Final Superdeck Flashcards

Question

What does the OS do?

Answer 1

Controls the entire operation of the system. All input and output performed on a computer system are channeled through the OS.

Answer 2

Pre-processor takes and expands symbol definitions. Inserts header file text. Compiler - Syntactically correct programs are translated into a lower form, assembly. Assembler - Translates assembly language statements into actual machine instructions (object code or .o files). Linker - links all object files together with system libraries to produce an executable file.

Answer 3

Compiling/linking a program. Leads to an executable.

Answer 4

target dependencies recipe recipe must be tab-indented

Answer 5

%i or %d (d for decimal, i detects base) or %o or %x for octal and hexadecimal

Answer 6

Guaranteed to be no smaller than 16 bits

Answer 7

%f or %e for exponential notation

Answer 8

Float: 32 Double: 64

Answer 9

Append an L on the end.

Answer 10

Floats are truncated (i.e 3/2 is 1). Ints have no change.

Answer 11

Simply omit curly braces. Ends at the semi-colon.

Answer 12

do statement; while (condition); or do { statements; } while (condition);

Answer 13

if (condition) statement; else statement;

Answer 14

switch (expression) { case value1: statement1; .... statementn; break; case value2: statement1; .... statementn; break; default: statement1; .... statementn; break; } Note: ONLY WORKS FOR INTEGER TYPES i.e. int, short, long, long long, char...

Answer 15

type name[N] = ... {1, 2, 3, 4,...} initialize in order (doesn't have to be all of them) or {[0] = 1, [2] = 3,...} specific indices

Answer 16

Just char arrays. Must always end with null-terminator (sometimes called zero-terminator).

Answer 17

type name[n][m] Notes: int A[2][2] = {1 2 3 4} is equivalent to { {1,2}, {3,4}} (but not recommended). can also do int A[2][2] = {[1][0]=3, [2][2]=4};

Answer 18

By value. This means that giving it an int x gives it an equivalent value, but not x. However, giving it a pointer to x lets it access the value at the pointer to change x.

Answer 19

Outside of other scopes. I.e. same scope as the include statements.

Answer 20

Cannot be explicit, aside from first. I.e. A[][] is invalid. A[10][10] is valid A[][10] is valid

Answer 21

added/removed files files renamed/moved insertions/deletions in a file (lines changed) timestamp user message more...

Answer 22

-Wall -Werror -std=c99 -pedantic -g

Answer 23

Enables all warnings. can catch questionable constructions.

Answer 24

Turns warnings into errors. Forces you to fix questionable code.

Answer 25

Selects a specific standard. Standards keep things portable.

Answer 26

Issue all warnings demanded by strict C standard.

Answer 27

Generate a debugging section in the executable. Needed to use gdb

Answer 28

step next (may jump over one line loops, function calls, etc). info break (list and give info about breakpoints). clear line-or-funciton-name (removes a breakpoint) delete breakpoints (duh) info locals set var x=2 (sets a variables value) bt (stacktrace (backtrace). useful when many functions)

Answer 29

struct { stuff; } var_name = {stuff}; Note, could use commas on the last line to declare many variables. This is not recommended.

Answer 30

Top to bottom. (high to low address) Command line arguments. Stack Heap Uninitialized data segment initialized data segment text/code segment Dynamic includes from command line arguments to heap. Static elsewhere.

Answer 31

Instructions reside here.

Answer 32

Holds literals and constants.

Answer 33

Contains static and global variables.

Answer 34

Only can push and pop, which makes stack perfect for nested scopes (functions calling functions).

Answer 35

An entry is pushed onto the stack including arguments, space for automatically allocated variables inside the function, and a return address. Once done, it's popped from the stack.

Answer 36

When the stack overflows. i.e. too many recursive functions. The stack runs out of space, or runs into the heap.

Answer 37

Dynamic memory allocation.

Answer 38

From high level language, compiler translates to assembly. Assembler then translates to machine code to make an object file. Linker combines objects and libraries, resolves references, and makes an executable. Finally, the loader loads the executable into a suitable memory location and begins execution (which may involve more linking during runtime).

Answer 39

An OS concept that can be though of as a container for a single executable. Programs usually only have 1 process, but they could have many. There can be many running processes at the same time. The OS provides a method to switch between them (scheduling).

