Operating Systems Final
A direct access file is of a fixed length of __________ records
Logical records
An unmounted file system must be mounted at a
Mount point
A file system must be _____________ before it may be accessed
Mounted
File sharing is useful on
Multi user systems
What are the 7 attributes associated with a file?
Name - duh Identifier - unique tag identifying file in FS Type - for systems supporting diff. file types Location - POINTER to location on device Size - Protection - who can read/write/execute Time/Date/User identification -
What are the issues with 2-level directory structure? What are they comprised of?
No grouping capabilites Master file directories contain several directories each, each of which contain a file
Is open file locking a part of all file systems?
No, only some file/operating systems allow for open file locking
How do general graph directories avoid cycling?
Only allow for links to files, not subdirectories Garbage collection Whenever a link is added, check for validity with cycle detection algorithm
In what 5 ways is data kept to manage open files?
Open-file table - File pointer - pointer to last read/write location PER PROCESS open on the file File-open counter - counter of number of times a file is open by a process; allows for removal from OFT when last process closes it Disk location of the file Access rights: permissions per process
3 types of access on unix/linux:
Owner access, Group Access, Public Access in RWX format owner access - 7 - 111 group access - 6 - 110 public access - 1 - 001
What is a file pointer?
Pointer to last read/write location PER PROCESS open on the file
What permissions can be granted to users/groups?
Read/Write/Execute/Append/Delete/List
What are the 6 directory operations?
Search for a file Create a file Delete a file List the contents of the directory Rename Traverse the file system
What are components of an acyclic-graph directory?
Shared subdirectories/files Aliasing Backpointers/ daisy chain organization Links/ link resolution
What is a group id?
Similar to a user id, but amongst an entire group
An operating system may have general and what other kind of file system?
Special-purpose file system
What are some properties of a complex file structure? How can these be simulated by a simple structure?
Formatted documents, relocatable load file; these can be simulated using control characters
What are the issues with 1-level directory structure? What are they comprised of?
Grouping/Naming Comprised of a directories each pointing to an individual file
In a sequential access file's diagram, we keep track of the file's ___________, the current _____________ for read/write, and ____________. We may _____________ from the current position, and read/write until we reach the end.
In a sequential access file's diagram, we keep track of the file's beginning, the current position for read/write, and end. We may rewind from the current position, and read/write until we reach the end.
Access methods generally involve the creation of an _________ for the file
Index
Contents of a file are defined by
The file's creator
What is the purpose of the file-open counter?
The file-open counter records the number of times a file is open by a process; allows for removal from OFT when last process closes it
If disks/partitions aren't being used raw. What is the alternative?
They may be formatted by a filesystem.
The entity containing the filesystem is called the
Volume
What is an exclusive lock?
When a statement given by a transaction modifies data, it's transaction holds a lock over the data, preventing other transactions from accessing it until a commit/rollback is issued
The 4 access methods for a sequential access file are:
Where n is the relative block number: read n write n position to n: read next position to n: write next rewrite n
A ____________ path name is the location of the filesystem object relative to the root
absolute
Explain chgrp G game:
chgrp changes the group associated with file game. G is the name of the group. game is the name of the file.
Explain chmod 761 game:
chmod is the command to change permissions. 761 indicates that the owner of game has full access of 7 (111), the group associated with game has access of 6 (110), and the public has access of 1 (001)
How can a read next operation on a direct access file be simulated as sequential access?
read next == read cp; cp = cp + 1
The 3 access methods for a sequential access file are:
read next, write next, reset NOTE: there is no read after the last write possible. --- (NO REWRITE)
A _________ path name specifies location relative to the working directory
relative
How can a reset operation on a direct access file be simulated as sequential access?
reset == cp = 0
How can a write next operation on a direct access file be simulated as sequential access?
write next == write cp; cp = cp + 1;
What is a user id?
An identification medium given to users to determine permissions/protections
A disk may be divided into ____________. These ____________ may be ________ protected.
A disk may be divided into partitions. These partitions may be RAID (redundant array of independent disks) protected.
What is an NFS?
A network file system - a type of distributed file system where access is shared across a network
What are tree-structured directories comprised of? What are their benefits?
A tree-structured directory consists of a root directory, which points to other directories, which either contains a file, or another directory. Tree directories allow for absolute/ relative path names. Also, tree directories have grouping capabilities and efficient searching.
A file is an __________ data type
Abstract
Disks/partitions be used raw, what does this mean?
Accessing of the data directly at the individual byte level
What does RAID protection do?
Combines multiple physical disk components to a single logical disk
What are some properties of a simple file structure?
Composed of lines, fixed length, variable length
What are the 7 operations on a file? What do they do?
Create - Write - write to file at write pointer location Read - read to file at read pointer location Reposition within file - Delete - Truncate - Open (Fi) - search dir on disk for entry Fi, then move content of Fi to memory Close (Fi) - move content of entry(Fi) in memory to dir on disk
What is the directory structure?
A collection of nodes storing information about all files.
All files fall under two basic types
Data (numeric, character, binary) Program
Each volume containing a file system track's file info in the ______________ directory or ______________ __ _____________
Device directory or table of contents
All file information is kept in what structure?
Directory structure
What are the 3 reasons for a directory to be logically organized?
Efficiency Naming - two users name have the same name for different files/ vice versa Grouping - grouping of files by their properties
What are the benefits of a 2-level directory?
Efficient search Path names Different users can share file names
What is a shared lock?
Essentially when two transactions are granted read access. One transaction requests data and is locked, the other is locked upon request of the same data. When the lock is released it is released for both transactions at the same time.
What are 4 specified file types, how are they defined?
Executable - ready to run ML program Source - source code in various languages Batch - holds commands to be interpreted Text - textual data