Elance System Programming Test Answers 2015
·
Where would you expect to encounter the
following code? for (i=1; i<argc; i++) { if (argv[i][0] == '-') {
Anywhere at all
In the beginning of the main() function
In the scanning for an internals function
In the iteration of the fscanf() function
Which of the following could the fork()
command return to the child process?
-1
19456
2054
0
If a function is a 'blocking function' then:
The function must terminate before control returns
to caller
This function has the highest possible priority
This function's purpose is to block unstructured
calls
The function is written using block structuring
Any code that calls a function whose interface
includes the line raises(aLibrary:BookIsMissing); should do which one?
Implement an exception handler
#include errno.h header file
Pass both parameters by reference
Properly pass parameter for Book
In UNIX, a program requires higher privileges
in order to do which of the following?
Create a file in the /tmp directory
Listen on a port below 1024
Open a file in the owner’s directory
exec() a new process
Which of the following is correct for the
standard file descriptors that are automatically opened in UNIX?
STDIN_FILENO = 0, STDERR_FILENO = 1, STDOUT_FILENO
= 2
STDERR_FILENO = 0, STDOUT_FILENO = 1, STDIN_FILENO
= 2
STDOUT_FILENO = 0, STDERR_FILENO = 1, STDERR_FILENO
= 2
STDIN_FILENO = 0, STDOUT_FILENO = 1, STDERR_FILENO
= 2
Which of the following is true of hard links?
Files are deleted from disk when a hard link is
removed
Hard links are directory entries that point to the
same inode as another file
Hard links can cross filesystems
When a new process is created using fork(),
which of the following describes the state of open file descriptors?
The child inherits the parent’s
The child always has an empty set of closed
descriptors
The child overwrites the parent’s
The child has distinct copies of the parent’s
Which of the following methods is used by
system programs to access a character device (such as keyboards, audio cards,
etc) on a UNIX system?
Pipes
It depends on the device
Standard file access functions
Which of the following fields in the stat
struct contain last time the file was modified?
st_atime
st_mtime
st_ctime
What is thread safety?
Threads don’t start until all of the resources they
require are available
Threads can only access the data in its process
Multiple threads can be executed without corrupting
shared data
Given the following line: my_fd =
open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_APPEND, 0644); Which statement
is true?
Runtime error opening the file as the various flags
and modes are in conflict
Syntax error; the function takes only one more
argument after 'filename'
Syntax error; the second argument should be a
single integer type
Opens a file descriptor, bitwise OR'ing output
flags and in mode 644
Threads and processes are related in which one
of the following ways?
Each process exists within a thread
Threads and processes exist separately
Each thread exists within a process
An orphan process occurs as a result of which
of the following conditions?
Parent process terminates before its child process
Child process terminates before its parent process
Parent and child process terminate simultaneously
Which one of the following is NOT applicable
in real-time Systems Programming?
Sequence Diagram
E-R Schema
Event Trace
Timing Diagram
You want the same codebase to conditionally
compile on and for different target platforms. Which of the following would you
use?
Bit flags and bitwise OR'ing
#itdef, #ifndef, and #endif
if, else if, and else blocks
Use host-specific linkers
Race conditions are caused by which of the
following conditions in a multithreaded system?
Proper program function requires all threads to run
quickly
Proper program function is dependent on the
execution sequence and timing of each thread
Proper program function requires that all threads
run at the same speed
Using strncpy() to copy strings can help
prevent which of the following attacks?
Buffer overflow
Password cracking
Denial of service
Man-in-the-middle
The language of choice for Systems Programming
is:
None of these
LISP
PHP
ALGOL
You see the line: listen (s, 3); You are
looking at code for:
A server's socket
A client's server
A server's clients
A client's socket
You want to listen on a port for some
user-defined data stream. Would you use port 80?
Yes, it is best ot use low numbers for port
numbers.
Yes, it is as good as any other port number.
No, it is best to use three or four digit port
numbers.
No, it is a 'well-defined' or reserved port.
Some programme that streams data to a
hard-disk file in a loop crashed before it closed the FILE pointer. When the
output file is inspected side-by-side with the logs, it is clear that the
fprintf() function previous to the crash was unsuccessful. Such a situation can
be averted using which one of the following?
fscanf()
fflush()
fbuffer()
sscanf()
Using a terminal you want to log in to an
account on a remote computer and securely build. Which would you use?
RSH
rlogin
SSH
EncryptoTelnet
When communicating across sockets, which of
the following functions must be used when the socket is in a connected state?
send()
sendto()
sendmsg()
The purpose of the poll() and select() system
calls is to perform which of the following functions?