Answer 40

A path of execution. One process can have one or many threads. Many threads can run at any given time. Like processes, they are scheduled by the OS or within each process. Each thread will need its own stack if multiple in a program.

Answer 41

Most in standard directories; /bin, /usr/bin, usr/local/bin, /opt/X11/bin Some commands aren't binaries, but are shell programs.

Answer 42

locate command

Answer 43

Use which or whereis command

Answer 44

Makes a constant pointer. c can change, but charPtr will always point to it.

Answer 45

Notes that the contents of &c do not change, although charPtr can change.

Answer 46

Makes the pointer and the value both constant.

Answer 47

Make it point to the type held by the array. I.e. A pointer to an int array is the same as a pointer to an int.

Answer 48

Represents the pointer.

Answer 49

Yes. This can be useful at times, for example when checking if something may exceed the bounds of an array.

Answer 50

return-type (*pointer-var-name) (arg-type1, ...); i.e. int (*fnPtr) (void);

Answer 51

Traditional access permissions and ACLs (Access Control Lists).

Answer 52

The owner of the file (owner/user), a member of a group that the file is associated with (group), everyone else (other)

Answer 53

read form it write to it execute it

Answer 54

- for ordinary files d for directories

Answer 55

symbolic arguments i.e. chmod a+rw gives (+) read-write (rw) permissions to all users (a). Also can use o (other) g (group) u (user or owner)

Answer 56

just give it an octal number. i.e. chmod 600 somefile somefiles permissions would be rw------- Note that this sets permissions.

Answer 57

A user with root privileges. Note that if something is encrypted, they may not be able to understand what's in a file anyways.

Answer 58

read - list contents write - add new files/subdirectories to it execute - lets user cd into it

Answer 59

Finger-grained control over which users can access specific directories or files. Note that ACLs must be enabled for the system. Note that not all utiliites preserve ACLs when moving, copying, or archiving. Note that ACLs are not recommended on system files where traditional permissions are sufficient due to performance reasons.

Answer 60

A pointer to a file.

Answer 61

ln existing-file new-link The absence of the -s or --symbolic option means it makes a hard link and not a symbolic link.

Answer 62

Appears as another file. Must have a different name if in the same directory. Can only make a hard link from within the filesystem that holds the file. Editing the file from any hard link edits the same file. All hard links are of equal value. As long as one hard link remains, the file exists. It is removed when all hard links disappear.

Answer 63

A pointer to a file. Indirect (like a double pointer). Contains the pathname of the pointed-to file. Can link to non-existent files, files on different file systems, link to a directory (unlike a hard link).

Answer 64

list directory contents

Answer 65

make a directory

Answer 66

rmdir remove an empty directory

Answer 67

copy files

Answer 68

move or rename files

Answer 69

delete files/directories (rm -r for non-empty directories)

Answer 70

create links between files

Answer 71

determine file type

Answer 72

display file status

Answer 73

change access permissions

Answer 74

change group of a file/dir

Answer 75

change owner of a file/dir (admin only)

Answer 76

Like a file structure, the process structure is hierarchical with parents, children, and a root. A parent process forks (or spawns) a child process, which in turn can fork other processes. Initially, the forks are identical, but one is identified as a parent, and the other the child. fork()

Answer 77

A Linux system begins execution by starting the init daemon, a single process (called a spontaneous process) with PID 1. The ancestor of all processes the system and users work with.

Answer 78

When a system is in multi-user mode, init (recall the init daemon) calls getty or mingetty processes that display logic prompts on terminals and virtual consoles. Then, when a user responds (and pushes RETURN), getty or mingetty passes control to the login utility, that checks the user-name and password. After that, the login process becomes the user's shell process.

Answer 79

The shell forks (fork()) a new process, which create a duplicate of the shell (a subshell). Recall how fork makes a parent and child process. The new process attempts to exececute (exec()) the program. exec() causes a process's image (the entire memory layout) to be replaced by that of a different executable file (invoking the loader of the system). Remember: fork() exec() load

Answer 80

enum nameofnewtype { list, of, permissible, identifiers } can then assign values like enum nameofnewtype varname = permisible; and do things like if (varname == of)

Answer 81

The C compiler treats them as integer constants. Each name sequentially assigned an integer starting with 0. Note that you can manually control these too. i.e. enum whatever { thingone, thingtwo = 42, thingthree }; Note that thingthree then gets value 43. Can use type cast operators to cast integers to enums. i.e. thisMonth = (enum month) (monthValue - 1); makes thisMonth 1 less than monthValue.

