Difference between revisions of "COMP 3000 2012 Midterm Material Answers"

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(my notes about the answers)
 
(Replaced content with "MOVED")
 
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Here are some (unofficial) answers to the midterm practice questions
MOVED
 
1) False.  Sparse file means holes. Zeroes aren't holes.
YOu need to move the file pointer. You have to use a
seek. The data will be READ as zeros, though...
Look up truncate command and strace it. It ain't just writing zeros
 
2)
Nothing happens. Env vars aren't globals. They're passed in with Execve. Environments
variables are typically process specific.
 
3)
rwx
 
4)
Kill the parent
Why? init will own the zombie process and then kill it
 
5)
chmod +x
Default non executable. Need to make it executable. (--x)
 
6)
Software interrupt
 
7)
Don't know... Undefined. Can not depend on ordering
 
8)
True. That's the purpose of signals
Register a normal C function as a signal handler
Some are implemented by default (sigkill)
Signals can be called at any point in execution.
 
9)
Sequentially (sysV). Shell script that runs every ''command'' sequentially
 
Upstart does in in parrallel though...
 
10)
execve DOES NOT RETURN ANYTHING. Process image is replaced.
 
The program itself calls the signal handler
 
11)
fsck <- wrapper function
fsck.FMT <- called by fsck for a specific format (ex: fsck.ext4)
 
12)
The kernel. The kernel is the only thing that can allocate.(execve)
This also makes sense because execve is a system call.
 
13)
Sparse file.
 
14)
lspci, lshw.
In /proc/, you may be able to also.
These commands display the machine's "hardware".
 
Not /dev/ because that's the abstraction.
 
 
15)
At the command line, the $PATH variable is where the shell looks for binaries/files.
The path is walked when the fullPATH/filename of the command line hasn't been specified
 
16)
Some libraries make no sys calls (strlen). Libraries that do basic string and math
operations -> no sys calls
 
Programs with lots of I/O will use lot of sys calls
 
17)
nice and renice
nicess is policy value (default value and you can modify this)
priority (dynamic) is based on niceness and the amount of time the process has run on
cpu
Priority doesn't apply to I/O. I/O will continue despite other processing having high
priority. I/O will always slow down the system.
 
18)
The former requires a library card and a telephone.

Latest revision as of 23:57, 24 October 2012

MOVED

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