Module 3a - Processes

Question 1

What does “ps” command in linux do?

Answer 1

Lists running processes

Question 2

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<p>What does the "top" command do in linux?</p>

Answer 2

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<p>Displays processes with top resource usage</p>

Question 3

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<p>What does the "kill" / "pkill" / "killall" command do in linux?</p>

Answer 3

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<p>terminates a process</p>

Question 4

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<p>What does "jobs" do in linux?</p>

Answer 4

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<p>Lists currently running jobs</p>

Question 5

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<p>What does "bg" do in linux?</p>

Answer 5

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<p>Backgrounds a job</p>

Question 6

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<p>What does "fg" do in linux?</p>

Answer 6

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<p>Foregrounds a job</p>

Question 7

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<p>What does "nice" / "renice" do in linux?</p>

Answer 7

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<p>Sets the priority of a process</p>

Question 8

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<p>What makes IPC (inter-process communication) using a named pipe in linux/unix costly?</p>

Answer 8

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<p>IPC with a pipe requires the operating system to make a context switch from user space to kernel space, and then back from kernel space to user space</p>

Question 9

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<p>How do threads running in the same process typically communicate?</p>

Answer 9

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<p>Directly through shared memory</p>

Question 10

If an OS kernel supports multithreading through lightweight processes, what does this mean in terms of address spaces?

Answer 10

Lightweight processes will share the same address space, just like threads

Question 11

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<p>Describe how a multi-threaded server which follows the dispatcher/worker design</p>

Answer 11

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<p>The dispatcher thread (which does mostly I/O work) receives requests from the network, and feeds them to a pool or worker threads (which do CPU intensive tasks)</p>

Question 12

Applications caninteract with the hardware’s resources through several ways:

• Directly from the application
• Through a library that interacts with the OS which interacts with the hardware

How exactly dothese interactionswork? Are they the same privilege?

Answer 12

• An application’s general instructions are always processed by the CPU (direct unprivilegedinteraction)
• An application can makea call to a library function, or make a system call to the OS
• A library can make a system call to the OS
• OS can execute privileged instructions that the application cannot
  When the OS accesses the hardware, it is privileged (kernel). When the application does it directly, it is unprivileged)

Question 13

What is “virtualization” when running applications?

Answer 13

Applications often run in a virtualized environment such as JRE or JVM. This isolates the applications from the underlying hardware platform (and sometimes the OS)

Question 14

<p>What are benefits of "virtualization"?</p>

Answer 14

• improves safety since the application won’t be able to access the files, and privileged resources
• makes the application more replicable
• easier to maintain

Question 15

How do networked applications communicate?

How is the format of a message (Binary vs JSON vs text, etc) determined?

Answer 15

• They communicate by exchanging messages through additional infrastructure such as middleware
• Message passing protocol determines the format of the message (binary vs JSON, vs text, etc)

Question 16

<p>What is the difference between an application-specific messaging protocol and an application-independent protocol?</p>

Answer 16

<p>Application specific protocols operate purely on the application layer whereas application-independent protocols use the middleware infrastructure to communicate messages</p>

Question 17

<p>Suppose we have a server cluster of many applcation/compute servers. What kind of infrastructure does the system need in order to forward requests from the client?</p>

Answer 17

<p>The system needs a load balancer component which opperates as a logical switch (or multiple)</p>