Answer 82

enum {thing1, thing2, thing3...} varname;

Answer 83

Lets you assign an alternate name to a data type. i.e. typedef int Counter; defines the name Counter to be equivalent to int. Some uses beyond readability. i.e. typedef char Linebuf[81]; defines an array of 81 chars, so Linebuf text; is equivalent to char text[81];

Answer 84

Write a statement as if declaring a variable of the underlying type. Write the name of the type definition where the variable name would normally be. Put typedef in front of everything. i.e. typedef struct { int a; int b; } nameofnewtype;

Answer 85

By the # sign which must be the first non-space character on the line. Note that their syntax differs.

Answer 86

#define ABCDEF GHIJKL would replace all instances of ABCDEF with GHIJKL. ABCDEF is the name, GHIJKL is the value. Note that this doesn't apply to the inside of character strings. Note that this is a text replacement, not a variable. Conventionally, #define names are in capital letters to distinguish them.

Answer 87

It takes longer to compile a larger file. Larger programs often take the efforts of many programmers. A single source file can become unmanageable.

Answer 88

A C preprocessor, C compiler, and linker.

Answer 89

Performs steps 1-3. It doesn't link files together. To link them together, omit the -c.

Answer 90

When it uses, or implements the functions listed in a particular header file.

Answer 91

It asks the C preprocessor to literally "include" the code found.

Answer 92

<...> tells the preprocessor to search system locations. Usually for standard libraries and libraries your program builds. "..." tells the preprocessor to search first in the current directory, and then in system locations. This is usually used for header files local to your project.

Answer 93

-I (capital i) and a directory. i.e. -I/abs/path/to/project -I. for example tells it to consider the current directory in its list of places to search.

Answer 94

-I checks given path before system paths with <>. -I checks the current directory, then the given path, then system paths.

Answer 95

ar rcs libname.a mod1.o mod2.o... Makes a static library called libname.a that contains mod1.o mod2.o...

Answer 96

Must start with lib, and end with .a for static or .so for dynamic.

Answer 97

Use the -L and -l (lowercase L) opinions when invoking gcc in the linking step. -L followed by a directory (like -L/home/pathstuff) says where to look for library files. -I (like -Inameoflib) tells gcc to link a specific library from one of the locations given by -L. For example, -larrayutil (looks for libarrayutil.a)

Answer 98

Static linking: Linking of a library before a program is run. Dynamic linking: Delaying linking until program is run. Uses less space (can share libraries), reduced load time (not all libraries are needed every time the program runs). Allows plugins (dynamically-linked libraries with a standard interface). There are more, but these are examples. Must still use -L and -l (lowercase L) to make an executable that knows where to search for a particular dynamic library.

Answer 99

dirname/$(shell uname -s)-$(shell uname -m)

Answer 100

$? Is a special variable that gets the exit code of the last process

Answer 101

test EXPRESSION where EXPRESSION is = strings match != strings don't match -eq integers are equal -ne integers are not equal -gt int1 greater than int2 -ge int1 greater than or equal to int2 -lt less than -le less than or equal to -e file exists -f file exists and is an ordinary file -d file exists and is a directory -a AND -o OR

Answer 102

-e FILE for if it exists -f FILE for if it exists and is an ordinary file -d FILE for if it exists and is a directory

Answer 103

if tests then stuff fi

Answer 104

0 if expression is true. 1 if expression is false. Note that bash if and while statements check the return code and treat 0 as true and 1 as false*verify.