Watch a set of file descriptors to see which are
ready
Frequently check email and other network services
Sample system process information for use by the
top command
If you see: int ff; write(ff, data,
sizeof(data)); you know that ff is:
a file descriptor
a file function
a file pointer
a file struct
Is it good programming that the following
function call is recursive? void func(unsigned long a) { unsigned long x;
struct t_struct[] *p; : p = (struct t_struct *)alloca(a*sizeof(t_struct)); :
While (x = f2()) func(x); : return; }
No, because there is more than one 'long integer'
type
Yes, because recursion is always preferable to
iteration
No, because iteration is always preferable to
recursion
No, because both stack depth and stack-frame size
are unpredictable
The sticky bit is used to enable which of the
following features?
Aggressive caching of a process
Keep a process from swapping out of memory
Prevent users from renaming or deleting files
created by other users
Which of the following provides the most
random seed source for a pseudo random number generator?
/dev/random
C rand() function
What does the following line do? memset((char
*)&ctl_addr, 0, sizeof(ctl_addr));
Given that 0 is passed, it unsets the memory of
ctl_addr
Initializes a subset of memory pointed to by
&ctl_addr
Initializes the region of memory pointed to by
&ctl_addr
Allocates and initializes memory for variable
ctl_addr
Correct the following code: 10 int my_sock; :
20 my_sock = socket(anaddr.sin_family, SOCK_STREAM, 0); 21 if (my_sock >= 0)
{ /* error processing */ : }
line 20: my_sock = socket(SOCK_STREAM,
anaddr.sin_family, 0);
line 20: my_sock = (int *)socket(anaddr.sin_family,
SOCK_STREAM, 0);
line 10: SOCKET * my_sock;
line 21: if (my_sock < 0) {
Which of the following IPC mechanisms has an
inode?
unnamed pipe
shared memory
named pipe
semaphore
The ioctl() function is used to interact with
which of the following?
Disk Drives
Virtual TTY lines
Special character devices
Which of the following is an advantage of
using pipes over shared memory for interprocess communication?
Pipes connect processes on multiple machines
Pipes can be shared by more processes
No additional work required on multiple CPU systems
without cache coherence
Faster access time
Thread joining synchronizes threads by doing
which of the following?
The joined threads are added to a queue and
executed serially
The thread that calls join blocks until all of the
joinable threads complete
The system manages the shared resources for the
joined threads
Which of the following best describes the
purpose of the unlink() call?
Moves the file in from one directory to another
Sets the file’s inode count to one (1)
Removes the file from its directory
Using two resident processes on a PC and a
Unix box, you are streaming unbuffered the contents of a text-file byte by byte
from the PC to the Unix box where it is written byte by byte to the local hard
disk. Eyeing the written file it is obvious that it is not quite right. You
have likely run into which problem?
Text file versus binary file
Ignoring the parity bit
Not using buffered streaming
Big endian versus littlen endian
What does the following function return? Class
retVal = [self class]; if ([retVal class] != [NSObject class]) { while ([retVal
superclass] != [NSObject class]) retVal = [retVal superclass]; } return retVal;
The present object's superclass or base class
The present object's ultimate superclass or base
class below the root object
The root object
The present object's class
The following code is written to be accessed
by multiple detached threads. : const char * c; char * d; : /* no lock and no
mutex is used in any way here */ my_print_func (c, &d); : Which one of the
following will happen when this code is re-entered by multiple threads?
One thread will run while others will crash or
abort
It isn't possible to tell without looking at
my_print_func()
The code will sometimes run and sometimes cause a
crash
The code will always cause a crash
When there are more fork() calls than wait()
calls, which of the following is created?
daemon
orphan
zombie
thread
What does the line #define S_IRWXG 0000070
relate to?
Alpha-numeric interchange
Defining bitwise flags
User-defined typing
Flags for file access
You want a char * that will contain the
timestamp as YYYYMMDD-hh:mm:ss . You would use:
sprintf()
get_datetime()
localtime()
strftime()
Given: int s, l; struct sockaddr_un
sock_struct; Choose the option that corrects the following line: bind(s,
sock_struct, l);
bind(s, sizeof(sock_struct), l);
bind(sock_struct, s, l);
bind(s, l, sock_struct);
bind(s, &sock_struct, l);
What type of attack can be mitigated by using
ulimit, setrlimit(), and quotactrl()?
Buffer Overflow
Password cracking
Man-in-the-middle
Denial of service
Which of the following can be called to remove
zombie processes?
close()
free()
flush()
wait4()
Thrashing caused by loading a large file can
be reduced by mapping the file to memory due to which of the following
features?
