-
Kernel:
The core of OS that performs the most basic computing
functions, such as memory management, process administration, and
management of the hardware.
-
Process:
is a executing program or a task, or independently
run program with its own set of resources.
-
Zombie:
is a process
that has died but has not yet relinquished its process table slot
-
Subprocess:
is a program run and controlled by a process.
-
File system:
determines how information is stored on a storage media.
-
System Services:
are services run
by computer.
-
Directories:
are containers that store files.
-
Ellipsis:
are dots after parent's menu.
-
Emblem: is
small icon that you can add to a file or folder in a GUI so you
may visually mark the item.
-
Widgets: are
graphical control elements for specific tasks.
-
Virtual
Console: called terminal up to 63, outside GUI, each
with its own shell command prompt, there
are 7 default virtual consoles. You can move among them by pressing.
Ctrl+Alt and F1-F7.
# (To return to X go to virtual console F7.
-
Daemon:
is background process that takes predefined action when certain
event occur. Does not need to be called by a user.
-
Delimiters
(/): are the slashes in the path between directories.
They indicate when one item is ending and another beginning.
-
Meta Data:
is data about data.
-
Ext 3: current
executed file system 3 introduced in RedHat 7.2 is Journaling File
System. Other file system that Linux supports are: MSDOS(8.3
file names), UMSDOS(Long File Names), VFAT and VFAT32(win95/98),
NTFS.
-
Shell:
is a program that interprets keyboard command and acts as
a buffer between you and OS.
Most popular shells are:
sh
-
Bourne; csh -
Cshell; tcsh -
Look-alike C shell; ash -
look like Bourne shell;
ksh
-
Public domain Korn shell (mix of all)
-
Syntax: command
typed in the correct order.
-
Bash:
Decedent from the Bourne Again Shell (Unix, Shell), Bash is a GNU
product and it is a standard command line interface on most Linux
machines.
-
Absolute Path:
is complete and total
hierarchical structure.
-
Relative Path:
is designed of the
location of a file in relation to the current working directory.
-
Meta characters:
are those characters
that have special meaning to the shell.
-
Globing: is
shell feature, using wildcards.
-
Ambiguous File
References: are
the file names that uses wildcards.
-
Recursively:
list all columns
that way means that command traverse the directory tree from the
top down and shows all the directories as well as the files in those
subdirectories.
-
LDP:
Linux Documentation Project site.
-
Journaling
File System:
is one that in general writes Meta Data to a journal on the
disk, before it is actually used to modify the file. Good in crash,
when there is enough uncorrupted data available to finish writing
original file.
-
Variable:
is a value that can change depending on conditions or on
information passed to the program.
-
Shell
Variables:
are those that you create at the command line or in the shell
script.
-
Environmental
Variable:
is a name assigned to a string(value) of data.
S1:
is a primary prompt environmental variable. It is asking you to
key a command.
PS2:
is a secondary environmental variable. It shows up on continuation
lines of command that are longer than one line.
-
PATH
Variable:
is a variable specifies the directories to be searched as
well as the order in which they will be searched for any command
that you key in. Each directory in the PATH variable must be separated
by a colons (:)
-
Ordinary
Files:
Consist of programs (executable files)
-
Character
Special Files:
produce a stream of bytes, one character at a time. This
produces something called raw data. These types of files are related
to a serial I/O devices such as printer.
-
Block
Special Files:
as their name indicates, process their data a block at a
time and are used for reading or writing of data to a devices such
as disk.
-
Link
File:
is a special directory entry that can specify that one file
points to another file
(link).
-
Hard
Link: associate two or more files with the
same Inode. Hard links share the same data blocks on the hard disk,
while they continue to behave as independent files. Disadvantage
of using hard links is that they can't span partitions, because
Inode numbers are only unique within a given partition.
-
Soft
Link: is
a small file that is a pointer to another file. A symbolic link
contains the path to the target file instead of a physical location
on the hard disk
-
EOF:
End Of File
-
Hypertext
utility:
means that you can jump between logically connected items
with a click of a mouse.