Answer 105

They are synonymous. However, if you want to use AND and OR, you must use [[ ]] which uses && and || Note that there is also [[ ]] which

Answer 106

* any character, 0 or more ? any character, just 1 [...] Any character in the brackets, 1 Causes bash to generate all matches. I.e. stat myfiles/* calls stat on every file in myfiles/

Answer 107

= in [[ ]] tests for pattern match, not just equality. [[ string = pattern ]] NOTE: pattern MUST appear on right side of the equal sign. i.e. abc = a* is true abc = a?c is true

Answer 108

case teststring in pattern1) stuff ;; pattern2) stuff ;; esac

Answer 109

until. loops until a test holds. i.e. until i=2 runs as long as i is not 2 until testcommand do stuff done

Answer 110

let "val=val * 10 + new" Enclose it in quotes

Answer 111

for (( expr1 ; expr2 ; expr3 )) do commands done expre1 is first evaluated expr2 is the condition expr3 is run whenever expr2 is true Recall int i=0; i<10; i++ from C

Answer 112

You don't all variables are string, but interpretations of those change. Strings can also be interpreted as lists by separating them with newlines or spaces. Note that lists are different than arrays in bash.

Answer 113

for loopindex in list do commands done i.e. list="1 2 3 4 5" for i in $list do echo $i done or for i in a b c d e f

Answer 114

$0 i.e. ./abc $0 is ./abc i.e. /home/name/abc $0 is /home/name/abc

Answer 115

Using the shift command. $2 goes into $1, $3 goes into $2... Repeatedly using shift can be a convenient way to loop over all arguments that expect an arbitrary number of arguments

Answer 116

Separate with ; i.e. x ; y ; z

Answer 117

&& and || && causes the shell to test the exit status of the preceding command. If exit code is 0 (indicating success) run the command, else skip it. || does the opposite. Runs if it fails.

Answer 118

fname () { stuff } or function fname () { stuff } Arguments to a function become positional parameters within it. $# holds number of positional parameters $0 is unchanged when return is executed in a function, the function complete and execution continues after where the function was called. Note that you can give a numeric argument to return for an exit status

Answer 119

Normally shared, but can be declared local with the local builtin. local variables are only visible to the funciton and the commands it invokes they can shadow variables with the same name declared at previous scopes

Answer 120

declare -a name

Answer 121

declare -A name

Answer 122

name[subscript]=value name=(value1,value2,...) automatically creates an array and assigns values

Answer 123

name+=(value1,value2,...)

Answer 124

$(name[subscript]} gets an element $(name[@]} obtains the entire array as a list *verify

Answer 125

Detects repeated lines (they must be adjacent though, so consider using sort).

Answer 126

Searches for files in a directory hierarchy. -L to follow symbolic links, -H to follow links in arguments only find [-H|-L] path... [operand_expression...]

Answer 127

'command' or $(command) but the slides say this one is rarely used. i.e. $(< file) does the same thing as cat

Answer 128

i.e. for i in @([a-z][0-9])

Answer 129

(( )) is a synonym for let Can have spaces in the expression without needing double quotes.

Answer 130

Using let, separate with spaces. Using (( )), separate with commas

Answer 131

malloc() allocates uninitialized memory calloc() does the same but initialized to all 0s calloc() example: void * calloc(size_t nmemb, size_t size); the block of memory has nmemb elements each that are size bytes long

Answer 132

No type. Compiler doesn't associate one with it. Cannot be de-referenced with * since the data type it contains is unknown. Cannot do pointer arithmetic since that needs the C compiler to know the size of each element in bytes. Pointer comparison is still allowed. Must be cast into other types before use.

Answer 133

typecast *(int *) ptr) = 4;

Answer 134

Returns the size of the data element in bytes. Its arguments can be a variable an array name a basic data type the name of a derived data type an expression

Answer 135

Always check the returned pointer. It may return NULL if it fails, in which case something very bad has happened. I.e. the system has run out of memory, or some other error.

Answer 136

According to Stack Overflow. The specified amount of memory to allocate when using malloc() is more than what you give it. It includes extra information, including how big the block is. free() can look at this extra information.

Answer 137

Memory that has been allocated by the programmer but never free()ed.

Answer 138

An uninitialized pointer.

Answer 139

A pointer left pointing to a region of memory that has been free()ed.

Answer 140

Lets you change the size of a previously allocated memory block (keeping the data). void * realloc(void *ptr, size_t size); Note: reallocarray() does the same, but better syntax for arrays. void * reallocarray(void *ptr, size_t nmemb, size_t size);

Answer 141

Acts like malloc.

Answer 142

If the new size is greater, no.

