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| A running instance of a program. |
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Virtual File System.
Abstraction layer between user and real file systems like ext2, iso9660, nfs, etc., |
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root is the super user with user id '0'
root can do anything |
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| The top level node of the file system Tree |
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Manual
man command can be used to view documentation of various commands |
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The ability to access a file or directory
read, write and execute permissions are the 3 basic levels of permissions |
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| mechanism used by an application to request special privileged services from the operating system |
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virtual memory
A system allowing a computer program to behave as though the computer's memory was larger than the actual physical RAM |
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| The essential part of an OS that allocates resources, abstracts low level hardware interfaces, provides security, schedules processes, etc., |
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A program that loads the OS into the main memory of the computer.
It is typically loaded from the MBR by the BIOS. |
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Master Boot Record
A reserved region in storage devices where boot loader program is stored |
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A way of storing / retrieving files from a storage device
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| ext2 is a simple file system that is supported by the linux kernel |
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| ext3 is an advanced version of the 'ext2' file system with 'journal'ing support |
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| A journaling file system avoids inconsistencies by allowing us to construct the previous state of the file system. It is useful in recovering from unclean shutdown or outage of a computer |
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A signal is a high level interrupt to a running process
signals can be used to send an event to a running process |
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Time based job scheduler
Can be used to run programs at periodic intervals
(once in every N minutes / hours / days / etc.,) |
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Every process in unix has three I/O streams
Standard Input, Standard Output and Standard Error.
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| An asynchronous buffer from which the output of one program can become the input of another program |
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the return value of the main function of a program
exit code is often used as a convention by the calling program (such as the shell) to determine the successful operation of a unix command |
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A mechanism for virtual connection between processes.
There are two types of sockets in (BSD-like) Unixes:
Stream - bi-directional
Datagram - fixed length messages |
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| A special file system which exposes kernel's internals via the VFS |
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Network File System
A client-server file system which is accessed over the network |
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| Mechanism to bind a real file system to the VFS |
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A data structure holding information about files.
Every file is uniquely identified by an inode. |
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A mechanism of dividing a physical storage device into multiple virtual storage devices.
unix command: fdisk |
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| Extended memory stored in a slower, secondary storage device (like hard disk). |
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| Refers to "#!" (Hash Exclamation) used in the first line of a script to denote what interpreter to use to execute the said interpreted program |
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command line interpret that allows users to type commands
to control and use the operating system's services |
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A system call used to create a copy of a process
After fork executes, there will be two processes. The parent process will get the pid of the child process from fork. The child process will get 0 as the return value from fork. |
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| A System call that replaces the current process with executable code from provided argument |
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Typically the first process in unix
Used to start / initiate various services in Unix |
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Disk and Execution Monitor
A program that is constantly running in the background waiting to take action whenever a system or network event occurs |
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The number of active processes waiting to be scheduled
It indicates how CPU starved a system is |
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a shell command which is interpreted directly by the shell
as opposed to forking and execing an external program found in the VFS |
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Basic Input Output System
BIOS helps primarily in starting up a computer |
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The 'niceness' of a process controls how much CPU time a process gets.
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| A snapshot of memory of a terminated process that is saved for debugging purposes |
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