Mapped memory is cached
Mapped memory uses prefetching
Mapped memory uses lazy loading
In Multi-Threaded programming you want an
active thread to push itself back in the background in favour of some other
thread. You will use which function:
pthread_detach()
pthread_setschedparam()
pthread_cancel()
sched_yield()
What is a UNIX directory?
A special type of inode
A file that contains other files
A list of files
Which of the following is the result of a
process calling UNIX exec()?
The process is completely overwritten
A new process is created
The process blocks waiting for another process to
run
The process becomes executable
In an IDL which one of the following is NOT a
valid declaration?
enum
oneread
readonly
oneway
In order to prevent signal handler race
conditions, a developer must do which of the following?
Call sigaction() to block the signal and set the
signal mask at the same time
Call sigsetmask() to set the signal mask to be
blocked
Create a mutex within the handler to protect shared
resources
CORBA's DII allows a client to do which one of
the following?
Discover new objects and interfaces at runtime
Connect with proxy objects across platforms
Dynamically link with cross-platform libs
Generate client-side stubs for interfaces
In a Publish-And-Subscribe implementation, a
subscriber must:
Know the event name or event identifier for one or
more events
Use two-way messaging
(all of these)
Be connected to one or more event publishers
A thread has its own copy of which of th
following?
Address space
Files
Stack
Variables
Which is true, given the following code: tok =
strtok_r(data, " ”, &last); while (tok) { strcat(strcpy(full_name,
the_path), tok); make_secondary(eAma_full_name, TRUE); tok = strtok_r(NULL,
" ”, &last); }
Should not pass last by reference inside the
while() loop
Re-entrantly tokenizes on delimiter " ” to
stringify something
The syntax is wrong; it should be strtok(char *,
const char *)
Passing NULL as the first param to strtok_r() is an
error
A 'crashed' software needs to be debugged
using its core dump. You would start by doing:
backface
step
inspect
attach
What will happen when the compiler 'sees' the
following code? #define FTP_TYPE "" #ifdef -FTP #define FTP_TYPE
"FTP" #elif #ifdef -PASV #ifndef FTP_TYPE #define FTP_TYPE
"PASV" #endif #endif
Compile will proceed with a warning of #define'ing
a symbol as a string
It's not a question of 'when' but if: compiler will
'see' it only if -FTP or -PASV is set
Compile will fail with an error of #define'ing a
symbol as a string
It is neither 'code' nor will the compiler 'see' it
Which one is not a difference between exit()
and _exit()?
One is for the main process; the other for forked
processes
One does some work on its own, then calls the other
One flushes and closes I/O streams; the other
doesn't
One is a true system call; the other is a library
routine
The result of calling kill(6003, 0) is which
of the following?
Process 6003 terminates
The signal 0 is sent to process 6003
The existence of process 6003 is checked
The signal 6003 is sent to process 0
Which of the following techniques can help
keep system programs secure?
Limit system calls to administrators
Check all system calls for error conditions
Setuid important processes to the root user
Encrypt every process’ executable
What is the purpose of a semaphore?
To protect a shared memory region
To protect shared variables
To protect a critical section of code
Which of the following advocates the use of
memmove() over memcopy() for performing fast data copying from one buffer to
another correctly?
The buffers will not overlap
The buffers may overlap
The buffers are large
The buffers are small
Wha does the following line do? unsigned
transOK : 1;
It sets the transOK flag to 1
Declares an unsigned integer and sets it to 1
Identifies a bit in a byte to use as a flag
Conducts a bitwise operation on transOK and 1
You want to copy binary contents of memory
from one location to another. Which one of these h-files will you #include?
stdio.h
locate.h
string.h
mem.h
You are coding a multi-threaded server in
which n detached threads will listen on n ports with a permanent one-to-one association
between threads and ports during the lifetime of the process. You want to
uniquely identify each thread-port pair. To do so you:
can use thread-id but not port number
may use either thread-id or port number
must use both thread-id and port number
can use port number but not thread-id
Yousee the following function call in some
code: pthread_setspecific(key, value); What will this allow the coder to do?
Insert key-value pairs into a thread's dictionary
Access thread-specific data outside the thread
Use a key to identify a thread
Enable a thread to set and use data
Sharing memory between processes using mmap
vs. shm_open has which of the following advantages?
The memory buffer is destroyed when the processes
end
The memory buffer is persistent beyond the life of
the processes
The memory buffer automatically expands to meet the
needs of the processes
The memory buffer more quickly accessed
Calling mmap(0, 4096, PROT_READ | PROT_WRITE,
MAP_SHARED, input_fd, 4096), where input_fd is the file descriptor of a 16KB
file will cause which of the following to occur?