Answer 143

memcpy() and memmove() void *memcpy(void *restrict dst, cont void *restrict src, size_t n); void *memmove(void (*dst, cont void *src, size_t len); memcpy does not work on overlapping regions memmove does work on overlapping regions Note that neither deallocate (free) the src. The memory there is still valid. Be vary careful when deallocating if regions overlap.

Answer 144

When moving moving data around, it is fastest when able to move things in words and multiples of words. If it does not align, the compiler will determine the necessary bit shifts and masks to move it anyways. It can be faster to move bytes until it aligns and then use words until bytes are necessary again...

Answer 145

break filename.c:linenum if condition_involving_vars

Answer 146

void *memset(void *s, int c, size_t n);

Answer 147

Overflow: values too large (towards +infinity or -infinity) Underflow: very tiny fractions (close to 0 from either positive or negative)

Answer 148

git branch newbranchname

Answer 149

git switch or git switch -c or git switch -c

Answer 150

--hard erases your work too. just reset unstages changes

Answer 151

git blame or git praise

Answer 152

stdin stdout and stderr

Answer 153

When you open it in write or append mode. If in read mode, and it doesn't exist, and error occurs. Note: Always check return values from system calls and library funcitons.

Answer 154

FILE *someFile = fopen(const char *pathname, const char *mode);

Answer 155

r: read r+: read and write. w: truncate and write. w+: read and write. Creates file if it doesn't exist. a: appending. Created if file doens't exit. a+: reading and appending. File is created if it doesn't exist.

Answer 156

fprintf() and fscanf() do the same as printf() and scanf(), but take FILE* as the first argument. For entire lines of data, fputs() and fgets() fgets(buffer, n, filePtr); (1 less than n chars) fputs(buffer, filePtr); (note doesn't include null terminator by default)

Answer 157

command > outFile 2>errorFile Redirects stdout to outFile and stderr to errorFile command > outFile 2>&1 redirects stdout to outFile and stderr to stdout.

Answer 158

fclose(inputFile);

Answer 159

Best practice is as soon as you are done with it.

Answer 160

feof(filtePtr) returns non-zero if an attempt has been made to read past the file end

Answer 161

Use open() int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode); Returns -1 if an error occured. pathname and flags similar to fopens arguments. when a file is created, mode (access permissions) must be given Mandatory flags are one of O_RDONLY O_WRONLY O_RDWR Additionally, can use O_APPEND O_CREAT O_TRUNC can be combined with bitwise OR

Answer 162

close() int close(int fd); Returns non-zero if an error occured.

Answer 163

errno() Can check it yourself or use perror() or strerror() to get a description of the error.

Answer 164

ssize_t read(int fd, void *buf, size_t count); ssize_t write(int fd, const void *buf, size_t count); Let you read from and write to a file descriptor. Return value is number of bytes actually read/written (which may be less than requested).

Answer 165

lseek() off_t lseek(int fd, off_t offset, int whence); returns the associated file offset. whence: SEEK_SET: bytes from beginning of file SEEK_CUR: bytes from current position SEEK_END: bytes form end of the file

Answer 166

Encrypts all traffic, including passwords, which can thwart attackers.

Answer 167

Put in in quotes. i.e. awk '/h/' cars

Answer 168

Pattern matches like grep, but can make changes to the lines.

Answer 169

#define MACRO_NAME(arguments) (replacement) Remember to use parenthesis to prevent accidentally mixing in unexpected ways. I.e. passing x+1 to x * x gets 2x+1 when x^2+2x+1 is likely meant. i.e. #define SQUARE(x) ((x) * (x))

Answer 170

Replaces the macro argument with a string constant. It literally just inserts double quotes around it. Note that it preserves other quotes and backslashes automatically.

Answer 171

Joins two tokens together.

Answer 172

I.e. #ifdef UNIX # define DATADIR "/some/path" #else # define DATADIR "\some\path" #endif

Answer 173

condition ? isTrueExpression : isFalseExpression

Answer 174

If a function makes heavy use of a variable, you can ask it to make it fast as possible by using register. i.e. register int index; register char *textPtr;

Answer 175

Like the opposite of const Says that the specified variable will change its value explicitly (which prevents it optimizing it out which can be useful for things like device I/O).