far to flip the switch to turn it from a default to an option.

Not cleaning up user sessions after logout is not only ugly and somewhat hackish but also a security problem.

One need not look far to find criticism of Lennart's code, attitude, ancestry, or hair style, but one would be hard put to find accusations that he or the systemd development community as a whole is unwilling to dare to make disruptive changes.What system is the father of almost all modern multiuser systems?

i multiuser operating system allow many people on many different computer to use and do that same tasks at the same time.

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A filesystem that doesn't work on modern machines (disks above 2GB, GPT partition tables, UEFI, sectors bigger than bytes), gets corrupted on a crash, suffers from a ridiculous level of fragmentation, has bizarre limitations on file names (, all caps, half of ASCII banned), and so on. What system is the father of almost all modern multiuser systems?

Mainframe computer systems Which paper is the foundation of all subsequent studies of computer security? It was the first and operating system created with security as its primary goal. Shortly after the restructuring of MULTICS, several key engineers started working on.

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Network-on-Chip (NoC) was presented as a new System-on-Chip (SoC) paradigm to solve the problem associated with shared buses in multi-core systems by replacing the traditional bus based on-chip. Paul's blog Friday, December 23, Kindle Fire. Almost all modern emulators use the latter approach if they can get away with it.

You can run a combination of different operating systems as long as those systems all support the kernel you're running.

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