The first 4KB of the file will be loaded into a 4KB
memory location
The second 4KB of the file will be loaded into a
4KB memory location
The fourth 4KB of the file will be loaded into a
4KB memory location
The third 4KB of the file will be loaded into a 4KB
memory location
In gdb before using 'jump' you would typically
do which one of the following:
Do a backtrace
Either 'step' or 'next'
Set a breakpoint
gdb has no 'jump' instruction
Given: int s, l; struct sockaddr_un
sock_struct; The following function call: connect(s, &sock_strict, l);
fails. Which one is NOT a reason for it to fail?
sock_struct passed by reference
No server bound on sock_struct
Sercer not listening on sock_struct
The value of s is negative
Changing the mode of a file to be -rwxr-xr-x
via the chmod system call can be achieved by setting the mode to which of the
following values?
S_ISVTX | S_ISUID | S_IRGRP | S_IWGRP | S_IRXOTH
S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH
S_IRWXU | S_IWGRP | S_IXOTH | S_IRWXO
S_IRUSR | S_IRWXG | | S_IROTH | S_IXOTH
Which one of the folloing is NOT necessary for
a basic CORBA system?
Naming Services
Stub and skeleton
CORBAfacilities
IDL files
How can two processes communicate despite
having firewalls between them?
SOCKS
HTTP
HTTPS
(none of these)
Which of the following functions sends a
signal to the executing process?
raise()
signal()
call()
send()
An Internet socket connection essentially is:
The ANSI-defined SOCK_ADDR * structure
A combination of file pointers and streams
A specific, system-defined socket structure
Two host addresses and two port numbers
Choose the answer that corrects the following
code. FILE * file1; : if ((file1 = open("/valid_dir/existing_file",
O_RDONLY, 0666)) == ERROR) { /* /valid_dir/existing_file is guaranteed to exist
*/ :
Replace the declaration with: int file1;
Use either one of 'O_RDONLY' and '0666'
Bitwise OR O_RDONLY with another flag
Do not open a file within a condition
What does this code do: [aLock
lockWhenCondition:(int)self beforeDate:[NSDate
dateWithTimeIntervalSinceNow:maxTimeInterval]];
A lock is locked if and when self is instantiated
before a specific date-time
A lock is set using a compound condition comprising
of self and a time interval
Control blocks for some time on a lock on a
condition that is unique to an instance
It will have no effect at all
It is not possible to set the sticky bit of a
file when creating it. Therefore it is necessary to create the directory and
then set the sticky bit by executing: mkdir(“/tmp/dir”, 0744);
chmod(“/tmp/dir”, 07744). Why?
The mkdir() command is privileged, and doesn’t
allow any modification to permissions
The behavior of mkdir() is undefined if anything
other than permission bits is set
UNIX requires that directories be created before
any non-permission bits are set
In a Unix toolchain, which one of these pairs
does not fit with the others?
Object file and linker
Header file and preprocessor
Executable and compiler
Quads and assembler
A pipe has been created, and fork() and exec()
calls have been completed. What steps must be taken next in order to establish
communication from the parent to the child?
The child must create a new pipe
The parent must close pipe_fd[0], and the child
must close pipe_fd[1]
The parent must create a new pipe
The parent must close pipe_fd[1], and the child
must close pipe_fd[0]
In order to create a counting mutex, which
mode does it need to use?
PTHREAD_MUTEX_NORMAL
PTHREAD_MUTEX_ERRORCHECK
PTHREAD_MUTEX_DEFAULT
PTHREAD_MUTEX_RECURSIVE
What does this code do: BOOL sharedLockSuccess
= NO; NSLock *aMutex; : sharedLockSuccess = [aMutex lockWhenCondition:1
beforeDate:[NSDate dateWithTimeIntervalSinceNow:(NSTimeInterval)3600]]; :
A mutex is tried to be locked within a specific
time
A mutex is being set to be locked at a specific
time
A mutex is tried to be locked with a specific
condition
A mutex is being set to be locked upon a specific
condition
Which of the following could the fork()
command return to the parent process?
-1
4066
206896
0
Recently your office's UNIX tool-chain was
updated. Now, code that previously used to build and run still builds without
any warnings or errors but displays load-time errors due to symbols not found
in shlibs. You have ensured that all necessary shared libraries are present in
the path 'pointed to' by the appropriate environment variable. Which is true?
Shared libraries should have been updated
Debugging info flags missing in Makefile
Outdated symbols in symbol table or link table
Compiler-Dynamic Linker incompatibility
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