-
Wildcards:
allows you to operate on group of files rather than a single
file. (?), (*), ([])
-
FILO:
First-in last -out.
-
CLI:
Commands Line Interface.
-
Partition:
Partitioning is a means to divide a single hard
drive into many logical drives. A partition is a contiguous set
of blocks on a drive that are treated as an independent disk.
-
Swap Space:
Expansion
of the computers physical memory, extra memory on hard disk.
-
Regular
Expressions:
are wildcards patterns built using a special characters.
A regular expression is a pattern that describes a set of strings.
-
Permissions:
is the ability to access (read, write, execute, traverse,
etc) a file or directory.
-
Sockets:
provide a method for communication between a client program and
a server program in a network. A socket is defined as “the
endpoint in connection”. Sockets are created and used with
a programing requests sometimes called the sockets application programing
interface. (API)
-
Inode:
is a computer-stored
description of an individual file. It is a data structure that holds
information about every file.
Each
Inode contains the following information:
-
Superblock:
is a record that
describes the characteristics of a file system. It has information
about disk block size, the size and location of the Inode table,
the disk block map, usage information, and so on.
-
Cache:
is a small, fast memory area that holds recently accessed
data. When you access a file, Linux caches the necessary Inode information
in buffer.
-
Buffer:
a temporary storage spaced which holds data
for future processing. The data may be stored on a hard disk, RAM
or on specialized chips.
-
UID:
user ID. When new user account is created the UID by default
is a number greater than 500 and greater than all other existing
user ID's.
-
GID:
group
ID. When new user account is created the GID by default is a smallest
number greater than 500 that is greater than all other group ID.
(the group name is the user's login name).
-
SUID,
SGID, sticky bit:
are
three more permissions that control special attributes for executable
files and directories. The SUID bit is for executable files only.
This offers anyone temporarily root access for entire time the program
is executing. An example of this is the passwd command. The /etc/passwd
file can be modified only by root. However, you want to grant users
the right to change their password, where SUID and SGID comes in
play. The SUID works the same way, for example
if you have a directory called
/politics with group politicians and the SGID is set, then all files
created in that directory will have the group politician assigned
to it, regardless of the creators group. (rws indicates that the
SUID is on. Example ls -l /usr/bin/passwd)
-
Sticky
bit:
is used with directories. If its on, only the
owner of a file within that directory can rename or delete that
file(r-s indicates that sticky bit is on)
-
Shell
Parameter:
-
Positional
Parameter:
-
Special
Parameters:
-
Mount
Point:
All partitions are attached
to the system via mount point. The mount point defines the place
of a particular data set in the file system. Usually, all partitions
are connected through the
root
partition ( / )
-
Fork:
the term indicates that, as with a fork in the road, one process
turns into two. A new process is created because an existing process
makes an exact copy of itself. This child process has the same environment
as its parent, only process ID number is different.
-
Spontaneous
process:
is the first process PID1 executed by Linux
when the system boots. Its a ancestor of all processes that system
and users work with.
-
Sleep:
while the child process is executes the command
the parent process sleeps. When the child process finishes executing
the command, it tells its parent of its success or failure via its
exit status and then dies.
-
PID:
process identification number.
-
PPID:
parent process identification number.
-
Alias:
is a name that shell translates into another
(usually longer) name or (complex) command. They are typically placed
in the ~/.bashrc.
-
Keywords:
are words
that have special meaning to the shell as if, while and
until.
-
Functions:
are groups of commands organized as separate routines. Functions
are similar to aliases, but typically are more complex.
-
Control
Structures:
allow you to write scripts that can loop over
command line arguments, make decisions based on the value of a variable,
set up menus, and more.
-
Hashing:
is
the transformation of a string of characters into a usually shorter
fixed length value or key that represents the original string. It
is used to retrieve commands that are constantly used so that they
can be retrieved more quickly.
-
Escape
Sequences:
are series of characters that start with the
escape character and are often used to control display devices.
(Backspace, return, bell)
-
Command
line expansion:
is what shell must do to the command line before
it passes it on to the program that is being called.
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