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29 Cards in this Set
- Front
- Back
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What is the purpose of a directory |
To map a file name to an inode
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What is a hard link |
Points to an inode Can have many of them to one file Inode keeps track of how many hard links there are to a file |
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What is a soft link |
Contains the name of a file to point to
No guarantee name exists Can work across mount points |
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What are the different sections on a hard disk and what do they do |
Boot block - allows OS to tell where different partitions are
Super block- No. of blocks and No. of free ones also points to start of inode and free inode lists Inode table - holds information on where all inodes are Inodes - hold actual data |
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Do hard links work across mount points? Why? |
No because different partitions have different inode structures |
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How are open files managed |
Each process has its own unique open file table Which maps to a system wide (kernel mode ) open file table - same files in different process map to the same entry This then maps to an inode table |
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How and where is access control information held |
In the inode 3 bits for each owner, group and world signify read,write and execute privileges |
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What do Setuid and Setgid allow you to do |
Normally processes run with the privileges of the invoking user When setuid is active it allows the user of the file to have owner privileges - it is able to change effective permissions level |
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What is the file deletion procedure |
check if have sufficient access to file check if have sufficient access to directory Remove entry decrement inode reference count if 0 then free data blocks and free inode If there is a crash must check entire system to see if any block is unreferenced or double referenced |
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What are the free segments of a unix process |
stack data text |
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How does the unix system start |
Kernel loaded from disk Root file system mounted First process created - init |
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How does the shell work |
Works just like every other process Creates children |
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What are the 3 file descriptors a process has on creation |
stdin: where to read input from stdout: where to send output stderr: where to send diagnostics |
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How do pipes work in unix |
They all you to pass the output from one process to the input of another |
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What is a filter in unix |
It takes the output of one function and performs an action on it |
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Unix: |
It is a form of Inter process communication that is sent between processes or between threads in a process to notify it of an event Some are able to be caught |
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Unix: What is an example of a signal |
Program error Death of child |
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What are the 2 categories of IO |
Block and character |
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What are the properties of character IO |
Low rate Complex Most functionality comes from the cooked interface |
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What does Block IO rely on |
The buffer cache |
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What is the buffer cache |
Keep parts of disk in memory for speed Prevents 85% of disk accesses |
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What happens in the buffer cache on read |
Locate relevant inodes Check if in buffer cache already if not read disk blocks into memory return data to buffer cache |
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What happens during a buffer cache write |
Locate relevant inodes Check if in buffer cache already write data onto buffer cache every 30 seconds data is flushed to the disk |
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What scheduling scheme does unix use? |
Round robin with priorities |
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How do nice values effect scheduling |
The nice value effects the priority It can be set by the user between 20 and -20 IO bound tasks can have there nice value changed to make them a higher priority |
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What is the HAL |
Hardware abstraction layer Hides hardware details Interrupt mechanisms DMA |
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What are the four main responsibilities of the windows kernel |
CPU scheduling Interrupt and exception handling Low level processor synchronization Recovery after power failure |
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How does the NT interrupt and exception handler work |
Handles interrupts and exceptions either from hardware or software. Interrupts handled by the ISR |
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